RU2388791C2 - Method of obtaining gas oil through catalytic cracking of fischer-tropsch synthesis product - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: method involves (a) extraction from a Fischer-Tropsch synthesis product of a first gasoline fraction which boils out at 25-215°C, a first gas oil fraction which boils out at 215-325°C and a fraction which boils in a temperature interval higher than that of the gas oil fraction. The method also involves (b) brining the heavier fraction into contact with a catalyst system. The system contains a catalyst which contains an acid matrix and a coarse-pored molecular sieve in a vertical reactor at temperature 450-650°C, contact time 1-10 seconds and ratio between amount of catalyst to amount of oil equal to 2-20 kg/kg, (c) extraction from the product from step (b) of a second gasoline fraction and a second gas oil fraction, (d) combining the first and second gas oil fractions.

EFFECT: obtaining gas oil through catalytic cracking of a Fischer-Tropsch synthesis product.

11 cl, 7 tbl, 14 ex

Description

Technical field

The invention relates to a joint method for producing gas oil and gasoline fraction by catalytic cracking of a Fischer-Tropsch synthesis product.

State of the art

It is known that paraffin products boiling in the gas oil boiling range can be obtained from the Fischer-Tropsch synthesis product. However, the solution to the problem of obtaining a gasoline fraction with an acceptable octane number and paraffin gas oil from the Fischer-Tropsch product in one stage is not obvious. The reason for this is the fact that the Fischer-Tropsch synthesis product, as such, contains a significant amount of normal paraffins having a low octane number. In a large number of publications, catalytic cracking is described as a process for producing a gasoline fraction with an acceptable octane value from a Fischer-Tropsch product. So, for example, in US-A-4684756 describes a method for producing a gasoline fraction by direct catalytic cracking of wax obtained in the Fischer-Tropsch process in the presence of an iron catalyst. The yield of gasoline fraction is 57.2%.

The disadvantage of some of the processes described above, including the catalytic cracking stage, is the extremely low cetane number and low yield of the gas oil fraction obtained together with the gasoline fraction.

The purpose of the invention is to obtain high-quality paraffin gas oil using the Fischer-Tropsch catalytic cracking process, the main product of which is the gasoline fraction.

SUMMARY OF THE INVENTION

A method for producing gas oil includes

(a) recovering from the Fischer-Tropsch synthesis product a first gasoline fraction boiling in the range 25-215 ° C, a first gas oil fraction boiling in the range 215-325 ° C and a fraction boiling above the boiling temperature range of the gas oil fraction,

(b) contacting the heavier fraction with a catalyst system comprising a catalyst containing an acid matrix and a large-pore molecular sieve in a vertical reactor at a temperature of 450-650 ° C, a contact time of 1-10 seconds and the ratio between the amount of catalyst and the amount of oil 2-20 kg / kg

(c) recovering from the product from step (b) a second gasoline fraction and a second gas oil fraction;

(d) combining the first and second gas oil fractions.

Disclosure of the invention

The inventors found that the first gas oil fraction obtained in step (a) improves the cetane number of the second gas oil fraction obtained by catalytic cracking of a Fischer-Tropsch synthesis product. According to a preferred embodiment of the invention, a relatively heavy Fischer-Tropsch product is used as feed for step (b) of the catalytic cracking. The enrichment with paraffins obtained in stage (a) of the gas oil fraction subjected to catalytic cracking increases the cetane number to a value that makes gas oil suitable for use as a mixed component of diesel fuel. Another advantage is the ability to use well-known fluidized-bed catalytic cracking (FCC) processes, step (b).

In principle, the Fischer-Tropsch synthesis product may be any product obtained by carrying out the well-known Fischer-Tropsch synthesis reaction. In step (b), it is preferable to use a relatively heavy Fischer-Tropsch product. Preferably, such a heavy feed contains at least 30 wt.%, Preferably at least 50 wt.% And more preferably at least 55 wt.% Of compounds containing 30 carbon atoms. The mass ratio between the number of compounds containing at least 60 or more carbon atoms and the number of compounds containing at least 30 carbon atoms in the Fischer-Tropsch product is at least 0.2, preferably at least 0.4, more preferably at least 0.55. It is desirable that the Fischer-Tropsch product contains a C ₂₀₊ fraction having an ASF-alpha value (Anderson-Schulz-Flory chain growth factor) of at least 0.925, preferably at least 0.935, more preferably at least , 0.945, even more preferably at least 0.955.

