CA1234396A - Process for the preparation of hydrocarbons - Google Patents
Process for the preparation of hydrocarbonsInfo
- Publication number
- CA1234396A CA1234396A CA000466256A CA466256A CA1234396A CA 1234396 A CA1234396 A CA 1234396A CA 000466256 A CA000466256 A CA 000466256A CA 466256 A CA466256 A CA 466256A CA 1234396 A CA1234396 A CA 1234396A
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- hydrocarbons
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- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
- C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
- C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
- C07C1/0425—Catalysts; their physical properties
- C07C1/043—Catalysts; their physical properties characterised by the composition
- C07C1/0435—Catalysts; their physical properties characterised by the composition containing a metal of group 8 or a compound thereof
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
- C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
- C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
- C07C1/0425—Catalysts; their physical properties
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C1/00—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon
- C07C1/02—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon
- C07C1/04—Preparation of hydrocarbons from one or more compounds, none of them being a hydrocarbon from oxides of a carbon from carbon monoxide with hydrogen
- C07C1/0485—Set-up of reactors or accessories; Multi-step processes
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G47/00—Cracking of hydrocarbon oils, in the presence of hydrogen or hydrogen- generating compounds, to obtain lower boiling fractions
- C10G47/02—Cracking of hydrocarbon oils, in the presence of hydrogen or hydrogen- generating compounds, to obtain lower boiling fractions characterised by the catalyst used
- C10G47/10—Cracking of hydrocarbon oils, in the presence of hydrogen or hydrogen- generating compounds, to obtain lower boiling fractions characterised by the catalyst used with catalysts deposited on a carrier
- C10G47/12—Inorganic carriers
- C10G47/14—Inorganic carriers the catalyst containing platinum group metals or compounds thereof
-
- C—CHEMISTRY; METALLURGY
- C10—PETROLEUM, GAS OR COKE INDUSTRIES; TECHNICAL GASES CONTAINING CARBON MONOXIDE; FUELS; LUBRICANTS; PEAT
- C10G—CRACKING HYDROCARBON OILS; PRODUCTION OF LIQUID HYDROCARBON MIXTURES, e.g. BY DESTRUCTIVE HYDROGENATION, OLIGOMERISATION, POLYMERISATION; RECOVERY OF HYDROCARBON OILS FROM OIL-SHALE, OIL-SAND, OR GASES; REFINING MIXTURES MAINLY CONSISTING OF HYDROCARBONS; REFORMING OF NAPHTHA; MINERAL WAXES
- C10G69/00—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one other conversion process
- C10G69/02—Treatment of hydrocarbon oils by at least one hydrotreatment process and at least one other conversion process plural serial stages only
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
- C07C2521/02—Boron or aluminium; Oxides or hydroxides thereof
- C07C2521/04—Alumina
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
- C07C2521/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
- C07C2521/06—Silicon, titanium, zirconium or hafnium; Oxides or hydroxides thereof
- C07C2521/08—Silica
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2521/00—Catalysts comprising the elements, oxides or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium or hafnium
- C07C2521/12—Silica and alumina
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C2523/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00
- C07C2523/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group C07C2521/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
- C07C2523/24—Chromium, molybdenum or tungsten
- C07C2523/26—Chromium
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- Chemical & Material Sciences (AREA)
- Organic Chemistry (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Oil, Petroleum & Natural Gas (AREA)
- Engineering & Computer Science (AREA)
- General Chemical & Material Sciences (AREA)
- Inorganic Chemistry (AREA)
- Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
- Catalysts (AREA)
- Hydrogen, Water And Hydrids (AREA)
Abstract
A B S T R A C T
PROCESS FOR THE PREPARATION OF HYDROCARBONS
C5+ hydrocarbons are prepared from C4- hydrocarbons by a two-stage process comprising steam reforming or partial oxidation followed by Fischer-Tropsch synthesis over a special cobalt-containing catalyst; the feed for the second stage contains CO2 and/or N2 as contaminants, which contaminants are already present in the feed for the first stage and/or have been introduced in the syngas by using air in the partial oxidation step.
PROCESS FOR THE PREPARATION OF HYDROCARBONS
C5+ hydrocarbons are prepared from C4- hydrocarbons by a two-stage process comprising steam reforming or partial oxidation followed by Fischer-Tropsch synthesis over a special cobalt-containing catalyst; the feed for the second stage contains CO2 and/or N2 as contaminants, which contaminants are already present in the feed for the first stage and/or have been introduced in the syngas by using air in the partial oxidation step.
Description
3~3~
PROCESS FOR THE PREPARATION OF HYDROCARBONS
The invention relates to a process for the preparation of hydrocarbons having at least five carbon atoms per molecule.
Hydrocarbons of at least five carbon atoms per molecule (hereinafter referred to as "Cs~ hydrocarbons") can be prepared frGm hydrocarbons having at most four carbon ato~s per molecule (hereinafter referred to as "C4- hydrocarbons") by a two-step process in which in the first step the C4- hydrocarbons are converted by steam reforming or partial oxidation into a mixture of carbon monoxide and hydrogen~ which mixture is contacted in the second step at elevated tem~erature and pressure with a catalyst and thus converted into a mixture of hydrocarbons consisting substantial-ly of Cs~ hydrocarbons. The reaction which takes place in the second step of the process is known in the literature as the Fischer-Tropsch hydrocarbon synthesis. Catalysts often used for this reaction contain one or more metals from the iron group together with one or more promotors and a carrier material.
A catalyst's usefulness for the preparation of Cs+ hydro-carbons from H2/CO mixtures is mainly determined by its activity, Cs~ selectivity and stability, the catalyst being regarded as more useful according as these parameters have a higher value. In the preparation of Cs~ hydrocarbons from H2/CO
mixtures according to a single step process the catalyst's Cs+
selectivity and stability draw most emphasis; For according as the catalyst has a higher Cs+ selectivity, less C4- hydrocarbons will be formed as by-product and according as the catalyst has higher stability, the process can be carried out for a longer period before it becomes necessary to replace the catalyst. It is true that, according as the catalyst has a lower activity, less of the H2/CO mixture can be converted per reactor throughput; however, 3o by recirculation of unconverted H2 and CO a higher conversion of the H2/CO mixture can nevertheless be realised. In the preparation of Cs~ hydrocarbons from C4- hydrocarbons according to the afore-mentioned two-step process most emphasis lies on the catalyst's
PROCESS FOR THE PREPARATION OF HYDROCARBONS
The invention relates to a process for the preparation of hydrocarbons having at least five carbon atoms per molecule.
Hydrocarbons of at least five carbon atoms per molecule (hereinafter referred to as "Cs~ hydrocarbons") can be prepared frGm hydrocarbons having at most four carbon ato~s per molecule (hereinafter referred to as "C4- hydrocarbons") by a two-step process in which in the first step the C4- hydrocarbons are converted by steam reforming or partial oxidation into a mixture of carbon monoxide and hydrogen~ which mixture is contacted in the second step at elevated tem~erature and pressure with a catalyst and thus converted into a mixture of hydrocarbons consisting substantial-ly of Cs~ hydrocarbons. The reaction which takes place in the second step of the process is known in the literature as the Fischer-Tropsch hydrocarbon synthesis. Catalysts often used for this reaction contain one or more metals from the iron group together with one or more promotors and a carrier material.
