Method and apparatus for separating naphtha by membrane

Abstract

The present application relates to a method for separating normal and isomeric alkanes in naphtha by inorganic membrane, which matches the membrane separation process with the actual working condition in industrial application to realize continuous production and directly obtain the purified product. The process first carries out hydrogenation pretreatment on full-range naphtha, then directly enters the membrane separation unit without pressure and temperature adjustment, and then obtains separated normal / isomeric alkane products, and finally enters the subsequent application production unit. The product rich in normal alkanes obtained on the permeation side after membrane separation can be used as high-quality raw material for the subsequent ethylene cracking section, and the product rich in isomeric alkanes obtained on the retentate side can be used as high-quality catalytic reforming or high-quality gasoline raw material. Coupling the membrane separation with the naphtha production process does not introduce the third component, is simple to operate, and has low energy consumption. The present application mainly solves the practical problems in the prior art, such as the difficulty in recovering the adsorbent, the large amount of desorbent, and the high energy consumption in the separation process when the adsorption method is used to separate normal and isomeric alkanes.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for separating naphtha by inorganic membrane, in particular to a coupling process for naphtha production and separation, and belongs to the field of petroleum chemical industry. BACKGROUND

[0002] Naphtha is the fraction between the initial boiling point and about 200 DEG C obtained by atmospheric distillation of crude oil. Its main components are C4-C10 hydrocarbons, usually including normal alkanes, isomeric alkanes, aromatic hydrocarbons, naphthenes and a small amount of unsaturated hydrocarbons, among which normal alkanes, such as n-pentane (n-C5), n-hexane (n-C6) and n-heptane (n-C7), are the main components, accounting for about 40% of naphtha, and are important raw materials for the production of ethylene; non-normal alkanes, such as 2-methylpentane, benzene, etc., are the main components, accounting for about 60% of naphtha. It is the main raw material for the production of aromatic hydrocarbons and blended gasoline. The traditional naphtha processing process usually adopts the method of fraction management, that is, through the preliminary distillation of crude oil, it is cut into products of different distillation ranges, and then enters the next section for production. Under this production process, the components of naphtha cannot be fully utilized, and the raw materials are impure, the process is complex, and the energy consumption is large. By separating normal and isomeric alkanes in naphtha, the utilization rate of naphtha can be greatly improved. High-purity normal alkanes are high-quality raw materials for the production of ethylene, and high-purity isomeric alkanes can be used to produce aromatic hydrocarbons or high-octane gasoline. Therefore, seeking a suitable separation method to separate normal / isomeric alkanes in naphtha is the key to improving the utilization rate of naphtha.

[0003] Adsorption separation is currently the main technology for separating normal / isomeric alkanes. British patent GB2119398 discloses the use of 5A molecular sieve to selectively adsorb normal alkanes by using the specific structure of the molecular sieve. Chinese patent CN106883086A discloses an optimization method for adsorptive separation of naphtha based on a simulated moving bed with 5A molecular sieve. This method is a continuous operation of liquid-solid adsorption separation, which has the problems of high consumption of desorbent, high pollution, high energy consumption and low yield.

[0004] In summary, there is a lack of a simple and efficient method for directly separating naphtha in the art. Therefore, there is an urgent need in the art to develop a technical solution that is simple to operate, continuous operation, low energy consumption for separation, and high product yield. SUMMARY

[0005] The technical problem to be solved by the present application is to separate normal / isomeric alkanes in naphtha. Due to the complexity of the components of naphtha, various separation methods cannot have good selective separation, and traditional adsorption separation methods also have the problems of high equipment investment, complex operation and high energy consumption.

[0006] The improved technical invention point of the present application is that the inorganic membrane separation unit is directly coupled and embedded into the naphtha production process, without the need for existing temperature reduction and pressure regulation treatment, realizing continuous separation and production of normal / iso-alkanes, which can significantly increase production capacity and improve economic benefits. In the present application, the naphtha separation process by membrane method only needs to build a membrane separation unit and embed it into the entire process to meet the product purity requirements, without the need for the addition of adsorbents and desorbents and other third components and re-separation. The retentate gas can be directly returned to the raw material, and the product rich in normal / iso-alkanes obtained after circulating membrane separation; the separation of normal / iso-alkanes in naphtha can be realized by membrane separation, which greatly improves the separation efficiency and reduces the operating cost.

