Kolmetz.com CMAI 2000 Joe Page 10
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The initial investment for the aromatics complex can be reduced because of lower-
cost paraxylene recovery facilities.
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Project schedules encompassing planning to startup activities can be compressed
because of more conventional equipment that does not require long lead times.
Project timing can often be the difference between a quick payout and a prolonged
one.
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For producers with existing reformer facilities or those considering adding new
facilities, this scheme represents the maximum utilization of the reformate/naphtha
feedstock to produce paraxylene. If the toluene component of the reformate is priced
at blend value, the project economics are further enhanced.
Conclusion
Traditional production methods for paraxylene have used crystallization or adsorption to
separate the isomer from a mixed xylene feedstock. The advent of selective toluene
disproportionation (STDP) and now, selective toluene alkylation causes one to re-think
how to design the optimal paraxylene production system. When combined with a low-
cost crystallization to purify the product, these two methods are a competitive alternative
for standalone and supplementary PX production.
Toluene-based production systems can have several advantages over the xylenes only
based systems. Capital cost for a standalone toluene conversion unit is less than for a
traditional xylenes complex; this makes the selective toluene conversion processes
relatively more efficient for small scale units. Feedstock utilization is more favorable,
particularly for toluene methylation, which uses low-cost methanol as a co-feedstock and
does not yield any appreciable by-products. This makes it cost-effective for an aromatics
complex that utilizes both toluene and mixed xylenes feedstock.
