GB2409460A - Blended syngas with variable H2:CO ratio - Google Patents

Blended syngas with variable H2:CO ratio Download PDF

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GB2409460A
GB2409460A GB0426607A GB0426607A GB2409460A GB 2409460 A GB2409460 A GB 2409460A GB 0426607 A GB0426607 A GB 0426607A GB 0426607 A GB0426607 A GB 0426607A GB 2409460 A GB2409460 A GB 2409460A
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syngas
ratio
fischer
blended
tropsch
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GB2409460B (en
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Rear Dennis O
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Chevron USA Inc
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    • C10G2/00—Production of liquid hydrocarbon mixtures of undefined composition from oxides of carbon
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Abstract

A process for producing blended syngas having a variable H2/CO ratio, comprising: <SL> <LI>a) feeding a first syngas having a H2/CO ratio of 1.25 to 2.1 into a Fischer-Tropsch reactor, and recovering an effluent therefrom; <LI>b) recovering a syngas from said effluent, said syngas having a higher H2/CO ratio then the first syngas; <LI>c) forming a third syngas having a H2/CO no greater than 1.5 from LPG and CO2; <LI>d) blending the second and third syngases to form a syngas having a H2/CO between 1.4 and 1.75; <LI>e) feeding the blended syngas into a second Fischer-Tropsch reactor. </SL>

Description

PROC'F,SS FOR CONVERSION OF LPG AND C114 TO SYN(,AS AND IIIGIIER VAI,UED
PRODUCTS
FIELD OF THE INVENTION
1] The present invention relates to a process for the production of a syngas feed with a variable Hz/CO ratio, which may be used in syngas conversion processes.
BACKGROUND OF THE INVENTION
10002] The conversion of natural gas assets into more valuable chemicals, including combustible liquid fuels, is desired to more effectively utilize these natural gas assets. The conversion of natural gas to more valuable chemical products generally involves syngas generation Syngas generation involves converting natural gas, which is mostly methane, to synthesis or syngas gas, which is a mixture of carbon monoxide and hydrogen. Syngas may be used as a feedstock for producing a wide range of chemicals, including combustible liquid fuels, methanol, acetic acid, dimethyl ether, oxo alcohols, and isocyanates.
3] There are two main approaches to convert remote natural gas assets into conventional transportation fuels and lubricants using syngas. Natural gas may be converted into syngas followed by a Fischer-Tropsch process, or natural gas may be converted into syngas followed by methanol synthesis, which is followed by a methanol to gas process (MTG) to convert methanol into highly aromatic gasoline. The syugas generation is the most costly step of these processes.
A critical feature of these processes is producing syngas with a desired Hz/CO ratio to optimize formation of the desired products and to avoid problems in the syogas formation step.
4] Syngas can be generated from three major chemical reactions. The first involves steam reforming of methane. The ratio of hydrogen to carbon monoxide, which is formed from this process, is typically approximately 3.0. A second process for syngas generation involves dry reforming of methane or the reaction between carbon dioxide and methane. An attractive feature of this method is that carbon dioxide is converted into syngas; however, this method has problems with rapid carbon deposition. The carbon deposition or coke formmg reaction is a separate reaction from the one that generates the syngas and occurs subsequent to the syngas formation reaction. However, the reaction of methane in dry reforming is slow enough that long residence times are required for high conversion rates and these long residence times lead to coke formation The ratio of hydrogen to carbon monoxide, winch is formed from this process, is typically approximately 1 0 A third process for synthesis gas generation involves partial oxidation of methane using oxygen, where the oxygen can be either air, cnnchcd air, or oxygen with a purity m excess of 90%, prcLerably m excess of 99'/O. l'hc ratio of hydrogen to carbon monoxide, which is formed from this process, is typically approximately 2. 0. However, n1 commercial practice, some amount of steam Is typically added to a partial oxidation refonner in order to control carbon formation and the addition of steam tends to increase the Hz/CO ratio above 2.0. Likewise it is common to add relatively small amounts of CO2 to the feed gas mixture in an attempt to adjust the ratio closer to 2.0.
5] Unless otherwise stated, syngas ratios (and percentage compositions) as described herein are in terms of molar ratios (and molar percentages).
[00061 It is possible to produce syngas with a Hz/CO ratio that is above the ratio ideally desired for the process in which the syngas is to be used, and then to remove excess hydrogen to adjust the ratio to the desired value. However, the H2 removal process employs expensive H2 separation systems that tend to foul and decline in performance with use.
100071 Through the use of a Caloric Calcor process, it is also known to produce high purity carbon monoxide or an oxo-feedstock of hydrogen and carbon monoxide in a ratio of between 0.5 and 1 using a LPG feedstock and carbon dioxide, as described in "Make CO from CO2, Hydrocarbon Processing, Vol. 64, May 1985, pp. 106-107 and "A new process to make Oxo feed," Hydrocarbon Processing, Vol. 66, July 1987, pg. 52.
8] The Inversion of natural gas to combustible liquid fuels may also involve the production of LPG. A syngas processing facility, such as, for example, a hydrocarbon synthesis facility, typically produces LPG as well as the desired products. The export of LPG from such a facility or from the parent natural gas field is often difficult and expensive. LPG must be compressed and liquefied, and the shipment requires the use of special ocean-going vessels.
Furthermore, the market for mixtures of propane and butane is small and of low value. Thus, the LPG must be separated into individual propane and butane of purity to meet specifications for sale. This complicated and expensive operation often results in high costs, which make the value of the LPG at the site of production small.
[00091 The conversion of natural gas to combustible liquid fuels further involves the production of some amount greenhouse gas emissions, such as CO2. The production of significant amount of CO2 is environmentally undesirable.
100101 Accordingly, there is a need for a process for producing a syngas with a pre-selected Hz/CO ratio that can be varied according to the process in which the syngas is to be employed and that avoids H2 separation and cokmg m the syngas formation step 'l'herc Is also a need for a process that minimizes or chminates production of LPG from a processing facility, such as, for cxamplc, a hydrocarbon synthesis facility Furthcrmorc, there Is a need to reduce the greenhosc emissions from a processing fachty, such as, for example, a hydrocarbon synthesis facility.
SUMMARY OF THE INVENTION
1] Methods for forming syngas with a variable Hz/CO ratio are disclosed. One aspect of the present invention is a process for the production of a blended syugas feed with a desired Hz/CO ratio. l his process comprises selecting a desired Hz/CO ratio of the blended syngas feed.
The desired syugas ratio may be in the range of from approximately l.0 to 3.0. The 1-12/CO ratio is selected on the basis of the process in which the syngas is to be used. In this process a first syngas is formed with a Hz/CO ratio of at least 2.0 by reacting methane with oxygen and water and a second syngas is formed with a Hz/CO ratio of no more than 1.5 by reacting LPG (liquified petroleum gas) with CO2. The first syngas and the second syngas are blended to form the blended syngas feed with the desired Hz/CO ratio. The blended syngas may be fed to a syngas conversion reactor, and this reactor may be used in a gas to liquid (GTL) conversion process.
The blended syngas feed may preferably be a feed for a Fiseher-Tropseh reactor, and therefore, the blended syngas may be fed to a FiseherTropseh reactor.
2] An additional aspect of the present invention is a process of using LPG and CO2 in preparing a syngas feed for a I iseher-Tropseh reactor. CO2 and LPG are contacted at reforming reaction conditions to form a first syngas with a Hz/CO ratio of not more than 1.5. I'he first syngas is blended with a second syngas with a Hz/CO ratio of no less than 2.0 to form a blended syngas feed. The blended syngas feed is fed into the Fiseher-Tropseh reactor.
3] A further aspect of the present invention is an integrated process for producing a blended syngas with a variable Hz/CO ratio for a FiseherTropseh reactor. this process a desired Hz/CO ratio of a blended syngas feed to a Fiseher-Tropseh reactor is selected. This process comprises reacting methane, oxygen, and steam to form a first syngas with a Hz/CO ratio of at least 2.0. A second syugas is formed with a Hz/CO ratio of no more than l.5 by reacting LPG and CO2. The first syngas and the second syngas are blended to form a blended syngas feed for the Fischer-Tropsch reactor having the desired Hz/CO ratio. A Fischer-Tropsch synthesis process is performed using the blended syngas feed. Unreacted syngas containing CO2, H2, CO, and CH4 is recovered from the Fischer-Tropsch reactor, and LPG is also recovered from the Fischer-Tropsch reactor.
