Pyrolysis Mechanism Of Biomass Research Articles

A study on the production of low-viscosity bio-oil from rapeseed by magnetic field pyrolysis

In order to investigate the biomass pyrolysis mechanism of rapeseed under magnetic field for their conversion to bio-oil, a technical study was carried out for reducing the bio-oil viscosity to enhance its quality. Rapeseed were used as the raw material, and pyrolysis experiments were conducted at the final temperature of 500 ℃ under four different conditions: no magnetic field, three normal magnetic fields with different magnetic induction intensities (3000 GS, 6000 GS, and 9000 Gs), and a Halbach array magnetic field with 6000 GS. An analysis was conducted on the yield of pyrolysis products, as well as the physicochemical properties and composition of bio-oil. The results indicated that, compared to pyrolysis in the absence of magnetic field, the pyrolysis under magnetic field accelerated the heating process of rapeseeds and affected the pyrolysis reaction. Compared to the pyrolysis without magnetic field, the yield of pyrolysis gas increased from 19.09% to 20.23%, 20.83%, and 21.41% for the magnetic induction intensities of 3000, 6000 and 9000 Gs, respectively. Additionally, with the change in the magnetic induction intensities through values of 3000, 6000 and 9000 Gs, the viscosity of bio-oil decreased from 17.21 mPa·s to 13.99 mPa·s, 11.45 mPa·s, and 10.09 mPa·s, respectively. This suggests that the magnetic field significantly reduced the viscosity of bio-oil derived from rapeseeds, and slightly promoted the conversion of pyrolysis products into pyrolysis gas. When the volume of the magnet decreased by 53.69%, the proportion of pyrolysis bio-oil increased by 8.99%, while the viscosity of the oil decreased by 23.47%, indicating a significant optimization effect. Physicochemical analysis reveals that the moisture content of the pyrolysis oil as well as the hydrophilic groups in the oil obtained under magnetic field conditions increased, which is the main reason for the reduction in the viscosity of the oil. Combined with the in-depth mechanism analysis of magnetic field pyrolysis using simulations in the software package COMSOL, it is concluded that magnetic field pyrolysis enhances heat transfer through magnetoconvection and alters the pyrolysis reaction pathway by affecting the combinations of free radicals.

Biomass catalytic pyrolysis over CaO microspheres: Relationship between the production of bio-oil components and CO2 capture

Biomass catalytic pyrolysis is a promising way for the clean and even “Carbon-Negative” utilization of biomass via the in-situ upgrading bio-oil and reducing the emissions of CO2. In this work, CaO microspheres (CaO-H) prepared via hydrothermal method were used to adsorb CO2 and catalyze the reforming of bio-oil in the pyrolysis process of rice straw (RS) simultaneously. The results showed that CaO-H had the more strong basic sites compared with commercial CaO and thus the better adsorption capacity of CO2 (∼0.5 g/g CaO) at 700 °C and the stronger effect on the generation of bio-oil components and CO2. And strong relationships presented between the formation of CO2 and the composition of bio-oil. The yield of phenols and ketones can be enhanced by 37.17% and 56.76% respectively via the addition of CaO-H at the pyrolysis temperature of 650 °C, companying with the decrease of CO2 yield by 35.13%. It is also inferred that the CO2 reforming of bio-oil and the insertion of CO in CO2 into bio-oil components was strengthened during the biomass pyrolysis over CaO-H especially at the temperature of 650 °C. The possible mechanism of biomass pyrolysis over CaO-H was also proposed.

