The effect of temperature and hemicellulose-lignin,cellulose-lignin,and cellulose-hemicellulose on char yield from the slow pyrolysis of rice husk

In this work, the effect of temperature on the char yield of untreated rice husk, cellulose removed (hemicellulose + lignin), hemicellulose removed (cellulose + lignin), and lignin removed (cellulose + hemicellulose) is investigated. The work compares the performance of acid and alkaline hydrolysis in the context of lignin removal as well. The effect of hemicellulose-lignin, cellulose-lignin, and cellulose-hemicellulose on char yield during slow pyrolysis of rice husk is also studied. The study reveals that only low temperatures favor char yield. Alkaline hydrolysis effects better lignin removal than acid hydrolysis. The effect of hemicellulose-lignin on char yield is more than cellulose-lignin and cellulose-lignin.     

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。     

Pyrolysis-catalytic steam reforming of agricultural biomass wastes and biomass components for production of hydrogen/syngas

The pyrolysis-catalytic steam reforming of six agricultural biomass waste samples as well as the three main components of biomass was investigated in a two stage fixed bed reactor. Pyrolysis of the biomass took place in the first stage followed by catalytic steam reforming of the evolved pyrolysis gases in the second stage catalytic reactor. The waste biomass samples were, rice husk, coconut shell, sugarcane bagasse, palm kernel shell, cotton stalk and wheat straw and the biomass components were, cellulose, hemicellulose (xylan) and lignin. The catalyst used for steam reforming was a 10 wt.% nickel-based alumina catalyst (NiAl₂O₃). In addition, the thermal decomposition characteristics of the biomass wastes and biomass components were also determined using thermogravimetric analysis (TGA). The TGA results showed distinct peaks for the individual biomass components, which were also evident in the biomass waste samples reflecting the existence of the main biomass components in the biomass wastes. The results for the two-stage pyrolysis-catalytic steam reforming showed that introduction of steam and catalyst into the pyrolysis-catalytic steam reforming process significantly increased gas yield and syngas production notably hydrogen. For instance, hydrogen composition increased from 6.62 to 25.35 mmol g^?1 by introducing steam and catalyst into the pyrolysis-catalytic steam reforming of palm kernel shell. Lignin produced the most hydrogen compared to cellulose and hemicellulose at 25.25 mmol g^?1. The highest residual char production was observed with lignin which produced about 45 wt.% char, more than twice that of cellulose and hemicellulose.     

Comparative studies on the pyrolysis of cellulose,hemicellulose, and lignin based on combined kinetics

The thermal degradation behavior and pyrolytic mechanism of cellulose, hemicellulose, and lignin are investigated at different heating rates from 10 Kmin^?1 to 100 Kmin^?1 with a step-size of 10 Kmin^?1 using thermogravimetric analysis (TGA) equipment. It is observed that there are one, two, and three stages of pyrolytic reactions takes place in cellulose, hemicellulose, and lignin respectively. Isoconversional method is not suitable to analyse pyrolysis of hemicellulose and lignin as it involves multi-step reactions. The activation energies of the main decomposition stage for cellulose, hemicellulose, and lignin are 199.66, 95.39, and 174.40 kJ mol^?1 respectively. It is deduced that the pyrolysis reaction of cellulose corresponds to random scission mechanism while the pyrolysis reaction of hemicellulose and lignin follows the order based reaction mechanisms.     

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.     

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.     

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.     

农林废弃物成分分析及其综合利用前景展望

选取杉木木屑、红木木屑、桦木木屑、水稻秸秆、油菜秸秆和稻壳等6种农林废弃物为原料,采用化学定量分析法测定了生物质原料中纤维素、半纤维素和木质素的含量;采用电感耦合等离子体光谱法测定了生物质原料中的金属离子含量.在此基础上,探讨了各类农林废弃物综合利用的发展前景.     

