ENHANCEMENT OF FISCHER-TROPSCH PROCESS FOR HYDROCARBON FUEL FORMULATION IN A GTL ENVIRONMENT

Abstract

An enhanced natural gas processing method using Fischer-Tropsch (FT) process for the synthesis of sulfur free, clean burning, hydrocarbon fuels, examples of which include syndiesel and aviation fuel. A selection of natural gas, separately or combined with portions of natural gas liquids and FT naphtha and FT vapours are destroyed in a syngas generator and used or recycled as feedstock to an Fischer-Tropsch (FT) reactor in order to enhance the production of syndiesel from the reactor. The process enhancement results are the maximum production of formulated syndiesel without the presence or formation of low value by-products.

Claims

1-47. (canceled)

48. A method for producing synthetic hydrocarbons comprising: providing a feedstock consisting of 20% ethane, propane, butane and/or pentane, and 80% methane, feeding said feedstock to a syngas generator comprising steam methane reformer (SMR) to produce a hydrogen-rich syngas stream; and catalytically converting the hydrogen rich syngas stream in a Fischer-Tropsch reactor to produce synthetic hydrocarbons.

49. The method of claim 48, wherein the feedstock comprises 20% propane and/or butane.

50. The method of claim 48, further comprising a scrubbing unit to remove one or more components from the syngas stream.

51. The method of claim 50, wherein the one or more components comprise one or more of ammonia, sulfur compounds, and carbon dioxide.

52. The method of claim 48, wherein the feedstock is provided to a combined steam methane reformer and an autothermal reformer.

53. The method of claim 48, wherein the synthetic hydrocarbons produced comprise diesel fuel.

54. The method of claim 48, wherein the synthetic hydrocarbons produced comprise jet fuel.

55. The method of claim 48, wherein the synthetic hydrocarbons produced have an absence of sulfur.

56. The method of claim 48, wherein the synthetic hydrocarbons produced have an increased cetane rating as compared to the cetane rating of petroleum based diesel.

57. The method of claim 48, which is performed in a gas to liquid (GTL) plant.

58. The method of claim 48, wherein said synthetic hydrocarbons contain at least naphtha; and said method further comprises recycling at least a portion of said naphtha to said steam methane reformer to form an enhanced hydrogen rich syngas stream; and re-circulating said enhanced hydrogen rich syngas stream for conversion to synthetic hydrocarbons.

59. The method of claim 48, wherein said synthetic hydrocarbons contain at least naphtha and unconverted FT (Fischer-Tropsch) vapours; and said method further comprises recycling at least a portion of said naphtha and unconverted FT vapours to said syngas generator to form an enhanced hydrogen rich syngas stream; and re-circulating said enhanced hydrogen rich syngas stream for conversion to synthetic hydrocarbons.

60. The method of claim 52, wherein the hydrogen-rich syngas stream has a hydrogen to carbon monoxide ratio of greater than 2:1.

61. The method of claim 48, wherein the hydrogen-rich syngas stream has a hydrogen to carbon monoxide ratio of greater than 3:1.

62. The method of claim 52, wherein the hydrogen-rich syngas stream has a hydrogen to carbon monoxide ratio of approximately 2.5:1.

63. The method of claim 48, wherein the hydrogen-rich syngas stream has a hydrogen to carbon monoxide ratio of from 3:1 to 5:1.

64. The method of claim 48, further comprising separating a portion of hydrogen from the syngas.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] FIG. 1 is a process flow diagram of methodology known in the prior art using autothermal reformer technology;

[0050] FIG. 2 is a process flow diagram of methodology known in the prior art using steam methane reformer technology;

[0051] FIG. 3 is a process flow diagram similar to FIG. 1, illustrating a first embodiment of the present invention;

[0052] FIG. 4 is a process flow diagram similar to FIG. 2, illustrating a further variation of the present invention;

[0053] FIG. 5 is a process flow diagram of a still further embodiment of the present invention showing the combination of autothermal and steam methane reforming technologies;

[0054] FIG. 6 is a process flow diagram illustrating a still further variation of the present methodology, showing the integration of the autothermal and steam methane technologies;

[0055] FIG. 7 is a schematic diagram illustrating a conventional hydrocarbon liquids extraction plant; and

[0056] FIG. 8 is a process flow diagram illustrating a still further variation of the present methodology within a natural gas processing facility.

