Hydrothermal pretreatment of press mud: Characterization and potential application of hydrochar and process water

In the present study, press mud (PM), a major waste by-product from sugar industries, was subjected to hydrothermal pretreatment (HTP) to create resource recovery opportunities. The HTP process was performed with the PM samples in a laboratory scale high pressure batch reactor (capacity = 0.7 L) at 160 °C and 200 °C temperatures (solids content = 5 % and 30 %). The pretreatment resulted in separation of solid and liquid phases which are termed as solid hydrochar (HC) and process water (PW), respectively. High heating value (HHV) of HC was ∼14-18 MJ kg-1, slightly higher than that of PM (14 MJ kg-1). The thermogravimetric analysis showed about 1.5-1.7 times higher heat release from HC burning compared to that observed from combustion of PM. Apart from this, the HC and PM showed no phytotoxicity during germination of mung bean (Vigna radiata). Moreover, the biochemical methane potential test on the PW showed a generation of 167-245 mL biogas per gram of chemical oxygen demand added. Hence, the HTP offers several resource recovery opportunities from PM which may also reduce the risks of environmental degradation.

Polyurethane reinforced with micro/nano waste slag as a shielding panel for photons (experimental and theoretical study)

This study not only provides an innovative technique for producing rigid polyurethane foam (RPUF) composites, but it also offers a way to reuse metallurgical solid waste. Rigid polyurethane (RPUF) composite samples have been prepared with different proportions of iron slag as additives, with a range of 0-25% mass by weight. The process of grinding iron slag microparticles into iron slag nanoparticles powder was accomplished with the use of a high-energy ball mill. The synthesized samples have been characterized using Fourier Transform Infrared Spectroscopy, and Scanning Electron Microscope. Then, their radiation shielding properties were measured by using A hyper-pure germanium detector using point sources 241Am, 133 BA, 152 EU, 137Cs, and 60Co, with an energy range of 0.059-1.408 MeV. Then using Fluka simulation code to validate the results in the energy range of photon energies of 0.0001-100 MeV. The linear attenuation coefficient, mass attenuation coefficient, mean free path, half-value layer and tenth-value layer, were calculated to determine the radiation shielding characteristics of the composite samples. The calculated values are in good agreement with the calculated values. The results of this study showed that the gamma-ray and neutron attenuation parameters of the studied polyurethane composite samples have improved. Moreover, the effect of iron slag not only increases the gamma-ray attenuation shielding properties but also enhances compressive strength and the thermal stability. Which encourages us to use polyurethane iron-slag composite foam in sandwich panel manufacturing as walls to provide protection from radiation and also heat insulation.

Turning trash into treasure: Torrefaction of mixed waste for improved fuel properties. A case study of metropolitan city

Solid waste management is one of the biggest challenges of the current era. The combustible fractions in the waste stream turn out to be a good energy source if converted into refuse-derived fuel. Researchers worldwide are successfully converting it into fuel. However, certain challenges are associated with its application in gasifiers, boilers, etc. to co-fire it with coal. These include high moisture content, low calorific value, and difficulty to transport and store. The present study proposed torrefaction as a pretreatment of the waste by heating it in the range of 200 °C-300 °C in the absence of oxygen at atmospheric pressure. The combustible fraction from the waste stream consisting of wood, textile, paper, carton, and plastics termed as mixed waste was collected and torrefied at 225 °C, 250 °C, 275 °C, and 300 °C for 15 and 30 min each. It was observed that the mass yield and energy yield decreased to 45% and 62.96% respectively, but the energy yield tended to increase by the ratio of 1.39. Proximate analysis showed that the moisture content and volatile matter decreased for torrefied samples, whereas the ash content and fixed carbon content increased. Similarly, the elemental analysis revealed that the carbon content increased around 23% compared to raw samples with torrefaction contrary to hydrogen and oxygen, which decreased. Moreover, the higher heating value (HHV) of the torrefied samples increased around 1.3 times as compared to the raw sample. This pretreatment can serve as an effective solution to the current challenges and enhance refuse-derived fuel's fuel properties.

Correlation analysis and predicting modeling of pyrolysis gas based on landfill excavated waste pyrolysis characteristics

The contribution of excavated waste to waste management is multifaceted, including minimization, non-hazardous disposal, access to useable land resources, improved waste management techniques and public environmental awareness, consistent with recent circular economy initiatives. Pyrolysis can be converted into tar, pyrolysis gas and char with recyclable utilization, enriching the application of pyrolysis technology in the field of excavation waste. In this study, the pyrolysis system includes horizontal tube furnace, gas collection device and Micro GC. The excavated waste was pyrolyzed at a temperature of 500∼900 °C with a heating rate of 10 °C/min. Pyrolysis gases include H2, CO, CO2, CH4, C2H4, C2H6 and C3H8. Pyrolysis was divided into four stages, the main decomposition range is 230∼500 °C, with a weight loss rate of 68.49% and a co-pyrolysis behavior. As the temperature increases, the tar and char decreased and the gas production increased significantly, and the pyrolysis gas reached 47.02% at 900 °C. According to Pearson correlation coefficient analysis, the generation of H2 and CO is positively correlated with temperature. Therefore, the target products can be influenced by changing the parameters, when considering the practical utilization of the excavated waste pyrolysis products. On this basis, the prediction models were built by polynomial fitting method. This model can reduce the experimental exploration cycle, reduce the cost, and accurately predict the pyrolysis gas, which has practical guidance for the application of pyrolysis industry, and provides a theoretical basis for the resource recycling and energy recovery of landfill.

Structural and thermal investigation of lignocellulosic biomass conversion for enhancing sustainable imperative in progressive organic refinery paradigm for waste-to-energy applications

The depletion of finite fossil fuel reserves and the severe environmental degradation resulting from human activities have compelled the expeditious development and application of sustainable waste to energy technologies. To encapsulate energy and environment in sustainability paradigm, bio waste based energy production is need to be forged in organic bio refinery setup. According to world bioenergy association, biomass can cover 50 % of the primary energy demand of the world. Therefore, the present study focuses on reforming the energy mix for a clean energy generation, where, sample composition of cotton stalk was acidified in dilute (5% wt.) hydrochloric acid (HCL) for analyzing material burnout patterns in biomass conversion systems utilized in organic bio refinery sector. Advanced thermochemical burning technique, which includes pyrolysis and combustion was applied at four different leaching times from 0 to 180 min under nitrogen environment from 0 °C to 500 °C and air from 500 °C to 900 °C, respectively. Different analyses including proximate, ultimate, gross calorific value (GCV), thermos-gravimetric, kinetic, XRD, FTIR, SEM-EDS were used for analyzing the degradation of demineralized cotton stalk at different treatment rates. Proximate study demonstrated that cotton stalk leaching for 180 min has efficiently infused HCL, leading in a significant increase in fixed carbon and higher heating value of 20.23 % and 12.48%, respectively, as well as a reduction in carbon footprint of around 54.80%. The findings of proximate was validated by GCV analysis and CHNS analysis as value of carbon and hydrogen has shown increasing behavior with the time delay in demineralization Thermo-gravimetric and derivative thermo-gravimetric data analyses shows an increasing trend of conversion efficiency, with the maximum increase of 98 % reported for sample 3H.TT.DEM. XRD characterization has reported 23° to 25° angle for all the observed peaks. Sample 3H.TT.DEM has shown maximum angle inclination along with matured crystalline peak. The latter observations has been validated by FTIR spectroscopy as sample 3H.TT.DEM has reported maximum O-H group formation. Sample 3H.TT.DEM has reported lowest activation energy of 139.51 kJ*mole-1 and lowest reactivity of 0.000293649%*min 0C, due to moderate and stable reactiveness. In SEM examination, increment in pore size and number of pores within the structural matrix of cotton stalk was observed with the enhancement in acidulation process. Furthermore, in EDS analysis, 3H.TT.DEM has shown most balanced distribution of the elements. In this research, sustainable transformation of biomass is envisioned to improve the waste bio refinery system, significantly contributing to the achievement of Sustainable Development Goals 7, 12 and 13.

