The influence of temperature and heating rate on the slow pyrolysis of biomass

The slow pyrolysis of biomass in the form of pine wood was investigated in a static batch reactor at pyrolysis temperatures from 300 to 720°C and heating rates from 5 to 80 K min⁻¹. The compositions and properties of the derived gases, pyrolytic oils and solid char were determined in relation to pyrolysis temperatures and heating rates. In addition, the wood and the major components of the wood—cellulose, hemicellulose and lignin—were pyrolysed in a thermogravimetric analyser (TGA) under the same experimental conditions as in the static batch reactor. The static batch reactor results showed that as the pyrolysis temperature was increased, the percentage mass of solid char decreased, while gas and oil products increased. There was a small effect of heating rate on product yield. The lower temperature regime of decomposition of wood showed that mainly H₂O, CO₂ and CO were evolved and at the higher temperature regime, the main decomposition products were oil, H₂O, H₂, hydrocarbon gases and lower concentrations of CO and CO₂. Fourier transformation infra-red spectroscopy and elemental analysis of the oils showed they were highly oxygenated. The TGA results for wood showed two main regimes of weight loss, the lower temperature regime could be correlated with the decomposition of hemicellulose and the initial stages of cellulose decomposition whilst the upper temperature regime correlated mainly with the later stages of cellulose decomposition. Lignin thermal decomposition occurred throughout the temperature range of pyrolysis.     

Hydrogen production via catalytic pyrolysis of biomass in a two-stage fixed bed reactor system

This study introduces an innovative process of generating hydrogen-rich gas from biomass through the catalytic pyrolysis of biomass in a two-stage fixed bed reactor system. Water hyacinth was used as the biomass feedstock. The effects of various factors such as pyrolysis temperature, catalytic bed temperature, residence time, catalyst, and the nickel content of the catalyst on the pyrolysis productivity were investigated and the yields of H₂, CO, CH₄, and CO₂ were obtained. Results showed that the high productivity of hydrogen can be obtained particularly by increasing the catalytic bed temperature, residence time, and catalysts. The favorable reaction conditions are as follows: a first-stage pyrolysis temperature of 650 °C–700 °C, a second-stage catalytic bed temperature of 800 °C, a catalytic pyrolysis reaction time of 17 min, and a nickel content of 9% (wt %).     

Supercritical water gasification of real biomass feedstocks in continuous flow system

In this study, supercritical water gasification of the selected five biomass samples (cauliflower residue, acorn, tomatoes residue, extracted acorn and hazelnut shell) was investigated. Lignocellulosic feedstocks were gasified in a continuous flow reactor at 600 °C and 35 MPa. The product gas is composed of hydrogen, carbon dioxide, methane, carbon monoxide and a small amount of C₂ compounds. Quantitative analysis of product gas was performed by Gas chromatography device. Potassium carbonate (K₂CO₃) and Trona (Na₂CO₃·NaHCO₃·2H₂O) were used as catalysts. Carbon gasification efficiencies were improved by addition of these catalysts into the reacting system. Moreover, carbon gasification efficiency changes with type of biomass that includes different ratio of cellulose, hemicellulose and lignin. The H₂ yield (mol gas/kg C in feed) of acorn in the presence of Trona was found to be 7 times higher than that of without catalyst.     

Thermogravimetric characteristics and kinetics of sawdust pyrolysis catalyzed by potassium salt during the process of hydrogen preparation

Pyrolysis experiments of sawdust with KOH and K₂CO₃ catalysts were carried out under different heating rate in nitrogen atmosphere using thermogravimetric analyzer. The distributed activation energy model (DAEM) was used to analyze pyrolysis kinetics of sawdust. The results showed that both KOH and K₂CO₃ had strong catalytic effect on sawdust pyrolysis, which reduced the pyrolysis temperature of sawdust and increased the yield of char. There was only one main peak in DTG curve, which means that the pyrolysis behavior of cellulose and hemicellulose in sawdust was greatly changed. The catalytic performance of KOH was found to be more excellent in sawdust pyrolysis. Also KOH could catalyze the pyrolysis of sawdust at low temperature. The kinetic analysis results showed that the two kinds of catalysts could reduce the activation energy of sawdust pyrolysis and maintain a similar catalytic trend, but KOH had a more stable catalytic performance.     