A catalyst's usefulness for the preparation of Cs+ hydro-carbons from H2/CO mixtures is mainly determined by its activity, Cs~ selectivity and stability, the catalyst being regarded as more useful according as these parameters have a higher value. In the preparation of Cs~ hydrocarbons from H2/CO
mixtures according to a single step process the catalyst's Cs+
selectivity and stability draw most emphasis; For according as the catalyst has a higher Cs+ selectivity, less C4- hydrocarbons will be formed as by-product and according as the catalyst has higher stability, the process can be carried out for a longer period before it becomes necessary to replace the catalyst. It is true that, according as the catalyst has a lower activity, less of the H2/CO mixture can be converted per reactor throughput; however, 3o by recirculation of unconverted H2 and CO a higher conversion of the H2/CO mixture can nevertheless be realised. In the preparation of Cs~ hydrocarbons from C4- hydrocarbons according to the afore-mentioned two-step process most emphasis lies on the catalyst's
- 2 ~ 3~
stability. Lower activity can be set off - as in the single-step ~ process - by recirculation of unconverted H2 and CO. Since in the first step of the two-step process C4- hydrocarbons are converted into a H2/CO mixture, lower Cs+ selectivity of the catalyst in the second step can be set off by recirculation of the C~~ hydro-carbons formed as by-product. On account of the possibilities of compensating for lower activity and Cs+ selectivity offered by the two-step process, for carrying out the process on a technical scale preference will often be given to a catalyst for the second step which, though it does not have the highest activity and Cs~ selectivity, is the most stable.
The afore-going observation was made on the assumption that the H2/CO mixture used as feed for the second step is a relatively pure synthesis gas, so that the proposed recycling operations can be carried out without the need of costly separating operations. If that is the case, the catalyst's stability in the second step is indeed its most important parameter. The picture is entirely different when the H2/CO mixture which is used as feed for the second step is highly contaminated with nitrogen andtor carbon dioxide. These contaminants may have found their way into the synthesis gas in different ways. In the first place the feed for the first step in addition to C4- hydrocarbons may contain more than 20 %v nitrogen and/or carbon dioxide. In this connection it should be noted that natural gas, which is known to consist mainly of methane where hydrocarbons are concerned, may contain up to 75 ~v of said contaminants. When for the first step a feed is used which is contaminated with nitrogen and/or carbon dioxide, these contaminants will pass through the reactor unchanged and find their way into the feed for the second step. And also, when the first step is carried out by partial oxidation using an oxygen-containing gas mixture containing more than 50 ~v n-trogen, such as air or oxygen-enriched air, instead of oxygen, there will be obtained a feed for the second step which, in addition to hydrogen and carbon monoxide, contains the nitrogen present in the gas used. If the feed for the first step _ 3 _ ~2~
contains nitrogen and/or carbon dioxide by nature, then, with partial oxidation using a nitrogen and oxygen containing gas mixture, said contaminants will be found in the feed for the second step in addition the nitrogen from the gas mixture used.
As regards the catalysts which are eligible for use in the second step of the afore-mentioned two-step process in which the feed for the second step is heavily contaminated by nitrogen and/or carbon dioxide as a result of the use of a feed for the first step containing more than 20 %v nitrogen and/or carbon dioxide, and/or the use in the first step of partial oxidation using an oxygen-containing gas mixture containing more than 50 ~v nitrogen, the following may be observed. If, in order to set off too low activity and/or selectivity of the catalyst in the second step, it should be contemplated to recirculate as indicated hereinbefore, unconverted H2 and C0 and/or C4- hydrocarbons formed it should be taken into account that when a H2/C0 mixture thus contaminated with nitrogen and/or carbon dioxide i5 used as feed for the second step, this is possible only after said contaminants have been removed from the recirculation streams. Such removal entails considerable expenses, and for that reason it is not suitable for use on a technical scale.
This involves that for carrying out the process on a technical scale the two possibilities of compensation mentioned hereinbefore cease to be applicable, so that in the second step a catalyst will necessarily have to be used which not only has the high stability mentioned hereinbefore, but whose activity and Cs+ selectivity in the presence of nitrogen and carbon dioxide are sufficiently high for the process to be realised on a technical scale without recirculation.
In order to get a fair knowledge of the influence of nitrogen and carbon dioxide on the performance of Fischer-Tropsch catalysts an investigation was carried out in which these catalysts were used for the conversion of gas mixtures some of which in addition to H2 and C0, contained nitrogen or carbon dioxide some not. It was found that the presence of nitrogen and carbon dioxide in the H2/C0 mixture lessens the activity of these catalysts, the decrease becoming larger as the mixture contained more nitrogen and carbon _ 4 _ ~ ~3~3~
dioxide. It is true that by increasing the severity of the reaction - conditions - notably raising the temperature and/or pressure - in the presence of nitrogen and carbon dioxide an activity level could be attained which corresponded with that of a nitrogen and carbon dioxide-free operation, but this was accompanied by a loss of the catalysts' stability, which became larger as severer reaction conditions were used. It was further found that the Cs+ selectivity of these catalysts was barely influenced by the presence of nitrogen and/or carbon dioxide in the H2/C0 mixture. As regards the stability the investigation produced a surprising finding. In contrast with other Fischer-Tropsch catalysts whose stability - as well as Cs+
selectivity - was barely influenced by the presence of nitrogen and/or carbon dioxide, there was a certain group of cobalt catalysts of which the stability was found to be considerably increased by the presence of nitrogen and/or carbon dioxide, the increase being larger according as the mixture contained mOFe nitrogen and carbon dioxide. The Fischer-Tropsch caealysts displaying this surprising behaviour comprise silica, alumina or silica-alumina as carrier material and cobalt together with zirconium, titanium and/or chromium as catalytically active metals in such quantities that in the catalysts there are present 3-60 pbw cobalt and 0.l-l00 pbw zirconium~
titanium,ruthenium and/or chromium per l00 pbwcarriermaterial. The catalysts were prepared by depositing the metals concerned by kneading and/or impregnation on the carrier material. For further information on the preparation of these catalysts by kneading and/or impregnation reference is made to the Canadian patent application no. 453,317 recently filed in the name of the Applicant.
When a cobalt catalyst belonging to the afore-mentioned class is used for the conversion of a H2/C0 mixture containing no nitrogen or carbon dioxide, under the given reaction conditions this catalyst is seen to have not only high stability and Cs+ select-ivity, but also very high activity. When the same catalyst is used under similar reaction conditions for the conversion of a gas mixture which, in addition to H2 and C0, contains nitrogen and/or carbon dioxide, a decrease in activity is seen as ~ell as a consider-able increase in stability, as was re-narked hereinbefore. In view of ~Y~
~3~3~
the very high activity level of the present cobalt catalysts, some ~ loss of activity in return for a considerable increase in stability is quite acceptable for an operation carried out on a technical scale. Another option is to raise the activity to its original level by increasing the severity of the reaction conditions; this i9 coupled with some loss of stability. However, it has surprisingly been found that this loss of stability is amply compensated for by the increase in stability due to the presence of nitrogen and/or carbon dioxide. This means that when the cobalt catalysts belonging to the above-mentioned class are used for converting a H2/C0 mixture which is heavily contaminated with nitrogen and/or carbon dioxide, a level of activity can be realised which is very similar to that seen in the nitrogen and carbon dioxide free operation, whilst the stability is higher. These special properties render the cobalt catalysts eminently suitable for use in the second step of said two-step process in which the feed for the second step is heavily contaminated with nitrogen and/or carbon dioxide. As to the carbon dioxide which may occur in the feed for the second step as contaminant, the following should be remarked. Depending on the reaction conditions used in the steam reforming and the partial oxidation, minor quantities of carbon dioxide may be formed as by-product in the first step as a result of side reactions. This carbon dioxide, together with carbon dioxide which may already have been present in the feed for the first step, finds its way into the feed for the second step as contaminant. In view of the amounts of contaminants that land in the feed for the second step as a result of the use of a feed for the first step containing more than 20 %v nitrogen and/or carbon dioxide, and/or as a result of the use of the partial oxidation of an oxygen-containing gas containing more than 50 %v nitrogen, the amount of carbon dioxide which, when the steam reforming or partial oxidation is carried out in a normal operation, may find its way into the feed for the second step as a result of said side reactions, is of secondary importance. Therefore the presence of contaminants in the feed for the second step is mainly , . .
- 6 - ~ 3~
due to the use of a contaminated feed for the first step and/or to the use of partial oxidation with an oxygen-containing gas containing nitrogen.
