Microwave-assisted co-pyrolysis of Chlorella vulgaris and wood sawdust using different additives

Interaction Effects between the Main Components of Protein-Rich Biomass during Microwave-Assisted Pyrolysis

The interaction effects between the main components (proteins (P), carbohydrates (C), and lipids (L)) of protein-rich biomass during microwave-assisted pyrolysis were investigated in depth with an exploration of individual pyrolysis and copyrolysis (PC, PL, and CL) of model compounds. The average heating rate of P was higher than those of C and L, and the interactions in all copyrolysis groups reduced the max instant heating rate. The synergistic extent (S) of PC and PL for bio-oil yield was 16.78 and 18.24%, respectively, indicating that the interactions promoted the production of bio-oil. Besides, all of the copyrolysis groups exhibited a synergistic effect on biochar production (S = 19.43-28.24%), while inhibiting the gas generation, with S ranging from -20.17 to -6.09%. Regarding the gaseous products, apart from H2, P, C, and L primarily generated CO2, CO, and CH4, respectively. Regarding bio-oil composition, the interactions occurring within PC, PL, and CL exhibited a significantly synergistic effect (S = 47.81-412.96%) on the formation of N-heterocyclics/amides, amides/nitriles, and acids/esters, respectively. Finally, the favorable applicability of the proposed interaction effects was verified with microalgae. This study offers valuable insights for understanding the microwave-assisted pyrolysis of protein-rich biomass, laying the groundwork for further research and process optimization.

Green Synthesis of Advanced Carbon Materials Used as Precursors for Adsorbents Applied in Wastewater Treatment

Huge amounts of vegetable waste, mainly resulting from the food industry, need large areas for storage, as they could cause hazardous environmental impact, leading to soil and water pollution or to CO₂ emissions during accidental incineration. This work was aimed at recycling certain lignocellulosic waste (walnut shells, kernels of peach, apricot, and olive) to design advanced carbon material precursors (ACMP) to be used for obtaining nano-powders with high applicative potential in pollution abatement. Both waste and ACMP were characterized using proximate and elemental analysis, and by optical microscopy. Complex characterization of raw materials by FTIR, TGA-DTG, and SEM analysis were carried out. The ACMP were synthetized at 600-700 °C by innovative microwave heating technology which offers the advantages of lower energy consumption using 3.3 kW equipment at laboratory level. The ACMP ash < 3% and increased carbon content of 87% enabled the development of an extended pore network depending on degassing conditions during heating. TEM analysis revealed a well-developed porous structure of the synthesized ACMP carbonaceous materials. Due to the presence of oxygen functional groups, ACMPs exhibit adsorption properties highlighted by an iodine index of max. 500 mg/g and surface area BET of 300 m²/g, which make them attractive for removal of environmental pollutants such as dyes having molecule sizes below 2 nm and ions with pore dimensions below 1 nm, widely used industrially and found in underground waters (NO₃^-) or waste waters (SO₄^2-).

Bio-oil and biochar from the pyrolytic conversion of biomass: A current and future perspective on the trade-off between economic, environmental, and technical indicators

Over the years, the transformation of biomass into a plethora of renewable value-added products has been identified as a promising strategy to fulfil high energy demands, lower greenhouse gas emissions, and exploit under-utilized resources. Techno-economic analysis (TEA) and life-cycle assessment (LCA) are essential to scale up this process while lowering the conversion cost. In this study, trade-offs are made between economic, environmental, and technical indicators produced from these methodologies to better evaluate the commercialization potential of biomass pyrolysis. This research emphasizes the necessity of combining LCA and TEA variables to assess the performance of the early-stage technology and associated constraints. The important findings based on the LCA analysis imply that most of the studies reported in literature focussed on the global warming potentials (GWP) under environmental category by considering greenhouse gases (GHGs) as evaluation parameter, neglecting many other important environmental indices. In addition, the upstream and downstream processes play an important role in understanding the life cycle impacts of a biomass based biorefinery. Under upstream conditions, the use of a specific type of feedstock may influence the LCA conclusions and technical priority. Under downstream conditions, the product utilization as fuels in different energy backgrounds is crucial to the overall impact potentials of the pyrolysis systems. In view of the TEA analysis, investigations towards maximizing the yield of valuable co-products would play an important role in the commercialization of pyrolysis process. However, comprehensive research to compare the conventional, advanced, and emerging approaches of biomass pyrolysis from the economic perspective is currently not available in the literature.