[0007] A method for separating naphtha by membrane separation, comprising the following steps:

[0008] Step 1: gas phase or liquid phase naphtha is sent into a membrane separation device for separation; normal alkane components are obtained on the permeation side of the membrane separation device, and iso-alkane components are obtained on the retentate side of the membrane separation device;

[0009] Step 2: the separated normal / iso-alkanes are liquefied to obtain liquid products.

[0010] In one embodiment, the MFI zeolite membrane used in the membrane separation device is a random orientation type MFI zeolite membrane prepared by Sillicalite-1 seeds.

[0011] In one embodiment, the MFI zeolite membrane used in the membrane separation device is a random orientation type MFI zeolite membrane prepared by Sillicalite-1 seeds.

[0012] In one embodiment, the naphtha is one or a mixture of several of straight-run naphtha, hydrocracking naphtha or hydrocracking naphtha.

[0013] In one embodiment, the naphtha is hydrocracking naphtha or hydrocracking naphtha, and after the hydrogenation treatment process, it is directly separated into the membrane separation device in step 1 without cooling.

[0014] In one embodiment, the naphtha contains C5-C6 alkanes, and the content of C5-C6 alkanes ranges from 60% to 90%.

[0015] In one embodiment, the naphtha to be separated contains a mixture of two or more components of iso-pentane, n-pentane, 2-methyl-pentane, 3-methyl-pentane and n-hexane.

[0016] In one embodiment, in step 1, the naphtha to be separated is pretreated by a pretreatment unit.

[0017] In one embodiment, the pretreatment includes drying, filtering, pressurizing, heating or converting into a gaseous state.

[0018] In one embodiment, the gas product on the retentate side of the membrane separation device is controlled by a back pressure valve.

[0019] In one embodiment, the working temperature of the membrane separation device is 0-400℃, and the feed pressure is controlled at 0.01-5MPa.

[0020] A device for separating naphtha by using a molecular sieve membrane, comprising:

[0021] A hydrogenation reaction device for hydrogenating and reducing unsaturated hydrocarbons in naphtha and removing N and S impurities in naphtha;

[0022] A pretreatment device connected to the hydrogenation reaction device for pretreating naphtha obtained from the hydrogenation reaction device;

[0023] A membrane separation device connected to the pretreatment device for separating normal and iso alkanes in naphtha;

[0024] Wherein, the connecting pipeline between the hydrogenation reaction device and the membrane separation device does not contain a heat exchange device.

[0025] A device for separating naphtha by using a molecular sieve membrane, comprising:

[0026] A pretreatment device for pretreating naphtha;

[0027] A membrane separation device connected to the pretreatment device for separating normal and iso alkanes in naphtha.

[0028] For the above two membrane separation devices, the following technical solutions can also be included:

[0029] In one embodiment, the membrane separation device is installed with an MFI molecular sieve membrane.

[0030] In one embodiment, the MFI molecular sieve membrane is a random orientation type MFI molecular sieve membrane prepared by using Sillicalite-1 seeds.

[0031] In one embodiment, the pretreatment device is selected from one or a combination of a gas compression device, a gas drying device, a gas heating device, a gas filtering device or a gaseous naphtha generating device; the gaseous naphtha generating device is used to convert liquid naphtha into a gaseous state.

[0032] The gaseous naphtha generating device refers to a bubbler or a vaporizer, which respectively converts liquid naphtha into a gaseous state by a bubbling method or a heating vaporization method.

[0033] In one embodiment, the membrane separation device comprises a plurality of membrane modules, and the membrane modules are connected in series; the retentate side outlet of the upper membrane module is connected to the retentate side inlet of the lower membrane module.

