油棕废弃物及生物质三组分的热解动力学研究

主要利用热重分析仪(TG)对油棕废弃物和生物质的三组分(半纤维素,纤维素和木质素)的热解特性进行了系统研究,对比分析了热解特性,计算了其热解动力学参数,并研究了升温速率对生物质热解特性的影响。研究发现半纤维素和纤维素易于热降解而木质素难于热解;油棕废弃物的热解可以化分为:干燥、半纤维素热解、纤维素热解和木质素热解4个阶段;生物质的热解反应主要是一级反应,油棕废弃物的活化能很低,约为60kJ/kg;升温速率对生物质影响很大,随升温速率加快,生物质热解温度升高,热解速率降低。     

Two-step steam pyrolysis of biomass for hydrogen production

In this study, different char based catalysts were evaluated in order to increase hydrogen production from the steam pyrolysis of olive pomace in two stage fixed bed reactor system. Biomass char, nickel loaded biomass char, coal char and nickel or iron loaded coal chars were used as catalyst. Acid washed biomass char was also tested to investigate the effect of inorganics in char on catalytic activity for hydrogen production. Catalysts were characterized by using Brunauer–Emmet–Teller (BET) method, X-ray diffraction (XRD) analyzer, X-ray fluorescence (XRF) and thermogravimetric analyzer (TGA). The results showed that the steam in absence of catalyst had no influence on hydrogen production. Increase in catalytic bed temperature (from 500 °C to 700 °C) enhanced hydrogen production in presence of Ni-impregnated and non-impregnated biomass char. Inherent inorganic content of char had great effect on hydrogen production. Ni based biomass char exhibited the highest catalytic activity in terms of hydrogen production. Besides, Ni and Fe based coal char had catalytic activity on H₂ production. On the other hand, the results showed that biomass char was not thermally stable under steam pyrolysis conditions. Weight loss of catalyst during steam pyrolysis could be attributed to steam gasification of biomass char itself. In contrast, properties of coal char based catalysts after steam pyrolysis process remained nearly unchanged, leading to better thermal stability than biomass char.     

Gasification efficiencies of cellulose,hemicellulose and lignin fractions of biomass in aqueous media by using Pt on activated carbon catalyst

The diversity in the chemical composition of lignocellulosic feedstocks can affect the conversion technologies employed for biofuel production. Aqueous-phase reforming (APR) activities of cellulose, hemicellulose and lignin components of lignocellulosic biomass materials were evaluated for production of hydrogen content gas mixture using platinum catalyst on activated carbon support. Wheat straw, an abundant by-product from wheat production and kenaf (Hibiscus cannabinus L.), an annual herbaceous plant growing very fast with low lodging susceptibility were used as lignocellulosics in the present study. The hydrolysates of cellulose fractions of biomass materials showed the best performance for gasification. The results indicated that hemicellulose isolated from kenaf was more sensitive to degradation and therefore, produced more gaseous products than that of wheat straw. The hemicellulose isolated from kenaf biomass left the lowest amount of ungasified solid residue in APR among other cellulose and hemicellulose materials studied. Lignin fractions of both biomass materials were not reactive in APR to produce hydrogen rich gas mixture.Gasification efficiencies of kenaf and wheat straw's hemicelluloses were also compared with xylans from beechwood and oat spelts which were commercially available as hemicellulosic fractions.Oat spelts xylan showed better reforming activity over the beechwood xylan.     

Thermal processing of biomass natural fibre wastes by pyrolysis

Waste biomass material in the form of natural fibres used in the production of textile products were examined for their potential to produce activated carbon by physical activation. The five biomass types were hemp, flax, jute, coir and abaca. Each biomass was pyrolysed in a fixed bed reactor and the char characterized. The char was subsequently, activated with steam in a char activation reactor. The surface area and porosity of the derived activated carbon was determined. Surface areas of between 770 and 879 m² g^?1 were achieved. The yield of activated carbon was mostly less than 20 wt% of the original biomass. The five biomass samples were also pyrolysed in a thermogravimetric analyser. The thermal degradation of the biomas samples were discussed in terms of the thermal degradation of the main components of the biomass, cellulose, hemicellulose and lignin. Copyright © 2004 John Wiley & Sons, Ltd.     