Microwave catalytic co-pyrolysis of Chlorella vulgaris and high density polyethylene over activated carbon supported monometallic: Characteristics and bio-oil analysis

Activated carbon (AC) has attracted much attention owing to its low cost and abundant sources. In this paper, three monometallic supported catalysts were prepared using AC as support (Ce/AC, Fe/AC, Ni/AC), and the effects of three catalysts on the microwave co-pyrolysis of Chlorella vulgaris (C. vulgaris) with high density polyethylene (HDPE) were studied. The results showed that the co-pyrolysis characteristics of C. vulgaris/HDPE = 1:1 (C1HP1) were significantly improved by three catalysts at high additions (>20 %). Among them, the C1HP1 group with 50 % Fe/AC addition had the shortest co-pyrolysis reaction time (2901 s). Besides, Ce/AC and Fe/AC have a promoting effect on bio-oil yields, while Ni/AC has an inhibiting effect. The maximum bio-oil yield (25.6 %) was obtained under 40 % addition of Fe/AC. Moreover, Ce/AC obtained the highest hydrocarbons content (66.68 %), while Fe/AC obtained the highest aromatic hydrocarbons content (36.64 %). Additionally, Ce/AC had the highest deoxygenation efficiency (47.33 %) and denitrification efficiency (42.28 %).

Microwave catalytic co-pyrolysis of chlorella vulgaris and oily sludge: Characteristics and bio-oil analysis

Co-pyrolysis of Chlorella vulgaris (CV) and Oily sludge (OS) under different mixing ratios were investigated by microwave furnace. NiO, activated carbon (AC) and their 1:1 compound (N1A1) with different additions (5%, 10%, 15% and 20%) were selected as microwave additives to study the effects on optimum mixing ratio of co-pyrolysis. The results indicated that mixing ratio of CV/OS = 1:1 (C1O1) was optimum for co-pyrolysis. Besides, 10% AC was optimal on improving pyrolysis characteristics of the C1O1 group. The most significant synergistic interaction of NiO and AC occurred in the 10% N1A1 group. Moreover, hydrocarbons in bio-oil of the C1O1 group increased by 31.84% compared with theoretical values, while nitrogenous, oxygenated compounds decreased by 74.18% and 19.01%. Addition of 10% N1A1 in the C1O1 group increased aliphatic hydrocarbons by 22.44%, and decreased nitrogenous, oxygenated compounds by 41.79% and 36.58%. Overall, 10% N1A1 was conducive for the C1O1 group to obtain high-quality bio-oil.

Study on co-pyrolysis and products of Chlorella vulgaris and rice straw catalyzed by activated carbon/HZSM-5 additives

The weight loss characteristics, product distribution and bio-oil composition of co-pyrolysis of rice straw (RS) and Chlorella vulgaris (CV) were investigated by microwave oven. Then, the catalytic effect of activated carbon (AC) and HZSM-5 on these characteristics were studied. Results showed that AC strongly improved co-pyrolysis weight loss characteristics and obtained maximum average weight loss rate (R_a) at 30% addition with 0.01639 wt.%/s. While HZSM-5 promoted the characteristics as addition was lower than 10%. In the case of compound additives, 20% A7H3 obtained the maximum R_a (0.01413 wt.%/s). Furthermore, both single AC and HZSM-5 showed negative effect on bio-oil production, while 20% A7H3 (AC/HZSM-5 = 7:3) achieved the maximum production (24%). For bio-oil composition, 30% A10H0 showed strong selectivity for phenol and N-heterocycle and 10% A0H10 showed strong aromatization capacity, and the addition of 20% A7H3 increased the hydrocarbons content from 20.79% to 31.63% compared with the blank group.