4] An additional aspect of the present invention is a process for the production of a blended syngas feed with a variable Hz/CO ratio. In this process a first syngas comprising H2 anti CO anti having a 1-12/CO ratio m the range of from approximately I 4 to 1.75 is fed mto a first FischerTropsch synthesis reactor and at least one eMucnt Is recovered therefrom A second sagas comprsng H2 and CO is recovered from the eMucnt wherein the second syugas has a lower 112/CO ratio than that of the first syngas. A third syngas with a Hz/CO ratio of at least 2.0 s formed by reacting methane with an oxygen source. 'the second syngas is blended with the third syngas to form a blended syngas feed having a Hz/CO ratio in the range of 1.4 to 1.75. 'lathe blended syngas feed is fed into a second Fischer-Tropsch reactor.
100151 In a further aspect the present invention is directed to a process for the production of a blended syngas feed with a variable Hz/CO ratio. In this process a first syngas comprising H2 and CO and having a H2 and CO ratio in the range of 1.25 to 2.1 is fed into a first Fischer Tropsch synthesis reactor and at least one effluent is recovered therefrom. A second syugas is recovered from the effluent wherein the second syngas has a higher Hz/CO ratio than that of the first syngas. A third syngas with a Hz/CO ratio of no more than 1.5 is formed by reacting LPG with CO2. The second syngas is blended with the third syngas to form a blended syngas feed having a Hz/CO ratio in the range of 1.4 to 1.75. The blended syngas feed is fed into a second Fischer-Tropsch reactor.
6] In an additional aspect, the present invention is directed to a process for producing fuel comprising reacting LPG and CO2 to form a first syngas with a Hz/CO ratio of no more than 1.5. The syngas is reacted in a Fischer-Tropsch process to produce a hydrocarbonaceous effluen and at least a portion of the hydrocarbonaceous effluent is converted into at least one fuel.
7] In a separate embodiment, the present invention is directed to a process for converting gaseous and/or liquid hydrocarbons into C5+ hydrocarbons, wherein the process has a carbon efficiency of greater than 75%. The process may comprise reforming to convert gaseous and/or liquid hydrocarbons into a syngas, hydrocarbon synthesis to convert the syngas to a hydrocarbonaceous product, separating the hydrocarbonaceous product to recover CO2 and C5+ hydrocarbons, and converting at least a portion of the CO2 into C5+ hydrocarbons. In this process a desired HJCO ratio of a blended syngas feed to a Fischer-Tropsch reactor is selected. This process comprises reacting methane, oxygen, and steam to form a first syngas with a Hz/CO ratio of at least 2.0. A second syngas is formed with a Hz/CO ratio of no more than 1.5 by reacting 1:,PG and CO2. The first syngas and the second syngas are blended to form a blended syngas feed for the Fischer-Tropsch reactor having the desired HJCO ratio. A Fischer-Tropsch synthesis process Is performed using the blended syngas feed. Unreacted syngas containing CO2, H2, CO, and CH4 is recovered from the Fischer-Tropsch reactor, and LPG is also recovered from the Fischer-Tropsch reactor.
BRIEF DESCRIPTION OF TIFF DRAWINGS
[00181 Figure l illustrates a block diagram of a conventional IischerTropsch synthesis process in which a single syngas stream is formed by reacting methane with oxygen and steam and this stream is fed into a Fischcr-Tropsch reactor.
l0019l Figure 2 illustrates a block diagram of a specific embodiment of an mtograted Fischer-Tropsch process of the present invention using a blended syngas feed with a variable Hz/CO ratio.
DETAILED DESCRIPTION OF Il,LUSTRATIVE EMBODIMENTS
0] The present invention relates to methods for forming syngas with a desired Hz/CO ratio, which may be selected according to the process in which the syngas is to be used.
However, prior to describing this invention in further detail, the following terms will first be defined.
Definitions: [0021] The following terms will be used throughout the specification and will have the following meanings unless otherwise indicated.
[00221 The term "integrated process" means a process comprising a sequence of steps, some of which may be parallel to other steps in the process, but which are interrelated or in some way dependent upon either earlier or later steps in the total process. Thus, a hydrocarbonaceous feed to a step in an integrated process comprises a product from a preceding step in the process; alternatively, a product of a step in an integrated process is a feed, either alone or as a blend with other feeds, for one or more subsequent steps in an integrated process.
l0023l The term "syngas" means a mixture that includes hydrogen and carbon monoxide. In addition to these species, others may also be present, including, for example, water, carbon dioxide, unconverted light hydrocarbon feedstock, and various impurities. A typical syngas contains at least 5 mol% of each CO and H2.
4] For the purposes of this invention, the term "LPG" (liquefied petroleum gas) refers to a mixture of light hydrocarbons comprising propane and/or butane. As used herein, the term refers to a blend of hydrocarbons. Unless otherwise stated, LPG may be in cutler a gaseous or liquid state. The term does not necessarily refer to a liquid phase blend comprising hydrocarbons.
5] I he term "syngas conversion reactor" means a reactor for converting syngas gas into more valuable conventional transportation fuels and lubricants A syngas conversion reactor may also be known as a Gas to Liquid (C,TL) reactor. Syngas conversion reactors include, for example, Fischer-] ropsch reactors and methanol synthesis reactors.
[00261 The present nvcnton relates to methods for forming syngas with a desired I-12/CO ratio. T he desired Hz/CO ratio may be selected according to the process in which the syngas is to be used. The stoichiometry of syngas conversion processes varies, and thus, the desired ratio of Hz/CO of syngas to be used in the syngas conversion process varies accordingly. In addition, depending on the conditions and catalysts used in the syngas conversion process, the HJCO ratio of the syngas needed for that process under those conditions also may vary. For a syngas conversion process, it may be important to control the Hz/CO ratio of the syngas to a relatively narrow range around the ideal ratio. According to the present invention, a syngas may be formed with a Hz/CO ratio set for the process in which it is to be used.
7] According to the present invention, a Hz/CO ratio may be selected in the range of l.O to 3.0 on the basis of the process in which the syngas is to be used, and a syngas may be formed with the selected Hz/CO ratio. Generally, the Hz/CO ratio of the blended syngas feed is in the range of 1.0 to 3.0, preferably in range of 1.25 to 2.1, and more prefereably in the range of 1.4 to 1.75. In the present invention, a blended syngas feed is utilized to form the syngas with the selected Hz/CO ratio. It has been discovered that a syngas feed from a methane conversion and a sagas feed from a LPG conversion may be blended to for!n a blended syagas feed with a selected Hz/CO ratio.
[00281 It has been discovered that using a syngas feed produced from LPG and carbon dioxide, which is recovered from a syngas conversion process, such as a Fischer-Tropsch process, reduces unwanted carbon dioxide emissions of the conversion process. In addition, blending syngas streams to generate a blended syngas with the desired Hz/CO ratio is much simpler than the current alternative processes of removing excess H2 from a Hzrich syngas to form a syngas with a desired Hz/CO ratio.
Blended Syngas Feed [0029] According to the present invention, one syngas feed may be generated using a methane conversion. Methane may be used to produce a syngas with a Hz/CO ratio of at least 2.0. Catalysts and conditions for converting methane into syngas are well known to those of skill in the art. Commercial processes for converting methane to syngas mclude partial oxidation, catalytic partial oxidation, steam reforrnng, autothcrmal reforming, series reforming, convective reforrnng, gas heated reforming, and the lilac. ()
100301 These rcformmg processes are well known in the art The rcfomnng processes all produce syngas from methane and an oxidant (steam, oxygen, carbon dioxide, air, enriched air or combinations thereof). The effluent from the reforming processes typically contains some carbon dioxide and steam in addition to CO and H2. Series reforming, convective rcformmg and autotherrnal reforming incorporate more than one syngas forming reaction In order to better utilize the heat of reaction. The processes for producing synthesis gas or syngas from C-C3 alkalies are well known in the art. Steam reformation is typically effected by contacting C-C3 alkalies with steam, preferably in the presence of a reforming catalyst, at a temperature in the range of about 1300 F (705 C) to about 1675 F (913 C) and pressures from about 10 psia (0.7 bars) to about 500 psia (34 bars).
[00311 The reforming can be operated in two stages with the first called a pre-reformer. A pre-reforrner is often used when the gas feed contains hydrocarbons other than methane (e.g., C:+ hydrocarbons). Without a prereformer, the C2+ hydrocarbons can cause operational problems due to coking and metal dusting. As the hydrocarbons in the feed to the reforming section become heavier, the need for a pre-reformer become greater. Suitable reforming catalysts which can be used include, for example, nickel, palladium, nickel-palladium alloys, and the like.
Additional information regarding steam reforming C-C3 alkanes, e.g., methane, to syngas can be found in U.S. Patent No. 5,324,335 hereby incorporated by reference ill its entirety.
