JP2005171246A - Method for producing steam cracker sulfur-containing feedstock - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing steam cracker sulfur-containing feedstock from a natural gas by combining a paraffinic feedstock such as obtained by a Fischer-Tropsch process with a sulfur-containing feedstock from another feed source. <P>SOLUTION: The method for producing a sulfur-containing steam cracker feedstock from a crude natural gas comprises the steps of (a) separating a sulfur-containing liquid gas field condensate fraction from a crude natural gas, (b) dividing the liquid gas field condensate into a high-boiling fraction and a low-boiling fraction, (c) producing a carbon monoxide/hydrogen mixture from the gas obtained from step (a), (d) producing a paraffin product by performing a Fischer-Tropsch reaction by using the carbon monoxide and the hydrogen from step (c), and (e) obtaining the sulfur-containing steam cracker feedstock of a sulfur content of 50 to 1,000 ppm by blending at least part of the paraffin product with the low-boiling fraction obtained in step (b). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

FIELD OF THE INVENTION The present invention produces a steam cracker sulfur-containing feedstock from natural gas by combining paraffinic feedstocks such as those obtained by the Fischer-Tropsch process with sulfur-containing feedstocks from other sources. It is aimed at how to do.

Background of the Invention In the field of steam cracking, it is well known to add sulfur to the feedstock to reduce coke formation. Coke formation in a steam cracking furnace tube is formed in principle by two mechanisms: a pyrolysis reaction and a catalytic dehydrogenation reaction. The pyrolysis reaction is minimized by lowering the operating pressure, using a high steam to hydrocarbon ratio on the order of 30% to 60%, and preventing the possibility of excessive tube metal temperatures and non-volatile feedstocks entering the hot zone. Become. In order to withstand high tube metal temperatures of 2100 ° F., alloys with a high nickel and chromium content, eg nickel 35% and chromium 25%, are used. These metals catalyze the dehydrogenation reaction and need to be passivated. Sulfurization is the usual solution for passivation. For steam cracking operators, it is normal practice to inject a coke inhibitor immediately after the decoking operation. This is the point at which the catalytic activity of the tube wall metal is highest. Before supplying the hydrocarbon raw material to the furnace, DMS or DMDS is injected into the coil together with water vapor to form a sulfide film. For typical liquid feeds, the sulfur content in the feed is usually sufficient to maintain the sulfide level during the actual steam cracking process. If sufficient sulfur is not originally present in the raw material, sulfur may be added to the raw material. In this case, sulfur is probably added from 20 ppm to 100 ppm to minimize coke and CO production.

  It is also well known to use naphtha paraffin products such as those obtained by the Fischer-Tropsch process as a steam cracker feed. For example, “The Markets for Shell Middle Distillate Synthesis Products”, Presentation of Peter J. et al. A. Tijm, Shell International Gas Ltd. , Alternative Energy '95, Vancouver, Canada, May 2-4, 1955, page 5, SMDS naphtha, ie, the Fischer-Tropsch derived naphtha fraction of the shell MDS process, is used as a steam cracker feedstock, for example in Singapore It has been said.

  Since Fischer-Tropsch derived products contain almost undetectable levels of sulfur, sulfur must be added to this feed before it can be used as a steam cracker feed mixture. Sulfur can be added by adding a sulfur additive such as dimethyl disulfide (DMDS), or using a Fischer-Tropsch feed, 'Preliminary Survey on GTL Business Based on SMDS technology, June 2001, JETRO, Section 6. 2.3. Can be blended with high sulfur content materials as described in detail in.

  The addition of sulfur to the Fischer-Tropsch derived feed of the steam cracking process is also described in a more recent patent publication US-A-2003 / 0135077. In this publication, a low sulfur Fischer-Tropsch derived naphtha is produced remotely, the product is transported to a steam cracker, and then the naphtha is used before being used as a steam cracker feed. The addition of a sulfur compound is described.

WO-A-9937736 discloses a process for reducing sulfur levels by hydrotreating a gas field condensate separated from crude natural gas. According to this publication, sulfur needs to be removed because it can be used as a fuel or blended with other hydrocarbons and used as a raw material for chemical processes.
The disadvantage of WO-A-9937736 is that it requires a separate hydroprocessing unit.
WO-A-9937736 US-A-4372925 “The Markets for Shell Middle Distillate Synthesis Products”, Presentation of Peter J. et al. A. Tijm, Shell International Gas Ltd. , Alternative Energy '95, Vancouver, Canada, May 2-4, 1955, page 5. Preliminary Survey on GTL Business Based on SMDS technology, June 2001, JETRO, section 6.2.3. Gas Purification, Part 5 / Arthur Kohl and Richard Nielsen, 1997, Gulf Publishing Company, ISBN 0-88415-220-0 Chapter 1

SUMMARY OF THE INVENTION It is an object of the present invention to make more efficient use of a high sulfur content gas field condensate separated from crude natural gas so that no separate hydrotreatment is required.

