GB2126246A - Preparation of motor spirit - Google Patents

Abstract

Motor spirit is made by (a) contacting C3 and/or C4 hydrocarbons with supported gallium dehydrocyclisation catalyst (b) isomerising C5 and/or C6 paraffins, (c) blending aromatic product from (a) and isomerisate from (b) with not more than 35% weight of straight run components. Motor spirit obtained by simple process from materials which can be separated from natural gas.

Description

SPECIFICATION Preparation of motor spirit This invention relates to a process for the production of motor spirit from natural gas and gas condensate.

Motor spirit is a liquid fuel having a combination of properties such that it is capable of being used as a satisfactory fuel in a spark ignition internal combustion engine supplied with a fuel air mixture by means of a carburettor. (Motor spirit can of course also be used in spark ignition engines provided with fuel injection means instead of a carburettor). The precise requirements which a motor spirit has to meet will depend upon the engine in which it is to be used. There are specifications for premium and regular grade motor spirit and these specifications are different in different parts of the world. However there are certain minimum standards which a motor spirit must meet if it is to have any prospect of being sold as such somewhere in the world.A liquid fuel is considered to be a motor spirit for the purposes of this specification if it has a volatility in the range of 36 to 70% volume distilled at 1000C, its vapour pressure does not exceed 89.6 kPa (13 psi), and it has a minimum octane number of 80 by the Research method. The volatility is measured in accordance with ASTM (American Society for Testing Materials) Test No D-86, and the vapour pressure is determined by the Reid method (ASTM D-323).

Even to meet this broad specification a complex mixture of components may be necessary. In practice in many countries more demanding specifications for motor spirit are laid down. Because of this, motor spirit is usually a blend of several components, produced in a refinery where the primary feedstock is crude oil. The majority of the refinery feedstocks used in preparing these components boil above ca. 1 00 C. Motor spirit components can include straight run distillate, catalytically cracked material, steam-cracked fractions and catalytically reformed products.

Natural gas is found in certain localities and is often produced in association with crude petroleum. It contains mostly methane which is a valuable fuel and/or chemical feedstock, but significant proportions of higher boiling material are also present which are separated during treatment of the gas. Amongst these are C3 and C4 fractions which are generally maintained as liquids under pressure and C5 and C6 fractions which are volatile liquids boiling below 1000C and form the major proportion of natural gas condensate. A heavier material, boiling above 1 000 C, is also frequently available as a relatively small part of the natural gas condensate.

It is desirable to produce motor spirit meeting the minimum specification given above from materials of the type which are available from the processing of natural gas by a simple combination of primary and secondary processes which do not require the complex combipation of processes needed for the production of motor spirit by the refining of crude oil. This would enable motor spirit to be produced at locations close to natural gas fields but which are remote from existing oil refineries, without the expense associated with constructing a full scale refinery capable of producing motor spirit. It would be even more desirable if motor spirit meeting the specifications of the most demanding markets for premium motor spirit could be produced from materials obtained from natural gas with the minimum amount of materials from other sources.

GB 2 031 014 discloses a process for producing gasoline from C3/C4 olefins. A complex combination of process steps is required which involves the steps of (1) separating C3 and C4 olefins (2) oligomerising C3 olefins (3) etherifying isobutene olefins and (4) alkylating the remaining C4 olefins. An external source of methanol is required for the etherification step. The process cannot handle saturated C3 and C4 materials such as are found in gas condensates.

The process is described as producing "gasoline". However the term "gasoline" is often used in a loose way to indicate products having a given boiling range rather than to mean a product capable of meeting motor spirit specifications. From the information given in the Example it is possible to determine the characteristics of the gasoline produced. The octane number is higher than is needed, but the volatility is likely to be excessive for a motor spirit.

The desirability of using CHIC4 hydrocarbons in the production of gasoline is mentioned in US 4 324 937. This discloses a process for making motor fuel blending stocks from propane and butane. A complex combination of individual process steps is used. A C3/C4 stream is (1) split into a C3 and a C4 stream, (2) the C3 is dehydrogenated, (3) the C4 stream is separated into normal butane and isobutane, (4) the isobutane is reacted with propylene from the dehydrogenation step to give C5 and higher hydrocarbons. No information is provided on the quality of the products produced or on their suitability for use in motor spirit. The process of US 4 324 937 involves using fractional distillation 1) to separate C3 and C4 hydrocarbons and 2) to separate n-butane and isobutane.Carrying out these separations on a large scale involves expensive equipment and high energy costs. The process of US 4 324 937 also involves an alkylation step using corrosive acid catalysts such as HF, which again is an expensive process to operate. The process of US 4 324 937 produces a product consisting essentially of isoparaffins and such products are usually regarded as only one component of a motor spirit. The patent does not allege that it makes motor spirit but only that is makes blending components.

