Pyrolysis Of Switchgrass Research Articles

Exploring kinetic and thermodynamic mechanisms of switchgrass pyrolysis using iterative linear integral isoconversional method and master plots approach

This study aimed to explore the kinetic mechanism of switchgrass pyrolysis through isoconversional kinetic analysis and master plots approach. The pyrolysis kinetics of switchgrass was experimentally studied by thermogravimetric analysis at 5, 10, 20, and 40 K min−1. The experimental kinetic data of switchgrass pyrolysis was processed by the iterative linear integral isoconversional method and the obtained effective activation energies varied significantly with conversion: from 190.3 to 216.7, 217.3 ± 0.9 and 219.4 to 301.4 kJ·mol−1 in the conversion range of 0.05 – 0.45, 0.45 – 0.75 and 0.75 – 0.95, respectively. The significant conversion dependence of activation energies indicated switchgrass pyrolysis was a kinetically complex process, which was caused by the overlapping decomposition reactions of lignocellulosic components contained in switchgrass. Based on the master plots approach and the general empirical reaction model, the pyrolysis kinetic process of switchgrass pyrolysis followed the reaction model: f(α) = α-0.307·(1–1.020α)2.276. The frequency factor of switchgrass pyrolysis varied from 4.2 × 1012 to 3.9 × 1018 s−1 in the conversion range of 0.05 – 0.95, and a kinetic compensation effect between the frequency factor and activation energy was discovered. Based on the kinetic results, the changes in Gibbs free energy, enthalpy and entropy for switchgrass pyrolysis were calculated. It is expected that this study can provide a methodological guideline for the kinetics and thermodynamics of lignocellulosic biomass pyrolysis.

Phenolic-rich bio-oil production by microwave catalytic pyrolysis of switchgrass: Experimental study, life cycle assessment, and economic analysis

This study aims to determine the environmental impacts and feasibility of optimizing the production of phenolic-rich bio-oil, via switchgrass microwave catalytic pyrolysis. K3PO4 (Tripotassium phosphate) was used as the catalyst, at different temperatures, throughout this life cycle assessment (LCA) study. Results were compared with non-catalytic microwave pyrolysis (SiC-400) and conventional pyrolysis. K3PO4 (KP) was used as the microwave absorber and catalyst to enhance the low microwave absorption of switchgrass during microwave pyrolysis, and to improve the bio-oil quality and selectivity for phenolics production. Pyrolysis temperatures made a considerable difference to the LCA. There was an 86% reduction in the pyrolysis time when heating the sample to 300 °C (KP-300), as compared to 400 °C (KP-400), resulting in a significant reduction of the amount of energy required, and GHG's emitted. The total global warming potential (GWP) for microwave catalytic pyrolysis is observed within 159–223 kg CO2-eq/1000 kg of dried switchgrass (SG), with the baseline case (SiC-400) being the highest, and KP-300 being the lowest. Using the produced biochar, which is rich in nutrients for soil application, brings the net GWP to negative values through carbon sequestration. KP-300 also showed the highest selectivity for phenol and alkylphenols production, which increased by 252% and 420% respectively, compared to the baseline. The results clearly indicate that introducing K3PO4 showed great potential for accelerating microwave heating, and improving bio-oil selectivity towards alkylphenols, which can be used to replace petroleum-based phenol. This in turn can reduce GHG emissions, due to higher conversion efficiencies and lower energy consumption compared with non-catalytic microwave pyrolysis and conventional pyrolysis.

Detailed biomass fast pyrolysis kinetics integrated to computational fluid dynamic (CFD) and discrete element modeling framework: Predicting product yields at the bench-scale