Catalytic mechanism of N-containing biochar on volatile-biochar interaction for the same origin pyrolysis

Nitrogen, as a common element, is widely present in biomass. The effects of nitrogenous substances on the same origin pyrolysis of biomass and the consequences of N-containing biochar on the catalytic process of volatiles are important for further analyzing the pyrolysis mechanism of biomass. In this research, N-containing biochar was prepared under different conditions, and the interaction between N-containing biochar and biomass pyrolysis volatiles at 400–700 °C was studied. The results show that N-containing biochar can simultaneously participate in reactions as adsorbents, catalysts, and reactants. Its catalytic effect is obviously different for various N configurations. Pyridinic N and pyrrolic N can promote the cracking of lignin into methoxy phenol compounds and promote the further cracking of 5-hydroxymethylfurfural. Graphitic N and oxidized N can promote the further decomposition of phenol and the conversion of D-xylose into small-molecule ketones. In addition, oxidized N can also inhibit the cracking of lignin to produce guaiacol. In the long-term interaction, the highly active pyridinic N tends to convert to a more stable graphitic N.

Biomass pyrolysis mechanism for carbon-based high-value products

The utilization of biomass, the only carbon-bearing renewable energy source, is critical for environmental and energy sustainability as well as carbon neutrality. Pyrolysis is the efficient conversion of biomass to fuel gas, liquid oil, and solid char. It is necessary to understand the mechanism of biomass pyrolysis for valuable and efficient utilization. In this review, recent progress with respect to biomass pyrolysis properties, the pyrolysis process, and product upgrading strategies focusing on carbon-based high-value liquid fuels and carbon-bearing materials are summarized. First, the correlations between the pyrolysis behavior and biomass structure and process conditions are considered. The mechanisms of the biomass pyrolysis of hemicellulose, cellulose, and lignin as well as the potential effect of inorganic matter on biomass pyrolysis are discussed. Furthermore, the regulation and controlling strategies for the biomass pyrolysis of high-value products are outlined. Finally, the challenges and prospects are discussed in order to provide a comprehensive picture of biomass pyrolysis development, which is significant for the understanding of biomass pyrolysis and the development of biomass utilization technology.

Kinetic parameters and reaction mechanism study of biomass pyrolysis by combined kinetics coupled with a heuristic optimization algorithm

Kinetic reaction mechanism plays a key role in accurately predicting biomass pyrolysis behavior. However, the order-based reaction mechanism is usually defined as the default in the existing kinetic studies. For the purpose of exploring the exact kinetic reaction mechanism of biomass pyrolysis, the combined kinetic method is tried here by coupling two common kinetic models (one-step global reaction and three-parallel reaction). The decomposition rate expressed by the method is related to three key parameters, whose values are corresponding to the establishment of reaction mechanism. The combined kinetic method is further coupled with a heuristic optimization algorithm to obtain more exact kinetic parameters in order to explore the reaction mechanism. The results show that it is hard to infer the reaction mechanism based on one-step global reaction, while based on three-parallel reaction, the respective reaction mechanism of each component can be established as Power law for cellulose, Order-based for hemicellulose and lignin by comparing with the thermogravimetric data. More importantly, the established mechanism and optimized parameters can be used to accurately predict the micro-scale pyrolysis behavior of biomass (beech) at a wider range of heating rates.

Hierarchical gallium-modified ZSM-5@SBA-15 for the catalytic pyrolysis of biomass into hydrocarbons

The catalytic pyrolysis of biomass is a sustainable approach for biofuel production, contributing to replacing fossil resources with renewable resources. The ZSM-5 zeolite remains an attractive catalyst in the catalytic pyrolysis of biomass, and how to reduce the product diffusion resistance and regulate the surface acidity of ZSM-5 should be explored more deeply. Herein, a hierarchical gallium-modified ZSM-5@SBA-15 catalyst is fabricated through coating a mesoporous layered SBA-15 shell on a hollow ZSM-5 core with gallium modified on the surface, which is effective for increasing hydrocarbon production during the catalytic pyrolysis of biomass process. The synergistic effect of hollowness, mesoporosity, and activity in the hierarchical gallium-modified ZSM-5@SBA-15 catalysts is found to affect the yield and quality of bio-oil. Accordingly, the hierarchical gallium-modified ZSM-5@SBA-15 catalyst with 11 wt% Ga loading exhibits a superior deoxygenation ability, and the relative content of hydrocarbons in bio-oil reach to 49.76 area% which is much higher than that of ZSM-5 (35.30 area%). Furthermore, a possible catalytic pyrolysis mechanism of biomass was also proposed to clarify the potential application of hierarchical gallium-modified ZSM-5@SBA-15 catalysts.