2] The partial oxidation of C-C3 alkanes to syngas is also conducted at high temperature and while the partial oxidation may be conducted without a catalyst it is more effectively conducted in the presence of a catalyst. In general Group VIII metals can be used as the catalyst typically supported on a mineral oxide or synthetic support, e.g., alumina. Typically, the partial oxidation is conducted at temperatures in about the range of 1500 F (815 C) to about 2000 F (1093 C) and pressures in about the range from atmospheric to 3000 psia (1 to 20.4 bars). Space velocities can vary over a very wide range and typical range from 100 to 100,000 ho and even higher depending on the particular catalyst used and the type of reactor. A discussion of nickel silica alumina and nickel/magnesium oxide and cobaltlmagnesium oxide and other oxidation catalysts may be found in A. Sautes et al., "Oxidation of Methane to Synthesis Gas in Fluidized Bed Reactor using MgO-Based Catalysts", Journal of Catalysis, Vol. 158 (1996) pp. 81-91 hereby incorporated by reference in its entirety. The partial oxidation may also be conducted using a perovskite catalyst partial oxidation process such as described in U.S. Patent No. 5,]49,516 hereby incorporated by reference in its entirety. Perovskites are materials having essentially the same crystal structure as the mineral pcrovskite (Ca T 03) without limitation as to the elemental constituents thereof. Such materials can be represented by the formula XYO3 whercn X and Y can be Ninety of clcmcnts For example, X can be La, Ca, Sr, Ba, Na, K, Ag, Cd and mixtures thereof and Y can be Ta, Co, To, Ga, Nb, Fc, Ni, Mn, Or, V, 'I'h, lab, Sn, Mo, Zn and mxturcs thereof. Partial oxidation reactions using a perovskte catalyst are typically conducted at temperatures in the range of about from 600 to 900 C, pressures of about front 0.1 to 100 bar and gas hourly space velocities of from 100 to 300,000 hr. These space velocities are determined using a gas volume based on NTP conditions (25 C and one atmosphere of pressure).
The mol ratio of lower alkane can vary from 1:1 to 100:1 moles of alkane to oxygen.
3] If the amount of Ci-C3 alkancs exceeds the capacity of the synthesis gas unit, the surplus C-C3 alkanes can be used to provide energy throughout the facility. For example, excess Ct-C3 alkalies may be burned in a steam boiler to provide the steam used in the thermal cracking step of the present process.
4] Autothermal reforming of methane is a preferred process for converting methane to syngas. In autothermal reforming methane is reacted with water, oxygen and optionally CO2 to produce a syngas with a Hz/CO ratio of greater than 1.5, preferably a Hz/CO ratio in the range of 2.0 to 2.5. Autothermal reforming combines features of both partial oxidation of methane and steam reforming of methane in a single reactor. In this process, methane is partially oxidized in a specially-designed burner and the resulting hot gas passes through a catalyst bed where steam reforming occurs. Autothermal reforming is typically conducted at temperatures,of about 600 to 900 C, pressures of "gout from 0.1 to 100 bar and gas hourly space velocities of from 100 to 300,000 hr. A catalyst containing a Group VIII metal is preferably used. By way of example, nickel-containing catalysts may be used for autothermal reforming. Conditions for autothermal reforming of methane are well known to those of skill in the art.
5] A second syngas feed may be generated using a LPG conversion. Accordingly, LPG is used to produce a syngas with a HJCO ratio less than 2.0, preferably a Hz/CO ratio of no more than 1.5, more preferably of no more than 1.0, and still more preferably in the range of 0.5 to 1.0.
If used alone, a syngas feed from a LPG conversion may have a Hz/CO ratio that is less than desired. Catalysts and conditions for converting LPG into a feed mixture of hydrogen and carbon monoxide are well known to those of skill in the art. Commerci 1l processes for converting LPG to a feed of hydrogen and carbon monoxide include dry reforming processes, such as the Calcor process.
[00361 In particular, the Calcor processes may be used to convert LPG into a feed of hydrogen and carbon monoxide, as described in, for example, "Make CO from CO2," llydrocurhon Processing, Vol 64, May 1985, pp. 106107 and "A new process to make Oxo fecd," lIylrocarhon Processing, Vol. 66, July 1987, pg 52. in the Calcor process, I.PG Is reacted with carbon dioxide to produce a hydrogen and carbon monoxdc product with a WACO ratio of 0.5 to 1 0. Typically, hydrogen would be removed and pure carbon monoxide would be isolated from the hydrogen/carbon monoxide product of the ('alcor processes. It has been discovered that the hydrogen/carbon monoxide product may be used as a syngas feed for a Fischer-Tropsch reactor without isolation of hydrogen, which is often a feature of the conventional Calcor process.
[00371 The process and conditions used for dry reforming of LPG are similar to those used in dry reforming of methane and arc well known to those of skill m the art. A catalyst containing a Group VIII metal may be used. In addition to the Group VIII metal catalysts, inert metal oxides, such as silica or alumina may be used as supports. Other metals, such as manganese or chromium may be used or used with a Group VIII metal as a promoter. To reduce coking, the acidity of the support should be reduced by using non-acidic aluminas, silicas, or by neutralization with Group I or II metals.
8] Before dry reforming, it is desirable to remove any sulfur compounds (e.g., hydrogen sulfide and mercaptans) contained in the LPG. Conditions and methods for removing sulfur/sulfur compounds from LPG are well known to those of skill in the art. By way of example, the sulfur compounds may be removed by passing LPG through a packed bed sulfur scrubber containing a zinc oxide bed or other slightly basic packing material. Sulfur compounds may also be removed by contacting the LPG with a caustic solution as used in Merox, Minalk, and related processes, the conditions of which are also well known to those of skill in the art.
9] Conditions for performing dry reforming of LPG are described in, for example, "Make CO from C02," Hydrocarbon Processing, Vol. 64, May 1985, pp. 106- 107. These conditions are well known to those of skill in the art. The preferred temperature is in the range of about 1300 F (705 C) to about 1675 F (913 C) and the preferred pressures are in the range of from about 10 psia (0.7 bars) to about 500 psia (34 bars). Preferably the pressure of the LPG conversion reactor is close (within 50 psi) to the pressure of the syngas conversion reactor, thus eliminating or at least reducing the need for compression. Contact time should be sufficient to convert at least 25% of the combined hydrocarbons boiling higher than propane in the feed, preferably at least 50%, more preferably at least 75%, and most preferably at least 90%.
0] After the dry reforming reactor, the effluent should be quenched as quickly as possible to avoid carbon/coke formation. This quenching can be done by heat exchange or by injection of a quenching matenal. These quenching materials include, for example, a cool hydrocarbon stream or water. Methods to control coking include devices to rapidly quench the syagas and to passivity the metal surfaces to avid carbon formation References for passvaton ncludc U S Patent No. G,274,113, U S. Patent No 5,863,418, U S. Patent No. 5,676,821, U.S. Patent No. 5,674,376, and U S Patent No. 5,658,452. Sulfur may be used to inhibit coking The problems associated with coking during the production of low Hz/CO syngas and the use of sulfur to inhibit this cokmg are described in "Sulfur passivated reforming process lowers syngas Hz/CO ratio" by N.R. Udcngaard ct al., Oil and Gas Journal, March 9, 1992, pages 62-67.
However, when the syngas is to be used for a sulfur-sensitive FischerTropsch process, passivatng the metal surfaces with sulfur Is undesirable. References for devices to rapidly quench and avoid coking include: U.S. Patent No. 4,703,793 and U.S. Patent No. 4,785,877. A venturi device can be used to rapidly quench the exit gas stream, and the feed to the venturi device consists of the outlet from the reformer and a cooled recycle gas stream. This device is shown in DE3941591A1.
1] The stoichiometric reactions for conversion of propane and butane by the Calcor dry reforming reactions are as follows: C4Ho+4CO2 - 8C0+5H2 C3H + 3CO2 6 CO + 4 H2 Thus, the stoichiometric ratio of CO2 to LPG in the feed varies between 3 and 4 depending on the proportion of butane and propane in the feed. In actual practice, the stoichiometric amount of CO2 needed can be calculated from the average feed composition. The molar ratio of Hz/CO in the product varies from 0.67 for propane to 0.62 for butane. Again, the molar ratio of Hz/CO in the product varies from 0.5 to I.0 depending on the composition of the feed, and typically varies from 0. 55 to 0.7. These ratios refer to the H2 and CO produced in the reaction of hydrocarbons with CO2 in the absence of other reactive species. If H2, H2O, O2 or CO are also in the feed to the Calcor process, the resulting ratios of HJCO can be different, but are usually still within the desired range of less than 2.0, typically less than 1.5.
