A process for the conversion of lower alkanes

Abstract

The application discloses a low carbon alkane conversion method. The method comprises the following steps: (1) mixing low carbon alkane with hydrogen and passing through a hydroconversion reaction zone, wherein the hydroconversion reaction zone is filled with a hydroconversion catalyst; (2) passing the hydroconversion reaction zone effluent into a separation system to obtain hydrogen-rich gas and a hydroconversion product. The method uses low carbon alkane as a raw material, can effectively convert isomeric alkanes in the low carbon alkane into normal alkanes, and improves the ethylene raw material quality.

Description

Technical Field

[0001] This invention belongs to the field of hydrocarbon hydroconversion, specifically relating to a hydroconversion method for producing high-quality ethylene feedstock from low-carbon alkanes. Background Technology

[0002] In petroleum processing, hydrocracking or aromatics extraction generates a significant amount of low-carbon alkanes. Since these low-carbon alkanes typically do not contain aromatics, they are commonly used as feedstock for ethylene. However, due to their high content of isoalkanes, these low-carbon alkanes result in low ethylene yields during steam cracking, making them less than ideal ethylene feedstocks and significantly impacting the overall economic efficiency of ethylene plants.

[0003] CN115612524A discloses a method for increasing the concentration of n-chain alkanes in a light naphtha feed stream. The method includes separating the naphtha feed stream into a stream rich in n-chain alkanes and a stream rich in non-n-chain alkanes. An isomerization feed stream is obtained from the non-n-chain alkanes stream and isomerized on an isomerization catalyst to convert the non-n-chain alkanes into n-chain alkanes and generate an isomerized effluent. Optionally, the isomerized effluent can be separated into a propane stream and a C4 stream in a single column. + Hydrocarbon feedstock. C4 + The hydrocarbon feed stream can be recycled to the step of separating the naphtha feed stream.

[0004] CN116023214A discloses a method and system for producing n-alkanes. The method involves contacting isobutane feedstock with an isobutane conversion catalyst in an isobutane conversion unit to carry out an isobutane conversion reaction. The isobutane conversion catalyst has high catalytic activity, is chlorine-free, safe and non-toxic, and reduces corrosion and wear on equipment. The resulting reaction product containing n-alkanes is introduced into a membrane separation unit for membrane separation treatment. The membrane separation element, including a molecular sieve membrane, enables efficient separation of n-alkanes and isoalkanes. The separation efficiency is high and the method is simple and easy to implement.

[0005] The above methods can all convert small molecule isoalkanes into n-alkanes, but the energy required for the conversion of hydrocarbons with different molecular structures is different, and it is difficult to effectively guarantee the yield of the target product by using a single conversion process. Summary of the Invention

[0006] In view of the problems existing in the prior art, the purpose of this invention is to provide a method for converting low-carbon alkanes. This method uses low-carbon alkanes as raw materials and can effectively convert isoparaffins in low-carbon alkanes into n-paraffins, thereby improving the quality of ethylene feedstock.

[0007] This invention provides a method for converting low-carbon alkanes, the method comprising:

[0008] (1) Low-carbon alkanes are mixed with hydrogen and passed through the hydroconversion reaction zone, which is filled with a hydroconversion catalyst.

[0009] (2) The effluent from the hydroconversion reaction zone enters the separation system, where hydrogen-rich gas and hydroconversion products are separated.

[0010] The content of C7-C8 isoalkanes in the low-carbon alkanes is 5wt% to 20wt%, and the content of C5-C6 isoalkanes is 40wt% to 80wt%, based on a total weight of 100wt% of the low-carbon alkanes.

[0011] According to the present invention, the initial boiling point of the low-carbon alkane is 20°C to 50°C, preferably 25°C to 35°C; the final boiling point is 90°C to 140°C, preferably 100°C to 120°C.

[0012] According to the present invention, in the low-carbon alkanes, the content of C7-C8 isoalkanes is 5wt% to 20wt%, the content of C5-C6 isoalkanes is 40wt% to 80wt%, the content of C5-C8 n-alkanes is 10wt% to 30wt%, preferably 15wt% to 25wt%, and the content of C5-C8 cyclic hydrocarbons is 1wt% to 20wt%, preferably 5wt% to 15wt%, based on a total weight of 100wt% of the low-carbon alkanes.

