Bio-oil production of softwood and hardwood forest industry residues through fast and intermediate pyrolysis and its chromatographic characterization

Design expert based optimization of the pyrolysis process for the production of cattle dung bio-oil and properties characterization

This study aimed to optimize pyrolysis conditions to maximize bio-oil yield from cattle dung, a waste product of livestock practices. Pyrolysis of cattle dung was carried out in batch type reactor. The pyrolysis process was optimized using a central composite design in response surface methodology, with conversion parameters such as pyrolysis temperature, vapor cooling temperature, residence time, and gas flow rate taken into account. The cattle dung bio-oil was analyzed using gas chromatography/mass spectroscopy (GC/MS), an elemental analyzer, a pH probe, and a bomb calorimeter. Furthermore, the ASTM standard procedures were used to determine the bio-fuel characteristics. The optimized conditions were found to be a pyrolysis temperature of 402 °C, a vapor cooling temperature of 2.25 °C, a residence time of 30.72 min, and a gas flow rate of 1.81 l min-1, resulting in a maximum bio-oil yield of 18.9%. According to the findings, the yield of bio-oil was predominantly affected by pyrolysis temperature and vapor cooling temperature. Moreover, the bio-oil that was retrieved was discovered to be similar to conventional liquid fuels in numerous ways.

Electrocatalytic valorization of lignocellulose-derived aromatics at industrial-scale current densities

Electrocatalytic hydrogenation of lignocellulosic bio-oil to value-added chemicals offers an attractive avenue to use the increasing intermittent renewable electricity and biomass-derived feedstocks. However, to date the partial current densities to target products of these reactions are lower than those needed for industrial-scale productivity, which limits its prospects. Here we report a flow-cell system equipped with a Rh diffusion electrode to hydrogenate lignocellulose-derived aromatic monomers, such as furans and lignin monomers, to value-added chemicals. We achieve high faradaic efficiencies up to 64% at industrial-scale current densities of 300-500 mA cm-2, representing high productivities to target products. A screening of electrocatalysts indicates that only by highly-electrolyte-permeable Rh diffusion electrodes are we able to unite current density with faradaic efficiency. We apply in-situ infrared reflection-absorption spectroscopy to investigate the electrode-potential-dependent reaction pathways and intermediates, confirming a wide potential window for efficient electrocatalytic hydrogenation of lignocellulose-derived aromatics to target products.

Revealing the Reactivity of Individual Chemical Entities in Complex Mixtures: the Chemistry Behind Bio-Oil Upgrading

Bio-oils are precursors for biofuels but are highly corrosive necessitating further upgrading. Furthermore, bio-oil samples are highly complex and represent a broad range of chemistries. They are complex mixtures not simply because of the large number of poly-oxygenated compounds but because each composition can comprise many isomers with multiple functional groups. The use of hyphenated ultrahigh-resolution mass spectrometry affords the ability to separate isomeric species of complex mixtures. Here, we present for the first time, the use of this powerful analytical technique combined with chemical reactivity to gain greater insights into the reactivity of the individual isomeric species of bio-oils. A pyrolysis bio-oils and its esterified bio-oil were analyzed using gas chromatography coupled to Fourier transform ion cyclotron resonance mass spectrometry, and in-house software (KairosMS) was used for fast comparison of the hyphenated data sets. The data revealed a total of 10,368 isomers in the pyrolysis bio-oil and an increase to 18,827 isomers after esterification conditions. Furthermore, the comparison of the isomeric distribution before and after esterification provide new light on the reactivities within these complex mixtures; these reactivities would be expected to correspond with carboxylic acid, aldehyde, and ketone functional groups. Using this approach, it was possible to reveal the increased chemical complexity of bio-oils after upgrading and target detection of valuable compounds within the bio-oils. The combination of chemical reactions alongside with in-depth molecular characterization opens a new window for the understanding of the chemistry and reactivity of complex mixtures.

Machine learning prediction of pyrolytic gas yield and compositions with feature reduction methods: Effects of pyrolysis conditions and biomass characteristics

This study aimed to utilize machine learning algorithems combined with feature reduction for predicting pyrolytic gas yield and compositions based on pyrolysis conditions and biomass characteristics. To this end, random forest (RF) and support vector machine (SVM) was introduced and compared. The results suggested that six features were adequate to accurately forecast (R² > 0.85, RMSE < 5.7%) the yield while the compositions only required three. Moreover, the profound information behind the models was extracted. The relative contribution of pyrolysis conditions was higher than that of biomass characteristics for yield (55%), CO₂ (73%), and H₂ (81%), which was inverse for CO (12%) and CH₄ (38%). Furthermore, partial dependence analysis quantified the effects of both reduced features and their interactions exerted on pyrolysis process. This study provided references for pyrolytic gas production and upgrading in a more convenient manner with fewer features and extended the knowledge into the biomass pyrolysis process.