The present patent application therefore relates to a process for the preparation of Cs+ hydrocarbons from C4- hydrocarbons, in which in the first step C4- hydrocarbons are converted by steam reforming or partial oxidation into a mixture of carbon monoxide and hydrogen, which mixture is subsequently, in a second step, converted into a mixture of hydrocarbons consisting mainly of Cs+ hydrocarbons by contacting it at elevated temperature and pressure with a catalyst comprising 3-60 pbw cobalt and O.l-lO0 pbw of at least one other metal chosen from the group formed by zirconium, titanium~ruthenium andchromium perlOOpbw silica, ~umina o~silica-alumina, which catalyst has been prepared by kneading and/or impregnation, in which the feed for the second step contains nitrogen and/or carbon dioxide as contaminants, the presence therein of these contaminants having been caused substantially by ehe fact that the feed for the first step contained more than 20 %v nitrogen and/or carbon dioxide and/or the fact that the first step was carried out by partial oxidation using an oxygen-containing gas mixture containing more than 50 ~v nitrogen.
In the process according to the invention the starting material may be a feed consisting substantially of one or more C4- hydro-carbons or a feed which, in addition to C4- hydrocarbons, contains nitrogen and/or carbon dioxide. Examples of C4- hydro-carbons which may occur in the feed individually or in admixture are methane, ethane, propane, butane and isobutane. Preference is given to carrying out the process with a feed in which the C4- hydro-carbons consist mainly of methane. Special preference is given to natural gas as feed.
In the process according to the invention in the first step steam reforming or partial oxidation is used to convert the C4- hydro-carbons into a mixture of carbon monoxide and hydrogen. The steam reforming is usually carried out by contacting the hydrocarbons to be converted together with steam at a temperature of 500-12004C, a pressure of 2-40 bar and a steam/hydrocarbon ratio of l-lO g mol H20/g atom C with a catalyst containing one or more metals from the iron group supported on a carrier. The steam reforming is prefer-ably carried out at a temperature of 700-1000C, a pressure of 2 25 bar and a steam/hydrocarbon ratio of 1.5-5 g mol H20/g atom C
and by using a nickel-containing catalyst. In order to prevent deposition of coke on the catalyst and also to remove coke already deposited from the catalyst by conversion into C0, it is preferred to use a catalyst containing an alkali metal, in particular potassium.
In order to avoid sintering of the catalyst, it is moreover preferred to use a catalyst containing an alkaline earth metal, in particular calcium. If the C4- hydrocarbons in the feed consist completely or to a considerable extent of hydrocarbons containing two or more carbon atoms per molecule, if it preferred to use a catalyst having cracking activity. The catalyst can be invested ~ith cracking activity by the use of a silica-alumina as carrier. In the process according to the invention the conversion of the C4- hydrocarbons into a mixture of carbon monoxide and hydrogen can also be carried out by partial oxidation instead of by steam reforming. This partial oxidation is usually carried out by contacting the hydrocarbons to be converted, together with oxygen or an oxygen-containing gas, at a temperature of 500-1750C, a pressure of 5-100 bar and an oxygen/
hydrocarbon ratio of 0.2-0.9 g mol 02/g atom C with a catalyst containing one or more metals from the iron group supported on a carrier. If desired, the partial oxidation can also be conducted in the absence of a catalyst. The partial oxidation is preferably carried out at a temperature of 1100-1500C, a pressure of 10-60 bar and an oxygen/hydrocarbon ratio of 0.35-0.75 g mol 02/g atom C and by using a nickel-containing catalyst. To the other components which 3Q may be present in the~e catalysts the same preference applies as stated for the steam reforming catalysts. Th~ partial oxidation is carried out by using oxygen or a gas which, in addition to oxygen, contains one or more other co~ponents, in particular nitrogen. If for the partial oxidation an oxygen/nitrogen mixture is used, it is preferred to choose air or oxygen-enriched air for the purpose. If in the process according to the invention partial oxidation is used in the first step, it is preferred in order to increase the H2/C0 molar ratio of the synthesis gas to be prepared, to add to the mixture to be subjected to partial oxidation a molar quantity of steam smaller than the molar quantity of oxygen used.
The process according to the invention is of particular importance for the preparation of Cs+ hydrocarbons from a natural gas which is contaminated with nitrogen and/or carbon dioxide, in particular a natural gas containing more than 30 %v of these contaminants. Such contaminated natural gases are amply available in nature. When the process according to the invention is used for preparing Cs~ hydrocarbons from natural gas which is contaminated with nitrogen and/or carbon dioxide, the first step is preferably carried out either by steam reforming, or by partial oxidation using oxygen.
If in the process according to the invention the starting material is a feed with a relatively high H/C ratio, such as natural gas which is contaminated by carbon dioxide, and if the first step of the process is carried out by steam reforming, the process offers the additional advantage that hydrocarbon selectivities above lO0 can be realised. (In the present two-step process hydrocarbon selectivity should be taken to be the number of g atom C present in the hydrocarbon product of the second step, calculated on the number of g atom C present in the part of the hydrocarbon feed for the first step whish is converted in the first step). This is mainly a result of the fact that feeds with a relatively high H/C ratio, such as methane, when steam reformed yield a synthesis gas having a H2/C0 molar ratio higher than 2, whilst the H2/C0 consumption ratio of the cobalt catalysts used in the second step is not higher 3o than about 2. When during the steam refor~ing carbon dioxide is present, part thereof will react with part of the excess of hydrogen produced by the reverse C0-shift reaction C2 + H2 ~ C0 + H20.
As a consequence9 a synthesis gas is obtained whose H2/C0 molar ratio is more in keeping with the H2/C0 consumption ratio of the cobalt catalysts, so that a hi8her conversion of the synthesis gas int~ hydrocarbons can be obtained.
~3~
g In the process of the invention it is preferred to use in the second step the cobalt catalysts which form the subject matter of Canadian patent ap~lication No. 453,317. These are catalys-ts which satisfy the relation (3 + 4 R) > - > (0.3 + 0.4 R), wherein S
L = the total quantity of cobalt present on the catalyst, expressed as mg Co/ml catalyst, S = the surface area of the catalyst, expressed as m~/ml catalyst, and R = the weighc.ratio of the quantity of cobalt deposited on the catalyst by kneading to the total quantity of cobalt present on the catalyst.
The preparation of the cobalt catalysts which are used in the second step of the process of the invention is preferably carried out according to one of the three procedures mentioned hereinafter:
a) first cobalt is deposited in one or more steps by impregnation and subsequently the other metal is deposited in one or more steps, also by impregnation, b) first the other metal is deposited in one or more steps by impregnation and subsequently the cobalt is deposiCed in one or more steps, also by impregnation, and c) first cobalt is deposited in one or more steps by kneading and . subsequently the other metal is deposited in one or more steps by impregnation.
In the process according to the invention preference is given to the use of cobalt catalysts containing i5-50 pbw cobalt per lO0 pbw carrier. The preferred quantity of other metal present in the cobalt catalysts depends on the way in which this metal has been deposited. In the case of catalysts where first cobalt has been deposited on the carrier, followed by the other metal, prefer-ence is given to catalysts containing 0.1-5 pbw other metal per lO0 pbw carrier. In the case of catalysts where first the other metal has been deposited on the carrier, followed by the cobalt, .
.~
stability. Lower activity can be set off - as in the single-step ~ process - by recirculation of unconverted H2 and CO. Since in the first step of the two-step process C4- hydrocarbons are converted into a H2/CO mixture, lower Cs+ selectivity of the catalyst in the second step can be set off by recirculation of the C~~ hydro-carbons formed as by-product. On account of the possibilities of compensating for lower activity and Cs+ selectivity offered by the two-step process, for carrying out the process on a technical scale preference will often be given to a catalyst for the second step which, though it does not have the highest activity and Cs~ selectivity, is the most stable.
