JP4955541B2 - Method for producing gas oil by catalytic cracking of Fischer-Tropsch products - Google Patents

Description

The present invention relates to a process for producing gas oil in combination with gasoline by catalytic cracking of Fischer-Tropsch products.

BACKGROUND OF THE INVENTION It is known that paraffinic products having boiling points in the boiling range of gas oils can be produced from Fischer-Tropsch derived synthesis products. However, it is not easy to produce gasoline and paraffinic gas oil having an octane number acceptable from the Fischer-Tropsch product using a single conversion process. This is because the Fischer-Tropsch product itself is mostly composed of normal paraffins that do not contribute to a low octane number or a low octane number. Various documents describing catalytic cracking are known as methods for producing gasoline having an acceptable octane number from Fischer-Tropsch products. For example, US-A-4684756 discloses a process for producing gasoline fractions by direct catalytic cracking of Fischer-Tropsch wax obtained by an iron-catalyzed Fischer-Tropsch process. The gasoline yield is 57.2% by weight.

Disadvantages of some of the above processes involving catalytic cracking are that the cetane number of the gas oil fraction produced in combination with gasoline is too low and the yield of gas oil is low.
US-A-4684756 WO-A-9934917 AU-A-698391 US-A-200201111521 WO-A-200095511 EP-B-832171

  The object of the present invention is to produce high quality paraffinic gas oils by catalytic cracking of Fischer-Tropsch products, where gasoline is produced as the main product.

SUMMARY OF THE INVENTION
(A) isolating the first gas oil fraction and the fraction having a boiling point higher than the gas oil fraction from the Fischer-Tropsch synthesis product;
(B) The heavy fraction is mixed with a catalyst system containing an acidic base material and a catalyst containing a large pore molecular sieve, in a riser reactor, at a temperature of 450 to 650 ° C., a contact time of 1 to 10 seconds, and a catalyst to oil. Contacting at a ratio of 2 to 20 kg / kg,
(C) isolating the second gas oil fraction from the product of step (b);
(D) combining the first gas oil fraction with the second gas oil;
by.

Detailed Description of the Invention Applicants have found that the first gas oil fraction obtained in step (a) improves the cetane number of the second gas oil obtained by catalytic cracking of the Fischer-Tropsch synthesis product. In a preferred embodiment, a relatively heavy Fischer-Tropsch product is used as feedstock for the catalytic cracking step (b). Enriching the catalytically cracked gas oil fraction with paraffin as obtained in step (a) increases the cetane number of the gas oil to a level suitable as a blend component of diesel fuel. Another advantage is that a well known process known as fluid catalytic cracking (FCC) process can be used in step (b).

The Fischer-Tropsch synthesis product may in principle be any reaction product obtained when a well-known Fischer-Tropsch synthesis reaction is performed. In step (b) it is preferred to use a relatively heavy Fischer-Tropsch product. The heavy raw material preferably contains a compound having 30 or more carbon atoms in an amount of 30% by weight or more, preferably 50% by weight or more, and more preferably 55% by weight or more. Further, the weight ratio of the compound having 60 or more carbon atoms and the compound having 30 or more carbon atoms in the Fischer-Tropsch product is at least 0.2, preferably at least 0.4, more preferably at least 0.55. The Fischer-Tropsch product has an ASF-α value (Anderson-Schulz-Flory chain growth factor) of at least 0.925, preferably at least 0.935, more preferably at least 0.945, and even more preferably at least 0.955. Of C ₂₀ + fractions.