This object is achieved by the following method.
(A) separating the sulfur-containing liquid gas field condensate fraction from the crude natural gas;
(B) dividing the liquid gas field condensate into a high boiling fraction and a low boiling fraction;
(C) producing a mixture of carbon monoxide and hydrogen from the gas obtained in step (a);
(D) a step of producing a paraffin product by carrying out a Fischer-Tropsch reaction using carbon monoxide and hydrogen in step (c), and (e) a paraffin product or a part thereof, step (b) Blending with the low-boiling fraction obtained in step 1 to obtain a sulfur-containing steam cracker feedstock with a sulfur content of 50-1000 ppm,
A process for producing a sulfur-containing steam cracker feedstock from crude natural gas.

  Applicants have found that, according to the method of the present invention, gas field gas condensate is superior to meet the standards for direct use, improving the quality of the Fischer-Tropsch product after a simple separation step, for example a distillation step. It has been found that it can be used to form a steam cracker feedstock. This is advantageous because it saves tank storage facilities at the Fischer-Tropsch manufacturing site and can be transported to overseas customers without dividing one product into two.

DETAILED DESCRIPTION OF THE INVENTION Step (a) can be carried out according to well-known methods. Usually, crude natural gas is obtained from underground wells. The gaseous hydrocarbons of 1 to 5 carbon atoms are usually separated from C ₅ + hydrocarbons after the gas has reached the surface, for example in a so-called slag trap. The liquid product thus obtained, also referred to as gas field condensate, can contain very high levels of sulfur, for example greater than 1500 ppm and even greater than 1900 ppm. Usually, the lower sulfur level is 1000 ppm. The natural gas from which the gas field condensate has been separated is said to be prepurified natural gas.

The liquid condensate obtained in step (a) has a very high final boiling point, even above 300 ° C, while at the same time the majority of the product has a boiling point below 300 ° C. By separating and removing the high-boiling fraction in, for example, a flushing step or a distillation step, a low-boiling fraction containing a sulfur compound and meeting the boiling range requirements for a steam cracker feed is obtained. This fraction is useful as a steam cracker feed and does not require further desulfurization treatment to be used as a blending component to obtain a mixture in step (e).
The final boiling point of this low boiling fraction isolated from gas field condensate is preferably 120-230 ° C, more preferably 140-215 ° C. Initial boiling point, consistent with the C ₅ hydrocarbons still present in the liquid gas field condensate. The final boiling point of the low boiling fraction depends on the sulfur content in the gas field condensate, the blend ratio of the sulfur containing low boiling fraction to the Fischer-Tropsch product in step (e), and the desired sulfur level of the resulting mixture. May change. The optimum operation may be determined by a conventional method. The high-boiling fraction rich in sulfur compounds and organic acids obtained in step (b) may be further processed in so-called local condensate refineries. The sulfur content of the low-boiling fraction is preferably 200 to 6000 ppm.

  Prior to performing step (c), most of the sulfur is separated from the prepurified natural gas obtained in step (a) by various possible methods. Sulfur is preferably removed from natural gas by the so-called absorbent type method. These well-known methods involve contacting natural gas with a liquid mixture containing a physical absorbent and a chemical absorbent. In this way, the gas mixture is continuously treated in two steps at atmospheric pressure with two different liquid mixtures containing a physical absorbent and a chemical absorbent. Conventional chemical absorbents are tertiary amines, especially tertiary amines having at least one hydroxyalkyl group. Triethanolamine, diethylethanolamine (DEMEA) and methyldiethanolamine (MDEA) are very suitable. Typical physical absorbents are propylene carbonate N-methylpyrrolidone, dimethylformamide, dimethyl ether of polyethylene glycol, tetraethylene glycol dimethyl ether and sulfolane. Examples of such methods are found in textbooks such as US-A-4372925 and Gas Purification, Volume 5 / Arthur Kohl and Richard Nielsen, 1997, Gulf Publishing Company, ISBN 0-88415-220-0. Has been described.

