DE69309729T2 - Process for working up a hydrocarbon feed - Google Patents

Description

The present invention relates to a process for refining a hydrocarbon-containing feedstock boiling largely in the gasoline range.

One of the main objectives of modern oil processing is to produce gasolines that meet the increasing environmental protection requirements for product quality and have a high octane number.

This means that the octane specification of the gasoline must now be achieved without lead-containing additives, with fewer aromatics, especially benzene, fewer olefins and lower gasoline vapor pressure.

The object of the present invention is to provide a process for producing gasolines that meet both the growing environmental protection requirements for product quality and the requirement for a high octane number.

It has now been found that gasolines with a high octane number and a reduced content of aromatics, in particular benzene, can be produced by a refining process comprising a specific sequence of process steps.

Accordingly, the present invention relates to a process for upgrading a hydrocarbon-containing feedstock boiling largely in the gasoline range, in which:

a) the feedstock is subjected to a separation treatment whereby normal paraffins and, where appropriate, monoisoparaffins are separated from diisoparaffins;

b) isolating therefrom a first separation effluent stream containing normal paraffins and optionally monoisoparaffins and a second separation effluent stream containing diisoparaffins;

c) separating at least a portion of the second separation effluent stream into a light fraction containing hydrocarbons of the C6-C10 range and a heavy fraction containing C8 and higher hydrocarbons;

and

d) producing a reformate from at least part of the heavy fraction containing C8 and higher hydrocarbons in a reforming step.

In this way, a direct increase in the octane number of the resulting gasoline blend pool is achieved, while at the same time a significant reduction in the aromatics content, in particular the benzene content. This increase in octane number can allow refineries to increase gasoline production that is limited by octane and/or capacity limits. In addition, a significant reduction in the amount of gas produced and the formation of low-octane hydrocarbons is achieved during the reforming step.

The hydrocarbon-containing feedstock boiling largely in the gasoline range can be conveniently obtained by distillation of crude oil or from catalytic cracking, but it can also be derived from other cracking processes, such as thermal cracking, delayed coking, viabreaking or flexicoking. Such gasoline feedstocks generally have unacceptably high sulfur and nitrogen contents and are advantageously subjected to a hydrogen treatment before being used in the process according to the invention. Although the feedstock can contain the entire fraction boiling in the gasoline range, it is preferred to use a cut thereof as the feedstock which boils largely in the range of 70 to 220ºC. The hydrocarbon-containing feedstock conveniently consists essentially of a Hydrocarbon mixture boiling in the gasoline range.

In step a), the separation treatment is advantageously carried out by introducing the feedstock into a separation zone which contains a shape-selective, separation-effective molecular sieve with a pore size of 4.5 x 4.5 Å or less, which, due to its shape, can selectively adsorb normal paraffins, in contrast to monoisoparaffins, diisoparaffins, other multiply branched paraffins, cyclic paraffins and aromatic hydrocarbons. This enables the selective separation of normal paraffins from monoisoparaffins and diisoparaffins. The first separation output stream, which essentially contains normal paraffins, can then be isolated and at least a portion of the second separation output stream, which contains diisoparaffins, can be subjected to the separation treatment according to step c). It is expedient to process at least a portion of the first separation effluent stream in step d). It is also expedient to use at least a portion of this separation effluent stream as a preferred chemical feedstock, e.g. for a highly selective cyclization process.

The process according to the invention is expediently carried out in such a way that in step a) both the normal paraffins and the monoisoparaffins are separated from the diisoparaffins. This is expediently done by introducing the hydrocarbon-containing feedstock into a separation zone which contains a shape-selective, separating molecular sieve with a pore size between 5.5 x 5.5 Å and 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å, whose pores are large enough for the entry of normal paraffins and monoisoparaffins, but not for the entry of diisoparaffins, other multiply branched paraffins, cyclic paraffins and aromatic hydrocarbons. In this way, the selective separation of the normal paraffins and monoisoparaffins from the diisoparaffins is achieved. The isolating the first separation effluent stream containing both normal paraffins and monoisoparaffins and subjecting at least a portion of the second separation effluent stream containing diisoparaffins to the separation treatment according to step c). At least a portion of this first separation effluent stream can expediently be processed in step d). At least a portion of this separation effluent stream can also expediently be used as the preferred chemical feedstock described above.