[0057] Similar numerals employed in the figures denote similar elements.

[0058] The dashed lines used in the Figures denote optional operations.

INDUSTRIAL APPLICABILITY

[0059] The present invention has applicability in the fuel synthesis art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0060] Referring now to FIG. 1, to illustrate prior art, shown is a process flow diagram of a circuit for converting gas-to-liquids with the result being the production of naphtha and syndiesel. The process is generally denoted by numeral 10 and begins with a natural gas supply 12, which feedstock can be in the form of raw field gas or pipeline quality treated gas, usually with bulk sulfur and hydrocarbon liquids removed. The natural gas is then pre-treated in a pre-treatment unit 20 to which steam 14, hydrogen 18 and optionally carbon dioxide 19 may be added as required. The pre-treatment unit may include, as is well known to those skilled in the art, such unit operations as a feed gas hydrotreater, sulfur removal and guard operation and a pre-reformer to produce a clean vapour feed stream 22 for the syngas generator, denoted in FIG. 1 as an autothermal reformer (ATR) unit 24. The ATR 24 may be any suitable catalytic partial oxidization unit, however, as an example, an ATR that is useful in this process is that of Haldor Topsoe A/S., Uhde GmbH and CB&I Lummus Company. The ATR process and apparatus have been found to be effective in the methodology of the present invention and will be discussed hereinafter.

[0061] Generally, as is known from the ATR process, the same effectively involves a thermal catalytic stage which uses a partial oxygen supply 16 to convert the preconditioned natural gas feed to a syngas 26 containing primarily hydrogen and carbon monoxide.

[0062] The so formed syngas is then subjected to cooling and cleaning operations 28 with subsequent production of steam 32 and removal of produced water at 34. Common practice in the prior art is to employ the use of a water gas shift reaction (WGS) on the clean syngas 30 to condition the hydrogen to carbon dioxide ratio to near 2.0:1 for optimum conditions for the Fischer-Tropsch unit 40. It is not preferred in this process to include a WGS reaction as all the carbon, primarily as CO is retained and used to maximize production of synthesis liquids product. The process may optionally use the supplemental addition of hydrogen 42 to maximize the conversion to syndiesel. The raw syngas may be further treated, as is well known to those skilled in the art, in various steps of scrubbing units and guard units to remove ammonia and sulfur compounds to create a relatively pure clean syngas 30 suitable for use in a Fischer-Tropsch unit. A carbon dioxide removal unit (not shown) may optionally be included in the clean syngas stream 30 to reduce the inert load and maximize the carbon monoxide concentration to the Fischer-Tropsch unit 40. The syngas is then transferred to a Fischer-Tropsch reactor 40 to produce the hydrocarbons and water. The so formed hydrocarbons are then passed on to a product upgrader, generally denoted as 50, and commonly including a hydrocarbon cracking stage 52, a product fractionating stage 60 with naphtha being produced at 66 as a fraction, as well as diesel 68 as an additional product. The diesel 68 formulated in this process is commonly known as syndiesel. As an example, this process results in the formulation of 1000 barrels per day (bbl/day) based on 10 to 15 thousand standard cubic feet/day (MSCFD) of natural gas. As is illustrated in the flow diagram, a source of hydrogen 74 is to be supplemented to the hydrocarbon cracking unit 52 denoted as streams 54. Further, energy 32 from the syngas generator 24, typically in the form of steam, may be used to generate power and this is equally true of the Fischer-Tropsch reactor 40 creating energy 46.