Fast pyrolysis is an intricate process due to the variability and anisotropy of lignocellulosic biomass and the complicated chemistry and physics during conversion in a bubbling fluidized bed reactor (BFBR). The complexity of biomass fast pyrolysis lends itself well to computational fluid dynamics (CFD) and discrete element (DEM) analysis, which promises to reduce experimental time and its associated cost. This study investigated switchgrass fast pyrolysis simulated by computational fluid dynamics coupled with a discrete element method to track individual reacting biomass particles throughout a bench-scale BFBR reactor. We accounted for the fast pyrolysis chemistry through a comprehensive reaction scheme with secondary cracking reactions. We performed a three-step reduction for secondary cracking reactions to convert the full cracking scheme into a reduced scheme easily incorporated into our model. We assessed the impact of operational conditions on the steady-state yields of liquid bio-oil, non-condensable gases (NCG), at 550 °C over a range of fluidization numbers (2 – 6 Umf), reported as a ratio to the minimum fluidization velocity (Umf). At steady-state, the volatile bio-oil yield had a range of 49.3–50.4 wt%. Levoglucosan was the primary volatile component present with 21 wt% of the bio-oil while water was the second largest with 20 wt%. The reduction of the secondary reaction schemes did not appreciably affect the overall yields of switchgrass pyrolysis compared to the full secondary scheme.

Co-production of phenolic-rich bio-oil and magnetic biochar for phosphate removal via bauxite-residue-catalysed microwave pyrolysis of switchgrass

Bauxite residue (BR) was tested as a low-cost microwave absorber and catalyst for microwave-assisted pyrolysis for producing phenolic-rich bio-oil, along with magnetic biochar that can be used as an adsorbent for capturing excess nutrients, such as phosphates, from eutrophic water or wastewater. Mixing BR alone with switchgrass (SG) did not enhance SG microwave absorption, while mixing 10 wt% clinoptilolite and 20 wt% BR (10Clino–20BR) with SG increased the heating rate by 382% in comparison with 10Clino alone, due to the formation of good microwave absorbers (i.e. maghemite and magnetite) on the biochar surfaces, confirming their synergistic effects. The addition of BR reduced the acidity of the bio-oil by up to 47%, and increased the production of aromatics and alkylated phenols by up to 180% and 319%, respectively, compared with 10Clino alone. Biochar produced from 10Clino–20BR had magnetic properties, which are very important for facilitating the separation of spent biochar from P-contaminated aqueous solutions in industrial applications. Using the magnetic biochar for phosphorus adsorption, the highest adsorption capacity of 64.4 mg PO43−/g (21 mg PO43--P/g) was measured for the biochar produced using 10Clino–20BR at pH 4, and the adsorption isotherm was fitted by the Freundlich model very well. The magnetic biochar showed a high adsorption capacity for phosphate removal. In addition, the P-loaded biochar could be marketed as a balanced fertilizer to increase soil fertility, converting BR into a valuable product, instead of a waste material.

Bauxite residue as a catalyst for microwave-assisted pyrolysis of switchgrass to high quality bio-oil and biochar

Bauxite residue (BR) is a highly alkaline type of solid waste generated by the aluminum industry that poses a significant environmental risk upon disposal. However, BR is abundant in metals, especially iron, that offer the desired catalytic activity for microwave pyrolysis. Thus, this study aimed to use BR as a low-cost microwave absorber and catalyst for biomass microwave pyrolysis to obtain higher quality bio-oil and biochar. The addition of BR to switchgrass, the representative biomass, did not facilitate microwave absorption because most of the iron in the BR was in the form of goethite and hematite. However, the addition of an efficient microwave-absorbing catalyst (e.g., K3PO4 or clinoptilolite) to the BR triggered synergistic effects, increasing the microwave heating rate by ~ 346% compared to K3PO4 or clinoptilolite alone, which was attributed to the reduction of hematite and goethite to maghemite and/or magnetite. The addition of 10% BR to a mixture of 10% K3PO4 and 10% bentonite further triggered synergistic effects that resulted in the highest microwave heating rate of 439 °C/min, which was a 211% increase compared to using 10% K3PO4 and 10% bentonite without BR, and doubled the Brunauer-Emmett-Teller (BET) surface area of the biochar, reduced the bio-oil acidity by up to 71% compared to that obtained using a single catalyst, and increased the alkylated phenols contents in the bio-oil by 339% compared to that produced without a catalyst. These results demonstrated that the synergistic effects of BR can only be triggered when mixed with another efficient microwave-absorbing catalyst.