10042] The molar ratio of initial feed of CO2 to LPG should be between 0. 5 and 1.5 of the stoichiometric amount needed to convert the product by the dry reforming reaction, preferably between 0.75 and 1.25 and most preferably between 0.9 and 1.1. Typically an excess of CO2 is added to assist in complete conversion of the LPG. In addition to CO2, the feed to the unit may also include some water and oxygen, as these will tend to increase the Hz/CO ratio. Furthermore, the feed may contain some H2 and CO in addition to CO2, since some Fischer-Tropsch product streams that arc rich in CO2 also contain some residual H2 and CO.
100431 Optionally, the elElucnt from the l PG conversion reactor can be further purified to remove mpuriies such as watcr, carbon dioxide, and traces of sulfur, nitrogen and acetylenc 1() compounds. The purificationcan be done by contacting the candent (uc., the syngas product) with an adsorbent, such as water, or by contact with a sohd adsorbent, such as a basic material capable of removing acidic compounds like CO2 and acetylenic compounds. al his purification of the syngas can be done on the syngas product from the LPG conversion reactor, or blends of the syngas product from the LPG conversion reactor with other syngas streams, such as a syngas product from a methane conversion reactor or a recycle syngas from the Fischer-Tropsch reactor.
100441 A key technical feature of the present invention is the recognition that the reaction of LPG with CO2 or water is much faster than the corresponding reaction with methane. The faster reaction permits the LPG to be converted at a high conversion rate to a syngas with a relative low Hz/CO ratio by use of a reactor with a short residence time. By rapidly quenching the product of the LPG conversion, subsequent coke formation can be minimized or avoided all together. In comparison, methane is much less reactive with CO2 than LPG, and high methane conversions are difficult if not impossible to achieve. Achieving them requires long residence times at high temperatures, which increase the likelihood of coking. Also, while unconverted methane is difficult to separate from syngas (and thus may build up in a syngas recycle loop), LPG can be separated from syngas. Accordingly, it is not essential to obtain a high conversion of LPG in a LPG to syngas conversion process. Therefore, LPG can be converted into a syngas with a Hz/CO ratio less than 2.0, preferably 1.5 or less, and most preferably 1.0 or less, while avoiding coke formation.
[00451 LPG used in the LPG conversion process can originate from a variety of sources. By way of example, the LPG can be isolated from a natural gas asset; it can be eo-produeed with methane from a hydrocarbon reservoir as a "wet gas or broad fraction"; it can be a recovered as a condensate during crude production; it can be recovered from a syngas conversion process (i.e., a Fiseher-Tropseh process); and it can be recovered as a product derived during upgrading of syngas conversion products, in particular a Fiseher-Tropseh conversion process. Due to increased efficiencies, preferably at least a portion of the LPG used in the LPG conversion process is recovered as a product of the syngas conversion process. Therefore, the syngas may be used in a syngas conversion process, for example, a Fischer-Tropsch process, and this process may produce a starting material used to generate the syngas.
6] Typically, LPG from the above-listed sources would be collected, shipped and sold; however, LPG has a lower value than higher boiling hydrocarbons. In addition, LPG is difficult to export and potentially dangerous, and thus expensive to ship and store. In the present invention, LEG is advantageously used to produce more valuable higher boiling hydrocarbon 1 1 products, thcrchy mmm.mg or avoiding the costly and hazardous faciltcs assocatcd with storage and transport of Ll'G.
[00471 Carbon dioxide used in the LPG conversion process can originate from a variety of sources. By way of example, the carbon dioxide may be recovered or extracted from a syngas stream product from a methane conversion process, from a syrups stream from a LPG reforming process, from a blended syngas stream, from urlreacted syngas from the syngas conversion process (i.e., a Fischer-Tropsch process), from a portion of unreacted syngas that is recycled to the syngas conversion process, from a portion of syugas that is used as fuel or for other purposes, or from a blend of a fresh syngas stream and a recycled, unconverted syngas stream. Carbon dioxide may also be obtained from other sources including, for example, an effluent of a Fischer- Tropsch reactor, a syngas stream from a methane conversion process, a natural gas asset, a furnace flue gas, and combinations thereof. The furnace flue gas may originate, for example, from furnaces used in a syngas conversion process (i.e., a Fischer-Tropsch process), from furnaces used in gas production equipment or a crude production process. Due to increased efficiencies, preferably at least a portion of the carbon dioxide used in the LPG conversion process is recovered from a syngas conversion reactor (i.e., a Fischer-Tropsch reactor).
Therefore, the syngas may be used in a syngas conversion process, for example, a Fischer- Tropsch process, and this process may produce a starting mater).' used to generate the syngas.
[00461 In the conventional Fischer-Tropsch process using, non-shifting catalysts, as shown in Figure 1, a methane-containing stream 10, with an added oxygen-containing stream 20, optionally which contains water, is converted to syngas 35 in syagas formation unit 30 (e.g. autotherrnal reformer). A blended syngas feed 37 is passed to a Fischer-Tropsch synthesis reactor 40. Products 45 from the Fischer-Tropsch synthesis reactor are passed to separator 50 for recovering hydrocarbon liquids 55, including C5+ hydrocarbon liquids. Light gas 51 is also recovered from separator 50. This light gas 51, which may contain one or more of LPG, H2, CO and CO2, may be recycled to the Fischer-Tropsch synthesis reactor through conduit 52, or to the syngas formation unit through conduit 53, or may be recovered as fuel gas 54.
100491 CO2 is produced in small amounts in the syngas formation unit 30 and Fischer- Tropsch hydrocarbon synthesis reactor(s) 40. However, it builds up to high levels, typically about 30% in the recycle gas streams. It is an inert in the Fischer-Tropsch reactor and as its concentration rises, the concentration of reactive H2 and CO drops, thus decreasing the effcrcncy of the process. A portion of the recycle gas stream 52 must be purged 54 (and used as a low- cnergy content fuel) to control the CO2 buildup. Use of the CO2 in this gas stream (either as separated CO2 or as at least a portion of the gas stream without separation of the CO2) enables the CO2 to be converted mto valuable products, Fscher-Tropsch reactor cfficcncy to be improved, and CO2 emissions to be reduced.
0] It has been discovered that Using a syngas produced from LPG and carbon dioxide, which is recovered from a syngas conversion process (i.e., a Fischer-rlropsch process), reduces the unwanted carbon dioxide emissions of the conversion process.
1] It has been discovered that the syngas stream from the methane conversion and the syngas stream from the LPG conversion advantageously may be blended to form a blended syngas feed. A desired Hz/CO ratio may be selected for this syngas feed based on the conditions of the syngas conversion to be performed. The syngas streams may be blended in such a way as to achieve the desired HJCO ratio. The blended syngas with the desired Hz/CO ratio may be fed to a reactor, which ideally requires a syngas feedstoek with the desired Hz/CO ratio. The blended syngas feed may preferably be a feed to a Fiseher-Tropseh reactor. An unreaeted, recycle syngas stream from the reactor may also be blended into the blended syngas stream and this further blended syngas stream may be fed into the reactor.
10052] Methods for blending the syngas streams and controlling the quantity of individual syugas streams added to form the blended syngas stream would be readily understood and devised by one of skill in the art. The syngas streams, which are blended to form a blended syngas, originate from a LPG conversion and a methane conversion and, optionally, an unreaeted, recycle syugas stream. As one of skill in the art would readily understand and be able to devise, these streams may be blended in a variety of ways to achieve the desired Hz/CO ratio.
The streams may be blended in a blending zone and one blended syngas is provided from the blending zone.
3] Blending of the syngas streams to generate a blended syngas with the desired Hz/CO ratio is much simpler than the current alternative processes of removing excess H2 from a H2-rieh syugas. The blending may be accomplished by conventional process control schemes. By way of example, to blend the syngas products, the syngas streams may be pumped together in specified amounts to achieve the selected HJCO ratio and then pumped into a syngas conversion reactor, preferably a Fiseher-Tropseh reactor. In general, it is desirable to eon' ol the composition of the final blended syngas that is fed to the syngas conversion reactor. As one of skill in the art would readily understand and be able to devise, controlling the blending of the syugas streams may be accomplished in a variety of ways. There are several process alternatives to control this blending operation, but m general, one stream Is produced in slight excess and during normal operation the excess can be used as fuel, recycled to a syngas conversion process, flared, or used m a separate syngas conversion process T he relative feed rates to the methane and LPG converters can also he controlled to generate the desrcd composition. Also, combmatons of control methods can be used to make both rapid and slower long-term adjustments.