[0063] Table 1 establishes a comparison between FT diesel and conventional petroleum based diesel.

TABLE-US-00001 TABLE 1 Specification of FT-diesel in comparison to conventional diesel Conventional Diesel Fuel Specification FT-Diesel Diesel Chemical formula Paraffin C.sub.12H.sub.26 Molecular weight (kg/kmol) 170-200 Cetane number >74 50 Density (kg/l) at 15 C. 0.78 0.84 Lower Heating Value (MJ/kg) at 15 C. 44.0 42.7 Lower Heating Value (MJ/l) at 15 C. 34.3 35.7 Stoichiometric air/fuel ratio (kg air/kg fuel) 14.53 Oxygen content (% wt) ~0 0-0.6 Kinematic viscosity (mm.sup.2/s) at 20 C. 3.57 4 Flash point ( C.) 72 77 Source: KMITL Sci. Tech. J. Vol. 6 No. 1 Jan.-Jun. 2006, p. 43

[0064] As a further benefit, known to those skilled in the art, the process as described by FIG. 1 and all configurations of the current invention, the addition of a further side stripper column (not shown) off the fractionation in stage 60 may be included to produce a new fraction of about 25% of the volume of the syndiesel fuel (200 to 300 barrels per day (bbl/day)), referred to as FT-jet fuel. Table 2 describes a typical characteristic of FT jet fuel.

TABLE-US-00002 TABLE 2 Typical Specification of FT-Jet Fuel Typical Product Specification FT Jet Fuel Acidity mg KOH/g 0.10 Aromatics % vol max <25.0 Sulfur mass % <0.40 Distillation C. 50% recovered Min 125 C. max 190 C. End Point 270 C. Vapor Pressure kPa max 21 Flash Point C. Density 15 C., kg/m3 750-801 Freezing Point C. max 51 Net Heat Combustion MJ/kg min 42.8 Smoke Point mm, min 20 Naphthalenes vol % max <3.0 Copper Corrosion 2 hr @ 100 C., max rating No 1 Thermal Stability Filter Pressure drop mm Hg, max 25 Visual Tube rating, max <3 Static Test 4 hr @ 150 C. mg/100 ml, max Existent Gum mg/100 ml, max

[0065] Naphtha 66 can be generally defined as a distilled and condensed fraction of the Fischer-Tropsch FT hydrocarbon liquids, categorized by way of example with a typical boiling range of 40 C. to 200 C., more preferred 30 C. to 200 C., and more preferred 80 C. to 120 C. The specific naphtha specification will be optimized for each application to maximize syndiesel production, maximize the recovery of light liquid hydrocarbon fractions such as propane and butane and partially or fully eliminate the naphtha by-product.

[0066] Suitable examples of FT reactors include fixed bed reactors, such as tubular reactors, and multiphase reactors with a stationary catalyst phase and slurry-bubble reactors. In a fixed bed reactor, the FT catalyst is held in a fixed bed contained in tubes or vessels within the reactor vessel. The syngas flowing through the reactor vessel contacts the FT catalyst contained in the fixed bed. The reaction heat is removed by passing a cooling medium around the tubes or vessels that contain the fixed bed. For the slurry-bubble reactor, the FT catalyst particles are suspended in a liquid, e.g., molten hydrocarbon wax, by the motion of bubbles of syngas sparged into the bottom of the reactor. As gas bubbles rise through the reactor, the syngas is absorbed into the liquid and diffuses to the catalyst for conversion to hydrocarbons. Gaseous products and unconverted syngas enter the gas bubbles and are collected at the top of the reactor. Liquid products are recovered from the suspending liquid using different techniques such as separators, filtration, settling, hydrocyclones, and magnetic techniques. Cooling coils immersed in the slurry remove heat generated by the reaction. Other possibilities for the reactor will be appreciated by those skilled.