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.     

Supercritical water gasification of biomass for hydrogen production

Hydrogen from waste biomass is considered to be a clean gaseous fuel and efficient for heat and power generation due to its high energy content. Supercritical water gasification is found promising in hydrogen production by avoiding biomass drying and allowing maximum conversion. Waste biomass contains cellulose, hemicellulose and lignin; hence it is essential to understand their degradation mechanisms to engineer hydrogen production in high-pressure systems. Process conditions higher than 374 °C and 22.1 MPa are required for biomass conversion to gases. Reaction temperature, pressure, feed concentration, residence time and catalyst have prominent roles in gasification. This review focuses on the degradation routes of biomass model compounds such as cellulose and lignin at near and supercritical conditions. Some homogenous and heterogeneous catalysts leading to water–gas shift, methanation and other sub-reactions during supercritical water gasification are highlighted. The parametric impacts along with some reactor configurations for maximum hydrogen production and technical challenges encountered during hydrothermal gasification processes are also discussed.     

Influence of mineral matter on pyrolysis of palm oil wastes

The influence of mineral matter on pyrolysis of biomass (including pure biomass components, synthesized biomass, and natural biomass) was investigated using a thermogravimetric analyzer (TGA). First, the mineral matter, KCl, K₂CO₃, Na₂CO₃, CaMg(CO₃)₂, Fe₂O₃, and Al₂O₃, was mixed respectively with the three main biomass components (hemicellulose, cellulose, and lignin) at a weight ratio (C/W) of 0.1 and its pyrolysis characteristics were investigated. Most of these mineral additives, except for K₂CO₃, demonstrated negligible influence. Adding K₂CO₃ inhibited the pyrolysis of hemicellulose by lowering its mass loss rate by 0.3 wt%/°C, while it enhanced the pyrolysis of cellulose by shifting the pyrolysis to a lower temperature. With increased K₂CO₃ added, the weight loss of cellulose in the lower temperature zone (200-315 °C) increased greatly and the activation energies of hemicellulose and cellulose pyrolysis decreased notably from 204 to 42 kJ/mol. Second, studies on the synthetic biomass of hemicellulose, cellulose, lignin, and K₂CO₃ (as a representative of minerals) indicated that peaks of cellulose and hemicellulose pyrolysis became overlapped with addition of K₂CO₃ (at C/W = 0.05-0.1), due to the catalytic effect of K₂CO₃ lowering cellulose pyrolysis to a lower temperature. Finally, a local representative biomass—palm oil waste (in the forms of original material and material pretreated through water washing or K₂CO₃ addition)—was studied. Water washing shifted pyrolysis of palm oil waste to a higher temperature by 20 °C, while K₂CO₃ addition lowered the peak temperature of pyrolysis by . It was therefore concluded that the obvious catalytic effect of adding K₂CO₃ might be attributed to certain fundamental changes in terms of chemical structure of hemicellulose or decomposition steps of cellulose in the course of pyrolysis.     

Conversion study from lignocellulosic biomass and electric energy to H2 and chemicals

The efficient use of lignocellulosic biomass resources is of great significance to solve environmental pollution and energy crisis. Therefore, the understanding of the reactivity of lignin, hemicellulose, and cellulose, which are the major components of lignocellulosic biomass, on chemical and hydrogen conversion is necessary. So combined with proton exchange membrane electrolysis cell, using polyoxometalate (POM) as the oxidizing agent and electron stockpile carrier, the cyclic electrolytic hydrogen production and degradation of lignin, hemicellulose, and cellulose have been researched in detail. Among them, lignin degraded the best (96.81%), and the average Faradaic efficiency of the herein system was also the highest (95.93%). These results exhibit high conversion efficiency from electric energy to hydrogen energy. Simultaneously, without harsh conditions, lignin is mainly degraded to vanillin, hemicellulose is mainly converted to ester compounds, and cellulose is mainly converted to alcohol compounds, which provides an experiment basis for future chemical conversion.     