The afore-going observation was made on the assumption that the H2/CO mixture used as feed for the second step is a relatively pure synthesis gas, so that the proposed recycling operations can be carried out without the need of costly separating operations. If that is the case, the catalyst's stability in the second step is indeed its most important parameter. The picture is entirely different when the H2/CO mixture which is used as feed for the second step is highly contaminated with nitrogen andtor carbon dioxide. These contaminants may have found their way into the synthesis gas in different ways. In the first place the feed for the first step in addition to C4- hydrocarbons may contain more than 20 %v nitrogen and/or carbon dioxide. In this connection it should be noted that natural gas, which is known to consist mainly of methane where hydrocarbons are concerned, may contain up to 75 ~v of said contaminants. When for the first step a feed is used which is contaminated with nitrogen and/or carbon dioxide, these contaminants will pass through the reactor unchanged and find their way into the feed for the second step. And also, when the first step is carried out by partial oxidation using an oxygen-containing gas mixture containing more than 50 ~v n-trogen, such as air or oxygen-enriched air, instead of oxygen, there will be obtained a feed for the second step which, in addition to hydrogen and carbon monoxide, contains the nitrogen present in the gas used. If the feed for the first step _ 3 _ ~2~
contains nitrogen and/or carbon dioxide by nature, then, with partial oxidation using a nitrogen and oxygen containing gas mixture, said contaminants will be found in the feed for the second step in addition the nitrogen from the gas mixture used.
As regards the catalysts which are eligible for use in the second step of the afore-mentioned two-step process in which the feed for the second step is heavily contaminated by nitrogen and/or carbon dioxide as a result of the use of a feed for the first step containing more than 20 %v nitrogen and/or carbon dioxide, and/or the use in the first step of partial oxidation using an oxygen-containing gas mixture containing more than 50 ~v nitrogen, the following may be observed. If, in order to set off too low activity and/or selectivity of the catalyst in the second step, it should be contemplated to recirculate as indicated hereinbefore, unconverted H2 and C0 and/or C4- hydrocarbons formed it should be taken into account that when a H2/C0 mixture thus contaminated with nitrogen and/or carbon dioxide i5 used as feed for the second step, this is possible only after said contaminants have been removed from the recirculation streams. Such removal entails considerable expenses, and for that reason it is not suitable for use on a technical scale.
This involves that for carrying out the process on a technical scale the two possibilities of compensation mentioned hereinbefore cease to be applicable, so that in the second step a catalyst will necessarily have to be used which not only has the high stability mentioned hereinbefore, but whose activity and Cs+ selectivity in the presence of nitrogen and carbon dioxide are sufficiently high for the process to be realised on a technical scale without recirculation.
In order to get a fair knowledge of the influence of nitrogen and carbon dioxide on the performance of Fischer-Tropsch catalysts an investigation was carried out in which these catalysts were used for the conversion of gas mixtures some of which in addition to H2 and C0, contained nitrogen or carbon dioxide some not. It was found that the presence of nitrogen and carbon dioxide in the H2/C0 mixture lessens the activity of these catalysts, the decrease becoming larger as the mixture contained more nitrogen and carbon _ 4 _ ~ ~3~3~
dioxide. It is true that by increasing the severity of the reaction - conditions - notably raising the temperature and/or pressure - in the presence of nitrogen and carbon dioxide an activity level could be attained which corresponded with that of a nitrogen and carbon dioxide-free operation, but this was accompanied by a loss of the catalysts' stability, which became larger as severer reaction conditions were used. It was further found that the Cs+ selectivity of these catalysts was barely influenced by the presence of nitrogen and/or carbon dioxide in the H2/C0 mixture. As regards the stability the investigation produced a surprising finding. In contrast with other Fischer-Tropsch catalysts whose stability - as well as Cs+
selectivity - was barely influenced by the presence of nitrogen and/or carbon dioxide, there was a certain group of cobalt catalysts of which the stability was found to be considerably increased by the presence of nitrogen and/or carbon dioxide, the increase being larger according as the mixture contained mOFe nitrogen and carbon dioxide. The Fischer-Tropsch caealysts displaying this surprising behaviour comprise silica, alumina or silica-alumina as carrier material and cobalt together with zirconium, titanium and/or chromium as catalytically active metals in such quantities that in the catalysts there are present 3-60 pbw cobalt and 0.l-l00 pbw zirconium~
titanium,ruthenium and/or chromium per l00 pbwcarriermaterial. The catalysts were prepared by depositing the metals concerned by kneading and/or impregnation on the carrier material. For further information on the preparation of these catalysts by kneading and/or impregnation reference is made to the Canadian patent application no. 453,317 recently filed in the name of the Applicant.
When a cobalt catalyst belonging to the afore-mentioned class is used for the conversion of a H2/C0 mixture containing no nitrogen or carbon dioxide, under the given reaction conditions this catalyst is seen to have not only high stability and Cs+ select-ivity, but also very high activity. When the same catalyst is used under similar reaction conditions for the conversion of a gas mixture which, in addition to H2 and C0, contains nitrogen and/or carbon dioxide, a decrease in activity is seen as ~ell as a consider-able increase in stability, as was re-narked hereinbefore. In view of ~Y~
~3~3~
the very high activity level of the present cobalt catalysts, some ~ loss of activity in return for a considerable increase in stability is quite acceptable for an operation carried out on a technical scale. Another option is to raise the activity to its original level by increasing the severity of the reaction conditions; this i9 coupled with some loss of stability. However, it has surprisingly been found that this loss of stability is amply compensated for by the increase in stability due to the presence of nitrogen and/or carbon dioxide. This means that when the cobalt catalysts belonging to the above-mentioned class are used for converting a H2/C0 mixture which is heavily contaminated with nitrogen and/or carbon dioxide, a level of activity can be realised which is very similar to that seen in the nitrogen and carbon dioxide free operation, whilst the stability is higher. These special properties render the cobalt catalysts eminently suitable for use in the second step of said two-step process in which the feed for the second step is heavily contaminated with nitrogen and/or carbon dioxide. As to the carbon dioxide which may occur in the feed for the second step as contaminant, the following should be remarked. Depending on the reaction conditions used in the steam reforming and the partial oxidation, minor quantities of carbon dioxide may be formed as by-product in the first step as a result of side reactions. This carbon dioxide, together with carbon dioxide which may already have been present in the feed for the first step, finds its way into the feed for the second step as contaminant. In view of the amounts of contaminants that land in the feed for the second step as a result of the use of a feed for the first step containing more than 20 %v nitrogen and/or carbon dioxide, and/or as a result of the use of the partial oxidation of an oxygen-containing gas containing more than 50 %v nitrogen, the amount of carbon dioxide which, when the steam reforming or partial oxidation is carried out in a normal operation, may find its way into the feed for the second step as a result of said side reactions, is of secondary importance. Therefore the presence of contaminants in the feed for the second step is mainly , . .
- 6 - ~ 3~
due to the use of a contaminated feed for the first step and/or to the use of partial oxidation with an oxygen-containing gas containing nitrogen.
The present patent application therefore relates to a process for the preparation of Cs+ hydrocarbons from C4- hydrocarbons, in which in the first step C4- hydrocarbons are converted by steam reforming or partial oxidation into a mixture of carbon monoxide and hydrogen, which mixture is subsequently, in a second step, converted into a mixture of hydrocarbons consisting mainly of Cs+ hydrocarbons by contacting it at elevated temperature and pressure with a catalyst comprising 3-60 pbw cobalt and O.l-lO0 pbw of at least one other metal chosen from the group formed by zirconium, titanium~ruthenium andchromium perlOOpbw silica, ~umina o~silica-alumina, which catalyst has been prepared by kneading and/or impregnation, in which the feed for the second step contains nitrogen and/or carbon dioxide as contaminants, the presence therein of these contaminants having been caused substantially by ehe fact that the feed for the first step contained more than 20 %v nitrogen and/or carbon dioxide and/or the fact that the first step was carried out by partial oxidation using an oxygen-containing gas mixture containing more than 50 ~v nitrogen.