Microwave pyrolysis coupled with conventional pre-pyrolysis of the stalk for syngas and biochar

The study presented a novel approach microwave pyrolysis coupled conventional pre-pyrolysis (MCCP) to dispose of the stalk for syngas and biochar. Impacts of preheating temperature (250 ∼ 450 °C) on pyrolysis property and products characteristics were investigated. Compared with microwave-assisted pyrolysis (MAP), the initial time for rapid temperature ramp in MCCP was distinctly advanced from 124 s to within 20 s; the biochar yields significantly increased from 24.19% to 33.24%, and the H₂ content of syngas in the second stage reached up to 64.65%. The biochar from MCCP had higher carbon content (greater than 70%), carbon retention (greater than 50%), and BET surface area (141.69 m²/g) than MAP. A high degree of aromatization and complete carbon skeleton structure was observed in the biochar from MCCP. Finally, a mobile application system based on MCCP was proposed, increasing the energy efficiency from 13.5 ∼ 27% (MAP) to 58.5 ∼ 76.5%.

Co-pyrolysis of biomass and polyvinyl chloride under microwave irradiation: Distribution of chlorine

Co-pyrolysis of sophora wood (SW) and polyvinyl chloride (PVC) was conducted in a microwave reactor at different temperatures and different mixing ratios, and the transformation and distribution of chlorine in pyrolysis products were investigated. Microwave pyrolysis is a simple and efficient technique with better heating uniformity and process controllability than conventional heating. Compared with PVC pyrolysis, the addition of SW significantly reduced CO₂ yield and greatly increased the yield of CO. The yield and quality of pyrolysis oil were effectively improved by SW, and the content of chlorine-containing compounds in the oil was suppressed to <1% at low temperatures (<550 °C). Co-pyrolysis of SW and PVC reduced the chlorine emissions from 59.07% to 28.09% and promoted the retention of chlorine in char (from 0.33% to 4.72%). Cellulose, hemicellulose, and lignin were co-pyrolyzed with PVC to investigate their effects on chlorine distribution. The experiments demonstrated that lignin had the most significant effects on reducing gas phase chlorine emission and achieving chlorine immobilization, and chlorine mainly existed in the form of sodium chloride in the char of lignin-PVC co-pyrolysis. Hence co-pyrolysis of lignocellulosic biomass and PVC provides a practical pathway for utilization of PVC waste in an environmentally friendly manner, realizing efficient chlorine retention and significantly reducing chlorine-related emissions.

Co-pyrolysis of microalgae and other biomass wastes for the production of high-quality bio-oil: Progress and prospective

Microalgae are the most prospective raw materials for the production of biofuels, pyrolysis is an effective method to convert biomass into bioenergy. However, biofuels derived from the pyrolysis of microalgae exhibit poor fuel properties due to high content of moisture and protein. Co-pyrolysis is a simple and efficient method to produce high-quality bio-oil from two or more materials. Tires, plastics, and bamboo waste are the optimal co-feedstocks based on the improvement of yield and quality of bio-oil. Moreover, adding catalysts, especially CaO and Cu/HZSM-5, can enhance the quality of bio-oil by increasing aromatics content and decreasing oxygenated and nitrogenous compounds. Consequently, this paper provides a critical review of the production of bio-oil from co-pyrolysis of microalgae with other biomass wastes. Meanwhile, the underlying mechanism of synergistic effects and the catalytic effect on co-pyrolysis are discussed. Finally, the economic viability and prospects of microalgae co-pyrolysis are summarized.

Microwave-assisted co-pyrolysis of chlorella vulgaris and polypropylene: Characteristic and product distribution analyses

The co-pyrolysis characteristics and product yield of Chlorella vulgaris (CV) and polypropylene (PP) under different mixing ratios (10:0, 8:2, 6:4, 5:5, 4:6, 2:8 and 0:10) were studied by microwave oven. Then the effects of different graphite (GP) additions (10%, 20%, 30% and 40%) on the optimum mixing ratio of CV and PP were investigated. The composition of bio-oil was analyzed by GC-MS. The results indicated that the C8P2 (CV/PP = 8:2) group had the best pyrolysis characteristics. The maximum weight loss rate (R_m) and average weight loss rate (R_v) of the C8P2 with 30% GP addition achieved the peak value. In the absence of GP, compared with C10P0 group, the contents of nitrogen compounds in bio-oil of the C8P2 group decreased by 21.58%. After adding GP to the C8P2 group, the nitrogen compounds in bio-oil of 30% GP group was 1.93% lower than that in 0% GP group.

