Process and system for the production of isobutane by n-butane isomerization

Abstract

The present application relates to n-butane isomerization technical field, disclose a kind of n-butane isomerization production isobutane method and system, the method includes: under hydrogen condition, under isomerization reaction condition, n-butane raw material is contacted with catalyst;The catalyst includes active matrix, and active metal component is supported on the active matrix;Wherein, the active matrix includes acidic active component SO4 2‑ / ZrO2, full-silica molecular sieve with MFI structure and alumina;The active metal component is selected from at least one of noble metal elements;Wherein, the density of strong acid center in the catalyst is 0.1-1 μmol / m 2 The method has high n-butane conversion rate and isobutane selectivity, and good reaction stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of n-butane isomerization, in particular to a method and system for producing isobutane by n-butane isomerization. BACKGROUND

[0002] Isobutane is an important light hydrocarbon resource. In recent years, with the construction of isobutane-butene alkylation, isobutane dehydrogenation, and isobutane-propylene co-oxidation devices in China, isobutane resources are increasingly scarce. N-butane isomerization is a technology that can efficiently convert n-butane in C4 resources into isobutane. There are two types of traditional n-butane isomerization catalysts, one is Pt-containing chlorinated alumina (Pt / Al2O3-Cl) catalyst, and the other is Pt or Pd-loaded zeolite molecular sieve (Pt(Pd) / zeolite) catalyst. Pt / Al2O3-Cl catalyst has the advantages of low reaction temperature and high single-pass conversion rate, but the disadvantages are that the catalyst is sensitive to impurities in the raw material, which requires strict refining of the raw material to remove impurities such as sulfur and water, and that the catalyst needs to be continuously injected with chlorine to maintain its activity during the isomerization reaction, and the catalyst cannot be regenerated, which further limits the application of this technology. Pt(Pd) / zeolite catalyst has a relatively loose requirement for impurities in the raw material, but the n-butane isomerization activity and selectivity are low.

[0003] Solid superacid catalyst is a new type of catalyst developed in recent years. Inorganic acid-promoted zirconium-based solid superacid catalysts have shown good performance in n-butane isomerization reactions, but in order to ensure high n-butane conversion, the reaction usually needs to be carried out at low space velocity and high hydrogen to oil ratio. For example, CN109265308A discloses a production method for n-butane isomerization using a solid acid bifunctional catalyst, at least one of CuGa-SO4 2- / ZrO2, NiGa-SO4 2- / ZrO2, PtGa-SO4 2- / ZrO2, PbGa-SO4 2- / ZrO2 as the catalyst, under the conditions of pressure 1.5-3.0 MPa, reactor inlet temperature 200-250℃, hydrogen to hydrocarbon volume ratio 1-5, n-butane mass space velocity 0.2-1.0, the n-butane single-pass conversion rate is 50-55%, and the isobutane selectivity is 80-85%. CN107051420A discloses a lanthanum and molybdenum modified zirconium sulfate type n-butane isomerization catalyst and its use method. When the catalyst is used for n-butane isomerization reaction, under the conditions of 220℃, 2.0 MPa, feed mass space velocity 2.0 h -1Under the condition of a hydrogen / hydrocarbon molecule ratio of 1.2, the isomerization rate of n-butane reaches a maximum of 39.7%. CN112705201A discloses a method for preparing and using a n-butane skeletal isomerization catalyst, wherein the reaction temperature is 200℃, the pressure is 1MPa, and the butane volume hourly space velocity is 1h. -1 Under conditions of a hydrogen-to-hydrocarbon molar ratio of 1:1, the single-pass conversion of n-butane obtained is 12%-48%, and the selectivity of isobutane is 85%-95%. CN106732676A discloses a solid acid catalyst for the catalytic isomerization of n-butane, the catalyst being composed of zirconium oxide, gallium oxide, and a transition metal element sulfated with sulfur-containing compounds. When the catalyst is used in the n-butane isomerization reaction at 250℃, 2.0 MPa, and a feed mass hourly space velocity of 0.4 h⁻¹, the results are satisfactory. -1 Under conditions of a hydrogen-to-hydrocarbon ratio of 3, the conversion rate of n-butane is 46.85-54.42%, and the selectivity of isobutane is 81.75-87.99%.