The hydrocarbon compound having 3 or more carbon atoms is preferably separated from natural gas before being converted to synthesis gas. Separation is preferably performed by cooling natural gas to temperature and pressure conditions at which these hydrocarbons liquefy. In this way, the liquid product can be easily separated from the natural gas. Cooling can be preferably performed by indirect heat exchange with liquid nitrogen. The liquid nitrogen may preferably be the excess nitrogen obtained when separating air to obtain pure oxygen used in step (c). A more preferred method is to reduce the pressure, separate the condensed C ₃ + hydrocarbons, and then optionally increase the pressure level before using natural gas to make synthesis gas. The gas is reduced from a pressure above 50 bar to a pressure below 40 bar, preferably below 30 bar. After separation of the liquid hydrocarbon, the gas pressure is increased above 50 bar, preferably to a level of 50-80 bar. The C ₃ and C ₄ hydrocarbons thus obtained may be blended with the LPG product isolated from the product of step (d). The C ₅ + hydrocarbon is preferably sent to step (e) and blended with the fraction mentioned in step (e) to obtain more steam cracker feed.

The synthesis gas to be used for the Fischer-Tropsch reaction is produced in step (c) from the gas obtained in step (a) by partial oxidation and / or steam / methane reforming.
Carbon dioxide and / or water vapor may be introduced into the partial oxidation process to adjust the H ₂ / CO ratio in the synthesis gas. The H ₂ / CO ratio of the synthesis gas is suitably 1.3 to 2.3, preferably 1.6 to 2.1. If desired, steam methane reforming may produce (small) additional amounts of hydrogen, preferably in combination with a water gas shift reaction. The additional hydrogen may also be used in other methods, such as hydrocracking.

In other embodiments, the H ₂ / CO ratio of the synthesis gas obtained in the catalytic oxidation process may be reduced by removing hydrogen from the synthesis gas. This can be done with conventional techniques such as pressure swing adsorption or cryogenic methods. A preferred choice is separation by membrane technology. Part of the hydrogen may be used in the hydrocracking process of the heaviest hydrocarbon fraction of the Fischer-Tropsch reaction.

The synthesis gas obtained by the method as described above, usually having a temperature of 900 to 1400 ° C., is preferably 100 to 500 ° C., preferably 150 to 450 while preferably generating power, for example, power in the form of water vapor. Cool to a temperature of ° C, preferably 300-400 ° C. Further cooling to a temperature of 40 to 130 ° C., preferably 50 to 100 ° C., is carried out with a conventional heat exchanger, in particular a tubular heat exchanger. A guard bed may be used to remove impurities from the synthesis gas. In particular, certain catalysts may be used to remove all trace amounts of HCN and / or NH ₃ . Trace amounts of sulfur that may still be present in the gas used in step (c) may be removed by adsorption using iron and / or zinc oxide.

The purified gaseous mixture based on hydrogen, carbon monoxide and optionally nitrogen is contacted with a suitable catalyst in the catalytic conversion stage, usually forming a liquid hydrocarbon.
In step (d), the catalyst used for catalytic conversion of a mixture comprising hydrogen and carbon monoxide to hydrocarbon is known in the art and is commonly referred to as a Fischer-Tropsch catalyst. The catalyst used in this process often contains a Group VIII metal of the Periodic Table of Elements as a catalytically active component. Particularly catalytically active metals include ruthenium, iron, cobalt and nickel. In view of the heavy Fischer-Tropsch hydrocarbons that can be produced, cobalt is the preferred catalytically active metal. As mentioned above, the preferred hydrocarbonaceous feedstock is natural gas or associated gas. With these feedstocks, cobalt is a very good Fischer-Tropsch catalyst, since synthesis gas with a H ₂ / CO ratio of about 2 is usually obtained and the user ratio for this type of catalyst is also about 2.

The catalytically active metal is preferably supported on a porous carrier. The porous support can be selected from any suitable refractory metal oxide or silicate known in the art or combinations thereof. Examples of certain preferred porous supports include silica, alumina, titania, zirconia, ceria, gallia and mixtures thereof, particularly silica, alumina and titania.
The amount of catalytically active metal on the support is preferably in the range of 3 to 300 parts by weight, more preferably 10 to 80 parts by weight, especially 20 to 60 parts by weight per 100 parts by weight of the support material.