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.

Microalgae as Contributors to Produce Biopolymers

Biopolymers are very favorable materials produced by living organisms, with interesting properties such as biodegradability, renewability, and biocompatibility. Biopolymers have been recently considered to compete with fossil-based polymeric materials, which rase several environmental concerns. Biobased plastics are receiving growing interest for many applications including electronics, medical devices, food packaging, and energy. Biopolymers can be produced from biological sources such as plants, animals, agricultural wastes, and microbes. Studies suggest that microalgae and cyanobacteria are two of the promising sources of polyhydroxyalkanoates (PHAs), cellulose, carbohydrates (particularly starch), and proteins, as the major components of microalgae (and of certain cyanobacteria) for producing bioplastics. This review aims to summarize the potential of microalgal PHAs, polysaccharides, and proteins for bioplastic production. The findings of this review give insight into current knowledge and future direction in microalgal-based bioplastic production considering a circular economy approach. The current review is divided into three main topics, namely (i) the analysis of the main types and properties of bioplastic monomers, blends, and composites; (ii) the cultivation process to optimize the microalgae growth and accumulation of important biobased compounds to produce bioplastics; and (iii) a critical analysis of the future perspectives on the field.

Fuel, thermal and surface properties of microwave-pyrolyzed biochars depend on feedstock type and pyrolysis temperature

We evaluated the fuel, thermal and surface properties of twelve biochars produced from three lignocellulosic (canola straw, sawdust, wheat straw) and one non-lignocellulosic feedstock (manure pellet) pyrolyzed at three temperatures using a microwave. Regardless of feedstock type, increasing pyrolysis temperature progressively reduced the abundance of -OH functional group and yield, but increased pH and thermal stability of biochar. Gross calorific values (GCV), carbon stability, and degree of aromaticity of biochars derived from lignocellulosic feedstocks increased with increasing temperature due to decreased elemental oxygen content. However, high ash content in the non-lignocellulosic feedstock retarded its thermal degradation, producing biochars with low GCV. The specific surface area of biochars was low, with the highest value of 43 m² g^-1 achieved for sawdust biochar produced at 500 °C. We conclude that the fuel, thermal, and surface properties of the biochars were dependent on the feedstock type and pyrolysis temperature.

Evaluation of Joint Management of Pine Wood Waste and Residual Microalgae for Agricultural Application

This work addresses the joint management of residual microalgae and pine wood waste through pyrolysis to obtain a solid product for its use as soil amendment and two other by-products (liquid and gaseous) that can be used for energy purposes. Two management routes have been followed. The first route is through the co-pyrolysis of mixtures of both residual materials in several proportions and the later use of their solid fraction for soil amendment. The second route is the pyrolysis of pine wood waste and its direct combination with dried residual microalgae, also using it as soil amendment. The solid fraction assessment shows that from seven solid products (biochar) three stand out for their positive applicability in agriculture as soil amendment. In addition, they also present the benefit of serving as carbon sink, giving a negative balance of CO2 emissions. However, caution is suggested due to biochar applicability being subject to soil characteristics. To ensure the sustainability of the overall process, the energy available in liquid and gaseous fractions has been assessed for covering the drying needs of the residual microalgae in both cases. These results suggest that the pyrolysis process is a sustainable way to manage specific evaluated residues and their products.

