Hydrocarbon Processing - June 2022 - 24

Process Optimization
Raffinate
Reformer
H2
Benz/tol
extraction
R
S
Benzene Tolulene
Benz/tol
fractionation
Paraxylene
Separation
X
C
Liquid phase
isomerization
H
A
R
Heavies
FIG. 3. Integration of an LPI unit in the design of a planned facility with a xylene loop operating
an EB-reforming VPI unit.
TABLE 2. Feed and energy consumption reduction achieved by the integration of
an LPI unit in a grassroots complex operating an EB-reforming VPI in a xylene loop
Case Study 2
Xylene loop feed consumption
(reformate, transalkylate)
PX production
Electricity consumption
Fuel gas consumption
PX production cost, $/t
GHG emissions, 1 t CO2 equivalent/t PX
an EB-reforming VPI unit. The proposed
LPI process addition includes a single
unit (shown in green) operating in parallel
with the EB-reforming VPI unit.
Overall
energy credits
and material
balance credits are summarized in
TABLE 2. Energy credits are substantially
higher in Case Study 2 (LPI process integration
in a grassroots complex) vs.
Case Study 1 (LPI process addition to an
existing complex). In Case Study 1, the
base case heat integration scheme is optimized,
while heat integration optimization
is limited following the addition of
LPI because the constraints associated
with existing units cannot be changed.
In Case Study 2, both the base case
and the case integrating the LPI process
have their equipment size and heat
integration scheme optimized-hence,
the higher energy credits for the flow
scheme including LPI. Feed consumption
credits are similar for Case Study 1
and Case Study 2, and they correspond
to the expected feed savings associated
with the addition of an LPI unit. As
pointed out in Case Study 1, feed con24
JUNE 2022 | HydrocarbonProcessing.com
EB-reforming VPI only
Base
Base
Base
Base
Base
Base
EB-reforming VPI + LPI
96%
100%
86%
90%
96%
68%
sumption reduction benefits could also
be represented in terms of a production
increase at constant feed consumption.
However, in an evaluation at constant
PX production, feed consumption is cut
by 4%, while electricity consumption decreases
by 14% and fuel gas consumption
decreases by 10%. The overall PX production
cost is reduced by 4% on a $/t
basis-an outcome like Case Study 1,
despite slightly higher feed savings and
significantly higher utilities savings. This
is because Case Study 2 was realized in a
region of the world where feed and energy
costs are substantially lower than in
the location of Case Study 1. Conversely,
GHG emissions were reduced by more
than 30% on a 1 t CO2
Transalkylation
tion at constant PX production increases
proportionally to EB content in the fresh
C8
aromatics feed, since EB is converted
EB reforming
isomerization
to benzene instead of to PX in such a scenario.
Consequently, of all the possible
options, the scheme integrating EB-reforming
VPI and LPI processes offers the
lowest PX production cost and the lowest
GHG emissions/t of PX produced.
Benzene or PX? Benzene and PX
prices have been close in recent years,5
to the point where converting EB to
benzene rather than to PX constituted
no economic hurdle for most aromatics
facilities. This situation could change,
however, due to a wave of planned steam
cracking facilities-a wave unprecedented
by both the number and size of these
projects, which includes plants in China,
Korea and on the U.S. Gulf Coast.6,7,8
Even if pygas benzene production depends
on steam cracker feed (i.e., ethane
crackers will produce considerably less
pygas than naphtha crackers), benzene is
still expected to be widely abundant because
of the number and size of naphtha
cracking facilities. Furthermore, reformers
shifting to aromatics mode because
of the decreasing gasoline demand are
expected to process more benzene precursors,
thus delivering more benzene
to the market. While benzene becomes
increasingly available, the future of some
benzene derivatives is presently being reevaluated.
For example, a potential ban
on polystyrene is under consideration in
multiple locations in the U.S.9,10
Simultaneously,
Europe is assessing more restrictive
regulations impacting bisphenol
A,11
which may also include future bans.
In a world combining increased benzene
availability and potentially lower interest
in benzene derivatives, converting EB to
xylene rather than to benzene-using a
combination of EB-reforming VPI and
LPI processes-would represent an environmentally
friendly and cost-competitive
solution for aromatics complexes.
equivalent/t PX
basis, owing to a very energy-efficient
design, along with substantial reductions
in both high-pressure and medium-pressure
steam consumption, which are not
reported in TABLE 2.
Since Case Study 2 was evaluating
a grassroots facility, a third case was assessed,
combining EB-dealkylation VPI
with LPI. As expected, feed consumpEB-reforming
VPI process combined
with the LPI process: Additional
considerations. The following
are additional items for consideration:
* No PX recovery limitation
for existing complexes when
adding the LPI process:
The addition of a technology
(such as LPI) that is low cost,

http://www.HydrocarbonProcessing.com

Hydrocarbon Processing - June 2022

Table of Contents for the Digital Edition of Hydrocarbon Processing - June 2022