[0034] The permeate side outlet of the last membrane module is connected to a first gas component receiving pipeline; and the retentate side outlet of the first membrane module is connected to a second gas component receiving pipeline.

[0035] In one embodiment, an alkane cracking reactor is further connected to the first gas component receiving pipeline and / or the second gas component receiving pipeline, for cracking the alkane in the retentate side outlet and / or the rejection side outlet to produce ethylene.

[0036] In one embodiment, the retentate side outlet of the lower membrane module is connected to the upper membrane module through a trace gas pump.

[0037] In one embodiment, the pretreatment unit is connected to the naphtha separation device through a mass flow controller.

[0038] In one embodiment, the pretreatment unit is connected to any membrane module.

[0039] Advantages

[0040] 1. The present application provides a new process for separating normal and isomeric alkanes in naphtha, which can efficiently separate normal and isomeric alkanes in naphtha products, and has the advantages of high separation factor and good separation effect in the separation of mixed hydrocarbons.

[0041] 2. The naphtha separation process of the present application can replace the adsorption separation method in the prior art, and the gas separation membrane method can realize the purpose of directly separating the hydrogenated naphtha by molecular sieve membrane without cooling treatment, thereby saving energy consumption, avoiding the heat loss caused by the need to cool the hydrogenated material to a suitable temperature for entering the adsorbent in the prior art method, and avoiding the problems of high cost and high energy consumption of the adsorption equipment, and poor maintenance.

[0042] 3. The method of the present application can realize high-precision separation of normal and isomeric alkanes in mixed alkanes, and can realize the purpose of achieving a purity of 99% for normal and isomeric alkanes; wherein the isomeric alkane product has the characteristics of high purity, and can significantly improve the octane number of gasoline when applied in the process of gasoline blending; in addition, the normal alkane can have a high reaction yield when applied in the process of cracking to produce ethylene.

[0043] The application is simple in operation, and the coupling membrane separation unit in the production process can realize separation and concentration of the target product. The pretreatment section and the separation section have consistent operation conditions, and the operation conditions do not need to be changed. The device has low investment, can realize separation of naphtha under conventional production operation conditions, is energy-saving and environment-friendly, and has remarkable economic benefits. BRIEF DESCRIPTION OF DRAWINGS

[0044] Figure 1 It is a schematic diagram of the "integrated" naphtha production-membrane separation coupling process.

[0045] Figure 2 It is a device for membrane separation of naphtha.

[0046] Figure 3 It is another device for membrane separation of naphtha.

[0047] Figure 4 It is the permeability of MFI molecular sieve membrane to each component in naphtha at different temperatures.

[0048] Figure 5 It is the concentration of each component at the outlet of the naphtha membrane separation unit with temperature change.

[0049] Figure 6 It is the separation performance of MFI molecular sieve membrane to normal and isoalkanes in naphtha at different temperatures.

[0050] Figure 7 It is the long-term running stability of the naphtha membrane separation unit.

[0051] 1, hydrogenation reaction device; 2, pretreatment device; 3, membrane separation device; 4, alkane cracking reactor; 5, gas filtering device; 6, gas compression device; 7, gas drying device; 8, gas heating device; 9, second gas component receiving pipeline; 10, first gas component receiving pipeline; 11, gaseous naphtha generating device. DETAILED DESCRIPTION

[0052] The application point of the application is that normal and isoalkanes can be simply obtained from a complex naphtha system and production process by membrane separation; in the separation process, the separation effect is not easily disturbed by other components, and the obtained product has good purity and high separation coefficient. At the same time, without any temperature and pressure treatment and multi-stage separation process, the production energy consumption of related products is significantly reduced, and the production process is shortened.

[0053] In this invention, the naphtha used can be selected from straight-run naphtha, hydrocracked naphtha, or hydropyrolyzed naphtha. The naphtha feedstock used includes branched or unbranched alkanes containing 2-12 carbon atoms. In this method, the use of hydrotreated naphtha allows for the complete conversion of olefins in the naphtha into alkanes, involving only the separation of normal and isoalkanes.