Insight into biomass pyrolysis mechanism based on cellulose, hemicellulose, and lignin: Evolution of volatiles and kinetics, elucidation of reaction pathways, and characterization of gas, biochar and bio‐oil

Pyrolysis is the first step of gasification and combustion. The pyrolysis process of biomass is complicated, which is generally considered to consist of the pyrolysis of the three major components (i.e., cellulose, hemicellulose, and lignin). Understanding the pyrolysis behavior and product of each component holds a key to understanding the biomass pyrolysis mechanism. In this work, the pyrolysis behavior, pyrolysis kinetics, volatile evolution, and product characterization of the three major components are investigated. Results showed that pyrolysis characteristics and thermal stability of the three components were closely related to their unique chemical structures. During pyrolysis, the main pyrolytic volatiles of hemicellulose appeared first, followed by cellulose and then lignin volatiles in the 3D FTIR spectra. In term of pyrolysis products, gases were generated by the cracking of specific functional groups. Hemicellulose had the highest CO2 yield, whereas lignin had the highest CH4 yield due to the aromatic rings and methoxy groups in lignin structure. Whereas cellulose demonstrated the highest CO yield at high temperatures (above 550 °C). With increasing temperature, the carbon structures of carboxylic-C and O-alkyl-C in biochar decreased, while aryl-C was enhanced. This was due to the deoxygenation reactions such as dehydroxylation, decarboxylation, decarbonylation, and demethoxylation, resulting in a reduction in the number of oxygen-containing functional groups (such as –OH, –C=O, –COOH, and –OCH3), as well as the polycondensation reactions that formed more polycyclic aromatic hydrocarbon units during pyrolysis. The major components of cellulose bio-oil included anhydrosugars and furans. Whereas the bio-oils derived from hemicellulose and lignin showed the highest relative content of acids and phenols, respectively. Based on this analysis, the thermal decomposition pathways of cellulose, hemicellulose, and lignin were proposed.

Impact of biomass constituent interactions on the evolution of char’s chemical structure: An organic functional group perspective

An in-depth investigation of the chemical structural evolution of char throughout the pyrolysis process is critical for subsequent biochar utilization. Therefore, the interaction mechanism among biomass constituents was studied by the examination of product distribution, bio-oil and bio-gas composition, organic functional groups, and two-dimensional correlation infrared spectrum characteristic of char. Char evolution was influenced by primary interaction (at 300 or 400 °C) and secondary interaction (at 500 or 650 °C). Polymer depolymerization and phenylpropane side chain breaking were aided by the primary interaction. Due to a “melting and wrapping” effect, it hindered ring opening, recombination, and polymerization of D-allose/D-xylose molecules, allowing the char to preserve its original C-O-C and C-OH structure. The secondary interaction stimulated the cyclization and intramolecular dehydration of D-allose, leading pyrolysis to advance to the pyran pathway. It also encouraged the ring opening, cyclization, rearrangement, and polymerization of monomer molecules, resulting in the char's C = O, C = C, and C-OH structures with greater aromatization degree. The discovery advances the understanding of the interacting mechanism of biomass pyrolysis and char formation.

In situ evolution of functional groups in char during cellulose pyrolysis under the catalysis of KCl and CaCl2

