Abstract

Role of Aromatic and Hydroaromatic Hydrogen of Coal with Alkali for Generating Clean Fuel Hydrogen

Author(s): Atma Ram Singh, Shubha Srivastava, S.K .Srivastava and G. Kumar

Studies on pyrolysis of different ranks of coal viz. Jeypore (sub-bituminous), Swang (Bituminous), Dakra Bukbuka (Sub-bituminous), Mahuda (High rank) and Neyveli lignite (Lignite), in presence of different alkalies viz. Sodium hydroxide, sodium carbonate, calcined lime and calcium carbonate were carried out under different reaction conditions for the production of clean and green fuel hydrogen. Pyrolysis of different ranks of coals in presence of sodium hydroxide produces clean and green fuel hydrogen. Amongst the various coals used, the maximum yield of gas obtained was 3.2l/10 g of coal with hydrogen content of 80 % (v/v) from the medium rank Swang coal (carbon 85.5% on dmf basis). It was also observed that two coals of same carbon and hydrogen content exhibit different behavior due to their different chemical and physical makeup. For example, the coal which has rich vitrinite maceral produces better yield of hydrogen in comparison to other coals having more of inertinite maceral. Effect of temperature, nature of alkali, coal-alkali ratio, rank of coal, coal particle size etc. on the yield and quality of gas obtained from coal-alkali interaction were studied to find out optimum reaction conditions. It was found that 6000C is the optimum temperature and 1 : 1.3 is the optimum coal : alkali ratio for this reaction. This paper reports the data obtained on five coals-four alkalies interaction under optimum reaction conditions. No tarry product was obtained during the course of pyrolysis of coal in presence of alkali. Similarly, under optimum reaction conditions, no carbon monoxide and carbon dioxide were found as it reacted with alkali. It is well known that the hydroaromatic part of the coal is mainly responsible for production of tarry component during coal pyrolysis and CO & CO2 are the products of coal pyrolysis. But addition of alkali changes the reaction mechanism of normal pyrolysis of coal in such a way that no tarry product was obtained. The active hydrogen of methylene interacts with hydrogen of sodium hydroxide to form hydrogen gas at the temperature range from 3500C to 4000C. Aromatic hydrogen also participates in the same fashion but the elimination temperature range for aromatic hydrogen is higher than that of active methylene groups. Under optimum reaction conditions, the yields of hydrogen and methane were 500 m3 and 75 m3 per ton of coal, respectively. The recovery of alkali was 87%. Part of alkali has reacted with the mineral matter. The results have been interpreted in terms of macerals, functional groups, aromaticity and hydroaromaticity of coal.