[0067] In the FT process, H.sub.2 and CO combine via polymerization to form hydrocarbon compounds having varying numbers of carbon atoms. Typically 70% conversion of syngas to FT liquids takes place in a single pass of the FT reactor unit. It is also common practice to arrange the multiple FT reactors in series and parallel to achieve conversion levels of 90+%. A supplemental supply of hydrogen 42 may be provided to each subsequent FT reactor stages to enhance the conversion performance of the subsequent FT stages. After the FT reactor, products are sent to the separation stage, to divert the unconverted syngas and light hydrocarbons (referred to as FT tailgas), FT water and the FT liquids, which are directed to the hydrocarbon upgrader unit denoted as 50. The FT tailgas becomes the feed stream for subsequent FT stages or is directed to refinery fuel gas in the final FT stage. The upgrader unit typically contains a hydrocracking step 52 and a fractionation step 60.

[0068] Hydrocracking denoted as 52 used herein is referencing the splitting an organic molecule and adding hydrogen to the resulting molecular fragments to form multiple smaller hydrocarbons (e.g., C.sub.10H.sub.22+H.sub.2fwdarw.C.sub.4H.sub.10 and skeletal isomers+C.sub.6H.sub.14). Since a hydrocracking catalyst may be active in hydroisomerization, skeletal isomerization can occur during the hydrocracking step. Accordingly, isomers of the smaller hydrocarbons may be formed. Hydrocracking a hydrocarbon stream derived from Fischer-Tropsch synthesis preferably takes place over a hydrocracking catalyst comprising a noble metal or at least one base metal, such as platinum, cobalt-molybdenum, cobalt-tungsten, nickel-molybdenum, or nickel-tungsten, at a temperature of from about 550 F. to about 750 F. (from about 288 C. to about 400 C.) and at a hydrogen partial pressure of about 500 psia to about 1,500 psia (about 3,400 kPa to about 10,400 kPa).

[0069] The hydrocarbons recovered from the hydrocracker are further fractionated in the fractionation unit 60 and refined to contain materials that can be used as components of mixtures known in the art such as naphtha, diesel, kerosene, jet fuel, lube oil, and wax. The combined unit consisting of the hydrocracker 52 and hydrocarbon fractionator 60 are commonly known as the hydrocarbon upgrader 50. As is known by those skilled in the art, several hydrocarbon treatment methods can form part of the upgrader unit depending on the desired refined products, such as additional hydrotreating or hydroisomerization steps. The hydrocarbon products are essentially free of sulfur. The diesel may be used to produce environmentally friendly, sulfur-free fuel and/or blending stock for diesel fuels by using as is or blending with higher sulfur fuels created from petroleum sources.

[0070] Unconverted vapour streams, rich in hydrogen and carbon monoxide and commonly containing inert compounds such as carbon dioxide, nitrogen and argon are vented from the process as FT tail gas 44, hydrocracker (HC) offgas 56 and fractionator (frac) offgas 62. These streams can be commonly collected as refinery fuel gas 64 and used as fuel for furnaces and boilers to offset the external need for natural gas. These streams may also be separated and disposed of separately based on their unique compositions, well known to those skilled in the art.

[0071] A supplemental supply of hydrogen 74 may be required for the HC unit 54 and the natural gas hydrotreater 18. This hydrogen supply can be externally generated or optionally provided from the syngas stream 30 using a pressure swing absorption or membrane unit (not shown), although this feature will increase the volume of syngas required to be generated by the syngas generator 24.

[0072] Further, useable energy commonly generated as steam from the syngas stage, denoted by numeral 32, may be used to generate electric power. This is equally true of useable energy that can be drawn from the Fischer-Tropsch unit, owing to the fact that the reaction is very exothermic and this represents a useable source of energy. This is denoted by numeral 46.

