Page 40 - Plant design and economics for chemical engineers

PROCESS DESIGN DEVELOPMENT 23

tion of the design will be attempted at this point.? However, sufficient detail will
be given to outline the important steps which are necessary to prepare such a
preliminary design. The problem presented is a practical one of a type fre-
quently encountered in the chemical industry; it involves both process design
and economic considerations.

Problem Statement
A conservative petroleum company has recently been reorganized and the new
management has decided that the company must diversify its operations into the
petrochemical field if it wishes to remain competitive. The research division of
the company has suggested that a very promising area in the petrochemical field
would be in the development and manufacture of biodegradable synthetic
detergents using some of the hydrocarbon intermediates presently available in
the refinery. A survey by the market division has indicated that the company
could hope to attain 2.5 percent of the detergent market if a plant with an
annual production of 15 million pounds were to be built. To provide manage-
ment with an investment comparison, the design group has been instructed to
proceed first with a preliminary design and an updated cost estimate for a
nonbiodegradable detergent producing facility similar to ones supplanted by
recent biodegradable facilities.

Literature Survey
A survey of the literature reveals that the majority of the nonbiodegradable
detergents are alkylbenzene sulfonates (ABS). Theoretically, there are over
80,000 isomeric alkylbenzenes in the range of C,, to C,, for the alkyl side chain.
Costs, however, generally favor the use of dodecene (propylene tetramer) as the
starting material for ABS.
There are many different schemes in the manufacture of ABS. Most of the
schemes are variations of the one shown in Fig. 2-3 for the production of
sodium dodecylbenzene sulfonate. A brief description of the process is as
follows:
This process involves reaction of dodecene with benzene in the presence
of aluminum chloride catalyst; fractionation of the resulting crude mixture to
recover the desired boiling range of dodecylbenzene; sulfonation of the dodecyl-
benzene and subsequent neutralization of the sulfonic acid with caustic soda;
blending the resulting slurry with chemical “builders”; and drying.
Dodecene is charged into a reaction vessel containing benzene and alu-
minum chloride. The reaction mixture is agitated and cooled to maintain the
reaction temperature of about 115°F maximum. An excess of benzene is used to
suppress the formation of by-products. Aluminum chloride requirement is 5 to
10 wt% of dodecene.

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Kompletion of the design is left as an exercise for the reader.