Study on the Comprehensive Utilization of Bitter Almond Shell

Abstract

A comprehensive process was developed to make full use of the solid and liquid products during the production of activated carbon. Almond shell waste was modified with phosphoric acid and thermally treated to give activated carbon. Wood vinegar was generated and collected within the temperature range of 90 to 500 °C, and the maximum amount of the wood vinegar was in the range of 170 to 370 °C, which also gave the strongest anti-pathogens activities with the lowest pH and the highest organic acid content. The remaining residue after wood vinegar generation was further calcined in inert atmosphere to obtain high surface area activated carbon. The pre-treatment of almond shell with H3PO4 leads to the higher surface area, but H3PO4 solution with concentration more than 40% does not increase the surface area further. The impregnation of H3PO4 helps the formation of pores in the almond shell during the calcination, and gives higher iodine number and methylene blue sorption capacity of the resultant activated carbon materials. Education, Northwest A&F University, Yangling 712100, China; b: Guangzhou Boxenergytech Ltd, Guangzhou Hightech Zone, P R China; c: Inorganic Chemistry Laboratory, Oxford University, South Parks Road, OX1 3QR, UK; * Corresponding authors: zhaozh@nwsuaf.edu.cn; xiao.tiancun@chem.ox.ac.uk Keywords: Almond shell; Activated carbon; Wood vinegar; Comprehensive utilization Contact information: a: Key Laboratory of Environment and Ecology in Western China of Ministry of INTRODUCTIONAlmond is the general name of Prunus dulcis or Prunus amygdalus L. Almond fruit consists of the hull, shell, and kernel (nut). The almond tree can grow to a height of seven to ten meters, and it has been a main source of almond fruit worldwide (Schirra 1997;Choudhari et al. 2013). It has been estimated that the annual output in north China is up to 40 thousand tons, and the amount has tended to increase due to a strong demand for the fruit (Wang et al. 2010). During the harvest period, the hull and kernel are the desirable products; the almond shell consists of 70% of the dry mass of a whole almond fruit. These nutshells can be collected on a community basis for reuse Gonzalez et al. 2005;Izquierdo et al. 2011; Meenakshi Sundaram and Sivakumar 2012;Pirayesh and Khazaeian 2012;Tiryaki et al. 2014). Almond nutshells are abundant, inexpensive and readily available lignocellulosic materials, which contain a high content of carbon and other renewable chemicals. There have been many studies on converting almond shell into activated carbons (Gonzalez-Vilchez et al. 1979; RodriguezReinoso et al. 1982;Linares-Solano et al. 1984;Rodriguez-Reinoso et al. 1984;Torregrosa and Martin-Martinez 1991;Hayashi et al. 2002;Toles and Marshall 2002;Gonzalez et al. 2005 4994 Yuso et al. 2014). Gonzalez et al. (2009) carried out a study of the pyrolysis of various biomass residues including almond shell for the production of activated carbons. It was shown that the four biomass residues used are versatile precursors that allow the preparatio...

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