Novel biocompatible denture material incorporating type I collagen with improved functional properties for oral health

The use of collagen is the recent development in various medical fields. Huge quantities of hide and skin trimmings are generated during the leather processing are wasted or underutilized. Trimmings contain collagen which can be beneficially extracted and utilized for high value products. Poly methyl methacrylate based denture materials exhibit serious concerns such as high porosity, presence of residual monomer, shrinkage, distortion and high rate of deterioration of the materials. This study aims to incorporate extracted Type I collagen with polymer to obtain denture base and investigate its chemical and mechanical properties. The present research methodology also reduces the quantity of monomer and acrylic resin usage. The collagen was extracted from animal skin and hide trimmings which are otherwise disposed as wastes. This study investigated the effect of visco-elastic characteristics of resulted specimens and their transition temperature, mechanical properties, decomposition temperature and leachability. The collagen-based specimens have better tensile strength with high decomposition temperature compared to control specimens. Scanning Electron Microscopy analysis revealed that the experimental specimens was cohesive and homogeneous which explained the higher tensile and decomposition values. The study suggests that collagen cross-linked acrylic denture base exhibit better mechanical and thermal resistance properties when compared to control specimens. The study indicates that biomaterials are emerging as smart products of value in human health.

Co-hydrothermal carbonization of microalgae and digested sewage sludge: Assessing the impact of mixing ratios on the composition of primary and secondary char

The role of microalgae cultivation in wastewater treatment and reclamation has been studied extensively, as has the potential utility of the resulting algal biomass. Most methods for processing such biomass generate solid residues that must be properly managed to comply with current sustainable resource utilization requirements. Hydrothermal carbonization (HTC) can be used to process both individual wet feedstocks and mixed feedstocks (i.e., co-HTC). Here, we investigate co-HTC using microalgae and digested sewage sludge as feedstocks. The objectives were to (i) study the material's partitioning into solid and liquid products, and (ii) characterize the products' physicochemical properties. Co-HTC experiments were conducted at 180-250°C using mixed microalgae/sewage sludge feedstocks with the proportion of sewage sludge ranging from 0 to 100 %. Analyses of the hydrochar composition and the formation and composition of secondary char revealed that the content of carbonized material in the product decreased as the proportion of sewage sludge in the feedstock increased under fixed carbonization conditions. The properties of the hydrochars and the partitioning of material between the liquid phase and the hydrochar correlated linearly with the proportion of microalgae in mixed feedstocks, indicating that adding sewage sludge to microalgae had weak or non-existent synergistic effects on co-HTC outcomes. However, the proportion of sewage sludge in the feedstock did affect the secondary char. For example, adding sewage sludge reduced the abundance of carboxylic acids and ketones as well as the concentrations of higher molecular weight cholesterols. Such changes may alter the viable applications of the hydrochar.

Exploring multistep bischofite waste pyrolysis: insights from advanced kinetic analysis and thermogravimetric techniques

Pyrolysis technology is crucial for realizing waste bischofite resource utilization. However, previous studies overlooked the complexity of multistep pyrolysis, resulting in a lack of thorough knowledge of the pyrolysis behavior and kinetics. The pyrolysis products were characterized using XRD and FTIR to indicate the bischofite pyrolysis behavior. Additionally, the multistep kinetics was studied using the segmented single-step reaction (SSSR) and Fraser-Suzuki combined kinetic (FSCK) methods. The results show that the bischofite pyrolysis is divided into dehydration and hydrolysis. The former refers to removing crystalline water from MgCl2·nH2O (n = 4,6). At the same time, the latter is related to the removal of HCl, characterized by the strengthening of the Mg-O bond in the FTIR analysis and the emergence of MgOHCl·1.5H2O in the XRD examination. The two main stages are divided into three dehydration reactions (D-1, D-2, D-3) and three hydrolysis reactions (H-1, H-2, H-3) by DTG-DDTG or Fraser-Suzuki deconvolution. Compared with the SSSR method, the FSCK method has improved model repeatability for multistep kinetic parameters. Following Fraser-Suzuki deconvolution, the FSCK method creates almost the same activation energy results when using the Friedman (FR), Kissinger-Akahira-Sunose (KAS), and Vyazovkin (VZK). This work provides fundamental data to promote the maximizing waste bischofite resource utilization.

Identification of microplastics extracted from field soils amended with municipal biosolids

Microplastic particles in arable soil are expected to impact the environment and potentially human health. The application of municipal biosolids (MBs) to agricultural land presents a further dilemma in that biosolids act as a fertilizer for crop growth, and a disposal pathway for wastewater treatment plants. They are also a direct path for emerging contaminants, such as microplastics to enter the terrestrial environment. Reliable methods are needed to identify and quantify microplastics, found in agricultural soils to determine how microplastics are being cycled in the terrestrial environment. In this study, we developed a method for extracting microplastics from soil, and characterized their composition and identity for particles sized 5 μm to 2 mm. Method development was initially completed using natural soils spiked with microplastics and MBs, followed by the analyses of soil sampled from an agricultural field where MBs were recently applied at a rate of 13 tons dw/ha. The procedures that used the spiked samples showed that microplastics can be reliably extracted from soil in a laboratory setting, and identified and semi-quantified by thermogravimetric analysis combined with Fourier-transform infrared spectroscopy (TGA-FTIR). However, when the same methods were applied to the soil samples collected from the agricultural field, reproducibility became a challenge, as the number and type of microplastics changed even within the same soils (i.e., collected the same day from the same exact location). The variation in reproducibility observed between laboratory and field samples underscores the significant heterogeneity present in the environment. This heterogeneity, in turn, affects the identification and quantity of microplastics detected, a phenomenon observed even when comparing different fields within a single treatment regimen.

Enhanced energy and nutrient recovery via hydrothermal carbonisation of sewage sludge: Effect of process parameters

Integration of waste management with energy and resource recovery is being widely explored to achieve sustainability. To achieve this, sewage sludge was treated with hydrothermal carbonisation (HTC) at temperatures ranging from 180 °C-260 °C with an increment of 20 °C for three different duration of 1 h, 3 h, and 5 h. The energy and resource recovery potential of the HTC treatment was evaluated through of hydrochar (HC) and process water (PW) properties. Dehydration and decarboxylation reactions resulted in reduced H/C and O/C atomic ratios of 1.35 and 0.45 respectively in HC-260-3, exhibiting peat-like propertied. The calorific value of HC-260-5 was enhanced to 5.9 MJ/kg (increase of 25.8 %) due to the combined effect of H/C and O/C atomic ratios, increased volatile organics and fixed carbon. A maximum energy recovery efficiency of 82.44 % was realised at 240 °C for 3 h rendering it the optimal process condition to ensure energy enrichment. Thermogravimetric analysis (TGA) of HC samples indicated an enhanced combustion behaviour with an increased HTC severity. The elevated levels of volatile fatty acids (VFAs) in PW (maximum 2296 mg/L) made it viable for energy recovery in anaerobic digestion units. Additionally, the PW contains significant concentrations of N and P (2091.68 mg/L and 40.51 mg/L, respectively), indicating enhanced resource/nutrient recovery potential.

Oat straw pyrolysis with ammonium chloride doping: Analysis of evolved gases, kinetic triplet, and thermodynamic parameters

The purpose of this work was to determine the effect of the addition of NH4Cl to oat straw on the evolved gases, kinetic triplet, and thermodynamic parameters of the pyrolysis process at 873 K. A complementary approach allowed to assess the effects of the pyrolysis of chlorine- and nitrogen-enriched biomass. The thermal analysis of biomass was performed for four heating rates (5, 10, 20, and 30 K/min). The doping of NH4Cl in the straw favoured i) carbonisation of the chars, ii) formation of C-N bonds, iii) reduction of evolved CH4 and CO2, and iv) an increase in the mean values of the effective activation energy and all thermodynamic parameters. A group of reactions that best fit the experimental data of the pyrolysis process was selected. It was necessary to use unspecified mechanisms to describe the reaction model, particularly for samples enriched with NH4Cl.

Thermal evaluation of plant biomass from the phytostabilisation of soils contaminated by potentially toxic elements

The combination of phytoremediation of soils contaminated by potentially toxic elements with energy production by combustion of the generated biomass can be a sustainable land management option, combining the production of renewable bioenergy with soil restoration while minimising energy consumption and CO2 emission. In this work, plant biomass from phytoremediation of soils contaminated by potentially toxic elements was studied as solid biofuel for combustion by thermal analysis and biomass composition. Six plant species were grown in two soils with differing degrees of contamination: Brassica juncea, Cynara cardunculus, Atriplex halimus, Nicotiana glauca, Dittrichia viscosa, Retama sphaerocarpa and Salvia rosmarinus. The composition of the plant biomass was characterised chemically and thermogravimetric analyses were performed for the mass loss (TG), derivative curves of mass loss (DTG) and temperature difference (DTA) signal. The cellulose concentration correlated with the parameters of the thermal analysis in the low temperature range (150-350 °C), while lignin correlated with the thermal parameters of the second peak in the high temperature range. Salvia rosmarinus and R. sphaerocarpa showed the best combustion characteristics according to the thermal profile and mineral residue results. The accumulation of potentially toxic elements in B. juncea grown in heavily contaminated soil led to a higher amount of residue at 750 °C, with a global activation energy lower than the one obtained when this species was grown in a soil with lower contamination. Therefore, the most beneficial combination of soil phytoremediation and energy production (combustion) that can be suggested would depend on the level of soil contamination: in heavily contaminated soil, phytostabilisation using R. sphaerocarpa and S. rosmarinus; in slightly contaminated soil, B. juncea due to its high energy of activation, although the concentrations of potentially toxic elements in the residue must be controlled, as well as possible particulate matter emissions during combustion.

