US3660272A - Gasoline production from wellhead natural gas - Google Patents

Abstract

A PROCESS FOR THE PRODUCTION OF GASOLINE FROM WELLHEAD NATURAL GAS IS DISCLOSED IN WHICH LIGHT HYDROCARBON COMPOUNDS FOUND IN WELLHEAD NATURAL GAS ARE CONVERTED BY AN INTEGRATED PROCESS OF OPERATIONS INTO SALABLE GASOLINE AND NATURAL GAS PRINCIPALLY COMPOSED OF METHANE.

Description

GASOLINE PRODUCTION FROM WELLHEAD NATURAL GAS Filed Dec. 50, 1970 G. W. FRICK May 2, 1972 3 Sheets-Sheet 1 m 29 6%. Q .5 E553 no. v:

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GEORGE W. FRICK, INVENTOR.

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GASOLINE PRODUCT GEORGE W. ERICK INVENTOR.

BY WW ATTORNEY.

United States Patent 3,660,272 GASOLINE PRODUCTION FROM WELLHEAD NATURAL GAS George W. Frick, I-Iightstown, N.J., assignor to Cities Service Oil Company, Tulsa, Okla. Filed Dec. 30, 1970, Ser. No. 102,687 Int. Cl. Cg 39/00 US. Cl. 208-93 5 Claims ABSTRACT OF THE DISCLOSURE A process for the production of gasoline from wellhead natural gas is disclosed in which light hydrocarbon compounds found in wellhead natural gas are converted by an integrated process of operations into salable gasoline and natural gas principally composed of methane.

BACKGROUND OF THE INVENTION The present invention relates to the production of gasoline from wellhead natural gas. More particularly, the process of the present invention is for the production of gasoline suitable for use as motor fuel from compounds found in wellhead natural gas.

Usually, the low boiling range of light hydrocarbon intermediates, including ethane, propane, normal butane, isobutane and natural gasoline precludes or limits the use of these components directly as motor fuel. Ethane, propane, and butane tend to be used as petrochemical feedstocks or as a source of household bottled gas. In addition, the octane quality of natural gasoline, the C and higher boiling hydrocarbons, is such that the material cannot normally be utilized as a premium motor fuel component. In remote oil and gas producing regions light hydrocarbon compounds are difficult to dispose of profitably. It is desirable in such situations that the light hydrocarbon intermediates from the wellhead natural gas be utilized profitably instead of being flared or used as refinery fuel. Therefore, what is required is a process by which the light hydrocarbon compounds contained within wellhead natural gas may be converted to a salable gasoline product.

It is an object of the present invention to provide a process for the profitable utilization of light hydrocarbons found in wellhead natural gas.

It is a further object of the present invention to provide an integrated series of processes for the separation of methane and the upgrading of ethane and heavier hydrocarbons into a salable gasoline product.

With these and other objects in mind, the present invention can be more fully understood by referral to the accompanying drawings and following description:

SUMMARY OF THE INVENTION The objects of the present invention are accomplished by a process for the conversion into gasoline of the light hydrocarbons contained within wellhead natural gas. The process comprises fractionation of the wellhead natural gas into a C and lighter gas fraction and a C and higher liquid fraction. The C and lighter gas fraction is then separated into a C and lighter gas fraction and a C liquid fraction. The ethane and propane contained in the C and lighter gas fraction is cryogenically separated into a methane rich pipeline gas product and a condensed ethane and propane stream. The ethane/propane stream is then pyrolized into olefins and methane with the methane being separated therefrom and added to the pipeline gas product. The C fraction from the debutanizing process is fed to a de-isobutanizing unit to produce a normal butane stream which is sent to gasoline blending and an isobutane stream which is subjected to dehydro- 3,660,272 Patented May 2, 1972 genation to form an isobutane and isobutene product mixture. The olefins produced in the pyrolysis step are then reacted with isobutane to produce a lean alkylate product which is then de-butanized in the de-isobutanization vessel previously described.

Further modifications upon the process for the converslon of light hydrocarbons contained in the wellhead natural gas may comprise separating the C and heavier hydrocarbons produced from the pyrolysis process and introducing these C and heavier hydrocarbons with those contained within the C and heavier liquid fraction obtained from the fractionation process into a catalytic reforming unit to form a C and lighter hydrocarbon fraction, which is recycled to the fractionating step for further separation, and a reformate for gasoline blending. The process also may comprise withdrawing a C fraction from the fractionating process, separating isopentanes from the C fraction to be added to the gasoline inventory while introducing the normal pentanes from this fraction into the pyrolysis unit. The ethylene produced from the pyrolysis unit may be separated and introduced with a portion of the isobutane extracted from the de-isobutanization process into an alkylation unit to produce an alkylated isobutane product which is then reinjected into the de-isobutanization process. The process may further comprise extracting normal butane from the de-isobutanization process, isomerizing the normal butane and reintroducing the isomerized normal butane into the de-isobutanization process.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention may be more fully understood by referral to the accompanying drawings in which:

FIG. 1 represents the basic process of the present invention for the conversion of light hydrocarbons contained in a wellhead natural gas to pipeline natural gas and gasoline products; and

FIG. 2, consisting of 2a and 211, represents the integrated use of various refinery processes as presented in the present invention for the conversion of hydrocarbons contained in a wellhead natural gas into pipeline natural gas and gasoline products.