In the process according to the invention the starting material may be a feed consisting substantially of one or more C4- hydro-carbons or a feed which, in addition to C4- hydrocarbons, contains nitrogen and/or carbon dioxide. Examples of C4- hydro-carbons which may occur in the feed individually or in admixture are methane, ethane, propane, butane and isobutane. Preference is given to carrying out the process with a feed in which the C4- hydro-carbons consist mainly of methane. Special preference is given to natural gas as feed.
In the process according to the invention in the first step steam reforming or partial oxidation is used to convert the C4- hydro-carbons into a mixture of carbon monoxide and hydrogen. The steam reforming is usually carried out by contacting the hydrocarbons to be converted together with steam at a temperature of 500-12004C, a pressure of 2-40 bar and a steam/hydrocarbon ratio of l-lO g mol H20/g atom C with a catalyst containing one or more metals from the iron group supported on a carrier. The steam reforming is prefer-ably carried out at a temperature of 700-1000C, a pressure of 2 25 bar and a steam/hydrocarbon ratio of 1.5-5 g mol H20/g atom C
and by using a nickel-containing catalyst. In order to prevent deposition of coke on the catalyst and also to remove coke already deposited from the catalyst by conversion into C0, it is preferred to use a catalyst containing an alkali metal, in particular potassium.
In order to avoid sintering of the catalyst, it is moreover preferred to use a catalyst containing an alkaline earth metal, in particular calcium. If the C4- hydrocarbons in the feed consist completely or to a considerable extent of hydrocarbons containing two or more carbon atoms per molecule, if it preferred to use a catalyst having cracking activity. The catalyst can be invested ~ith cracking activity by the use of a silica-alumina as carrier. In the process according to the invention the conversion of the C4- hydrocarbons into a mixture of carbon monoxide and hydrogen can also be carried out by partial oxidation instead of by steam reforming. This partial oxidation is usually carried out by contacting the hydrocarbons to be converted, together with oxygen or an oxygen-containing gas, at a temperature of 500-1750C, a pressure of 5-100 bar and an oxygen/
hydrocarbon ratio of 0.2-0.9 g mol 02/g atom C with a catalyst containing one or more metals from the iron group supported on a carrier. If desired, the partial oxidation can also be conducted in the absence of a catalyst. The partial oxidation is preferably carried out at a temperature of 1100-1500C, a pressure of 10-60 bar and an oxygen/hydrocarbon ratio of 0.35-0.75 g mol 02/g atom C and by using a nickel-containing catalyst. To the other components which 3Q may be present in the~e catalysts the same preference applies as stated for the steam reforming catalysts. Th~ partial oxidation is carried out by using oxygen or a gas which, in addition to oxygen, contains one or more other co~ponents, in particular nitrogen. If for the partial oxidation an oxygen/nitrogen mixture is used, it is preferred to choose air or oxygen-enriched air for the purpose. If in the process according to the invention partial oxidation is used in the first step, it is preferred in order to increase the H2/C0 molar ratio of the synthesis gas to be prepared, to add to the mixture to be subjected to partial oxidation a molar quantity of steam smaller than the molar quantity of oxygen used.
The process according to the invention is of particular importance for the preparation of Cs+ hydrocarbons from a natural gas which is contaminated with nitrogen and/or carbon dioxide, in particular a natural gas containing more than 30 %v of these contaminants. Such contaminated natural gases are amply available in nature. When the process according to the invention is used for preparing Cs~ hydrocarbons from natural gas which is contaminated with nitrogen and/or carbon dioxide, the first step is preferably carried out either by steam reforming, or by partial oxidation using oxygen.
If in the process according to the invention the starting material is a feed with a relatively high H/C ratio, such as natural gas which is contaminated by carbon dioxide, and if the first step of the process is carried out by steam reforming, the process offers the additional advantage that hydrocarbon selectivities above lO0 can be realised. (In the present two-step process hydrocarbon selectivity should be taken to be the number of g atom C present in the hydrocarbon product of the second step, calculated on the number of g atom C present in the part of the hydrocarbon feed for the first step whish is converted in the first step). This is mainly a result of the fact that feeds with a relatively high H/C ratio, such as methane, when steam reformed yield a synthesis gas having a H2/C0 molar ratio higher than 2, whilst the H2/C0 consumption ratio of the cobalt catalysts used in the second step is not higher 3o than about 2. When during the steam refor~ing carbon dioxide is present, part thereof will react with part of the excess of hydrogen produced by the reverse C0-shift reaction C2 + H2 ~ C0 + H20.
As a consequence9 a synthesis gas is obtained whose H2/C0 molar ratio is more in keeping with the H2/C0 consumption ratio of the cobalt catalysts, so that a hi8her conversion of the synthesis gas int~ hydrocarbons can be obtained.
~3~
g In the process of the invention it is preferred to use in the second step the cobalt catalysts which form the subject matter of Canadian patent ap~lication No. 453,317. These are catalys-ts which satisfy the relation (3 + 4 R) > - > (0.3 + 0.4 R), wherein S
L = the total quantity of cobalt present on the catalyst, expressed as mg Co/ml catalyst, S = the surface area of the catalyst, expressed as m~/ml catalyst, and R = the weighc.ratio of the quantity of cobalt deposited on the catalyst by kneading to the total quantity of cobalt present on the catalyst.
The preparation of the cobalt catalysts which are used in the second step of the process of the invention is preferably carried out according to one of the three procedures mentioned hereinafter:
a) first cobalt is deposited in one or more steps by impregnation and subsequently the other metal is deposited in one or more steps, also by impregnation, b) first the other metal is deposited in one or more steps by impregnation and subsequently the cobalt is deposiCed in one or more steps, also by impregnation, and c) first cobalt is deposited in one or more steps by kneading and . subsequently the other metal is deposited in one or more steps by impregnation.
In the process according to the invention preference is given to the use of cobalt catalysts containing i5-50 pbw cobalt per lO0 pbw carrier. The preferred quantity of other metal present in the cobalt catalysts depends on the way in which this metal has been deposited. In the case of catalysts where first cobalt has been deposited on the carrier, followed by the other metal, prefer-ence is given to catalysts containing 0.1-5 pbw other metal per lO0 pbw carrier. In the case of catalysts where first the other metal has been deposited on the carrier, followed by the cobalt, .
.~
3~
preference is given to catalysts containing 5-40 pbw of the other metal per ~00 pbw carrier. Preference is given to zirconium as other metal and to silica as carrier material. In order to be suitable for use the cobalt catalysts should first be reduced. This reduction may suitably be carried out by contacting the catalyst at a temperature between 200 and 350C with a hydrogen-containing gas.
In the process according to the invention the second step is preferably carried out at a temperature of 125-350 C and a pressure of 5-100 bar. Special preference is given to the use of a temperature 10 of 175-275C and a pressure of 10-75 bar in the second step.
In addition to their afore-mentioned surprising increase in stability in the presence of nitrogen and/or carbon dioxide the cobalt catalysts used in the second step have the special property of yielding a product in which only very minor quantities of olefins and oxygen-containing organic compounds occur and in which the organic part consists virtually completely of unbranched paraffins a considerable part of which boil above the middle distillate - range. In the present patent application middle distillates are taken to be hydrocarbon mixtures whose boiling range corresponds substantially with that of the kerosine and gas oil fractions obtained in the conventional atmospheric distillation of crude mineral oil. l'he middle distillate range lies substantially between about 150 and 360C, the fractions boiling between about 200 and 360C generally being refered to as gas oils. Owing to the high normal paraffins/isoparaffins ratio and the low content of olefins and oxygen-containing organic compounds of the product prepared over the cobalt catalysts, the gas oil present therein has a very high cetane number. It has been found that by hydrocracking in the presence of a catalyst containing one or more noble metals from Group VIII supported on a carrier the high-boiling part of said product can be converted in high yield into middle distillate. As feed for the hydrocracking at least the part of the product is chosen whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as end product. The hydrocracking, which is characterized by a very low hydrogen consumpt-ion, yields a product in which, owing to the high normal paraffins/
3f~ 3~i isoparaffins ratio, the gas oil has a very high cetane number.
