Torrefaction Pretreatment Research Articles

Catalytic pyrolysis of wheat straw based on dual catalyst CaO/ZSM-5 with acid washing and torrefaction pretreatment to enhance aromatic yield in bio-oils

In this paper, the catalytic pyrolysis integrating combined pretreatment (acid washing and torrefaction) and dual catalysts was adopted to improve the quality of bio-oil and the selectivity of aromatic hydrocarbons. Combined pretreatment is a highly effective method to improve the quality of biomass feedstock. It was capable of the removal of alkali and alkaline earth metals from wheat straw, with a K removal rate of 97.79 %. Under the combined pretreatment, the aromatic hydrocarbon content in bio-oil increased to 68.8 % using the ZSM-5 catalyst alone. Compared with ZSM-5, CaO could remove part of the oxygenated functional groups and had a better acid removal effect, but the aromatic hydrocarbon yield was low to 7.95 %. After combined pretreatment using simulated aqueous phase bio-oil for acid washing, catalytic pyrolysis using CaO/ZSM-5 dual catalysts greatly enhanced the quality of the bio-oil. The oxygenated compounds content was reduced to 17.58 %, and the total hydrocarbon yield was increased to 82.42 %, especially the aromatic hydrocarbons yield was increased to 79.91 %, of which the monocyclic aromatic hydrocarbons were as high as 68.38 %, and the benzene, toluene, and xylene content reaching 49.39 %. Thus, integrating dual catalysts (CaO/ZSM-5) with combined pretreatment can effectively increase the aromatic yield for producing high-quality bio-oil.

Towards the production of 1,4:3,6-dianhydro-α-d-glucopyranose from biomass fast pyrolysis based on oxalic acid-assisted torrefaction pretreatment

Pyrolysis, a promising thermochemical conversion technique, can convert lignocellulosic biomass into various value-added products. Herein, the selective production of 1,4:3,6-dianhydro-α-d-glucopyranose (DGP) was achieved through fast pyrolysis of cellulose based on oxalic acid-assisted torrefaction (OAT) pretreatment. The mixture of cellulose and oxalic acid first underwent torrefaction, followed by fast pyrolysis to yield DGP. Simultaneously, the air atmosphere was considered to facilitate the formation of esterification intermediates, thereby promoting the formation of DGP. The effects of torrefaction temperature, oxalic acid amount, as well as pyrolysis temperature were carefully explored for DGP production. A yield of 9.6 wt% and a selectivity of 57.5 % for DGP were achieved from the micro-scale pyrolysis of cellulose under the optimized conditions. In lab-scale tests, the DGP yield reached 12.5 wt% from cellulose. The OAT-based pyrolysis was confirmed to be applicable to the waste cellulose-rich materials, with a DGP yield of 8.2 wt% from waste cotton and 6.0 wt% from spent paper in lab-scale experiments. Additionally, the OAT-based pyrolysis also showed the potential for poly-generation of DGP and formic acid at different stages.

Investigation of pyrolysis productions (pyrolysis oil, pyrolysis gas and carbon nanotubes) distribution in co-pyrolysis of torrefied oiltea camellia shells and polypropylene

The co-pyrolysis of torrefied oiltea camellia shells (OCS) and reused polypropylene (PP) was investigated for pyrolysis oil, pyrolysis gas and carbon nanotubes (CNTs) distribution characters in a two-stage pyrolysis system. Compared with raw OCS/PP, the quality of pyrolysis oil from torrefied OCS and PP was upgraded while yield decreased gradually. In particular, torrefaction pretreatment was beneficial to the formation of aromatic hydrocarbons and the higher selectivity of phenols in pyrolysis oil. And serious N2 torrefaction (260 N) and slight CO2 torrefaction (200C) is more conducive to the synthesis of C6–C11 (gasoline component). In addition, torrefaction could contribute to lower volatiles, which resulted in a lower yield of CNTs. For comparison, higher graphitized CNTs was prepared from the co-pyrolysis of torrefied OCS and PP. Appropriate torrefaction temperature and atmosphere have a potential for high value conversion of pyrolysis oil, pyrolysis gas and CNTs from co-pyrolysis of biomass and plastics.