[0073] Referring now to FIG. 2, to further illustrate the prior art, shown is an alternate process flow diagram of a circuit for converting gas-to-liquids with the result being the production of naphtha and syndiesel. The components of this process are generally the same as that described in FIG. 1 with the common elements denoted with the same numbers. For this process, the syngas generator is changed to be a steam methane reformer (SMR) 25. The SMR 25 may be any suitable catalytic conversion unit, however, as an example, an SMR that is useful in this process is that of Haldor Topsoe A/S., Uhde GmbH., CB&I Lummus Company, Lurgi GmbH/Air Liquide Gruppe, Technip Inc, Foster Wheeler and others. The SMR process and apparatus have been found to be effective in executing the methodology of the present invention to be discussed hereinafter. Generally, as is known from the SMR process, the same effectively involves a thermal catalytic stage which uses steam supply and heat energy to convert the preconditioned natural gas feed to a syngas 27 containing primarily hydrogen and carbon dioxide.

[0074] An advantage of the SMR technology is that the syngas is very rich in hydrogen with a ratio of hydrogen to carbon monoxide typically greater than 3.0:1. This exceeds the typical syngas ratio of 2.0:1 usually preferred for the Fischer-Tropsch process. As such, a hydrogen separation unit 33 may be used to provide the hydrogen requirement 74 for the GTL process. As discussed previously, well known to those skilled in the art, the hydrogen separator may be a pressure swing adsorption or a membrane separation unit. Further, although the SMR does not require an oxygen source as with the ATR technology, the SMR process requires external heat energy, typically provided by natural gas 13 or optionally by use of the excess refinery gas 76 derived from the FT tail gas 44 or upgrader offgases 56 & 62.

[0075] The SMR 25 may contain any suitable catalyst and be operated at any suitable conditions to promote the conversion of the hydrocarbon to hydrogen H.sub.2 and carbon monoxide. The addition of steam and natural gas may be optimized to suit the desired production of hydrogen and carbon monoxide. Generally natural gas or any other suitable fuel can be used to provide energy to the SMR reaction furnace. The catalyst employed for the steam reforming process may include one or more catalytically active components such as palladium, platinum, rhodium, iridium, osmium, ruthenium, nickel, chromium, cobalt, cerium, lanthanum, or mixtures thereof. The catalytically active component may be supported on a ceramic pellet or a refractory metal oxide. Other forms will be readily apparent to those skilled.

[0076] Turning now to FIG. 3, shown is a preliminary embodiment of the technology of the instant invention. As is evinced from FIG. 3, many of the preliminary steps are common with that which is shown in FIG. 1. At least a portion of the less desirable FT product, naphtha 66 is recycled as ATR 24 feed through the pre-treatment unit 20 and is fully destroyed and converted to additional syngas. Based on the full recycle and conversion of the naphtha, the diesel production increase of greater than 10% can be realized, with the elimination of an undesirable by-product stream.

[0077] As a key point, one of the most effective procedures in the instant technology, relates to the fact that once the product fractionation stage has been completed and the naphtha 66 formulated, it has been found that by recycle and full conversion of the naphtha, significant results can be achieved in the production of the synthetic diesel.

[0078] In the embodiment shown in FIG. 3, several other optional features are desirable in addition to naphtha recycle, to enhance the production of syndiesel, including; (i) a hydrogen separation unit is added to remove excess hydrogen from the enhanced syngas for supply to the FT unit 40 and product upgrader 50; (ii) A portion of hydrogen rich streams not desired to be used as fuel, separately or combined all together as refinery fuel 64, can be recycled back 102 to the ATR 24 by way of the pre-treatment unit 20; (iii) A optional carbon dioxide removal stage 21 may be installed on the FT syngas feedstream to reduce the inert vapour load on the FT unit 40, and at least a portion of the carbon dioxide 12 may be reintroduced into the ATR 24 by way of the pre-treatment unit 20 for purposes of reverse shifting and recycling carbon to enhance the production of syndiesel.