The initial boiling point of the Fischer-Tropsch product used in stage (b) may be in the range of 200-450 ° C. The preferred initial boiling point is 300-450 ° C when all compounds with a boiling point in the boiling range of gas oil are separated from the Fischer-Tropsch synthesis product before use in step (b). The inventors have found that a high gas oil yield can be achieved using a Fischer-Tropsch product, from which fractions boiling in the gas oil boiling range are excluded. The relatively heavy Fischer-Tropsch synthesis product can be obtained by any method that provides a relatively heavy Fischer-Tropsch product. Such a product is not obtained in all Fischer-Tropsch processes. For this purpose, it is preferable to use the Fischer-Tropsch processes catalyzed by cobalt compounds. An example of a suitable Fischer-Tropsch process is described in WO-A-9934917 and in AU-A-698391. These processes can provide the Fischer-Tropsch product described above.

A preferred catalyst used to prepare the relatively heavy Fischer-Tropsch synthesis product is a cobalt-containing catalyst, which is obtained (aa) by mixing to form a mixture of (1) titanium oxide or its precursor, (2) a liquid and (3) a cobalt compound, which, at least partially insoluble in the amount of liquid used; (bb) molding and drying the resulting mixture; and (c) calcining the resulting composition.

It is desirable that at least 50 wt.% Cobalt, more preferably at least 70 wt.%, Even more preferably at least 80 wt.% And most preferably at least at least 90% by weight. A preferred cobalt compound is cobalt metal powder, cobalt hydroxide or cobalt oxide, more preferably Co (OH) ₂ or Co ₃ O ₄ . The cobalt compound is used in an amount of up to 60 wt.%, More preferably 10-40 wt.% Of the amount of refractory oxide. It is desirable that the catalyst contains at least one metal promoter, preferably manganese, vanadium, rhenium, ruthenium, zirconium, titanium or chromium, with the most preferred promoter being manganese. The metal promoter (s) are preferably used in such an amount that the atomic ratio between the amount of cobalt and the metal promoter is at least 4, more preferably at least 5. It is desirable that at least at least one is present in step (aa) , one metal promoter. The cobalt compound is obtained by precipitation with optional subsequent calcination. It is desirable to obtain a cobalt compound and at least one of the derivatives of the metal promoter by coprecipitation, more preferably by co-precipitation at a constant pH. It is desirable to carry out the deposition of cobalt in the presence of at least a portion of titanium oxide or its precursor, preferably in the presence of the entire amount of titanium oxide or its precursor. The mixing in step (aa) is preferably carried out by kneading or grinding. After that, the resulting mixture is molded using granulation extrusion methods, or crushing, preferably extrusion. It is desirable that the resulting mixture has a solids content in the range of 30-90 wt.%, Preferably 50-80 wt.%. The mixture obtained in stage (aa) is a suspension, which is subjected to molding and spray drying. It is desirable that the resulting suspension has a solids content in the range of 1-30 wt.%, More preferably 5-20 wt.%. Calcination is preferably carried out at temperatures of 400-750 ° C, more preferably 500-650 C. Additional details are described in WO-A-9934917.

The Fischer-Tropsch process is usually carried out in the temperature range 125-350 ° C, preferably 175-275 ° C. The pressure is usually 5-150 bar abs., Preferably 5-80 bar abs., Especially 5-70 bar abs. Hydrogen (H ₂ ) and carbon monoxide (synthesis gas) are usually introduced into the process in a molar ratio of 0.5-2.5. The hourly average flow rate (GHSV) of synthesis gas in the method according to the invention can vary over a wide range and is usually 400-10000 nl / l / h, for example 400-4000 nl / l / h. The term GHSV is well known in the art and refers to the volume of gas synthesis in normal liters (NL), i.e. liters under standard conditions (0 ° C and 1 bar abs.), which is contacted in one hour with one liter of catalyst particles, i.e. excluding free volume between particles. In the case of a fixed catalyst bed, GHSV can also be expressed per liter of catalyst bed, i.e. taking into account the free space between particles. The Fischer-Tropsch synthesis may be carried out in a slurry reactor or, preferably, in a fixed bed reactor. Further details are described in WO-A-9934917.