Kinetic and thermodynamic analysis on preparation of belite-calcium sulphoaluminate cement using electrolytic manganese residue and barium slag by TGA

Electrolytic manganese residue (EMR) is a solid filter residue obtained from manganese carbonate ore during the production of metal manganese. A potential avenue towards large-scale utilisation of EMR is its use in cement preparation. However, the preparation of cement materials using EMR requires high-temperature calcination. In this study, the thermal properties and pyrolysis kinetics of belite-calcium sulfoaluminate cement raw meal were systematically studied using a multiple-heating-rate method based on thermogravimetric analysis and a kinetic model. The kinetic and thermodynamic parameters was studied using non-isothermal Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS), Friedman and Kissinger methods. The results showed that from 30 to 1300°C, the pyrolysis reaction of cement raw meal was mainly divided into four steps: the crystalline water removal from calcium sulphate dihydrate and bauxite, the ammonia nitrogen removal from ammonium salts and the calcium sulphate crystal transformation; the decomposition of calcium carbonate and carbon-containing organic matter; the sulphate and carbonate substance decomposition and the clinker mineral phase formation. The average activation energies calculated when using the non-isothermal FWO, KAS, Friedman and Kissinger methods were 244.49, 240.7, 239.24 and 380.60 kJ/mol and the average pre-exponential factors were 1.75 × 1020, 3.65 × 1020, 7.11 × 1021 and 1.55 × 1013 s-1, respectively. Herein, the pyrolysis kinetics of the cement raw meal was divided into two main stages: In stage 1 (α: 0.15-0.8, 524°C-754°C), the mechanism of P2/3 accelerated nucleation in the Mampel Power rule, and the reaction mechanism function was G(α)=α3/2. In stage 2 (α: 0.80-0.95, 754°C-1165°C), during the local conversion of α = 0.2-0.8, when α was <0.5, the chemical reaction mechanism of the R3 phase boundary was noted and the mechanism function was G(α) = 1 - (1-α)1/3; however, when α was >0.5, a random nucleation and subsequent growth mechanism of A6 was noted and the mechanism function was G(α) = [-ln(1 - α)]2/3.

Independent parallel pyrolysis kinetics of model components in sewage sludge analyzed by BPM neural network

Analyzing the kinetic behavior of sewage sludge pyrolysis is essential for the design of efficient reactors to produce biofuel and syngas. To understand the complex pyrolysis process of sewage sludge, we pyrolyzed six model components (i.e., cellulose, hemicellulose, lignin, protein, soluble sugars, and lipid) using a thermogravimetric analyzer. The effects of the heating rate on the pyrolysis process were examined at four different heating rates (5, 15, 25, and 50 °C/min). As temperature increased, the derivative thermogravimetric peaks shifted to higher temperature zones. The temperature ranges of the maximum mass loss rate for cellulose, hemicellulose, lignin, protein, soluble sugars, and lipid were within 326.1-368.0 °C, 288.7-315.5 °C, 375.1-429.4 °C, 291.9-308.0 °C, 251.0-314.1 °C, and 410.8-454.1 °C, respectively. The apparent activation energies of the model components were obtained using non-isothermal kinetic analysis methods (Flynn-Wall-Ozawa and Kissinger-Akahira-Sunose). In addition, a back-propagation artificial neural network with a momentum algorithm (BPM) was developed to predict the relationship between the pyrolysis experiment and the activation value. The best BPM model (BPM5) for predicting the cellulose pyrolysis was identified.

In-situ pyrolysis kinetic analysis and fixed-bed pyrolysis behavior of ex-service wind turbine blades

After the peak of rapid wind power development, a large amount of wind turbine blades reach/exceed their service life due to aging or damage. These ex-service wind turbine blades (EWTB) will increase the issue of its high-efficient utilization in the future decades. Among several treatment methods, pyrolysis has been considered as a promising solution to separate inorganic fiberglass and make organic epoxy resin (OER) high-value-added converted. However, the pyrolysis mechanism, chemical composition, and fiberglass separation of EWTB have not been deeply studied. In this paper, the synthetic model compound of epoxy resin was firstly used to investigate the thermal weight loss and pyrolysis kinetics, the thermal weight loss temperature range of which was 300 ∼ 480 °C. The apparent activation energy was minimum when the conversion rate was 0.6, and the pyrolysis mechanism was determined by the Coats-Redfern method as a diffusion control. On this basis, a lab-scale fixed-bed was conducted to study fast-heating pyrolysis characteristics of EWTB. It could be analyzed that the chemicals in the pyrolytic liquid were a series of phenolics with methyl and vinyl substituted benzene rings (e.g., bisphenol A, p-isopropenyl phenol, and phenol). Bisphenol A presented a relatively high selectivity of 51.02%, which could be recycled as the main raw material for the synthesis of epoxy resins. Furthermore, clean fiberglass could be separated by combusting the residual carbon in pyrolytic solids. These results might be useful for achieving the separation and resource utilization of organic and inorganic components of EWTB.

Investigation of thermodynamic and kinetic parameters of Albizia lebbeck seed pods using thermogravimetric analysis

Thermodynamic and kinetic studies are very necessary to evaluate the conversion efficiency of biomass to energy. Therefore, this current work reported the thermodynamic and kinetic parameters of Albizia lebbeck seed pods through thermogravimetric analysis, which was carried out at temperatures from 25 °C to 700 °C, and heating rates of 5, 10, 15, and 20 °C/min. Apparent activation energies were determined by applying three iso-conversional model-free methods including Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW), and Starink. Resultantly, average apparent activation energy values for the three models of KAS, OFW, and Starink were found to be 155.29, 156.14, and 155.53 kJ/mol, respectively. In addition, thermodynamic triplets such as enthalpy, Gibbs free energy, and entropy were obtained as 151.16 kJ/mol, 150.64 kJ/mol, and -7.57 J/mol·K, respectively. The above results suggest Albizia lebbeck seed pods could become a potential source for bioenergy production aiming to achieve the sustainable goal and waste-to-energy strategy.

Determination of thermal degradation behavior and kinetics parameters of chemically modified sun hemp biomass

Sun hemp fibers are natural fibers obtained from plants grown in India and nearby countries. It is lignocellulosic biomass having the complex structure of hemicelluloses, cellulose and lignin. Chemical treatment of natural fibers is in practice to enhance the properties being used as reinforcement. Alkaline-treated fiber was sampled and thermal stability along with kinetic parameters was assessed with thermo gravimetric data at heating rates 10, 20 and 30 °C/min using four model-free methods Kissinger-Akahira-Sunose (KAS), Flynn-Wall-Ozawa (FWO), Friedman (FM), Starink (STAR) along with Distributed activation energy model (DAEM) to calculate pre-exponential factor. The calculated activation energy E_a by these model-free methods were in the range of 93.3-104.8 kJ/mol and pre-exponential factor (A) was observed between the range 46.6 x10³-90.5 x10⁶/min by the DAEM method. The standard deviation (σ) calculated from average activation energy using all four methods was 4.5 kJ/mol, which showed the consistency in the methods employed to determine the activation energy of sun hemp.

Thermal behaviour of hydrochar derived from hydrothermal carbonization of food waste using leachate as moisture source: Kinetic and thermodynamic analysis

The effect of leachate (L) as a reaction medium in hydrothermal carbonization (HTC) of food waste (FW) on the thermal behaviour of the resulting hydrochar (H) was investigated. The physicochemical and structural characterization of FW hydrochar produced using leachate (FWH-L) at different process temperatures (180/210/240 °C) confirmed the improved properties over raw FW. Kinetic analysis using Flynn-Wall-Ozawa (FWO), Kissinger-Akahira-Sunose (KAS) and Friedman methods revealed that FWH-L have a lower activation energy (E_a) than raw FW. The average E_a values for raw FW by FWO, KAS and Friedman methods were 196.18, 196.85, 206.34 kJ/mol, respectively, while for FWH-L they were 127.89, 124.22 and 134.5 kJ/mol, respectively. The computed thermodynamic parameters showed that FWH-L has improved combustion behaviour. The results of FWH-L are well comparable to FW hydrochar produced using distilled water (FWH-DW). These findings demonstrated that residual ions in leachate would act as a catalyst, benefiting the HTC degradation reaction path.