Char formation during pyrolysis of torrefied cellulose: Role of potassium catalysis and torrefaction pretreatment

Torrefaction is an efficient pretreatment technology for large-scale and high-value utilization of biomass fuel. This study aims to enhance the understanding of the thermochemical conversion of torrefied biomass by delineating the role of potassium and torrefaction on primary/secondary charring reactions during pyrolysis of torrefied cellulose. Celluloses with varying potassium loading levels were torrefied at temperatures ranging from 200 to 320 °C and subsequently pyrolyzed at 1000 °C. Two contrasting pyrolysis conditions, i.e., limiting and enhancing transport resistance, were employed to tune the occurrence of secondary reactions, thereby determining the role of torrefaction and potassium on primary and secondary charring reactions. Potassium content, torrefaction severity, and pyrolysis conditions both profoundly affects char formation during pyrolysis of torrefied cellulose, resulting in a wide range of pyrolysis char yields from 1.95 wt% to 64.35 wt%. The structural changes induced by torrefaction, including the depolymerization of the carbohydrate structure and the formation of crosslinking structures, promote the char formation. Potassium enhances the char formation of torrefied cellulose in two ways: i) by catalyzing the transformation of the carbohydrate structure into the crosslinking structure during torrefaction, and ii) by catalyzing the charring reactions of both the carbohydrate and the crosslinking structures during pyrolysis. Raman spectral analysis of the char carbon structure indicates that increased potassium loading level and torrefaction severity enlarge the aromatic system of the char. The findings highlight the potential of optimizing biomass pyrolysis through controlled torrefaction and potassium, paving the way for more efficient biofuel production and high-quality biochar applications.

Exploring the biorefinery potential of sweet potato crop residues through torrefaction and pyrolysis: Processing of leaves, stems, and peel

The utilization of neglected agro-industrial waste is essential for mitigating environmental impacts. This study aims to characterize the products of using sweet potato peels, leaves and stems via pyrolysis and torrefaction techniques. Additionally, the study examined the impact of the torrefaction pre-treatment on pyrolysis products. Solid, liquid, and gaseous products were characterized. Results indicated that torrefaction pre-treatment increased biochar yield but diminished bio-oil and gas yields. Thermal treatments had minimal impact on the specific surface area of formed solids and biochars. Bio-oils showed a proclivity towards basicity with increasing temperature. Phenols predominated in the organic fraction of bio-oils, with torrefaction pre-treatment resulting in reduced alcohol and increased hydrocarbon concentration. Gas composition revealed elevated CO2 levels during torrefaction, while torrefaction pre-treatment amplified CH4 concentration. These findings suggest potential for extracting chemical inputs like phenolic resins and biocides from sweet potato waste bio-oils, though further treatments are required for effective solid adsorption.

Upgrading the quality of biomass by advanced oxidative torrefaction pretreatment: Rebuilding the oxidative torrefaction mechanism based on hemicellulose, cellulose, and lignin

The oxidative torrefaction pretreatment (OTP) is a promising approach to upgrade the quality of biomass. This work investigated the oxidative torrefaction mechanism based on the OTP experiment of biomass pseudo component (cellulose, hemicellulose, and lignin) at varying OTP temperatures and oxygen concentrations. Results showed that more mass of biomass was transferred into the torrefied gaseous and liquid products with OTP temperature and oxygen concentration increasing, remaining less mass in torrefied solid product. The element distribution in biomass pseudo component was optimized after OTP, presenting as the removal of oxygen element and the enrichment of carbon element. The variation of these two elements in hemicellulose after OTP was much higher than that of cellulose and lignin due to the more intensive thermal decomposition reaction in hemicellulose. The chemical compounds in torrefied liquid products from biomass pseudo component were highly differentiated with each other, the anhydrosugars (e.g., levoglucosenone (LGO) and levoglucosan (LG)) and furans (e.g., furfural (FF)) from OTP of cellulose, the furans (e.g., furfural (FF)) and acids (e.g., acetic acid (AA)) from OTP of hemicellulose, the phenols from OTP of lignin. The concentrations of the released gas components during OTP of biomass pseudo component were ranked as CO2 > CO > H2 ≈ CH4. The thermal degradation mechanism of biomass OTP was revealed.

