Abstract:
A method of preparing a catalyst for conversion of syngas to Fischer-Tropsch hydrocarbon products comprising providing a reduced oxide Fischer-Tropsch catalyst and treating the reduced oxide catalyst with acetylene.

Description:
FIELD 
       [0001]    The present invention relates generally to methods of preparing catalysts for converting carbon containing products, such as natural gas, to liquid hydrocarbons or fuels, and more particularly, to methods for preparing catalysts for converting synthesis gas or “syngas” (carbon monoxide (CO) and hydrogen (H 2 )) into hydrocarbon products utilizing Fischer-Tropsch (F-T) reactions and to Fischer-Tropsch reactions utilizing such catalysts. 
       BACKGROUND 
       [0002]    It is often desirable to convert solid or gaseous carbon-containing products into hydrocarbon liquids using Fischer-Tropsch (F-T) reactions. For example, the carbon based product might be coal, biomass or natural gas. These starting products are converted in a syngas generator to a synthesis gas, hereinafter referred to as “syngas”, which contains carbon monoxide (CO) and hydrogen (H 2 ) gases. The syngas is then converted in a Fischer-Tropsch reactor, typically in the presence of a Fischer-Tropsch catalyst which is frequently an iron or cobalt based catalyst and under suitable temperature and pressure conditions, into hydrocarbon products and other byproducts. These hydrocarbon products are usually widely distributed in carbon chains of length (C 1 -C 100+ ). At temperatures of approximately 22° C. and at atmospheric pressure, these produced hydrocarbon products include significant quantities of gas (C 1 -C 4 ), liquid (C 5 -C 20 ) and waxy (C 20+ ) products. These designations of chain length for gas, liquid and waxy (solids) products are, of course, also dependent upon the relative branching of the hydrocarbon chains of the products and other known factors. 
         [0003]    Conventional F-T synthesis of hydrocarbon products has several shortcomings. First, the synthesis is not particularly selective and can generate wide range of hydrocarbon products having carbon chain lengths of C 1  to C 100+ . Light hydrocarbons of very short chain lengths often need recycling and further processing in the F-T reactor to produce more desirable medium chain length hydrocarbons. Alternatively, these light gases can be burned as fuel to produce heat. Hydrocarbons having chain lengths in the upper end of this chain range, in general from C 21  to C 100+ , are considered to be waxy rather than liquid at the above described temperature of 22° C. and pressure of 1 atmosphere. Often hydrocracking is required to break these long chain length hydrocarbons down into shorter, less viscous and more desirable liquid hydrocarbon products. However, in some locations, such as on offshore oil and gas producing platforms, it is undesirable to locate hydrocracking facilities due to weight, space and economic limitations. Thus using conventional F-T conversion processes on an offshore platform is less than desirable. Also, in remote land locations, it may be undesirable to include a hydrocracking unit as the addition of this unit raises the capital and operating expenses associated with F-T production of hydrocarbon products. 
       SUMMARY 
       [0004]    There is provided a method of preparing a Fischer-Tropsch catalyst comprising providing a reduced oxide catalyst and treating the reduced oxide catalyst with acetylene. 
         [0005]    The catalyst is preferably treated with acetylene in a gas mixture comprising the acetylene and an inert gas such as nitrogen. 
         [0006]    The reduced oxide catalyst may be prepared by subjecting an oxide catalyst to reduction with a gas mixture comprising hydrogen and an inert gas, under conditions well described in the literature. 
         [0007]    The F-T catalyst may be used in conversion of synthesis gas by a method comprising:
       A catalyst reduction step   providing synthesis gas to an F-T reactor   reacting the synthesis gas in the presence of the F-T catalyst according to any one of the previous claims to produce F-T hydrocarbon products; and   recovering the F-T hydrocarbon products.       
 