In step a), it is advisable to first separate the normal paraffins from the monoisoparaffins and diisoparaffins and then the monoisoparaffins from the diisoparaffins. For this purpose, a multiple adsorption-selective molecular sieve system with special separation properties can be used. The multiple separation sieve system to be used preferably consists of a first molecular sieve with a pore size of 4.5 x 4.5 Å or less, which due to its shape can selectively adsorb normal paraffins, as opposed to monoisoparaffins, diisoparaffins, other multiply branched paraffins, cyclic paraffins and aromatic hydrocarbons, and a second molecular sieve with a pore size between 5.5 x 5.5 Å and 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å, which is selected so that it can adsorb monoisoparaffins (and any residues of normal paraffins), as opposed to diisoparaffins, other multiply branched paraffins, cyclic paraffins and aromatic hydrocarbons. In the process, the hydrocarbon-containing feedstock is first passed into a first separation zone containing the first shape-selective separating molecular sieve described above to obtain the first separation effluent stream containing the normal paraffins and the second separation effluent stream containing both mono- and diisoparaffins. the latter hydrocarbon effluent stream is fed into a second separation zone which contains the second shape-selective separating molecular sieve described above. A third separation effluent stream containing monoisoparaffins can then be isolated and at least a portion of a fourth separation effluent stream containing diisoparaffins can be separated in step c) into a light and a heavy fraction.

It is expedient to process at least a portion of the first and/or the third separation effluent stream in step d). It is also expedient to use at least a portion of these streams as the preferred chemical feedstock described above.

The multiple adsorption selective molecular sieve system described above contains at least two molecular sieves. These can be arranged in separate vessels or in one vessel in a stacked flow pattern.

The first molecular sieve can be a 5 Å zeolite in the calcium form or any other sieve with similar pore dimensions, i.e. with pore dimensions of 4.5 x 4.5 Å. The first sieve is preferably, but not necessarily, dimensioned such that the normal paraffins are completely adsorbed, so that the second molecular sieve does not need to serve as an adsorption sieve for normal paraffins.

An example of a second sieve in a multiple adsorption-selective molecular sieve system is a molecular sieve with eight- and ten-membered rings and pore dimensions between 5.5 x 5.5 Å and 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å.

As a preferred second molecular sieve according to the invention, a ferrierite molecular sieve in a hydrogen form is used, for example, but alternatively also in a form with a cation of an alkali metal, alkaline earth metal or transition metal The molecular sieves according to the invention include ferrierite or analogous shape-selective materials with pore openings with dimensions between those of the 5 Å zeolite in the calcium form and ZSM-5. Other examples of crystalline sieves are aluminophosphates, silicoalumophosphates and borosilicates.

The aluminophosphate, silicoaluminophosphate and borosilicate type molecular sieves that can be used as second molecular sieves have pore openings between 5.5 x 5.5 Å and 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å.

The molecular sieve may also contain a large pore zeolite exchanged with cations to reduce the effective pore size of the sieve to the above-mentioned size range.

When using multiple adsorption-selective molecular sieve systems, whether in separate containers or in a stacked version, the order of the sieves is very important. If the sieves are swapped, the process loses effectiveness because the larger sieve quickly fills up with normal paraffins, preventing the effective adsorption of the monoisoparaffins.

The respective sieves used in a multiple adsorption selective molecular sieve system should be arranged in such a process sequence that they first adsorb sufficient normal paraffin hydrocarbons and then monoisoparaffins. The respective sieves can be supplied with a common desorbent stream or with their own desorbent streams. The desorbent is preferably a gaseous material such as a hydrogen gas stream.

Alternatively, one can first use a molecular sieve as described above to separate the normal paraffins from the monoisoparaffins and diisoparaffins and then The second separation effluent stream containing monoisoparaffins and diisoparaffins can be separated in step c) into a light fraction containing hydrocarbons in the C₆-C₁₀ range and a heavy fraction containing C₈ and higher hydrocarbons. The heavy fraction obtained can then be subjected to a separation treatment as described above, in which the monoisoparaffins are separated from the diisoparaffins. A third separation stream containing monoisoparaffins can then be isolated and at least part of a fourth separation effluent stream containing diisoparaffins can be subjected to the reforming step. At least part of the streams containing normal or diisoparaffins can be processed in step d) or used as the preferred chemical feedstock described above.

The light and heavy fractions according to step c) can be conveniently obtained by distillation.

In a preferred embodiment of the inventive processes described above, at least a portion of the reformate is subjected to a separation treatment, whereby normal paraffins and optionally monoisoparaffins are separated from diisoparaffins and whereby a first hydrocarbon product stream containing normal paraffins and a second hydrocarbon product stream containing diisoparaffins are isolated.