Hydrodeoxygenation of Guaiacol over Pd–Co and Pd–Fe Catalysts: Deactivation and Regeneration

In bio-oil upgrading, the activity and stability of the catalyst are of great importance for the catalytic hydrodeoxygenation (HDO) process. The vapor-phase HDO of guaiacol was investigated to clarify the activity, stability, and regeneration ability of Al-MCM-41 supported Pd, Co, and Fe catalysts in a fixed-bed reactor. The HDO experiment was conducted at 400 °C and 1 atm, while the regeneration of the catalyst was performed with an air flow at 500 °C for 240 min. TGA and XPS techniques were applied to study the coke deposit and metal oxide bond energy of the catalysts before and after HDO reaction. The Co and Pd–Co simultaneously catalyzed the CArO–CH3, CAr–OH, and multiple C–C hydrogenolyses, while the Fe and Pd–Fe principally catalyzed the CAr–OCH3 hydrogenolysis. The bimetallic Pd–Co and Pd–Fe showed a higher HDO yield and stability than monometallic Co and Fe, since the coke formation was reduced. The Pd–Fe catalyst presented a higher stability and regeneration ability than the Pd–Co catalyst, with consistent activity during three HDO cycles.

Conversion of guaiacol as lignin model component using acid-treated, multi-walled carbon nanotubes supported Ru–MnO bimetallic catalysts

Acid-treated, multi-walled carbon nanotube (AMWCNT) supported Ru and MnO bimetallic catalysts were prepared for liquid phase hydrodeoxygenation of guaiacol. The physicochemical properties of the prepared catalysts were characterized by FTIR, XRD, NH3-TPD, CO2-TPD, TEM, and XPS. MnO species were loaded on the inner surface of carbon nanotubes and were helpful for Ru particle dispersion. The 6%Ru-8%MnO/AMWCNTs with smaller Ru particle size, better dispersion, and more basic sites gave the best catalytic performance of 99.38% conversion of guaiacol and 85.84% selectivity to cyclohexanol. The effects of reaction conditions on liquid phase guaiacol hydrodeoxygenation were discussed and a possible reaction path was proposed.

Food and Market Waste-A Pathway to Sustainable Fuels and Waste Valorization

Food and market waste (FMW) is one of the most abundant unrecycled products which poses waste management issues and negative environmental impacts. Thermo-catalytic reforming (TCR) is a pyrolysis based technology which can convert a wide range of biomass wastes into energy vectors bio-oil, syngas, and char. This paper investigates the conversion potential of FMW into sustainable biofuels. The FMW was processed using a laboratory scale 2 kg/h TCR reactor. The process produced 7 wt % organic bio-oil, 53 wt % permanent gas, and 22 wt % char. The bio-oil higher heating value (HHV) was found to be 36.72 MJ/kg, comparable to biodiesel, and contained a low oxygen content (<5%) due to cracking of higher molecular weight organics. Naphthalene was detected to be the most abundant aromatic compound within the oil, with relative abundance of 12.95% measured by GC-MS. The total acid number of the oil (TAN) and viscosity were 11.7 mg KOH/g and 6.3 cSt, respectively. The gross calorific value of the produced biochar was 23.64 MJ/kg, while the permanent gas showed a higher heating value of approximately 17 MJ/Nm³. Methane (CH₄) was found to be the largest fraction in the permanent gases reaching over 23%. This resulted either due to the partial methanation of biosyngas over the catalytically active FMW biochar or the hydrogenation of coke deposited on the biochar in the post reforming stage.

Physicochemical, Performance, Combustion and Emission Characteristics of Melaleuca Cajuputi Oil-Refined Palm Oil Hybrid Biofuel Blend

To reduce the economic impact caused by the fossil fuel crisis and avoid relying on existing biofuels, it is important to seek locally available and renewable biofuel throughout the year. In the present work, a new light biofuel—Melaleuca Cajuputi oil (MCO)—was introduced to blend with refined palm oil (RPO). The physicochemical properties, combustion characteristics, engine performance, and exhaust emissions were comprehensively examined. It was found that the higher the percentage of MCO, the lower the viscosity and density of the blends obtained. Calorific value (CV) was increased with the increase of MCO fraction in the blend. Regression analysis has suggested that the blend of 32% (v/v) of RPO and 68% (v/v) of MCO (RPO32MCO68) is optimal to obtain viscosity and density in accordance with ASTM 6751/EN 14214 standards. The experimental results show that the in-cylinder pressure, brake torque, and brake power of the optimal blend were slightly lower than those of baseline diesel fuel. Brake specific fuel consumption (BSFC), carbon monoxide (CO), and unburnt hydrocarbon (HC) were found to be slightly higher compared to diesel fuel. Notably, nitrogen oxides (NOx) and smoke opacity were found to be decreased over the entire range of the test. Overall, the optimal blend of RPO32MCO68 has shown a decent result which marks it as a potential viable source of biofuel.

