EP0555301B1 - Process and installation for producing liquid fuels and raw chemicals - Google Patents

Abstract

PCT No. PCT/DE91/00851 Sec. 371 Date May 10, 1993 Sec. 102(e) Date May 10, 1993 PCT Filed Oct. 30, 1991 PCT Pub. No. WO92/07921 PCT Pub. Date May 14, 1992The 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 C4 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.

Description

The invention relates to a method and a plant for the production of liquid fuels and chemical raw materials from petroleum in the context of a refinery process.

A refinery process usually consists of a combination of numerous physical and chemical sub-processes. Particularly noteworthy here are the processes for distillation (at different pressures), for catalytic reforming, for hydrorefining and for cracking higher hydrocarbons. In the following, the hydrocarbons are often shortened depending on the number of C atoms with C₁, C₂, C₃, C₄, C₅⁺ (five and more C atoms).

A rough diagram of such a refinery process according to the prior art is shown in FIG. 1. Crude oil (CRUDE) is divided in a distillation unit (DEST) into a number of different fractions, which are usually not homogeneous substances but represent mixed products.

A relatively light fraction (C₁-C₁₀, H₂S) leaves the distillation unit as the top product and is separated into a gaseous and a liquid phase in a collecting container (ACCU). The lightest components (C₁, C₂, H₂S) are placed in a plant (ASR) in which they are freed of sulfur by amines. The resulting products are a gas stream G and a volume stream (S) of sulfur.

The heavier components (raw naphta, predominantly C₃ to C₁₀) are given from the collection container (ACCU) in a naphtha hydrogenation treatment (VNHDT), but can also be marketed directly as chemical raw material (CF). The naphtha hydrogenation treatment results in a salable naphtha (NA), which is further processed by a catalytic reforming treatment (CREF), in which in particular an H₂-rich gas (H₂R) and gasoline (Reformate REF, predominantly C₅-C₁₀) are produced can be. Otherwise, naphtha hydrogenation treatment (VNHDT) and catalytic reforming (CREF) each result in mixtures of substances consisting of liquefied petroleum gas (LPG) (mainly C₃ and C₄), with some naphtha hydrogenation treatment (VNHDT) also containing some C₅- Components are removed. These intermediates (mainly C₃-C₅) are then divided into different fractions in a fractionation system (VRU). The remaining gaseous components (in particular H₂, CO, CO₂, C₁, C₂) are added to the gas stream G already mentioned, while the other fractions (C₃, C₄, C₅) in subordinate (parallel) process steps (AIDP), the one Alkylation, isomerization, dimerization and also polymerisation can be further processed to various gasoline products (GP).

The kerosene and diesel fractions separated in the distillation unit (DEST) are each subjected to a desulfurization and hydrogenation treatment (HDS) and then represent salable products.

The lighter part of the heavy hydrocarbons is fed to a catalytic cracking unit (FCC), but can also be used as heavy fuel oil (FO). The bottom product of the distillation unit (DEST) is also fed into the catalytic cracking unit (FCC) after passing through a vacuum distillation (VDEST). If necessary, the cracking can also be carried out with the addition of H₂. The resulting gaseous fraction (C₁, C₂, NH₃, H₂S) is fed into the ASR system, while the liquid gas components (C₃, C₄) are passed as LPG into the fractionation system (VRU). Any diesel components generated are added to the diesel power (DIE). The main end product in the catalytic cracking plant (FCC) is a stream of high-quality motor gasoline (FCCG). The remaining heavy hydrocarbons are used as heavy heating oil (FO) as is the bottom product from vacuum distillation (VDEST), which can also be subjected to a thermal cracking process (VISBR).

FIG. 2 shows a similar refinery process which is also part of the prior art. Instead of a catalytic cracker (FCC), a hydrocracker (HYCR) was used in this case, which delivers cracking products in a different quality and quantity composition. These are each added to the similar or related end or intermediate product streams that have arisen elsewhere in the refinery process. From the fractionation unit (VRU), the end product is a stream of C₃ and C₄ components and a stream of gasoline products (C₅⁺). Immediate further processing of the gasoline as in FIG. 1 is not provided in this case, but can of course also take place.

Typically, the gasoline products produced in the refinery process still contain significant amounts of dissolved butane. For reasons of environmental protection, there is an increasing demand to reduce the content of the volatile butane in petrol to a comparatively low residual value. Corresponding legal provisions already exist in the USA and can also be expected for other countries. Measures to lower the butane content are known. However, the question arises of how this excess butane can be used as sensibly as possible. Flaring, as is still often the case in oil production, is undoubtedly the least desirable "use". The obvious use for the production of process steam is not always useful, because there is often no need for the additional steam generated. In addition, this is not desirable for economic reasons because the combustion destroys a relatively high-quality raw material.