Engineered biochars from catalytic microwave pyrolysis for reducing heavy metals phytotoxicity and increasing plant growth

Pb, Ni, and Co are among the most toxic heavy metals that pose direct risks to humans and biota. There are no published studies on biochars produced at low temperatures (i.e., 300 °C), which possess high sorption capacity for heavy metal remediation and reclamation of contaminated sandy soils. This research studied the effect of catalytic microwave pyrolysis of switchgrass (SG) using bentonite and K3PO4 to produce biochar at low temperature (300 °C) with high sorption capacity for reducing the phytotoxicity of heavy metals, and investigated the synergistic effects of catalyst mixture on biochar sorption capacity. The quality of the biochars was examined in terms of their impacts on plant growth, reducing phytotoxicity and uptake of heavy metals in sandy soil spiked with Pb, Ni, and Co. All catalysts increased the micropore surface area and cation-exchange capacity of biochars, and resulted in biochars rich in plant nutrients, which not only decreased heavy metal phytotoxicity, but also boosted plant growth in the spiked soil by up to 140% compared to the sample without biochar. By mixing bentonite and K3PO4 with SG during microwave pyrolysis, the efficacy of biochar in reducing phytotoxicity and heavy metals uptake was further enhanced because of the highest micropore surface area (402 m2/g), moderate contents of Ca, Mg, K, and Fe for ion-exchange and moderate concentration of phosphorus for the formation of insoluble heavy metal compounds. Generally, the biochar created at 300 °C (300-30KP) showed similar performance to the biochar created at 400 °C (400-30KP) in terms of reducing heavy metal bioavailability.

Production of Partially Deoxygenated Pyrolysis Oil from Switchgrass via Ca(OH)2, CaO, and Ca(COOH)2 Cofeeding

The effect of calcium additives on the fast pyrolysis of switchgrass was studied by continuously pyrolyzing physical mixtures of the biomass with Ca(OH)2, CaO, and Ca(COOH)2 in a laboratory scale f...

Pyrolysis of switchgrass in an auger reactor for biochar production: A greenhouse gas and energy impacts assessment

A life cycle approach was used to assess greenhouse gas (GHG) emissions and energy balances of switchgrass pyrolysis in an auger reactor for biochar production, with bio-oil and syngas as co-products. The system boundaries included the cultivation of switchgrass on marginal lands, harvesting, transport, conditioning, pyrolysis, the amendment of biochar in soil to sequester carbon (C) and to reduce N2O emissions, and the valorisation of bio-oil and syngas as energy sources. Two pyrolysis scenarios were evaluated. Scenario A involves a lower pyrolysis temperature and a shorter solid residence in the reactor as compared to scenario B. A negative GHG emissions balance of −2110 and −2561 kg CO2e Mg−1 biochar was obtained for scenarios A and B, respectively. Biochar C sequestration contributed the most to the reduction of GHG emissions in scenario B due to the high C content and stability in biochar. However, scenario B resulted in a higher energy consumption (13,563 MJ Mg−1 biochar) than scenario A (2925 MJ Mg−1 biochar) due to a higher energy consumption of the pyrolysis unit. These results confirm that pyrolysis of switchgrass for biochar and bio-oil production can be a negative emission technology, but pyrolysis operating parameters should be selected carefully.

Phosphorus Distribution in Soils Treated with Bioenergy Co‐product Materials following Corn Growth

Core Ideas Biochar changes chemical distribution of P in soils.Biochar changes the distribution of hydrolysable organic P in soils.No two biochar materials are alike. This research was conducted to investigate the impact of corn cob gasification biochar (CCGB), switchgrass pyrolysis biochar (SPB), turkey manure ash (TMA), and triple superphosphate fertilizer (TSP) on soil phosphorus (P) distribution in three agricultural soils from Minnesota, USA. Understanding how biochar can change soil P distribution is crucial to develop best management practices for recycling biochar products. Phosphorus sources were incorporated at rates of 0, 28, 56, and 84 mg P2O5 kg−1 to 1.5 kg of each soil in 2‐L pots. Corn (Zea mays L.) plants were grown (2 plants pot−1) in treated soils for 56 d after emergence. After 56 d, plants were harvested and soil samples collected for sequential P fractionation (H2O, 0.5 mol L−1 NaHCO3, 0.1 mol L−1 NaOH, and 1.0 mol L−1 HCl) and enzymatic hydrolysis. The results of the sequential fractionation showed that CCGB and SPB were as effective as TSP and TMA at increasing total P extractable in water and HCl. In contrast, the increase in NaHCO3 and NaOH extractable total P was higher with TSP and TMA than with the CCGB and SPB. In most cases, the increase in inorganic P was similar between biochar and TSP, suggesting that biochar could supply equal amounts of plant available P as commercial fertilizer. The effects of biochar on enzymatically hydrolysable P were not consistent and varied by soil. In conclusion, the results of this study showed that biochar has potential to increase the available P pools in soils similar to commercial fertilizer.