Pyrolysis of oil palm mesocarp fiber catalyzed with steel slag-derived zeolite for bio-oil production

The pyrolysis of oil palm mesocarp fiber (OPMF) was catalyzed with a steel slag-derived zeolite (FAU-SL) in a slow-heating fixed-bed reactor at 450 °C, 550 °C, and 600 °C. The catalytic pyrolysis of OPMF produced a maximum yield of 47 wt% bio-oil at 550 °C, and the crude pyrolysis vapor (CPV) of this process yielded crude pyrolysis oil with broad distribution of bulky oxygenated organic compounds. The bio-oil composition produced at 550 °C contained mainly light and stable acid-rich carbonyls at a relative abundance of 48.02% peak area and phenolic compounds at 12.03% peak area. The FAU-SL high mesoporosity and strong surface acidity caused the conversion of the bulky CPV molecules into mostly light acid-rich carbonyls and aromatics through secondary reactions. The secondary reactions mechanisms facilitated by FAU-SL reduced the distribution of the organic compounds in the bio-oil to mostly acid-rich carbonyls and aromatic in contrast to other common zeolite.

Analytical Strategies Involved in the Detailed Componential Characterization of Biooil Produced from Lignocellulosic Biomass

Elucidation of chemical composition of biooil is essentially important to evaluate the process of lignocellulosic biomass (LCBM) conversion and its upgrading and suggest proper value-added utilization like producing fuel and feedstock for fine chemicals. Although the main components of LCBM are cellulose, hemicelluloses, and lignin, the chemicals derived from LCBM differ significantly due to the various feedstock and methods used for the decomposition. Biooil, produced from pyrolysis of LCBM, contains hundreds of organic chemicals with various classes. This review covers the methodologies used for the componential analysis of biooil, including pretreatments and instrumental analysis techniques. The use of chromatographic and spectrometric methods was highlighted, covering the conventional techniques such as gas chromatography, high performance liquid chromatography, Fourier transform infrared spectroscopy, nuclear magnetic resonance, and mass spectrometry. The combination of preseparation methods and instrumental technologies is a robust pathway for the detailed componential characterization of biooil. The organic species in biooils can be classified into alkanes, alkenes, alkynes, benzene-ring containing hydrocarbons, ethers, alcohols, phenols, aldehydes, ketones, esters, carboxylic acids, and other heteroatomic organic compounds. The recent development of high resolution mass spectrometry and multidimensional hyphenated chromatographic and spectrometric techniques has considerably elucidated the composition of biooils.

A xylanase-aided enzymatic pretreatment facilitates cellulose nanofibrillation

Although biological pretreatment of cellulosic fiber based on endoglucanases has shown some promise to facilitate cellulose nanofibrillation, its efficacy is still limited. In this study, a xylanase-aided endoglucanase pretreatment was assessed on the bleached hardwood and softwood Kraft pulps to facilitate the downstream cellulose nanofibrillation. Four commercial xylanase preparations were compared and the changes of major fiber physicochemical characteristics such as cellulose/hemicellulose content, gross fiber properties, fiber morphologies, cellulose accessibility/degree of polymerization (DP)/crystallinity were systematically evaluated before and after enzymatic pretreatment. It showed that the synergistic cooperation between endoglucanase and certain xylanase (Biobrite) could efficiently "open up" the hardwood Kraft pulp with limited carbohydrates degradation (<7%), which greatly facilitated the downstream cellulose nanofibrillation during mild sonication process (90Wh) with more uniform disintegrated nanofibril products (50-150nm, as assessed by scanning electron microscopy and UV-vis spectroscopy).