Pyrolysis activation energy of cellulosic fibres investigated by a method derived from the first order global model

The pyrolysis kinetics of cellulosic fibres, a natural cotton yarn (NCY) and a mercerized cotton yarn (MCY), has been explored with a modified first order global analysis method (FOG), via a series of non-isothermal experiments, using thermogravimetric analysis (TGA). The modified FOG analysis routine was developed to overcome discrepancy in heating rate and the difference between exact results and approximations in integrals. The intrinsic pyrolysis activation energy, with temperature range tending to zero, was found to be independent of heating rate and approximation used, giving average values of 153 ± 2 kJ/mol for NCY and 192 ± 7 kJ/mol for MCY. This proves the applicability of the reported analysis routine under the conducted TGA measurements. The reasons for different values were hypothesized to be the difference in chemical composition and crystalline structure. The findings provide a new approach in the investigation on pyrolysis kinetics of biomass and factors impacting their pyrolytic behaviour.

Preparation of ultrafiltration membrane from discarded polyethylene terephthalate bottles

In this study, the polymeric membranes were prepared using discarded polyethylene terephthalate (PET) bottles. The fabrication of the membrane process was carried out using a dope solution composed of polyethylene terephthalate (polymer), O-cresol (as a solvent), and polyethylene glycol 400 (as an additive). The solubility parameters were studied to dissolve the polymer into the solvent at a specific temperature. The melt flow index and thermal analysis were evaluated for the discarded bottles and prepared membranes to ensure the quality and thermal stability of the PET. The porosity of the membranes was determined using scanning electron microscopy. The temperature required to prepare the dope solution was 80 °C with a stirring speed of 350 rpm. Non-solvent-induced phase separation method was used to fabricate the membranes. The coagulation bath was composed of a water-ethanol mixture. The porosity of the prepared membranes ranges between 30 and 50%. The contact angle was determined for the membrane in the range of 40° to 80°. The flux of the membranes was evaluated using membrane testing cell at a specified pressure which ranges from 80 to 150 Lm^-2 h^-1. The prepared membranes could be used in various industries like dairy, pharmaceutical, juice, and beverages to separate temperature-sensitive substances.

Investigation of zeolite H-β effect on pyrolysis of polystyrene by multiple kinetic analysis methods

For studying the effects of H-β zeolite on the pyrolysis of polystyrene (PS), non-isothermal thermogravimetric measurements were conducted in N₂ under 5, 10, 15, and 20 K/min. The results show that the addition of 10 ~ 30 wt.% H-β zeolite can significantly decrease the initial pyrolysis temperature of PS, indicative of the catalytic effect of zeolite used. Through kinetic analysis of the pyrolysis of PS blends, the isoconversional activation energies are calculated to be 121.8 ~ 191.9, 92.1 ~ 173.8, and 116.7 ~ 192.4 kJ/mol for the PS blends with zeolite loading of 10, 20, and 30 wt.%, respectively. Meanwhile, the pyrolysis degradation functions are determined through the Master-plots method integrated with a recently developed compensation-effect method to follow chemical reaction mechanism with the reaction order of 0.9, 1.0, and 0.6 for PS/zeolite blends of 10, 20, and 30 wt.% loading, and their pre-exponential factors are respectively calculated to be 6.18 × 10⁸ ~ 5.71 × 10¹¹, 2.36 × 10⁶ ~ 9.23 × 10¹¹, and 8.38 × 10⁷ ~ 1.11 × 10¹² min^-1. Our work may provide some insights for how to better describe experimental results with theoretical predications and necessary information for performing any potential pyrolysis designs.

Pyrolysis of Canarium schweinfurthii hard-shell: Thermochemical characterisation and pyrolytic kinetics studies

Canarium schweinfurthii fruit used in food and cosmetics produces waste nuts with a hard shell (hard-shell) and kernel. The hard-shell contained lignin and holocellulose, besides 51.99 wt% carbon, 6.0 wt% hydrogen, 41.68 wt% oxygen, and 70.97 wt% volatile matter. Therefore, this study commenced thermochemical investigations on the hard-shell through extensive intermediate pyrolysis and kinetic studies. During the active stage of thermogravimetric pyrolysis, the hard-shell lost a maximum of 56.45 wt%, and the activation energies obtained by the Kissinger-Akahira-Sunose, Flynn-Wall-Ozawa, and Starink methods were 223, 221 and 217 kJ/mol, respectively. The Flynn-Wall-Ozawa method depicted the degradation process accurately, where the Coat-Redfern method's contraction and diffusion mechanisms governed the pyrolysis reactions at activation energies of 16.62 kJ/mol and 38.83 kJ/mol, respectively. The pyrolysis process produced 25 wt% biochar and 25 wt% bio-oil under optimum conditions. The calorific values of the bio-oils with 6.81-7.11 wt% hydrogen and 68.01-71.12 wt% carbon was 26.32-27.83 MJ/kg, with phenolics and n-hexadecanoic and oleic acids as major compounds. Biochar, by contrast, has a high carbon content of 75.11-79.32 wt% and calorific values of 25.45-28.61 MJ/kg. These properties assert the biochar and bio-oils among viable bioenergy sources.

The invasive Egeria densa macrophyte and its potential as a new renewable energy source: A study of degradation kinetics and thermodynamic parameters

The increase in global demand, along with environmental concerns, has led to the need for new sources that can supply the energy needed for socioeconomic development while reducing pollutant emissions. Aquatic biomasses, especially those of invasive aquatic macrophytes, can be potential energy sources, and this study evaluated the thermal degradation of the invasive Egeria densa macrophytes (EDM) in an inert environment at four heating rates to evaluate its potential as a low-cost biomass and bioenergy source. Pyrolysis experiments were performed using a thermogravimetric analyzer. The thermal profile of invasive EDM has three main events (multiple stages). Stages (i) and (ii) occur at a temperature range of 125-395 °C and represent the decomposition of carbohydrates such as hemicellulose and cellulose. Stage (iii) occurs between 395 and 500 °C and mainly relates to the decomposition of lignin. Thermal data have been used to analyze kinetic parameters through isoconversional methods, and the activation energy (E_a) value of EDM showed variation at different conversion points. The highest E_a values were observed for conversion rates of 0.3-0.6 due to the increased energy required to break down the lignocellulosic chains during decomposition. The small difference between the enthalpy change and E_a values for the different isoconversional methods can be due to a small potential energy barrier, which reflects the feasibility that the reaction can occur under the expected conditions. Gibbs free energy (137-145 kJ mol^-1) and high heating value (13.40 MJ/kg) revealed a significant bioenergy potential for EDM biomass.

Plastic litter in coastal sand dunes: Degradation behavior and impact on native and non-native invasive plants

Pollution associated to marine plastic litter is raising increasing concerns due to its potential harmful effects on human health, biota, and coastal ecosystems. However, limited information is available on the degradation behavior of plastics, especially biodegradable ones, in dune habitats. Moreover, the effects of plastics on dune plant growth and ability to withstand environmental stresses and invasion by non-native plants have been largely neglected. This is a particularly relevant issue since biological invasions are major threats to dune ecosystems. In this 18-month study, we examined the degradation behavior of two plastic bags, non-biodegradable (NBP) or biodegradable/compostable (BP), in the dune environment by visual observations and analytical techniques. Concomitantly, we investigated the individual and combined effects of bag type and sand burial (no burial vs. partial burial) on the performance of a native dune plant (Thinopyrum junceum) and an invasive plant (Carpobrotus sp.) and on their interaction. NBP did not show relevant degradation signs over the experimental period as expected. BP exhibited gradual surface modifications and changes in chemical functionality and were almost disintegrated after 18 months. Bags and burial reduced independently T. junceum survival and growth, and most plants died within 8 months of plastic exposure. Bags and burial did not affect Carpobrotus survival. However, burial decreased Carpobrotus growth while NBP increased it. Both plastics increased Carpobrotus competitive ability, and no T. junceum plants survived to co-occurrent Carpobrotus, BP, and burial. These findings indicate that removing all littered plastics from beach-dune systems not only is critical to reduce plastic pollution but also to prevent further spread of invasive species in coastal dunes.