Slow Pyrolysis Kinetics of Two Herbaceous Feedstock: Effect of Milling, Source, and Heating Rate

Kinetic models for pyrolysis of switchgrass and tall fescue were obtained using thermogravimetric analysis and a newly proposed parameter-extraction methodology. The optimization strategy demonstrates the use of the Akaike information criterion for the statistical identification of the number of distinct processes and a robust global search method. The effects of sample mass, heating rates, particle size, and crystallinity index on the kinetic parameters of each feedstock were considered. For whole biomass particles, the kinetic parameters of the cellulose component was found to be similar to that of pure microcrystalline cellulose. Further particle size reduction through extensive milling reduced the activation energy of cellulose by 48%. X-ray diffraction indicated that the cellulose fraction of highly milled whole biomass becomes largely amorphous and that the amorphization of the cellulose, not the particle size reduction, is likely responsible for the decrease in activation energy.

Engineered biochar from microwave-assisted catalytic pyrolysis of switchgrass for increasing water-holding capacity and fertility of sandy soil

Engineered biochars produced from microwave-assisted catalytic pyrolysis of switchgrass have been evaluated in terms of their ability on improving water holding capacity (WHC), cation exchange capacity (CEC) and fertility of loamy sand soil. The addition of K3PO4, clinoptilolite and/or bentonite as catalysts during the pyrolysis process increased biochar surface area and plant nutrient contents. Adding biochar produced with 10wt.% K3PO4+10 wt.% clinoptilolite as catalysts to the soil at 2wt% load increased soil WHC by 98% and 57% compared to the treatments without biochar (control) and with 10wt.% clinoptilolite, respectively. Synergistic effects on increased soil WHC were manifested for biochars produced from combinations of two additives compared to single additive, which may be the result of increased biochar microporosity due to increased microwave heating rate. Biochar produced from microwave catalytic pyrolysis was more efficient in increasing the soil WHC due to its high porosity in comparison with the biochar produced from conventional pyrolysis at the same conditions. The increases in soil CEC varied widely compared to the control soil, ranging from 17 to 220% for the treatments with biochars produced with 10wt% clinoptilolite at 400°C, and 30wt% K3PO4 at 300°C, respectively. Strong positive correlations also exist among soil WHC with CEC and biochar micropore area. Biochar from microwave-assisted catalytic pyrolysis appears to be a novel approach for producing biochar with high sorption affinity and high CEC. These catalysts remaining in the biochar product would provide essential nutrients for the growth of bioenergy and food crops.

Effects of Various Reactive Gas Atmospheres on the Properties of Bio-Oils Produced Using Microwave Pyrolysis

Fast pyrolysis of lignocellulosic biomass produces organic liquids (bio-oil), biochar, water, and noncondensable gases. The noncondensable gas component typically contains syngas (H2, CO, and CO2) as well as small hydrocarbons (CH4, C2H6, and C3H8). To understand the influence of reactive gas in various pyrolysis processes, we have employed a laboratory scale microwave reactor and performed pyrolysis of switchgrass under varying gaseous atmospheres and characterized the bio-oils obtained. The batch (100 g of biomass) microwave pyrolysis was performed at 900–1000 W over the course of 7 min in the presence of a microwave absorber (10 g of activated charcoal). The products formed were quantified and the bio-oils were characterized by GC–MS, elemental analysis, Karl Fischer and TAN titrations, bomb calorimetry, and 13C NMR spectroscopy. Pyrolysis experiments performed under a N2 atmosphere were used as the control and then compared to experiments performed under various reactive gases (CO, H2, and CH4) and a ...