The synthesis gas can be obtained by well-known methods such as partial oxidation and steam conversion of hydrocarbon feedstocks, as well as using a combination of these processes. Examples of possible feeds include natural gas, associated gas, refinery off-gas, residual fractions of crude oil, coal, petroleum coke and biomass, such as wood. Partial oxidation can be carried out in the presence or absence of a catalyst. Steam conversion can be a traditional process, autothermal (ATR) reforming, and convective steam reforming. Examples of suitable partial oxidation processes include the Shell Gasification Process (Shell gasification process) and the Shell Coal Gasification Process (Shell coal gasification process).

The Fischer-Tropsch synthesis product does not contain sulfur or nitrogen-containing compounds, or contains them in small quantities. This is typical of a product obtained in the Fischer-Tropsch reaction, in which almost no impurity synthesis gas is used as raw material. Sulfur and nitrogen are usually below the limits of determination, which are currently 5 ppm for sulfur and 1 ppm for nitrogen. The Fischer-Tropsch product can be directly used in step (a) without hydrotreating the feed to remove olefins and / or oxygenates.

The catalyst system used in step (b) comprises a catalyst comprising a matrix and a large pore molecular sieve. Examples of large porous molecular sieves include faujasite (FAU) materials such as zeolite Y, ultrastable zeolite Y, and zeolite X. The matrix is preferably an acid matrix. The acid matrix contains amorphous alumina and, preferably, more than 10% of the catalyst is amorphous alumina. In addition, the matrix may contain aluminum phosphate, clay and silica, as well as mixtures thereof. Amorphous alumina can also be used as a binder to form a matrix having sufficient molecular sieve binding ability. Examples of suitable catalysts include commercially available catalysts used in liquid phase catalytic cracking processes, such catalysts containing zeolite Y and at least alumina as a matrix.

The contact temperature of the feedstock with the catalyst is 450-650 ° C. It is preferable to use a temperature above 475 ° C and even more preferably above 500 ° C. Good yields of gasoline fraction are observed at temperatures above 600 ° C. However, at temperatures above 600 ° C, thermal cracking reactions occur, leading to the formation of undesirable gaseous products such as methane and ethane. For this reason, it is preferable to use a temperature below 600 ° C. The process can be carried out in various types of reactors. Since coke formation occurs to a relatively small extent compared to FCC processes that use petroleum feedstocks, it is possible to carry out the process in a fixed-bed reactor. In order to facilitate catalyst regeneration, preference is given to a fluidized bed reactor or a vertical reactor. In the case of carrying out the process in a vertical reactor, the preferred contact time is 1-10 seconds, more preferably 2-7 seconds. The preferred ratio between the amount of catalyst and oil is 2-20 kg / kg. It was found that good results can be obtained with low ratios of the amount of catalyst to the amount of oil having a value of less than 15, and even less than 10 kg / kg

This fact is an advantage, since it provides for an increase in the productivity of the catalyst when using equipment with a smaller volume, a smaller amount of catalyst, and with less energy.

The catalytic system can advantageously consist of a molecular sieve with an average pore size so as to provide a high yield of propylene and other lower olefins after the gasoline fraction. It was established that the gas oil yield increases in the presence of such molecular sieves with an average pore size. Preferred medium pore molecular sieves are zeolite beta, erionite, ferrierite, ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23 or ZSM-57. The mass fraction of crystals with an average pore volume, based on the total number of molecular sieves used in the process, is preferably 2-20 wt.% A molecular sieve with an average pore size and a molecular sieve with a large pore size can be present together in one catalyst particle or in different catalyst particles . For practical reasons, it is preferred that coarse and medium pore molecular sieves are present in various catalyst particles. So, for example, the operator can enter into the system two of the indicated components of the catalytic system with different speeds. This may be necessary due to the different rates of deactivation of the two indicated catalysts. A suitable matrix is alumina. The molecular sieve may be dealuminated, for example, by steaming or other known processing methods.