[0079] As has been discussed herein previously, it is unusual and most certainly counter-intuitive to effectively destroy the naphtha in order to generate a hydrogen rich stream as the naphtha is commonly desired as primary feedstock for gasoline production. Although this is the case, it is particularly advantageous in the process as set forth in FIG. 3.

[0080] FIG. 4 sets forth a further interesting variation on the overall process that is set forth in FIGS. 2 and 3. As is evinced from FIG. 4, many of the preliminary steps are common with that which is shown in FIG. 2. In this variation, and similar to the variation described by FIG. 3, the process employs the recycle of at least a portion of the naphtha 100 to enhance the production of syndiesel using a SMR syngas generator. Similarly the optional features described for FIG. 3 can equally apply to FIG. 4.

[0081] A further variation of the overall process embraced by the technology discussed herein is shown in FIG. 5. In essence, the process flow as shown in FIG. 5 combines the unit operations of the SMR 25 and the ATR 24 syngas generators with the primary embodiment of this invention, namely the recycle of at least a portion of the naphtha, to create the maximum conversion of carbon to syndiesel. Further, the optional features as described in FIGS. 3 and 4, combined with the naphtha recycle, may create even further benefits to further enhancement of syndiesel production without any nonuseful by-products. The sizing of the ATR and SMR syngas generators are specific to each feed gas compositions and site specific parameters to optimize the production of syndiesel. Further the feedstreams for the ATR and SMR may be common or uniquely prepared in the pre-treatment unit to meet specific syngas compositions desired at 26 and 27. Similarly, the hydrogen rich syngas stream or portion thereof, from the SMR can be optionally preferred as the feed stream to the hydrogen separation unit 33. By way of example, the preferred steam to carbon ratios at streams 22 and 23 for the ATR and SMR may be different, thereby requiring separate pre-treatment steps.

[0082] Turning to FIG. 6, as shown is yet another variation of the overall process according to the present invention combining the benefits of FIGS. 3 and 4. In this embodiment, both the SMR and ATR unit operations, combined with the naphtha recycle are amalgamated into an integrated unit operation whereby the heat energy created by the ATR 24 becomes the indirect heat energy required by the SMR reactor tubes 25. This embodiment allows the integrated ATR/SMR unit, the XTR to be strategically designed to maximize the carbon conversion to syndiesel by creating the optimum Fischer-Tropsch 40 and hydrogen separator 33 syngas feed with optimum hydrogen to carbon monoxide ratio and the minimum quantity of natural gas, steam and oxygen, while maximizing syndiesel production without the production of any nonuseful by-product. All other optional features remain the same as FIGS. 3, 4 and 5. As used herein, integrated in reference to the ATR/SMR means a merged unit where the two distinct operations are merged into one.

[0083] Turning to FIG. 7, shown is a schematic illustration of a conventional hydrocarbon liquids extraction plant commonly known in the art. The overall plant is denoted with numeral 110. The hydrocarbon liquid extraction gas plant typically includes refrigerated dewpoint control units, lean oil absorption plants or deep cut turbo expander plants. All of these process units employ an extraction technique to remove ethane, propane, butane and pentanes as well as higher alkanes referred to as pentanes plus C.sub.5+(typically referred as condensates) singly or as blends from the methane gas stream. These techniques are well known and will not be elaborated upon here. Generally speaking, any of the above mentioned alkanes other than the C.sub.5+ alkanes can remain in the sales gas to increase heat content provided that the sales gas hydrocarbon dewpoint specification is not exceeded.

[0084] Turning now to FIG. 8, shown is a further variation of the methodology of the present invention. The original feedstock, namely raw natural gas 114 is introduced into the plant 112 at which point the C.sub.5+ condensates can be removed at 116 with the passage of the methane 118, ethane 120, and propane and butane 122 introduced into a gas to liquids GTL plant 124, which includes a Fischer-Tropsch unit.