Estimating the bioaccessibility of flocculants in the presence of sediments in model wastewater

The cationic degradable polymer poly(lactic acid) choline iodide ester methacrylate, poly(PLA₄ChMA), can be used to flocculate particles and dewater sediments from tailings ponds and wastewater. A suitable bioaccessibility method is required to characterize the interactions of this novel flocculant in the human gastrointestinal system. To this end, a physiologically based extraction test (PBET) was modified to evaluate the bioaccessibility of flocculants. Bioaccessibility (bioaccessible fraction) is a measure of the solubility of a contaminant in gastrointestinal fluids and that may be available for systemic absorption. The flocculants poly(PLA₄ChMA), SNF C3276, and FLOPAM A3338 were tested at a solid-to-liquid ratio of 1:200 in the absence and presence of kaolin clay, which is used as a model sediment compound. Bioaccessible fractions were characterized by proton nuclear magnetic resonance spectroscopy and estimated by gravimetry. The bioaccessibility of poly(PLA₄ChMA) in gastric and intestinal PBET solutions decreases from 78% to 100%, respectively, in the absence of kaolin to approximately 0% with kaolin, indicating that poly(PLA₄ChMA) remains adsorbed onto the clay surface throughout the PBET, a result confirmed by thermogravimetric analysis. The bioaccessibility of cationic SNF C3276 and anionic FLOPAM A3338 in gastric solution is approximately 76% and 26%, respectively, and is not affected by the presence of kaolin. However, in intestinal solutions, the bioaccessibility of SNF C3276 and FLOPAM A3338 (60-85% in the absence of kaolin) changes to 0% and 100%, respectively, in the presence of kaolin. These results, interpreted in terms of solution pH and surface charge, demonstrate that interactions with kaolin influence the solubility of flocculants and must be considered in the evaluation of bioaccessibility. In future works, such bioaccessibility methods can be applied to assess the human-health safety of using flocculants in wastewater treatments.

Isolation, partial characterization and in vitro digestion of starch from Ariopsis peltata and Lagenandra toxicaria tuber

The starch from two aroid tuber viz. Ariopsis peltata and Lagenandra toxicaria were isolated and evaluated for their morphological, physical and chemical properties. The tubers of these plants are used as food and medicine by the indigenous communities. The starch yield from A. peltata tuber was 25 ± 1.7% with an amylose content of 10 ± 0.9%, while the tuber of L. toxicaria contained 28 ± 6.5% starch with 15 ± 0.5% of apparent amylose in it. The starch isolated from both the tubers was highly pure (99%) starch exhibiting an A-type X-ray diffraction pattern. The starch granules of L. toxicaria were of various shapes and exhibited a smooth surface without any cleft or break. While the starch granules of A. peltata were spherical with smooth surface, as well as rough surface. The breaks and clefts were apparent on the rough-surfaced granules. The gelatinization temperature range for A. peltata and L. toxicaria starch is approximately 23 °C and 19 °C respectively. A. peltata starch showed higher thermal stability compared to L. toxicaria starch and either of the starch was rapidly digestible as evident from in vitro digestion study. The physicochemical properties of both the starches render them stable to withstand extreme processing. Besides they also mimic simple sugar in digestibility. So it can be utilized as a substitute for simple sugars in brewing and pharmaceutical industries.

pCold-assisted expression of a thermostable xylanase from Bacillus amyloliquefaciens: cloning, expression and characterization

The biotechnological application of bacterial xylanases requires a high thermostability, a catalytically active state for a broad pH range. The Bacillus amyloliquefaciens (MTCC 1270) xynA gene was amplified and cloned into the pCold vector and was expressed in Escherichia coli to evaluate the expressed proteins' thermostability. The pCold, compared to other similar vectors, has unique properties-including pH and temperature tolerance due to the presence of the cspA promoter. The recombinant xynA-pCold (rxynApC) showed the expression of xynA gene with a molecular weight of ~ 27 kDa, confirmed on SDS-PAGE. The rxynApC exhibits optimal activity at 70 °C and pH 8.0. The residual activity of the recombinant enzyme was 90% at pH 8.0. The thermal decomposition temperature (T d) value for the rxynApC enzyme was 93.33 °C obtained from the thermogravimetric analysis, indicating the potent stability of the cloned enzyme. The specific activity of native xylanase and rxynApC under optimal conditions was 32.35 and 105.5 U/mg, respectively. The structural model of the xynA gene was predicted using the in silico tool along with the active site (containing four important Tyr-166, Gly-7, Try-69 and Arg-112 amino acids). The predicted biophysical parameters of the in silico model were similar to the experimental results. The unique feature of the cspA promoter is that it gave a high expression of rxynApC enzyme having alkali and thermostable properties with high yield in surrogate host E. coli. Thus, the recombinant xynA gene can potentially be applied to different industrial needs by looking at its thermostability and enhanced enzyme activity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03315-y.

Enhancement of mechanical and thermal properties of Ixora coccinea L. plant root derived nanocellulose using polyethylene glycol-glutaraldehyde system

Nanocellulose fibers are widely acknowledged as a more sustainable alternative to polyimide and polyethylene terephthalate-based plastic films derived from petrochemicals. Cellulose is also utilised in packaging, tissue engineering, electronic, optical, and sensor applications, pharmaceutical applications, cosmetic applications, insulation, water filtration, and hygiene applications, as well as vascular grafts. In the present study to improve the tensile and thermal properties of cellulose nanofibers, polyethylene glycol (PEG 600) with varying concentrations was produced by solvent casting and chemically crosslinked with glutaraldehyde (GA). The effects of various PEG 600 concentrations on nanofibers and the morphology of the resulting nanofibers were investigated. The effects of GA on PEG-nanocellulose morphology, average diameter, tensile strength, elongation, and thermal characteristics were investigated. Strong (GA)-based acetal linkages are used to substitute secondary hydrogen bonds in nanocellulose films. The 1% PEG 600 plasticized nanocellulose scaffolds cross-linked with GA showed a higher tensile modulus (93 MPa) than its GA untreated nanocellulose scaffolds (69 MPa). The Young's modulus of the scaffold is increased up to 83.62 MPa. The crystallinity index values of GA-treated scaffolds were increased, and the mechanical characteristics were greatly improved, according to Fourier transform infrared (FTIR) and XRD analysis on the films. The thermogravimetric analysis (TG/DTG/DSC) of the GA treated plasticized nanocellulose scaffold showed maximum decomposition temperature (T_max) at 360.01 °C.

Combustion kinetics of hydrochar from cow-manure digestate via thermogravimetric analysis and peak deconvolution

Hydrothermal carbonization (HTC) can convert wet biomass into hydrochar (HC), a solid carbonaceous material exploitable as fuel. In this study, HTC was applied to anaerobic digestate from cow manure. HCs obtained at three HTC temperatures (180, 220, 250 °C) were characterized in detail and their combustion behavior was investigated by thermogravimetric analysis (TGA) coupled with peak deconvolution. Increasing HTC temperatures increased the fixed carbon content (17.9-20.7%), the ash content (27.2-32.5%) and the calorific value (14.3-18.2 MJ/kg), while decreased the hydrogen (5.01-4.54%) and oxygen content (24.09-12.35%) of HCs. DTG profiles peak deconvolution unveils the presence of five major components in the HCs. HCs combustion kinetics were studied applying the KAS method. Average apparent activation energy values of 100, 88, 67 kJ mol^-1 were obtained for HC180, HC220, HC250, respectively. HTC at 250 °C produced the HC with the best fuel characteristics.

Pyrolysis of anaerobic digested residues in the presence of catalyst-sorbent bifunctional material: Pyrolysis characteristics, kinetics and evolved gas analysis

We investigated the potential application of anaerobically digested residues for generating bioenergy in the presence of alkali bifunctional material, sodium zirconate (Na₂ZrO₃, NZ) using a thermogravimetric analyzer connected to a mass spectrometer. Isoconversional kinetic models, compensation effect and master-plots method were used on data obtained under multiple heating rates (10, 15 and 20 °C min^-1) to calculate the activation energy (E_α) and pre-exponential value (A) and reaction mechanism. The average E_α for blend samples C-DSW (NZ mixed with digested municipal solid waste (DSW)), and C-DSM (NZ mixed with digested swine manure (DSM)) were 172.24 and 171.63 kJ mol^-1, which were much lower when compared to plain samples, DSW (202.51 kJ mol^-1) and DSM (215.22 kJ mol^-1). The total gas yields increased by 19.5 and 17.1% for NZ blended samples C-DSW and C-DSM, respectively. In addition, the hydrogen yields also increased by 79 and 44% for C-DSW and C-DSM, respectively.