         [0012]    The gas feed used in the F-T reaction need not comprise acetylene and indeed it is preferred that the F-T catalyst is used in an F-T conversion using a gas mixture comprising syngas which comprises less than 0.5% acetylene preferably less than 0.01 mol % acetylene and most preferably free of acetylene. 
         [0013]    Throughout the description and the claims of this specification the word “comprise” and variations of the word, such as “comprising” and “comprises” is not intended to exclude other additives, components, integers or steps. 
       DETAILED DESCRIPTION 
       [0014]    We have found that acetylene pretreatment of an F-T catalyst provides a significant change in distribution of products of F-T conversion of syngas. Acetylene is used in a pretreatment and provides advantageous conversion of the syngas into Fischer-Tropsch products. 
         [0015]    Surprisingly, a Fischer-Tropsch (F-T) conversion of syngas to hydrocarbon products can be effected, subsequent to pretreatment of the catalyst by an acetylene-containing gas mixture, selectively to enhance the production of medium chain length hydrocarbons while reducing the production of high end chain length hydrocarbons. The selected F-T catalyst ideally has a sufficient quantity of active sites to convert carbon monoxide to medium chain length hydrocarbon products. For purposes of this application, low chain length can be considered as being C 1-5 , medium chain length as C 6-20 , and long chain lengths as C 21+ . 
         [0016]    Acetylene may be incorporated with a nitrogen feed supplied to an F-T reactor. Alternatively, acetylene can be added directly to an F-T reactor, however separately from the syngas feed, in a manner to ensure acetylene is delivered evenly to the catalyst. This may involve pretreatment in a fixed or fluid bed. 
         [0017]    Ideally, the catalyst used in acetylene enhanced syngas conversion has sufficient active sites to catalyse or oligomerise synthesis gas (CO and H 2 ) into hydrocarbon products of sufficient chain length such that a large portion of the F-T hydrocarbon products are liquid at ambient conditions, i.e., 1 atmosphere and 22° C., while ideally not producing significant amounts of waxy products, i.e., C 21+ . Such a product can ideally be transported on a conventional transport ship at approximately ambient conditions while remaining in a generally liquid or flowable state. While the F-T product is primarily liquid under such conditions and may contain some hydrocarbon gases and waxes, ideally it would still be generally “pumpable” at ambient conditions. 
         [0018]    In the presence of an appropriate F-T catalyst and under suitable reaction conditions, an advantageous distribution of hydrocarbon products can be produced relative to those hydrocarbon products produced by conventional F-T processes. Waxy F-T products are minimized with the increase in the formation of medium chain length hydrocarbons products. Such F-T products are generally flowable at ambient conditions, i.e., 1 atmosphere and moderate temperatures. i.e., 22° C. Because of the limited amount of waxy hydrocarbon products produced, hydrocracking may be limited or eliminated when using the present acetylene enhanced syngas conversion to hydrocarbon products as compared to conventional F-T processes. 
         [0019]    While not wishing to be held to a particular theory, the following mechanisms are believed to be involved in acetylene enhanced syngas conversion to F-T hydrocarbon products. Fischer Tropsch processing involves hydrogenation and polymerisation on the active sites of the catalyst. Pretreatment with acetylene causes conversion of acetylene to carbonaceous species if carried out under appropriate conditions. It is suggested that such carbonaceous species are deposited on highly active sites responsible for polymerisation in the Fischer Tropsch processing. Thus, the deactivation of highly active polymerisation sites by carbonaceous deposits during pretreatment leads to a smaller extent of polymerisation during the subsequent F-T reaction, to smaller amounts of heavy hydrocarbons and to increased amounts of middle distillates. 
         [0020]    Embodiments of the invention are described in part with reference to the drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]    In the drawings: 
           [0022]      FIG. 1  shows a process scheme showing a process for pretreatment of and F-T catalyst and for converting carbon containing products into F-T hydrocarbon products using the catalyst; 
           [0023]      FIG. 2  A schematic diagram of an acetylene enhanced syngas conversion process; 
           [0024]      FIG. 3  is a column chart showing the hydrocarbon distribution of FT runs at pressure of 20 atm and temperature of 220 degrees C. without and with 4.0% C 2 H 2  pretreatment; 
           [0025]      FIG. 4  is a column chart comparing products in the tail gas obtained from FT runs with 4.0% C 2 H 2 /N 2  pretreatment and without pretreatment; 
           [0026]      FIG. 5  is a column chart comparing the hydrocarbon distribution of FT runs at pressure of 20 atm and temperature of 220 degrees C. without and with 4% C 2 H 2  pretreatment with various acetylene concentrations; 
           [0027]      FIG. 6  is a column chart comparing products in the tail gas obtained from FT runs with 3.98% C 2 H 2 /N 2  pretreatment and without pretreatment at different pretreatment time; 
           [0028]      FIG. 7  is a graph comparing the hydrocarbon distribution of FT runs at pressure of 20 atm and temperature of 220 degrees C. without and with 4% C 2 H 2  pretreatment at different pretreatment time; and 
           [0029]      FIG. 8  is a column chart comparing the hydrocarbon distribution of FT runs at pressure of 20 atm and temperature of 220 degrees C. without and with 4% C 2 H 2  offline-pretreatment. 
       
    
    