We have now found a simple process for converting paraffin containing C3 to C6 hydrocarbons into higher boiling products which makes possible the production of acceptable motor spirit, and which can be operated so as to produce motor spirit meeting recognised specifications for high quality motor spirit.

According to the present invention the process for the production of motor spirit from paraffincontaining feedstocks consisting predominantly of hydrocarbons boiling in the range C3 to C5 comprises the step of a) contacting a feedstock consisting predominantly of C3 and/or C4 hydrocarbons with a supported gallium dehydrocyclodimerisation catalyst to give a product containing aromatic hydrocarbons b) contacting a feedstock consisting predominantly of C5 and/or C6 paraffins with a paraffin isomerisation catalyst to give an isomerised product, and c) blending the product containing aromatic hydrocarbons with the isomerised product and with not more than 35% by weight of straight run motor spirit blending components in proportions selected so as to give motor spirit.

By "straight run motor spirit blending components" we mean components separated from naturally occurring materials e.g. by distillation, as opposed to materials obtained by chemical conversion processes e.g. alkylation, dehydrogenation, isomerisation.

Persons of ordinary skill in the blending of motor spirit could not have predicted that the solution to the problem of producing motor spirit from materials of the type obtainable from natural gas was to produce a blend consisting mainly of products of dehydrocyclodimerisation and isomerisation. However once this idea is disclosed by this specification, persons skilled in gasoline blending will be able to select suitable proportions of the dehydrocyclodimerisation and isomerisation products to meet the motor spirit specification set out above.

We have already defined a broad specification for motor spirit in this specification. However in order to be saleable in more demanding markets the motor spirit must meet more restrictive specifications, e.g. those for premium and regular motor spirit. For the purpose of this specification a motor spirit is considered to be a premium motor spirit if it meets the following specifications: Research Octane Number; 97 minimum, with 'anti-knock' additives such as tetramethyi lead and 91.5 minimum, without lead 'anti-knock' additives Volatility; 43 to 65% volume evaporated at 1000C (ASTM) Vapour pressure; to be no more than 12.5 psi (87 kPa) by the Reid method of test.

A motor spirit is considered to be of regular grade if it meets the evaporation and vapour pressure specifications defined above for premium grade but with a lower minimum research octane number of 85 assuming addition of lead 'anti-knock' compounds.

By "motor spirit blending components" we mean materials which are intended to be used as fuel as opposed to those additives added in minor amounts to modify the behaviour of the fuel e.g. tetraethyl lead added to reduce knock.

It should be noted that although octane number can be increased by the addition of lead compounds, relatively high octane numbers can be obtained without the addition of lead compounds.

The step a) of converting C3 and/or C4 hydrocarbons into an aromatic containing product is a known process and is described for example in GB 1 561 590. Thus step a) may be carried out by bringing the hydrocarbons into contact at elevated temperatures e.g. 450O to 7000C over a catalyst composition comprising an aluminosilicate having gallium deposited thereon and/or an aluminosilicate in which cations have been exchanged with gallium ions. The alumino silicate preferably has a silica to alumina molar ratio of between 20:1 and 70:1.

Further details of methods of carrying out the process of step a) are given in the specifications of GB 1 561 590, the disclosure of which is incorporated by reference.

The process of step a) can be carried out with saturated and unsaturated feedstocks. However a particular advantage of the present invention is that it may be applied to paraffinic hydrocarbons separated from methane in the production of natural gas. The C3 and/or C4 saturated hydrocarbons may be supplemented by unsaturated C3 and/or C4 hydrocarbons if these are available. However, preferably the feed to step a) is a material consisting predominantly (at least 90% wt) of C3 and C4 paraffins boiling in the range -42.2 to -0.60C at atmospheric pressure.

The process of isomerising C5 and/or C6 paraffins is a well known one. An isomerisation process which may be used is disclosed in GB 953 1 89. Thus the isomerisation step may be carried out by contacting the C5/C6 paraffinic feedstock at a temperature below 200cm with a catalyst prepared by contacting a hydrogen containing alumina with a compound of general formula XYCCI2, where X and Y may be the same or different and are selected from H, Cl, Br, F or SCI, or where X and Y together may be O or S, under non-reducing conditions and at a temperature such that chlorine is taken up by the alumina without production of free aluminium chloride.

The feed to the isomerisation process preferably consists predominantly of C5 and/or C6 paraffins, and is most preferably a paraffinic material boiling in the range 0 to 750C at atmospheric pressure. Such materials are available from the treatment of natural gas to separate methane from other constituents.

Preferably the catalyst of stage (b) incorporates a platinum group metal, most preferably platinum itself.