In this way, the normal paraffins and optionally monoisoparaffins initially present are separated from diisoparaffins before the reforming step, whereas after the reforming step, normal paraffins and optionally monoisoparaffins that were still present in the separation effluent stream containing diisoparaffins are separated together with those formed in the reforming step from diisoparaffins.

The downstream reforming step Separation treatment can be conveniently carried out by introducing at least part of the reformate into a separation zone which contains a shape-selective molecular sieve with a pore size of 4.5 x 4.5 Å or less, which due to its shape can selectively adsorb normal paraffins, in contrast to monoisoparaffins, diisoparaffins, other multiply branched paraffins, cyclic paraffins and aromatic hydrocarbons. This enables the selective separation of the normal paraffins from the monoisoparaffins and the diisoparaffins. At least part of the first hydrocarbon product stream thus obtained, which essentially contains normal paraffins, can conveniently be used as the preferred chemical feedstock described above. In another suitable embodiment of the process according to the invention, at least part of this stream is processed in step d).

The process according to the invention is preferably carried out in such a way that after the reforming step both the normal paraffins and the monoisoparaffins are separated from the diisoparaffins. To this end, at least part of the reformate can be introduced into a separation zone which contains a shape-selective, separation-effective molecular sieve with a pore size of 5.5 x 5.5 Å to 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å, whose pores are large enough for the entry of normal paraffins and monoisoparaffins, but not for the entry of diisoparaffins, other multiply branched paraffins, cyclic paraffins and aromatic paraffins. In this way, the selective separation of the normal paraffins and monoisoparaffins from the diisoparaffins is achieved. A first hydrocarbon product stream containing both normal paraffins and monoisoparaffins and a second product stream containing diisoparaffins can then be isolated. The upstream and downstream of the reforming step Separation treatments can conveniently be carried out in the same separation zone.

Conveniently, at least a portion of the first hydrocarbon product stream can be used as the preferred chemical feedstock described above or co-processed in step d).

Preferably, in the second separation treatment, the normal paraffins are first separated from the monoisoparaffins and diisoparaffins and then the monoisoparaffins are separated from the diisoparaffins. For this purpose, a multiple adsorption-selective molecular sieve system can be used, as described above. This enables the selective separation of a first hydrocarbon product stream containing normal paraffins and a second hydrocarbon product stream containing monoisoparaffins from a third hydrocarbon product stream containing diisoparaffins. At least part of the first and/or second hydrocarbon product stream can expediently be used as the preferred chemical feedstock described above or processed in step d).

The use of a multiple adsorption selective molecular sieve system both before and after the reforming step is very attractive as it offers product flexibility combined with product quality. It is convenient to feed at least a portion of the resulting reformate to a hydrogenation unit before subjecting it to one of the separation treatments described above.

It is advantageous to separate at least part of the reformate obtained into a gaseous fraction, a light fraction containing C₅-C₆ hydrocarbons and a gasoline fraction, for example by distillation. At least part of the light fraction can be fed together with another light refinery hydrocarbon stream containing C₅-C₆ hydrocarbons to a isomerization plant. The isomerate obtained in this way can then be fed into the gasoline blending pool.

The resulting gasoline fraction can then be fed directly to the gasoline mixing pool or subjected to a separation treatment in which normal paraffins and, if necessary, monoisoparaffins are separated from diisoparaffins as described above.

At least a portion of the light fraction obtained in step c) can be fed directly to the gasoline blending pool. In a preferred embodiment of the present invention, at least a portion of the light fraction obtained in step c) is processed together with the reformate and subjected to a separation treatment as described above, in which normal paraffins and optionally monoisoparaffins are separated from diisoparaffins. Alternatively, the light fraction obtained in step c) can be subjected directly to the separation treatment following the reforming step, in which the monoisoparaffins are separated from the diisoparaffins.

The light and heavy fractions according to step c) are conveniently obtained by distillation.

Conveniently, at least a portion of one or more of the separation effluent streams containing normal paraffins and/or monoisoparaffins can be processed together with the heavy fraction in step d).

It is advisable to add butane to the gasoline obtained in the gasoline blending pool in order to obtain an overall gasoline with the highest possible permissible RVP (Reid Vapour Pressure) specification.

It is expedient to separate at least part of the gasoline fraction obtained after the reforming step into a light gasoline fraction containing hydrocarbons in the C6-C10 range and a heavy gasoline fraction containing C8 and higher hydrocarbons, for example by distillation.