       [0030]    Referring to  FIG. 1  there is shown a process flow diagram for converting carbon containing products into F-T hydrocarbon products. Carbon containing products may first be converted into syngas with methods which are known for converting coal and biomass into syngas. However, it is particularly desirable to convert natural gas to liquid hydrocarbons. Subsequent conversion of syngas to liquid hydrocarbons by the Fischer-Tropsch (F-T) process may then be effected. 
         [0031]    This conversion allows hydrocarbons to be transported, such as in marine ships, in an energy efficient manner, without having to resort to liquefying or compressing the natural gas. 
         [0032]    Acetylene can be made by the cracking of hydrocarbons or from calcium carbide. Other known techniques can be found in the Encyclopedia of Chemical Technology, Acetylene, Volume 1, 3.sup.rd Edition, Wiley, N.Y., 1978. Those skilled in the art will appreciate there are numerous other well know means of making acetylene. 
         [0033]    Mixtures of acetylene and an inert gas such as nitrogen, argon or other mixtures, may then be supplied to the reactor containing the reduced catalyst under controlled conditions (see step  20  below). The resulting acetylene/gas feed ideally has molar ratio of greater than 0.01 of acetylene to gas, more preferably, a molar ratio in the range of 0.01 to 0.5 such as 0.011-0.10, and even more preferably a molar ratio from 0.020-0.040 or from about 0.03-0.04. 
         [0034]    The acetylene pretreatment is generally carried out on a reduced oxide catalyst. The process involved in reduction will change with the nature of the catalyst. The treatment of the reduction of the oxide catalyst may be conducted at elevated temperature such as a temperature in the range of from 150° C. to 400° C., preferably 200° C. to 350° C. 
         [0035]    In the case of a cobalt based catalyst, a typical procedure would involve slow heating of the catalyst to ca 300° C. under a stream of inert gas (such as nitrogen, argon or mixtures thereof) containing 10-70% hydrogen. However, it should be emphasised that the optimal reduction procedure does depend on the components of the catalyst and should be established by reference to the literature or by a second study. 
         [0036]    In step  40  a Fischer-Tropsch conversion is performed on the acetylene-pretreated catalyst to produce an F-T product. In this particular embodiment, a conventional fixed bed Fischer-Tropsch reactor may be used for the conversion. In this example, ideally a cobalt based catalyst is used in the F-T reactor. The catalyst should contain an adequate supply of active sites to produce a significant distribution of hydrocarbon products in the range of C 5-20 . The F-T hydrocarbon products produced generally have an enhanced distribution of medium chain length hydrocarbons and a reduced distribution of short-chain (gaseous) and long chain (waxy) hydrocarbons as compared to products produced by conventional F-T processes. 
         [0037]    The F-T product produced in the F-T reactor is then separated in step  50  into a liquid F-T product and a gaseous F-T product. This is accomplished using a liquid trap which captures liquids while allowing tail gases to escape. Ideally, the captured liquid F-T product is sufficiently limited in long-chain or waxy product that the F-T liquid is flowable or pumpable at ambient temperatures, i.e. 22° C. or slightly warmer. For example, the F-T liquid product preferably has a cloud point of below 10° C. The F-T liquid product may then be placed in storage such as on a marine vessel for transport to a land based facility or else sent on for further processing and refining in a refinery. 
         [0038]    The escaping tail gas F-T product or byproduct includes unreacted CO and H 2 , methane, ethane, ethylene, CO 2 , and traces of water vapor and C 3 -C 5  hydrocarbons. Valuable products, such as C 3 -C 5 , may be separated from the rest of the tail gas and stored. The residual gaseous F-T product, including C 1 -C 2  may then be reintroduced into the F-T reactor, or into the acetylene syngas generator, or else used as a fuel gas to generate heat. 
       (a) Relative Amounts of Acetylene for Catalyst Pretreatment: 
       [0039]    In one embodiment of acetylene-enhanced syngas conversion, the molar ratio of acetylene introduced into the F-T reactor relative to that of the inert gas feed is greater than 1 and less than 10%. In another embodiment, the range of acetylene used in the feed shall be 2-5% by molar ratio. In yet another embodiment, the amount of acetylene may range from 3-4% by molar ratio relative to the gas feed. 
       (b) Catalyst Type 
       [0040]    A cobalt-based catalyst is an ideal catalyst to use in the F-T reactor. The cobalt catalyst should have a sufficient number of active sites to promote the growth of hydrocarbon products of significant medium chain length, i.e., C 5 -C 20 , without producing an oversupply of longer chain length products, i.e. C 21+ . The cobalt-based catalyst should contain cobalt and ideally have at least 100 .mu.mol of surface metal sites per cm 3  of catalyst as measured by hydrogen chemisorption. In another example, the catalyst should ideally have at least 150 .mu.mol of surface metal sites per cm 3  of catalyst. In yet another example, at least 200 .mu.mol/cm 3  may be used. 
         [0041]    For example, in an experimental test setup to be described below, the catalyst used was a pretreated 20 wt % Co-0.5 wt % Ru-1.0 wt % La 2 O 3  on 78.5 wt % alumina catalyst which was mixed with inert .alpha.-alumina particles, which happens to have a similar size to the catalyst. 