Although in the preparation of middle distillates from the product obtained over the cobalt catalyst the part of the product whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as end product will do as hydro-cracking feed, for this purpose it is preferred to use the total Cs~ fraction of the product prepared over the cobalt catalyst because it has been found that the catalytic hydrotreatment leads to enhanced quality of the gasoline, kerosine and gas oil fractions present therein.
The hydrocracking catalyst used by preference is a catalyst containing 0.1-2 %w and in particular 0.2-l ~w of one or more noble metals from Group VIII supported on a carrier. Preference is given to catalysts comprising platinum or palladium as Group VIII noble metal and silica-alumina as carrier. The hydrocracking in which the feed, together with added hydrogen, is passed over the noble metal catalyst is preferably carried out at a temperature of 200-400~C and in particular of 250-350C and a pressure of 5-lO0 bar and in particular of 10-75 bar.
If the two-step process according to the invention is combined with a hydrocracking treatment as a third step for the preparation of middle distillates, the second and third step can be carried out in 'series-flow', provided that the reaction product of the second step still contains sufficient unconverted hydrogen for carrying out the hydrocracking. It is a matter of common knowledge that carrying out a multi-step process in 'series-flow' comprises using the total reaction product - without any components being removed therefrom or added thsreto - of a certain step as feed for the following step, which is carried out substantially at the same pressure as the preceding step. If desired, the whole three-step process can be carried out in 'series-flow'.
The invention is now illustrated with the aid of the following example.
Example Feed 1: A natural gas consisting substantially of methane.
Feed 2: A natural gas consisting substantial].y of a mixture of methane and carbon dioxide in a volume ratio l:l.
Catalyst 1: Ni/Ca/K/A12O3 catalyst containing 13 phw nickel, 12 pbw calcium and 0.2 pbw potassium per 100 pbw alumina.
Catalyst 2: Fe/K/SiO2 catalyst containing 50 pbw iron and 4 pbw potassium per lO0 pbw silica. Catalyst 2 had been prepared by three-step co-impregnation of a silica carrier with a solution of potassium nitrate and ferric nitrate in water.
Catalyst 3: Co/ZriSiO2 catalyst containing 25 pbw cobalt and 0.9 pbw zirconium per lO0 pbw silica. Catalyst 3 had been prepared by one-step impregnation of a silica carrier with a solution of cobalt nitrate in water, followed by one-step impregnati,on of the cobalt-loaded carrier with a solution of zirconium nitrate in water.
For Catalyst 3 L was 98 mg/ml and S was 96 m2/ml, and therefore L/S was 1.02 mg/m2.
In the preparation of Catalysts 2 and 3 a quantity of solution was used in each impregnation step whose volume corresponded substant-ially with the pore volume of the carrier. After each impregnation step the material was dried and then calcined at 500C.
Seven two-step experiments (Experiments 1-7) were carried out in which in the first step Feeds l and 2 were subjected to steam reforming or partial oxidation in the presence of Catalyst l to be converted into H2 and C0 containing gas mixtures. From the gas mixtures prepared by the first step of Experiments 1, 3, 6 and 7 the carbon dioxide formed was removed. Moreover, by selective removal of hydrogen from the gas mixtures prepared by the first step of Experi-ments l and 3 the H2/CO molar ratio of these mixtures was reduced to 2, corresponding with the H2/CO molar ratio of gas mixtures prepared by the first step of Experiments 2 and 4-7. Subsequently the gas mixtures were contacted in the second step at a temperature of 220C and at various space velocities with Catalysts 2 and 3 which had previously been subjected to reduction at 250C in a hydrogen-containing gas.
- 13 ~ 6 In Experiments 1-5 the first step was carried out by steam reforming at a tempeature of 930C, a pressure of 22 bar and a steam/hydrocarbon ratio of 2.5 g mol H20/g atom C. In Experiments 6 and 7 the first step was carried out by partial oxidation with air and by adding steam at a temperature of 1225C, a pressure of 30 bar, an oxygen/hydrocarbon ratio of 0.60 g mol 02/g atom C and a steam/hydrocarbon ratio of 0.27 g mol ~20/g atom C. The results of Experiments 1-7, as well as the conditions under which the second step was carried out in each of these experiments, are given in the appending Table.
Of Experiments 1-7 only Experiments 4-7 are experiments according to the invention. In the first step of Experiments 4 and 5 a carbon-dioxide-contaminated synthesis gas was prepared by stea~
reforming of a heavily carbon-dioxide-contaminated natural gas. In the first step of Experiments 6 and 7 a nitrogen-contaminated synthesis gas was prepared by partial oxidation with air of a natural gas subs-tantially consisting of methane. In Experiments 4-7 the second step was carried out by using a cobalt catalyst belonging to the class described hereinbefore. Experiments 1-3 fall outside the scope of the invention. They have been included in the patent application for comparison. In the first step of Experiment 1 and 3 no contaminated synthesis gas as expressed in the present patent application was prepared. In the second step of Experiments 1 and 2 use was made of an iron catalyst.
As regards the results mentioned in the Table the following may be observed.
1) Comparison of the results of Experiments 1 and 2 shows that when an iron catalyst is used, contamination of the synthesis gas with 15 %v carbon dioxide results in a decrease in activity, with unchanging stability.
2) Comparison of the results of Experiments 3 and 4 shows that when a cobalt catalyst belonging to the afore-described class is used, contamination of the synthesis gas with 15 %v carbon dioxide also leads to a decrease in ativity (which by the way is considerably smaller than in the case of the iron catalyst) J but an increase in stability.
- 14 ~ 3~
.
3) Comparison of the results of Experiments 3 and 6 shows that when a cobalt catalyst is used, contamination of the synthesis gas with 45 %v nitrogen also leads to a decrease in activity and an increase in stability.
preference is given to catalysts containing 5-40 pbw of the other metal per ~00 pbw carrier. Preference is given to zirconium as other metal and to silica as carrier material. In order to be suitable for use the cobalt catalysts should first be reduced. This reduction may suitably be carried out by contacting the catalyst at a temperature between 200 and 350C with a hydrogen-containing gas.
In the process according to the invention the second step is preferably carried out at a temperature of 125-350 C and a pressure of 5-100 bar. Special preference is given to the use of a temperature 10 of 175-275C and a pressure of 10-75 bar in the second step.
In addition to their afore-mentioned surprising increase in stability in the presence of nitrogen and/or carbon dioxide the cobalt catalysts used in the second step have the special property of yielding a product in which only very minor quantities of olefins and oxygen-containing organic compounds occur and in which the organic part consists virtually completely of unbranched paraffins a considerable part of which boil above the middle distillate - range. In the present patent application middle distillates are taken to be hydrocarbon mixtures whose boiling range corresponds substantially with that of the kerosine and gas oil fractions obtained in the conventional atmospheric distillation of crude mineral oil. l'he middle distillate range lies substantially between about 150 and 360C, the fractions boiling between about 200 and 360C generally being refered to as gas oils. Owing to the high normal paraffins/isoparaffins ratio and the low content of olefins and oxygen-containing organic compounds of the product prepared over the cobalt catalysts, the gas oil present therein has a very high cetane number. It has been found that by hydrocracking in the presence of a catalyst containing one or more noble metals from Group VIII supported on a carrier the high-boiling part of said product can be converted in high yield into middle distillate. As feed for the hydrocracking at least the part of the product is chosen whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as end product. The hydrocracking, which is characterized by a very low hydrogen consumpt-ion, yields a product in which, owing to the high normal paraffins/
3f~ 3~i isoparaffins ratio, the gas oil has a very high cetane number.