Pretreatment and fractionation of barley straw using steam explosion at low severity factor

Agricultural residues represent an abundant, readily available, and inexpensive source of renewable lignocellulosic biomass. However, biomass has complex structural formation that binds cellulose and hemicellulose. This necessitates the initial breakdown of the lignocellulosic matrix. Steam explosion pretreatment was performed on barley straw grind to assist in the deconstruction and disaggregation of the matrix, so as to have access to the cellulose and hemicellulose. The following process and material variables were used: temperature (140–180 °C), corresponding saturated pressure (500–1100 kPa), retention time (5–10 min), and mass fraction of water 8–50%. The effect of the pretreatment was assessed through chemical composition analysis. The severity factor R_o, which combines the temperature and time of the hydrolytic process into a single reaction ordinate was determined. To further provide detailed chemical composition of the steam exploded and non-treated biomass, ultimate analysis was performed to quantify the elemental components. Data show that steam explosion resulted in the breakdown of biomass matrix with increase in acid soluble lignin. However, there was a considerable thermal degradation of cellulose and hemicellulose with increase in acid insoluble lignin content. The high degradation of the hemicellulose can be accounted for by its amorphous nature which is easily disrupted by external influences unlike the well-arranged crystalline cellulose. The carbon content of the solid steam exploded product increased at higher temperature and longer residence time, while the hydrogen and oxygen content decreased, and the higher heating value (HHV) increased.     

A novel integrated process for hydrogen production from biomass

A novel process, which integrated with biomass pyrolysis, gas–solid simultaneous gasification and catalytic reforming processes, was utilized to produce hydrogen. The effects of gasification temperature and reforming temperature on hydrogen yield and carbon conversion efficiency were investigated. The results showed that both higher gasification temperature and reforming temperature led to higher hydrogen yield and carbon conversion efficiency. Compared with the two-stage pyrolysis-catalytic reforming process, hydrogen yield and carbon conversion efficiency were greatly increased from 43.58 to 75.96 g H₂/kg biomass and 66.18%–82.20% in the integrated process.     

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.     

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.     

Comparative study on pyrolysis and catalytic pyrolysis upgrading of biomass model compounds: Thermochemical behaviors,kinetics, and aromatic hydrocarbon formation

In order to understand the pyrolysis mechanism, reaction kinetic and product properties of biomass and select suitable agricultural and forestry residues for the generation desired products, the pyrolysis and catalytic pyrolysis characteristics of three main components (hemicellulose, cellulose, and lignin) of biomass were investigated using a thermogravimetric analyzer (TGA) with a fixed-bed reactor. Fourier transform infrared spectroscopy (FTIR) and elemental analysis were used for further characterization. The results showed that: the thermal stability of hemicellulose was the worst, while that of cellulose was higher with a narrow range of pyrolysis temperatures. Lignin decomposed over a wider range of temperatures and generated a higher char yield. After catalytic pyrolysis over HZSM-5 catalyst, the conversion ratio increased. The ratio for the three components was in the following order: lignincellulose < biomass < xylan. The Starink method was introduced to analyze the thermal reaction kinetics, activation energy (Ea), and the pre-exponential factor (A). The addition of HZSM-5 improved the reactivity and decreased the activation energy in the following order: xylan (30.54%) > biomass(15.41%) > lignin (14.75%) > cellulose (6.73%). The pyrolysis of cellulose gave the highest yield of bio-oil rich in levoglucosan and other anhydrosugars with minimal coke formation. Xylan gave a high gas yield and moderate yield of bio-oil rich in furfural, while lignin gave the highest solid residue and produced the lowest yield of bio-oil that was rich in phenolic compounds. After catalytic pyrolysis, xylan gave the highest yield of monocyclic aromatic hydrocarbons, 76.40%, and showed selectivity for benzene and toluene. Cellulose showed higher selectivity for xylene and naphthalene; however, lignin showed enhanced for selectivity of C10 + polycyclic aromatic hydrocarbons. Thus, catalytic pyrolysis method can effectively improve the properties of bio-oil and bio-char.     