         [0042]    Alternatively, iron-based catalysts may also be used. The catalysts are selected so that under suitable reaction conditions of temperature and pressure, the acetylene-pretreated, enhanced syngas conversion is converted produces primarily into liquid F-T products in the range C 3 -C 20  while reducing the amount of short chain C 1-2  or “lights” and long chain (C 20+ ) or “heavy” F-T products. 
       (c) F-T Reactor Types 
       [0043]    A variety of different types of F-T reactors may benefit from utilizing acetylene-enhanced syngas conversion. In a first embodiment, such as with the experimental set-up, the F-T reactor is a fixed or packed bed reactor. Alternatively, fluidized and spouted bed reactors may also be used. The use of a slurry bed F-T reactor is not as desirable since this type of reactor relies upon the use of waxy hydrocarbon products as the slurry medium. These products are severely limited in F-T syngas conversion using an acetylene-pretreated catalyst. Thus, a constant replenishment of the slurry medium would be required. 
       (d) Reactor Pressure: 
       [0044]    Pressure can affect the pretreatment by acetylene and the carbon number distribution of the F-T product produced in the F-T reactor. The pressure during pretreatment needs not necessarily be the same as the pressure during subsequent F-T processing. For conventional F-T processing, and by way of example and not limitation, exemplary ranges of pressures at which a fixed bed reactor may be operated include 2-35 atmospheres, 20-30 atmospheres 25-30 atmospheres and 10-20 atmospheres. 
         [0045]    Pretreatment, on the other hand, could be carried out at different pressures, covering the same pressures as those preferred for F-T. However, pretreatment at 10 atmospheres pressure is the preferred value. 
         [0046]    In one embodiment, the acetylene pressure in the pretreatment of the F-T catalyst will stay at approximately 0.1-0.5, preferably 0.4, atmospheres in an overall pressure of 10 atmospheres with the overall pressure in the subsequent F-T reactor being held at 2-35 atmospheres. 
       (e) Reactor Operating Temperature: 
       [0047]    Treatment of the reduced oxide catalyst with acetylene is typically conducted at a temperature in the range of from 150° C. to 250° C., preferably 150 to 220° C. Temperature is also believed to affect the chain length distribution of the F-T product produced in the F-T reactor. 
         [0048]    Ideally, the temperature will be held between 175-230° C. for a fixed bed reactor using a cobalt-based catalyst. More preferably, the range of operating temperature would be between 190-210° C. If an iron(Fe)-based catalyst is used, then the preferred temperature would be higher with a range of 240-270° C., and more preferably, between 250-260° C. 
         [0049]    Pretreatment temperatures need not necessarily be the same as those used for F-T processing. Pretreatment can be carried out under the same conditions as above, but the preferred temperature is at about 190° C. Some difficulty may be experienced in maintaining this temperature during pretreatment. 
       (f) H 2 /CO Syngas Ratio: 
       [0050]    The preferred range of H 2 /CO to be fed to an F-T reactor subsequent to pretreatment is between 2.0:1 and 2.2:1 by volume. One H 2  per CO is used to convert the O to H 2 O, another H 2  per CO is used to convert the C to —CH 2 — groups in the interiors of hydrocarbon chains. Any additional H 2  per CO is needed to saturate the end carbons of the hydrocarbons to CH 3 (methyl) groups. If these are not saturated and olefins are formed, then the usage ratio is H 2 /CO=2. The H 2 /CO ratio of the synthesis gas fed to the inlet of the reactor is preferably less than the usage ratio, however, in order to minimize methane formation. This is accomplished by operating at partial conversion with recycle of the dry gas after liquid (water and C 5+  hydrocarbons) products are removed by condensation. Consuming H 2  and CO at the usage ratio in the reactor will cause the recycle H 2 /CO ratio to be lower than the inlet ratio, but that can be made up by blending the recycle flow with fresh feed that has the H 2 /CO usage ratio. Varying the relative ratio of H 2  /CO can be used to alter the chain length distribution produced in the F-T reactor, but lower ratios lead to reduced synthesis rates. Preferable inlet ratios are between 1.4 and 1.7, more preferably between 1.5 and 1.6, with per pass CO conversion near 50%. 
       (g) Alternative Components in Syngas Feed: 
       [0051]    In addition to the syngas in the feed, other components may be included, such as alpha-olefins. These components can initiate hydrocarbon chains on the catalysts leading to enhanced C 5+  paraffin and isoparaffin production. 
         [0052]    The invention may be used with a gas feed that includes acetylene but in one set of embodiments the F-T catalyst is used in an F-T conversion using a gas added mixture comprising syngas which comprises less than 0.5% acetylene preferably less than 0.01 mol % acetylene and most preferably free of acetylene. 
       (h) Residence Time in the F-T Reactor: 
       [0053]    Residence time also affects the distribution of the F-T product produced in the F-T reactor. Residence time is the void volume in the catalyst bed divided by the volumetric flow rate corrected to the pressure and temperature at reaction conditions. It decreases as temperature goes up and increases as pressure increases. Sufficient residence time should be allowed to insure a high rate of conversion of the syngas to F-T hydrocarbon products. Ideally, the residence time is held between 1 seconds and 20 seconds, more preferably between 2 seconds and 10 seconds, and most preferably in the range of 3-5 seconds. 
         [0054]    The residence time of the pretreatment stream depends to some extent on the concentration of acetylene in the stream. A flow rate of pretreatment gas of between 40 and 70 ml/min passing over 1 g catalysts is a typical flow, the preferred value being 60 ml/min. when the pretreatment gas contains ca 4% of C 2  H 2 . 