[0004] Existing methods for n-butane isomerization based on zirconium sulfate-type solid superacid catalysts suffer from a trade-off between space velocity and conversion rate, resulting in low n-butane conversion efficiency. Furthermore, the reaction has a high hydrogen-to-hydrogen ratio, necessitating hydrogen separation from the reaction products and recycling using a recirculating hydrogen compressor in practical applications. This leads to complex processes, high equipment investment, and significantly increased energy consumption and operating costs. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of existing technologies, such as difficulty in achieving both high space velocity and high conversion rate in the n-butane isomerization reaction, poor stability, complex process flow, and high cost. This invention provides a method and system for producing isobutane from n-butane isomerization, which has high n-butane conversion efficiency, high isobutane yield, and good operational stability.

[0006] To achieve the above objectives, the present invention provides a method for producing isobutane by isomerization of n-butane, the method comprising: contacting n-butane feedstock with a catalyst under hydrogen-exposed conditions and under isomerization reaction conditions;

[0007] The catalyst includes an active matrix and an active metal component supported on the active matrix;

[0008] The active matrix includes the acidic active component SO4. 2- / ZrO2, an all-silica molecular sieve with an MFI structure, and alumina; the active metal component is selected from at least one noble metal element;

[0009] In the catalyst, the density of strong acid centers is 0.1-1 μmol / m³. 2 .

[0010] Preferably, the isomerization reaction conditions include: a reaction temperature of 160-240℃, more preferably 170-225℃; a pressure of 1-4 MPa, more preferably 1.5-3.5 MPa; and a mass hourly space velocity (HHSV) of 0.5-10 h⁻¹ for the n-butane feedstock. -1 Preferably 1-5h -1 More preferably 1.2-4h -1 The hydrogen / hydrocarbon molar ratio is 0.02-0.3, preferably 0.03-0.2.

[0011] A second aspect of the present invention provides a system for producing isobutane by isomerization of n-butane, the system comprising: a feeding unit, a preheating device, a reactor 4, a light component separation device 5, and an isobutane removal tower 6;

[0012] The feeding unit is connected to the feed inlet of the preheating device, and n-butane raw material and hydrogen are fed into the preheating device for preheating.

[0013] The outlet of the preheating device is connected to the feed inlet of the reactor 4, and the preheated raw material is fed into the reactor 4 to contact the catalyst.

[0014] The catalyst includes an active matrix and an active metal component supported on the active matrix;

[0015] The active matrix includes the acidic active component SO4. 2- / ZrO2, an all-silica molecular sieve with an MFI structure, and alumina; the active metal component is selected from at least one noble metal element;

[0016] In the catalyst, the density of strong acid centers is 0.1-1 μmol / m³. 2 ;

[0017] The light component separation device 5 is used to separate the reaction products from reactor 4, recover the obtained light components, and send the obtained heavy components to the isobutane removal tower 6; wherein, the light components include C1-C3 hydrocarbons and H2, and the heavy components include C4 hydrocarbons. + hydrocarbon;

[0018] The isobutane removal tower 6 is used to separate isobutane products and n-butane, and the separated n-butane is returned to the feed unit.