[0085] As an option, at least a portion of the methane 118, ethane 120 and butane and propane 122 can be removed as sales gas 126 or in the case of the ethane 120 this may be supplied optionally to the petrochemical market. Similarly, with respect to the propane (C3) and butane (C4) 122 this may be entirely removed or a portion thereof from the circuit at 128.

[0086] As is known, once the alkane feedstock is passed into the gas to liquid plant 124 by use of the known components of the gas to liquid plant including, namely the syngas generator, syngas conditioning circuit, and upgrading circuit, the result is synthetic diesel fuel 130 and/or synthetic jet fuel 132 as illustrated in the Figure.

[0087] The GTL plant 124 is capable of receiving the combined raw gas stream with primarily the C.sub.5+ components removed for converting the rich raw natural gas to synthetic diesel and synthetic jet fuel. It has been found that over dry methane gas feed, the GTL plant 124 will generate a 20% to 30% increase in synthetic diesel product yield using the rich natural gas feed. It is also been noted that a significant increase in synthetic diesel production is realized as the composition contains high concentrations of butane and propane. It has further been found that if the feed is restricted to 100% propane or butane, the synthetic diesel production increases two to three times respectively to approximately 200% to 300% of the production based on dry methane gas.

[0088] It will be appreciated that the feedstock can take any form and can include any combination of the byproducts or any of the byproducts singly, namely, the C.sub.2+, C.sub.3+, C.sub.3 and C.sub.4 and/or C.sub.5+. The arrangement is particularly beneficial, since the operator can select an option to adjust the economical business model to optimize the economics for a particular market situation.

[0089] Clearly there are significant advantages that evolve from unifying the gas plant with the use of the byproduct technology set forth herein. These include, for example: i) Production of natural gas to be sustained during surplus natural gas market conditions; ii) The use of unfavourable natural gas components (byproducts) which can be reformed to high value synthetic diesel and synthetic jet fuel to increase market potential; and iii) The use of rich feed streams to the GTL plant to dramatically increase synthetic diesel production.

[0090] With respect to the efficiency of the overall system, in Table 3 there is tabulated information regarding the natural gas feed and the result of total synthetic diesel production.

TABLE-US-00003 TABLE 3 Overall Process Summary of GTL Case 1 Pipeline Mixed Case 2 Case 3 Case 4 Natural GTL LPG Pure Pure Gas Feed Blend Propane Butane GTL Feedstock Feed Rate (MMSCFD) 12.5 12.5 12.5 12.5 12.5 Feed Composition (mole fraction) Nitrogen 0.0197 0.0 0.0 0.0 0.0 Methane 0.9700 0.8 0.0 0.0 0.0 Ethane 0.0010 0.0 0.0 0.0 0.0 Propane 0.0040 0.1 0.5 1.0 0.0 Butane 0.0040 0.1 0.5 0.0 1.0 Pentane Plus 0.0013 0.0 0.0 0.0 0.0 Total Diesel Product 996.5 1179.0 2748 2355.0 3093 (bpd)

[0091] As is evident from the Table, the natural gas feed to the GTL circuit has a total diesel production barrels per day (bpd) of 996.5. Cases 1 though 4 vary the feed composition to the GTL circuit with very pronounced results. In the instance of Case 4 where the feed is straight butane, the result is 3093 bpd of syndiesel which, represents approximately a 300% increase from the use of conventional natural gas with all of the byproducts present. Case 3 indicates straight propane as an option with an indicated total syndiesel product of 2355 bpd. Case 2 demonstrates a mix between propane and butane as the feedstock, also illustrating a significant increase in product yield showing 2748 bpd of syndiesel relative to the use of natural gas only. It will be appreciated that in the instances of Cases 1 through 4, these are demonstrative of the increase in volume of the syndiesel produced when used in combination with the typical natural gas composition under column Pipeline Natural Gas.

[0092] Clearly, the methodology facilitates an increased yield of synthetic fuel production by use of natural gas byproducts with or without natural gas. This advantageously provides process flexibility and definition economics.