Examples of the catalyst and process conditions employed in stage (b) are more fully described in British Patent specification 953189, the disclosures of which are also hereby incorporated into the present specification by reference.

If desired the Cs/C6 feedstock may be subjected to a conventional desulphurisation process.

Hydrogen for this process may be obtained as a by-product from stage (a).

Primary products from the separation of natural gas into its constituents, including natural gas condensate are particularly suitable feedstocks for the present invention.

Thus motor spirit can be prepared from natural components in a self containing system independent of a conventional oil refinery.

It is particularly preferred that any additional motor spirit blending components incorporated in the motor spirit are materials recovered from natural gas. Examples of motor spirit blending components which may be incorporated in the motor spirit are butane and "heavy condensate".

Butane may be obtained by taking a portion of the C3/C4 feed to the dehydrocyclodimerisation process and recovering butanes as required. The C3 and surplus C4 hydrocarbons can be passed on to the dehydrocyclisation step.

By "heavy condensate" we mean throughout this specification a material boiling predominantly above 1 OO"C at atmospheric pressure, which has been separated from natural gas.

It is possible by selecting appropriate ratios of components using blends consisting only of the products of the dehydrocyclodimerisation step a) and the isomerisation step b) to make products which meet the broad specification for motor spirit, although the octane number of the product may be higher than needed for the lowest quality grades i.e. regular motor spirit.

However it will generally be desirable to use additional blending components e.g. butane and/or heavy condensate in producing material to meet the more demanding specification for premium motor spirit.

In order to obtain the best properties in the resulting motor spirit it is preferred to blend the product of step (a) hereinafter called DHCD'ate (DHCD = dehydrocyclodimerisation) with the product of step (b), hereinafter called isomerisate, in weight ratios in the range 0.5 to 2.5, more preferably 1.0 to 2.0. The preferred blend ratios may depend on whether the motor spirit contains lead derivatives to improve octane number. Thus for a lead-containing motor spirit the preferred ratio of DHCD'ate and isomerisate may be in the range 0.8 to 2.0, while for a lead-free motor spirit it may be in the range 0.5 to 2.5.

It may be preferred to subject the DHCD'ate from step (a) to a benzene removal step to reduce the benzene content before the DHCD'ate is blended with the isomerisate. Low benzene content are desirable in motor spirit because benzene is toxic.

Where butanes are added the total amount is preferably not greater than 1 0% by total weight of motor spirit, preferably 37%. Where heavy condensate is added the quantity used is preferably 1 0-25% of the total weight of motor spirit.

The invention is illustrated with reference to the following example which gives the properties of three blends according to the invention.

EXAMPLE Blends were prepared from the materials listed below.

Cs/C6 Isomerisation product This was a material available from a commercial scale isomerisation process carried out using a catalyst consisting of a platinum containing chlorine treated alumina catalyst such as is disclosed in GB 953188.

The feedstock to such a process is typically a mixture of straight run pentanes and hexanes which has undergone conventional catalytic hydrotreatment to reduce its benzene and sulphur contents to acceptable levels for subsequent isomerisation. Operating conditions are typically temperatures in the range 120 to 1 600C and pressures up to 550 psig (38 bar g, 3.8 MPa).

The feedstock to the hydrotreatment stage comprised pentanes (53%wt), hexanes (44%wt) and the balance cyclic compounds such as benzene and cyclohexane. The desulphurised feedstock of very low benzene content was isomerised under the following conditions.

reaction temperature, 1 400C pressure, 39 bar (3.9 MPa) absolute pressure liquid hourly space velocity, 2 hydrogen to hydrocarbon molar recycle ratio, 1.5/1 Organic chloride was injected into the reactor feed throughout processing to maintain catalyst activity.

Naphtha A naphtha or benzine fraction distilling in the range 70 to 1 500C at atmospheric pressure was used. Material boiling in this range is often available in natural gas condensate. However as material from natural gas condensate was not available it was replaced by a petroleum distillate fraction.

Butanes The butanes used were a commercial mixture comprising normal butane (73 vol%) isobutane (21 vol%), and the balance propane and pentanes.

Dehydrocyclisation reaction product An aromatics-containing product was produced from a lower normal-paraffin feedstock at a reaction temperature of 5350C at 6 bar (0.6 MPa) absolute pressure and a liquid hourly space velocity (LHSV) of 2. The catalyst used was a gallium exchanged material produced by refluxing a crystalline aluminosilicate, such as Zeolite ZSM-8, with an aqueous acidic solution containing gallium ions. Three runs were carried out using n-butane as feedstock and two runs were carried out using propane.

Samples of the product from the three runs were blended. Half of the blended material was then distilled to remove benzene. The undistilled material is hereinafter identified as DHCD 1, and the distilled material is identified as DHCD 2.