It is expedient to subject at least a portion of the light gasoline fraction obtained to a separation treatment as described above, in which normal paraffins and optionally monoisoparaffins are separated from diisoparaffins. At least a portion of the heavy gasoline fraction obtained can be fed directly to the gasoline mixing pool.

Any conventional reforming catalyst can be used in the reforming step. Preferably, a catalyst with significant (dehydro)cyclization activity is used. An example of a conventional reforming catalyst is a platinum-containing catalyst, for example with a platinum content in a range of 0.005% by weight to 10.0% by weight. The metals that are catalytically active in the reforming process are preferably noble metals from group VIII of the periodic table of elements, such as platinum and palladium. The reforming catalyst can be present on its own or in a mixture with a binder.

Of course, the use of reforming catalysts containing precious metals generally requires pretreatment of the feedstock to be refined in the form of catalytic hydrogen treatment. In this way, nitrogen and sulfur compounds can be removed from the feedstock, which would otherwise significantly reduce the performance of the reforming catalyst.

The reforming step can be conveniently carried out under conventional reforming conditions. As a rule, the process is carried out at a temperature of 450ºC to 550ºC and a pressure of 3 to 20 bar. The reaction section intended for carrying out the reforming step can be conveniently divided into different stages or reactors.

The present invention will now be explained in more detail using the following example.

Example

A method according to the invention is carried out according to the flow diagram shown schematically in Figure 1.

A hydrocarbon-containing feedstock boiling largely in the gasoline range and having the properties listed in Table 1 is fed via a line 1 into a distillation column 2, where the feedstock is separated into a first fraction containing hydrocarbons in the C5-C6 range and a heavy fraction containing C6 and higher hydrocarbons. The light fraction is withdrawn via a line 3 and fed into an isomerization unit 4. The isomerate output obtained therefrom is withdrawn via a line 5 and fed into the gasoline blending pool 6, while a gaseous fraction is withdrawn via a line 7. The heavy fraction is withdrawn via a line 8 and fed into a separation zone 9 containing two molecular sieves 10 and 11.

Molecular Sieve No. 1 (10) is a commercially available zeolite with a pore size of 4.5 by 4.5 Å or less. Molecular Sieve 11, designated Molecular Sieve No. 2, has a pore size between 5.5 by 5.5 Å and 4.5 by 4.5 Å, but excluding 4.5 by 4.5 Å.

The first molecular sieve 10 adsorbs normal paraffins selectively over monoisoparaffins, diisoparaffins, other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons. A fraction containing the normal paraffins is withdrawn via a line 12. The separation discharge stream, which is largely freed from normal paraffins, is withdrawn via a line 13 and brought into contact with molecular sieve No. 2 (11). In this special sieve, monoisoparaffins are adsorbed, while diisoparaffins and other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons are adsorbed. Hydrocarbons are passed through the sieve without adsorption. A fraction containing monoisoparaffins is withdrawn via a line 14 and the remaining separation output (diisoparaffin fraction), now largely freed of normal paraffins and monoisoparaffins, is withdrawn via a line 15. The separation output containing the diisoparaffins is then fed to a distillation column 16 and separated there into a light fraction containing hydrocarbons in the C6-C10 range, which is fed to the gasoline mixing pool 6 via a line 17, and a heavy fraction containing C8 and higher hydrocarbons. The heavy fraction is withdrawn via a line 18 and then fed to a reforming reactor 19. Reforming takes place at a temperature of 498ºC, a pressure of 10.6 bar, a catalyst loading of 1.8 kg/kg/h and a hydrogen/feed ratio of 510 Nl/kg. The commercially available reforming catalyst contains platinum and tin on aluminum oxide. The fractions withdrawn via lines 12 and 14 are also processed in the reforming step. The reformate obtained is then withdrawn via a line 20 and introduced into a distillation column 21. In the distillation column 21, the reformate is separated into a gaseous fraction, a second light fraction containing C₅-C₆ hydrocarbons and a gasoline fraction. The gaseous fraction is removed via line 22, the second light fraction is processed via line 23 together with the first light fraction containing C₅-C₆ hydrocarbons, and the gasoline fraction is removed via line 24. The gasoline fraction is passed via line 24 to a separation zone 25 containing molecular sieves 26 and 27. Molecular sieve No. 3 (26) is a technical zeolite with a pore size of 4.5 by 4.5 Å or less. Molecular sieve 27, referred to as molecular sieve No. 4 has a pore size between 5.5 x 5.5 Å and 4.5 x 4.5 Å, but excluding 4.5 x 4.5 Å.

