Effect of conditions on fast pyrolysis of bamboo lignin

doi:10.1016/j.jaap.2010.08.007

Journal of Analytical and Applied Pyrolysis

Volume 89, Issue 2, November 2010, Pages 191-196

https://doi.org/10.1016/j.jaap.2010.08.007 Get rights and content

Abstract

Products derived from bamboo EMAL pyrolysis were investigated by means of pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) and the effects of temperature and catalyst (sodium chloride, permutite) on the yields of pyrolysis products were probed in detail. The results showed that thermal degradation of EMAL mainly occurred at the temperature range from 250 °C to 600 °C, and both the temperature and catalyst in EMAL pyrolysis were important factors in the formation or inhibition of products. The products that derived from p-hydroxyphenylpropanoid, guaiacylpropanoid, and syringylpropanoid of lignin units by pyrolytic reactions were classified as the heterocycle (2,3-dihydrobenzofuran), phenols, a small quantity of acetic acid and furans, etc. With an increase of pyrolysis temperature, the amount fraction of 2,3-dihydrobenzofuran (DHBF) decreased from 66.26% to 19.15%. Moreover, when the additive catalyst increased from 5% to 20%, permutite catalyst improved in the formation of DHBF from19.15% to 24.19%, whereas NaCl catalyst was effective to inhibit the production of DHBF from 19.15% to 13.08%. Permutite promoted the production of coke from EMAL pyrolysis, conversely, NaCl had an inhibiting effect on the generation of coke. And NaCl catalyst had a significant catalytic effect on raising or reducing of the product yields in bamboo lignin pyrolysis.

Introduction

Biomass from herbaceous crops is the largest renewable source for the production of bioproducts and biofuels. The available information about lignins in straw of herbaceous crops is scattered and the available reviews generally address wood lignins. Lignin is the third most abundant natural polymer present in nature after cellulose and hemicelluloses and also the most abundant polymeric aromatic organic substance in the plant world [1], [2]. The lignin contents on a dry basis range from 10% to 40% by weight in various herbaceous species, such as bagasse, bamboo, corncobs, peanut shells, rice hulls and straws [3].

Lignin in herbaceous plants is receiving increasing attentions for two primary reasons: annual renewability and herbaceous plants have the largest annual biomass stock (1549 million tons/year worldwide) [4]. Lignin, highly branched and substituted, is a mononuclear aromatic polymer in the cell walls of certain biomass, and is often bound to adjacent cellulose fibers to form a lignocellulosic complex. Therefore, the extraction of lignin from herbaceous plants is of paramount importance and the utilization of extracted lignin will lead to the industrial production of valuable food and industrial products such as vanillin, ferulic acid, vinylguaiacol and optically active lignans, and the dimers of monolignols.

Herbaceous biomass is generally considered as an important energy resource, but its varied composition (cellulose, hemicellulose, and lignin) has a great influence on thermochemical conversion to energy and chemicals. Pyrolysis technology is one of the leading-edge technologies of bio-energy research that is currently and widely used in biomass conversion. Pyrolysis of biomass can be described as the direct thermal decomposition of the organic matrix in the absence of oxygen to obtain an array of solid (char), liquid (tar) and gas products. Since lignin is an important constituent of herbaceous biomass, it is of interest to determine how the composition and the aromatic structure of lignin affects the characterization and reactivity of char from lignin. A number of studies have been reported in the literature on pyrolysis of lignin [5], [6], [7], [8], [9], [10], [11]. The relative distribution of products is dependent on pyrolysis conditions, i.e. pyrolysis temperature [12], heating rate, pyrolysis atmosphere and catalyst. Catalyst or other materials are added in pyrolysis process to jointly carry out pyrolysis and the gas heat value and the composition of gas products can be markedly improved by adding catalyst. Britt et al. [13] reported that lignin pyrolysis occurred mainly by a free-radical reaction mechanism. Pyrolysis products contained acids, alcohols, aldehydes, esters, heterocyclics and aromatic compounds. The pyrolysis products have a potential to be used as bio-oil substitute or commercial chemicals.