  The initial boiling point of the Fischer-Tropsch product used in step (b) may suitably be in the range of less than 200 ° C to 450 ° C. If all the compounds having a boiling point in the gas oil range are separated from the Fischer-Tropsch synthesis product before the Fischer-Tropsch synthesis product is used in step (b), the initial boiling point is preferably 300 to 450 ° C. Applicants have found that starting from such Fischer-Tropsch products and thus eliminating Fischer-Tropsch fractions having boiling points in the gas oil range, gas oils can be obtained in high yields. Such a relatively heavy Fischer-Tropsch product can be obtained by any method that produces a relatively heavy Fischer-Tropsch product. Not all Fischer-Tropsch processes necessarily produce such heavy products. A preferred method is the cobalt catalyzed Fischer-Tropsch process. An example of a suitable Fischer-Tropsch method is described in WO-A-9934917 and AU-A-698392. These methods can produce a Fischer-Tropsch product as described above.

  Preferred catalysts used to obtain a relatively heavy Fischer-Tropsch product are preferably (aa) (1) titania or titania precursor, (2) liquid and (3) the amount of liquid used. Obtained by mixing at least partly insoluble cobalt compound to form a mixture, (bb) shaping and drying the mixture thus obtained, and (cc) calcining the composition thus obtained. It is a cobalt-containing catalyst.

Preferably 50% by weight or more of this cobalt compound, more preferably 70% by weight or more, still more preferably 80% by weight or more, and most preferably 90% by weight or more is insoluble in the amount of liquid used. The cobalt compound is preferably metallic cobalt powder, cobalt hydroxide or cobalt oxide, more preferably Co (OH) ₂ or Co ₃ O ₄ . The cobalt compound is preferably used in an amount of 60% by weight or less, more preferably 10 to 40% by weight, based on the amount of refractory oxide. The catalyst preferably contains at least one promoter metal, preferably manganese, vanadium, rhenium, ruthenium, zirconium, titanium or chromium, most preferably manganese. The promoter metal is used in an amount such that the atomic ratio of cobalt to promoter metal is preferably at least 4, more preferably at least 5. Preferably at least one promoter metal compound is present in step (aa). Preferably the cobalt compound is optionally obtained by calcination after precipitation. The cobalt compound and the at least one promoter metal compound are preferably obtained by coprecipitation, more preferably by coprecipitation at a constant pH. Preferably the cobalt compound is precipitated in the presence of at least a portion of titania or titania precursor, preferably in the presence of all titania or titania precursor. The mixing in the step (aa) is preferably performed by kneading or grinding. The mixture thus obtained is then shaped by pelletization, extrusion, granulation or crushing, preferably by extrusion. The obtained mixture preferably contains a solid content in the range of 30 to 90% by weight, preferably 50 to 80% by weight. Preferably, the mixture obtained in step (aa) is a slurry, and the slurry thus obtained is shaped and dried by spray drying. The solid content of the obtained slurry is preferably in the range of 1 to 30% by weight, more preferably 5 to 20% by weight. The calcination is preferably performed in the range of 400 to 750 ° C, more preferably in the range of 500 to 650 ° C. Further details are described in WO-A-9934917.

The Fischer-Tropsch process is usually performed at a temperature in the range of 125 to 350 ° C, preferably 175 to 275 ° C. The pressure is usually in the range from 5 to 150 bar absolute, preferably from 5 to 80 bar absolute, in particular from 5 to 70 bar absolute. Hydrogen _{(H 2)} and carbon monoxide (synthesis gas) is supplied to the process at a molar ratio in the range of 0.5 to 2.5. In the process according to the invention, the gas hourly space velocity (GHSV) can vary over a wide range and is usually in the range of 400 to 10000 Nl / l / h, for example 400 to 4000 Nl / l / h. The term GHSV is well known in the art and is contacted for 1 hour with Nl volume of synthesis gas, ie, 1 liter of catalyst excluding voids between the particles in STP state (0 ° C., 1 bar absolute pressure). Concerning the number of liters. In the case of a fixed catalyst bed, GHSV can also be expressed as a catalyst bed, ie per liter of catalyst bed excluding voids between particles. Fischer-Tropsch synthesis can be carried out in a slurry reactor, preferably in a catalyst bed. Further details are described in WO-A-9934917.