Effect of calcium based catalyst on production of synthesis gas in gasification of waste bamboo chopsticks

This study investigated the effects of calcium based catalyst (calcium oxide) on variation of gas composition in catalytic gasification reaction stages by controlling the gasification temperature between 600 °C and 900 °C whilst varying a catalyst/biomass ratio from 0 to 0.2 w/w. The tested biomass generated from used bamboo chopsticks were used as the feedstock. To assess the gas composition variation, the ratio of H₂/CO, H₂/CO₂, CO/CO₂, and 3H₂/CH₄ are four important factors that affect the performance of catalytic gasification process. The maximum ratio of H₂/CO increased from 0.23 to 0.72 in the gasification temperature range between 600 °C and 900 °C and 0%–20% calcium based catalyst addition ratio. This is due to enhanced H₂ production as a result of the facilitated water–gas shift reaction. The ratios of CO/CO₂ and 3H₂/CH₄ increased significantly from 0.9 to 2.1 and from 2.6 to 4.1, respectively, when the gasification temperature increased from 600 °C to 900 °C and 20% catalyst addition ratio. Obviously, the high temperature and catalyst addition are favorable for production of CO and H₂ during gasification of tested biomass. In conclusion, the tested mineral calcium based catalyst (CaO) can help facilitating the reaction rate of partial oxidation and water–gas shift reaction, enhancing the quality of synthesis gas, and reduction of the gasification reaction time. This catalyst has potential application in gasification of waste bamboo chopsticks in the future.     

Isothermal torrefaction kinetics of hemicellulose, cellulose, lignin and xylan using thermogravimetric analysis

In recent years, torrefaction, a mild pyrolysis process carried out at the temperature range of 200-300 °C, has been considered as an effective route for improving the properties of biomass. Hemicellulose, cellulose, lignin and xylan are the basic constituents in biomass and their thermal behavior is highly related to biomass degradation in a high-temperature environment. In order to provide a useful insight into biomass torrefaction, this study develops the isothermal kinetics to predict the thermal decompositions of hemicellulose, cellulose, lignin and xylan. A thermogravimetry is used to perform torrefaction and five torrefaction temperatures of 200, 225, 250, 275 and 300 °C with 1 h heating duration are taken into account. From the analyses, the recommended values of the order of reaction of hemicellulose, cellulose, lignin and xylan are 3, 1, 1 and 9, respectively, whereas their activation energies are 187.06, 124.42, 37.58 and 67.83 kJ mol⁻¹, respectively. A comparison between the predictions and the experiments suggests that the developed model can provide a good evaluation on the thermal degradations of the constituents, expect for cellulose at 300 °C and hemicellulose at 275 °C. Eventually, co-torrefaction of hemicellulose, cellulose and lignin based on the model is predicted and compared to the thermogravimetric analysis.     

Study on catalytic properties of potassium carbonate during the process of sawdust pyrolysis

In order to investigate the effect of potassium carbonate on biomass pyrolysis properties, sawdust was used as raw material and different amounts of K₂CO₃ were added by impregnation method to carry out thermogravimetric and pyrolysis experiments. The effects of pyrolysis temperature and the amount of K₂CO₃ addition on the pyrolysis of sawdust were studied using a self-made fixed-bed pyrolysis furnace. Calculation of pyrolysis kinetics shows that the existence of K₂CO₃ catalyst changes the pyrolysis path of sawdust, so that the activation energy of pyrolysis sawdust decreases at low temperature and increases at high temperature. The pyrolysis experiments shows that the addition of K₂CO₃ and the increase of pyrolysis temperature both reduce the yield of the pyrolysis oil of sawdust and increase the yield of the pyrolysis syngas. However, K₂CO₃ catalyst promotes the yield of char, the increase of pyrolysis temperature decreases the yield of char. Analysis of the pyrolysis products finds that the addition of K₂CO₃ and the increase of pyrolysis temperature both improve quality of the pyrolysis oil, form more microporous surface of char, and increase the hydrogen content in the pyrolysis syngas. It is considered that the optimal process for producing pyrolysis syngas is 900 °C of pyrolysis temperature and 10% of K₂CO₃ addition.     

Potassium catalytic hydrogen production in sorption enhanced gasification of biomass with steam

Sorption enhanced gasification (SEG) of biomass with steam was investigated in a fixed-bed reactor to elucidate the effects of temperature, catalyst type and loading on hydrogen production. K₂CO₃, CH₃COOK and KCl were chosen as potassium catalyst precursors to improve carbon conversion efficiency in gasification process. It was indicated that from 600 °C to 700 °C, the addition of K₂CO₃ or CH₃COOK catalyzed the gasification for hydrogen production, and hydrogen yield and carbon conversion increased with increasing catalyst loadings of K₂CO₃ or CH₃COOK. However, the hydrogen yield and carbon conversion decreased as the amount of KCl was increased due to inhibition of KCl on gasification. The maximum carbon conversion efficiency (88.0%) was obtained at 700 °C corresponding to hydrogen yield of 73.0 vol.% when K₂CO₃ of 20 wt.% K loading was used. In particular, discrepant catalytic performance was observed between K₂CO₃ and CH₃COOK at different temperatures and the corresponding mechanism was also discussed.     