[0019] The method for producing isobutane by isomerization of n-butane provided by this invention uses an acidic active component SO4 in the catalyst. 2-ZrO2 and the active metal component provide strong and weak acids, respectively. The density of the strong acid centers in the catalyst is modulated through the synergistic effect of an all-silica molecular sieve with an MFI structure and alumina. This method is mild, environmentally friendly, and exhibits high single-pass conversion of n-butane, high selectivity for isobutane, and good stability. It can utilize n-butane to increase isobutane production, providing feedstock for alkylation, isobutane dehydrogenation, C3 / C4 mixed dehydrogenation, PO / MTBE, and other units, thus realizing the value-added utilization of butane resources. In preferred conditions, this method can efficiently isomerize n-butane to isobutane under reaction conditions of lower temperature, lower hydrogen-to-oil ratio, and higher space velocity, which is beneficial for further reducing energy consumption and process costs. Attached Figure Description

[0020] Figure 1 These are the XRD patterns of the all-silica MFI molecular sieve (Si-1) and ZSM-5 molecular sieve (Si-2) used in the embodiments and comparative examples of this invention;

[0021] Figure 2 These are the XRD patterns of the active matrices prepared in Preparation Examples 1-3 and Comparative Preparation Example 1 of this invention;

[0022] Figure 3 This is a schematic diagram of a system for producing isobutane by isomerization of n-butane according to one embodiment of the present invention.

[0023] Explanation of reference numerals in the attached figures

[0024] 1. Feed pump 2. Heat exchanger 3. Heater

[0025] 4 Reactor; 5 Light component separation unit; 6 Isobutane removal tower Detailed Implementation

[0026] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0027] The first aspect of the present invention provides a method for producing isobutane by isomerization of n-butane, the method comprising: contacting n-butane feedstock with a catalyst under hydrogen-exposed conditions and under isomerization reaction conditions;

[0028] The catalyst includes an active matrix and an active metal component supported on the active matrix;

[0029] The active matrix includes the acidic active component SO4. 2- / ZrO2, an all-silica molecular sieve with an MFI structure, and alumina; the active metal component is selected from at least one noble metal element;

[0030] In the catalyst, the density of strong acid centers is 0.1-1 μmol / m³. 2 .

[0031] In this invention, the phase analysis of the catalyst sample was performed using a Rigaku D / MAX-3A XRD instrument. The analysis conditions were: CuKα target as the X-ray source, Ni filter, scanning range of 5°-70°, and step width of 0.02°.

[0032] The catalyst provided by this invention has a suitable density of strong acid centers, while the density of strong acid centers in the super-strong solid acid zirconium sulfate in the prior art is relatively high, generally higher than 2 μmol / m³. 2 The inventors of this invention discovered in their research that an excessively high density of strong acid centers is detrimental to the isomerization selectivity of the catalyst.

[0033] According to the present invention, a small amount of all-silica molecular sieve with MFI structure and alumina can modulate the distribution of strong acid centers in a solid acid catalyst, thereby giving the catalyst higher isomerization activity and selectivity. Furthermore, the synergistic effect of the noble metal component and zirconium sulfate in the active matrix, through the combined action of strong and weak acid centers, can improve the stability of the catalyst. This is because the all-silica molecular sieve with MFI structure possesses a special pore structure, is essentially non-acidic, and has excellent thermal stability, which helps optimize the distribution of strong acid centers in zirconium sulfate. This facilitates the efficient activation and conversion of light hydrocarbon molecules via a single-molecule pathway, promotes the diffusion of reactants and products, and effectively avoids secondary reactions.

[0034] According to some preferred embodiments of the present invention, the density of strong acid centers in the catalyst is 0.2-0.7 μmol / m³. 2 For example, the concentrations can be 0.2, 0.3, 0.4, 0.5, 0.6, or 0.7 μmol / m 2 Typical, but not limiting, values ​​or ranges between them. In the preferred embodiments described above, it is advantageous to further improve the activity and selectivity of n-butane isomerization.