[0013] According to the present invention, the low-carbon alkane is a mixture of light naphtha and aromatic raffinate, wherein the mass ratio of light naphtha to aromatic raffinate is 5:1 to 1:5, for example, but not limited to 5:1, 4:1, 3:1, 2:1, 1:1, 1:2, and any range between any two values.

[0014] According to the present invention, the light naphtha is preferably hydrocracked light naphtha, and the aromatic raffinate is preferably raffinate obtained by aromatic extraction from reforming oil. In the hydrocracked light naphtha, the content of C5-C6 isoalkanes is 60wt% to 90wt%, preferably 70wt% to 80wt%; C7... + The hydrocarbon content is 0–10 wt%, preferably 0.5 wt%–5 wt%; the C5–C6 n-alkanes content is 9 wt%–30 wt%, preferably 15 wt%–25 wt%; C4 - The hydrocarbon content is 0-10 wt%, preferably 2 wt%-5 wt%; the cyclic hydrocarbon content is 1 wt%-10 wt%, preferably 2 wt%-5 wt%; and the total weight of the hydrocracked light naphtha is 100 wt%.

[0015] According to the present invention, the aromatic raffinate contains 15 wt% to 45 wt% of C7-C8 isoalkanes, 20 wt% to 45 wt% of C6 isoalkanes, preferably 25 wt% to 40 wt%; <5 wt% of C5 isoalkanes; 10 wt% to 40 wt% of C5-C8 n-alkanes, preferably 20 wt% to 30 wt%; and 3 wt% to 15 wt% of C6-C8 cyclic hydrocarbons, preferably 5 wt% to 12 wt%, based on a total weight of 100 wt% of the aromatic raffinate.

[0016] According to the present invention, the hydroconversion reaction zone is filled with a hydroconversion catalyst. The hydroconversion catalyst comprises a molecular sieve, an active metal, and a binder. The molecular sieve is a shape-selective catalytic sieve, preferably mordenite. Further, the mordenite has a SiO2 / Al2O3 molar ratio of 10–50 and a specific surface area of ​​300–600 m². 2 / g, with a pore volume of 0.15–0.35 mL / g. Further, in the hydroconversion catalyst, based on the weight of the catalyst, the content of mordenite is 30 wt%–80 wt%, preferably 40 wt%–70 wt%.

[0017] According to the present invention, the binder is preferably alumina. Further, in the hydroconversion catalyst, the binder content, calculated as oxide, is 5 wt% to 65 wt%, preferably 10 wt% to 35 wt%, based on the weight of the catalyst.

[0018] According to the present invention, the active metal component is selected from one or more of Group VIB metals and Group VIII non-noble metals of the periodic table. The Group VIB metals are preferably selected from one or more of molybdenum and tungsten, and the Group VIII non-noble metals are preferably selected from one or more of cobalt and nickel. Further, in the hydroconversion catalyst, based on the weight of the catalyst, the content of the Group VIB metals, calculated as oxides, is 5.0 wt% to 30.0 wt%, preferably 10 wt% to 20 wt%; the content of the Group VIII non-noble metals, calculated as oxides, is 0.5 wt% to 15 wt%, preferably 3 wt% to 10 wt%.

[0019] According to the present invention, a fixed-bed reactor is used for the hydrogenation conversion reaction.

[0020] According to the present invention, preferably, the hydroconversion reaction zone is filled with at least two hydroconversion catalyst beds, more preferably two to three hydroconversion catalyst beds. Further, along the flow direction, the ratio of the upstream catalyst loading volume to the downstream catalyst loading volume in two adjacent catalyst beds is 1:3 to 3:1, preferably 1:2 to 2:1.

[0021] According to the present invention, along the flow direction, the active metal content of the hydroconversion catalyst packed in two adjacent catalyst beds decreases sequentially; preferably, along the flow direction, the active metal content in the downstream catalyst, calculated as oxides, is 1-20 percentage points lower than the active metal content in the upstream catalyst, calculated as oxides, in the hydroconversion catalyst packed in two adjacent catalyst beds. More preferably, it is 5-10 percentage points lower. Preferably, in the hydroconversion catalyst packed in two adjacent catalyst beds, the mass content of Group VIB metals in the downstream catalyst, calculated as oxides, is 1-15 percentage points lower than the mass content of Group VIB metals in the upstream catalyst, calculated as oxides, more preferably 4-8 percentage points lower; and the mass content of Group VIII non-precious metals in the downstream catalyst, calculated as oxides, is 1-2 percentage points lower than the mass content of Group VIII non-precious metals in the upstream catalyst, calculated as oxides.

