Elsevier

Bioresource Technology

Volume 70, Issue 1, October 1999, Pages 61-67
Bioresource Technology

Rapid liquefaction of lignocellulosic waste by using ethylene carbonate

https://doi.org/10.1016/S0960-8524(99)00008-5Get rights and content

Abstract

Cyclic carbonates were selected as novel liquefying reagents in order to establish a rapid liquefaction technique converting lignocellulosic waste into useful chemicals. Lignocellulosic materials such as wood and cellulose were liquefied using ethylene carbonate (EC) or propylene carbonate (PC) in the presence of acid catalyst at elevated temperature (120–150°C). Very rapid and complete liquefaction occurred in the EC-liquefaction of cellulose and white birch (hardwood). The rate of the EC-liquefaction of cellulose was approximately 10 times faster than that of current polyhydric alcohol liquefaction. Conversely, liquefaction was not accomplished due to the formation of insoluble lignin derivatives when applied to softwood (Japanese cedar and Japanese cypress). Satisfactory liquefaction is dependent on the type of lignin, i.e. hardwood lignin or softwood lignin. This problem was solved by blending ethyleneglycol (EG) with EC. 13C-NMR revealed that the EC liquefaction products from cellulose include levulinic acid compounds, which also results from EG liquefaction of cellulose.

Introduction

In recent years, effective utilization of lignocellulosic resources has received considerable attention from the starting point of environmental protection. However, large quantities of lignocellulosics such as woody wastes from building materials, sawdust, waste paper, bark are still incinerated or discarded in the environment. Considerable research on conversion into useful materials has been conducted for several decades. This has included techniques referred to as `wood liquefaction' due to the conversion of wood chemically or thermochemically into liquid materials.

Since wood and cellulose were converted into liquid by Fierz-David (1925), numerous studies have been reported on the liquefaction of bioresources (Appell et al., 1971). The primary objective has always been conversion of lignocellulosic materials into fuels. The typical liquefaction was conducted under drastic conditions, such as under high pressure, at high temperature (about 300–500°C) and in the presence of catalyst and/or reducing gases. Although these liquefactions required large quantities of energy, the yield of liquefied products did not reach even 90%.

Recently, liquefying techniques have been much improved, so that whole woody materials can be completely converted into substances soluble in widely used organic solvents such as dioxane, DMSO, DMF, acetone or methyl alcohol. Hesse and Jung (1980)patented a simple wood liquefaction method where they used phenol in the presence of conc. H2SO4, to obtain molding compounds and coating resins in addition to hexamethylenetetramine or epoxy resins. This method was further improved by Ono et al. (Ono and Sudo, 1989Ono et al., 1996).

Shiraishi et al. (1992)adopted polyhydric alcohols such as ethyleneglycol (EG), polyethyleneglycol (PEG) and glycerin instead of phenols as liquefaction solvents and liquefied lignocellulosic materials almost completely in the presence of acid catalyst at approximately 150°C under atmospheric pressure (alcohol liquefaction). Techniques where woody materials are considered to be liquefied completely through solvolysis are of interest because the product could be used as chemicals instead of petroleum resources. Foamed materials have been prepared from the products by polyhydric alcohol liquefaction in cooperation with isocyanates on the basis of the idea that woody components in the products would bear hydroxy groups (Kurimoto et al., 1992).

However, the use of the polyhydric alcohols for liquefaction has a drawback in liquefaction speed. We have found cyclic carbonates provide more rapid liquefaction for cellulose and hardwood than polyhydric alcohols. In this paper, we describe the features of liquefaction and of its product by using cyclic carbonates as a novel liquefying reagent for wood and cellulose.

Section snippets

Materials

Sawdusts of white birch (Betura Platyphylla Sukatchev var. japonica Hara), Japanese cedar (Cryptomeria japonica D. Don) and Japanese cypress (Chamaecyparis obtusa Endl) wood (30–80 mesh) were obtained from a circular saw bench (Shoda Iron Works) and used as lignocellulosic waste. They were dried in an oven at 105°C for 12 h and kept in a desiccator at room temperature before use. A commercial cellulose from linter pulp (100–200 mesh, Toyo Roshi) was dried in vacuo and used for the model

Liquefaction of cellulose in the presence of cyclic carbonates

The average residue content as a function of liquefaction time is shown in Fig. 1. Six experiments were carried out for each plot in order to examine variation. The residue contents are plotted in logarithmic scale. It is implied from this figure that the liquefaction of cellulose follows the pseudo-first-order reaction during the early stage. In the case of ethylene glycol (EG), the liquefaction is sufficiently slow that 30% residue still remains at 120 min. Even in the case of using PEG400/EG

Conclusion

Rapid liquefaction of lignocellulosic materials such as cellulose and softwood were achieved by using EC or PC as novel liquefying reagents. The liquefaction of cellulose follows the pseudo-first-order reaction in the early stage. When compared with EG, EC and PC gave almost 28 and 13 times faster liquefaction rates, respectively. Judging from the rate of liquefaction and generation of toxic gas from PC during decomposition, EC could be an effective liquefying reagent for cellulose

Acknowledgements

This work was supported in part by a Integrated Research Program for Effective Use of Biological Activities to Create New Demand (Bio Renaissance Program) from the Ministry of Agriculture, Forestry and Fisheries (No. BRP97-III-B-1).

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