Catalytic pyrolysis of torrefied biomass with molecular sieve catalysts to produce hydrocarbon rich biocrude

AbstractThe downstream processing of biocrudes obtained from direct biomass pyrolysis poses significant challenges due to stability issues, necessitating costly upgrading for further coprocessing with refinery feeds. This study examines the impact of torrefaction pretreatment on pyrolysis product distribution and biocrude composition using sawdust (SD) and groundnut shell (GS) feeds. Torrefaction was conducted at varying temperatures (200, 250 and 300°C) for 30 min under different reactor conditions. Increasing the severity of torrefaction resulted in decreased biocrude yields with reduced water content and gas formation, particularly evident with GS. A torrefaction temperature of 250°C and 30 min of pretreatment yielded higher phenolics and hydrocarbons. This increase in phenolics can be attributed to lignin enrichment during torrefaction, which, in the presence of a catalyst, undergoes deoxygenation leading to hydrocarbon formation. The influence of feed particle size, whether in powder or pellet form, on biocrude yield and composition was found to be minimal. Catalytic pyrolysis of SD using molecular sieve catalysts yielded the highest hydrocarbon (42%) and aromatic content (44%) at catalyst to biomass ratios of 1:1 and 2:3. The combination of torrefaction and pyrolysis was shown to enhance the quality of biocrude by increasing its hydrocarbon content, but at the expense of lower liquid yields. Experimental observations were supported by statistical analysis tools such as principal component analysis, which assessed pyrolysis product yields and composition.

Modeling and exergy-economy analysis of residential building energy supply systems combining torrefied biomass gasification and solar energy

A novel hybrid energy system driven by torrefied biomass gasification and solar energy is proposed for the first time, and their complementarity to enhance the system’s energy efficiency is analyzed and shown. The system mainly combines biomass torrefaction, biomass gasification subsystem, solar heat collection and absorption refrigeration technology. The effects of different operating parameters on the gasification products were studied. The economic analysis is carried out based on the theory of exergy economy. The results show that torrefaction pretreatment of biomass can significantly improve its fuel quality and gasification performance. With the increase of torrefied temperature, the volume fraction of CO2 and H2 decreased while the volume fraction of CH4 and CO increased. The economic analysis shows that the expected annual income is $72,735, and the investment recovery period is 2.89 years. Through the calculation of the energy-saving and environmental benefits, it can be concluded that the hybrid energy system can save 1.05 × 106 MJ of heat per year. This equates to about 358.26 tons of standard coal or a CO2 emission reduction of 550.59 tons, the participation of solar energy is conducive to the system emission reduction. By tuning the parameter sensitivity, the influence of biomass price change on the unit exergy cost of system products was more obvious.

A review of technoeconomic benefits of torrefaction pretreatment technology and application in torrefying sawdust

Economic analysis of torrefaction process centers on assessment of the economic feasibility of the production and utilization of torrefied biomass using developed models such as costs of biomass, electricity, labour, investment, transportation etc. to evaluate the cost of biomass torrefaction. The increase in energy usage over the past century has raised concern over the energy insecurity and environmental unsustainability of current fossil fuel utilization; therefore, there is need for energy diversification. An attractive alternative is the biomass. However, the poor performance of raw biomass in energy generation further necessitate development of refined technologies to enhance its performance, particularly at low temperatures between 200–300 ℃. This study therefore reviews the technoeconomic benefits of torrefaction technology and reactors and its application in the pretreatment of sawdust. An overview of torrefaction technology, torrefied product characteristics, and economic analysis of torrefier reactor and torrefaction cost/ton were reviewed. From the review, torrefaction significantly improved the physical, combustion and performance characteristics of torrefied products, with comparable durability and storability to raw biomass. Comparing with other thermal pretreatment methods, torrefaction is an economical way of improving biomass properties.