[0022] According to the present invention, the specific surface area of ​​the hydroconversion catalyst is 200-400 m². 2 / g, with a pore volume of 0.15~0.35mL / g.

[0023] According to the present invention, the preparation method of the hydrogenation conversion catalyst can be carried out according to conventional methods in the art. The preparation method includes the preparation of a support and the loading of an active metal component, wherein the preparation process of the support is as follows: molecular sieves and binders are mechanically mixed, shaped, and then dried and calcined to form a catalyst support. The drying and calcination of the support can be carried out under conventional conditions. The drying conditions are: drying at 100℃~150℃ for 1~12 hours. The calcination conditions are: calcination at 450℃~550℃ for 2.5~6.0 hours.

[0024] According to the present invention, in the preparation method of the hydroconversion catalyst, the method of loading the active metal component is a conventional method, such as kneading, impregnation, etc., with impregnation being preferred. The impregnation method can be a saturated impregnation method, an excess impregnation method, or a complex impregnation method, that is, impregnating the catalyst support with a solution containing the desired active component, followed by drying and calcination to obtain the hydroconversion catalyst. The drying conditions are: drying at 100℃~150℃ for 1~12 hours. The calcination conditions are: calcination at 450℃~550℃ for 2.5~6.0 hours.

[0025] According to the present invention, the hydroconversion reaction conditions are as follows: the reaction pressure is 0.5 MPa to 10.0 MPa, preferably 2.0 MPa to 5.0 MPa; the reaction temperature is 250°C to 500°C, preferably 350°C to 450°C; and the liquid hourly space velocity is 0.1 h⁻¹. -1 ~15.0h -1 0.5h is preferred -1 ~5.0h -1The hydrogen-to-oil volume ratio is 10:1 to 2500:1, preferably 100:1 to 2000:1, and more preferably 100:1 to 1000:1.

[0026] According to the present invention, the hydrogenation conversion product comprises C2-C6 alkanes, wherein the mass ratio of n-alkane yield to fresh feedstock is 0.6-0.8:1, preferably 0.65-0.75:1.

[0027] According to the present invention, the effluent from the hydrogenation reaction zone enters the separation system, and the separated hydrogen is a hydrogen-rich gas that is used as recycled hydrogen.

[0028] According to the present invention, the hydroconversion products are fed into a steam cracking ethylene production unit to obtain the main target products ethylene, propylene, and butadiene, wherein the yields of the trienes are the mass percentages of the ethylene, propylene, and butadiene production relative to the feed amount. The operating conditions for the steam cracking ethylene production are: reaction temperature 860–890°C, reaction pressure 0.1–0.3 MPa, and water-to-oil mass ratio 0.2–0.6.

[0029] Compared with the prior art, the present invention has the following beneficial technical effects:

[0030] (1) In the hydroconversion process, the first step is dehydrogenation. The smaller the molecular weight of the isoalkanes, the more difficult it is for them to undergo dehydrogenation. Therefore, the hydrogenation performance of the hydroconversion catalyst directly affects the conversion efficiency of isoalkanes. That is, catalysts with stronger hydrogenation performance are more likely to undergo dehydrogenation, generating carbocations, thus enabling subsequent hydroconversion processes. Our research has found that low-carbon alkanes, particularly aromatic raffinate, have a high content of C7-C8 isoalkanes. This component is prone to dehydrogenation during the reaction to generate olefins. These intermediate olefins are more likely to trigger the dehydrogenation of C5-C6 isoalkanes in the feedstock, effectively increasing the hydroconversion reaction rate. Further research has revealed that mordenite with a high content of moderately strong acids tends to undergo n-alkanization during hydroconversion. Preferably, the method of this invention, by loading a hydroconversion catalyst bed with varying active metal contents, and with the active metal content gradually decreasing along the flow direction, can significantly increase the yield of n-alkanes in the product by matching the dehydrogenation performance of the catalyst.