Effects of K2CO3 on pyrolysis characteristics of Xinjiang cotton stalk

The horizontal fixed bed pyrolysis method was used in this study to examine the reaction parameters of K in-situ catalytic pyrolysis of the cotton stalk at 600 °C. The pyrolysis conversion mechanism of cotton stalk under the influence of K was investigated in conjunction with gas chromatography analysis, FT-IR analysis, and GC-MS analysis. According to the findings, the gas production of a mixture of 1 g cotton stalks grew from 215 mL (0.0 %- K₂CO₃) to 275 mL (7.5% -K₂CO₃), but it was inhibited to 263 mL when K₂CO₃ addition was at 10.0%. According to the results of the characterization, K₂CO₃ might accelerate the breakdown of oxygen-containing rings in cellulose and hemicellulose, encourage the conversion of furan structure into ketones, and prevent the transformation of furan into long-chain alkanes. The addition of K₂CO₃ introduces more K into the cotton stalk. Under the influence of K, long-chain alkanes, phenols, and esters will be further cracked and polymerized to create more stable aromatic hydrocarbons. According to quantum chemical calculations, xylose's oxygen-containing ring opened first without the presence of K, then H transfer, dehydrogenation, dehydration, and cyclization to generate the cyclopentanone structure. The oxygen-containing groups in the xylose side chain preferentially bind to K in the presence of K, and the bond length between the O and C rings of the side chain is lengthened, while without K, the C–O bond length of the preferred ring opening is shortened.     

Thermogravimetric study on the pyrolysis kinetics of apple pomace as waste biomass

Biomass waste-to-energy is an attractive alternative to fossil feedstocks because of essentially zero net CO₂ impact. A viable option consists in an integrated process, in which biomass is partly used to produce valuable chemicals with residual fractions employed for hydrogen production. One example of a biomass waste is the apple pomace, which is the residue generated in the process of extraction of apple juice. In this research, a kinetic study of the pyrolysis of apple pomace biomass (APB) was performed by TGA aiming its liquid and gaseous products be utilized for the production of valuable chemicals and hydrogen. Characterization of APB consisted in calorific value, compositional, proximal and elemental analyzes. Kinetics were evaluated using three iso-conversional TGA models at 5, 10, 15 and 20 °C/min. Activation energy values of 213.0 and 201.7 kJ/mol were within the range for hemicellulose and cellulose, respectively, which are the main components of biomass.     

Plate reactor as an analysis tool for rapid pyrolysis of biomass

This work presents a study of the performance of the modified plate reactor by rapid pyrolysis experiments with different biomass samples (MDF, bark pine and Avicel cellulose). The use of the plate instead of a grid allowed us to achieve a more homogeneous temperature distribution across the plate and, therefore, biomass sample. The mass yields of the major pyrolysis products CO, CO₂, C₂H₂, CH₄, C₂H₄ and C₂H₆ are measured as a function of the holding time (from 0 to 50 s) for a number of the final temperatures (from 435 to 1100 C) using the novel approach to quantitative FTIR analysis of biomass pyrolysis spectra. Special care was taken to demonstrate the influence of the secondary tar cracking on the yields of the permanent gases. Yields of major permanent gases plotted versus each other on a logarithmic scale show two distinctive regions reflecting primary and secondary kinetic processes. The experiments show that the modified plate reactor can be used for studying the kinetics of the primary decomposition of the biomass at temperatures ≤600 C.     

Effects of biochemical composition on hydrogen production by biomass gasification

Gasification of cellulose, hemicellulose, lignin and three types of real biomass was conducted using an updraft fixed-bed reactor to investigate the effects of temperature (in the range of 920–1220 °C) on the yield and chemical composition of the produced syngas. The experimental results showed that the gasification products of cellulose and hemicellulose were similar to each other, but they were different from those of lignin; it is likely due to the difference in volatile compounds. Cellulose and hemicellulose can be gasified more rapidly producing more CO and CH₄ and less H₂ and CO₂ than lignin, and the real biomass fell in between. Biomass with more lignin produced more hydrogen than others. These differences were resulted from the relative amount of lignin, hemicellulose, and cellulose in the biomass. Linear superposition method was used to simulate the gasification characteristics of real biomass and it showed a certain linear correlation between the simulation and experimental data.     