Production of Biofuel by Catalytic and Non-Catalyst Pyrolysis of Plantain Stalk

The depletion of global fossil fuel reserves and environmental concerns associated with its production are driving the shift towards biomass as a renewable energy source, which can be converted into biofuels and biogas for diverse energy applications. Hence, we conducted pyrolysis experiments on plantain stalk samples to examine the impact of pyrolysis temperature and heating rate on product yields and their chemical compositions. Optimal conditions for maximum bio-oil yield (22%) were identified at a torrefaction pre-treatment temperature of 300℃. The highest biochar yield (16.88%) was achieved at 300℃, while the highest biogas yield (61.85%) was observed at 150℃. Detailed elemental, proximate, and ultimate analyses of the bio-oil were performed, and its chemical composition was analyzed using Gas Chromatography-Mass Spectrometry (GC-MS). The chromatographic and spectroscopic studies confirmed that bio-oil derived from plantain stalk is a promising renewable fuel and chemical feedstock, indicating its potential in sustainable energy applications.

Progress in Torrefaction Pretreatment for Biomass Gasification

Torrefaction is an effective method to improve the quality of biomass feedstocks for a subsequent thermal conversion process. Torrefaction has been widely developed for biomass upgrading in terms of increasing...

Effect of torrefaction pretreatment on combustion behaviour of different agricultural wastes

In this study, which was carried out to investigate the effect of the torrefaction process on the combustion behaviour of agricultural wastes, almond hulls and shells, olive seeds and corn stalks were used. The samples, dried in a laboratory atmosphere, were torrified at 300 5ºC for 41 minutes. The change in fuel properties was determined by making proximate analyses of the solid product obtained after the process and compared with the raw sample. The effects of the torrefaction process on the combustion behaviour of agricultural wastes of different structures were investigated by burning the 1 0.15 g weighted raw and torrefied samples at 700ºC furnace initial temperature in a fixed bed system. Biochars containing higher fixed carbon were obtained with the torrefaction process applied to agricultural waste, and it was determined that this caused biochars to burn more efficiently and for a longer time than raw biomass. As a result, it was determined that biochar with better properties was produced by the torrefaction process applied to agricultural wastes and it was suitable for burning in solid fuel combustion systems. Thus, biochar obtained will both contribute to the country's economy and add value to agricultural wastes that cause problems during storage, transportation, loading into the burning system, and combustion.

Effects of various pretreatments on fast pyrolysis of biomass to bio-oil: A case study of levoglucosan

Levoglucosan (LG), a valuable chemical derived from carbohydrates, is challenging to obtain with high yield directly from raw biomass. In this study, pyrolysis of a lignocellulosic biomass to LG was studied with various pretreatment methods, including acid, alkali, and torrefaction pretreatments. The results indicated that the hydrochloric acid washing effectively promoted the production of LG when the concentration of HCl was lower than 0.5 mol/L, mainly caused by the improved crystallinity of the cellulose fraction and the removal of alkali and alkaline earth metals (AAEMs). When 4% of NaOH solution was employed for the alkali pretreatment, the relative content of LG significantly increased from 3.07 to 73.59 with the temperature ranging from 130 to 170 ℃, owing to the effective removal of lignin and hemicellulose fractions. Biomass torrefaction at temperature lower than 250 ℃ slightly promoted LG production, but it inhibited the formation of LG when the temperature reached 300 ℃.

Effect of torrefaction pretreatment on the selectivity improvement of lignin pyrolysis products

Pre-regulating the molecular composition and structural characteristics of lignin before pyrolysis is of great significance for the lignin valorization. In this work, torrefaction pretreatment of softwood kraft lignin (SKL) is carried out at different temperatures, and the characterization results show that torrefaction pretreatment is beneficial for removing oxygen element from SKL, which increases the high heating value of torrefied lignins (TLs). In addition, torrefaction pretreatment has a destructive effect on Cβ-O-C4 linkages, and reduces the molecular weight of TLs. Torrefaction pretreatment also removes the thermally unstable components from SKL and increases the release rate of pyrolysis volatiles. Furthermore, torrefaction pretreatment degrades the methoxy group (-OCH3) in SKL into phenolic hydroxyl group, which reduces the yield of guaiacyl type phenols in TLs pyrolysis products, and significantly increases the yield of catechol type phenols from 23.59% in SKL to 47.50% in TL300.