  If desired, the catalyst may also contain one or more metals or metal oxides as promoters. Suitable metal oxide promoters can be selected from Group IIA, IIIB, IVB, VB and VIB of the Periodic Table of Elements, or actinides and tantanides. In particular, oxides of magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, titanium, zirconium, hafnium, thorium, uranium, vanadium, chromium and manganese are very suitable promoters. Particularly preferred metal oxide promoters for the wax production catalyst used in the present invention are manganese and zirconium oxides. Suitable metal promoters may be selected from groups VIIB or VIII of the periodic table. Rhenium and Group VIII noble metals are particularly preferred, with platinum and palladium being particularly preferred. The amount of promoter present in the catalyst is suitably in the range of 0.01 to 100 parts by weight, preferably 0.1 to 40 parts by weight, more preferably 1 to 20 parts by weight per 100 parts by weight of the support. The most preferred promoter is selected from vanadium, manganese, rhenium, zirconium and platinum.

  The catalytically active metal and promoter, if present, may be deposited on the support material by any suitable process, such as impregnation, kneading and extrusion. After depositing the metal and, if appropriate, the promoter on the carrier material, the load carrier is usually calcined. The effect of this calcining treatment is to remove crystal water, decompose volatile decomposable products, and convert organic and inorganic compounds to oxides. After calcination, the resulting catalyst may be activated by contacting it with hydrogen or a hydrogen-containing gas, usually at a temperature of about 200-350 ° C. Other methods of making a Fischer-Tropsch catalyst include a kneading / mulling step and, in many cases, an extrusion, drying / calcination and activation step.

The catalytic conversion process may be performed under conventional synthetic conditions known in the art. The catalytic conversion may usually be carried out at a temperature in the range of 150 to 300 ° C, preferably 180 to 260 ° C. The total pressure in the catalytic conversion process is usually in the range of 1 to 200 bar absolute pressure, more preferably 10 to 70 bar absolute pressure. In the catalytic conversion process, in particular C ₅ + hydrocarbons are formed in an amount of more than 75% by weight, preferably more than 85% by weight. Depending on the catalyst and conversion conditions, the amount of heavy wax (C ₂₀ +) is 60% by weight or less, sometimes 70% by weight or less, and sometimes even 85% by weight or less. Preferably a cobalt catalyst is used, the H ₂ / CO ratio is low (especially 1.7 or even lower), the temperature is low (190-240 ° C.) and optionally combined with high pressure . In order to avoid the formation of coke, the H ₂ / CO ratio is preferably at least 0.3. In order to obtain a product having at least 20 carbon atoms, the ASF-α value (Anderson-Schulz-Flory chain growth factor) is at least 0.925, preferably at least 0.935, more preferably at least 0.945, and still more It is particularly preferred to carry out the Fischer-Tropsch reaction under conditions such that it is preferably at least 0.955. Fischer-Tropsch hydrocarbon _{stream, C 30} + at least 40 wt%, preferably at least 50 wt%, more preferably comprises at least 55 wt%, and _C 60 + _{/ C 30} + weight ratio of at least 0.35 , Preferably at least 0.45, more preferably at least 0.55.

Preferably, a Fischer-Tropsch catalyst is used which gives a substantive amount of paraffin, more preferably a substantially unbranched paraffin. The most preferred catalyst composition for this purpose is a cobalt-containing Fischer-Tropsch catalyst. Such catalysts are described in the literature (see eg AU 698392 and WO 99/34917).
The Fischer-Tropsch process may be a slurry FT process or a fixed bed FT process, in particular a multi-tube fixed bed process.

The paraffin product may be isolated by distillation directly from the product obtained in step (d). Such fractions are preferably first hydrogenated to remove olefins and oxygenated compounds that may adversely affect the properties of the blend obtained for the steam cracker feed. The paraffin product may be isolated from the effluent of the hydrocracking process performed on all or part of the product obtained in step (d). Such paraffin products are rich in isoparaffins. The ratio of isoparaffin to normal paraffin in the paraffin product is less than 0.5, preferably less than 0.3.
Paraffin product contains more than compound 90 wt% of C _{5 to} to compounds of boiling point 370 ° C.. More preferably, paraffinic product has a boiling point in the range of naphtha, preferably comprises a compound from the compounds from C ₅ begins to compounds having a boiling point of 204 ° C. more than 90% by weight.

The paraffin product is blended in step (e) with the liquid condensate fraction obtained in step (b). The weight ratio of the product of step (d) to the product of step (b) is preferably 30: 1 to 5: 1. The resulting blend preferably has the following properties:
Specific gravity 0.65-0.74,
Saybolt chromaticity +20,
Unsaturates <1% by volume,
Paraffin content 65% to 100% by volume,
Iso-normal paraffin ratio less than 0.5,
Sulfur content 50-650 ppm, preferably 100-650 ppm,
Final boiling point 150-204 ° C,
Reed vapor pressure at 37.8 ° C., 13 psi or less,
Have

  The present invention is also directed to the use of the blends obtained by the process of the present invention as a steam cracker feed for the production of lower olefins, especially propylene and / or ethylene.

