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How can the production of dihydrogen, obtained from .coal gasification. be increased ? |
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Answer» Solution :(i) Electrolysis of acidified water using platinum electrodes gives hydrogen. `2H_2O_((l)) underset"Traces of acid/base"overset"Electrolysis"to 2H_(2(g)) + O_(2(g))` (ii) High purity (`gt`99.95 %) dihydrogen is obtained by electrolysing warm aqueous barium hydroxide solution between nickel electrodes. (iii) It is obtained as a byproduct in the manufacture of sodium hydroxide and chlorine by the electrolysis of brine solution. During electrolysis, the reactions that take place are : at anode : `2Cl_((aq))^(-) to Cl_(2(g)) + 2E^(-)` at cathode : `2H_2O_((l)) + 2e^(-) to H_(2(g)) + 2OH_((aq))^(-)` The overall REACTION is : `{:(2Na_((aq))^(+)+ 2Cl_((aq))^(-) + 2H_2O_((l))),(""darr),(Cl_(2(g)) + H_(2(g)) + 2Na_((aq))^(+) + 2OH_((aq))^(-)):}` (iv) Reaction of steam on hydrocarbons or coke at high temperatures in the presence of catalyst yields hydrogen. `C_n H_(2n+2) + nH_2O underset"Ni"overset"1270 K"to nCO+(2n+1)H_2` e.g. , `CH_(4(g)) + H_2O_((g)) underset"Ni"overset"1270 K"to ubrace(CO_((g))+3H_(2(g)))_("water gas ")` The mixture of CO and `H_2` is called water gas. As this mixture of CO and `H_2` is used for the synthesis of methanol and a number of hydrocarbons, it is also called synthesis gas or .syngas.. Nowadays .syngas. is produced from sewage, saw-dust, scrap wood, NEWSPAPERS etc. The process of producing .syngas. from coal is called .coal gasification.. `C_((s))+H_2O_((g)) overset"1270 K"to CO_((g)) + H_(2(g))` The production of dihydrogen can be increased by reacting carbon monoxide of syngas mixtures with steam in the presence of iron chromate as catalyst. `CO_((g))+ H_2O_((g)) underset"catalyst"overset"673 K"to CO_(2(g)) + H_(2(g))` This is called water-gas shift reaction. Carbon dioxide is removed by scrubbing with sodium arsenite solution. Presently - 77% of the industrial dihydrogen is produced from petrochemicals, 18% from coal, 4% from electrolysis of aqueous solutions and 1% from other sources. |
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