[0031] (2) The hydroconversion process of the present invention is simple. By blending some aromatic raffinate, the dehydrogenation reaction of hydrocracking light naphtha is promoted, thereby increasing the reaction rate. At the same time, the mordenite catalyst with a high content of medium strong acid is loaded in the hydroconversion reaction zone. The synergistic effect of the two greatly increases the content of n-alkane in the hydrogenation product, thereby increasing the ethylene yield of the ethylene unit. It has broad application value. Attached Figure Description

[0032] Figure 1This is a schematic diagram of the process flow according to an embodiment of the present invention;

[0033] Explanation of key figure labels:

[0034] 1-Low-carbon alkanes, 2-Hydrogen, 3-Hydroconversion reaction zone, 4-Hydroconversion reaction zone effluent, 5-Separation system, 6-Hydrogen-rich gas, 7-Hydroconversion products. Detailed Implementation

[0035] The following examples further illustrate the function and effect of the present invention, but the following examples do not constitute a limitation on the method of the present invention.

[0036] Unless otherwise specified, all percentages in this invention refer to mass fractions.

[0037] The method of the present invention, such as Figure 1 As shown, the process includes: low-carbon alkanes 1 and hydrogen 2 are mixed and enter the hydrogenation conversion reaction zone 3 for hydrogenation conversion reaction; the hydrogenation conversion reaction effluent 4 enters the separation system 5; the separated gaseous stream 6 is recycled; and the hydrogenation conversion product 7 is used directly as ethylene feedstock.

[0038] In this invention, the hydroconversion catalysts in each example are designated as Cat-A followed by a number, such as Cat-A1, Cat-A2, Cat-A3, and Cat-A4. The hydroconversion catalysts were prepared using a conventional active metal saturation impregnation method, and the physicochemical properties of the obtained catalysts are shown in Table 1.

[0039] In this invention, the low-carbon alkanes used in each example are a mixture of light naphtha and aromatic raffinate, wherein the mass ratio of light naphtha to raffinate is 2:1, and their main properties are shown in Tables 3 and 4.

[0040] In this invention, the n-alkanes in Table 5 include ethane, propane, n-butane, n-pentane, and n-hexane.

[0041] In this invention, the yield of n-alkanes = n-alkanes yield in hydrogenation conversion products / fresh feed amount × 100%, by mass.

[0042] Example 1

[0043] The conversion method for low-carbon alkanes employs methods such as... Figure 1 The process is shown below. The method specifically includes:

[0044] (1) Low-carbon alkanes are mixed with hydrogen and passed through the hydrogenation conversion reaction zone, which is then sequentially filled with hydrogenation conversion catalysts Cat-A1 / Cat-A4.

[0045] (2) The effluent from the hydrogenation reaction zone enters the separation system. The hydrogen-rich gas obtained after separation is used as recycled hydrogen, and the hydrogenation product is used directly as ethylene feedstock.

[0046] The process conditions and hydrogenation effect in this example are shown in Table 5.

[0047] Example 2

[0048] The conversion method for low-carbon alkanes employs methods such as... Figure 1 The process is shown below. The method specifically includes:

[0049] (1) Low-carbon alkanes are mixed with hydrogen and passed through the hydrogenation conversion reaction zone, which is then sequentially filled with hydrogenation conversion catalysts Cat-A1 / Cat-A5.

[0050] (2) The effluent from the hydrogenation reaction zone enters the separation system. The hydrogen-rich gas obtained after separation is used as recycled hydrogen, and the hydrogenation product is used directly as ethylene feedstock.

[0051] The process conditions and hydrogenation effect in this example are shown in Table 5.

[0052] Example 3

[0053] The conversion method for low-carbon alkanes employs methods such as... Figure 1 The process is shown below. The method specifically includes:

[0054] (1) Low-carbon alkanes are mixed with hydrogen and passed through the hydrogenation conversion reaction zone, which is then sequentially filled with hydrogenation conversion catalysts Cat-A3 / Cat-A2.

[0055] (2) The effluent from the hydrogenation reaction zone enters the separation system. The hydrogen-rich gas obtained after separation is used as recycled hydrogen, and the hydrogenation product is used directly as ethylene feedstock.

