CHAPTER 1.3
BP PARA-XYLENE PROCESS
Homok Lee and Elizabeth Tyson
McDermott, Bloomfield, New Jersey
INTRODUCTION
The BP para-xylene process, which is licensed by McDermott’s Lummus Technology, is
an unparalleled,
energy efficient method employing crystallization for para-xylene recovery, This
technology was
developed by Amoco (now BP) in the 1960s for use in their own plants. For more than
50 years, BP
has continually improved both process performance and technical design of this
technology producing
a highly optimized and cost-advantaged route to para-xylene separation. In 2000, BP
commercialized
an innovative crystallization system, dramatically reducing energy requirements by
50 percent. In
2010, BP and Lummus Technology, formed a partnership to license the BP para-xylene
process. This
strong collaboration pairs an operating company well versed in para-xylene
production, vendor relationships, and plant maintenance with an industry leading licensing/engineering
firm.
In 2012, this technology was selected for a 2,250,000 metric tons per year (MTA)
para-xylene grassroots aromatics complex, the largest in the world. Moreover, the BP para-xylene
process can achieve
capacities in excess of 4,000,000 MTA with a single fractionation column,
Para-xylene (pX) is a C8 aromatic hydrocarbon primarily used in the production of
purified terephthalic acid (PTA), a precursor to polyethylene terephthalate (PET). PET, a
polyester, isa worldwide
commodity used to make fibers, film, and packaging materials, Para-xylene, its
isomers (ortho-xylene
(oX), meta-xylene (mX), and ethylbenzene), are produced via a variety of
petrochemical processes
including naphtha reforming, toluene disproportionation (TDP), transalkylation, and
as a by-product
of ethylene plants, For all production routes, a mixture of C8 aromatics isomers,
termed “mixed
xylenes.” is generated from which para-xylene must be separated into a high-purity
product to meet
commercial requirements for downstream process units.
All C8 isomers boil within a few degrees of each other (Table 1.3.1). Thus
traditional fractionation
is not a practical method to separate para-xylene from the other mixed xylenes.
Para-xylene, however,
has a significantly higher freezing point than the other C8 aromatics isomers.
The BP para-xylene process exploits the large differences in freezing points of the
C8 aromatic
{ isomers to separate pX from the mixture via crystallization. Refrigeration is
utilized to crystallize
j para-xylene from the other components. Ortho- and meta-xylenes are isomerized via
a fixed-bed
reaction system to increase the overall pX yield,
Figure 1.3.1 depicts a simplified configuration of the BP para-xylene process.
Since feed sources to
i the para-xylene unit can contain light (C7—) and heavy material (C9+), upstream
fractionation is
often required to ensure a C8 aromatic-rich stream enters the recovery section.
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