       (i) It is Not Necessary to Carry Out the Pretreatment Procedure Immediately Before the F-T Processing. 
       [0055]    It is possible, using the procedures described below, to pretreat a reduced catalyst with an acetylene-containing gas in separate equipment. Subsequent to pretreatment, the catalyst should be rinsed with an inert gas while cooling to ambient conditions. Once the temperature has stabilised, a stream of oxygen-containing gas (usually containing 0 to 5% oxygen, but preferably ca 2% oxygen) is passed over the catalyst until the surfaces of the metals are solid is oxidised (usually overnight). The catalyst may then be removed, stored, and later transported to another position and inserted in a suitable reactor. After rinsing with inert gas the catalyst is then taken to 250-300° C. under a stream of hydrogen-containing gas. The concentration of hydrogen may vary from 10% to 70%, preferably ca 10-20%. Once reduction is complete (about 6 hours), F-T processing as described above may be initiated. 
       (j) F-T Product Characteristics: 
       [0056]    In one set of embodiments the F-T hydrocarbon product is condensed to produce a gas and an oil product at a temperature below 40° C. (at 1 atm) and the oil product comprises less than 5%, preferably less than 3% and most preferably less than 2% of hydrocarbons of at least 21 carbon atoms. 
         [0057]    Ideally, the non-gaseous or liquid oil portion of the captured F-T product is highly liquid at ambient conditions, i.e. a temperature of 22° C. and 1 atmosphere of pressure. While the liquid will contain dissolved hydrocarbon gases and liquids, ideally the liquid would be quite flowable or pumpable. By way of example and not limitation, the liquid oil product collected from the F-T reactor ideally has the following characteristics: 
         [0058]    Pour Point Range: −5° C. to +5° C. 
         [0059]    Wax Content Range: 0-10% 
         [0060]    Carbon Distribution: C 5 -C 25    
         [0061]    Cloud Point: below 10 degree C. 
         [0062]      FIG. 2  shows an experimental setup  100  used to examine process variables in an acetylene enhanced syngas conversion process. Feed gases are supplied by cylinders to F-T reactors which produce F-T hydrocarbon products. These products are separated into light tail gases (C 1 -C 2  hydrocarbons, CO 2 , unreacted CO and H 2 ), heavy tail gases (C 3 -C 4  hydrocarbons), liquid hydrocarbons (C 5 -C 20 ), oxygenates and water, and solid hydrocarbons (C 21+ ). Analysis equipment is used to investigate the composition of the F-T products. 
         [0063]    With respect to supply cylinders of gas, cylinder  102  supplies carbon monoxide (CO). Cylinder  104  contains hydrogen gas (H 2 ). Nitrogen gas (N 2 ) is provided by cylinder  106  and can serve as a tracer. A mixture of acetylene (C 2 H 2 , ranging from 2 mol %-5 mol %) in an inert gas such as nitrogen or argon is supplied by cylinder  110 . Finally, cylinder  112  ontains a 3-10% mixture of hydrogen gas (H 2 ) and helium (He), which serves as a reducing gas to activate F-T catalysts. All gases are fed via Brooks 5850 mass flow controllers (MFC). 
         [0064]    A two-way switching valve  114  fluidly connects cylinders  102 ,  104 ,  106  and  110  to either of two four-way switching valves,  116  or  120 . Similarly, a four-way switching valve  122  fluidly connects cylinder  112  with a vent  124 . Switching valve  116  can be adjusted to deliver gas to a vent  126  or else to the first F-T reactor  130  (a fixed-bed tubular reactor, 400 mm long and 80 mm diameter. A temperature controller  132  is used to control the temperature of a furnace that encloses this reactor. A thermocouple, which can move freely in a sheath mounted to the reactor, is used to monitor the temperature along the catalyst bed in reactor  130 . Pressure transducers  134  and  144  measure the pressures at the top and bottom, respectively, of reactor  130 . The four-way switching valve  120  alternatively connects with a vent  124  or else delivers gas to a second F-T reactor  136 . Again, a temperature controller  140  and a pressure transducer  142  are placed upstream of second F-T reactor  136 . 
         [0065]    F-T products and effluents from reactor  130  pass through lines held at approximately 150° C. to a hot trap or condenser  146 . It is operated at approximately 120° C., and can capture output product from reactor  130 , mainly waxes. A valve  150  can be opened to pass the waxy product to a sample vial  152 . Output from reactor  130  goes to a two-way switch valve  154 , that can route it directly to a four-way switching valve  156 , or first through water trap  160  and then to valve  156 . The water trap  160  allows liquid output, such as water and liquid hydrocarbons, by way of a valve  162 , to be captured in a sample vial  164 . The four-way switching valve  156  sends the vapor phase flow either to vent  166  or to another four-way switching valve  170 . 
         [0066]    F-T products and other effluents from the second F-T reactor  136  (also a fixed-bed tubular reactor, 400 mm long and 80 mm diameter) are routed past pressure transducer  172  via a heated line (at 120° C.) to product trap  174 . That trap is maintained at room temperature. A valve  176  permits samples to be extracted from product trap  174  to a sample vial  180 . Product trap  174  also connects to moisture trap  182  which, in turn, connects to four-way switching valve  170 . A vent  184  may vent gases received from four-way switch  170 . The purpose of valve  170  is to select one of the two vapor-phase product streams from the two F-T reactors for analysis in the analytical section. 
