CATEGORY: LIGHT OLEFINS
Process For The Production Of Light Olefins And Btx Using A
Catalytic Cracking Unit, Ncc, Processing A Naphtha Type Feed, A Catalytic Reforming Unit And An
Aromatics Complex (United States Patent Application 20150284646 IFP Energies
Nouvelles)
United States Patent Application 20150284646 IFP
Energies Nouvelles
October 8, 2015
Assignee: IFP Energies Nouvelles
Abstract
The
present invention concerns a process for the production of light olefins and
BTX using a catalytic cracking unit, NCC, processing a naphtha type feed, and
an aromatics complex. It can be used to exploit the synergies between these two
units. The thermal balance of the NCC, which is intrinsically deficient in
coke, is resolved by the optimal use of heat from the reforming furnaces in
order to preheat the feed for the NCC, and by introducing at least a portion of
the raffinate obtained from the aromatics complex as a mixture with the
naphtha.
FIELD OF THE INVENTION
[0001] The interest in cracking paraffinic straight run type gasoline feeds in
FCC units in order to upgrade them to propylene and ethylene is relatively
recent. This interest derives from the necessity for the provision of light
olefins, ethylene and propylene for petrochemistry, in addition to the
traditional source constituted by steam cracking. Cracking of a gasoline or
naphtha type cut leads to a modification of the operating conditions for FCC
and the use of a ZSM-5 type zeolite. Currently, the market price differential
between light olefins and gasoline is motivation to improving the margins made
from gasoline by transforming it into these light olefins. In addition,
improvements in zeolitic catalysts have resulted in more interesting yields in
this transformation of light olefins.
[0002] The current term for this new type of FCC unit is NCC, for "Naphtha
Catalytic Cracking".
[0003] In addition to producing olefins, cracking reactions are accompanied by
the formation of aromatic molecules which in themselves have generally not been
upgraded because the cost of separating them proved to be of little or no
benefit.
[0004] Further, cracking light cuts in the FCC process poses a problem, because
this type of feed does not produce sufficient coke under FCC conditions, and
thermal balance of the FCC can only be obtained by adding external heat to the
process.
[0005] The present invention proposes an original solution for overcoming this
problem by exchanging streams with the aromatics complex.
BRIEF DESCRIPTION OF THE INVENTION
[0013] The present invention describes a layout for a refining and petrochemistry
process which integrates three units: the FCC, processing a light naphtha type
feed, termed NCC, the catalytic reforming which processes heavy naphtha, and
the aromatics complex AC, which produces BTX.
[0014] These three units are integrated both by means of exchanging material
streams and also by using the convection zone of the reforming furnaces to
pre-heat the naphtha feed of the NCC.
[0015] The advantages of integrating the NCC unit and the aromatics complex AC
may be summarized in the following points:
[0016] The simultaneous production of light olefins and aromatics starting from
an initial naphtha feed.
[0017] The NCC unit benefits from the proximity of a high coking feed in order
to compensate for the deficit of coke in the light naphtha feed, and from a
surplus of feed in the form of raffinate originating from the aromatics
complex, to produce more light olefins.
[0018] Integrating the NCC with the aromatics complex means that a process
layout can be obtained which in the end reduces emissions of fuel gas
(essentially H.sub.2 and C.sub.1), light olefins (C.sub.2.dbd. and
C.sub.3.dbd.) and BTX.
[0019] Recycling the other effluents to exhaustion, for example the raffinate
and the heavy aromatics fraction obtained from the aromatics complex (CA),
means that both the production of light olefins, ethylene and propylene, can be
increased and also the thermal balance of the NCC can be ensured. For this
reason, it is possible to speak of a true synergy between the NCC and the
aromatics complex.
[0020] The "heavy aromatics" stream from the aromatics complex AC is
thus reduced as far as possible or even eliminated, to the benefit of the coke
produced during the catalytic cracking reaction, and burned in the NCC
regenerator in order to reach thermal balance.
[0021] The stream of raffinate 12 from the aromatics complex is also reduced as
far as possible or even eliminated, to the benefit of the light olefins
produced by cracking in the NCC.
[0022] The feed for the NCC is preheated by the furnaces of the catalytic
reforming unit FREF, preferably in the convection zone thereof, which means
that the thermal balance of the coke-deficient NCC can be better equilibrated.
[0023] More precisely, the present invention describes a process layout which
allows the simultaneous production of light olefins (principally ethylene and
propylene) and BTX, calling upon three units functioning in a synergistic
manner: a FCC unit processing a light naphtha type feed termed NCC, a unit REF
for catalytic reforming of the heavy naphtha cut, and an aromatics complex (CA)
producing BTX.