Structural Analysis of Pyrolytic Lignins Isolated from Switchgrass Fast-Pyrolysis Oil

Structural characterization of lignin extracted from the bio-oil produced by fast pyrolysis of switchgrass (Panicum virgatum) is reported. This is important for understanding the utility of lignin as a chemical feedstock in a pyrolysis-based biorefinery scheme. Pyrolysis induces a variety of structural changes to lignin in addition to reduction in molecular weight. The guaiacol structural units remain largely intact, and some hemicellulose stays covalently linked to the lignin. However, two-dimensional 1H–13C HSQC NMR analysis shows an absence of γ-methylene hydrogens from β-O-4 linkages, implying that rearrangements in the propyl linking chains have occurred. Ferulate and hydroxyl phenol esters are still present in the pyrolyzed lignin, but at lower concentrations than in unpyrolyzed switchgrass lignin.

Microwave-assisted catalytic pyrolysis of switchgrass for improving bio-oil and biochar properties

Solid additives were used as a microwave absorber to improve the low microwave absorption rate of switchgrass going through pyrolysis, and as a catalyst to improve the bio-oil and biochar characteristics. The synergistic effects were manifested in the presence of a mixture of K3PO4 and clinoptilolite or bentonite compared with single catalyst, resulting in increased microwave absorption rate, and improved bio-oil and biochar quality. The sample of microwave heating switchgrass with 10wt.% K3PO4+10wt.% bentonite reached 400°C after 2.8min, compared with 28.8min through conventional heating, producing biochar with increase in BET surface area from 0.33m2/g to 76.3m2/g compared with conventional heating. Furthermore, water content of the bio-oil reduced from 22.7 to 15.0wt.% compared with biomass mixed with 20wt.% SiC, a chemically-inert microwave absorbing material used to increase microwave heating. Introducing catalysts showed a great potential for accelerating microwave heating and improving bio-oil and biochar qualities.

Coprocessing of Agricultural Plastic Waste and Switchgrass via Tail Gas Reactive Pyrolysis

Pyrolysis of mixtures of agricultural plastic waste in the form of polyethylene hay bale covers (PE) (4–37%) and switchgrass were investigated using the US Department of Agriculture’s tail gas reactive pyrolysis (TGRP) process at different temperatures (400–570 °C). TGRP of switchgrass and plastic mixtures significantly reduced the formation of waxy solids that are produced during regular pyrolysis. Under an atmosphere of approximately 70% recycled tail gas, mostly noncondensable gases were produced along with highly deoxygenated and aromaticized pyrolysis oil. When the atmosphere was diluted further to a recycled tail gas concentration of about 55%, higher yields of liquid product were achieved but with less deoxygenation. TGRP of low plastic mixtures (4–8%) produced oils with increased carbon and reduced oxygen content compared to the fast pyrolysis of switchgrass alone. Noncondensable gas fractions containing high concentrations of H2, CO, ethylene, and other light hydrocarbons remained a significant p...

Hydrogen production from switchgrass via an integrated pyrolysis–microbial electrolysis process

A new approach to hydrogen production using an integrated pyrolysis–microbial electrolysis process is described. The aqueous stream generated during pyrolysis of switchgrass was used as a substrate for hydrogen production in a microbial electrolysis cell, achieving a maximum hydrogen production rate of 4.3LH2/L anode-day at a loading of 10g COD/L-anode-day. Hydrogen yields ranged from 50±3.2% to 76±0.5% while anode Coulombic efficiency ranged from 54±6.5% to 96±0.21%, respectively. Significant conversion of furfural, organic acids and phenolic molecules was observed under both batch and continuous conditions. The electrical and overall energy efficiency ranged from 149–175% and 48–63%, respectively. The results demonstrate the potential of the pyrolysis–microbial electrolysis process as a sustainable and efficient route for production of renewable hydrogen with significant implications for hydrocarbon production from biomass.