It has been found that the combination of a highly porous molecular sieve, preferably an FAU type, with a medium pore molecular sieve is an important factor for ensuring high selectivity for lower olefins. The inventors have found that when implementing the method according to the invention with the combined use of a large-pore molecular sieve, preferably of the FAU type, and the above-described molecular sieve with an average pore size, not only the yield of olefins is increased, but also the yield of iso- and normal pentenes as well as hexenes . According to such an embodiment of the invention, pentenes and hexenes are oligomerized to form compounds boiling in the gas oil boiling range. This approach is preferred for at least two reasons, including increasing the total yield of gas oil and removing low-octane compounds from the gasoline fraction. Oligomerization is a well-known process, an example of which is described in US-A-20020111521.

In step (c), the second gas oil fraction is separated from the product from step (b) and the main gasoline fraction. The selection of these fractions is carried out using distillation. According to the invention, the gas oil or its fraction is a fraction of more than 90%, preferably more than 95% of which boils in the range of 25-215 ° C. The gas oil or gas oil fraction is a fraction, more than 90 wt.% Of which boils in the range of 200-370 ° C, preferably in the range of 215-350 ° C.

If necessary, the first and second gas oil fraction separately or together can be subjected to additional catalytic dewaxing in order to lower the pour point to an acceptable value. This treatment not only provides a decrease in pour point, but also helps to reduce the content of aromatic compounds formed in stage (a). The preferred pour point is below -10 ° C, even more preferably below -15 ° C. The catalytic dewaxing of gas oil can be carried out using a catalyst containing a binder, a molecular sieve and a hydrogenating metal component. As the binder component, any binder may be used, for example alumina, silica-alumina or silica. A preferred molecular sieve is a zeolite or aluminosilicate phosphate (SAPO) material. Preferred zeolites have a pore diameter of 0.35-0.8 nm. Preferred medium pore zeolites are mordenite, zeolite beta, ZSM-5, ZSM-12, ZSM-22, ZSM-23, MCM-68, SSZ-32, ZSM-35, ZSM-48. Preferred aluminosilicate phosphate (SAPO) materials are SAPO-11. A preferred hydrogenation component is a Group VIII metal, more preferably nickel, cobalt, platinum or palladium. Most preferably, noble metals of group VIII are used. The conditions for catalytic dewaxing are known to the person skilled in the art and usually include operating temperatures in the range of 200-500 ° C, preferably 250-400 ° C, partial hydrogen pressures in the range of 10-200 bar, preferably 15-100 bar, hourly average feed rates ( WHSV) in the range of 0.1-10 kg of oil per liter of catalyst per hour (kg / l / h), preferably 0.2-5 kg / l / h, more preferably 0.5-3 kg / l / h and the ratio between the amount of hydrogen and the amount of oil in the range of 100-2000 liters of hydrogen per liter of oil. Examples of dewaxing processes and catalysts for their implementation are given in WO-A-200029511 and EP-B-832171.

Comparative Examples A-D

The product of the Fischer-Tropsch synthesis without any separation, the characteristics of which are shown in the following Table 1, was brought into contact with the hot regenerated catalyst at various temperatures and contact times with a ratio between the amount of catalyst and oil of 4 kg / kg. The catalyst used was an industrial FCC catalyst containing an alumina-based matrix and ultrastable zeolite Y obtained from an industrial-mode FCC unit. Zeolite Y was used in an amount of 10 wt.%. The operating conditions of the experiments are presented in Table 3.