It is generally known to process butane into usable products. These products include gasoline additives to increase the octane number, which are used as an alternative to the lead compounds previously used for this purpose. For environmental reasons, the use of lead compounds is increasingly restricted. Instead, substances such as MTBE (methyl tertiary butyl ether) and ETBE (ethyl tertiary butyl ether) are used, which are usually produced in separate large-scale plants. Butane is used as the starting material, the n-butane portion of which is first converted into isobutane and then converted into isobutylene. This implementation takes place in the form of a catalytic process. Thermal cracking of isobutane is also fundamentally known, in which in addition to isobutylene, proportions of propylene and ethylene in particular are formed which cannot be used for the production of MTBE or ETBE.

The actual generation of MTBE or ETBE takes place by reacting isobutylene with methanol or ethanol in the presence of acidic catalysts (e.g. ion exchangers).

An obvious possibility of recycling the excess butane obtained in the refinery process can therefore be seen in using this butane as a feedstock in such large plants. A significant disadvantage is the effort required to transport the butane (e.g. pipeline or tanker).

Attention is also drawn to EP 0 332 243 A1, from which a process for the production of normally liquid hydrocarbon products from linear or branched olefins is known. Essentially, the branched olefins are selectively converted into liquid hydrocarbon products in the presence of a catalyst, the linear olefins are separated from these products and these are then converted into liquid hydrocarbons in the presence of a solid catalyst.

The invention is based on the object of proposing a recycling option which is as favorable as possible in terms of the requirements of environmental protection in technical and economic terms.

This object is achieved by a method having the features of patent claim 1. Advantageous further developments of this method are specified in subclaims 2 to 5. A system according to the invention for carrying out this method has the features of patent claim 6 and can be configured in an expedient manner by the characterizing features of patent claims 7 to 11.

The invention is explained in more detail below with reference to FIGS. 1 to 3, FIGS. 1 and 2 showing conventional refinery processes with a fluid bed cracker (FCC) or with a hydrocracker (HYCR) and FIG. 3 showing a possible circuit diagram for supplementing the refinery process according to the invention.

Since FIGS. 1 and 2 have already been explained in detail at the beginning, there is no need to go into this again. The scheme of Figure 3 can follow these two refinery processes, for example. The connection point between the individual figures can be seen in each case in the fractionation system (VRU), which in particular includes the various flows of the liquefied petroleum gas LPG produced in the refinery process.

These are symbolized by arrow 1 in FIG. The purely gaseous components (in particular H₂, C₁, C₂, CO, CO₂) are separated off before further processing of the other components (arrow 2). This further processing, which is summarized in FIG. 1 by the AIDP unit, is further divided in FIG. 3 into an alkylation ALK and into the further processes IDP (isomerization, dimerization, polymerization). In the ALK catalytic alkylation process, high-quality alkylate gasoline (arrow 7) is produced from a stream 3 which comes from the VRU fractionation system and contains butane and butylene and propylene. With the mass flow 4, C₃, C₄ and C₅⁺ components, which were separated in the VRU fractionation system, are added to the further processes IDP and processed into gasoline products 8. At least some of the C₄ components, which usually contain isobutylene in an order of magnitude of about 20% by weight, are led according to the invention as mass flow 5 together with a stream of methanol 6 into an MTBE plant for the production of methyl tertiary butyl ether. The MTBE product stream generated is designated by 9. Alternatively, ETBE can be produced in the same way by adding ethanol instead of methanol. Since only the isobutylene in the MTBE plant takes part in the conversion to MTBE, the proportion of the non-converted C₄ components is subjected to a cracking treatment to produce isobutylene.

In the present case, the stream 10 of the C₄ components is first passed into a separation 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 returned from this to the separating device SP (line 12) to separate the isobutane. The formation of isobutane is thus carried out in a secondary circuit in the case shown, so that the cracking plant CR, into which the isobutane passes via line 13, is not burdened with the proportion of the undesired n-butane. It is also possible to bypass part of the mass flow 5 in a bypass past the MTBE plant directly into the complex of the isomerization and isobutylene production.