[0054] In the method of this patent, the hydrogenated raw material can be processed using an MFI molecular sieve membrane. Since the molecular sieve membrane can be adapted to separation operation under high temperature feeding conditions, the hydrogenated material can be directly fed into the molecular sieve membrane for processing without cooling, avoiding the energy loss problem caused by the cooling / heating process. However, if traditional adsorption treatment is used, the adsorbent needs to be processed at low temperature, and the hydrogenated material needs to be cooled to the working temperature of the adsorbent, which consumes a lot of energy.

[0055] For the above-mentioned naphtha raw materials, under normal circumstances, the main alkanes they contain have carbon chain lengths of C5-C6, and the content of these alkanes is generally between 60% and 90%, which are the main components of naphtha.

[0056] In a typical implementation, the composition may include one or a mixture of several of the following components: isopentane, n-pentane, 2-methylpentane, 3-methylpentane, and n-hexane. In some specific feedstock compositions, the composition includes 20-30% isopentane, 25-35% n-pentane, 12-22% 2-methylpentane, 5-15% 3-methylpentane, and 12-24% n-hexane. For complex mixtures like naphtha, the separation of isoalkanes and n-alkanes can be challenging due to the very similar molecular weights and physicochemical properties of 2-methylpentane, 3-methylpentane, and n-hexane. In the separation of normal and isoparaffins, the method of the present invention is more suitable for separating alkane mixtures that do not contain branches (or contain only one branch). For this type of alkane mixture, due to the small number of branches and the similar properties, separation is more difficult. However, if there are many branches, the kinetic diameter of the molecules will change significantly, the steric hindrance will increase sharply, the separation mechanism will change, and the combined effect of adsorption separation and molecular sieving will be transformed into simple molecular sieving, thereby reducing the separation difficulty.

[0057] In addition, compared with the binary mixture prepared in the experiment, there is competitive adsorption in the complex system. The more effective carbons there are, the greater the steric hindrance, and the greater the impact on separation. (Meng Fanlei, Zhou Xiang, Guo Jinbiao, et al. Study on the correlation between effective carbon number and physical properties of isoparaffins [J]. Computer and Applied Chemistry, 2010, 27(12): 1638-1642).

[0058] Therefore, the present application finds that the isomeric and normal alkanes in naphtha and other components can be separated by using MFI molecular sieve membrane due to its special pore structure. The MFI molecular sieve membrane is a dense membrane material formed by MFI type molecular sieve intergrowth, and its pore structure is formed by cross-linking of 10-membered ring straight pores and 10-membered elliptical sinusoidal pores, and its average pore size is 0.5-0.6 nm. The separation of components is realized by using the regular pore of the molecular sieve. The following examples are exemplarily described by taking the random orientation type MFI molecular sieve membrane prepared by using Sillicalite-1 seed as an example.

[0059] The separated normal / isomeric alkanes are directly sent into the next production section, and the high-purity isomeric alkanes can be obtained from the naphtha by the above method, which is applied to the production of ethylene. When the purity of the normal alkanes reaches 99%, the energy consumption required for thermal cracking is significantly reduced, and therefore, better economic benefits can be obtained when it is applied to the production process of ethylene.

[0060] The pore has obvious adsorption selectivity to the normal alkanes, thereby exhibiting excellent normal / isomeric alkane separation performance. On the other hand, the operation conditions of the separation process can be well matched with the previous pretreatment section, thereby realizing the "integrated" design and production.

[0061] In the following examples, the components of the naphtha to be separated are 27.2% isopentane, 29.1% n-pentane, 17.6% 2-methylpentane, 10.7% 3-methylpentane and 15.4% n-hexane.