[0056] The process conditions and hydrogenation effect in this example are shown in Table 5.

[0057] Example 4

[0058] The conversion method for low-carbon alkanes employs methods such as... Figure 1 The process is shown below. The method specifically includes:

[0059] (1) Low-carbon alkanes are mixed with hydrogen and passed through the hydroconversion reaction zone, which is sequentially filled with hydroconversion catalysts Cat-A1 / Cat-A2.

[0060] (2) The effluent from the hydrogenation reaction zone enters the separation system. The hydrogen-rich gas obtained after separation is used as recycled hydrogen, and the hydrogenation product is used directly as ethylene feedstock.

[0061] The process conditions and hydrogenation effect in this example are shown in Table 5.

[0062] Comparative Example 1

[0063] The difference from Example 1 is that the hydroconversion reaction zone is sequentially filled with hydroconversion catalysts Cat-A4 and Cat-A1.

[0064] The process conditions and hydrogenation effect in this example are shown in Table 5.

[0065] Comparative Example 2

[0066] The difference from Example 1 is that the hydroconversion reaction zone is only filled with the hydroconversion catalyst Cat-A1.

[0067] The process conditions and hydrogenation effect in this example are shown in Table 5.

[0068] Comparative Example 3

[0069] The difference from Example 1 is that the hydroconversion reaction zone is sequentially filled with hydroconversion catalysts Cat-B1 and Cat-A1.

[0070] The process conditions and hydrogenation effect in this example are shown in Table 5.

[0071] Table 1. Composition and physicochemical properties of hydroconversion catalysts

[0072]

[0073]

[0074] Table 2 Composition and physicochemical properties of hydroconversion catalysts

[0075] Catalyst number Cat-B1 Catalyst properties <![CDATA[Pore volume, cm 3 / g]]> 0.30 <![CDATA[Specific surface area, m 2 / g]]> 350 Catalyst composition Beta, wt% 50 Alumina, wt% 20 <![CDATA[MoO3,wt%]]> 25 NiO, wt% 5 Properties of Beta molecular sieves <![CDATA[SiO2 / Al2O3 molar ratio of Beta zeolite]]> 30 <![CDATA[Specific surface area of Beta zeolite, m 2 / g]]> 350 Pore ​​volume of Beta molecular sieve, mL / g 0.30

[0076] Table 3 Composition and properties of hydrocracked light naphtha

[0077]

[0078]

[0079] Table 4 Composition and properties of aromatic hydrocarbon raking oil

[0080] Hydrocarbon composition <![CDATA[n-Pentane in C5, %]]> 3.89 <![CDATA[C5 Isoparaffin, %]]> 2.02 <![CDATA[n - hexane, %]]> 13.03 <![CDATA[C6 Isoparaffin, %]]> 33.10 <![CDATA[n - C7 - C8 paraffin, %]]> 7.43 <![CDATA[C7-C8 Isoparaffin, %]]> 32.41 <![CDATA[C6-C8 cycloalkanes, %]]> 7.99 Total aromatics 0.13 Initial boiling point, ℃ 55 Final boiling point, ℃ 114

[0081] Table 5. Process conditions and conversion results of the examples and comparative examples.

[0082]

[0083] The specific embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including any other combinations of the various technical features.

[0084] Any combination of these simple variations and combinations in an appropriate manner should also be considered as part of the content disclosed in this invention and fall within the protection scope of this invention.

Claims

1. A method for converting low-carbon alkanes, the method comprising: (1) Low-carbon alkanes are mixed with hydrogen and passed through the hydroconversion reaction zone, which is filled with a hydroconversion catalyst. (2) The effluent from the hydroconversion reaction zone enters the separation system, where hydrogen-rich gas and hydroconversion products are separated. The content of C7-C8 isoalkanes in the low-carbon alkanes is 5wt% to 20wt%, and the content of C5-C6 isoalkanes is 40wt% to 80wt%.

2. The conversion method according to claim 1, characterized in that: The initial boiling point of the low-carbon alkane is 20℃~50℃, preferably 25℃~35℃; the final boiling point is 90℃~140℃, preferably 100℃~120℃.