Hydrothermal pretreatment of switchgrass and corn stover for production of ethanol and carbon microspheres

Pretreatment of biomass is viewed as a critical step to make the cellulose accessible to enzymes and for an adequate yield of fermentable sugars in ethanol production. Recently, hydrothermal pretreatment methods have attracted a great deal of attention because it uses water which is a inherently present in green biomass, non-toxic, environmentally benign, and inexpensive medium. Hydrothermal pretreatment of switchgrass and corn stover was conducted in a flow through reactor to enhance and optimize the enzymatic digestibility. More than 80% of glucan digestibility was achieved by pretreatment at 190 °C. Addition of a small amount of K₂CO₃ (0.45-0.9 wt.%) can enhance the pretreatment and allow use of lower temperatures. Switchgrass pretreated at 190 °C only with water had higher internal surface area than that pretreated in the presence of K₂CO₃, but both the substrates showed similar glucan digestibility. In comparison to switchgrass, corn stover required milder pretreatment conditions. The liquid hydrolyzate generated during pretreatment was converted into carbon microspheres by hydrothermal carbonization, providing a value-added byproduct. The carbonization process was further examined by GC-MS analysis to understand the mechanism of microsphere formation.     

Hydrogen synthesis from biomass pyrolysis with in situ carbon dioxide capture using calcium oxide

Hydrogen (H₂) and other gases (CO₂, CO, CH₄, H₂O) produced during the pyrolysis of cellulose, xylan, lignin and pine (Pinus radiata), with and without added calcium oxide (CaO), were studied using thermogravimetry-mass spectrometry (TG-MS) and thermodynamic modeling. CaO improved the H₂ yield from all feedstocks, and had the most significant effect on xylan. The weight loss of and gas evolution from the feedstocks were measured over the temperature range 150-950 °C in order to investigate the principle mechanism(s) of H₂ formation. Without added CaO, little H₂ was produced during primary pyrolysis; rather, most H₂ was generated from tar-cracking, reforming, and char-decomposition reactions at higher temperatures. When CaO was added, significant H₂ was produced during primary pyrolysis, as the water-gas shift reaction was driven toward H₂ formation. CaO also increased the formation of H₂ from reforming and char gasification reactions. Finally, CaO increased the extent of tar cracking and char decomposition, and lowered their onset temperatures. The production of H₂ from pine over the course of pyrolysis could be modeled by summing the H₂ evolutions from the separate biomass components in relevant proportions.     

Integrated catalytic adsorption (ICA) steam gasification system for enhanced hydrogen production using palm kernel shell

This paper investigates the integrated catalytic adsorption (ICA) steam gasification of palm kernel shell for hydrogen rich gas production using pilot scale fluidized bed gasifier under atmospheric condition. The effect of temperature (600–750 °C) and steam to biomass ratio (1.5–2.5 wt/wt) on hydrogen (H₂) yield, product gas composition, gas yield, char yield, gasification and carbon conversion efficiency, and lower heating values are studied. The results show that H₂ hydrogen composition of 82.11 vol% is achieved at temperature of 675 °C, and negligible carbon dioxide (CO₂) composition is observed at 600 °C and 675 °C at a constant steam to biomass ratio of 2.0 wt/wt. In addition, maximum H₂ yield of 150 g/kg biomass is observed at 750 °C and at steam to biomass ratio of 2.0 wt/wt. A good heating value of product gas which is 14.37 MJ/Nm³ is obtained at 600 °C and steam to biomass ratio of 2.0 wt/wt. Temperature and steam to biomass ratio both enhanced H₂ yield but temperature is the most influential factor. Utilization of adsorbent and catalyst produced higher H₂ composition, yield and gas heating values as demonstrated by biomass catalytic steam gasification and steam gasification with in situ CO₂ adsorbent.     

Conversion of carbon dioxide and methane in biomass synthesis gas for liquid fuels production

The premise of this research is to find whether methane (CH₄) and carbon dioxide (CO₂) produced during biomass gasification can be converted to carbon monoxide (CO) and hydrogen (H₂). Simultaneous steam and dry reforming was conducted by selecting three process parameters (temperature, CO₂:CH₄, and CH₄:steam ratios). Experiments were carried out at three levels of temperature (800 °C, 825 °C and 850 °C), CO₂:CH₄ ratio (2:1, 1:1 and 1:2), and CH₄:steam ratio (1:1, 1:2 and 1:3) at a residence time of 3.5 × 10³ g_cat min/cc using a custom mixed gas that resembles biomass synthesis gas, over a commercial catalyst. Experiments were conducted using a Box-Behnken approach to evaluate the effect of the process variables. The average CO and CO₂ selectivities were 68% and 18%, respectively, while the CH₄ and CO₂ conversions were about 65% and 48%, respectively. The results showed optimum conditions for maximum CH₄ conversion was at 800 °C, CO₂:CH₄ ratio and CH₄:steam ratios of 1:1.     