         [0067]    Thus, four-way switching valve  170  is also connected through a back-pressure regulator  182  to a gas chromatograph-FID  184 . Gas chromatograph  184  delivers light tail gas sample to gas chromatograph-TCD  196 , which in turn, supplies gas chromatograph-TCD  202 . Effluent from these gas chromatographs goes to vent  204 . A pressure relief valve  186  allows pressure to be bled off from back-pressure controller  182 . Cylinders  190  and  192 , containing hydrogen gas (H 2 ) and compressed air, supply gas chromatograph  184 . Cylinder  194  carries helium gas (He) and supplies carrier gas to gas chromatograph  184  and also to gas chromatograph-TCD  196 . Argon, stored in cylinder  200 , is connected to gas chromatograph  202 . 
         [0068]    Gas chromatograph-FID  184  (Shimadzu GC8A with FID detector and a Restek Rtx®-1, 60 m long, 0.53 mm internal diameter column) is utilized to analyze light hydrocarbons (C 1 -C 12 ). Gas chromatograph-TCD  196  (Shimadzu GC8A with TCD detector and a CTR-I packed column) analyzes CO, CO 2 , C 2 H 2 , N 2  and CH 4 . Gas chromatograph  202  (Shimadzu GC8A chromatograph with a TCD detector and a 13× Molecular Sieve column) is used to measure the hydrogen (H 2 ) concentration. 
         [0069]    Either first F-T reactor  130  or else second reactor  136  may be used in the acetylene enhanced syngas conversion of syngas to F-T products. In cases where it is suspected that waxes will be produced, first F-T reactor  130  is used in association with hot trap  146 . If little or no significant amounts of waxy product (C 20+ ) is expected to be produced, then second F-T reactor  136  may be employed in F-T product synthesis. 
         [0070]    Liquid products are identified off line by injection into a GC-MS (Shimadzu Model QP-5050 equipped with another Rtx®-1 capillary column, also 60 m long but of 0.25 mm diameter) for qualitative analysis and a GC-FID (Shimadzu GC-17 with a FID detector fitted with a Rtx®-1 capillary column, 60 m long and 0.25 mm diameter) for quantitative analysis. 
         [0071]    A number of experiments were conducted with experimental setup  100 . 
         [0072]    Pretreated or untreated forms of a 20 wt % Co-0.5 wt % Ru-1.0 wt % La 2 O 3  on 78.5 wt % alumina catalyst were mixed with inert .alpha.-alumina particles (which have similar size to the catalyst) and packed and supported between two quartz wool plugs in the test reactor. 
         [0073]    The first stage of pretreatment consisted of reducing the catalyst in flowing, 70% hydrogen at atmospheric pressure while heating slowly (1° C./minute) to 300° C. and holding for at least 6 hours, cooling to ambient temperature, purging in nitrogen, passivating the catalyst in nitrogen-diluted air at ambient temperature, reoxidizing it by heating slowly to 300° C. in flowing air, cooling again, purging in nitrogen, then repeating the reduction and passivation steps. This redox treatment makes the catalyst much easier to activate later in either diluted hydrogen or at lower temperatures or both. These preliminary reduction and oxidation steps were done outside the test reactor. 
         [0074]    In the second stage of pretreatment, the catalyst was then transferred to the reactor and reduced in situ in 10% H 2 /N 2  at 300° C. for ca. 20 hr (by ramping temperature to 150° C. at 10° C./min and holding for 1 hour, followed by increasing the temperature to 300° C. at 3° C./min and holding for 20 hours). 
         [0075]    The third stage of pretreatment involved contact with acetylene. The reactor temperature was slowly decreased to room temperature in 5% H 2 /N 2 . Before switching an acetylene in nitrogen (or other inert gas) blend to the reactor for pretreatment, the inlet compositions of the acetylene blends were analysed for N 2  and C 2  H 2  by diverting those gas mixtures to GC  196  and GC  184 , respectively. Pretreatment with acetylene was initialized by switching the inlet gas to the reactor ( 130  or  136 ) from the hydrogen in nitrogen blend to an acetylene in nitrogen blend and then ramping the temperature (at a rate of 5° C./min) and pressure to the target values. After the pretreatment had proceeded for the desired time, the catalyst was rinsed with N 2  for 15 minutes. 
         [0076]    Subsequent to this rinsing, syngas was admitted to the reactor ( 130  or  136 ) at the desired concentrations (as described in step  40  section 2), and the temperature was slowly increased to the desired value. Analytical measurements were carried out to determine when the process approached steady state—usually after some 100 minutes operation. Reproducible analytic measurements were then taken every 1-2 hours. During the reaction, online gas analyses were conducted via GC-FID ( 184 ), GC-TCD ( 196 ) and GC-TCD ( 202 ) for C 1 -C 12  light hydrocarbons, CO, CO 2 , N 2 , C 2 H 2 , CH 4  and H 2 , respectively. The liquid product collected was analyzed quantitatively and qualitatively offline, using GC-FID and GC-MS for condensed high hydrocarbons (C 5+ ) and oxygenates. 
         [0077]    The invention will now be described with reference to the following examples. It is to be understood that the examples are provided by way of illustration of the invention and that they are in no way limiting to the scope of the invention. 
       Examples 
       [0078]    The following exemplary range of process variables might be used in the experimental setup  100 . In commercial set ups, of course, a broader range of the process variables can be practiced, as described elsewhere in this specification.
   Pretreatment temperature: 190° C.   Acetylene content: 0-4% (vol)   Pretreatment: total flow rate: 60 ml/min.   Pressure: 10 atmospheres   Pretreatment time: 60 minutes   Catalyst loading: 1 gram/cubic centimeter of reactor void   F-T reaction temperatures: 190-210° C.   [H 2 :CO ratio: 2.0-2.3   F-T reactor pressure: 5, 10, 20 atmospheres   Total inlet gas flowrate: 60-120 mL/min   Reaction time: 18-48 hours;   
 