The CR cracking system works according to the thermal cracking process. In the present case, this is significantly cheaper than a catalytic conversion, since a thermal cracker, in addition to isobutylene, in particular also produces considerable amounts of propylene, which is very desirable in the refinery process as a particularly high-quality salable product or for subsequent processing. In contrast, catatytic conversion of isobutane would only provide isobutylene in amounts such that its further processing into MTBE (or ETBE) or atylate gasoline would produce an unnecessarily large amount of the gasoline additive in relation to the amounts of the other gasoline products produced. The isobutylene passes from the cracking plant CR with the unconverted proportion of isobutane via line 14 into the fractionation plant VRU. From there, the cycle of the unconverted C₄ components can begin again via the MTBE production plant.

In some cases it is advantageous to feed a partial stream 17 of the isobutane separated in the separating device SP into the alkylation ALK in order to produce a higher proportion of alkylate gasoline 7 there. This is particularly useful if additional quantities of butane are to be processed from outside the actual refinery process (e.g. from oil production). In FIG. 3, this is represented by the dashed arrow 15, which leads into the separating device SP. The additional butane could also be introduced elsewhere (e.g. into the VRU system). Furthermore, reference is made to the dashed arrow 16, which represents the possibility of adding additional partial amounts of isobutane directly into the alkylation ALK from the outside. Finally, the flow of various gasoline products (C₅⁺) designated 18, which is led out of the VRU fractionation system, should also be mentioned.

The inclusion according to the invention of MTBE or ETBE production with an attached butane cracking plant in a conventional refinery process enables the use of the butane quantities obtained in an optimal manner. A particularly valuable gasoline additive (MTBE or ETBE) is produced which, due to the use of thermal cracking, which is unusual per se, provides the isobutylene in such quantities that it is possible to produce the quantity of gasoline additive adapted to the requirements of the gasoline product quantities. It is very important that a lot of economically particularly valuable propylene is formed in this process. The refinery process as a whole can be operated with a balanced energy balance, so that neither imports nor exports of energy or process steam are required.

The required technical extensions are comparative. taking into account the value of the products that can be produced, this is not very expensive, so that the capital return times for corresponding investments are considerably shorter than in the case of a large-scale MTBE system with the catalytic cracker which has been customary to date. It is particularly advantageous that both the transport of excess butane to MTBE / ETBE antagen and the return transport of the MTBE / ETBE produced to the refinery for the purpose of mixing with the gasoline products produced are eliminated.

The effectiveness of the method according to the invention is explained in more detail using a comparative example according to the prior art and an embodiment of the invention. In each case, a refinery process was assumed as it corresponds to FIG. 1, with the same quantities (100% by weight) of the same crude oil being processed. This resulted in a volume flow entering the VRU fractionation with the following composition (in% by weight of the crude oil used): Propylene 1.50% propane 1.54% Isobutylene 0.70% n-butylene 1.70% Isobutane 0.36% n-butane 2.60% C₅⁺ 0.90% 9.30%

In the comparative example, a gas stream (propane) of 1.54% by weight was separated off by fractionation VRU. The remaining part was reacted in an alkylation with an additional directly supplied amount of 3.47% by weight of isobutane, a product stream having the following composition (% by weight) being formed: Alkylates 8.46% n-butane 1.87% C₅⁺ 0.90% 12.77%

When carrying out the example according to the invention, an input stream of the same composition into the fractionation VRU and the same direct feed of 3.47% by weight of isobutane into the alkylation was assumed. In contrast to the comparative example, however, devices for isomerization of butane, for thermal cracking of isobutane and for producing MTBE were provided for the fractionation VRU in the sense of FIG. 3. An additional 0.54% by weight of methanol was added to the MTBE unit from the outside. Devices for further processes IDP as in FIG. 3 were not provided. The mass flow 14 returned from the thermal cracking plant CR into the fractionation VRU had the following composition (% by weight): gas 0.86% Propylene 0.72% propane 0.04% Isobutylene 0.89% n-butylene - Isobutane 2.08% n-butane 0.01% C₅⁺ 0.07% 4.67%

This resulted in a fraction of a gas amount (C₁-C₃) of 2.43 wt .-% in the fractionation. The product stream from the alkylation had the following composition: Alkylates 8.01% n-butane 0.39% C₅⁺ 0.97% MTBE 1.49% 10.86%

The process according to the invention thus made it possible to reduce the butane content in the end product from 1.87% by weight to only 0.39% by weight, that is to say to approximately 20% of the original value. At the same time, an amount of 1.49% by weight of valuable MTBE was produced as a gasoline additive, for which purpose only 0.54% by weight of methanol had to be added from the outside. The amount of alkylates decreased relatively slightly by about 0.4% by weight, while the amount of C₅⁺ products increased by about 0.1% by weight. Of particular importance is the increase in the amount of gas separated in the fractionation by approximately 0.9% by weight, that is to say by almost 60% of the original value, since this increase is essentially due to additionally produced high-quality propylene.