4] Also as one of skill m the art would readily understand and be able to devise, the Hz/CO ratio may be monitored in a variety of ways. By way of example, the Hz/CO ratio may be monitored in the Individual syngas streams and/or in the blended syngas by gas chromatography, mass spectrometry, gas density, Orsat chemical analysis, and the like. In the alternative, the Hz/CO ratio may be approximated based on the conversion conditions, and a quantity of the syngas streams may be blended to achieve the selected Hz/CO ratio using the approximate ratios.
By way of example, if a higher Hz/CO ratio was selected, a larger quantity of syngas stream from the methane conversion may be blended, and in the alternative, if a lower Hz/CO ratio was selected, a larger quantity of syngas stream from the LPG conversion may be blended. Methods for controlling and monitoring the quantity of individual syngas streams added to form the syngas blend would also be readily understood and devised by one of skill in the art.
5] Although this process requires construction of two separate syngas generators, there is no loss of economic efficiency because there is a limit to the scale on which syngas generators can be built. This limit in scale demands that for large syngas conversion facilities, which typically produce >30,000 BI'D (barrels per day) of product, such as Fischer-Tropsch facilities, more than one syngas generator will likely be needed anyway.
Gas to Liquid Conversion Processes [0056] Remote natural gas assets may be converted into conventional transportation fuels and lubricants by two main processes. Both processes use syngas as an intermediate, and depending on the catalysts and conditions, each process has an ideal Hz/CO ratio for the syngas.
These syngas conversion processes include Fischer-Tropsch processes and methanol synthesis coupled with the methanol to gasoline (MTG) processes.
[00571 According to the present invention, a preferred conversion process is a Fischer Tropsch process. The Fischer-Tropsch products include, for example, gasoline, naphtha, diesel fuel, Jet fuel, lube base stocks, and the like. Fischer-Tropsch processes utilize natural gas (which is mostly methane) that has been converted to synthesis gas, or syngas, which is a mixture of carbon monoxide and hydrogen.
[00581 The syngas generation Is the most costly step of the FischerTropsch synthesis process. It has been dscovcred that a critical feature of the Fischer- f ropsch process is producing syngas with a desired Hz/CO ratio to optimize formation of the desired Fischer-Tropsch products and avoid problems in the syngas formation step.
[00591 Fischer-Tropsch products possess many desirable properties. By way of example, Fischer-Tropsch products are highly paraffinic and have very low levels of sulfur, ntrogcn, aromatics, and cycloparaffins. FischerTropsch products also have excellent combustion and lubricating properties. However, a disadvantage of a typical Fischer-Tropsch process is that relatively large amounts of CO2 are emitted during the conversion of natural gas into Fscher Tropsch products.
0] Catalysts and conditions for performing Fischer-Tropsch synthesis are well known to those of skill in the art, and are described, for example, in EP 0 921 184 Al, the contents of which are hereby incorporated by reference in their entirety.
1] In the Fischer-Tropsch process, liquid and gaseous hydrocarbons are formed by contacting a synthesis gas, comprising a mixture of H2 and CO, with a Fischer-Tropsch catalyst under suitable temperature and pressure reactive conditions. Reaction conditions for the Fischer Tropsch reaction typically include operating at temperatures of about 300 to 700 F (149 to 371 C), preferably about from 400 to 550 F (204 to 228 C); pressures of about from lO to 600 psia, (0.7 to 41 bars), preferably 30 to 300 psia, (2 to 21 bars) and catalyst space velocities of from about 100 to about 10,000 cc/g/hr., preferably 300 to 3,000 cc/g/hr. Examples of conditions for performing Fischer- l'ropsch type reactions are well known to those of skill in the art.
[00621 The products of the Fischer-Tropsch synthesis process may range from Cat to C200+ with a majority in the C5 to C'oo+ range, and the products may be distributed in one or more product fractions. The reaction can be conducted in a variety of reactor types, for example, fixed bed reactors containing one or more catalyst beds, slurry reactors, fluidized bed reactors, or a combination of different type reactors. Such reaction processes and reactors are well known and documented in the literature. In the Fischer-Tropsch process, the desired Fischer-Tropsch product typically will be isolated by distillation. A particularly preferred Fischer-Tropsch process is taught in EP 0609079, herein incorporated by reference in its entirety.
l0063l In general, suitable Fischer-Tropsch catalysts comprise one or more Group VIII catalytic metals such as Fe, Ni, Co, Ru and Re. Additionally, a suitable catalyst may contain a promoter. Certain catalysts are known to provide chain growth probabilities that are relatively low to moderate, for example, iron-containing catalysts, and the reaction products include a relatively high proportion of low molecular (C2 a) weight olcfins and a relatively low proportion of high molecular weight (Cart+) waxes Certain other catalysts (e.g. cobalt- contanng catalysts) are known to provide relatively high chain growth probabltcs, anal the reaction protects mclubc a relatively low proportion of low molecular (I c., C2 I) wcg}lt olcfins and a relatively high proportion ol high molecular wcght (he., Call-) waxes. Such catalysts are well known to those of skill in the art and can be readily obtained and/or prepared. The preferred catalysts of this invention contain either Fe or Co, with Co being preferred.
t0064l The product from the Fischer-Tropsch process may be further processed using, for example, hydrocracking, hydroisomcrizaton, and hydrotreating. Such processes crack and/or isomerizc the larger synthesized molecules into fuel range and lube range molecules with more desirable boiling points, pour points, and viscosity index properties. Such processes may also saturate oxygenates and olefins to meet the particular needs of a salable products (naphtha, diesel, jet, lube base stock). These processes are well known in the art and do not require further
description here.
[00651 Due to the net stoichiometry for a Fischer-Tropsch reaction, the desired Hz/CO ratio of the syngas is approximately 1.5. If the syngas has a Hz/CO ratio in excess of the desired value, the formation of unwanted methane in the conversion process becomes excessive. If the Hz/CO ratio becomes too low, the catalyst can coke, or the formation of oxygenated species, olefins, and very heavy waxes can become excessive. Therefore, it has been discovered that it is important to control the syngas HJCO ratio to be fed to the Fischer-Tropsch reactor to relatively narrow ranges. The values of the range depend on the catalyst used in the syngas conversion step.
While the ideal ratio for conversion is 1.5, actual ratios needed in the syngas fed to the reactor may differ in practice. Typical gas compositions are as follows: 1(, Stream Reference No 1 12/CO '02, (Fig] ) _ __molc'lio Syngas from Reformer 35 1.95 5 Syngas Blend to Flscher-Tropsch 37 1.5 Light Gas Recycle to Flscher-Tropsch 52 1.0 30 Light Gas Recycle To Reformer 53 l.O 30
_
Fuel Gas 54 1.0 30 [0066] By way of example, iron Fischer-Tropsch catalysts typically may operate at lower Hz/CO ratios than cobalt Fischer-Tropsch catalysts because iron catalysts may also catalyze the water shift reaction: CO+H20 - CO2+H2 The water for this reaction is produced by the Fischer-Tropsch reaction. If conversion for the Fischer-Tropsch reaction is high and significant amounts of water are present, significant amounts of carbon monoxide may be converted to H2, increasing the HJCO ratio and thus leading to excessive methane formation. To counter this effect, the syngas Hz/CO ratio used with iron Fischer-Tropsch catalysts may be less than 1. and is typically close to 1.0. Fischer- Tropsch catalysts that promote the water gas shift reaction, such as iron, are known as shifting synthesis catalysts. In contrast, a cobalt Fischer- Tropsch catalyst catalyzes the water gas shift reaction to a much smaller extent and thus is referred to as non-shifting Fischer-Tropsch catalyst.
Therefore, the syngas Hz/CO ratio used with cobalt Fischer-Tropsch catalysts is closer to the stoichiometric required ratio of 2.0 and is typically 1.5 to 1.75. With cobalt catalysts, the ratios are kept below 2. 0 in an effort to minimize methane formation and maximize the production of heavy products. Unreacted Hz-rich syngas is blended with Hz-deficient syngas made in the syngas reactor and recycled to the Fischer-Tropsch reactor as shown in Figure 1.
[00671 Accordingly, it has been discovered that the syngas Hz/CO ratio needs to be adjusted to values that depend on the characteristics of the Fischer-Tropsch catalyst being used, the desired products, and the reaction conditions. The method of the present invention for forming a blended syugas with a desired Hz/CO ratio allows the syngas ratio to be readily adjusted for the syngas conversion reaction being performed.