       Analysis Performed Online: 
       [0090]      
         [0000]    
       
         
               
               
             
           
               
                   
               
             
             
               
                 Tail gas (GC-TCD) 
                 CO, CO 2 , N 2 , H 2 , CH 4 , C 2 H 2   and C 1 — 
               
               
                 GC-FID (Rtx-1 capillary column) 
                 C 12   
               
               
                   
               
             
          
         
       
     
       Offline Liquid Product Analysis: 
       [0091]      
         [0000]    
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 GC-MS (Shimadzu Model QP-5050)  
                 Qualitative analysis 
               
               
                   
                 GC-FID (Shimadzu GC-17) 
                 Quantitative analysis 
               
               
                   
                   
               
             
          
         
       
     
       Comparative Example 1 
       [0092]    A first, generally acetylene free run was made utilizing the experimental test setup  100  above. The process variables for normal F-T reaction are shown in the below table: 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 FT conditions 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Acetylene (dry volume %)  
                 0% 
               
               
                   
                 Catalyst 
                 1 gram 
               
               
                   
                 Reactor temperature 
                 220° C. 
               
               
                   
                 Reactor pressure 
                 20 atm 
               
               
                   
                 H 2 /CO ratio 
                 2.1 
               
               
                   
                 Reaction time 
                 15 hours 
               
               
                   
                 Residence time 
                 150.0 mmol/h/g  catalyst   
               
               
                   
                   
               
             
          
         
       
     
       Results: 
       [0093]    The conversions of carbon monoxide and hydrogen were about 76.2% and 76.4%, respectively, at these conditions. The carbon number distribution of the F-T product oil from the reactors is shown in  FIG. 3 . The selectivities to carbon dioxide and light hydrocarbons (C 1 -C 6 ) in the tail gas is shown in  FIG. 4 . 
       Example 2 
       [0094]    Firstly, acetylene pretreatment was performed on a reduced Co-based catalyst at 10 atm and 190° C. with 4% acetylene/nitrogen. After flushing under nitrogen, a conventional FT run was carried out on the pretreated catalyst at 20 atm and 220° C. The process variables for this run are shown in Table 2: 
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                 TABLE 2 
               
               
                   
               
             
             
               
                 Acetylene pretreatment conditions 
               
               
                   
               
             
          
           
               
                   
                 Acetylene (dry volume %)  
                 3.98% 
               
               
                   
                 Catalyst 
                 1 gram 
               
               
                   
                 Pretreatment temperature 
                 190° C. 
               
               
                   
                 Pretreatment pressure 
                 10 atm 
               
               
                   
                 Pretreatment time 
                 7 hours 
               
               
                   
                 Residence time 
                 144.5 mmol/h/g  catalyst   
               
               
                   
               
             
          
           
               
                 FT conditions 
               
               
                   
               
             
          
           
               
                   
                 Acetylene (dry volume %) 
                 0% 
               
               
                   
                 Catalyst 
                 1 gram 
               
               
                   
                 Reactor temperature 
                 220° C. 
               
               
                   
                 Reactor pressure 
                 20 atm 
               
               
                   
                 Reaction time 
                 5 hours 
               
               
                   
                 Residence time 
                 150.0 mmol/h/g  catalyst   
               
               
                   
               
             
          
         
       
     
       Results: 
       [0095]    The conversions of CO and H 2  were about 53% and 57%, respectively after acetylene pretreatment, which only slightly decreased compared with F-T run without acetylene pretreatment. The carbon number distribution of the F-T product oil from the reactor is shown in  FIG. 3 . The long tail of oil products usually observed for F-T runs became insignificant after acetylene pretreatment and the hydrocarbon distribution shifted towards much lighter hydrocarbon fractions (C 6 -C 11 ). More than 90% of the liquids were C 5 -C 20  products and less than 4% were C 21+  heavy products. The resulting F-T oil after acetylene pretreatment was very clear. The results of tail gas analysis shown in  FIG. 4  indicated that the formation rate of carbon dioxide also dropped after acetylene pretreatment. 
       Example 3 
       [0096]    Effect of Acetylene Concentration on F-T Product Distribution. 
         [0097]    A study on the effect of acetylene concentration during pretreatment on the subsequent F-T product distribution was carried out at 190° C. and 10 atm for 7 hours, according to the process conditions of acetylene pretreatment and F-T reaction shown in Table 3: 
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                 TABLE 3 
               
               
                   
               
               
                   
                   
                   
                 Reaction 
                   
                   
               
               
                   
                 Temperature 
                 Pressure 
                 time 
                 Acetylene, 
                 SV, 
               
               
                 Run 
                 ° C. 
                 atm 
                 hr 
                 % 
                 mmol/h/g cat   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 1.8% C 2 H 2 /N 2    
                 190 
                 10 
                 7 
                 1.8 
                 144.5 
               
               
                 4.0% C 2 H 2 /N 2   
                 190 
                 10 
                 7 
                 4.0 
                 140.2 
               
               
                 FT, after C 2 H 2   
                 220 
                 20 
                 15 
                 0 
                 142.8 
               
               
                   
               
             
          
         
       
     
