Study On Preparation Technology, Mechanism And Pore Structure Of Wood-based Granular Activated Carbon By Chemical Method

In recent years, the emission of volatile organic compounds and oil vapor has become more and more serious, e.g. over 0.1 billion tons (3% of the global oil amount mined) of oil vapor as well as 10 million tons of VOCs in China emitting into the air every year. The recovery of VOCs and oil vapor could not only mitigate environmental pollution but also save energy and increase economic benefit. Therefore,the study on technology and equipments of recovering VOCs and oil vapor by granular activated carbon (GAC) with high butane working capacity (BWC) is a hot topic currently.Thus, there is a significant meaning for carrying out research and development on this product. Because this action could improve the grade of demestic activated carbon and fill in the gaps in the production of this species of activated carbon and form independent intellectual property rights and shorten the gap with the foreign one. At home and abroad, study on the activation mechanism of granular activated carbon prepared by phosphoric acid are so few that the activated carbon manufacture still depends on experiences. During the producing process of AC, the quality of production is not stabilized due to lacking in theoretical guidance. Therefore, study on the preparation technology and mechanism of AC by phosphoric acid exhibits a significant meaning for guiding industrial production.Specific research contents and achievements in this paper are as follows:1) Preparation technology A desired result of high BWC granular activated carbon was obtained by adding concentrated sulfuric acid during the process of traditional phosphoric acid activation. When 6% of concentrated sulfuric acid was added, the BWC of granular activated carbon was increased from 11.9g/100ml without adding sulfuric acid to 14.4g/100ml, with an efficiency of 21%; Vmes from 0.508 cm~3/g to 0.939 cm~3/g, with an efficiency of 85%; Vtot from 1.029 cm~3/g to 1.685 cm~3/g, with an efficiency of 64%; Vmic from 0.521 cm~3/g to 0.746cm~3/g, with an efficiency of 43%; SBET from 1902 m~2/g to 2325 m~2/g, with an efficiency of 22%.2) Optimum technology The optimum technology attained by Orthogonal experiment and range analysis is as following: phosphoric acid concentration 56%, impregnation ratio 1.9:1, sulfuric acid amount 6%, sulfuric acid concentration 80%, drying temperature 300℃, drying time 3h, activation temperature 450℃, activation time 60min. The dosage of concentrated sulfuric acid was an important factor for high BWC granular activated carbon. The resulting production from optimum technology exhibited a BWC of 16.5g/100ml along with an apparent density of 0.24g/ml, a specific surface area of 2627m~2/g and a total pore volume of 1.574cm~3/g.3) Activation mechanism To certain extent surface area and pore development of AC varied directly with the reducing sugar content, obtained from dilute acid hydrolysis of oligosaccharide produced during the stage of phosphoric acid impregnation. However, excessive hydrolysis produced oligosaccharide with lower molecule size, unfavorable to form larger topological structure and on the contrary decreasing surface area and pore development. Therefore, control of saccharification degree during phosphoric acid impregnation stage would direct AC production. Under this experimental condition, for sulfuric acid concentration and impregnation ratio, the surface area and pore development of AC developed with the increase of reducing sugar content and for sulfuric acid amount ideal saccharification degree presented at when 6% was added and for phosphoric acid concentration when 60% adopted.In a word, this paper proposed a simple and novel preparation technology high performance shaped granular AC from China fir by phosphoric acid activation. Through the technology, products with high abrision resistance, high surface area, high pore volume and high BWC were not only prepared, but also the preparation period could be shortened from previous 20~70h to less than 5h on the basis of high butane working capacity, which improved the continuous automaticity of industrial production process and reduced the labor intensity. Based on the laboratory achievements, the reliability of this novel technology was verified by pilot test and advanced international standards products were manufactured successfully. Through the study of activation mechanism, granular AC could be prepared to meet the demands of suggested application fields.