Recovery of renewable aromatic and aliphatic hydrocarbon resources from microwave pyrolysis/co-pyrolysis of agro-residues and plastics wastes

The present study focussed on recovering the valuable carbon resources from agro-residues (wheat straw, rice husk) and waste plastics (polypropylene, polystyrene) using microwave pyrolysis and co-pyrolysis. The main objective of this study is to investigate the effect of the susceptor blending mechanism on the co-pyrolysis product distribution. Graphite was mixed with feedstock in a new approach to achieving homogeneity, and microwave power of 600 W was used. The average heating rate (52-67 (°C/min)), microwave energy required (2267-2936 (J/g)), heat energy utilized (1410-1444 (J/g)), and conductive heat losses (85-110 (J/g)) were analyzed. The selectivity of cyclic alkanes and alkenes (65.5%) was found to be high in polypropylene pyrolysis oil. Polystyrene pyrolysis oil predominantly contained cyclooctatetraene (61%) compound. Bio-oil obtained from wheat straw predominantly contained aromatic hydrocarbons (85%), whereas rice husk oil also contains high selectivity aromatic hydrocarbons (37.8%) along with aliphatic hydrocarbons (54.9%). The co-pyrolysis oils has high selectivity of aromatics.

Biomass Pyrolysis Technology by Catalytic Fast Pyrolysis, Catalytic Co-Pyrolysis and Microwave-Assisted Pyrolysis: A Review

With the aggravation of the energy crisis and environmental problems, biomass resource, as a renewable carbon resource, has received great attention. Catalytic fast pyrolysis (CFP) is a promising technology, which can convert solid biomass into high value liquid fuel, bio-char and syngas. Catalyst plays a vital role in the rapid pyrolysis, which can increase the yield and selectivity of aromatics and other products in bio-oil. In this paper, the traditional zeolite catalysts and metal modified zeolite catalysts used in CFP are summarized. The influence of the catalysts on the yield and selectivity of the product obtained from pyrolysis was discussed. The deactivation and regeneration of the catalyst were discussed. Catalytic co-pyrolysis (CCP) and microwave-assisted pyrolysis (MAP) are new technologies developed in traditional pyrolysis technology. CCP improves the problem of hydrogen deficiency in the biomass pyrolysis process and raises the yield and character of pyrolysis products, through the co-feeding of biomass and hydrogen-rich substances. The pyrolysis reactions of biomass and polymers (plastics and waste tires) in CCP were reviewed to obtain the influence of co-pyrolysis on composition and selectivity of pyrolysis products. The catalytic mechanism of the catalyst in CCP and the reaction path of the product are described, which is very important to improve the understanding of co-pyrolysis technology. In addition, the effects of biomass pretreatment, microwave adsorbent, catalyst and other reaction conditions on the pyrolysis products of MAP were reviewed, and the application of MAP in the preparation of high value-added biofuels, activated carbon and syngas was introduced.

Algae as green energy reserve: Technological outlook on biofuel production

Depletion of fossil fuel sources and their emissions have triggered a vigorous research in finding alternative and renewable energy sources. In this regard, algae are being exploited as a third generation feedstock for the production of biofuels such as bioethanol, biodiesel, biogas, and biohydrogen. However, algal based biofuel does not reach successful peak due to the higher cost issues in cultivation, harvesting and extraction steps. Therefore, this review presents an extensive detail of deriving biofuels from algal biomass starting from various algae cultivation systems like raceway pond and photobioreactors and its bottlenecks. Evolution of biofuel feedstocks from edible oils to algae have been addressed in the initial section of the manuscript to provide insights on the different generation of biofuel. Different configuration of photobioreactor systems used to reduce contamination risk and improve biomass productivity were extensively discussed. Photobioreactor performance greatly relies on the conditions under which it is operated. Hence, the importance of such conditions alike temperature, light intensity, inoculum size, CO_2, nutrient concentration, and mixing in bioreactor performance have been described. As the lipid is the main component in biodiesel production, several pretreatment methods such as physical, chemical and biological for disrupting cell membrane to extract lipid were comprehensively reviewed and presented. This review article had put forth the recent advancement in the pretreatment methods like hydrothermal processing of algal biomasses using acid or alkali. Eventually, challenges and future dimensions in algal cultivation and pretreatment process were discussed in detail for making an economically viable algal biofuel.