A combination of in situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, perturbation-correlation moving-window two-dimensional correlation spectroscopy (PCMW2D) and two-dimensional correlation spectroscopy (2D-COS) was used to reveal the catalytic mechanism of KCl and CaCl2 on cellulose char evolution during slow pyrolysis. Pretreatments of the one-dimensional spectra ensure the semi-quantitative analysis of the evolution of functional groups in pyrolysis char, which invoked principal component analysis followed by a Butterworth filter for denoising and extended multiplicative scatter correction. Through the differential processing of the absolute changes, the char evolution product was divided into ‘char rearrangement’ and ‘char devolatilization’ processes containing a high contribution from chemical reactions and physical migration, respectively. The ‘char rearrangement’ of cellulose pyrolysis consists of four stages, i.e. the budding, development, climax and decline stages, which were dominated by H-bond network reconfiguration, the consumption of C–O–C and OH, homogeneous devolatilization and aromatization, respectively. The uppermost influence of the two salts on the pyrolysis is the relationship alteration of C–O–C cleavage, dehydration reactions and ‘char devolatilization’. For neat, KCl-loaded and CaCl2-loaded cellulose, the unsaturated bonds were formed in the light reaction intermediate, heavy reaction intermediates and cellulose chain, respectively. Especially, the cleavage of most C–O–C following dehydration reactions conduced a shoulder peak in the differential thermogravimetry curve before the maximum weight loss rate of CaCl2-loaded sample. Due to the alteration, the pyrolysis was advanced but slowed down by the high content of unsaturated bonds in char. This study provides a powerful tool for the in situ semi-quantitative analysis of char evolution during the non-catalytic and catalytic thermo-chemical conversion of solid fuels and waste, and the results benefit to both biomass pyrolysis mechanism revelation and industrial production of biochar.

A mechanistic investigation of lignin dimer fast pyrolysis from reactive molecular dynamics simulation

The investigation of biomass pyrolysis mechanism is crucial for the advancement of pyrolysis-based technology and it is still quite challenging due to the complex nature of lignocellulosic biomass. The application of reactive molecular dynamics simulation offers a powerful strategy to probe more essential information along the reaction process beyond advanced experimental techniques. In this work, the fast pyrolysis process of a lignin dimer, DMPD with representative β-O-4 linkage, is investigated using the ReaxFF method to explore the reaction characteristics, mechanism, and kinetics. The results elucidate that higher temperatures are favorable for the formation of CO, the transformation of guaiacol to catechol, and the breaking of bonds when varying the temperature from 1400 to 2400 K. Guaiacol achieves the highest yield of 13.37% at 2000 K while catechol and CO obtain the highest yield of 6.67% and 8.22% at 2400 K, respectively. Higher heating rates promote the generation of C5-12 products (increased from 70.59% to 78.23%) and the breaking of C-O bond regarding the investigated range of 15.5–170 K/ps. Based upon the time evolution of the reactant and final product distribution under various operating conditions, a first-order kinetic model is derived to calculate the activation energies of C-C, C-H, C-⎔O bonds, and DMPD to be 122.41, 35.18, 52.58, and 52.18 kJ/mol, respectively. A reaction pathway is proposed from the product distribution along the DMPD pyrolysis at 2000 K. The detailed characteristics from ReaxFF simulations enable a better understanding of the complicated pyrolysis mechanism of biomass from a molecular level.

An integrated study on the pyrolysis mecanism of peanut shell based on the kinetic analysis and solid/gas characterization

An in-depth understanding of peanut shell pyrolysis reaction is essential for its efficient utilization. Detailed analysis of thermodynamics, kinetics, and reaction products can provide valuable information about pyrolysis reaction. In this work, pyrolytic reaction mechanism was elucidated with the analysis of thermogravimetric-mass spectrometry and the structural characterization of the derived biochar. The thermodynamic and kinetic parameters of three sub-stages were matched well in different model-free methods. The positive ΔH and ΔG values indicated that the pyrolysis reactions for three stages were endothermic and nonspontaneous. The reaction mechanism predicted by integral master-plots were F3 (f(α) = (1-α)3), F1 (f(α) = (1-α), and F3 (f(α) = (1-α)3) for the three sub-stages, respectively. The negative ΔS in the third stage was related to the reduced releasing of low-molecular weight gases and ordered graphite-like carbon structure. This study provides a prospective approach to understand the pyrolysis mechanism of biomass.