Inegruted I'rocesses for l'rolucug Varahle H2/C'O 5'yngas Feel 10068] Figure l illustrates an exemplary conventional Fischer-Tropsch synthesis system with typical gas compositions, as described herehbefore Figure 2 illustrates an exemplary integrated Fischer-Tropsch synthesis system according to the present invention using two syngas formation steps, one of which is a methane conversion and the other is a LPG conversion. Exemplary gas compositions are as follows: Stream Reference No. HJCO CO2, (Fig 2) Mole Syngas from Reformer 135 2.1 3 Syngas Blend to FischerTropsch 137 1.5 10 Light Gas Recycle to Fischer-Tropsch 152 1.0 15 Light Gas Recycle To Reformer 153 1.0 15 Fuel Gas 154 1.0 15 Syngas from LPG Converter 164 0.8 lO [0069] It is important to note that the CO2 in the recycle gas steams and the fuel gas have been reduced in comparison to the conventional case in Figure 1. In the process illustrated in Figure 2, a desired syngas Hz/CO ratio of approximately 1.5 is selected for the syngas feed 137 to the Fischer-Tropsch reactor 140. To form the syngas feed for the Fischer- Tropsch GTL facility, methane 110 is mixed with oxygen and steam 120. The mixture is fed into a methane syngas generator zone 130, for example, an autothermal reformer, to generate a first syngas feed with a HJCO ratio in excess of 2.0, for example, approximately 2.1.
0] Also to form the syngas feed, LPG 161, C02162, and recycle syngas 153, containing CO2, CO, H2, and CH4, are mixed. This mixture 163 is fed into a LPG syngas generator zone 160, for example a dry reforming reactor, to generate a second syngas feed 164 with a total Hz/CO ratio less than 2.0, preferably no more than 1.5, for example 0.8. The Hz/CO ratio initially produced by the reaction of CO2 and LPG Is approximately 0.65. This ratio is increased to 0.8 by use of the external recycle stream 153 that already contained H2 and CO with a ratio of 1.0.
[007ll The first syngas feed 135, an internal recycle syngas stream 152 with a Hz/CO ratio of l.O and the second syngas feed 164 are blended in a blending zone 170 to form a third syngas stream 137 with a Hz/CO ratio of approximately 1.5. The blended syngas feed 137 is fe 1 into a FischerTropsch reactor zone 140 'l'he effluent from the l*'schcr-'l'ropsch reactor 145, which consists of gas and hound products and unrcacted syngas, Is separated, typically by distillation, In the scparaton zone 150 to provide unreacted, recycle syngas 151 and hydrocarbon products t55.
A portion of the nrcacted syngas 154 may be used as fuel. Recycle LPG may also be obtained from the Fischer-Tropsch reactor. Since the methane m the recycle syngas will not be converted to a great extent in the LPG converter due to the lower reactivity of the methane relative to LPG, optionally a portion of the recycle syngas may also be sent to the methane syngas generator zone.
[00721 In a separate embodiment of the invention, the present process is useful for maintaining the desired Hz/CO ratio in each of a multiplicity of Fischer-Tropsch reactors, each operated in series with respect to the flow of syngas from each reactor to a succeeding reactor In the series. In this embodiment of the invention, a first syngas, comprising H2 and CO and having a Hz/CO ratio in the range of 1.25 to 2.1, preferably in the range of 1.4 to 1.75, is fed into a first Fischer-Tropsch synthesis reactor, which is maintained at Fischer-Tropsch operating conditions.
The preferred Fischer-Tropsch catalyst in the first Fischer-Tropsch synthesis reactor of this embodiment comprises cobalt. The first syngas may be formed as a blend of a syngas formed by an autotherrnal reformer and having a Hz/CO ratio in the range of 2.0 to 2.5, blended with a syngas formed by a dry reforming reaction and having a HJCO ratio of no more than 1.0. A second syngas is recovered from the effluent from the Fischer-Tropsch synthesis reactor, wherein the second syngas has a lower Hz/CO ratio than that of the first syngas. Before passing the second syugas to a second Fischer-Tropsch synthesis reactor, it is desirable to increase the Hz/CO ratio in the second syngas to a desired ratio appropriate for the catalyst and conditions of the second Fischer-Tropsch synthesis reactor. According to the invention, the Hz/CO ratio may be increased by adding a third gas having a higher Hz/CO ratio. The process then includes forming a third syngas with a Hz/CO ratio of at least 2.0 by reacting methane with an oxygen source; blending the second syngas with the third syngas to form a blended syngas feed having a Hz/CO ratio in the range of 1.25 to 2.1, preferably in the range of 1.4 to 1.75; and feeding the blended syngas into a second Fischer-Tropsch reactor. Preferably, the third syngas is formed by an autothermal reformer and has a Hz/CO ratio in the range of 2.0 to 2.5.
100731 In another separate embodiment, it may be desired to conduct the Fischer-Tropsch reactions m a series of reactors, in which one or both reactors produce a syngas effluent m which the Hz/CO ratio increases during the Fischer-Tropsch reaction. An example of such a Fischer- Tropsch reaction would include one conducted over a shifting (i.e., ironcontaining) catalyst. In this embodiment, a first syngas, comprising HI and CO and having a EI2/CO ratio In the range of 1.0 to 2.1, preferably h1 the range of I. I to 1.75, is fed into a first Fischer- [ ropsch synthesis reactor, which is mantancd at Fischer-Tropsch opcratng conditions The first syngas may be formed as a blcud of a syngas conned by an autothermal reformer and having a 112/CO ratio in the range of 2.0 to 2 5, blended with a syngas formed by a dry refonnmg reaction and having a HJCO ratio oi'no more than 1.0. A second syngas is recovered from the effluent from the Fischer-Tropsch synthesis reactor, wherein the second syngas has a higher Hz/CO ratio than that of the first syngas. Before passing the second syngas to a second Fischer-Tropsch synthesis reactor, it is desirable to decrease the Hz/CO ratio in the second syngas to a desired ratio appropriate for the catalyst and conditions of the second Fischer-Tropsch synthesis reactor.
According to the invention, the Hz/CO ratio may be decreased by adding a third gas having a lower Hz/CO ratio. The process then includes forming a third syngas with a Hz/CO ratio of no more than 1.0 by reacting LPG with CO2; blending the second syngas with the third syngas to form a blended syngas feed having a HJCO ratio in the range of 1.0 to 2.1, preferably in the range of 1.1 to 1.75; and feeding the blended syngas into a second Fischer-Tropsch reactor.
10074] The present process further provides a method for preparing hydrocarbons via a Fischer-Tropsch synthesis process using a syngas feed having an unusually low Hz/CO ratio.
Thus, a process is provided for producing a fuel, the process comprising: reacting LPG and CO2 to form a syngas with a Hz/CO ratio of no more than 1.5; reacting the syngas in a Fischer- Tropsch process to produce a hydrocarbonaceous effluent; and converting the hydrocarbonaceous effluent into at least one fuel. The fuel which may be prepared in this process boils in the range of C3 - 700 F, preferably in the range of C5 - 650 F. LPG, naphtha, jet and diesel are particular fuels which may be made as described herein. In addition, the hydrocarbonaceous effluent may be further converted into at least one lubricant base stock. This lubricant base stock, optionally after additional processing using hydrotreating, hydrocracking, hydroisomerization, dewaxing, hydrofinishing, or a combination of these additional processes, preferably has a viscosity, measured at 100 C, of greater than 3 cSt, a viscosity index of greater than 120, and a pour point of less than about -9 C.
Reduction of Green House Emissions [00751 In a separate embodiment, the present process is also directed to a method for reducing greenhouse gas emissions from a Gas to Liquids (GTL) facility by improving the proportion of resource carbon that is converted into useful product (i.e., by increasing carbon efficiency of the GTL facility). 'I'hc proportion of carbon in methane that is converted to heavier hydrocarbon products in Fischer-Tropsch GTI processes is estimated to be about 68%, with the remaining 32 y, of the carbon being converted to some hghtcr hydrocarbons and to significant amounts of CO2. The cstmated carbon effccncy is taken from "CO2 Abatement in GTL Plant: Fscher-Tropsch Synthesis," Report #PH3/15, November 200O, published by IFA Greenhouse Gas R&D Programme, and Is based on a GTL facility using cryogenic air separation, an autothermal rcEormer, a slurry bed Fischer-Tropsch unit and a hydrocracker for converting heavy wax into saleable products. GTL facilities using alternative technologies would exhibit similar carbon conversion efficiencies and CO2 emissions. While the IEA report describes how CO2 extraction methods using amine scrubbers can reduce CO2 emissions, it does not describe methods to improve the carbon efficiency of the process to reduce the CO2 emissions.