Section snippets

Materials

Bamboo (Phyllostachys pubescens Mazel ex H. de Lehaie) was collected from Hunan Province without leaves. After being dried, milled and finally extracted for 48 h with acetone, the obtained powder was milled in a porcelain ball jar for 240 h at a rotation speed of 36 rpm, and then was used to separate lignin by means of enzymatic/mild acidolysis method [14], [15], [16], [17], [18]. Finally, the isolated enzymatic/mild acidolysis lignin (EMAL) was employed to pyrolyze in the experiment. Particle

Effect of temperature on the solid yield from EMAL pyrolysis

The obtained solid yields from EMAL pyrolysis at the varied temperature were shown in Fig. 1. From the results, it can be observed that pyrolysis reaction mainly occurred at the temperature range from 250 °C to 600 °C, and the weight loss of EMAL was 61.76 wt% at 600 °C. With increasing temperature upto 800 °C, the yield of volatile matter from EMAL pyrolysis increased from 9.95 wt% to 71.74 wt%.

Effect of temperature on pyrolysis products from EMAL

Lignin was a simple phenol polymer from alcohol derivatives (p-coumarylalcohol, coniferylalcohol,

Conclusions

Pyrolysis temperature, as a vital factor, had a marked effect on the volatile yield and yield distribution of products from EMAL pyrolysis. The release of the volatile matter occurred mainly in a long temperature range from 250 °C to 600 °C, and the amount of volatiles increased with temperature rising. Thus, high temperature (above 600 °C) favoured the conversion of EMAL pyrolysis. With an increase of pyrolysis temperature, the yield of 2,3-dihydrobenzofuran (DHBF) decreased visibly, but phenolic

Acknowledgements

This work was supported by the National Basic Research Program of China (973 Program, 2007CB210201), the National High Technology Research and Development Program of China (863 Program, 2007AA05Z456) and the Key Laboratory of Renewable Energy and Gas Hydrate, Chinese Academy of Sciences.

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Citation Excerpt :
The peak at 1604 cm−1 stood for C=C stretching vibrations in the benzene ring of lignin decreased; while the signal at 1510 cm−1 representing the aromatic skeletal vibrations (in which G unit contributed more significantly than S unit) slightly decreased, which indicated the dissolution conversion of easily degradable structures in lignin, especially for G unit. The peak at 1326 cm−1 represented C-C (C-O) of syringyl rings of lignin [7,8], and this peak in MgCl2-pretreated samples showed slight decreases, indicating the promoted dissolution conversion of lignin by MgCl2. Characteristic absorbance of cellulose was obtained at 1379 cm−1, and C-O-C asymmetric at β-1, 4-glycosidic linkage existed in cellulose was represented by the peak 1166 cm−1.
Room temperature pretreatment of pubescens by soaking in MgCl₂ aqueous solution with different concentrations was studied. The solid residues were analyzed by Van Soest chemical titration, XRD, FT-IR, and XPS, while the filtrates were analyzed by GPC, HPLC, ESI-MS, and 2D HSQC. The soaking by 20 wt% MgCl₂ solution resulted in relatively higher conversion rates of both hemicellulose (8.3 wt%) and lignin (5.3 wt%). Trace amounts of glucose and xylose were obtained in the filtrates, and the amounts were hardly varied by the addition of MgCl₂. However, compared with the filtrate from the sample pretreated by water, different oligomers were detected in the filtrates, indicating that MgCl₂ might be able to change the mechanism of dissolution conversion of pubescens, meanwhile, no LCC was found, indicating that MgCl₂ pretreatment could promote the breakage of ether linkage between carbohydrate part and lignin part in LCCs. A new monophenol (LIG9) might be obtained from LIG1, which might be attributed to the promoted breakage of β-O-4 in lignin by MgCl₂ pretreatment. Compared with the sample pretreated by pure water, GPC analysis revealed that the proportion of larger compounds (M_n > 1700 Da) decreased while those of smaller compounds (M_n = 180-300, 300-800, and 800–1700 Da) all rose.

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Effect of conditions on fast pyrolysis of bamboo lignin

Abstract

Introduction

Section snippets

Materials

Effect of temperature on the solid yield from EMAL pyrolysis

Effect of temperature on pyrolysis products from EMAL

Conclusions

Acknowledgements

J. Ind. Crops Prod.

J. Biomass Bioenergy

J. Fuel

J. Anal. Appl. Pyrol.

J. Appl. Energy

J. Anal. Appl. Pyrol.

J. Chemosphere

Wood: chemistry ultrastructure, reactions

Biomass for renewable energy, fuels, and chemicals

J. Forest. Stud. China

J. Agric. Food Chem.