Investigation into the combustion kinetics and spontaneous ignition of sweet sorghum as energy resource

This study investigated the combustion kinetics and spontaneous ignition of sweet sorghum using thermogravimetric analysis and the Frank-Kamenetskii theory. The aim was to determine the proper operating conditions for a direct combustion reactor and predict the safe ambient temperature limits for given silo designs. Oxidative heating rates of 2, 5, and 10 °C/min were set up. Graphical observation shows that combustion was composed of two different stages representing the overlapping processes of pyrolysis and char oxidation, at 131-336 °C and 336-475 °C, respectively. Samples were found to ignite at 215 °C and were extinguished at 433 °C. Different heating rates shifted combustion characteristics to higher temperatures and increased reactivity for ignition and combustion indices up to 12 and 10 times higher. The Friedman method determined the apparent activation energies representing the combustion reaction by 132.91 kJ/mol. Regarding spontaneous ignition, the temperature safe limits were predicted to be 83-84 °C and 84-87 °C for cylindrical and box silos with diameter and height of 15 and 10 m, respectively. Calculations of silos were designed within the limits of certain dimension ratios.

Surface chemistry of metal oxide nanoparticles: NMR and TGA quantification

Surface functionalization is widely used to control the behavior of nanomaterials for a range of applications. However, methods to accurately quantify surface functional groups and coatings are not yet routinely applied to nanomaterial characterization. We have employed a combination of quantitative NMR (qNMR) and thermogravimetric analysis (TGA) to address this problem for commercial cerium, nickel, and iron oxide nanoparticles (NPs) that have been modified to add functional coatings with (3-aminopropyl)triethoxysilane (APTES), stearic acid, and polyvinylpyrrolidone (PVP). The qNMR method involves quantification of material that is released from the NPs and quantified in the supernatant after removal of NPs. Removal of aminopropylsilanes was accomplished by basic hydrolysis whereas PVP and stearic acid were removed by ligand exchange using sodium hexametaphosphate and pentadecafluorooctanoic acid, respectively. The method accuracy was confirmed by analysis of NPs with a known content of surface groups. Complementary TGA studies were carried out in both air and argon atmosphere with FT-IR of evolved gases in argon to confirm the identity of the functional groups. TGA measurements for some unfunctionalized samples show mass loss due to unidentified components which makes quantification of functional groups in surface-modified samples less reliable. XPS provides information on the presence of surface contaminants and the level of surface hydroxylation for selected samples. Despite the issues associated with accurate quantification using TGA, the TGA estimates agree reasonably well with the qNMR data for samples with high surface loading. This study highlights the issues in analysis of commercial nanomaterials and is an advance towards the development of generally applicable methods for quantifying surface functional groups.

Insight into the thermal kinetics and thermodynamics of sulfuric acid plant sludge for efficient recovery of sulfur

The disposal and management of sulfur-rich sludges (SRS) are challenging issues for the industries due to their adverse environmental impact. The present study reports the detailed characterizations and assessment of the thermo-kinetics of sludge generated from the sulfuric acid plant. In addition, the sulfur was retrieved with the help of the evaporation-condensation method. In the active devitalization zone (200-400 °C), a substantial mass loss (91 ± 3%) was observed, primarily due to the vaporization of sulfur. The isoconversional model-free methods were used to appraise kinetic parameters for the pyrolytic process. The average activation energy (64.5 kJ mol^-1) estimated by the Starink method admired the less energy-intensive process and validated the occurrence of thermochemical reactions at low temperatures. The thermodynamic parameters and frequency factor calculated at 10 °C min^-1 were ΔG* = 149.1 kJ mol^-1, ΔH* = 59.8 kJ mol^-1, ΔS* = -0.157 kJ mol^-1K^-1, and A = 2.1 × 10⁵ s^-1. Criado's Z-master plot revealed the dominance of the diffusion mechanism on the process. The efficient recovery of sulfur (≈96% with purity 99 ± 0.5%) was achieved at 440 °C by evaporation-condensation technique, and the findings closely complemented the kinetic and thermodynamic parameters. This study provides a background for a better understanding SRS and efficient sulfur recovery.

Study on microwave pyrolysis and production characteristics of Chlorella vulgaris using different compound additives

Pyrolysis characteristics and bio-oil of Chlorella vulgaris were investigated under SiC and ZnO (SZ) mixture (compound additive) with various mixing ratios (S/Z = 10:0, 7:3, 5:5, 3:7, 0:10) and addition amounts (5%, 10%, 15%) by thermogravimetric analysis and GC-MS. At three experimental groups of 10% compound additive, as ZnO in compound additive increased, maximum weight loss rate (R_p) increased, the time (t_p) corresponding to R_p and the weight stabilization time (t_f) first decreased and then increased, while average rate of weight loss (R_a) and total weight loss (M) first increased and then decreased; maximum temperature rising rate (H_x) and average rate of temperature rising (H_g) increased, while the time (t_x) corresponding to H_x decreased. Compound additives reduced the bio-oil yield, increased the gas yield, and reduced the acid compounds in bio-oil. Besides, it might promote the production of alicyclic hydrocarbons and oxygen/nitrogen-containing long-chain compounds.

Faecal sludge pyrolysis: Understanding the relationships between organic composition and thermal decomposition

Sludge treatment is an integral part of faecal sludge management in non-sewered sanitation settings. Development of pyrolysis as a suitable sludge treatment method requires thorough knowledge about the properties and thermal decomposition mechanisms of the feedstock. This study aimed to improve the current lack of understanding concerning relevant sludge properties and their influence on the thermal decomposition characteristics. Major organic compounds (hemicellulose, cellulose, lignin, protein, oil and grease, other carbohydrates) were quantified in 30 faecal sludge samples taken from different sanitation technologies, providing the most comprehensive organic faecal sludge data set to date. This information was used to predict the sludge properties crucial to pyrolysis (calorific value, fixed carbon, volatile matter, carbon, hydrogen). Samples were then subjected to thermogravimetric analysis to delineate the influence of organic composition on thermal decomposition. Septic tanks showed lower median fractions of lignin (9.4%dwb) but higher oil and grease (10.7%dwb), compared with ventilated improved pit latrines (17.4%dwb and 4.6%dwb respectively) and urine diverting dry toilets (17.9%dwb and 4.7%dwb respectively). High fixed carbon fractions in lignin (45.1%dwb) and protein (18.8%dwb) suggested their importance for char formation, while oil and grease fully volatilised. For the first time, this study provided mechanistic insights into faecal sludge pyrolysis as a function of temperature and feedstock composition. Classification into the following three phases was proposed: decomposition of hemicellulose, cellulose, other carbohydrates, proteins and, partially, lignin (200-380 °C), continued decomposition of lignin and thermal cracking of oil and grease (380-500 °C) and continued carbonisation (>500 °C). The findings will facilitate the development and optimisation of faecal sludge pyrolysis, emphasising the importance of considering the organic composition of the feedstock.

Pyrolysis of de-oiled yeast biomass of Rhodotorula mucilaginosa IIPL32: Kinetics and thermodynamic parameters using thermogravimetric analysis

The increasing demand for natural resources has highlighted the need to search for unutilized carbon resource that satisfy the demand and pose a minor threat to the environment. Yeast is a microbe with large industrial applications, and the biomass leftover after fermentation needs utilization for achieving increased efficiency. De-oiled yeast biomass (DYB), the residue after yeast lipid extraction, has not yet been evaluated for its potential application in the pyrolysis process. The present study was performed to understand its detailed pyrolysis kinetics. The observed activation energy (87-216 KJ/mol), random nucleation mechanism, pre-exponential factor (7.87 × 10³¹-3.24 × 10³¹/min), and thermodynamic profile showed the DYB pyrolysis process to be feasible. .

CaO recovered from eggshell waste as a potential adsorbent for greenhouse gas CO2

The growing number of industrial carbon emissions have resulted in a significant increase in the greenhouse gas carbon dioxide (CO₂), which, in turn, will have a major impact on climate change. Therefore, the reduction, storage, and reuse of CO₂ is an important concern in modern society. Calcium oxide (CaO) is known to be an excellent adsorbent of CO₂ in a high-temperature environment. However, since deterioration of the adsorbent is likely to occur after repeated cycles of adsorption under high temperature conditions, it would be desirable to mitigate this phenomenon, in order to maintain the stability of CaO. In the present study, common eggshell waste was used as the starting material. The main component of eggshell waste is calcium carbonate (CaCO₃), which was purified to produce CaO. Different surfactants and amino-containing polymers were added to synthesize CaO-based adsorbents with different configurations and pore sizes. The amount of CO₂ adsorbed was determined using a thermogravimetric analyzer (TGA). The results showed that the CO₂ adsorption capacity of the synthetic CaO recovered from purified eggshell waste could reach 0.6 g-CO₂/g-sorbent, indicating a good adsorption capacity. CaO modified with a dopamine-containing polymer was shown to have an adsorption capacity of 0.62 g-CO₂/g-sorbent. Moreover, it showed an excellent adsorption capacity of 0.40 g-CO₂/g-sorbent, even after 10 cycles of CO₂ adsorption. The present study suggests that using eggshell waste to synthesize CaO-based adsorbents for effective CO₂ adsorption can not only reduce environmental waste, but also have the potential to capture greenhouse gas CO₂ emissions, which conforms to the principles of green chemistry.