       Results: 
       [0098]      FIG. 5  shows the carbon number distribution of the oil products during the F-T reaction without pretreatment and after pretreatment with various concentrations of acetylene in the nitrogen feed. The CO conversions in these runs were 74% without pretreatment, 69% after treatment with 1.8% acetylene, and 53% after treatment with 4% acetylene. It is clearly demonstrated that the long tail of oil products for the F-T reaction is also reduced after acetylene pretreatment with the lower acetylene concentration. As shown in  FIG. 5 , the hydrocarbon distribution shift towards lighter products is almost the same for the two acetylene concentrations. With 1.8% acetylene pretreatment, the selectivity to the C 5 -C 9  fraction increased to 47% and the selectivity to C 21+  wax decreased from 13.7% to 5.8%. Further increasing acetylene concentration to 4.0%, the selectivity to C 5 -C 9  fractions was about the same, at 45%, but the selectivity to C 21+  wax further decreased to 3.1%. The oil liquid collected from the F-T reaction after pretreatment in 1.8% acetylene was a milky liquid, containing some insoluble wax, whereas that for F-T synthesis after treatment with 4.0% acetylene was clear, with no indication of wax. 
       Example 4 
       [0099]    Effects of Acetylene Pretreatment Time on Subsequent F-T Product Distributions. 
         [0100]    The acetylene pretreatment was performed at 190° C. and 10 atm with 4.0% acetylene/nitrogen. The pretreatment time was varied from 3 to 12 hours. After acetylene pretreatment, F-T synthesis was performed at 220° C. and 20 atm for 15 hours. The process conditions during acetylene pretreatment are shown in Table 4. 
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                 TABLE 4 
               
               
                   
               
               
                   
                 Temper- 
                   
                 Reaction 
                   
                   
               
               
                   
                 ature 
                 Pressure 
                 time 
                 Acetylene  
                 SV 
               
               
                 Run 
                 ° C. 
                 P 
                 hr 
                 % 
                 mmol/h/g cat   
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 C 2 H 2 /N 2 — 5 hr 
                 190 
                 10 
                 5 
                 4.0 
                 140.2 
               
               
                 C 2 H 2 /N 2 — 7 hr  
                 190 
                 10 
                 7 
                 4.0 
                 140.2 
               
               
                 C 2 H 2 /N 2 — 10 hr  
                 190 
                 10 
                 10 
                 4.0 
                 144.5 
               
               
                   
               
             
          
         
       
     
       Results: 
       [0101]    The CO conversions in subsequent F-T runs were 59%, 53% and 52%, respectively, after treatments at 5, 7, and 10 hours in 4% acetylene. Compared with the normal F-T run without pretreatment, these CO conversions are lower by 20%-30%.  FIG. 6  shows selectivities of products in the tail gas during F-T reactions without and with 4% acetylene pretreatment for various times. Note that the selectivities to C 3 -C 5  in the tail gas phase increased after acetylene pretreatment. 
         [0102]    Liquid hydrocarbons collected from the cold traps showed that there were still waxes being formed after short (3-5 hour) pretreatments. By extending the pretreatment time to 7 and 10 hours, clear, wax-free liquids were collected. After the 7 hour pretreatment, the hydrocarbon liquid was pale yellow; while after pretreatment for 10 hours, the color of the oil liquid turned bright yellow. 
         [0103]    With increasing pretreatment time, the relative amounts of C 5 -C 9  fractions and C 10 -C 20  fractions in the liquids from the F-T runs increased significantly. They went from &lt;0.1% without treatment to 15.0% at 5 hours and 45% at 7 hours. The C 21 + fractions decreased from 14% without treatment to 9% at 5 hours and 3% at 7 hours. 
         [0104]      FIG. 7  presents the carbon number distributions of the oil products in F-T runs with or without acetylene pretreatment. It is apparent that the long tail (the C 26+  fractions) of oil products for F-T is reduced significantly after pretreatment and the hydrocarbon distribution shifts to lighter hydrocarbon fractions (mainly C 6 -C 17 ) as the pretreatment time increases from 3 hours to 10hours. 
         [0105]    4% acetylene pretreatment at 190° C. effectively modifies carbon number distributions during subsequent syngas conversion at 220° C. and 20 atm. It shifts them from broad distributions extending out to C 30  hydrocarbons to naphtha and diesel/gasoline-range hydrocarbons (C 6 -C 17 ). The optimum pretreatment time for the catalyst tested was 7 h with 4% C 2 H 2 /N 2  at 190° C. and 10 atm. 
       Example 5 
       [0106]    F-T Reaction on Offline-Acetylene-Pretreatment Catalysts 
         [0107]    Offline acetylene pretreatment on F-T catalysts is investigated. A reduced catalyst was pretreated with an acetylene-containing gas in separate equipment and then be removed, stored, and later transported to another position and inserted in a suitable reactor. Before running the F-T reaction, the offline-acetylene-pretreated catalyst was initially reduced at 300° C. under a stream of hydrogen-containing gas. The concentration of hydrogen may vary from 10% to 70%, preferably ca 10-20%. Once reduction is complete (about 6 hours), F-T processing as described above is performed at 220° C. and 20 atm for 15 h. 
       Results: 
       [0108]    The conversions of CO and H 2  for F-T reaction on this acetylene-pretreated catalyst remain the same value compared with the unpretreated catalyst. The clear oil products were collected from the cold trap.  FIG. 8  shows the carbon number distributions of the oil products in F-T runs with or without acetylene pretreatment. It is apparent that the long tail (the C 27+  fractions) of oil products for F-T is reduced significantly after offline pretreatment and the hydrocarbon distribution shifts to lighter hydrocarbon fractions (mainly C 6 -C 17 ) as in-suit acetylene pretreatment. Therefore, this confirmed that it is possible to pretreat F-T catalysts and store and later transport them to another place without losing the desired effect