DETAILED DESCRIPTION OF THE INVENTION As disclosed, the present invention is a process for the production of gasoline from natural gas and is particularly useful in remote areas Where the light hydrocarbon compounds found in natural gas do not have a ready market. Accordingly, in the present invention production of gasoline from natural gas is performed by con verting and separating the C and higher hydrocarbons contained in the natural gas to alkylates and reformates which are desirable as high octane motor fuel components.

The C through C natural gas liquid fraction recovered from natural gas normally consists essentially of saturated hydrocarbons, for example ethane, propane, isobutane, and normal butane. Natural gasoline fractions recovered from natural gas typically comprise mostly C to C hydrocarbons and contain substantial quantities of both straight chain, branched chain and ring types. In use as gasoline, it is desirable that as much as possible of the natural gasoline fraction be in the branched chain or aromatic form. Accordingly, the natural gasoline fraction recovered from natural gas is preferably treated first to separate isomers from straight chain hydrocarbons and then to isomerize and reform the straight chain hydrocarbons into the desired branched chain and aromatic hydrocarbons. Therefore, the process of the present invention both upgrades the C to C hydrocarbons into longer chain molecules which may be utilized in high octane gasoline blends and also upgrades the C to C hydrocarbons contained within the nautral gas liquid fraction such that a high octane gasoline product is produced with a natural gas pipeline product and no intermediate light hydrocarbons.

In the process for the conversion of light hydrocarbons contained in a wellhead natural gas, the initial step of the process comprises the fractionating of the wellhead natural gas into a C and lighter hydrocarbon gas fraction and C and heavier hydrocarbon liquid fraction. In general, a material balance must be calculated for each individual wellhead natural gas stream to be treated so as to determine the amount of refiux heat required, the number of plates in the fractionation column required and the total thermal requirements for the separation desired. As fractionation columns and related equipment are mechanical devices for repeatedly establishing equilibrium between an ascending vapor and descending liquid for the continuous separation of the two phases, a complete separation of the two phases must be incorporated in any successful design. The number of plates and reflux ratio for a fractionation column may be designed so as to give a specific reid vapor pressure gasoline therefrom. In general, the fractionation column will have from 50 to 200 plates within the distillation tower. The reformate therefrom containing C and heavier hydrocarbons is blended into a finished gasoline product. The reid vapor pressure of the gasoline may be adjusted by the addition of sufiicient butane or other low boiling materials, for its intended uses.

The debutanizing of the gas fraction from the overhead of the fractionation column is accomplished in a debutanization fractionation column generally having from 25 to 100 plates and using a reflux ratio in the range of 2 to 10. During debutanization, the C hydrocarbons are removed from the fractionation column and sent to the deisobutanizer, while the overhead constituents from the debutanizer of the C and lighter hydrocarbon gas fraction is subjected to demethanization in a cryogenic light ends recovery unit which may consist of but is not restricted to a molecular sieve packed fractionating column operating at cryogenic temperatures so as to remove the ethane and propane hydrocarbons therefrom and produce a pipeline, methane rich gas product.

The ethane and propane from the demethanization unit are converted to polyolefins in accordance with the present invention. The conversion to an olefinic material is accomplished through a pyrolysis reaction conducted in a conventional pyrolysis unit widely used in commercial processes. Pyrolysis processes generally utilize temperatures between about 1400 and 1700 F., approximately atmosphere pressures and reaction times between about 0.7 and 1.3 seconds. Partial pressures of hydrocarbons are preferably maintained at about 10 to p.s.i.a. with steam generally used as a dilutant to achieve the desired partial pressure. The effluent from the pyrolysis reactor is usually quenched to stop the reaction, water and aromatic based oil are commonly used as quenching media. The degree of conversion of paraffins to olefins is not critical, but with the practice of the present invention it is preferably maintained between about 70 and about 90% by weight of the feed mixture by varying operating conditions in accordance with known techniques of operation.

The different products from the pyrolysis reaction include an olefin-rich stream, a tail gas consisting essentially of hydrogen and methane and a liquid fraction. The tail gas and liquid are separated from the pyrolysis products with the tail gas, essentially a methane rich gas fraction, added to the pipeline product gas stream. The olefin-rich product stream is reacted in an alkylation unit with isobutane obtained from the deisobutanizing operation.