Inhibition of steam gasification of biomass char by hydrogen and tar

The influence of hydrogen and tar on the reaction rate of woody biomass char in steam gasification was investigated by varying the concentrations in a rapid-heating thermobalance reactor. It was observed that the steam gasification of biomass char can be separated into two periods. Compared with the first period, in the second period (in which the relative mass of remaining char is smaller than 0.4) the gasification rate is increased. These effects are probably due to inherent potassium catalyst. Higher hydrogen partial pressure greatly inhibits the gasification of biomass char in the first and second periods. By calculating the first-order rate constants of char gasification in the first and second periods, we found that the hydrogen inhibition on biomass char gasification is caused by the reverse oxygen exchange reaction in the first period. In the second period, dissociative hydrogen adsorption on the char is the major inhibition reaction. The influence of levoglucosan, a major tar component derived from cellulose, was also examined. We found that not only hydrogen but also vapor-phase levoglucosan and its pyrolysates inhibited the steam gasification of woody biomass char. By mixing levoglucosan with woody biomass sample, the pyrolysis of char proceeds slightly more rapidly than with woody biomass alone, and gas evolution rates of H₂ and CO₂ are larger in steam gasification.     

Novel hydrogen‐rich gas production by steam gasification of biomass in a research‐scale rotary tubular helical coil gasifier

The concept of biomass steam gasification offers platform for production (i) of hydrogen, (ii) hydrocarbons and (iii) value added chemicals. Majority of these developments are either in nascent or in pilot/demonstration stage. In this context, there exists potential for hydrogen production via biomass steam gasification. Gaseous products of biomass steam gasification consist of large percentage of CO, CH₄ and other hydrocarbons, which can be converted to hydrogen through water‐gas‐shift reaction, steam reforming and cracking respectively. Although there are many previous research works showing the potential of production of hydrogen from biomass in a two stage process, challenges remain in extended biomass and char gasification so as to reduce the amount of carbon in the residual char as well as improve conversion of heavy hydrocarbon condensates to hydrogen rich gas. In the current work, the characteristics of biomass steam gasification in an in‐house designed rotary tubular helical coil reactor at temperatures less than 850 °C, in the presence of superheated steam, were presented. The objectives were to obtain high carbon conversion in the primary biomass steam gasification step (upstream) and high product gas yield and hydrogen yield in the secondary fixed bed catalytic step (downstream). The influence of temperature, steam‐to‐biomass ratio and residence time on product gas yield in the rotary tubular helical coil gasifier was studied in detail using one of the abundantly available biomass sources in India‐rice husk. Further, enhancement of product gas yield and hydrogen yield in a fixed bed catalytic converter was studied and optimized. In the integrated pathway, a maximum gas yield of 1.92 Nm³/kg moisture‐free biomass was obtained at a carbon conversion efficiency of 92%. The maximum hydrogen purity achieved under steady state conditions was 53% by volume with a hydrogen yield of 91.5 g/kg of moisture‐free biomass. This study substantiates overall feasibility of production of high value hydrogen from locally available biomass by superheated steam gasification followed by catalytic conversion. Copyright © 2016 John Wiley & Sons, Ltd.     

A study on torrefaction of various biomass materials and its impact on lignocellulosic structure simulated by a thermogravimetry

Torrefaction processes of four kinds of biomass materials, including bamboo, willow, coconut shell and wood (Ficus benjamina L.), were investigated using the thermogravimetric analysis (TGA). Particular emphasis is placed on the impact of torrefaction on hemicellulose, cellulose and lignin contained in the biomass. Two different torrefaction processes, consisting of a light torrefaction process at 240 °C and a severe torrefaction process at 275 °C, were considered. From the torrefaction processes, the biomass could be divided into two groups; one was the relatively active biomass such as bamboo and willow, and the other was the relatively inactive biomass composed of coconut shell and wood. When the light torrefaction was performed, the results indicated that the hemicellulose contained in the biomass was destroyed in a significant way, whereas cellulose and lignin were affected only slightly. Once the severe torrefaction was carried out, it further had a noticeable effect on cellulose, especially in the bamboo and willow. The light torrefaction and severe torrefaction were followed by a chemically frozen zone, regardless of what the biomass was. From the viewpoint of torrefaction application, the investigated biomass torrefied in less than 1 h with light torrefaction is an appropriate operation for producing fuels with higher energy density.     