Although in the preparation of middle distillates from the product obtained over the cobalt catalyst the part of the product whose initial boiling point lies above the final boiling point of the heaviest middle distillate desired as end product will do as hydro-cracking feed, for this purpose it is preferred to use the total Cs~ fraction of the product prepared over the cobalt catalyst because it has been found that the catalytic hydrotreatment leads to enhanced quality of the gasoline, kerosine and gas oil fractions present therein.
The hydrocracking catalyst used by preference is a catalyst containing 0.1-2 %w and in particular 0.2-l ~w of one or more noble metals from Group VIII supported on a carrier. Preference is given to catalysts comprising platinum or palladium as Group VIII noble metal and silica-alumina as carrier. The hydrocracking in which the feed, together with added hydrogen, is passed over the noble metal catalyst is preferably carried out at a temperature of 200-400~C and in particular of 250-350C and a pressure of 5-lO0 bar and in particular of 10-75 bar.
If the two-step process according to the invention is combined with a hydrocracking treatment as a third step for the preparation of middle distillates, the second and third step can be carried out in 'series-flow', provided that the reaction product of the second step still contains sufficient unconverted hydrogen for carrying out the hydrocracking. It is a matter of common knowledge that carrying out a multi-step process in 'series-flow' comprises using the total reaction product - without any components being removed therefrom or added thsreto - of a certain step as feed for the following step, which is carried out substantially at the same pressure as the preceding step. If desired, the whole three-step process can be carried out in 'series-flow'.
The invention is now illustrated with the aid of the following example.
Example Feed 1: A natural gas consisting substantially of methane.
Feed 2: A natural gas consisting substantial].y of a mixture of methane and carbon dioxide in a volume ratio l:l.
Catalyst 1: Ni/Ca/K/A12O3 catalyst containing 13 phw nickel, 12 pbw calcium and 0.2 pbw potassium per 100 pbw alumina.
Catalyst 2: Fe/K/SiO2 catalyst containing 50 pbw iron and 4 pbw potassium per lO0 pbw silica. Catalyst 2 had been prepared by three-step co-impregnation of a silica carrier with a solution of potassium nitrate and ferric nitrate in water.
Catalyst 3: Co/ZriSiO2 catalyst containing 25 pbw cobalt and 0.9 pbw zirconium per lO0 pbw silica. Catalyst 3 had been prepared by one-step impregnation of a silica carrier with a solution of cobalt nitrate in water, followed by one-step impregnati,on of the cobalt-loaded carrier with a solution of zirconium nitrate in water.
For Catalyst 3 L was 98 mg/ml and S was 96 m2/ml, and therefore L/S was 1.02 mg/m2.
In the preparation of Catalysts 2 and 3 a quantity of solution was used in each impregnation step whose volume corresponded substant-ially with the pore volume of the carrier. After each impregnation step the material was dried and then calcined at 500C.
Seven two-step experiments (Experiments 1-7) were carried out in which in the first step Feeds l and 2 were subjected to steam reforming or partial oxidation in the presence of Catalyst l to be converted into H2 and C0 containing gas mixtures. From the gas mixtures prepared by the first step of Experiments 1, 3, 6 and 7 the carbon dioxide formed was removed. Moreover, by selective removal of hydrogen from the gas mixtures prepared by the first step of Experi-ments l and 3 the H2/CO molar ratio of these mixtures was reduced to 2, corresponding with the H2/CO molar ratio of gas mixtures prepared by the first step of Experiments 2 and 4-7. Subsequently the gas mixtures were contacted in the second step at a temperature of 220C and at various space velocities with Catalysts 2 and 3 which had previously been subjected to reduction at 250C in a hydrogen-containing gas.
- 13 ~ 6 In Experiments 1-5 the first step was carried out by steam reforming at a tempeature of 930C, a pressure of 22 bar and a steam/hydrocarbon ratio of 2.5 g mol H20/g atom C. In Experiments 6 and 7 the first step was carried out by partial oxidation with air and by adding steam at a temperature of 1225C, a pressure of 30 bar, an oxygen/hydrocarbon ratio of 0.60 g mol 02/g atom C and a steam/hydrocarbon ratio of 0.27 g mol ~20/g atom C. The results of Experiments 1-7, as well as the conditions under which the second step was carried out in each of these experiments, are given in the appending Table.
Of Experiments 1-7 only Experiments 4-7 are experiments according to the invention. In the first step of Experiments 4 and 5 a carbon-dioxide-contaminated synthesis gas was prepared by stea~
reforming of a heavily carbon-dioxide-contaminated natural gas. In the first step of Experiments 6 and 7 a nitrogen-contaminated synthesis gas was prepared by partial oxidation with air of a natural gas subs-tantially consisting of methane. In Experiments 4-7 the second step was carried out by using a cobalt catalyst belonging to the class described hereinbefore. Experiments 1-3 fall outside the scope of the invention. They have been included in the patent application for comparison. In the first step of Experiment 1 and 3 no contaminated synthesis gas as expressed in the present patent application was prepared. In the second step of Experiments 1 and 2 use was made of an iron catalyst.
As regards the results mentioned in the Table the following may be observed.
1) Comparison of the results of Experiments 1 and 2 shows that when an iron catalyst is used, contamination of the synthesis gas with 15 %v carbon dioxide results in a decrease in activity, with unchanging stability.
2) Comparison of the results of Experiments 3 and 4 shows that when a cobalt catalyst belonging to the afore-described class is used, contamination of the synthesis gas with 15 %v carbon dioxide also leads to a decrease in ativity (which by the way is considerably smaller than in the case of the iron catalyst) J but an increase in stability.
- 14 ~ 3~
.
3) Comparison of the results of Experiments 3 and 6 shows that when a cobalt catalyst is used, contamination of the synthesis gas with 45 %v nitrogen also leads to a decrease in activity and an increase in stability.
4) Comparison of the results of Experiments 3 and 5, and of 3 and 7 shows that by raising the pressure in the experiments with contaminated synthesis gas the activity can be raised to the original level of the nitrogen and carbon dioxide free operation, but that in the latter the stability obtained is considerably higher. As regards the hydrocarbon selectivity (not mentioned in the Table) it may further be remarked that in Experiment 5 (according to the invention) a hydrocarbon selectivity of 116%
was achieved, whereas in Experiment 3 (not according to the invention) it was only 83%.
- 15~ 9.~j _ ~ o ~ ~
~ o~ oo _ _ _ ~O _ l u~ ~ OO CO `D
_ ~ _ ~ ,_ U~ C`l U~ l ~ o ~ CO
r _ _ .. . _ _ _ _ ~J C~l ~ l ~ O O Ir~
_ O C~l CO
_ _ ~ _ __ _ ~7 _ l l ~ O ~0 CO ~
_ _ . _ _ . __ C~l ~ U~ l ~ 00 ~ ~ C~l _ _ U~\ . _ ~ _ _ l l C~l O O ~ _ _ _ D
C~ _ ~ .
. 0 0. ~ . 0 _ Oa~ ~ ~o 0 ~ c z~ c cz r o .,i o o ~ o ... ~
Q~C u ua. C u ~o a~o ~J c 0 o c~ ? 5 ~JC O ~0 0 ~1 0 1 .-1 S: OC g D q~l O lu C C r ~J o ~ _ .,.~ ~ ~ I~ ~ U _I ~ . ~ O
o ~u ~ . a~ 0 ~ _~ 0 h C~
Z ~4.~ . ~ .,1 . 0 ~ +
~ ~ ~ C U _~ 21 ~
..o ~ o c .~ o 8 ~ u ~ ~
E o~ ~., .... 0 ~ + _. o ~ o ~r~ 4~ ~ C~ C ~ _ C~ O~n _, ~ ~ ~ ~
~ ~c 0~~ 0 ~a ~ ~ ~ +
X a~~ ~~ h ~ CL ~ ~ C~J O
. ~ O~O' ~ ~ ~ Z O ,~: ~
was achieved, whereas in Experiment 3 (not according to the invention) it was only 83%.