Characterization of free radicals by electron spin resonance spectroscopy in biochars from pyrolysis at high heating rates and at high temperatures

The concentration and type of free radicals from the decay (termination stage) of pyrolysis at slow and fast heating rates and at high temperatures (above 1000°C) in biomass char have been studied. A room-temperature electron spin resonance spectroscopy study was conducted on original wood, herbaceous biomass, holocelluloses, lignin and their chars, prepared at high temperatures in a wire mesh reactor, an entrained flow reactor, and a tubular reactor. The radical concentrations in the chars from the decay stage range up between 7·10¹⁶ and 1.5·10¹⁸ spins g⁻¹. The results indicated that the biomass major constituents (cellulose, hemicellulose, lignin) had a minor effect on remaining radical concentrations compared to potassium and silica contents. The higher radical concentrations in the wheat straw chars from the decay stage of pyrolysis in the entrained flow reactor compared to the wood chars were related to the decreased mobility of potassium in the char matrix, leading to the less efficient catalytic effects of potassium on the bond-breaking and radical re-attachments. The high Si levels in the rice husk caused an increase in the char radical concentration compared to the wheat straw because the free radicals were trapped in a char consisting of a molten amorphous silica at heating rates of 10³–10⁴ K s⁻¹. The experimental electron spin resonance spectroscopy spectra were analyzed by fitting to simulated data in order to identify radical types, based on g-values and line widths. The results show that at high temperatures, mostly aliphatic radicals (g = 2.0026–2.0028) and PAH radicals (g = 2.0027–2.0031) were formed.     

Experimental study on the ignition characteristics of cellulose,hemicellulose, lignin and their mixtures

Ignition behaviour of biomass is an essential knowledge for plant design and process control of biomass combustion. Understanding of ignition characteristics of its main chemical components, i.e. cellulose, hemicellulose, lignin and their mixtures will allow the further investigation of ignition behaviour of a wider range of biomass feedstock. This paper experimentally investigates the influences of interactions among cellulose, hemicellulose and lignin on the ignition behaviour of biomass by thermogravimetric analysis. Thermal properties of an artificial biomass, consisting of a mixture of the three components will be studied and compared to that of natural biomass in atmospheres of air and nitrogen in terms of their ignition behaviour. The results showed that the identified ignition temperatures of cellulose, hemicellulose and lignin are 410 °C, 370 °C and 405 °C, respectively. It has been found that the influence of their interactions on the ignition behaviour of mixtures is insignificant, indicating that the ignition behaviour of various biomass feedstock could be predicted with high accuracy if the mass fractions of cellulose, hemicellulose and lignin are known. While the deficiencies of the determined mutual interactions would be further improved by the analytical results of the activation energies of cellulose, hemicellulose, lignin, their mixtures as well as natural and artificial biomass in air conditions.     

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.     

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.     

生物质组分热解气化特性研究现状

为了提升生物质气化气热值,减少焦油产率,越来越多的研究者开始试图从生物质组分的角度对热解气化特性进行探索.概述了碱金属、温度、压力、升温速率在热解气化过程中对生物质组分造成的影响,以及纤维素、半纤维素、木质素、萃取物和组分间相互作用对生物质热解气化过程造成的影响.提出了在二组分相互作用研究的基础上,应继续开展三组分相互作用的实验研究,以及生物质模化物和生物质原料化学结构差异对生物质原料热解气化特性的影响.此外,提出了采用单变量对照实验方法研究单变量的作用大小.     

Development of an experimental technique for oil recovery during biomass pyrolysis

A new system to collect and analyse some of the condensable products of biomass pyrolysis is developed and tested. Pyrolysis of olive stone, oak pellet, pine pellet and major components of biomass (cellulose, hemicellulose and lignin) is performed by means of a thermogravimetric analysis (TGA). Some of the pyrolysis oil generated during the pyrolysis process condenses on an aluminium ring located in the gas exhaust of the device. The validity and repeatability of the method were shown when a similar oil mass was collected when the test conditions were repeated with the same material. In the biomass experiments, a larger amount of oil was collected from pellet samples, which have the highest cellulose content. This is consistent with the pure component experiments, as avicel cellulose shows the highest depositions. The depositions of the pure components show greater percentage of oil deposited than those of the biomass samples. The results reveal the important influence that the compositions of the biomass and the interactions among its major components have on the composition and quantity in the final deposit. Finally, the differences between deposits from biomass and deposits from mixed components were revealed by an FTIR analysis of the liquid products.     