The compositions of the blends and the results of distillation and octane number tests are given in Table 1. Qualities of DHCD 1 and 2 are given in Table 2.

TABLE 1

Blend No. 1 2 3 Blend Composition % vol (% wt) Butanes 4.0 (3.1) 4.0 (3.3) Straight Run Benzine - 11.0(10.7) 11.0(11.0) C,/C6 Isomerate 42.0(35.5) 39.0(33.0) 50.0(43.8) DHCD 1 50.0(56.7) - DHCD 2 - 46.0(53.2) 35.0(41.9) Density at 15 C kg/l 0.7660 0.7653 0.7392 Distillation IBP C 35.0 35.0 31.0 2% vol recovered at C 43.0 41.0 37.0 5 " " " C 48.0 47.0 41.0 10 " " " C C 53.0 52.0 46.0 20 " " " C 59.0 62.0 52.0 30 " " " C 67.0 74.0 59.0 40 " " " C 76.0 89.0 68.0 50 " " " C 88.0 105.0 81.0 60 " " " C 102.0 115.0 99.0 70 " " " C 112.0 121.0 115.0 80 " " " C 122.0 130.0 123.0 90 " " " C 139.0 157.0 138.0 FBP C 225.0 230.0 223.0 Recovery % vol 97.5 97.0 97.0 Residue %vol 1.0 1.0 1.5 Loss %vol 1.5 2.0 1.5 Recovered at 70 C % vol 34.0 27.0 42.5 " " 100 C % vol 59.0 46.5 60.5 " 140 C % vol | 90.5 | 86.0 | 91.0 RVP psi (kPa) 9.8(68) 10.5(72) 11.1(77) Lead content as TML gPb/l 0.15 0.15 0.0 Octane Ratings Research Method 97.8 97.4 92.4 Motor Method 89.7 89.4 84.3 Research Method (100 C) 89.8 88.8 Benzene Content (calc.) % wt 11.8 0.1 0.1 IBP = initial boiling point FBP = final boiling point RVP = Reid Vapour Pressure TML = tetramethyl lead TABLE 2

Blending Component DHCD 1 DHCD 2 Density at 150 0.8693 0.8850 Distillation IBP "C 54.0 114.0 2% vol recovered at C 85.0 116.0 5 C 95.0 117.0 10 "C 100.0 118.0 20 "C 104.0 119.0 30 C 106.0 120.0 40 "C 110.0 121.0 50 "C 114.0 123.0 60 C 120.0 126.0 70 "C 126.0 132.0 80 C 135.0 141.0 90 "C 164.0 170.0 FBP "C 245.0 245.0 Recovery % vol 98.5 99.5 Residue % vol 0.5 0.5 Loss %vol 1.0 - Recovered at 70 C % vol 0.5 ,,1000C %vol 10.0 - " " 140 C % vol 83.0 79.0 RVP psi(kPa) 6.9(47.5) 0.7(4.8) Lead content as TML gPb/l 0.15 0.15 Octane Ratings Research Method 118.9 119.7 Motor Method 103.0 107.7 Benzene Content % wt 23.6 0.2

Claims (7)

1. A process for the production of motor spirit from paraffin-containing feedstocks consisting predominantly of hydrocarbons boiling in the range C3 to C6 comprises the steps of a) contacting a feedstock consisting predominantly of C3 and/or C4 hydrocarbons with a supported gallium dehydrocyclodimerisation catalyst to give a product containing aromatic hydrocarbons, b) contacting a feedstock consisting predominantly of C5 and/or C6 paraffins with a paraffin isomerisation catalyst to give an isomerised product, and c) blending the product containing aromatic hydrocarbons with the isomerised product and with not more than 35% by weight of additional straight run motor spirit blending components in proportions selected so as to give a motor spirit.

2. A process according to claim 1 wherein the motor spirit consists essentially only of the products from steps a) and b).

3. A process according to any one of the preceding claims wherein the proportions of the blend are selected so as to give a premium motor spirit.

4. A process according to any one of the preceding claims wherein the C3 and/or C4 feedstocks consists predominantly of paraffins.

5. A process according to any one of the preceding claims wherein benzene is removed from the product from step a) before it is blended to give a motor spirit.

6. A process according to any one of the preceding claims wherein any additional motor spirit blending component consist only of butane or heavy condensate, separated from natural gas condensate.

7. A process according to any one of the preceding claims wherein the isomerisation step is carried out by contacting the C5/C6 paraffinic feedstock at a temperature below 2000C with- a catalyst prepared by contacting a hydrogen-containing alumina with a compound of general formula XYCCI2 where X and Y may be the same or different and are selected from H, CI, Br, F, or SCI or where X and Y together may be O or S, under non-reducing conditions and at a temperature such that chlorine is taken up by the alumina without production of free aluminium chloride.