[0035] In this invention, the density of the strong acid centers is the ratio of the amount of strong acid in the catalyst to its specific surface area. The method for testing the acid content in the catalyst includes using a Nicolet 6700 Fourier transform infrared spectrometer (4 cm⁻¹) manufactured by Thermo Fisher Scientific, USA. -1The sample was scanned 64 times. The sample was pressed into a self-supporting sheet with a diameter of 13 mm and then calcined at high temperature in a muffle furnace. After calcination, it was directly transferred to a desiccator for cooling at high temperature. After cooling to room temperature, it was placed in a self-made quartz infrared sample cell. It was first treated at 400℃ for 2 hours under normal pressure and flowing air, then cooled to 200℃ and vacuum purified for 4 hours. Finally, it was cooled to -190℃ with liquid nitrogen and saturated with purified CO probe molecules for 0.5 hours before desorption. The infrared spectrum of CO adsorption was obtained by subtracting the spectra before and after adsorption. The wavelength range was 2050-2250 cm⁻¹. -1 The spectrum at that location was processed to separate peaks, resulting in four absorption peaks with wavenumbers of 2186 cm⁻¹. -1 2167cm -1 2150cm -1 and 2125cm -1 The wave number is 2167 cm⁻¹. -1 The absorption peak at this point is the strong acid center, which is directly related to the catalyst performance, with a wavenumber of 2150 cm⁻¹. -1 The absorption peak at that point represents the weak acid center of the catalyst. The acid content N (in μmol / g) can be calculated according to equation (1).

[0036] N=A / (ρA0), Equation (1),

[0037] Where A is the integral area of ​​the absorption peak (unit: cm²). -1 ), where ρ is the mass of the catalyst support sheet per square centimeter (unit: g / cm²). 2 A0 is the molar extinction coefficient for a wavenumber of 2167 cm⁻¹. -1 and 2150cm -1 The spectral peak, A0 = 2.6 cm / μmol.

[0038] In this invention, the specific surface area of ​​the catalyst was characterized using the low-temperature nitrogen static capacity adsorption method (BET method). The instrument used was an ASAP2400 specific surface area analyzer manufactured by Micromeritics Instruments. The pretreatment conditions were: 250℃, 1.3 Pa, and treatment for 4 hours. The specific surface area (m²) was calculated using the BET formula. 2 / g).

[0039] According to some preferred embodiments of the present invention, the molar ratio of the strong acid to the weak acid in the catalyst is 4-8:1, for example, typical but not limiting molar ratios such as 4:1, 4.5:1, 5:1, 5.5:1, 6:1, 6.5:1, 7:1, 7.5:1, and 8:1. Preferably, the molar ratio of the strong acid to the weak acid in the catalyst is 4.5-6.8:1. In the above preferred embodiments, it is beneficial to further improve the stability of the catalyst.

[0040] According to some preferred embodiments of the present invention, the content of the active matrix is ​​99-99.95 wt%, preferably 99.5-99.9 wt%, based on the total mass of the catalyst; and the content of the active metal component is 0.05-1 wt%, preferably 0.1-0.5 wt%, based on elemental composition.

[0041] In this invention, a Lambda 35 UV-Vis spectrophotometer or ICP-AES is used to determine the content of the active metal component in the catalyst. When the catalyst contains only the active matrix and the active metal component, the sum of the contents of the active matrix and the active metal component is 100%.

[0042] According to some preferred embodiments of the present invention, the active metal component is selected from at least one of Pt, Pd, Ru and Rh, preferably Pt and / or Pd.

[0043] In this invention, the active metal component exists in an oxide and / or metallic state, and preferably, at least a portion of the active metal component exists in a metallic state.

[0044] According to some preferred embodiments of the present invention, the active matrix comprises zirconium, silicon, aluminum, and sulfur, respectively calculated as zirconium oxide, silicon oxide, aluminum oxide, and SO3. Based on the total mass of the active matrix, the content of zirconium oxide is 30-90 wt%, the content of silicon oxide is 1-35 wt%, the content of aluminum oxide is 5-50 wt%, and the content of SO3 is 1-10 wt%. Preferably, based on the total mass of the active matrix, the content of zirconium oxide is 50-80 wt%, the content of silicon oxide is 5-30 wt%, the content of aluminum oxide is 5-30 wt%, and the content of SO3 is 2-8 wt%. With the above preferred composition, it is beneficial to improve the thermal stability and specific surface area of ​​tetragonal zirconium oxide, thereby giving the catalyst a suitable distribution of strong acid centers and accessibility of active centers, further improving the catalytic activity of the catalyst.