深度共熔溶剂预处理对木质纤维素生物质作用机制的研究进展

深度共熔溶剂（DES）是一类可再生、对环境友好的新型混合溶剂体系,用于预处理木质纤维素生物质可有效去除半纤维素及木质素组分,并可保留较为完整的纤维素组分。本文综述DES预处理对木质纤维素生物质作用机制的研究进展。通常情况下,大部分DES对纤维素溶解性较差,但可改变纤维素的外貌形态;一些酸性DES对半纤维素具有良好的溶解性能;碱性DES及部分酸性DES对木质素具有优异的溶解性能,在预处理过程中木质素的结构发生解聚或缩合反应;三元DES体系在木质素提取、分离及回收等方面均展现出更多优势。DES对木质素的去除效果及作用机制受DES的构成、摩尔比、生物质类型及预处理条件如温度等多种因素的影响。理解DES在木质纤维素生物质预处理中结构与功能的关系,研究DES在预处理过程中对木质素及半纤维素去除的作用机制,有助于合理设计新的DES体系并为实现生物质三大组分的高效分离及转化奠定理论基础与技术指导。     

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.     

Evaluation of wet air oxidation as a pretreatment strategy for bioethanol production from rice husk and process optimization

The pretreatment of rice husk by the wet air oxidation (WAO) technique was investigated by means of a statistically designed set of experiments. Reaction temperature, air pressure, and reaction time were the process parameters considered. WAO pretreatment of rice husk increased the cellulose content of the solid fraction by virtue of lignin removal and hemicellulose solubilization. The cellulose recovery was around 92%, while lignin recovery was in the tune of 8–20%, indicating oxidation of a bulk quantity of lignin. The liquid fraction was found to be rich in hexose and pentose sugars, which could be directly utilized as substrate for ethanol fermentation. The WAO process was optimized by multi-objective numerical optimization with the help of MINITAB 14 suite of statistical software, and an optimum WAO condition of 185 °C, 0.5 MPa, and 15 min was predicted and experimentally validated to give 67% (w/w) cellulose content in the solid fraction, along with 89% lignin removal, and 70% hemicellulose solubilization; 13.1 gl^?1 glucose and 3.4 gl^?1 xylose were detected in the liquid fraction. The high cellulose content and negligible residual lignin in the solid fraction would greatly facilitate subsequent enzymatic hydrolysis, and result in improved ethanol yields from rice husk.     

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。     

Fast pyrolysis of date palm biomass using Py-GCMS

Pyrolysis of Date Palm Petiole (DPP) and Date Palm Seed (DPS) biomass was conducted by fast pyrolysis and on-line analysis of the outlet stream by gas chromatography connected to mass spectrometry (Py-GCMS) at different temperatures (450, 500 and 600 °C) in order to study the effect of this variable on the product distribution. The concentration of the components in the volatile stream (bio-oil and non-condensable gases) was greatly influenced by temperature and, to a minor extent, by the content of the biomass components (cellulose, hemicellulose and lignin). The most abundant compound families quantified are acids, anhydrosugars, ketones, furans and phenols. The most abundant compound identified was levoglucosan, which is mainly derived from the degradation of cellulose, with its relative content being as high as 18.3% for DPS pyrolysis at 450 °C and considerably lower for DPP pyrolysis (12.2%). The relative content of acetic acid was as higher as 10.2% at 450 °C for DPP pyrolysis. The knowledge of product composition is crucial for the development of large scale fast pyrolysis units for the valorization of these Tunisian agricultural wastes.