Table 1 Boiling point 100 ° C The number of fractions, boiling in the range of 25-215 "C (wt.%) 46.8 The amount of fraction boiling in the range 215-325 "C (wt.%) 42,2 The amount of fraction boiling above 325 ° C (wt.%) 11.0

Examples 1-4 (according to the invention)

The Fischer-Tropsch product, from which the first gas oil fraction was removed, with the properties listed in Table 2, was brought into contact with the hot regenerated catalyst at various temperatures and contact times similar to Examples A-D. The Fischer-Tropsch product was obtained according to the procedure of Example VII using the catalyst from Example III according to WO-A-9934917. The operating conditions of the experiments are presented in Table 3.

table 2 Boiling point 100 ° C Mass fraction containing 10 or less carbon atoms (%) 0 The mass of the fraction containing more than 30 carbon atoms (%) 80 The mass of the fraction containing more than 60 carbon atoms (%) fifty Ratio C ₆₀₊ / C ₃₀₊ 0.63

Table 3 Comparative example Example Temperature (° C) Contact time (seconds) BUT one 500 4.06 AT 2 and 5 525 0.7 FROM 3 and 6 525 4.06 D 4 and 7 625 0.7

After catalytic cracking, the second gas oil fraction was separated from the product by distillation and combined with the first gas oil fraction.

The results of comparative examples A-D and examples 1-4 are shown in table 4.

Table 4 Example The output of the gasoline fraction (wt.% Based on the total amount of product) (*) The yield of gas oil (wt.% Based on the total amount of product) (**) n- and isopentenes of gas oil (wt.% of the amount of gas oil fraction) BUT - - - one 74.00 11.06 16.92 AT 52,58 35.88 2.01 2 52.90 13.27 18.85 FROM 68.70 13.63 13.66 3 70.29 5.91 39.75 D 53.86 26.24 24.09 four 46.22 7.43 36.32 (*) the gasoline fraction is defined as the distillation fraction boiling in the range of 25-215 ° C (**) gas oil, defined as the fraction boiling over in the range 215-325 ° С

From the data shown in Table 4, we can conclude that the method according to the invention provides high yields of gasoline fraction and gas oil. The gas oil yields in Examples 1-4 are lower than in Examples B-D, however, the gas oil content in the feed for comparative examples B-D is 42.2 wt.% (Table 1), which is higher than the gas oil yield in any of the examples B-D. Accordingly, the total amount of gas oil, for example, in example 2 will be: 42.2+ (100-42.2) · 13.27 = 42.2 + 7.7 = 49.9 wt.%. In the examples in which all the material was in contact with the hot regenerated catalyst (comparative example B), the gas oil yield was 35.88 wt.%, I.e. only 72% of the yield of the invention.

In addition, the gasoline fractions obtained in experiments 1-4 contain a significant amount of normal and isopentenes, which can oligomerize with the formation of gas oil.

As follows from Table 4, high gasoline fraction yields are achieved with long contact times and relatively mild temperature conditions (Examples B and 2).

Examples 5-7

The procedure described in Examples 2-4 was repeated using the Fischer-Tropsch product, the properties of which are shown in Table 5 under the conditions indicated in Table 3. Raw materials whose characteristics are shown in Table 5 can be obtained from raw materials whose characteristics are shown in Table 1, by removing 22 wt.% Gas oil and a lighter fraction. The output values are presented in Table 6.

Table 5 Boiling point 100 ° C Mass fraction containing 10 or less carbon atoms (%) fourteen The mass of the fraction containing more than 30 carbon atoms (%) 62 The mass of the fraction containing more than 60 carbon atoms (%) 39 Ratio C ₆₀₊ / C ₃₀₊ 0.63

Table 6 Example The output of the gasoline fraction (wt.% Based on the total amount of product) (*) The yield of gas oil (wt.% Based on the total amount of product) (**) n- and isopentenes of gas oil (wt.% of the amount of gasoline fraction) 5 52.85 16.57 16.25 6 70.05 7.04 35.73 7 47.25 10.18 34.40 (*) the gasoline fraction is defined as the distillation fraction boiling in the range of 25-215 ° C (**) gas oil is defined as the fraction boiling in the range 215-325 ° С

Example 8

The procedure of Example 6 was repeated except that part of the catalyst was replaced with 25 wt.% Of the catalyst containing ZSM-5. The content of the catalyst based on ZSM-5 calculated on the entire loaded catalyst was 20 wt.% (Calculated on the total weight of the catalyst). The yield of gasoline fraction was 47.99 wt.%, And the yield of gas oil was 9.27 wt.% Based on the total amount of product. The content of normal and isopentenes in the gasoline fraction was 54.61 wt.%.