[00761 The processes of the present invention improve the carbon efficiency of hydrocarbon synthesis facilities, such as a GTL facilities using Fischer-Tropsch synthesis processes. Carbon efficiency can be visualized by drawing a material balance line around the entire GTL process, including reforming to convert gaseous and/or liquid hydrocarbons to a syngas, hydrocarbon synthesis to convert the syngas to a hydrocarbonaceous product, and separation of the hydrocarbonaceous product to recover C5+ hydrocarbons. Entering this material balance line are the feedstock streams, and exiting it are the net product streams. Within the material balance line, all processes derive the energy they need from thefeedstock stream. For purposes of this application, the carbon efficiency of a GTL process is defined as the mass of carbon exiting the material balance line which has been incorporated into Cs+ products, divided by the mass of carbon entering the material balance line in the original feedstock. Thus, Carbon Efficiency = 100 * Mass of C in C_ Products Mass of C in Feedstocks In practice, the flows entering and exiting the material balance line are preferably summed over a time period sufficient to generate steady state operation (typically one day).
[00771 If methane is the sole feedstock, and typical operations are performed which allow significant amounts of carbon in the feed to be converted to carbon dioxide, the carbon efficiency is approximately 68%, as outlined in the IEA eport. This represents current commercial operation. If hydrocarbons (LPG in this invention) are used to convert part of the CO2 from the GTL process, they must be counted as part of the denominator (Mass of C in Feedstocks) in the calculation of carbon efficiency.
[00781 By use of the invention described herein, a portion of the CO2 which would convcntonally have been vented through the material balance brie is converted into C5+ products According to the present Invention, a GTI process Is provdcd for convcrtng gaseous and/or liquid hydrocarbons to C5+ hydrocarbons This GTL process includes refomlng to convert gaseous and/or liquid hydrocarbons to a syngas, hydrocarbon synthesis to convert the syngas to a hydrocarbonaceous product, and scparaton of the hydrocarbonaccous product to recover C5 hydrocarbons. Accordingly, by rise of the processes described hcrcin, a hydrocarbon conversion process may be conducted at a carbon efficiency of greater than 75%, preferably greater than 85%, more preferably greater than 90%, and most preferably greater than 95% by the use of the present process.
9] In the process, carbon efficecncy is improved by deriving energy from a low value carbon source, and by converting at least a portion of the CO2 that would otherwise be vented from the Fisher-Tropsch unit into C5+ hydrocarbons. Additional carbon efficiency may be obtained by using non-carbon sources of energy, such as hydrogen, as a fuel. The hydrogen may be extracted from syngas or obtained by reforming light naphtha products from the Fischer Tropsch unit to form aromatics and hydrogen.
0] Specific further embodiments of the present invention include the use of supplemental CO2 in the LPG conversion reactor where the supplemental CO2 can be derived from the natural gas asset.
0081] Various modifications and alterations ofthis invention will become apparent to those skilled in the art without departing from the scope arid spirit of this invention. i

Claims (65)

  1. A process for the production of a blended syngas feed with a variable HJCO ratio comprising the steps of: (a) feeding a first syngas, comprising H2 and CO and having a Hz/CO ratio in the range of 1.25 to 2.1, into a first Fischer-Tropsch synthesis reactor and recovering at least one effluent therefrom; (b) recovering a second syngas from the effluent, wherein the second syngas has a higher HJCO ratio than that of the first syngas; (c) forming a third syngas with a Hz/CO ratio of no more than 1.5 by reacting LPG with CO2; (d) blending the second syngas with the third syngas to form a blended syngas feed having a Hz/CO ratio in the range of 1.4 to 1.75; and (e) feeding the blended syngas feed into a second Fischer-Tropsch reactor.
  2. 2. The process of claim 1, wherein the third syngas is formed by a dry reforming reaction and has a Hz/CO ratio of no more than 1.0.
  3. 3. The process of claim 2, wherein the Hz/CO ratio of the first syngas is in the range of 1.4 to 1.75.
  4. 4. A process as claimed in claim 1 wherein a hydrocarbonaceous effluent from one or other or both of the Fischer-Tropsch reactors is recovered and at least a portion thereof converted into at least one fuel, at least one lubricant stock, or combinations thereof.
  5. 5. A fuel or a lubricant stock prepared by the process of claim 4.
  6. 6. The fuel of claim 5, which is for use neat or as a blend stock.
  7. 7. A process for the production of a blended syngas feed with a desired Hz/CO ratio comprising the steps of: (a) selecting a desired Hz/CO ratio of a blended syngas feed; - 23 (b) forming a first syngas with a HJCO ratio of at least 2.0 by reacting methane with an oxygen source; (c) forming a second syngas with a Hz/CO ratio of no more than 1.5 by reacting LPG with CO2; and (d) blending the first syngas and the second syngas to form a blended syngas feed with the desired Hz/CO ratio.
  8. 8. The process of claim 7, wherein the Hz/CO ratio of the blended syngas feed is in the range of 1.0 to 3.0.
  9. 9. The process of claim 7, wherein the Hz/CO ratio of the blended syngas feed is in the range of 1.25 to 2.1.
  10. 10. The process according to claim 7, wherein the Hz/CO ratio of the blended syngas feed is in the range of 1.4 to 1.75.
  11. The process of claim 7, wherein the first syngas is formed by an autothermal reformer and has a Hz/CO ratio in the range of 2.0 to 2.5.
  12. 12. The process of claim 7, wherein the second syngas is formed by a dry reforming reaction and has a Hz/CO ratio of no more than 1.0.
  13. 13. :[ he process of claim 7, wherein the second syngas is formed by a dry reforming reaction and has a Hz/CO ratio in the range of 0.5 to 1.0.
  14. 14. The process of claim 7, wherein at least a portion of the LPG is recovered from a source selected from the group consisting of a natural gas asset, a syngas conversion reactor, a Fischer-Tropsch product upgrading reactor, and combinations thereof.
  15. 1 S. The process of claim 7, wherein at least a portion of the CO2 is recovered from a source selected from the group consisting of an effluent of a Fischer-Tropsch synthesis reactor, a - 24 syngas stream from a methane conversion process, a natural gas asset, a furnace flue gas, and combinations thereof.
  16. 16. The process of claim 7, wherein the oxygen source is selected from the group consisting of air, enriched air, purified oxygen, water, CO2 and combinations thereof.
  17. 17. The process of claim 16, wherein the purified oxygen contains at least 90% oxygen.
  18. 18. The process of claim 16, wherein the purified oxygen contains at least 95% oxygen.
  19. l 9. The process of claim 16, wherein the purified oxygen contains at least 99% oxygen.
  20. 20. The process of claim 16, wherein the oxygen source comprises water.
  21. 21. A process comprising the step of converting a blended syngas feed obtained by a process as claimed in any one of claims 7-20 in a syngas conversion reactor to produce a hydrocarbonaceous effluent.
  22. 22. The process of claim 21, wherein the syngas conversion reactor is a Fischer-Tropsch reactor.
  23. 23. The process of claim 21, wherein the syngas conversion reactor is a methanol synthesis reactor.
  24. 24. The process of claim 21, 22 or 23, further comprising converting at least a portion of the hydrocarbonaceous effluent into at least one fuel, at least one lubricant stock, or combinations thereof.
  25. 25. A blended syngas feed prepared by the process of any one of claims 7 to 20.
  26. 26. A fuel or a lubricant stock prepared by the process of claim 25. -
  27. 27. The fuel of claim 26, which is for use neat or as a blend stock.
  28. 28. A process of using LPG and CO2 in preparing a syngas feed for a Fischer-Tropsch reactor, comprising the steps of: (a) contacting LPG and CO2 at reforming reaction conditions to form a first syngas with a Hz/CO ratio of no more than 1.5; (b) blending the first syngas with a second syngas, said second syngas having a Hz/CO ratio of no less than 2.0, to form a blended syngas feed; and (c) feeding the blended syngas feed into a Fischer-Tropsch reactor.
  29. 29. The process of claim 28, wherein the second syngas is generated from a methane conversion process.
  30. 30. The process of claim 28, wherein the CO2 is recovered from a source selected from the group consisting of an effluent from a Fischer-Tropsch reactor, a syngas stream from a methane conversion process, a natural gas asset, a furnace flue gas, and combinations thereof.
  31. 31. The process of claim 30, wherein the CO2 is recovered from the effluent of a Fischer- Tropsch reactor.
  32. 32. The process of claim 28, wherein the LPG is recovered from a source selected from the group consisting of a natural gas asset, an effluent from a Fischer-Tropsch reactor, a Fischer-Tropsch product upgrading reactor, and combinations thereof.
  33. 33. The process of claim 32, wherein the LPG is recovered from an effluent from a Fischer- Tropsch reactor or a natural gas asset.
  34. 34. The process of claim 28, wherein the blended syngas feed has a Hz/CO ratio in the range of 1.4 to 1.75.