  Syngas is obtained by well known methods such as partial oxidation, steam reforming and combinations of these methods, starting with a carbon (hydrocarbon) feedstock. Examples of possible feedstocks are natural gas, associated gas, refinery offgas, residual fraction of crude oil, coal, pet coke, biomass such as wood. Partial oxidation may or may not be catalyzed. The steam reforming may be, for example, conventional steam reforming, autothermal reforming (ATR) and convective steam reforming. Examples of suitable partial oxidation methods are Shell gasification and Shell coal gasification.

  Fischer-Tropsch products contain no or only trace amounts of compounds containing sulfur and nitrogen. This is normal for the induced product of the Fischer-Tropsch reaction, which contains no or little impurities. In general, sulfur and nitrogen levels are currently below the detection limit of 5 ppm for sulfur and 1 ppm for nitrogen. The Fischer-Tropsch product has the advantage that it can be used directly as a raw material in step (a) without the need for hydroprocessing to remove olefins and / or oxygenates.

  The catalyst system used in step (b) is composed of a catalyst containing at least a base material and a large pore molecular sieve. Examples of suitable large pore molecular sieves are the faujasite (FAU) type such as zeolite Y, ultrastable zeolite Y and zeolite X. The base material is preferably an acidic base material. The acidic matrix suitably comprises amorphous alumina, preferably more than 10% by weight of the catalyst is amorphous alumina. The matrix may further contain, for example, aluminum phosphate, clay, silica and mixtures thereof. Amorphous alumina may also be used as a binder to obtain a matrix having a sufficient bonding function to properly bond the molecular sieve. Examples of suitable catalysts are commercially available catalysts used in fluid catalytic cracking processes. These catalysts contain zeolite Y as a molecular sieve and at least alumina in the base material.

  The contact temperature between the raw material and the catalyst is preferably in the range of 450 to 650 ° C. This temperature is more preferably greater than 475 ° C and even more preferably greater than 500 ° C. Good gasoline yield is seen at temperatures above 600 ° C. However, at temperatures above 600 ° C., pyrolysis reactions occur and undesired gaseous products such as methane and ethane are produced. For this reason, the temperature is more preferably less than 600 ° C. The process may be carried out in various reactors. This method can be carried out in a fixed bed reactor because coke formation is relatively small compared to the FCC method operating on petroleum derived feedstocks. However, a simpler priority for making the catalyst renewable is either a fluidized bed reactor or a riser reactor. When the process is carried out in a riser reactor, the preferred contact time is in the range 1-10 seconds, more preferably 2-7 seconds. The catalyst to oil ratio is preferably in the range of 2-20 kg / kg. It has been found that good results are obtained with a low catalyst to oil ratio of less than 15 kg / kg and even less than 10 kg / kg.

  This is advantageous, for example, because it means high productivity per catalyst amount, even with small equipment, low catalyst inventory, low energy, and / or high productivity.

  This catalyst system may also be advantageous if it also contains intermediate pore size molecular sieves, since propylene and other lower olefins are then obtained in high yields following the gasoline fraction. Preferred intermediate pore size molecular sieves are zeolite β, Erionite, ferrierite, ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23 or ZSM-57. The weight fraction of mesoporous crystals relative to the total amount of molecular sieve present in the process is preferably in the range of 2-20% by weight. The intermediate pore molecular sieve and the large pore molecular sieve may be incorporated in one catalyst particle or may be present in different catalyst particles. The medium pore molecular sieve and the large pore molecular sieve are preferably present in different catalyst particles for practical reasons. Thus, for example, an operator can add these two catalyst components of the catalyst system to the process at different addition rates. This is because the two catalyst components have different deactivation rates. A preferred matrix is alumina. For example, the molecular sieve may be dealuminated by steaming or other known methods.