[0062] Figure 1 It is shown that the raw gas is pretreated by the pretreatment unit, so that the parameters such as the water content, pressure and temperature of the raw gas reach the requirements. The pretreatment unit used in the present application is not particularly limited, and can be a compression device, a drying device, a filtering device or a heating device. The naphtha liquid phase raw material is pretreated before entering the membrane separation assembly, so as to reach the corresponding gas phase state requirements. The treated raw gas is adjusted in raw material partial pressure, and sequentially enters the naphtha membrane separation unit on the retentate side under appropriate feeding conditions and positions. After multi-stage membrane separation, the product rich in isomeric alkanes is obtained, and the normal alkane membrane separation product is removed in time to obtain the product rich in normal alkanes. The single membrane assembly used in the present application comprises a shell and an internal naphtha separation membrane. The shell is made of stainless steel or nylon material. The shell and the naphtha separation membrane divide the space in the assembly into the permeation side and the retentate side. The configuration is tubular, and the separation layer is selected to be located outside the hollow fiber type membrane. The outlet of the permeation side obtains the liquid phase product rich in normal alkanes. The outlet of the retentate side returns to the raw material tank or is subjected to multi-stage separation to obtain the liquid phase product rich in isomeric alkanes. The retentate gas can be adjusted as needed to enter the next stage of naphtha separation assembly to further separate the retentate side product.

[0063] The pressure range of the raw material feeding process of the single-stage membrane assembly is controlled in the range of 0.01-5 MPa.

[0064] The operating temperature range of the naphtha separation process of the membrane separation assembly is 0-400℃.

[0065] The gas reflux ratio of the retentate reflux process of each stage assembly is controlled in the range of <10 by means of a trace gas pump (the gas reflux ratio refers to the amount of gas refluxed on the retentate side of the membrane assembly and the amount of gas to be separated entering the gas separation equipment).

[0066] Based on the above method, the device provided by the application can be as shown in Figure 2 .

[0067] The hydrogenation reaction device 1 is used for carrying out hydrocracking or cracking reaction on naphtha;

[0068] The pretreatment device 2 is connected to the hydrogenation reaction device 2 and is used for carrying out pretreatment on the naphtha obtained from the hydrogenation reaction device 1;

[0069] The membrane separation device 3 is connected to the pretreatment device 2 and is used for carrying out separation of normal and iso alkanes on the naphtha.

[0070] The connecting pipeline between the hydrogenation reaction device 1 and the membrane separation device 3 does not contain a liquefaction device.

[0071] Another device is as shown in Figure 3 .

[0072] A device for separating naphtha by using a molecular sieve membrane, comprising:

[0073] The pretreatment device 2 is used for carrying out pretreatment on naphtha;

[0074] The membrane separation device 3 is connected to the pretreatment device 2 and is used for carrying out separation of normal and iso alkanes on the naphtha.

[0075] In an embodiment, the membrane separation device 3 is installed with an MFI molecular sieve membrane.

[0076] In an embodiment, the device further comprises a gaseous naphtha generating device 11 used for converting liquid naphtha into gaseous naphtha.

[0077] The pretreatment device 2 is connected to the gaseous naphtha generating device 11.

[0078] In an embodiment, the gaseous naphtha generating device 11 refers to a bubbler or a vaporizer, which respectively converts liquid naphtha into gaseous naphtha by means of bubbling or heating vaporization.

[0079] The two devices described above can also comprise the following technical solutions:

[0080] In one embodiment, the membrane separation device 3 is installed with MFI molecular sieve membrane.

[0081] In one embodiment, the pretreatment device is selected from one or a combination of the following: a gas compression device 6, a gas drying device 7, a gas heating device 8, or a gas filtration device 5.

[0082] In one embodiment, the membrane separation device 3 comprises a plurality of membrane assemblies, which are connected in series. The retentate outlet of the upper membrane assembly is connected to the retentate inlet of the lower membrane assembly.

[0083] The permeate outlet of the last membrane assembly is connected to the first gas component receiving pipeline 10, and the retentate outlet of the first membrane assembly is connected to the second gas component receiving pipeline 9.

[0084] In one embodiment, an alkane cracking reactor 4 is connected to the first gas component receiving pipeline 10 and / or the second gas component receiving pipeline 9, for cracking the retentate outlet and / or the retentate outlet to produce ethylene.

[0085] In one embodiment, the retentate outlet of the lower membrane assembly is connected to the upper membrane assembly by a trace gas pump.