The first molecular sieve 26 selectively adsorbs normal paraffins over monoisoparaffins, diisoparaffins, cyclic paraffins and aromatic hydrocarbons. A fraction containing the normal paraffins is withdrawn via a line 28. The separation effluent stream, which is largely freed from normal paraffins, is withdrawn via a line 29 and brought into contact with molecular sieve No. 4 (27). In this special sieve, monoisoparaffins are adsorbed, while diisoparaffins and other multi-branched paraffins, cyclic paraffins and aromatic hydrocarbons are passed through the sieve without adsorption. The fraction containing monoisoparaffins is withdrawn via a line 30 and the remaining separation discharge (diisoparaffin fraction), now largely freed from normal paraffins and monoisoparaffins, is withdrawn via a line 31 and fed into the gasoline mixing pool 6. The fractions withdrawn via lines 28 and 30 are also processed in the reforming step.

100 parts by weight of the feedstock in line 1 yield the various product fractions in the following quantities:

17.7 parts by weight of light fraction (line 3)

82.3 parts by weight of heavy fraction (line 8)

22.5 parts by weight of isomerate fraction (line 5)

2.2 parts by weight of gaseous fraction (line 7)

16.8 parts by weight of normal paraffin fraction (line 12)

65.5 parts by weight of separation discharge stream (line 13)

16.4 parts by weight of monoisoparaffin fraction (line 14)

49.1 parts by weight of diisoparaffin fraction (line 15)

31.9 parts by weight of light fraction (line 17)

17.2 parts by weight of heavy fraction (line 18)

52.2 parts by weight of reformate fraction (line 20)

12.0 parts by weight of gaseous fraction (line 22)

7.0 parts by weight of light fraction (line 23)

33.2 parts by weight of gasoline fraction (line 24)

0.6 parts by weight of normal paraffin fraction (line 28)

32.6 parts by weight of separation discharge stream (line 29)

1.2 parts by weight of monoisoparaffin fraction (line 30)

31.4 parts by weight of diisoparaffin fraction (line 31).

In the gasoline blending pool 6, 3.8 parts by weight of butane were added to the gasoline received via a line 32. In this way, 89.6 parts by weight of a total gasoline with the highest permissible RVP specification were obtained.

The total gasoline obtained in gasoline blending pool 6 has the properties listed in Table 2.

It is easy to see from Table 2 that a very attractive gasoline can be obtained with the process according to the invention in terms of octane number and aromatics content, particularly benzene. Conventional refining processes produce gasolines with a considerably higher aromatics content, particularly benzene. Table 1 Table 2 Properties of gasoline:

Claims (7)

1. Process for the refinement of a hydrocarbon-containing feedstock boiling largely in the gasoline range, in which: a) the feedstock is subjected to a separation treatment whereby normal paraffins and, where appropriate, monoisoparaffins are separated from diisoparaffins; b) isolating therefrom a first separation effluent stream containing normal paraffins and optionally monoisoparaffins and a second separation effluent stream containing diisoparaffins; c) separating at least a portion of the second separation effluent stream into a light fraction containing hydrocarbons of the C6-C10 range and a heavy fraction containing C8 and higher hydrocarbons; and d) producing a reformate from at least part of the heavy fraction containing C8 and higher hydrocarbons in a reforming step. 2. Process according to claim 1, in which a fraction boiling in the range from 70 to 220°C is used as the feedstock. 3. Process according to claim 1 or 2, in which in step a) both normal paraffins and monoisoparaffins are separated from the diisoparaffins. 4. Process according to claim 3, in which in step a) the normal paraffins are first separated from the monoisoparaffins and diisoparaffins and then the monoisoparaffins are separated from the diisoparaffins. 5. A process according to any one of claims 1-4, wherein at least a portion of the reformate is subjected to a separation treatment, whereby normal paraffins and optionally monoisoparaffins are separated from diisoparaffins and whereby a first normal A hydrocarbon product stream containing paraffins and a second hydrocarbon product stream containing diisoparaffins are isolated. 6. Process according to claim 5, in which both the normal paraffins and the monoisoparaffins are separated from the diisoparaffins. 7. Process according to claim 6, in which firstly the normal paraffins are separated from the monoisoparaffins and diisoparaffins and then the monoisoparaffins are separated from the diisoparaffins.