Synergetic deoxygenation and demineralization of biomass by wet torrefaction pretreatment and its influence on the compound distribution of bio-oil during catalytic pyrolysis

In this work, the synergetic deoxygenation and demineralization of biomass by wet torrefaction pretreatment (WTP) coupled with catalytic fast pyrolysis (CFP) using the metal incorporated hierarchical HZSM-5 were employed to enhance the concentration of light aromatics in bio-oil. Results showed that the removal rates of O, Na, K, Ca, and Mg increased with the raise of the WTP temperature, reaching their maximum rates of 47.96%, 81.13%, 90.99%, 66.09%, and 86.65%, respectively. In addition, the NaOH desilication pretreatment and the incorporation of metals (Zn, Ga, and Fe) on HZSM-5 could improve the pore size distribution by creating some mesopore in the framework, and thus provide more acid sites for the hydrodeoxygenation reaction. The optimal operation parameter for CFP was the wet torrefaction temperature of 220 ºC, pyrolysis temperature of 850 ºC, and the catalyst-to-feedstock ratio of 1:3 using the Zn incorporated hierarchical HZSM-5 as catalyst.

Optimization of torrefied black liquor and its combustion characteristics with pulverized coal

BackgroundBlack liquor, a byproduct from the pulping process, holds significant potential as a feedstock for biofuels. However, its inherent properties can pose challenges in direct combustion applications. The optimization of torrefaction pretreatment can potentially enhance its fuel properties, making it a more viable energy source. MethodsThis study aims to evaluate the combustion behavior of torrefied black liquor within a single pellet burner setup. Performance indicators such as ultimate analysis (EA), proximate analysis (PA), and Poison indices (PI) were employed to gage their efficacy. The Taguchi method was utilized to optimize experimental parameters for these indices. Significant findingsCompared to N2 flow rate, torrefaction duration, and heating rate, torrefaction temperature had a significant impact on black liquor torrefaction in Taguchi optimization. Higher torrefaction temperatures (300 °C) resulted in lower CO/CO2 ratios during 800 °C char combustion, dominating overall combustion efficiency. Torrefied black liquor's higher volatile content expedited combustion, while different ratios of torrefied black liquor and coal exhibited linear relationships between mixture proportions and combustion stage durations. Elevated torrefaction temperatures reduced sodium sulfate content in post-combustion ash, effectively preventing boiler fouling.

Effect of torrefaction on yield, reactivity and physicochemical properties of pyrolyzed char from three major biomass constituents

Torrefaction is an efficient pretreatment technology for large-scale and high-value utilization of biomass fuel. To understand the effects of torrefaction pretreatment on the physicochemical characteristics of the pyrolyzed char from the three major constituents of lignocellulosic biomass (cellulose, xylan-representative of hemicelluloses, and lignin), torrefied samples were produced at 200, 260, 320, and 380 ℃, and then pyrolyzed at 1028 ℃ with a heating rate of 65 ℃/s and 0.25 ℃/s, respectively. The experimental results demonstrate that the torrefaction temperature strongly influences the pyrolyzed char’s yields, oxidative reactivities, and physicochemical structure. The sensitivity of the accumulated char yield and char reactivity to the torrefaction temperature differed with varied constituents. Accurate modeling of accumulated char yield is achieved through a weighted summative law, showing a decreasing deviation from 2.4 wt% to 0.6 wt% as torrefaction temperatures increase. Raman spectra indicate that there is a strong correlation between the relative amount of small and large aromatic rings and the accumulated char yield of torrefied samples, with the determination coefficient R2 of 0.98, 0.88, and 0.77 for cellulose, xylan, and lignin, respectively.