Influence of curing modes on thermal stability, hardness development and network integrity of dual-cure resin cements

OBJECTIVE

To explore the effect of different curing modes of conventional and self-adhesive dual-cure resin cements on their rates of thermal decomposition, hardness development and network integrity.

METHODS

Five self-adhesive (PANAVIA SA, RelyX Universal Resin, RelyX Unicem 2, Bifix SE and SpeedCEM Plus) and three conventional (PANAVIA V5, Nexus Third Generation and RelyX Ultimate Universal) dual-cure resin cements were investigated. Thermal decomposition stages, initial onset temperatures, the maximum rate of mass-loss and the filler mass-fraction of each resin cement were analysed by thermogravimetric analysis (TGA). Surface hardness was measured at 1h post-cure and after 24h of dry storage at 37°C. The relative network integrities were estimated from reductions in hardness after 168h of water storage. Data were analysed via one-way ANOVA, Tukey post-hoc tests and paired/independent sample t-tests (a=0.05).

RESULTS

No difference was apparent between TGA data for self-cured and light-cured specimens. Numerical differentiation of mass-loss versus temperature showed either single or multiple peaks. For the set of 8 cements, the maximum rate of mass-loss (%/°C) correlated negatively with residual mass at 600°C. All dry-stored cements increased in hardness from 1 to 24h, ranging from 20.4% to 52.6% for light-cure mode and from 41.3% to 112.6% for self-cure. After 168h water storage, the hardness of cements decreased: by 18.5%-36.2% for light-cured and by 9.8%-17.9% for self-cured. Overall, surface hardness was greater for light-cured cements. The initial onset temperature (IOT) of thermal decomposition correlated negatively with the hardness decrease produced by water-storage: r²=0.77 for light-cure and r²=0.88 for self-cure. This provided the basis for a relative scale of composite network integrity, probably reflecting differences in cross-link density.

SIGNIFICANCE

Light-curing, where possible, remains beneficial to the hardness and related properties of dual-cure resin cements. Combination of TG analysis and solvent softening experiments give an indication of relative network integrity - between materials - and their relative cross-link densities.

Effect of latex reclaim on physico-mechanical and thermal properties of carbon black filled natural rubber/butadiene rubber composite

As a material having high rubber content, latex reclaim (white reclaim) has been used in the production of premium grade rubber products like tyres, retreading materials, etc. Introduction of latex reclaim (LR) is also an ideal method to reduce the cost of rubber products. In the present work, natural rubber (NR), butadiene rubber (BR), and latex reclaim (LR) combinations were prepared to develop cost efficient tread materials. LR was mixed with NR/BR at various proportions to produce tread materials which will comply with national specifications. The blends were prepared and the cure and mechanical properties were investigated. Results have indicated that the scorch time and cure time had decreased with the increase of reclaim loading. The mechanical properties like tensile strength, tear strength, abrasion resistance decrease with the increase in the LR content. It was found that 70–80% of the mechanical properties were retained even after addition of 30 phr of LR. The thermal behaviour and activation energy of NR/BR/LR system was investigated using thermogravimetry TGA analysis and increased activation energy showed that the thermal stability has increased when the amount of LR is high. SEM studies had indicated the morphology change due to the viscosity mismatch between NR and BR especially in the presence of LR.

Engineering of thermostable phytase-xylanase for hydrolysis of complex biopolymers

Industrial processing of enzymes requires higher heating that affects the thermal stability of the enzyme and increases the production cost. In this study, xylanase-phytase (XP) fusion protein was generated via co-expression in a single vector with a cold-shock promoter, leading to improved activity at optimal pH, temperature and the thermal behaviour of the protein. Xylanase-phytase (XP) fusion and phytase proteins were characterized by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The XP fusion was thermally stable up to 124 °C, higher than phytase which was steady up to 113.5 °C. XP fusion exhibits higher stability at its thermal transition midpoint (T _m) 108 °C, higher than the T _m value of phytase which is 90 °C. Industrially efficient and environment-friendly proteins with low production cost and higher stability can be generated by 'fusion protein' technology.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-02936-z.

Valorisation of medical waste through pyrolysis for a cleaner environment: Progress and challenges

The COVID-19 pandemic has exerted great shocks and challenges to the environment, society and economy. Simultaneously, an intractable issue appeared: a considerable number of hazardous medical wastes have been generated from the hospitals, clinics, and other health care facilities, constituting a serious threat to public health and environmental sustainability without proper management. Traditional disposal methods like incineration, landfill and autoclaving are unable to reduce environmental burden due to the issues such as toxic gas release, large land occupation, and unsustainability. While the application of clean and safe pyrolysis technology on the medical wastes treatment to produce high-grade bioproducts has the potential to alleviate the situation. Besides, medical wastes are excellent and ideal raw materials, which possess high hydrogen, carbon content and heating value. Consequently, pyrolysis of medical wastes can deal with wastes and generate valuable products like bio-oil and biochar. Consequently, this paper presents a critical and comprehensive review of the pyrolysis of medical wastes. It demonstrates the feasibility of pyrolysis, which mainly includes pyrolysis characteristics, product properties, related problems, the prospects and future challenges of pyrolysis of medical wastes.

Anthropogenic emissions from the combustion of composite coal-based fuels

Composite fuels made of waste from coal, petroleum and wood processing industries have a high environmental and economic potential. In this research, we experimentally studied the concentrations of the most hazardous gaseous anthropogenic emissions (CO₂, SO₂, NO) from waste-based fuel combustion. Using two techniques operating in complementary temperature ranges, we obtained data on SO₂ and NO emissions in the temperature range from 300 °C to 1000°C, including all the stages of thermochemical conversion of fuels. A quasi-stationary technique was used, based on a setup of thermogravimetric analysis with mass spectrometry, to obtain information in a low-temperature range (300-600°C). This technique allows the conversion at a low controlled rate of heating a sample together with the furnace. To obtain data in a high-temperature range (700-1000°C), a non-stationary technique was used, where the sample was introduced into a pre-heated furnace. The conditions were established in which it was possible to reduce the concentration of flue gases from the combustion of the compositions under study (replacement of the coal part with water, injection of water vapor, addition of biomass, selection of the temperature range). The impact of water vapors was determined when they were injected into the chemical reaction zone together with air and when they were formed naturally by evaporation from the fuel sample. Unlike biomass that reduces the emissions of sulfur oxides from composite fuels due to the mechanical dilution of the mixture, water vapor present in the heterogeneous reaction zone decreases the gaseous anthropogenic emissions through chemical reactions and conversion of a part of fuel sulfur and nitrogen to an inactive form (neutral to the environment).

Thermal degradation characteristics and gasification kinetics of camel manure using thermogravimetric analysis

In this work, the sustainable valorisation of camel manure has been studied using thermogravimetric analysis. The gasification tests were performed from ambient conditions to 950 °C at 10, 20, and 50 °C/min under an O₂ environment. The TGA data were applied to determine the kinetics of the O₂ gasification. Single-heating rate models (Arrhenius and Coats-Redfern) and multi-heating rate models (Distributed activation energy, Friedman, Flynn-Wall-Ozawa, Starink, and Kissinger-Akahira-Sunose) were applied to estimate the kinetics of the process. Between the two single-heating rate models, the Coats-Redfern method fitted best with the experimental data. Among the multi-heating rate models, the Flynn-Wall-Ozawa model fitted best with the experimental results. The kinetic parameters-frequency factor, activation energy, and order of reaction were estimated using the Flynn-Wall-Ozawa model (the best-fitting model) and the estimated kinetic parameters were used to calculate the thermodynamic properties-Gibbs free energy, enthalpy, and entropy. The information on these kinetic and thermodynamic properties can be useful for the design of gasifiers and for optimising the O₂ gasification operating conditions.

Thermal degradation characteristics and gasification kinetics of camel manure using thermogravimetric analysis

In this work, the sustainable valorisation of camel manure has been studied using thermogravimetric analysis. The gasification tests were performed from ambient conditions to 950 °C at 10, 20, and 50 °C/min under an O₂ environment. The TGA data were applied to determine the kinetics of the O₂ gasification. Single-heating rate models (Arrhenius and Coats-Redfern) and multi-heating rate models (Distributed activation energy, Friedman, Flynn-Wall-Ozawa, Starink, and Kissinger-Akahira-Sunose) were applied to estimate the kinetics of the process. Between the two single-heating rate models, the Coats-Redfern method fitted best with the experimental data. Among the multi-heating rate models, the Flynn-Wall-Ozawa model fitted best with the experimental results. The kinetic parameters-frequency factor, activation energy, and order of reaction were estimated using the Flynn-Wall-Ozawa model (the best-fitting model) and the estimated kinetic parameters were used to calculate the thermodynamic properties-Gibbs free energy, enthalpy, and entropy. The information on these kinetic and thermodynamic properties can be useful for the design of gasifiers and for optimising the O₂ gasification operating conditions.