Molten salt pyrolysis of biomass: The mechanism of volatile reforming and pyrolysis

A novel reactor with a short shrinking volatile catheter directly inserted into molten salt was applied to fast pyrolysis of cotton stalks and pyrolysis volatiles reforming in molten salt (Li2CO3–Na2CO3–K2CO3) at the temperature range of 450–850 °C with conventional pyrolysis as comparison. Simultaneously, the possible mechanism of biomass pyrolysis in molten salt was proposed according to the characteristics of products and the volatiles reforming under variant conditions. Compared with conventional pyrolysis, molten salt pyrolysis produced more gas, especially CO and H2 at 750–850 °C. It can be further revealed by experimental results of volatiles reforming in molten salt that syngas yield gradually increased with the increase of temperature. Besides, molten salt intensified the decomposition of acids/esters, producing a large amount of CO. It also promoted the conversion of methoxyphenol to alkylphenol and then to phenol, along with CH4 formation, and the evolution of multi-ring PAHs mainly naphthalene and acenaphthylene into small PAHs mainly alkylphenol and phenol. Eventually, high temperature around 850 °C was recommended to produce high quality syngas for molten salt pyrolysis of biomass. The syngas yield reached 72 vol% and the low heating value surpassed 14 MJ/Nm3.

On the mechanism of xylan pyrolysis by combined experimental and computational approaches

Pyrolysis is the initial stage of biomass combustion, whereas, the pyrolysis mechanism of biomass, especially the hemicellulose component, is still not well elucidated. Herein, a common hemicellulose polysaccharide, xylan, was investigated to reveal the evolution of volatiles and solid residue through combined thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR) and in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT) techniques. Quantum chemistry calculation was also conducted to analyze the primary xylan pyrolysis mechanism by using a long-chain xylan model which was built based on the structural characterization of xylan. The experimental results indicated that the functional groups in solid-phase evolved intensively during the main weight loss zone (200–350 °C), leading to the violent release of volatiles. The decomposition of branches, especially the arabinose unit, was prior to that of the backbone, with relatively low energy barriers and high rate constants. The initial enhancement of CO vibration in solid-phase above 200 °C derived from the formation of the furanose unit. Both dehydration and breakage of glycosidic bonds were responsible for the formation of CC bond in solid-phase from 300 °C. The cracking of the 4-O-Me group resulted in the release of aldehydes to gas-phase in the main weight loss zone (200–350 °C). The scission of the whole 4-O-MeGlc unit and/or the rupture of the uronic acid group led to the gas-phase CO bond formation.

A Comprehensive Characterization of Pyrolysis Oil from Softwood Barks.

Pyrolysis of raw pine bark, pine, and Douglas-Fir bark was examined. The pyrolysis oil yields of raw pine bark, pine, and Douglas-Fir bark at 500 °C were 29.18%, 26.67%, and 26.65%, respectively. Both energy densification ratios (1.32–1.56) and energy yields (48.40–54.31%) of char are higher than pyrolysis oils (energy densification ratios: 1.13–1.19, energy yields: 30.16–34.42%). The pyrolysis oils have higher heating values (~25 MJ/kg) than bio-oils (~20 MJ/kg) from wood and agricultural residues, and the higher heating values of char (~31 MJ/kg) are comparable to that of many commercial coals. The elemental analysis indicated that the lower O/C value and higher H/C value represent a more valuable source of energy for pyrolysis oils than biomass. The nuclear magnetic resonance results demonstrated that the most abundant hydroxyl groups of pyrolysis oil are aliphatic OH groups, catechol, guaiacol, and p-hydroxy-phenyl OH groups. The aliphatic OH groups are mainly derived from the cleavage of cellulose glycosidic bonds, while the catechol, guaiacol, and p-hydroxy-phenyl OH groups are mostly attributed to the cleavage of the lignin β–O-4 bond. Significant amount of aromatic carbon (~40%) in pyrolysis oils is obtained from tannin and lignin components and the aromatic C–O bonds may be formed by a radical reaction between the aromatic and aliphatic hydroxyl groups. In this study, a comprehensive analytical method was developed to fully understand and evaluate the pyrolysis products produced from softwood barks, which could offer valuable information on the pyrolysis mechanism of biomass and promote better utilization of pyrolysis products.

