Page 19 - Chemical and process design handbook

Speight_Part 1_A 11/7/01 3:04 PM Page 1.5

ALKYLATION 1.5

quality sufficient to meet the demands of the market. If not, other means of
purification may be necessary, such as crystallization or separation by
means of solvents. The choice of a proper solvent will, in many instances,
lead to the crystallization of the alkylated product and to its convenient
recovery.
The converse reactions dealkylation and hydrodealkylation are prac-
ticed extensively to convert available feedstocks into other more desirable
(marketable), products. Two such processes are: (1) the conversion of
toluene or xylene, or the higher-molecular-weight alkyl aromatic com-
pounds, to benzene in the presence of hydrogen and a suitable presence of
a dealkylation catalyst and (2) the conversion of toluene in the presence of
hydrogen and a fixed bed catalyst to benzene plus mixed xylenes.