Fast and quantitative compositional analysis of hybrid cellulose-based regenerated fibers using thermogravimetric analysis and chemometrics

Cellulose can be dissolved with another biopolymer in a protic ionic liquid and spun into a bicomponent hybrid cellulose fiber using the Ioncell^® technology. Inside the hybrid fibers, the biopolymers are mixed at the nanoscale, and the second biopolymer provides the produced hybrid fiber new functional properties that can be fine-tuned by controlling its share in the fiber. In the present work, we present a fast and quantitative thermoanalytical method for the compositional analysis of man-made hybrid cellulose fibers by using thermogravimetric analysis (TGA) in combination with chemometrics. First, we incorporated 0-46 wt.% of lignin or chitosan in the hybrid fibers. Then, we analyzed their thermal decomposition behavior in a TGA device following a simple, one-hour thermal treatment protocol. With an analogy to spectroscopy, we show that the derivative thermogram can be used as a predictor in a multivariate regression model for determining the share of lignin or chitosan in the cellulose hybrid fibers. The method generated cross validation errors in the range 1.5-2.1 wt.% for lignin and chitosan. In addition, we discuss how the multivariate regression outperforms more common modeling methods such as those based on thermogram deconvolution or on linear superposition of reference thermograms. Moreover, we highlight the versatility of this thermoanalytical method-which could be applied to a wide range of composite materials, provided that their components can be thermally resolved-and illustrate it with an additional example on the measurement of polyester content in cellulose and polyester fiber blends. The method could predict the polyester content in the cellulose-polyester fiber blends with a cross validation error of 1.94 wt.% in the range of 0-100 wt.%. Finally, we give a list of recommendations on good experimental and modeling practices for the readers who want to extend the application of this thermoanalytical method to other composite materials.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s10570-021-03923-6.

Auto-classification of biomass through characterization of their pyrolysis behaviors using thermogravimetric analysis with support vector machine algorithm: case study for tobacco

BACKGROUND

During the biomass-to-bio-oil conversion process, many studies focus on studying the association between biomass and bio-products using near-infrared spectra (NIR) and chemical analysis methods. However, the characterization of biomass pyrolysis behaviors using thermogravimetric analysis (TGA) with support vector machine (SVM) algorithm has not been reported. In this study, tobacco was chosen as the object for biomass, because the cigarette smoke (including water, tar, and gases) released by tobacco pyrolysis reactions decides the sensory quality, which is similar to biomass as a renewable resource through the pyrolysis process.

RESULTS

SVM algorithm has been employed to automatically classify the planting area and growing position of tobacco leaves using thermogravimetric analysis data as the information source for the first time. Eighty-eight single-grade tobacco samples belonging to four grades and eight categories were split into the training, validation, and blind testing sets. Our model showed excellent performances in both the training and validation set as well as in the blind test, with accuracy over 91.67%. Throughout the whole dataset of 88 samples, our model not only provides precise results on the planting area of tobacco leave, but also accurately distinguishes the major grades among the upper, lower, and middle positions. The error only occurs in the classification of subgrades of the middle position.

CONCLUSIONS

From the case study of tobacco, our results validated the feasibility of using TGA with SVM algorithm as an objective and fast method for auto-classification of tobacco planting area and growing position. In view of the high similarity between tobacco and other biomasses in the compositions and pyrolysis behaviors, this new protocol, which couples the TGA data with SVM algorithm, can potentially be extrapolated to the auto-classification of other biomass types.

Thermodynamics, kinetics and thermal decomposition characteristics of sewage sludge during slow pyrolysis

Pyrolysis has shown great potential for sewage sludge valorisation and management by producing value-added chemicals. Although the product process yields are extensively studied, a few studies exist without consensus on the kinetic properties of sewage sludge pyrolysis. As a result, a study to investigate the thermal decomposition characteristics of Gauteng sewage sludge (GSS) at various heating rates (10, 20, and 30 °C/min), its pyrolysis kinetic parameters, reaction mechanism and thermodynamic properties was meticulously conducted. The results show that sewage sludge decomposition occurs in three stages, whereby the main decomposition (active pyrolysis) takes place at 150-570 °C. Fourier transform infrared spectroscopy (FTIR) analysis results confirm progression of thermal decomposition of GSS and drive off volatile compounds and formation of aromatic structures during TGA studies of GSS. An increase in heating rate shifts the characteristic temperatures towards higher temperatures with the highest decomposition rate of 1.10%/min.mg at 30 °C/min. The activation energies of GSS pyrolysis were calculated using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Starink methods and averaged as 225.92, 218.04 and 218.97 kJ/mol, respectively. GSS pyrolysis involves complex reaction chemistry with high reactivity whereby reactions that follow third order and three-dimensional diffusion-reaction mechanisms dominated the process. However, these mechanisms cannot be used explicitly to define the global pyrolysis kinetics due to the occurrence of multiple simultaneous reactions. The obtained thermodynamic and kinetic data will advance and amplify the design, simulation and optimisation of global energy pyrolysis units for production of value-added chemicals.

Multi-response optimization toward efficient and clean (co-)combustions of textile dyeing sludge and second-generation feedstock

The rapid growth of textile dyeing sludge (TDS) necessitates feeding it back into a circular economy in an efficient and clean way. This study aimed to optimize the clean and efficient operational conditions to co-combust TDS and incense sticks (IS). The (co-)-combustions exhibited four distinctive stages of thermal degradation. According to the master-plots method, the reaction mechanisms of reaction order (F2.4 and F1.5), three-dimensional diffusion (D3), and nucleation growth (A1.5) best explained the four stages, respectively. The interaction between TDS and IS exerted an inhibition effect in the range of 400-500 °C and a facilitation effect in the range of 600-1000 °C. At 300 °C as the main reaction temperature, the main evolved gas and functional groups such as CO₂, H₂O, CH₄, C˭O, C-O, and C-H were detected. The addition of IS improved the comprehensive combustion index, inhibited SO₂, but enhanced CO₂, HCN, and NO_x emissions. CaO in IS enabled Fe to remain in TDS and fixed more S in ash. Multi-response optimizations based on the best-fit artificial neural networks revealed the range of 545-605 °C and the co-combustion of 25% TDS and 75% IS as the cleaner and more efficient operational conditions.

Management of off-specification compost by using co-hydrothermal carbonization with olive tree pruning. Assessing energy potential of hydrochar

In this work the management of a waste called off-specification compost (OSC) was proposed via hydrothermal carbonization (HTC). The composition of this residue makes it not suitable for agronomic purposes because of the Spanish regulation requirements. Therefore, a way of management and/or valorisation needs to be found. The energy recovery through co-HTC with olive tree pruning (OTP) was evaluated. Blending of OSC with lignocellulosic biomass allows to obtain a coal-like product with physicochemical properties similar to those of a lignite, characterised by its high carbon content. Blends of 25, 50 and 75% of OSC with OTP were analysed. The individual OSC does not present good parameters for being used as solid fuel based on its chemical composition, however, the blend of 75% of biomass with 25% of OSC does. With a higher heating value of 26.19 MJ/kg, this blend shows the best energy yield and energy densification ratio. Thermogravimetric and kinetic analysis reveal that as biomass content in the blend increases, the more the hydrochar behaves as a solid fuel, therefore OSC can be used for energy purposes while its current use of landfill disposal can be reduced.

Development of emulsion gelatin gels for food application: Physicochemical, rheological, structural and thermal characterization

The current work aimed to prepare emulsion gels based on European eel skin gelatin (ESG). The results revealed that the ESG exhibited interesting antioxidant and functional properties in a dose-dependent manner. The ESG has a gel strength of 354.86 g and high gelling and melting temperatures of about 33 and 43 °C, respectively. Hence, based on its interesting gelling ability, the ESG-based gel was employed to stabilize European eel oil (EO) emulsions. In this context, two emulsions were prepared by homogenization or homogenization followed by sonication at EO:ESG weight ratios of 1:2 and 1:4. The physicochemical, textural, structural and thermal properties of emulsion gelatin-based gels (EGGs) were evaluated. The EGGs had a rigid and a cohesive gel network, according to the textural and microstructural analysis. Structural and thermogravimetric analyses showed the effective entrapment of EO in the ESG gel network.