[0045] According to some preferred embodiments of the present invention, the mass ratio of SO3 to ZrO2 is (0.02-0.12):1, preferably (0.03-0.08):1.

[0046] In this invention, the composition of the active matrix is ​​characterized and analyzed using an XRF-1800 wavelength dispersive X-ray fluorescence spectrometer. Based on the intensity of the elements present in the sample obtained by scanning and the pure substance sensitivity of these elements in the instrument, the content of each element in the sample is obtained through theoretical calculation and mathematical correction.

[0047] According to some preferred embodiments of the present invention, in the active matrix, the mass ratio of the acidic active component (calculated as ZrO2) to the mass ratio of the all-silica molecular sieve (calculated as SiO2) is 1:(0.1-1), preferably 1:(0.15-0.5).

[0048] In this invention, there is no particular limitation on the shape of the catalyst, and those skilled in the art can select it according to actual needs. For example, it can be in the form of strips, small spheres, flakes, particles, or microspheres to suit fixed bed, moving bed, or fluidized bed reactions.

[0049] According to some preferred embodiments of the present invention, the preparation method of the catalyst includes: (1) mixing an all-silica molecular sieve having an MFI structure and zirconium hydroxide to obtain a mixture;

[0050] (2) Contact the mixture with a solution containing sulfate ions;

[0051] (3) The product obtained in step (2), the alumina precursor and the optional adhesive solvent are mixed, and then shaped and calcined to obtain the active matrix.

[0052] (4) Load the active metal component onto the active matrix.

[0053] According to the present invention, the above preparation method enables the all-silica molecular sieve with MFI structure to be uniformly distributed in the catalyst without clogging the catalyst pores. Without introducing new acid centers, the density of strong acid centers in zirconium sulfate is reduced. The presence of strong acid sites with suitable density and uniform strength has high activity and selectivity when applied to the n-butane isomerization reaction.

[0054] The present invention offers a wide range of options for the number and structure of pores in the all-silica molecular sieve. Any all-silica molecular sieve with an MFI structure can be applied to the present invention.

[0055] In some preferred embodiments, the specific surface area of ​​the all-silica molecular sieve is 400-500 m². 2 / g, preferably 420-460m 2 / g. Under the above-mentioned preferred conditions, it is beneficial to further optimize the density of strong acid centers in zirconium sulfate, improve the uniformity of strong acid sites in the catalyst, and thus improve the isomerization activity.

[0056] According to some preferred embodiments of the present invention, the mass ratio of the zirconium hydroxide, based on the mass of ZrO2, to the all-silica molecular sieve, based on the mass of SiO2, is 1:(0.15-0.5).

[0057] In this invention, an acidic active component is formed by contacting the mixture with a sulfate-containing solution in step (2). This contact can be performed in a manner conventional in the art, for example, by impregnating the mixture with a sulfate-containing solution.

[0058] The present invention does not impose any particular limitation on the specific operating conditions of the contact, as long as the catalyst composition range described above can be met. Those skilled in the art can make selections according to actual needs.

[0059] According to some preferred embodiments of the present invention, the contact temperature is 20-80°C, preferably 25-60°C; the contact time is 1-10h, preferably 2-5h.

[0060] The present invention has a wide range of choices for the specific types of solutions containing sulfate ions. Preferably, the solutions containing sulfate ions are selected from aqueous solutions of at least one of sulfuric acid, ammonium sulfate, and ammonium bisulfate.

[0061] Preferably, the sulfate concentration in the sulfate-containing solution is 1-10 wt%, more preferably 2-8 wt%. Using the above-mentioned preferred embodiments is beneficial for obtaining suitable SO3 content and strong acid center density.

[0062] The present invention does not impose a particular limitation on the amount of the sulfate-containing solution used, as long as it meets the SO3 content range requirement of the catalyst described in the first aspect. Those skilled in the art can select the appropriate amount based on actual needs. Preferably, the mass ratio of the sulfate-containing solution to the mixture is 0.3-5:1, more preferably 0.5-3:1.