  It has been found that when a large pore molecular sieve, more preferably a FAU type molecular sieve, is combined with a medium pore size molecular sieve, a high selectivity to lower olefins is obtained. Applicants have not only improved the yield of lower olefins when the method of the present invention is carried out in combination with large pore molecular sieves, more preferably FAU type molecular sieves, as described above, with intermediate pore size molecular sieves, It has been found that the yield of iso- and n-pentene and hexene is also increased. In such embodiments, the pentene and hexene are preferably oligomerized into compounds in the boiling range of the gas oil. This preference is due to at least two reasons because the ultimate yield of gas oil is increased and the low octane number causative compound is removed from the gasoline. Oligomerization is a well-known method, for example illustrated in US-A-200201111521.

  In step (c), a second gas oil fraction is isolated from the product of step (b) from the main product gasoline. These fractions are preferably isolated by distillation. In the present invention, gasoline or a gasoline fraction is a fraction having a boiling point range of 25 to 215 ° C., more than 90% by weight, preferably more than 95% by weight. The gas oil or gas oil fraction is a fraction having a boiling point of 200 to 370 ° C., preferably 215 to 350 ° C., more than 90% by weight.

  For the first and second gas oil fractions, a further catalytic dewaxing step may be performed separately or as a mixture to lower the pour point to an acceptable level if necessary. Such treatment is not only advantageous for pour point depression, but also reduces the content of any aromatic compounds produced in step (a). The pour point is preferably less than −10 ° C., more preferably less than −15 ° C. The catalytic dewaxing of the gas oil may be carried out using a catalyst preferably comprising a binder, molecular sieve and a metal hydride component. The binder can be any binder, preferably alumina, silica-alumina or silica. The molecular sieve is preferably a zeolite or silica-aluminophosphate (SAPO) material. The pore diameter of zeolite is preferably in the range of 0.35 to 0.8 nm. Suitable intermediate pore size zeolites are mordenite, zeolite beta, ZSM-5, ZSM-12, ZSM-22, ZSM-23, MCM-68, SSZ-32, ZSM-35 and ZSM-48. Preferably, the silica-alumina phosphate (SAPO) material is SAPO-11. The hydrogenation component is preferably a Group VIII metal, more preferably nickel, cobalt, platinum and palladium. Most preferably a Group VIII noble metal is used. Catalytic dewaxing conditions are known in the art and are usually 200-500 ° C, preferably an operating temperature in the range of 250-400 ° C, a hydrogen pressure in the range of 10-200 bar, preferably 15-100 bar. 0.1 to 10 kg of oil per liter of catalyst per hour (kg / l / hr), preferably 0.2 to 5 kg / l / hr, more preferably 0.5 to 3 kg / l / hr Weight hourly space velocity (WHSV) and hydrogen to oil ratio in the range of 100 to 2,000 liters of hydrogen per liter of oil. Suitable dewaxing processes and catalysts are described in WO-A-200029511 and EP-B-832171.

Examples A to D
Fischer-Tropsch products having the characteristics shown in Table 1 were contacted with the heat regenerated catalyst at a catalyst to oil ratio of 4 kg / kg at different temperatures and contact times. This catalyst is an industrial FCC catalyst containing an alumina base material and ultrastable zeolite Y obtained by an FCC unit for industrial operation. The content of zeolite Y is 10% by weight. The operating conditions are shown in Table 3.

Examples 1-4
A Fischer-Tropsch product having the properties shown in Table 2 was contacted with the heat regenerated catalyst at different temperatures and contact times as in Examples AD. The Fischer-Tropsch product was obtained according to Example VII using the catalyst of Example III of WO-A-9934917. The operating conditions are shown in Table 3.

From Table 4, it can be seen that according to the method of the present invention, gasoline and middle distillate or gas oil can be obtained in high yield. In Examples 1 to 4, the yield of gas oil is lower than in Examples B to D, but the gas oil content in the raw materials of Experiments B to D is 42.2% by weight (see Table 1). Is higher than the gas oil yield of any of Experiments B-D. Furthermore, the gasoline fractions obtained in experiments 1 to 4 contain a considerable amount of n- and iso-pentene. These pentenes can be oligomerized into gas oils.
Table 4 also shows that high gasoline yields can be obtained with long contact times and relatively mild temperatures (see Examples B and 2).

