Biomass conversion to carbon adsorbents and gas
Introduction
At present, agricultural by-products are mainly used as combustion feedstocks. There are, however, alternative utilization processes to convert agricultural by-products into solid, liquid and gaseous products for a more efficient exploitation of these materials [1]. Agricultural by-products have proved to be promising raw materials for the production of activated carbons because of their availability at a low price. They were used for the production of activated carbon with a high adsorption capacity, considerable mechanical strength, and low ash content [2], [3], [4], [5], [6], [7], [8]. The carbon adsorbents can be applied for the removal of trihalomethanes and metal ions from water, purification of waste solutions, separation and concentration of traces of elements and radioactive isotopes, production and analysis of high purity substances etc. [9], [10], [11]. One of the disadvantages of activated carbon is its relatively high cost. The main reason for this is the high expense of energy indispensable for its production. A simple one-step method for the production of activated carbons has been developed [12] to reduce the energy expenditure during the process. This method is a feasible alternative to the traditional two-stage process for the production of activated carbons by consecutive carbonization of the raw material and high temperature activation (900–1000°C) of the solid product from carbonization. Agricultural by-products (almond shells, nut shells, apricot stones, cherry stones and grape seeds) were subjected to steam pyrolysis-activation at treatment temperatures of 600–700°C [13]. The presence of water vapour during pyrolysis leads to a considerable increase in the liquid and gas product yields in addition to reducing the sulphur content in liquid and solid products. It was established that the properties of carbon adsorbents obtained by steam pyrolysis of agricultural by-products depend on the treatment conditions (the final temperature of treatment, duration of the treatment at the final temperature) and the choice of raw materials.
The general objective of this work is, on the basis of earlier and present investigations, to create a technology for the effective utilization of biomass by producing carbon adsorbents with different surface properties and gas products.
Section snippets
Preparation of activated carbon from biomass
The activated carbons have been prepared by one-step pyrolysis of almond shells, nut shells, apricot stones, cherry stones and grape seeds, in the presence of steam. Hundred grams each of the raw materials are heated in a laboratory installation in a flow of pure water vapour with a heating rate of 15°C/min to a final carbonization temperature of 800°C. In order to reduce the duration of treatment at the final temperature the temperature value is increased in comparison with
Carbon adsorbents from agricultural by-products
The chemical compositions of the carbon adsorbents obtained from different agricultural by-products are presented in Table 1. Activated carbons from almond shell, nut shell, apricot and cherry stones have low ash content. All samples have low sulphur content. The carbon from grape seeds has relatively high ash content. The carbons obtained from apricot stones and almond shells have higher carbon content and lower oxygen content than carbons obtained from cherry stones and grape seeds. The
Conclusions
The results described in this work show that steam pyrolysis produced different types of activated carbon from different agricultural by-products. The final physico-chemical properties of the activated carbons obtained at common conditions depend on the composition and the plant texture of the corresponding raw materials. Materials with a greater content of lignin (grape seeds, cherry stones) develop activated carbons with macroporous structure, while raw materials with a higher content of
Acknowledgements
The authors acknowledge financial support for this work from NATO.
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