Initial pyrolysis mechanism of cellulose revealed by in-situ DRIFT analysis and theoretical calculation

Cellulose is one of the major components of biomass. The study on its pyrolysis process will be beneficial to the in-depth understanding of biomass pyrolysis mechanism. In this work, in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT) combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) was first used to characterize the evolution process of the functional groups in cellulose during pyrolysis. The results showed that the degradation of carbon skeleton was prior to the dehydration of free hydroxyls after the destruction of hydrogen bond networks during pyrolysis. The thermal stability of CO in cellulose followed by the order of glycosidic bond <CO in glucopyranose ring <CO between glucopyranose ring and hydroxyl. Followingly, micro pyrolysis experiment was performed to analyze the pyrolysis products of cellulose at various temperatures. It was found that the rupture of glucopyranose rings to form 2C and 4C products was more difficult than the dissociation of C6 hydroxymethyls, and required higher pyrolysis temperature. Quantum chemistry calculation was further carried out to study the key reaction pathways including dehydration, cleavage of glycosidic bond, ring opening and fragmentation in the initial stage of cellulose pyrolysis. The result showed that the concerted cleavage of glycosidic bond to form LG-end short chain was the most favored with the lowest activation energy. The ring opening of the glucose unit in the chain occurred via the cleavage of C1-O. The formed ring opening product was more likely to degrade via the dissociation of C6 hydroxymethyl compared with the breakage of C2–C3 to form 2C and 4C products. Besides, the dehydration of hydroxyls in glucose units required high energy barriers and was difficult to occur.

Simulation of a tilted-slide reactor for the fast pyrolysis of biomass

The fast pyrolysis of sawdust biomass in the tilted-slide reactor was simulated and the product yields were compared with the experimental results. The biomass was pyrolyzed during it was transferred down to the reactor with the hot sand. The steady-state simulation was performed by a commercial computational fluid dynamics code for predicting the flow, temperature, and concentration of gaseous species together with the particle behaviors. Lagrangian multiphase model was used to simulate the transport of sand and biomass particles, and the kinetic mechanism of biomass pyrolysis was adopted. It was found that the volatile yield continuously increased with temperature due to the absence of the secondary cracking reactions while there is the maximum yield in the experiment. The 1-D calculation considering the secondary gas-phase reactions of the pyrolysis products showed the maximum volatile yield at the temperature about 30∼80˚C higher than the experimental results. At lower temperatures, the volatile yield was much smaller than the benchmark case while the char yield was much larger due to an incomplete conversion of biomass. The fast pyrolysis process in the tilted-slide reactor was investigated along the pyrolyzing particle tracks, and the solid-phase intermediate species were found to be important to evaluate the decomposition of biomass components.

The accuracy and efficiency of GA and PSO optimization schemes on estimating reaction kinetic parameters of biomass pyrolysis

Reaction kinetic parameters estimation of biomass pyrolysis is a relatively difficult optimization problem due to the complexity of pyrolysis model. Two common heuristic algorithms, Genetic Algorithm (GA) and Particle Swarm Optimization (PSO), are applied to estimate the kinetic parameters of three-component parallel reaction mechanism based on the thermogravimetric experiment in wide heating rates. The accuracy and efficiency of GA and PSO algorithms are compared with each other under the identical optimization conditions. The results indicate the better optimization abilities of PSO with the closer convergence solution to the global optimum and quicker convergence to the solution than GA based on the three-component parallel reaction mechanism of biomass pyrolysis. Especially, the improvement of best fitting value of PSO reaches up to 30% compared with that of GA. Furthermore, 14 estimated kinetic parameters of best fitting value are obtained and the mass loss rate predicted results including three separate components (hemicellulose, cellulose and lignin) are compared with experimental data.