  35. 35. A blended syngas feed prepared by the process of any one of claims 28 to 34. - 26
  36. 36. A process comprising the steps of preparing a blended syngas feed and feeding it to a Fischer-Tropsch reactor in accordance with the process oi any one of claims 28 to 34, and further performing a Fischer-Tropsch process on the blended syngas feed to produce a hydrocarbonaceous effluent.
  37. 37. A process according to claim 36, further comprising converting at least a portion of the hydrocarbonaceous effluent into at least one fuel, at least one lubricant stock, or combinations thereof.
  38. 38. A fuel or a lubricant stock prepared by the process of claim 37.
  39. 39. The fuel of claim 38, which is for use neat or as a blend stock.
  40. 40. An integrated process for producing a blended syngas feed with a variable Hz/CO ratio for a Fischer-Tropsch reactor comprising the steps of: (a) selecting a desired Hz/CO ratio of a blended syngas feed to a Fischer- Tropsch reactor; (b) reacting methane, oxygen, and steam to form a first syngas with a Hz/CO ratio of at least 2.0; (c) reacting LPG and CO2 to form a second syngas with a Hz/CO ratio of no more than 1.5; (d) blending the first syngas and the second syngas to form a blended syngas feed having the desired Hz/CO ratio; (e) feeding the blended syngas feed into the Fischer-Tropsch reactor; (f) performing a Fischer-Tropsch synthesis process using the blended syugas feed; (g) recovering a third syngas comprising unreacted CO2, 1 I2, CO, and CH4 from the Fischer-Tropsch reactor; and (h) recovering LPG from the Fischer-Tropsch reactor. - 27 l
  41. 41. The process of claim 40, wherein LPG recovered from the FischerTropsch reactor and the third syngas are used as sources of at least a portion of the LPG and CO2 reacted to form the second syngas in step (c).
  42. 42. The process of claim 40, wherein at least a portion of the third syngas is reacted with the methane, oxygen, and steam of step (b) to form the first syngas with a Hz/CO ratio of no less than 2.0.
  43. 43. The process of claim 40, further comprising adding the third syngas to the blended syngas feed and feeding the resultant blend into the Fischer-Tropsch reactor.
  44. 44. The process of claim 40, wherein the Hz/CO ratio of the blended syngas feed is in the range of 1.0 to 3.0.
  45. 45. The process of claim 40, wherein the Hz/CO ratio of the blended syngas feed is in the range of 1.4 to 1.75, the first syngas has a HJCO ratio of 2.0 to 2.5; and the second syngas has a Hz/CO ratio of between 0. 5 and 1.0.
  46. 46. The process of claim 40, wherein the Fischer-Tropsch reactor contains a non-shifting Fischer-Tropsch catalyst.
  47. 47. The process of claim 40, wherein the non-shifting catalyst is a cobalt catalyst.
  48. 48. The process of claim 40, wherein a hydrocarbonaceous effluent is recovered from the Fischer-Tropsch reactor in step (I) and at least a portion thereof converted into at least one fuel, at least one lubricant stock, or combinations thereof.
  49. 49. A fuel or a lubricant stock prepared by the process of claim 48.
  50. 50. The fuel of claim 49, which is for use neat or as a blend stock. - 28
  51. 51. A process for the production of a blended syngas feed with a variable Hz/CO ratio comprising the steps of: (a) feeding a first syngas, comprising H2 and CO and having a Hz/CO ratio in the range of 1.4 to 1.75 into a first Fischer-Tropsch synthesis reactor and recovering at least one effluent therefrom; (b) recovering a second syngas comprising H2 and CO from the effluent, wherein the second syngas has a lower Hz/CO ratio than that of the first syngas; (c) forming a third syngas with a Hz/CO ratio of at least 2.0 by reacting methane with an oxygen source; (d) blending the second syngas with the third syngas to form a blended syngas feed having a WACO ratio in the range of 1.4 to 1.75; and (e) feeding the blended syngas feed into a second Fischer-Tropsch reactor.
  52. 52. I he process of claim 51, wherein the third syngas is formed by an autothermal reformer and has a 142/CO ratio in the range of 2.0 to 2.5.
  53. 53. The process of claim 51, wherein the first Fischer-Tropsch synthesis reactor contains a Fischer-Tropsch catalyst comprising cobalt.
  54. 54. A process as claimed in claim 51, wherein a hydrocarbonaceous effluent from one or other or both of the Fischer-Tropsch reactors is recovered and at least a portion thereof converted into at least one fuel, at least one lubricant stock, or combinations thereof.
  55. 55. A fuel or a lubricant stock prepared by the process of claim 54.
  56. 56. The fuel of claim 55, which is for use neat or as a blend stock.
  57. 57. A process for producing fuel comprising: (a) reacting LEG and CO2 to form a first syngas with a Hz/CO ratio of no more than 1.5, (b) reacting the syngas in a Fischer-Tropsch process to produce a hydrocarbonaceous effluent, - 29 (c) converting at least a portion of the hydrocarbonaceous effluent into at least one fuel, at least one lubricant stock, or combinations thereof.
  58. 58. The process of claim 57 wherein the first syngas is blended with a second syngas having a Hz/CO ratio of at least 2.0 to form a blended syngas, and the blended syngas is reacted in the Fischer-Tropsch process to produce the hydrocarbonaceous effluent.
  59. 59. The process of claim 58 wherein the second syngas is formed in a reaction between CH4 and an oxygen source.
  60. 60. A fuel or a lubricant stock prepared by the process of claim 57, 58 or 59.
  61. 61. The fuel of claim 60, which is for use neat or as a blend stock.
  62. 62. A process for converting gaseous and/or liquid hydrocarbons into Cs hydrocarbons comprlsmg: (a) selecting a desired Hz/CO ratio of a blended syngas feed to a Fischer- Tropsch reactor; (b) reacting methane, oxygen, and steam to form a first syngas with a Hz/CO ratio of at least 2.0; (c) reacting LPG and CO2 to form a second syngas with a Hz/CO ratio of no more than 1.5; (d) blending the first syngas and the second syngas to form a blended syngas feed having the desired Hz/CO ratio; (e) feeding the blended syngas feed into the Fischer-Tropsch reactor; (I) performing a Fischer-Tropsch synthesis process using the blended syugas feed; (g) recovering a third syngas comprising unreacted CO2, H2, CO, and CH4 from the Fischer-Tropsch reactor; and (h) recovering LPG from the Fischer-Tropsch reactor; wherein the process has a carbon efficiency of greater than 75%. - 30
  63. 63. The process of claim 62, wherein a hydrocarbonaceous effluent is recovered from the Fischer-Tropsch reactor after step (f) and at least a portion thereof converted into at least one fuel, at least one lubricant stock, or combinations thereof.
  64. 64. A fuel or a lubricant stock prepared by the process of claim 63.
  65. 65. The fuel of claim 64, which is for use neat or as a blend stock. - 31
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WO2007009952A1 (en) 2005-07-20 2007-01-25 Shell Internationale Research Maatschappij B.V. Multi stage fischer-tropsch process
WO2008000784A1 (en) * 2006-06-30 2008-01-03 Shell Internationale Research Maatschappij B.V. Optimisation of a multi-stage fischer-tropsch synthesis process
CN102361958A (en) * 2009-03-27 2012-02-22 日本石油天然气·金属矿物资源机构 Method and system for synthesizing liquid hydrocarbon compound
US9828246B2 (en) 2014-02-28 2017-11-28 Haldor Topsoe A/S Process for the production of synthesis gas

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WO2007009952A1 (en) 2005-07-20 2007-01-25 Shell Internationale Research Maatschappij B.V. Multi stage fischer-tropsch process
AU2006271760B2 (en) * 2005-07-20 2009-06-25 Shell Internationale Research Maatschappij B.V. Multi stage Fischer-Tropsch process
US7795318B2 (en) 2005-07-20 2010-09-14 Shell Oil Company Multi stage Fischer-Tropsch process
WO2008000784A1 (en) * 2006-06-30 2008-01-03 Shell Internationale Research Maatschappij B.V. Optimisation of a multi-stage fischer-tropsch synthesis process
CN102361958A (en) * 2009-03-27 2012-02-22 日本石油天然气·金属矿物资源机构 Method and system for synthesizing liquid hydrocarbon compound
CN102361958B (en) * 2009-03-27 2014-11-26 日本石油天然气·金属矿物资源机构 Method and system for synthesizing liquid hydrocarbon compound
US9828246B2 (en) 2014-02-28 2017-11-28 Haldor Topsoe A/S Process for the production of synthesis gas

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GB0415568D0 (en) 2004-08-11
GB0426607D0 (en) 2005-01-05
GB2409460B (en) 2005-12-14

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