[0063] In this invention, step (2) includes, optionally, a drying and grinding step after the contact. The drying temperature can be 50-150°C, and the drying time can be 3-100 hours. The grinding is used to grind the dried solid into a powder of 100-300 mesh, which, in the preferred embodiment described above, is beneficial for improving the crushing strength of the catalyst.

[0064] In this invention, the alumina precursor refers to a substance that can be calcined to obtain alumina, as is well known to those skilled in the art. Preferably, the alumina precursor is boehmite and / or gibbsite, with boehmite being more preferred. In the above-mentioned preferred cases, it is beneficial to improve the thermal stability and crushing strength of the catalyst.

[0065] In this invention, the molding process described in step (3) can be carried out using conventional methods and conditions in the art. This invention does not impose any particular limitation on this process. The molding method can be selected according to actual application needs, for example, it can be selected from any one of extrusion molding, granulation molding, ball forming, and spray drying to form balls, with extrusion molding being preferred. Under the above preferred conditions, it is more suitable for fixed-bed reactors.

[0066] According to some preferred embodiments of the present invention, the ratio of the total mass of the adhesive solvent to the product obtained in step (2) and the alumina precursor is 0.3-1:1, preferably 0.4-0.8:1.

[0067] According to some preferred embodiments of the present invention, the colloidal solvent is an aqueous solution of an acid, preferably an aqueous solution selected from at least one of nitric acid, acetic acid, citric acid, oxalic acid and formic acid.

[0068] Preferably, the concentration of acid in the adhesive solvent is 2-10 wt%.

[0069] According to some preferred embodiments of the present invention, in step (3), the calcination temperature is 600-850℃, preferably 650-850℃, and the calcination time is 1-20h, preferably 3-12h. Under the above-mentioned preferred calcination temperature conditions, it is beneficial to form strong acid centers with suitable density, which have high activity and selectivity in the n-butane isomerization reaction, and good stability.

[0070] In this invention, a drying process may be included before the roasting in step (3). Preferably, the drying temperature is 80-140℃, more preferably 100-130℃, and the drying time is 5-30h, more preferably 8-24h.

[0071] In this invention, the active metal component can be loaded onto the active matrix using any conventional method in the art. Preferably, the method for loading the active metal component onto the active matrix includes: impregnating the active matrix with a solution of a soluble compound containing the active metal, followed by drying and calcination.

[0072] The present invention allows for a wide range of selection for soluble compounds of the active metal, which can be inorganic or organic salts of the active metal. When the active metal is Pt, the soluble compound of Pt is preferably at least one selected from chloroplatinic acid, platinum tetrachloride, ammonium chloroplatinate, and dinitrosodiamine platinum. When the active metal is Pd, the soluble compound of Pd can be, for example, palladium chloride.

[0073] In this invention, the solution containing the soluble compound of the active metal is a solution obtained by dissolving the soluble compound of the active metal in a solvent. This invention does not have specific limitations on the type of solvent, as long as it can dissolve the soluble compound of the active metal; for example, it can be water.

[0074] According to some preferred embodiments of the present invention, in order to more uniformly load the soluble compound containing the active metal onto the active matrix and further improve the stability of the catalyst, the solution also contains a competing adsorbent. The competing adsorbent is preferably at least one of sulfuric acid, nitric acid, and acetic acid, more preferably nitric acid.

[0075] Preferably, the mass ratio of the competing adsorbent to the soluble compound of the active metal is 1-20:1, more preferably 2-10:1. Using the above-mentioned preferred embodiments facilitates the uniform dispersion of the soluble compound containing the active metal in the active matrix, while effectively preventing the competing adsorbent from damaging the structure of the active matrix, thereby further improving the activity and stability of the catalyst.

[0076] The present invention does not impose a particular limitation on the amount of the solution containing the soluble compound of the active metal, as long as the amount of the active metal component meets the range described in the first aspect. Preferably, the mass ratio of the solution containing the soluble compound of the active metal to the active matrix is ​​0.4-1:1, more preferably 0.5-0.8:1.