Pyrolysis of oil palm mesocarp fiber and palm frond in a slow-heating fixed-bed reactor: A comparative study

Oil palm mesocarp fiber (OPMF) and palm frond (PF) were respectively devolatilized by pyrolysis to OPMF-oil and PF-oil bio-oils and biochars, OPMF-char and PF-char in a slow-heating fixed-bed reactor. In particular, the OPMF-oil and PF-oil were produced to a maximum yield of 48wt% and 47wt% bio-oils at 550°C and 600°C, respectively. The high heating values (HHVs) of OPMF-oil and PF-oil were respectively found to be 23MJ/kg and 21MJ/kg, whereas 24.84MJ/kg and 24.15MJ/kg were for the corresponding biochar. The HHVs of the bio-oils and biochars are associated with low O/C ratios to be higher than those of the corresponding biomass. The Fourier transform infrared spectra and peak area ratios highlighted the effect of pyrolysis temperatures on the bio-oil compositions. The bio-oils are pervaded with numerous oxygenated carbonyl and aromatic compounds as suitable feedstocks for renewable fuels and chemicals.

Combustion performance of biocrude oil from solvolysis liquefaction of Chlorella pyrenoidosa by thermogravimetry-Fourier transform infrared spectroscopy

The kinetic behavior and evolution characteristics of gaseous products during the combustion of biocrude oil from solvolysis liquefaction of Chlorella pyrenoidosa were investigated by thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The results indicated the biocrude oil obtained from different ethanol/water mixed ratio had obvious difference with each other. The ignition temperature of biocrude oil from ethanol-water co-solvent was lower than that from pure water solvent, which promoted the comprehensive combustion index. Especially, BO40 (biocrude oil obtained from 40% ethanol content) achieved the lowest ignition temperature (163.4°C) and high comprehensive combustion index (1.24×10^-06min^-2°C^-3). CH, CO, CC, CO₂, CO and HCN were the main gaseous products. Compared to other biocrude oil samples, BO40 had high first peak intensity of CH, CO and CC, and low peak intensity of CO, which performed better combustion characteristic.

Hydrodeoxygenation of gamma-valerolactone on transition metal phosphide catalysts

The catalytic hydrodeoxygenation (HDO) of the cyclic five-membered ester gamma-valerolactone (GVL-C₅H₈O₂) on a series of supported metal phosphide catalysts and a commercial Pd/Al₂O₃ catalyst was studied at 0.5 MPa.

Characterization and Comparison of Fast Pyrolysis Bio-oils from Pinewood, Rapeseed Cake, and Wheat Straw Using 13C NMR and Comprehensive GC × GC

Fast pyrolysis bio-oils are feasible energy carriers and a potential source of chemicals. Detailed characterization of bio-oils is essential to further develop its potential use. In this study, quantitative ¹³C nuclear magnetic resonance (¹³C NMR) combined with comprehensive two-dimensional gas chromatography (GC × GC) was used to characterize fast pyrolysis bio-oils originated from pinewood, wheat straw, and rapeseed cake. The combination of both techniques provided new information on the chemical composition of bio-oils for further upgrading. ¹³C NMR analysis indicated that pinewood-based bio-oil contained mostly methoxy/hydroxyl (≈30%) and carbohydrate (≈27%) carbons; wheat straw bio-oil showed to have high amount of alkyl (≈35%) and aromatic (≈30%) carbons, while rapeseed cake-based bio-oil had great portions of alkyl carbons (≈82%). More than 200 compounds were identified and quantified using GC × GC coupled to a flame ionization detector (FID) and a time of flight mass spectrometer (TOF-MS). Nonaromatics were the most abundant and comprised about 50% of the total mass of compounds identified and quantified via GC × GC. In addition, this analytical approach allowed the quantification of high value-added phenolic compounds, as well as of low molecular weight carboxylic acids and aldehydes, which exacerbate the unstable and corrosive character of the bio-oil.

Potential of genetically engineered hybrid poplar for pyrolytic production of bio-based phenolic compounds

Wild-type and two genetically engineered hybrid poplar lines were pyrolyzed in a micro-pyrolysis (Py-GC/MS) and a bench scale setup for fast and intermediate pyrolysis studies. Principal component analysis showed that the pyrolysis vapors obtained by micro-pyrolysis from wood of caffeic acid O-methyltransferase (COMT) and caffeoyl-CoA O-methyltransferase (CCoAOMT) down-regulated poplar trees differed significantly from the pyrolysis vapors obtained from non-transgenic control trees. Both fast micro-pyrolysis and intermediate pyrolysis of transgenic hybrid poplars showed that down-regulation of COMT can enhance the relative yield of guaiacyl lignin-derived products, while the relative yield of syringyl lignin-derived products was up to a factor 3 lower. This study indicates that lignin engineering via genetic modifications of genes involved in the phenylpropanoid and monolignol biosynthetic pathways can help to steer the pyrolytic production of guaiacyl and syringyl lignin-derived phenolic compounds such as guaiacol, 4-methylguaiacol, 4-ethylguaiacol, 4-vinylguaiacol, syringol, 4-vinylsyringol, and syringaldehyde present in the bio-oil.