[0024] The layout of the process of the present invention can be described as
follows:
[0025] The feed for the process is a naphtha cut which, in its broadest
definition, is that of a cut with an initial boiling point of at least
30.degree. C. and an end point of at most 220.degree. C. Any cut with a
distillation range within the broad range of 30.degree. C.-220.degree. C. is
considered to constitute a naphtha in the context of the present invention.
[0026] For simplicity, 30.degree. C. and 220.degree. C. will be considered to
be the typical initial and end points for a naphtha cut.
[0027] The naphtha feed 1 with a distillation range of 30.degree.
C.-220.degree. C. is sent to a hydrotreatment unit HDT which can be used to
eliminate the sulphur-containing and nitrogen-containing compounds it contains.
[0028] The hydrotreated naphtha feed 2 is sent to a separation unit SPLIT1
which can be used to separate a light fraction termed light naphtha, with a distillation
range of 30.degree. C.-T.sub.M.degree. C., and a heavy fraction termed heavy
naphtha, with a distillation range of T.sub.M.degree. C.-220.degree. C.
[0029] The value of the cut point T.sub.M.degree. C. may vary as a function of
the desired yields of the final products (ethylene and propylene and BTX).
[0030] In general, the temperature T.sub.M is in the range 80.degree. C. to
160.degree. C., and preferably in the range 100.degree. C. to 150.degree. C.,
and still more preferably in the range 110.degree. C. to 140.degree. C.
[0031] The light naphtha 3 is sent as a feed for the NCC.
[0032] The heavy naphtha 4 is sent as a feed for the catalytic reforming unit
REF.
[0033] The effluents 6 from the NCC are separated in a fractionation unit FRAC
which can be used to separate a light fraction 8 which is sent to a separation
unit termed the cold box, CBS, which can be used to isolate H.sub.2, CH.sub.4
and C.sub.2, C.sub.3, C.sub.4, C.sub.5 light paraffins, and ethylene,
C.sub.2.dbd., and propylene, C.sub.3.dbd..
[0034] The heavy fraction 7 obtained from the separator FRAC is sent, as a
mixture with the effluents 5 from the catalytic reforming REF, as a feed 10 for
the aromatics complex (CA).
[0035] The aromatics complex (CA) can be used to extract BTX, a raffinate 12
corresponding to the non-aromatic portion of the effluents, at least a portion
of which is sent as a mixture with the light naphtha 3 as a feed for the NCC,
and a fraction termed the heavy aromatics 11 which is also sent as a mixture
with the light naphtha 3 as a feed for the NCC, in order to obtain thermal
balance thereof due to its coking power.
[0036] In a first variation of the process of the invention, shown in FIG. 2,
the raffinate effluent 12 from the aromatics complex (CA) is sent to a separation
unit SPLIT2 which can be used to separate a light fraction 13 which is sent, as
a mixture with the light naphtha feed 3, to the catalytic cracking unit NCC,
and a heavy fraction 14 which is sent, as a mixture with the heavy naphtha feed
4, to the catalytic reforming unit REF.
[0037] In a second variation of the process of the invention shown in FIG. 3,
which variation may be combined with the first variation, the light C.sub.2 to
C.sub.5 paraffins produced as effluents from the catalytic cracking unit NCC
originating from the separation box CBS are sent to the catalytic cracking unit
NCC as a mixture with the light naphtha feed 3 in order to increase the yield
of light olefins, ethylene and propylene and to improve transport and
fluidization.
[0038] In a third variation of the process of the invention shown in FIG. 4,
which variation may be readily combined with the preceding variations, the
light C.sub.4 and C.sub.5 molecules obtained are sent from the separation box
CBS to an oligomerization unit OLG and the effluents from said oligomerization
unit OLG are sent to the catalytic cracking unit NCC as a mixture with the
light naphtha feed 3.
[0039] Finally, in all of the variations of the process of the present
invention, the light naphtha cut 3 obtained from the fractionation SPLIT1 is
preferably preheated in the convection zone of the catalytic reforming furnaces
(FREE) before being introduced as the feed for the catalytic cracking unit NCC.
[0040] The process for the production of light olefins and BTX of the present
invention preferably involves operating the NCC unit under severe cracking
conditions, i.e. a reactor outlet temperature, ROT, in the range 500.degree. C.
to 750.degree. C., and a ratio of the mass flow rate of catalyst to the mass
flow rate of feed (C/O) in the range 5 to 40.
[0041] The process for the production of light olefins and BTX of the present
invention uses, for the NCC unit, a catalyst comprising a proportion of zeolite
which is at least equal to 20%, and more particularly a proportion of ZSM-5
zeolite at least equal to 10% by weight with respect to the total catalyst.
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