3. The conversion method according to claim 1, characterized in that: The low-carbon alkane is a mixture of light naphtha and aromatic raffinate, wherein the mass ratio of light naphtha to aromatic raffinate is 5:1 to 1:

5. Preferably, the light naphtha is hydrocracked light naphtha, wherein the content of C5-C6 isoalkanes in the hydrocracked light naphtha is 60wt% to 90wt%, preferably 70wt% to 80wt%; C7 + The hydrocarbon content is 0–10 wt%, preferably 0.5 wt%–5 wt%; the C5–C6 n-alkanes content is 9 wt%–30 wt%, preferably 15 wt%–25 wt%; C4 - The hydrocarbon content is 0-10 wt%, preferably 2 wt%-5 wt%; the cyclic hydrocarbon content is 1 wt%-10 wt%, preferably 2 wt%-5 wt%; based on the total weight of the hydrocracked light naphtha as 100 wt%; Preferably, the aromatic raffinate contains 15 wt% to 45 wt% of C7-C8 isoalkanes, 20 wt% to 45 wt% of C6 isoalkanes, preferably 25 wt% to 40 wt%; <5 wt% of C5 isoalkanes; 10 wt% to 40 wt% of C5-C8 n-alkanes, preferably 20 wt% to 30 wt%; and 3 wt% to 15 wt% of C6-C8 cyclic hydrocarbons, preferably 5 wt% to 12 wt%, based on a total weight of 100 wt% of the aromatic raffinate.

4. The conversion method according to claim 1, characterized in that: The hydroconversion reaction zone is filled with a hydroconversion catalyst; preferably, the hydroconversion catalyst comprises a molecular sieve, an active metal, and a binder; preferably, the molecular sieve is mordenite; the active metal component is selected from one or more of Group VIB metals and Group VIII non-precious metals of the periodic table, wherein the Group VIB metal is preferably selected from one or more of molybdenum and tungsten, and the Group VIII non-precious metal is preferably selected from one or more of cobalt and nickel; the binder is preferably alumina.

5. The conversion method according to claim 4, characterized in that: The mordenite has a SiO2 / Al2O3 molar ratio of 10–50 and a specific surface area of ​​300–600 m². 2 / g, with a pore volume of 0.15~0.35mL / g.

6. The conversion method according to claim 4, characterized in that: In the hydroconversion catalyst, based on the weight of the catalyst, the content of mordenite is 30wt% to 80wt%, preferably 40wt% to 70wt%; the content of Group VIB metals as oxides is 5.0wt% to 30.0wt%, preferably 10wt% to 20wt%; the content of Group VIII non-precious metals as oxides is 0.5wt% to 15wt%, preferably 3wt% to 10wt%; and the content of binder as oxides is 5wt% to 65wt%, preferably 10wt% to 35wt%.

7. The conversion method according to claim 1, characterized in that: The hydroconversion reaction zone is filled with at least two hydroconversion catalyst beds; Preferably, along the flow direction, the ratio of the upstream catalyst loading volume to the downstream catalyst loading volume in two adjacent catalyst beds is 1:3 to 3:1, more preferably 1:2 to 2:

1.

8. The conversion method according to claim 7, characterized in that: Along the flow direction, the active metal content of the hydroconversion catalyst packed in two adjacent catalyst beds decreases sequentially. Preferably, along the flow direction, the active metal content in the downstream catalyst of the hydroconversion catalyst packed in two adjacent catalyst beds is 1 to 20 percentage points lower (calculated as oxides) than the active metal content in the upstream catalyst (calculated as oxides), and more preferably 5 to 10 percentage points lower.

9. The conversion method according to claim 4, characterized in that: The specific surface area of ​​the hydroconversion catalyst is 200–400 m². 2 / g, with a pore volume of 0.15~0.35mL / g.

10. The conversion method according to claim 1, characterized in that: The hydrogenation conversion reaction conditions are as follows: reaction pressure is 0.5 MPa to 10.0 MPa, preferably 2.0 MPa to 5.0 MPa; reaction temperature is 250℃ to 500℃, preferably 350℃ to 450℃; liquid hourly space velocity is 0.1 h⁻¹. -1 ~15.0h -1 Preferably 0.5h -1 ~5.0h -1 The hydrogen-to-oil volume ratio is 10:1 to 2500:1, preferably 100:1 to 2000:1, and more preferably 100:1 to 1000:1.

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