Wet torrefaction coupled pyrolysis of camel dung: Fuel properties, pyrolysis behaviors and evolved gases

Wet torrefaction (WT) pretreatment coupled with pyrolysis technology is proposed for improving the fuel properties of camel dung (CD) and regulating NOx emissions from thermal utilization. The fuel ratio, HHV and energy density of CD were significantly enhanced with the WT temperature. Especially, WTC-270 realized the highest energy yield (75.87%), energy-mass synergy efficiency index (EMCI, 19.27%), and the best thermal stability during pyrolysis. Besides, WT pretreatment elevated the release of H2 and CH4 and reduced H2O and CO2 during pyrolysis, apparently. Surprisingly, fewer gaseous pollutants were produced during pyrolysis, ascribing to nitrogen removal and nitrogen functionality stabilization by WT. Notably, NOx and NO emissions from WTC-270 pyrolysis were reduced by 84.6% and almost 100% compared to the CD. Overall, this study provided helpful guidance on the clean utilization and energy production of CD, as well as emission control of gaseous pollutants during energy utilization.

Influence of torrefaction as pretreatment on the fast pyrolysis of sugarcane trash

This study aims to perform a comprehensive analysis of the two-step pyrolysis process, including the three-phase products obtained from torrefaction followed by fast pyrolysis (FP), with particular attention to the redistribution of mass, elements and energy. Torrefaction pretreatment of sugarcane trash (ST) was carried out in a tube furnace at 220 °C, 260 °C and 300 °C for 60 min. Torrefaction results showed that the quality improvement of ST was in the increase in carbon content and the removal of low-calorific volatiles. Fast pyrolysis of raw and torrefied ST was carried out in a mechanically stirred fluidized bed reactor. The results showed that torrefaction pretreatment led to an increased biochar yield and a decreased bio-oil yield in the subsequent FP step. Nevertheless, the quality of obtained bio-oil was enhanced by the higher phenolic content and the lower water and acid contents. On the other hand, the total yield of liquid (including torrefaction liquid and FP bio-oil) of the two-step pyrolysis process decreased while the solid (biochar) yield increased and the total gas yield changed less, compared to the direct FP of raw ST. Furthermore, the elemental redistribution results revealed that most of the carbon (65.21–93.02 wt%) remained in ST after torrefaction, while considerable amounts of oxygen (26.14–69.58 wt%) and hydrogen (23.53–61.25 wt%) were transferred into the torrefaction liquid and non-condensable gases, including H2O, CO, and CO2, amongst others. Consequently, most of the feedstock energy (67.14–89.02 %) was transferred into FP products for the two-step pyrolysis process. In view of the redistribution properties and product quality (especially bio-oil), torrefaction prior to fast pyrolysis is recommended and 260 °C is regarded as a suitable temperature to balance product yield and quality. Overall, this study provides valuable data for a better understanding of the role of torrefaction pretreatment on biomass fast pyrolysis.

Effects of Torrefaction Pretreatment on the Structural Features and Combustion Characteristics of Biomass-Based Fuel.

Wheat straw, a typical agricultural solid waste, was employed to clarify the effects of torrefaction on the structural features and combustion reactivity of biomass. Two typical torrefaction temperatures (543 K and 573 K), four atmospheres (argon, 6 vol.% O2, dry flue gas and raw flue gas) were selected. The elemental distribution, compositional variation, surface physicochemical structure and combustion reactivity of each sample were identified using elemental analysis, XPS, N2 adsorption, TGA and FOW methods. Oxidative torrefaction tended to optimize the fuel quality of biomass effectively, and the enhancement of torrefaction severity improved the fuel quality of wheat straw. The O2, CO2 and H2O in flue gas could synergistically enhance the desorption of hydrophilic structures during oxidative torrefaction process, especially at high temperatures. Meanwhile, the variations in microstructure of wheat straw promoted the conversion of N-A into edge nitrogen structures (N-5 and N-6), especially N-5, which is a precursor of HCN. Additionally, mild surface oxidation tended to promote the generation of some new oxygen-containing functionalities with high reactivity on the surface of wheat straw particles after undergoing oxidative torrefaction pretreatment. Due to the removal of hemicellulose and cellulose from wheat straw particles and the generation of new functional groups on the particle surfaces, the ignition temperature of each torrefied sample expressed an increasing tendency, while the Ea clearly decreased. According to the results obtained from this research, it could be concluded that torrefaction conducted in a raw flue gas atmosphere at 573 K would improve the fuel quality and reactivity of wheat straw most significantly.