FIG. 1 illustrates the method of the present invention. In the slag trap 1, the gas field condensate 12 is separated from the natural gas 11 containing sulfur compounds. In the separator 2, the gas field condensate 12 is separated into a low-boiling fraction 13 and a high-boiling fraction 14. Fraction 14 is fed to any condensate refinery. In the sulfinol unit 4, sulfur is removed from the natural gas 15 with little condensate. In the separation unit 5, C ₃ + hydrocarbons 17 are separated from the gas 16 having a small amount of sulfur. The hydrocarbon 17 is further divided by the distillation unit 6 into a C ₃ and C ₄ stream 19 and a stream 18 based on C ₅ + hydrocarbons.

  The purified gas 20 is used in the synthesis gas production unit 7 where a synthesis gas 21 is obtained. This synthesis gas 21 is used as a feedstock in the Fischer-Tropsch reaction step 8, where a paraffinic product 22 is obtained. This product is separated into various fractions below the boiling point of naphtha fraction 24 (fraction 23) and above the boiling point (fractions 25, 26). In the mixing unit 10, this naphtha fraction 24 is mixed with the fractions 13, 18 to obtain a steam cracker feed 27 according to a preferred embodiment of the present invention.

It is process drawing of this invention method.

Explanation of symbols

1 Slag trap 2 Separator 4 Sulfinol unit 5 Separation unit 6 Distillation unit 7 Syngas production unit 8 Fischer-Tropsch reaction process 10 Mixing unit 11 Natural gas containing sulfur compounds 12 Gas field condensate 13 Low boiling fraction 14 High Boiling fraction 15 Natural gas with low condensate 16 Gas with low sulfur 17 C ₃ + Hydrocarbon 18 C ₅ + Hydrocarbon-based stream 19 C ₃ and C ₄ stream 20 Purified gas 21 Syngas 22 Paraffinic product 23 Fraction below the boiling point of the naphtha fraction 24 Naphtha fraction 25 Fraction above the boiling point of the naphtha fraction 26 Fraction above the boiling point of the naphtha fraction 27 Steam cracker feedstock

Claims (9)

(A) separating the sulfur-containing liquid gas field condensate fraction from the crude natural gas;
(B) dividing the liquid gas field condensate into a high boiling fraction and a low boiling fraction;
(C) producing a mixture of carbon monoxide and hydrogen from the gas obtained in step (a);
(D) a step of producing a paraffin product by carrying out a Fischer-Tropsch reaction using carbon monoxide and hydrogen in step (c), and (e) a paraffin product or a part thereof, step (b) Blending with the low-boiling fraction obtained in step 1 to obtain a sulfur-containing steam cracker feedstock with a sulfur content of 50-1000 ppm,
A process for producing a sulfur-containing steam cracker feedstock from crude natural gas.   The method according to claim 1, wherein the low-boiling fraction obtained in step (b) has a sulfur content of 200 to 6000 ppm.   The method according to claim 1 or 2, wherein the sulfur content of the crude natural gas exceeds 0.5% by volume.   The process according to any one of claims 1 to 3, wherein the ratio of isoparaffin to normal paraffin in the paraffin product is less than 0.5, preferably less than 0.3. The paraffinic product A method according to any one of claims 1 to 4, the compound of the compound of C ₅ to compounds of boiling point 370 ° C. containing more than 90%. The paraffinic product has a boiling point of naphtha range, preferably contains a compound to a compound of boiling point 204 ° C. 90 wt% starting from a compound of C _5, the paraffinic product obtained in step (c) 6. A process according to claim 5, which is a boiling fraction.   The process according to any one of claims 1 to 6, wherein the sulfur content of the steam cracker feedstock exceeds 50 ppm, preferably> 100 ppm. The steam cracker feedstock has the following characteristics:
Specific gravity 0.65-0.74,
Saybolt chromaticity +20,
Unsaturates <1% by volume,
Paraffin content 65% to 100% by volume,
Iso-normal paraffin ratio less than 0.5,
Sulfur content 50-650 ppm,
Final boiling point 150-204 ° C,
Reed vapor pressure at 37.8 ° C., 13 psi or less,
The method according to claim 1, comprising:   The method of using the blend obtained by the method of any one of Claims 1-8 as a steam cracker feedstock for a lower olefin manufacture.

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