Examples 5-7
Examples 2-4 were repeated with a Fischer-Tropsch product having the properties shown in Table 5 and the conditions in Table 3. The raw material of Table 5 is obtained by removing the gas oil of Table 1 and 22% by weight of a lighter fraction from the raw material of Table 2. It shows the yield in Table 6.

Example 8
Example 6 was repeated except that a portion of the catalyst was replaced with a catalyst containing 25 wt% ZSM-5. The content of ZSM-5 base catalyst relative to the total catalyst loading is 20% by weight (calculated with respect to the total catalyst weight). The gasoline yield was 47.9 wt% and the middle distillate yield was 9.27 wt% based on the total product. The content of n- and iso-pentene was 54.61% by weight in the gasoline fraction.

Example 9
Example 2 was repeated except that a portion of the catalyst was replaced with a catalyst containing 25 wt% ZSM-5. The content of ZSM-5 base catalyst relative to the total catalyst loading is 20% by weight (calculated with respect to the total catalyst weight). The results are shown in Table 7.

Example 10
Example 3 was repeated except that a portion of the catalyst was replaced with a catalyst containing 25 wt% ZSM-5. The content of ZSM-5 base catalyst relative to the total catalyst loading is 20% by weight (calculated with respect to the total catalyst weight). The results are shown in Table 7.

Examples 8-10 show that the addition of ZSM-5 increases the yield of gas oil.

Claims (11)

(A) isolating the first gas oil fraction and the fraction having a boiling point higher than the gas oil fraction from the Fischer-Tropsch synthesis product;
(B) a fraction having a higher boiling point than the gas oil fraction , a catalyst system comprising a catalyst containing an acidic matrix and a large pore molecular sieve, and a riser reactor, temperature 450-650 ° C., contact time 1 Contacting for 10 seconds and a catalyst to oil ratio of 2 to 20 kg / kg,
(C) isolating the second gas oil fraction from the product of step (b), and (d) combining the first gas oil fraction with the second gas oil,
A method for producing gas oil. In the raw material used in the step ( b ), the weight ratio of the compound having 60 or more carbon atoms and the compound having 30 or more carbon atoms is at least 0.2, and 30% by weight or more of these compounds has 30 carbon atoms. The method according to claim 1, which is as described above. The method according to claim 2, wherein 50% by weight or more of the compound in the raw material in the step ( b ) has 30 or more carbon atoms. The method according to claim 3, wherein the weight ratio of the compound having 60 or more carbon atoms and the compound having 30 or more carbon atoms in the Fischer-Tropsch product is at least 0.4 in the raw material of the step ( b ).   The method according to any one of claims 1 to 4, wherein the temperature in step (b) is less than 600C.   The method according to claim 1, wherein the acidic base material is alumina.   The method according to claim 1, wherein the large pore molecular sieve is of a faujasite (FAU) type.   The catalyst system of step (b) also comprises zeolite beta, erionite, ferrierite, ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23 or ZSM-57. The method according to claim 1. Iso - and normal - pentene and / or iso - and normal - to hexene, performs oligomerization, thereby producing a compound having a boiling point of the gas oil range, gas oil obtained in the compound step (d) 9. A method according to claim 8, which is blended with the product.   The method according to any one of claims 1 to 9, wherein the Fischer-Tropsch synthesis product used as a raw material in the step (a) is obtained by a cobalt-catalyzed Fischer-Tropsch synthesis method.   The cobalt catalyst is a mixture of (aa) (1) titania or titania precursor, (2) liquid, and (3) a cobalt compound that is at least partially insoluble in the amount of liquid used. 11. The method according to claim 10, obtained by forming, (bb) shaping and drying the mixture thus obtained, and then (cc) calcining the composition thus obtained.