The alkylation reaction is conducted at a temperature from 30 to 90 F. and at atmospheric pressure. Sulfuric acid catalyst is generally utilized as the catalyst, although hydrofluoric acid at pressures of -150 p.s.i.g. and temperatures in the range of 70 to 115 F. may be utilized. It is also within the scope of the present invention to utilize phosphoric acid or aluminum chloride as the catalyst or no catalyst may be utilized for the alkylation reaction, as well as thermal occulation, although the operation conditions change for these circumstances. Conventionally, however, the sulfuric acid alkylation process is utilized and therefore preferred. A typical product from the alkylation reaction of the olefinic materials with the isobutane-isobutene mixture, for example, from the reaction of ethylene with isobutane, is 2,2-dimethyl-butane, which has a high octane number and is an alkylate enhancement for the improvement of the octane number of the blended gasoline.

The basic process of the present invention may be more fully understood by referral to FIG. 1. Wellhead natural gas 101 is introduced into a fractionating column 102 from which a C and heavier liquid hydrocarbon fraction 103 is produced. A Q; and lighter gas hydrocarbon fraction 104 is produced from the upper portion of the fractionating column and introduced into a debutanizer 105 from which a C through C stream of light hydrocarbons 106 is produced from the upper portion thereof and introduced into a cryogenic light end recovery unit 107 from which methane 109 is produced as a pipeline gas product stream, and from the lower end of which an ethane and propane fraction 108 is produced which is introduced into a pyrolysis unit 111, and converted to olefins to form an olefin rich stream 112. This olefin rich stream 112 has the methane 113 stripped therefrom in separator 122. Separated methane is introduced into the pipeline product gas stream, while the ethylene and heavier olefin stream 114 is introduced into an alkylation unit 115. The C hydrocarbons from the debutanizer 105 and alkylation product 116 are introduced into a de-isobutanizing unit 118 from which alkylate 117 is produced and sent to gasoline blending. Isobutane separated from the de-isobutanizing column 118 is introduced into an isobutane dehydrogenation unit 120 from which hydrogen 123 is vented and dehydrogenated butane stream 121 also containing some isobutane is produced and introduced into the alkylation unit with the olefinic stream 114 for conversion into alkylate material. Therefore, through the use of the process of the present invention disclosed in FIG. 1, natural gas is separated into its methane component for pipeline product gas with the light hydrocarbon intermediates contained therein upgraded to alkylate materials which are blended with the heavier hydrocarbons for the production of a high octane gasoline product.

The process of the present invention may involve further upgrading of the light hydrocarbon fractions as depicted in FIG. 2. Specifically, wellhead natural gas 201 is introduced into fractionator 202 to form a stream of C and lighter hydrocarbons 204 which is then debutanized in a debutanizer 205 to form a C and lighter hydrocarbon stream 206 produced from the upper portion thereof which is introduced into a demethanizing cryogenic light ends recovery from which a methane product pipeline gas 209 is produced. The ethane and propane rich fraction from the cryogenic light end recovery 207 forms a stream 208 which is introduced into a pyrolysis furnace 211. The particular improvement of the pyrolysis intake stream is derived by extracing from the main fractionator 202 a C fraction 224 which is introduced into a deisopentanization column 225 from which isopentane 226 is produced and sent to gasoline blending, whereas the normal pentane stream 227 produced from the isopentane column 225 is introduced simultaneously with the propane and ethane stream 208 from the demethanizer 207 into the pyrolysis furnace 211. The olefinic product 212 produced from the pyrolysis furnace 211 is fed to an ethylene separation unit 228 from which an ethylene and methane stream 229 are produced and subjected to further gas separation in separator 231 of the methane 232 which is fed to the pipeline product gas stream 209. Ethy1= ene effluent 233 from the methane separator 231 is then introduced into an ethylene alkylation unit 234 which is supplied with isobutane for the production of alkylate. The alkylate product is introduced into a deisobutanizer column 218 with the Cl, stream 210 from the debutanizer 205 to form an alkylate 217 which is sent to gasoline blending. Isobutane is removed in stream 219 from the upper portion of the de-isobutanizer column 218 and fed into an isobutane dehydrogenation unit 220 from which hydrogen 223 is produced and an isobutane-isobutene mixture 221 is produced and introduced with the olefinic material from ethylene separator 218 into an alkylation unit 215. The dehydrogenation may be accomplished by subjecting the paraflins to temperatures between about 200 C. to 600 C. in a reaction zone in the presence of a suitable catalyst. The olefins 230 from the separation unit 228 are first subjected to purification unit 237 from which pyrolysis naphtha 243 is produced and fed to a catalytic reformer 244 from which gasoline 245 is produced. The C and heavier hydrocarbons separated from the main fractionator 202 in the form of stream 203 are also fed to the catalytic reformer 244 from which a hydrogen stream 246, a gasoline stream 245 and a C and lighter gas stream 247 are produced with the latter material reintroduced into the main fractionator 202.