Thermogravimetric analysis as a new method to determine the lignocellulosic composition of biomass

Biomass energy uses organic matter such as wood or plants - lignocellulosic biomass - for creating heat, generating electricity and producing green oil for cars. Modern biomass energy recycles organic leftovers from forestry and agriculture, like corn stovers, rice husks, wood waste and pressed sugar cane, or uses special, fast-growing “energy crops” like willow and switchgrass, as fuel. Biomass is composed of three major components: cellulose, hemicelluloses, and lignin. Their differences in chemical structures lead to different chemical reactivities, making the relative composition in cellulose, hemicelluloses and lignin in the biomass a crucial factor for process design. In this paper thermogravimetric analysis is investigated as a new method to obtain lignin, hemicellulose and ??-cellulose contents in biomass. It is shown that this alternative method lead to comparable results than common methods used for the determination of the ??-cellulose content, with an enhancement of the accuracy in the determination of the hemicellulose content. Unfortunately, this method cannot be adopted for the determination of the lignin amount.     

Co-torrefaction followed by co-combustion of intermediate waste epoxy resins and woody biomass in the form of mini-pellet

This study aimed to investigate co-torrefaction followed by co-combustion of intermediate waste epoxy resins and fir in the form of mini-pellet to evaluate the potential of industrial wastes as biofuels for alternatives of coals. Co-torrefaction and co-combustion of the materials were analyzed through thermogravimetric analysis (TGA) coupled with Fourier transform infrared (FTIR) spectrometer. The results suggested that most of the torrefaction had a slight influence on the wastes due to their thermal resistance properties. Conversely, fir was markedly affected by torrefaction, and the corresponding volatiles were the chemicals stripped or reacted from its components (hemicellulose, cellulose, and lignin). By introducing an index, both antagonistic and synergistic effects were discovered in the two-stage reaction because new compounds formed during the co-torrefaction and co-combustion processes, as a consequence of catalytic and blocking effects. Overall, co-torrefaction could make the quality of the biofuel from intermediate waste epoxy resins more homogeneous and is a promising route to transform waste epoxy resins into alternative fuels for industrial applications.     

Effect of cellulose and lignin content on pyrolysis and combustion characteristics for several types of biomass

Fundamental pyrolysis and combustion behaviors for several types of biomass are tested by a thermo-gravimetric analyzer. The main compositions of cellulose and lignin contents for several types of biomass are analyzed chemically. Based on the main composition results obtained, the experimental results for the actual biomass samples are compared with those for the simulated biomass, which is made of the mixture of the cellulose with lignin chemical. The morphological changes before and after the reactions are also observed by a scanning electron microscope. The main compositions in the biomass consisted of cellulose and lignin. The cellulose content was more than lignin for the biomass samples selected in this study. The reaction for the actual biomass samples proceeded with the two stages. The first and second stage corresponded to devolatilization and char combustion during combustion, respectively. The first stage showed rapid mass decrease caused by cellulose decomposition. At the second stage, lignin decomposed for pyrolysis and its char burned for combustion. For the biomass with higher cellulose content, the pyrolysis rate became faster. While, the biomass with higher lignin content gave slower pyrolysis rate. The cellulose and lignin content in the biomasses was one of the important parameters to evaluate the pyrolysis characteristics. The combustion characteristics for the actual biomass depends on the char morphology produced.     

生物质三组分的催化气化特性研究

以生物质三组分(纤维素、半纤维素和木质素)作为实验原料,采用常用的白云石作为催化剂,在小型气流床气化炉上进行气化催化实验。重点研究了白云石对生物质三组分的催化气化特性以及焦油析出特性的差异。结果表明:白云石对纤维素、半纤维素、木质素均起到正向催化作用,提高了三者的碳转化率、气化效率以及气体热值;同时,白云石对三组分的催化作用存在明显差异,其中,对半纤维素的促进催化作用最为显著,木质素次之,对纤维素的促进作用不明显。因此,针对不同组分含量和特性的生物质选择适当的催化剂是必要的。