Catalytic co-pyrolysis behaviors, product characteristics and kinetics of rural solid waste and chlorella vulgaris

Catalytic and non-catalytic co-pyrolysis behaviors, kinetics and products distribution of rural solid waste (RSW) and chlorella vulgaris (CV) were studied by thermogravimetric analysis (TGA) and fixed bed reactor. TGA results showed that co-pyrolysis of RSW and CV presented synergism by decreasing the temperature relating to the first mass loss peak. All the additives reduced residual mass for co-pyrolysis (5.21%, 1.57% and 4.89% for CaO, MgO and HZSM-5). Addition of CaO increased activation energy while HZSM-5 and MgO reduced it. Co-pyrolysis of RSW and CV remarkably reduced carboxylic acids and nitrogenous compounds especially for 1:1 ratio. (30.85% and 25.87%). Catalytic pyrolysis with CaO showed the best results by increasing aliphatic hydrocarbons especially light fraction (5.96%-11.98%), reducing acids (0%-30.85%) and nitrogenous compounds (0.08%-17.26%), causing higher HHV of oil. Overall, catalytic co-pyrolysis of CV and RSW with CaO could obtain bio-oil of higher quality.

Fast microwave-assisted pyrolysis of wastes for biofuels production - A review

Microwave-assisted pyrolysis of waste suffers from the problem that the waste generally has low microwave absorptivity thereby resulting in low heating rate and low pyrolysis temperature. In this case, fast microwave-assisted pyrolysis is proposed and developed to help the pyrolysis of waste. This study describes two methods that can be used to realize fast microwave-assisted pyrolysis of waste: (1) premixed method (wastes are mixed with microwave absorbent) and (2) non-premixed method (wastes are poured onto the heated microwave absorbent bed). Then, biofuels (bio-oil, bio-gas, and bio-char) produced from fast microwave-assisted pyrolysis of wastes are reviewed. The review results show that the yields of bio-oil, bio-gas, and bio-char obtained from fast microwave-assisted pyrolysis of wastes varied significantly in the ranges of 2-96 wt%, 2.4-86.8 wt%, and 0.3-83.2 wt%, respectively. Although the present research focused mainly on the premixed method, non-premixed/continuous fast microwave-assisted pyrolysis is still promising and challenging.

Reaction engineering and kinetics of algae conversion to biofuels and chemicals via pyrolysis and hydrothermal liquefaction

A state-of-the-art review on pyrolysis and hydrothermal liquefaction of algae to fuels and chemicals with emphasis on reaction chemistry and kinetics.

Thermal conversion of pineapple crown leaf waste to magnetized activated carbon for dye removal

Pineapple crown leaf was successfully converted to the magnetized activated carbon (MAC) as an attractive solution to overcome separation problems. The activated carbon (AC) was produced by an innovative method combining KOH activation and microwave heating while the magnetization process was prepared by a co-precipitation method. In this sense, the activation stage was studied at different impregnation ratio. The resulted magnetic adsorbent was further tested its feasibility for methyl violet dye removal. The result shows that MAC consists of both micropores and mesopores with more oxygen-containing functional groups, indicating it can be used to remove dye from contaminated water. The increase of impregnation ratio led to an increase in the MAC porosity and a decrease in the magnetic property. The adsorption behavior of methyl violet dye onto MAC was well described by the Redlich-Peterson isotherm model.

A review of catalysts used in microwave assisted pyrolysis and gasification

The review describes different catalysts and reactor-types used in microwave-assisted thermochemical biomass conversion. We present comparative review of various catalytic experiments and experimental conditions using catalysts in both in situ and ex situ processes. In situ catalytic processes are more frequently used due to simpler experimental set up. However, the process leads to higher catalytic deactivation rate and catalyst recovery is difficult. Catalysts used in ex situ processes require a more complex experimental set-up, the advantage being the fact that optimum temperature can be obtained to achieve best results catalyst recovery is facile, and its deactivation occurs at a lower rate. The catalysts described herein represent just a small part of the catalyst types/family that can be theoretically used. Commonly used catalysts are zeolites, metal oxides, various salts or carbon type materials but other materials or improvements of those mentioned need to be tested in the future.