As mentioned, the olefin stream 238 is introduced with the isobutane-isobutene stream 221 into an alkylation unit 215 from which alkylate 216 is fed to the de-isobutanizer column 218. A portion of isobutane stream 219 is extracted in the form of stream 236 and also introduced to the ethylene alkylation unit 234 and also introduced as stream 248 into alkylation unit 215. The alkylate stream 216 produced is added to alkylate stream 235 from the ethylene alkylation unit 234 and introduced into the deisobutanizer column 218. A further improvement of the present process is provided by the removal of normal butane from the de-isobutanizer column 218 in the form of a stream 239 which is split into a normal butane stream 240 some of which is added to the gasoline product and some of which is fed to a butane isomerization unit 241 for isomerization into an isobutane-normal butane mixture 242 which is reintroduced to the de-isobutanizer column 218. The isomerization may be accomplished by the use of an aluminum chloride catalyst with the straightchain material being isomerized and again passed through the catalyst to remove any unconverted straight-chain material for return to the isomerization unit. Other catalysts are available for use in the isomerization process, but are well known and need not be further described in detail.

In blending finished gasoline it is frequently necessary to adjust the reid vapor pressure. This adjustment is conveniently accomplished by adding butane to the finished products. The butane is added to adjust the reid vapor pressure of the finished gasoline product to the desired value which will vary according to the intended use of the gasoline as mentioned previously.

Therefore, through utilization of the processes of the present invention, a process is provided which is capable of converting lighter hydrocarbons, normally not of valuable use in remote areas, to alkylate and reformate materials which may be blended to high octane gasoline. The natural gas product stream is readily salable. Therefore, utilization of the present invention allows derivation of maximum value from hydrocarbon materials contained within the wellhead natural gas.

While the invention has been described above in respect to preferred embodiments thereof, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.

Therefore, I claim:

1. A process for the conversion of light hydrocarbons contained in a wellhead natural gas, which comprises:

(a) fractionating the wellhead natural gas into a C and lighter hydrocarbon gas fraction and a C and heavier hydrocarbon liquid fraction;

(b) debutanizing the C and lighter hydrocarbon gas fraction into a C and lighter hydrocarbon gas fraction and a C hydrocarbon fraction;

(c) condensing ethane and propane from the C and lighter gas fraction to produce a methane rich pipeline gas product;

((1) pyrolyzing the condensed ethane and propane to form olefins and methane, the methane being separated therefrom and added to the pipe line gas product;

(e) de-isobutanizing the C fraction from step (b) to produce normal butane stream and an isobutane stream which is subjected to dehydrogenation to form an isobutane-isobutene mixture;

(f) subjecting the olefins produced in step (d) and th isobutene-isobutane mixture to alkylation; and

(g) subjecting the alkylate product produced in step (f) to the de-isobutanization of step (e).

2. The process of claim 1 further comprising:

(a) separating the C and heavier hydrocarbons produced in the pyrolysis step; and

(b) subjecting the C and heavier hydrocarbons from step (a) and the C and heavier liquid fraction from the fractionating step to catalytic reforming to form a C and lighter fraction which is recycled to the fractionating step and a reformate for gasoline blending.

3. The process of claim 2 further comprising:

(a) withdrawing a C fraction from the fractionating step;

(b) separating the isopentane from the C fraction for addition to the gasoline inventory; and

(c) introducing the normal pen-tane into the pyrolysis step.

4. The process of claim 3 further comprising:

(a) separating the ethylene produced from the pyrolysis step;

(b) extracting a portion of the isobutane produced from the de-isobutanization step;

(c) subjecting the ethylene separated and isobutane extracted to alkylation to form an alkylate product of ethylene and isobutane; and

(d) introducing the ethylene alkylate product into the deisobutanization step.

5. The process of claim 4 further comprising:

(a) extracting normal butane from the de-isobutanization step;

(b) isomerizing part of the normal butane to form isobutane; and

(c) reintroducing the resultant isobutane product into the de-isobutanization step.

References Cited UNITED STATES PATENTS 3,060,116 10/1962 Hardin et al. 208-93 3,384,571 5/1968 Engel 208-93 3,409,540 11/1968 Gould et a1. 208-93 3,502,569 3/ 1970 Hervert 208-93 HERBERT LEVINE, Primary Examiner U.S. Cl. X.R.

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