Claims (11)

1. Process for producing liquid fuels and chemical raw materials from mineral oil within the framework of a refinery process with process stages for distillation, for thermal and/or catalytic cracking and also where necessary for re-constitution, whereby refinery gas and liquid petroleum gas (LPG) and also benzine (C₅+) are distributed into a fractional distillation (VRU) in a gas flow (H₂, CO, CO₂, C₁, C₂) and into flows of higher hydrocarbons (C₃, C₄ and C₅+), and a said flow of C₄ constituents contains n-butane, isobutane and isobutylene,
   wherein
   a refinery process is directly supplemented by the following process stages:

   - at least a part-current of C₄ constituents, together with a flow of methanol or ethanol, is subjected to a catalytic reaction for forming methyl-tertiary-butyl-ether (MTBE) or ethyl-tertiary-butyl-ether (ETBE).

   - the part of C₄ constituents containing n-butane which is not transformed in a catalytic reaction is subjected to isomerization in which a part of the said n-butane is transformed into isobutane,

   - at least part of isobutane concerned undergoes a heat-cracking process for forming isobutylene and propylene,

   - a flow which is the product of said cracking processing for forming isobutylene and propylene, is partly or fully fed back for distribution into a fractional distillation stage.
2. Process in accordance with claim 1,
   wherein
   a partial flow of C₄ constituents is fed into a catalytic reaction for forming MTBE or ETBE and goes directly into a process section in which isomerization of n-butane and heat-cracking of isobutane occurs.
3. Process in accordance with either claim 1 or 2,
   wherein
   an n-butane content is separated off before cracking processing of isobutane and is fed back into isomerization.
4. Process in accordance with any one claims 1 to 3,
   wherein
   a refinery process which includes a hydro-cracking process stage and an alkylation process stage for transforming part of isobutylene and/or propylene produced in heat-cracking processing into alkylate benzine follows fractional distillation.
5. Process in accordance with claim 4,
   wherein
   a partial flow of isobutane produced by isomerization is directly fed into alkylation, bypassing cracking processing.
6. Installation for effecting the process in accordance with claim 1 with units for distillation, thermal and/or catalytic cracking and, where necessary, for reconstitution of hydrocarbons and also with an installation for fractional distillation (VRU) of benzines, refinery gas and liquid petroleum gas, whereby gas (H₂, CO, CO₂, C₁, C₂) and higher hydrocarbons (C₃, C₄ and C₅+) can be extracted from a said fractional distillation installation (VRU) through separate pipes (2, 3, 4, 5), wherein

   - a pipe (5), through which C₄ constituents can be directed into apparatus for catalytic development of methyl-tertiary-butyl-ether (MTBE unit) or ethyl-tertiary-butyl-ether (ETBE unit) from a said fractional distillation unit (VRU), is provided,

   - a pipe (10), through which untransformed C₄ constituents from a said MTBE or ETBE unit can be directed into a distribution installation which contains at least one isomerization unit (ISO) for transforming n-butane into isobutane and a cracking unit (CR), which is connected with this, for producing isobutylene, is provided, and

   - a said cracking unit (CR) has a pipe (14) for feeding the product of cracking to a said fractional distillation installation (VRU).
7. Installation in accordance with claim 6,
   wherein
   a bypass-pipe from a pipe (5) to a pipe (10) is provided for bypassing a MTBE or ETBE unit.
8. Installation in accordance with either claim 6 or claim 7,
   wherein
   separation equipment (SP), with which isobutane can be separated from n-butane, is provided in a production plant, whereby n-butane which is separated off can be directed into a heat-cracking unit (CR) through a conduit (13), and n-butane can be directed into an isomerization unit (ISO) through a conduit (11).
9. Installation in accordance with claim 7,
   wherein
   a conduit (10) is connected from an MTBE or ETBE unit to a separation device (SP).
10. Installation in accordance with any one of claims 6 to 9,
    wherein
    an unit is provided for hydro-cracking (HYCR) and an alkylation installation (ALK) for transforming isobutylene and propylene into alkylate benzine is connected to a fractional distillation installation (VRU).
11. Installation in accordance with claim 10,
    wherein
    a conduit (17) through which isobutane from separation equipment (SP) can be directly fed into an alkylation installation (ALK), bypassing a cracking unit (CR) for isobutane, is provided.

Images