Example 9

The procedure of Example 2 was repeated except that part of the catalyst was replaced with 25 wt.% Of the catalyst containing ZSM-5. The content of the catalyst based on ZSM-5 calculated on the entire loaded catalyst was 20 wt.% (Calculated on the total weight of the catalyst). The results are presented in Table 7.

Example 10

The procedure of Example 3 was repeated except that part of the catalyst was replaced with 25 wt.% Of the catalyst containing ZSM-5. The content of the catalyst based on ZSM-5 calculated on the entire loaded catalyst was 20 wt.% (Calculated on the total weight of the catalyst). The results obtained are presented in Table 7.

Table 7 Example The output of the gasoline fraction (wt.% Based on the total amount of product) (*) The yield of gas oil (wt.% Based on the total amount of product) (**) n- and isopentenes of gas oil (wt.% of the amount of gasoline fraction) 2 52.90 13.27 18.85 3 70.29 5.91 39.75 9 55.88 13.39 11.47 10 45.76 8.07 67.14 (*) a gasoline fraction is defined as a distillation fraction boiling in the range of 25-215 ° C (**) gas oil is defined as the fraction boiling in the range 215-325 ° С

As follows from the results of Examples 8-10, the introduction of ZSM-5 leads to increased yields of gas oil.

Claims (11)

1. The method of producing gas oil, including
(a) recovering from the Fischer-Tropsch synthesis product a first gasoline fraction boiling in the range 25-215 ° C, a first gas oil fraction boiling in the range 215-325 ° C, and a fraction boiling above the boiling temperature range of the gas oil fraction,
(b) contacting the heavier fraction with a catalyst system comprising a catalyst containing an acid matrix and a large-pore molecular sieve in a vertical reactor at a temperature of 450-650 ° C, a contact time of 1-10 s and the ratio between the amount of catalyst and the amount of oil 2-20 kg / kg
(c) recovering from the product from step (b) a second gasoline fraction and a second gas oil fraction,
(d) combining the first and second gas oil fractions. 2. The method according to claim 1, in which the raw materials used in stage (a) are characterized by the ratio between the number of compounds containing at least 60 or more carbon atoms and the number of compounds containing at least 30 carbon atoms equal to at least 0.2, and in which at least 30 wt.% compounds contain at least 30 carbon atoms. 3. The method according to claim 2, in which at least 50 wt.% Of the compounds in the feed from step (a) contain at least 30 carbon atoms. 4. The method according to claim 3, in which the mass ratio between the number of compounds containing at least 60 or more carbon atoms, and the number of compounds containing at least 30 carbon atoms in the product of the Fischer-Tropsch synthesis, representing raw materials for stage (a), is at least 0.4. 5. The method according to any one of claims 1 to 4, in which stage (b) is carried out at a temperature below 600 ° C. 6. The method according to claim 1, in which the acid matrix is an alumina. 7. The method according to claim 1, in which the large-pore molecular sieve is a material of faujasite (FAU) type. 8. The method according to claim 1, in which the catalyst system from stage (b) also contains zeolite beta, erionite, ferrierite, ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23 or ZSM-57. 9. The method according to claim 8, in which iso- and normal pentenes and / or iso-and normal hexenes that are in the gasoline fraction obtained in stage (c) are subjected to oligomerization to obtain compounds boiling in the temperature range of gas oil boiling, moreover, these compounds are combined with gas oil obtained in stage (d). 10. The method according to claim 1, in which the product of the Fischer-Tropsch synthesis used as a raw material in stage (a) is obtained using the Fischer-Tropsch synthesis process using a cobalt catalyst. 11. The method according to claim 10, in which the cobalt catalyst is obtained (aa) by mixing to form a mixture of (1) titanium oxide or its precursor, (2) a liquid and (3) a cobalt derivative that is at least partially insoluble in the taken amount of fluid; (bb) molding and drying the resulting mixture; and (cc) calcining the resulting composition.