Page 33 - Chemical and process design handbook

Speight_Part 1_E&F 11/7/01 3:03 PM Page 1.19

FRIEDEL-CRAFTS

REACTIONS

Several chemicals are manufactured by application of the Friedel-Crafts
condensation reaction. Efficient operation of any such process depends on:
1. The preparation and handling of reactants
2. The design and construction of the apparatus
3. The control of the reaction so as to lead practically exclusively to the
formation of the specific products desired
4. The storage of the catalyst (aluminum chloride)

Several of the starting reactants, such as acid anhydrides, acid chlorides,
and alkyl halides, are susceptible to hydrolysis. The absorption of moisture
by these chemicals results in the production of compounds that are less
active, require more aluminum chloride for condensation, and generally
lead to lower yields of desired product. Furthermore, the ingress of mois-
ture into storage containers for these active components usually results in
corrosion problems.
Anhydrous aluminum chloride needs to be stored in iron drums under
conditions that ensure the absence of moisture. When, however, moisture
contacts the aluminum chloride, hydrogen chloride is formed, the quantity
of hydrogen chloride thus formed depends on the amount of water and the
degree of agitation of the halide. If sufficient moisture is present, particu-
larly in the free space in the container or reaction vessel or at the point of
contact with the outside atmosphere, then hydrochloric acid is formed and
leads to corrosion of the storage container.
In certain reactions, such as the isomerization of butane and the alkyla-
tion of isoparaffins, problems of handling hydrogen chloride and acidic
sludge are encountered. The corrosive action of the aluminum
o
chloride–hydrocarbon complex, particularly at 70 to 100 C, has long been
recognized and various reactor liners have been found satisfactory.

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