Hydrogen production by catalytic gasification of coal in supercritical water with alkaline catalysts: Explore the way to complete gasification of coal

Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by catalytic gasification of coal in supercritical water (SCW) was carried out in a micro batch reactor with various alkaline catalysts: Na₂CO₃, K₂CO₃, Ca(OH)₂, NaOH and KOH. H₂ yield in relation to the alkaline catalyst was in the following order: K₂CO₃ ≈ KOH ≈ NaOH > Na₂CO₃ > Ca(OH)₂. Then, hydrogen production by catalytic gasification of coal with K₂CO₃ was systematically investigated in supercritical water. The influences of the main operating parameters including feed concentration, catalyst loading and reaction temperature on the gasification characteristics of coal were investigated. The experimental results showed that carbon gasification efficiency (CE, mass of carbon in gaseous product/mass of carbon in coal × 100%) and H₂ yield increased with increasing catalyst loading, increasing temperature, and decreasing coal concentration. In particular, coal was completely gasified at 700 °C when the weight ratio of K₂CO₃ to coal was 1, and it was encouraging that raw coal was converted into white residual. At last, a reaction mechanism based on oxygen transfer and intermediate hybrid mechanism was proposed to understand coal gasification in supercritical water.     

Characterization and prediction of biomass pyrolysis products

In this study some literature data on the pyrolysis characteristics of biomass under inert atmosphere were structured and analyzed, constituting a guide to the conversion behavior of a fuel particle within the temperature range of 200-1000 °C. Data is presented for both pyrolytic product distribution (yields of char, total liquids, water, total gas and individual gas species) and properties (elemental composition and heating value) showing clear dependencies on peak temperature. Empirical relationships are derived from the collected data, over a wide range of pyrolysis conditions and considering a variety of fuels, including relations between the yields of gas-phase volatiles and thermochemical properties of char, tar and gas. An empirical model for the stoichiometry of biomass pyrolysis is presented, where empirical parameters are introduced to close the conservation equations describing the process. The composition of pyrolytic volatiles is described by means of a relevant number of species: H₂O, tar, CO₂, CO, H₂, CH₄ and other light hydrocarbons. The model is here primarily used as a tool in the analysis of the general trends of biomass pyrolysis, enabling also to verify the consistency of the collected data. Comparison of model results with the literature data shows that the information on product properties is well correlated with the one on product distribution. The prediction capability of the model is briefly addressed, with the results showing that the yields of volatiles released from a specific biomass are predicted with a reasonable accuracy. Particle models of the type presented in this study can be useful as a submodel in comprehensive reactor models simulating pyrolysis, gasification or combustion processes.     

Hydrogen production from autothermal CO2 gasification of cellulose in a fixed-bed reactor: Influence of thermal compensation from CaO carbonation

Biomass gasification is a promising technology to produce renewable syngas used for energy and chemical applications. However, biomass gasification has challenges of low process energy efficiency, low syngas production with low H₂/CO ratio and the sintering of biomass ash which limit the deployment of the technology. This work investigated the influence of in-situ generated heat from CaO–CO₂ on cellulose CO₂ gasification using a fixed bed reactor, thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR) and differential scanning calorimetry (DSC). Experimental results indicate an approximate 20 °C temperature difference in the fix-bed reactor between cellulose CO₂ gasification with the energy compensation of CaO carbonation (denoted auto-thermal biomass gasification) and conventional CO₂ gasification of cellulose after the power of external furnaces were turned off. Around 5 times H₂/CO molar ratio is obtained after switching off the power in the auto-thermal biomass gasification compared with conventional gasification. The gas yield enhances significantly from 0.29 g g^?1 cellulose to 0.56 g g^?1 cellulose when CaO/cellulose mass ratio increases from 0 to 5. Furthermore, the TGA-FTIR results demonstrate the feasibility of adopting energy compensation of CaO carbonation to reduce the gasification temperature. DSC analysis also proves that the released heat from the CaO–CO₂ reaction reduces the required energy for cellulose degradation.