- 15~ 9.~j _ ~ o ~ ~
~ o~ oo _ _ _ ~O _ l u~ ~ OO CO `D
_ ~ _ ~ ,_ U~ C`l U~ l ~ o ~ CO
r _ _ .. . _ _ _ _ ~J C~l ~ l ~ O O Ir~
_ O C~l CO
_ _ ~ _ __ _ ~7 _ l l ~ O ~0 CO ~
_ _ . _ _ . __ C~l ~ U~ l ~ 00 ~ ~ C~l _ _ U~\ . _ ~ _ _ l l C~l O O ~ _ _ _ D
C~ _ ~ .
. 0 0. ~ . 0 _ Oa~ ~ ~o 0 ~ c z~ c cz r o .,i o o ~ o ... ~
Q~C u ua. C u ~o a~o ~J c 0 o c~ ? 5 ~JC O ~0 0 ~1 0 1 .-1 S: OC g D q~l O lu C C r ~J o ~ _ .,.~ ~ ~ I~ ~ U _I ~ . ~ O
o ~u ~ . a~ 0 ~ _~ 0 h C~
Z ~4.~ . ~ .,1 . 0 ~ +
~ ~ ~ C U _~ 21 ~
..o ~ o c .~ o 8 ~ u ~ ~
E o~ ~., .... 0 ~ + _. o ~ o ~r~ 4~ ~ C~ C ~ _ C~ O~n _, ~ ~ ~ ~
~ ~c 0~~ 0 ~a ~ ~ ~ +
X a~~ ~~ h ~ CL ~ ~ C~J O
. ~ O~O' ~ ~ ~ Z O ,~: ~
Claims (10)
1. A process for the preparation of C5+ hydrocarbons from C4- hydrocarbons, characterized in that in a first step C4-hydrocarbons are converted by steam reforming or partial oxidation into a mixture of carbon monoxide and hydrogen, which mixture is subsequently converted in a second step into a mixture of hydro-carbons substantially consisting of C5+ hydrocarbons by contact-ing it at elevated temperature and pressure with a catalyst comprising 3-60 pbw cobalt and 0.1-100 pbw of at least one other metal chosen from the group formed by zirconium, titanium, ruthenium and chromium per 100 pbwsilica. alumina or silica-alumina, which catalyst has been prepared by kneading and/or impregnation, in which the feed for the second step contains nitrogen and/or carbon dioxide as contaminants, the presence therein of these contaminants having been caused substantially by the fact that the feed for the first step contained more than 20 %v nitrogen and/or carbon dioxide, and/or the fact that the first step was carried out by partial oxidation by using an oxygen-containing gas mixture containing more than 50 %v nitrogen.
2. A process as claimed in claim 1, characterized in that it is used with a feed in which the C4- hydrocarbons consist substantial-ly of methane.
3. A process as claimed in claim 2, characterized in that it is used with natural gas as feed.
4. A process as claimed in claim 3, characterized in that it is used with a natural gas which is contaminated with nitrogen and/or carbon dioxide.
5. A process as claimed in claim 4, characterized in that the natural gas is contaminated substantially with carbon dioxide.
6. A process as claimed in claim 4 or 5, characterized in that the natural gas contains more than 30 %v of said contaminants.
7. A process as claimed in any one of claims 1-3,characterized in that the first step is carried out by steam reforming at a temperature of 700-1000C, a pressure of 2-25 bar and a steam/hydro-carbon ratio of 1.5-5 g mol H2O/g atom C and using a nickel-containing catalyst.
8. A process as claimed in any one of claims 1-3,characterized in that the first step is carried out by partial oxidation with oxygen at a temperature of 1100-1500°C, a pressure of 10-60 bar and an oxygen/hydrocarbon ratio of 0.35-0.75 g mol O2/g atom C and using a nickel-containing catalyst.
9. A process as claimed in any one of claims 1-3, characterized in that in the second step a catalyst is used which satisfies the relation (3 + 4 R) > ? > (0.3 + 0.4 R), wherein L = the total quantity of cobalt present on the catalyst, expressed as mg Co/ml catalyst, S = the surface area of the catalyst, expressed as m2/ml catalyst, and R = the weight ratio of the quantity of cobalt deposited on the carrier by kneading to the total quantity of cobalt present on the catalyst.
10. A process as claimed in any one of claims 1-3,characterized in that in the second step use is made of a catalyst which per 100 pbw carrier contains 15-50 pbw cobalt and either 0.1-5 pbw of the other metal if during the preparation cobalt was first deposited and the other metal next, or 5-40 pbw of the other metal if in the preparation the other metal was first deposited and cobalt next.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL8303911 | 1983-11-15 | ||
| NL8303911A NL8303911A (en) | 1983-11-15 | 1983-11-15 | Fischer tropsch synthesis of higher hydrocarbon(s) - from feed contg. nitrogen or carbon di:oxide, on catalyst contg. cobalt and other metal |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1234396A true CA1234396A (en) | 1988-03-22 |
Family
ID=19842717
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000466256A Expired CA1234396A (en) | 1983-11-15 | 1984-10-25 | Process for the preparation of hydrocarbons |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1234396A (en) |
| NL (1) | NL8303911A (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0532116A1 (en) * | 1991-09-12 | 1993-03-17 | Shell Internationale Researchmaatschappij B.V. | Process for the preparation of hydrocarbon fuels |
| EP0532117A1 (en) * | 1991-09-12 | 1993-03-17 | Shell Internationale Researchmaatschappij B.V. | Hydroconversion catalyst |
| EP0532118A1 (en) * | 1991-09-12 | 1993-03-17 | Shell Internationale Researchmaatschappij B.V. | Process for the preparation of naphtha |
| EP0537815A1 (en) * | 1991-09-12 | 1993-04-21 | Shell Internationale Researchmaatschappij B.V. | Process for the preparation of middle distillates |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP1390325A2 (en) | 2001-05-25 | 2004-02-25 | Bp Exploration Operating Company Limited | Fischer-tropsch process |
| MY134279A (en) * | 2002-06-05 | 2007-11-30 | Shell Int Research | Process for the production of hydrocarbons from gaseous hydrocarbonaceous feed |
-
1983
- 1983-11-15 NL NL8303911A patent/NL8303911A/en not_active Application Discontinuation
-
1984
- 1984-10-25 CA CA000466256A patent/CA1234396A/en not_active Expired
Cited By (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0532116A1 (en) * | 1991-09-12 | 1993-03-17 | Shell Internationale Researchmaatschappij B.V. | Process for the preparation of hydrocarbon fuels |
| EP0532117A1 (en) * | 1991-09-12 | 1993-03-17 | Shell Internationale Researchmaatschappij B.V. | Hydroconversion catalyst |
| EP0532118A1 (en) * | 1991-09-12 | 1993-03-17 | Shell Internationale Researchmaatschappij B.V. | Process for the preparation of naphtha |
| EP0537815A1 (en) * | 1991-09-12 | 1993-04-21 | Shell Internationale Researchmaatschappij B.V. | Process for the preparation of middle distillates |
| AU653857B2 (en) * | 1991-09-12 | 1994-10-13 | Shell Internationale Research Maatschappij B.V. | Process for the preparation of naphtha |
| AU653856B2 (en) * | 1991-09-12 | 1994-10-13 | Shell Internationale Research Maatschappij B.V. | Process for the preparation of hydrocarbon fuels |
| AU653858B2 (en) * | 1991-09-12 | 1994-10-13 | Shell Internationale Research Maatschappij B.V. | Process for the preparation of middle distillates |
| AU662549B2 (en) * | 1991-09-12 | 1995-09-07 | Shell Internationale Research Maatschappij B.V. | Hydroconversion catalyst |
Also Published As
| Publication number | Publication date |
|---|---|
| NL8303911A (en) | 1985-06-03 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |