Process and installation for producing liquid fuels and raw chemicals

The invention is directed to a process and an installation for the production of liquid fuels and raw chemicals from crude petroleum within the framework of a refinery process with process steps for distillation, thermal and/or catalytic cracking, and possibly reformation. The refinery process is directly supplemented by various process steps, i.e. a partial flow of the C.sub.4 components together with a flow of methanol or ethanol is subjected to a catalytic reaction, the unconverted n-butane-containing portion of the components is subjected to isomerization, a part of the isobutane is subjected to a thermal cracking process, and finally the product flow emerging therefrom is guided back, in its entirety or in part, into the fractionation stage for splitting.

BACKGROUND OF THE INVENTION 
The invention concerns a process and an installation for producing liquid 
fuels and raw chemicals from crude petroleum within the framework of a 
refinery process. 
A refinery process conventionally includes a combination of numerous 
physical and chemical partial processes. Among these are particularly the 
processes for distillation (at various pressures), catalytic reformation, 
hydrorefining, and the cracking of higher hydrocarbons. In the following, 
the hydrocarbons are abbreviated and designated, depending on the number 
of carbon atoms, by C.sub.2, C.sub.3, C.sub.4, C.sub.5.sup.+ (five or more 
carbon atoms). 
A rough diagram of such a refinery process, according to the prior art, is 
shown in FIG. 1. In a distillation unit (DEST), crude petroleum (CRUDE) is 
split into a series of different fractions which are generally not 
homogeneous materials, but rather mixed products. 
A relatively light fraction (C.sub.1 -C.sub.10, H.sub.2 S) exits the 
distillation unit as head product and is separated into a gaseous phase 
and a liquid phase in a storage vessel (ACCU). The lightest components 
(C.sub.1, C.sub.2, H.sub.2 S) are fed to an installation (ASR) in which 
sulfur is removed by amines. The resulting products are a gas flow G and a 
quantitative flow (S) of sulfur. 
The heavier components (raw naphtha, predominantly C.sub.3 to C.sub.10) are 
fed to a naphtha hydrating treatment (VNHDT) from the storage vessel 
(ACCU), but can also be sold directly as raw chemicals or feedstock (CF). 
The naphtha hydrating treatment produces a marketable naphtha (NA), but 
this can also be processed further by means of catalytic reformation 
(CREF) in which in particular a hydrogen-rich gas (H.sub.2 R) and 
gasolines (reformates REF, predominantly C.sub.5-C.sub.10) are formed. For 
the rest, mixtures of material comprising liquid gas (LPG) (predominantly 
C.sub.3 and C.sub.4) occur in the naphtha hydrating treatment (VNHDT) and 
in the catalytic reformation (CREF). Some C.sub.5 components can also be 
removed from the naphtha hydrating treatment (VNHDT). These intermediate 
products (predominantly C.sub.3 -C.sub.5) are then divided into various 
fractions in a fractionating installation (VRU). The remaining gaseous 
components which are still contained (particularly H.sub.2, CO, CO.sub.2, 
C.sub.1, C.sub.2) are fed to the aforementioned gas flow G, while the 
other fractions (C.sub.3, C.sub.4, C.sub.5) are further processed to form 
various gasoline products (GP) in subsequent (parallel) process steps 
(AIDP) which can include alkylation, isomerization, dimerization, as well 
as polymerization. 
The kerosine and diesel fractions which are separated out in the 
distillation unit (DEST) are subjected to desulfurization and hydration 
(HDS) respectively, whereupon they represent salable products. 
The lighter part of the heavy hydrocarbons is fed to a catalytic cracking 
installation (FCC), but can also be used as heavy fuel oil (FO). The 
bottom product of the distillation unit (DEST) is likewise supplied to the 
catalytic cracking installation (FCC) after undergoing vacuum distillation 
(VDEST). If necessary, cracking can also be effected accompanied by the 
addition of hydrogen. The resulting gaseous fraction (C.sub.1, C.sub.2, 
NH.sub.3, H.sub.2 S) is guided into the ASR installation, while the liquid 
gas components (C.sub.3, C.sub.4) are directed into the fractionating 
installation (VRU) as LPG. If diesel proportions occur they are fed to the 
diesel flow (DIE). The essential end product formed in the cracking 
installation (FCC) is a flow of high-grade motor gasoline (FCCG). The 
remaining heavy hydrocarbons, as well as the bottom product occurring in 
the vacuum distillation (VDEST) which can be additionally subjected to a 
thermal cracking process (VISBR), are used as heavy fuel oil (FO). 
FIG. 2 shows a similar refinery process also belonging to the prior art. In 
this case, instead of a catalytic cracker (FCC), a hydrocracker (HYCR) is 
used which supplies cracked products of different quality and quantitative 
composition. The latter are fed to similar or related end product or 
intermediate product flows occurring in other places in the refinery 
process. A flow of C.sub.3 components and C.sub.4 components as well as a 
flow of gasoline products (C.sub.5.sup.+) result as end products in the 
fractionating installation (VRU). An immediate further processing of the 
gasolines as shown in FIG. 1 is not provided in this instance, but of 
course can also take place. 
The gasoline products produced in the refinery process normally contain 
further significant proportions of dissolved butane. For environmental 
reasons, there is a growing demand to reduce the content of highly 
volatile butane in gasolines to a comparatively small residual quantity. 
Corresponding legal regulations already exist in the United States and are 
also anticipated in other countries. Measures for reducing the butane 
content are known. However, the question remains of how this surplus 
butane can be used in the most productive manner. Burning off, which is 
still frequently carried out in crude petroleum extraction, is doubtless 
the least desirable "use". However, the obvious use for generating process 
steam is also not always advisable, as there is often no need for the 
additionally generated steam. Moreover, this is not desirable for economic 
reasons because a relatively valuable raw material is eliminated by 
burning. 
Further processing of butane to form useful products is generally known. 
Among these products are e.g. gasoline additives for increasing the octane 
number which are used as an alternative to lead compounds which were 
formerly used for this purpose. For environmental reasons, the use of lead 
compounds is increasingly restricted. Instead, materials such as MTBE 
(tert-butyl methyl ether) and ETBE (tert-butyl ethyl ether) are used, 
which are normally produced in separate large-scale installations. Butane 
is used as starting material, its n-butane proportion first being 
converted into isobutane and then into isobutylene. This conversion takes 
place in the form of a catalytic process. Thermal cracking of isobutane is 
also known in general, whereby, in addition to isobutylene, proportions of 
propylene and ethylene are also formed in particular. The latter cannot be 
used for the production of MTBE or ETBE. 
MTBE and ETBE are actually produced by converting isobutylene with methanol 
or ethanol, respectively, in the presence of acidic catalysts (e.g. ion 
exchangers). 
An obvious possibility for exploiting the surplus butane occurring in the 
refinery process therefore consists in using this butane as input material 
in such large-scale installations. However, the cost required for 
transporting the butane (e.g. pipeline or tank vehicles) is already a 
considerable disadvantage. 
SUMMARY OF THE INVENTION 
The invention has the object of suggesting the possibility for exploitation 
which is most advantageous with respect to environmental protection and in 
technical and economic respects.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Since FIG. 1 and 2 have already been discussed in detail in the preceding, 
they need not be addressed again. The diagram in FIG. 3, for example, can 
be linked to these two refinery processes. The common point between the 
individual figures consists in the fractionating installation (VRU); in 
particular, the various flows of liquid gas LPG occurring in the refinery 
process flow into the latter. 
These flows are symbolized in FIG. 3 by arrow 1. The purely gaseous 
components (particularly H.sub.2, C.sub.1, C.sub.2, CO, CO.sub.2) are 
separated out (arrow 2) before the rest of the components are further 
processed. This further processing, which is represented for the sake of 
brevity in FIG. 1 by the unit AIDP, is further divided in FIG. 3 into 
alkylation ALK and additional processes IDP (isomerization, dimerization, 
polymerization). In the catalytic alkylation ALK, valuable alkylate 
gasoline (arrow 7) is produced from a flow 3 which proceeds from the 
fractionating installation VRU and contains butane as well as butylene and 
propylene. C.sub.3 components, C.sub.4 components and C.sub.5.sup.+ 
components which have been separated out in the fractionating installation 
VRU are fed to additional processes IDP with the mass flow 4 and are 
further processed to form gasoline products S. At least a part of the 
C.sub.4 components, which as a rule contain isobutylene in an order of 
magnitude of approximately 20 percent by weight, is guided according to 
the invention as mass flow 5 along with a methanol 6 flow into an 
installation MTBE for the production of tert-butyl methyl ether. The 
produced MTBE product flow is designated by 9. Alternatively, it is 
possible to produce ETBE in the same manner by supplying ethanol instead 
of methanol. Since only the isobutylene takes part in the conversion to 
MTBE in the MTBE installation, the proportion of unconverted C.sub.4 
components is subjected to cracking for generating isobutylene. 
In the present instance, the flow 10 of C.sub.4 components is first guided 
into a separating device SP in which n-butane is separated from isobutane. 
The n-butane is fed from the separating device SP into an isomerization 
ISO (line 11) and is then guided back into the separating device SP again 
to separate out the isobutane (line 12). The isobutane is formed in the 
present example in a secondary circuit so that the cracking installation 
CR in which the isobutane arrives via line 13 is not charged with the 
proportion of unwanted butane. It is also possible to guide a part of the 
mass flow 5 directly into the complex for isomerization and isobutylene 
production, bypassing the MTBE installation. 
The cracking installation CR operates according to the thermal cracking 
process. In the present instance, this is decidedly more advantageous than 
a catalytic conversion, since, in addition to isobutylene, a thermal 
cracker in particular also generates considerable quantities of propylene 
which is very desirable as a particularly valuable saleable product in the 
refinery process or for subsequent further processing. On the other hand, 
a catalytic conversion of the isobutane would only produce isobutylene, 
specifically in such quantities that processing it further to form MTBE 
(or ETBE) or alkylate gasolines would yield an unnecessarily high amount 
of the gasoline additive compared to the quantities of the rest of the 
gasoline products produced. The isobutylene with the unconverted 
proportion of isobutane is guided from the cracking installation CR to the 
fractionating installation VRU via the line 14. From there, the 
circulation of unconverted C.sub.4 components can begin again via the MTBE 
production installation. 
In many cases, it is advantageous to guide a partial flow 17 of the 
isobutane separated out in the separating device SP into the alkylation 
ALK so as to produce a higher proportion of alkylate gasoline 7 in the 
latter. This is particularly advisable when additional quantities of 
butane are to be processed outside the actual refinery process (e.g. from 
the crude petroleum extraction). This is shown in FIG. 3 by the dashed 
arrow 15 leading into the separating device SP. The additional butane 
could also be introduced at another location (e.g. into the VRU 
installation). Reference is also made to the dashed arrow 16 which shows 
the possibility of feeding additional partial amounts of isobutane 
directly into the alkylation ALK from the outside. Finally, reference is 
made to the flow of various gasoline products (C.sub.5.sup.+), designated 
by 18, which is guided out of the fractionating installation VRU. 
The inclusion of MTBE or ETBE production, according to the invention, with 
linked butane cracking installation in a conventional refinery process 
makes it possible to exploit the occurring quantities of butane in an 
optimal manner. In so doing, a particularly valuable gasoline additive 
(MTBE or ETBE) is produced which, owing to the application of thermal 
cracking which is unconventional per se, supplies isobutylene in 
quantities which make it possible to produce quantities of gasoline 
additive adapted to the requirement of the gasoline product quantities. It 
is very important in doing so that a quantity of propylene is also formed 
in this process, as the latter has particular economic value. The refinery 
process as a whole can be operated with a balance of energy so that it is 
unnecessary to import or export energy or process steam. 
The required technical expansions with respect to the installation are 
comparatively inexpensive when the value of the producible products is 
taken into account, so that the payback period for corresponding 
investments is substantially shorter than in a large-scale MTBE 
installation with the formerly conventional catalytic cracker. It is 
particularly advantageous that there is no need to transport surplus 
butane to MTBE/ETBE installations or to transport the produced MTBE/ETBE 
back to the refinery for the purpose of mixing with the produced gasoline 
products. 
The efficiency of the process according to the invention is described in 
more detail with reference to a comparison example according to the prior 
art and an embodiment example of the invention. The examples are based on 
a refinery process corresponding to FIG. 1 in which identical quantities 
(100 percent by weight) of the same crude oil were processed. This 
resulted in a guantity flow into the fractionation installation VRU having 
the following composition (in percent by weight of the crude oil input): 
______________________________________ 
propylene 
1.50% 
propane 1.54% 
isobutylene 
0.70% 
n-butylene 
1.70% 
isobutane 
0.36% 
n-butane 
2.60% 
C.sub.5.sup.+ 
0.90% 
9.30% 
______________________________________ 
In the comparison example, a gas flow (propane) of 1.54 percent by weight 
was separated off by fractionation VRU. The remaining portion was 
converted by alkylation with an additional directly supplied quantity of 
3.47 percent by weight isobutane resulting in a product flow of the 
following composition (percent by weight): 
______________________________________ 
alkylates 
8.46% 
n-butane 
1.87% 
C.sub.5.sup.+ 
0.90% 
12.77% 
______________________________________ 
The example according to the invention was carried out with an input flow 
into the fractionation installation VRU having the same composition and 
the same direct feed of 3.47 percent by weight isobutane into the 
alkylation installation. In contrast to the comparison example, however, 
devices for isomerization of butane, thermal cracking of isobutane, and 
production of MTBE were provided at the fractionation installation VRU in 
the sense of FIG. 3. In so doing, 0.54 percent by weight methanol was 
additionally fed to the MTBE unit. Devices for additional processes IDP as 
in FIG. 3 were not provided. The quantity flow 14 fed back into the 
fractionation installation VRU from the thermal cracking installation CR 
had the following composition (percent by weight): 
______________________________________ 
gas 0.86% 
propylene 
0.72% 
propane 0.04% 
isobutylone 
0.89% 
n-butylene 
-- 
isobutane 
2.08% 
n-butane 
0.01% 
C.sub.5.sup.+ 
0.07% 
4.67% 
______________________________________ 
As a result, a gas quantity (C.sub.1 -C.sub.3) of 2.43 percent by weight 
was separated out in the fractionation. The product flow from the 
alkylation installation had the following composition: 
______________________________________ 
alkylates 
8.01% 
n-butane 
0.39% 
C.sub.5.sup.+ 
0.97% 
MTBE 1.49% 
10.86% 
______________________________________ 
Accordingly, the butane content in the end product of 1.87 percent by 
weight could be reduced to only 0.39 percent by weight, that is, roughly 
20% of the original value, by the process according to the invention. At 
the same time, it was possible to produce a quantity of 1.49 percent by 
weight of valuable MTBE as gasoline additive, which required an external 
supply of only 0.54 percent by weight methanol. The quantity of alkylates 
decreased relatively slightly by approximately 0.4 percent by weight, 
while the quantity of C.sub.5.sup.+ products increased by approximately 
0.1 percent by weight. The increase in the gas quantity separated out in 
fractionation by approximately 0.9 percent by weight, i.e. almost 60% of 
the original value, is particularly significant, since this increase is 
substantially brought about by additionally generated high-quality 
propylene.