Biomass pyrolysis and combustion integral and differential reaction heats with temperatures using thermogravimetric analysis/differential scanning calorimetry

Integral reaction heats of switchgrass, big bluestem, and corn stalks were determined using thermogravimetric analysis/differential scanning calorimetry (TGA/DSC). Iso-conversion differential reaction heats using TGA/DSC pyrolysis and combustion of biomass were not available, despite reports available on heats required and released. A concept of iso-conversion differential reaction heats was used to determine the differential reaction heats of each thermal characteristics segment of these materials. Results showed that the integral reaction heats were endothermic from 30 to 700°C for pyrolysis of switchgrass and big bluestem, but they were exothermic for corn stalks prior to 587°C. However, the integral reaction heats for combustion of the materials followed an endothermic to exothermic transition. The differential reaction heats of switchgrass pyrolysis were predominantly endothermic in the fraction of mass loss (0.0536–0.975), and were exothermic for corn stalks (0.0885–0.850) and big bluestem (0.736–0.919). Study results provided better insight into biomass thermal mechanism.

Effects of torrefaction and densification on switchgrass pyrolysis products

The pyrolysis behaviors of four types of pretreated switchgrass (torrefied at 230 and 270°C, densification, and torrefaction at 270°C followed by densification) were studied at three temperatures (500, 600, 700°C) using a pyroprobe attached to a gas chromatogram mass spectroscopy (Py-GC/MS). The torrefaction of switchgrass improved its oxygen to carbon ratio and energy content. Contents of anhydrous sugars and phenols in pyrolysis products of torrefied switchgrass were higher than those in pyrolysis products of raw switchgrass. As the torrefaction temperature increased from 230 to 270°C, the contents of anhydrous sugars and phenols in pyrolysis products increased whereas content of guaiacols decreased. High pyrolysis temperature (600 and 700°C as compared to 500°C) enhanced decomposition of lignin and anhydrous sugars, leading to increase in phenols, aromatics and furans. Densification enhanced depolymerization of cellulose and hemicellulose during pyrolysis.

Mild pyrolysis of P3HB/switchgrass blends for the production of bio-oil enriched with crotonic acid

The mild pyrolysis of switchgrass/poly-3-hydroxybutyrate (P3HB) blends that mimic P3HB-producing switchgrass lines was studied in a pilot scale fluidized bed reactor with the goal of simultaneously producing crotonic acid, a switchgrass-based bio-oil, and bio-char. Factors such as pyrolysis temperature, reactor residence time, flow rate and particle size of the P3HB were studied to determine their effects on the recovery of crotonic acid as a component of the pyrolysis oil produced from the mixture. Crotonic acid yields were maximized at 45wt% of the input P3HB by using small P3HB particles and a pyrolysis temperature of 375°C. The remaining components of the liquid product were similar to those produced via fast pyrolysis of switchgrass alone. Fractional collection within the condensation system of the pyrolysis process development unit (PDU) did not significantly fractionate crotonic acid more than the total liquids collected. Concentrations of 6 to 10wt% crotonic acid in the liquids were found in all fractions and crotonic acid was effectively collected by both condensation and electrostatic precipitation suggesting that pyrolysis of P3HB produces crotonic acid in both gas and aerosol phases.

Catalytic pyrolysis of individual components of lignocellulosic biomass

We report on the catalytic pyrolysis of switchgrass and its three main components (cellulose, hemicellulose and lignin) over H-ZSM5 catalyst. The yields of aromatic hydrocarbons for the three components decreased in the following order: cellulose > hemicellulose ≫ lignin. Moderately higher temperature favored formation of aromatics. The results indicate that H-ZSM5 catalyst did not remove oxygen in an optimal pathway for catalytic pyrolysis of biomass. Dehydration was the dominant oxygen removal mechanism for catalytic pyrolysis, while decarbonylation to CO was favored over decarboxylation to CO2. This suggests that higher yields of aromatics might be achieved by catalyst improvements or reactor design that optimizes deoxygenation pathway. For cellulose and hemicellulose, coke produced catalytically contributed a larger fraction of solid carbonaceous residue than char from purely thermal processes. In the case of lignin, thermal rather than catalytic processes primarily contribute to the production of solid carbonaceous residue. Product distribution from catalytic pyrolysis of switchgrass appeared to be the additive contribution of the three individual components, which indicates that there was no significant interaction among the biomass-derived products.