Mechanism study on the pyrolysis of the typical ether linkages in biomass

The in-depth study of the cleavage behaviors of linkages in biomass is important for the better understanding of biomass pyrolysis mechanism. This study aimed to clarify the pyrolysis mechanism of the typical ether linkages in biomass including β-1,4-glycosidic bond, α-O-4 bond and methoxyl using cellobiose, benzylphenyl ether and guaiacol as the model compounds. Combining the detection of the key intermediates, especially radicals by SVUV-PIMS and the evaluation of the reaction pathways by density functional theory (DFT) quantum chemical calculations, it was found that the concerted cleavage of β-1,4-glycosidic bond was more kinetically favorable than homolytic cleavage and heterolytic cleavage, and the ring opening of cellobiose via the breakage of C1′-O was likely to occur before the cleavage of glycosidic bond. The α-O-4 bond in benzylphenyl ether was mainly cleaved by Cα-O homolysis, and it was easy for the formed radicals to recombine with each other to yield phenolic dimers. In the initial evolution process of methoxyl in guaiacol, homolytic demethylation was the most important unimolecular reaction, while demethoxylation and radical-induced rearrangement reactions were difficult to occur due to their high energy barriers. In the presence of the formed methyl radicals from homolytic demethylation reaction, these two reactions would occur since their energy barriers were significantly reduced at this condition.

Greenhouse Gas Emission Analysis of Biomass Moving-bed Pyrolytic Polygeneration Systems based on Aspen Plus and Hybrid LCA in China

Under the existing scenario of greenhouse gas (GHG) emission reduction technologies, it is difficult to make the global temperature rise within 2°C in 2100. Thus, bio-energy with carbon capture and storage (BECCS) technology, as one of primary negative carbon emission methods, is urgent to deploy. In order to correctly recognize the development potential of bio-energy, the biomass pyrolytic polygeneration system, as the second novel bio-energy technology, should be carefully investigated in terms of GHG emission intensity and GHG emission reduction firstly. In this study, the material and energy flow in the process was carefully studied, and its environmental benefits was further researched. Based on the biomass pyrolysis mechanism and components pyrolysis property, the model of biomass pyrolytic polygeneration system was built on the Aspen Plus simulator, which is used to make an analysis of the life cycle greenhouse gas emission reduction. Results indicated that the agriculture process as the largest contributor to total GHG emissions with 86.03% of the total plant GHG emissions. In the entire pyrolysis temperature range, the intensity of GHG emissions from moving bed pyrolytic polygeneration system is from 4.15 to 6.12 g CO2-eq/MJ. Compared with other pyrolysis products, bio-char has a greater impact on the GHG emission reduction benefits of pyrolytic system. For the same system capacity, the system has the largest emissions reduction at a reaction temperature of 250°C, where also the bio-char yields is largest. If all of the bio-char returns to the field, the system can lead to negative carbon emission, which is 22 times larger than the system GHG emission when pyrolysis temperature is 250°C.

TG-FTIR and thermodynamic analysis of the herb residue pyrolysis with in-situ CO2 capture using CaO catalyst

Thermochemical conversion technology can be employed for the utilization of biomass resource, which not only disposes of the waste polluting the environment but also produces biomass gas and bio-oil for industrial applications. In this work, CaO catalyst was used to catalyze the pyrolysis of herb residues to produce biobased gas. The mechanism of biomass pyrolysis with in-situ CO2 capture was studied by experimental investigation and thermodynamic simulation. The results of the thermogravimetric and infrared analysis showed that CaO could promote biomass pyrolysis, water gas shift reaction, methanation reaction, and macromolecular transformation, thus significantly improving the quality of catalytic cracking gas. The further mechanistic study indicated that in-situ CO2 capture promoted by CaO relieved the thermodynamic constraints of methanation at high temperature and achieved a high CH4 selectivity in the temperature range of biomass pyrolysis and tar catalytic cracking, which is consistent with the result of the thermodynamic analysis. Mechanistically, CaO promotes the water gas shift reaction by absorbing CO2, reduces the volume contents of CO2 and CO in gas and improves H2 and CH4 concentration to afford high-quality gas.