[0086] In one embodiment, the pretreatment unit is connected to any level of the membrane assembly.

[0087] Example 1

[0088] The n-alkanes and iso-alkanes in naphtha were separated according to the method described above. The composition and physical properties of the raw materials are shown in Table 1.

[0089] Table 1 Composition and physical properties of simulated naphtha

[0090]

[0091]

[0092] The naphtha feedstock is heated to 25°C in a feedstock pretreatment unit, then fed into the membrane separation assembly by way of bubbling gas, diluted by the bubbling gas to a feedstock partial pressure of 25 kPa, and then enters the membrane separation assembly. The membrane separation assembly is two sets, and the membrane separation and membrane regeneration are used alternately and operated continuously. The separation membrane uses MFI molecular sieve membrane, the sweeping gas uses helium, the separation pressure is normal pressure, and the separation temperature is 80°C. It is determined that after separation by the single-stage membrane separation assembly, the n-alkane content at the outlet of the permeation side is 99.4% (mol), and the n-alkane content at the outlet of the retentate side is reduced from 58.6% (mol) to 31.9% (mol); the isoalkane content is increased from 41.4% (mol) to 68.1% (mol). The n-isoalkane separation selectivity reaches 775.7. The permeation side product is cooled to room temperature in a liquefaction device. The n-alkane product can be condensed, and the non-condensable gas can be recycled and used. The changes in the content of each component in the entire separation process are shown in Table 2, and the changes in the content of n-isoalkane are shown in Table 3.

[0093] Table 2 Changes in the content of each component in the membrane separation device

[0094]

[0095] Table 3 Changes in the content of n-isoalkane in the membrane separation device

[0096]

[0097] Example 2

[0098] This example investigates the influence of different operating temperatures on the separation characteristics. The separation is carried out at 80-200°C, the composition of the naphtha used is the same as in the above examples, the feedstock partial pressure is 25 kPa, and the other parameters are the same as in Example 1. The operating results are shown in Table 6. Figure 4 、 5 From the figure, it can be seen that in the controllable temperature range of the naphtha production section, Example 1 has the best operating conditions for the n-isoalkane separation factor.

[0099] Example 3

[0100] This example investigates the stability of the membrane separation process. The composition of the naphtha used at 120°C is the same as in the previous examples, the feedstock partial pressure is 25 kPa, and the other parameters are the same as in Examples 1 and 2. The operating results are shown in Table 6. Figure 7 The results show that the membrane separation section in this process can maintain stable operation for a long time under production operating conditions.

Claims

1. A membrane separation process for naphtha separation, characterized in that, Includes the following steps: Step 1: Naphtha in gaseous or liquid phase is fed into a membrane separation unit for separation; a component rich in n-alkanes is obtained on the permeate side of the membrane separation unit, and a component rich in iso-alkanes is extracted on the permeate side of the membrane separation unit. Step 2 involves liquefying the separated isoparaffins to obtain a liquid product. The membrane separation device uses an MFI molecular sieve membrane. This MFI molecular sieve membrane is a randomly oriented type prepared using Sillicalite-1 seed crystals. The naphtha is hydrocracked naphtha or hydropyrolyzed naphtha, and after hydrotreating, it enters the membrane separation device in Step 1 directly without cooling. The naphtha contains C5-C6 alkanes, with a C5-C6 alkanes content ranging from 60% to 90%. The naphtha contains a mixture of two or more components selected from isopentane, n-pentane, 2-methylpentane, 3-methylpentane, and n-hexane. In Step 1, the naphtha feedstock to be separated undergoes pretreatment in a pretreatment unit. This pretreatment includes drying, filtration, pressurization, heating, and conversion to a gaseous state.

2. The membrane separation process for naphtha separation according to claim 1, characterized in that, The gas product from the permeate side of the membrane separation unit is controlled by a back pressure valve for extraction.

3. The membrane separation process for naphtha separation according to claim 1, characterized in that, The membrane separation unit operates at a temperature of 0–400℃ and a feed pressure controlled between 0.01 and 5 MPa.

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