[0077] According to the present invention, the impregnated product is dried and calcined. The present invention does not have particular requirements for the specific drying conditions, and conventional drying conditions in the art can be used. Preferably, the drying temperature is 80-140°C, more preferably 100-130°C, and the drying time is 5-30 hours, more preferably 8-24 hours.

[0078] According to the present invention, preferably, the calcination temperature is 450-650℃, more preferably 480-600℃, and the calcination time is 1-10h, more preferably 3-5h.

[0079] According to some preferred embodiments of the present invention, the preparation method further includes: reducing the product obtained in step (4) in the presence of hydrogen.

[0080] According to some preferred embodiments of the present invention, the conditions for the reduction treatment include: a temperature of 200-300°C, preferably 220-260°C, a time of 1-10 h, preferably 3-5 h; and a gas-agent volume ratio of 300-1500, preferably 500-1200.

[0081] In a preferred embodiment, the isomerization reaction method provided by the present invention can efficiently convert n-butane into isobutane under reaction conditions of lower temperature, lower hydrogen-to-oil ratio, and higher space velocity.

[0082] According to some preferred embodiments of the present invention, the isomerization reaction conditions include: a reaction temperature of 160-240°C, preferably 170-225°C; a pressure of 1-4 MPa, preferably 1.5-3.5 MPa; and a mass hourly space velocity (HHSV) of 0.5-10 h⁻¹ for the n-butane feedstock. -1 Preferably 1-5h -1 The hydrogen / hydrocarbon molar ratio is 0.02-0.3, preferably 0.03-0.2. Adopting the above-mentioned preferred embodiment significantly reduces hydrogen consumption, thereby reducing energy consumption and raw material costs, and also simplifies post-processing and separation, resulting in good reaction economics. In contrast, existing technologies use SO4... 2- When using a catalyst with / ZrO2 as the acid center for isomerization reactions, the hydrogen-to-hydrocarbon molar ratio is usually not less than 1.

[0083] The present invention does not particularly limit the source of the n-butane feedstock, which includes n-butane and may also include impurity components. Preferably, the n-butane content in the n-butane feedstock is not less than 80 wt%, more preferably not less than 90 wt%, and more preferably 95-100 wt%.

[0084] Preferably, the impurity component is selected from at least one of C1-C3 alkanes, isobutane, C5+ alkanes, water, and sulfur.

[0085] Preferably, the content of C1-C3 alkanes in the n-butane feedstock is less than 1 wt%, and more preferably less than 0.5 wt%.

[0086] Preferably, the content of C5+ alkanes in the n-butane feedstock is less than 1.5 wt%, and more preferably less than 1 wt%.

[0087] Preferably, the isobutane content in the n-butane feedstock is less than 2 wt%, and more preferably less than 1 wt%. In this invention, the hydrocarbon content in the n-butane feedstock is obtained by gas chromatography, and then normalized to obtain the content of each component.

[0088] Preferably, the water content in the n-butane feedstock is less than 5 ppmw, and more preferably less than 3 ppmw.

[0089] Preferably, the sulfur content in the n-butane feedstock is less than 10 ppmw, and more preferably less than 5 ppmw.

[0090] According to some preferred embodiments of the present invention, the method further includes: preheating the n-butane feedstock and hydrogen to the isomerization reaction temperature before contacting them with the catalyst. In this invention, the n-butane feedstock and hydrogen can be preheated separately, or they can be mixed and preheated together. From an economic perspective, it is preferable to mix the n-butane feedstock and hydrogen and preheat them together.

[0091] Preferably, the preheating includes primary preheating and secondary preheating. The primary preheating method includes exchanging heat between the product of the isomerization reaction and the n-butane feedstock and / or hydrogen. The primary preheating can be carried out using conventional heat exchange devices in the art, such as shell-and-tube heat exchangers. The secondary preheating can be carried out using a gas-fired furnace, an electric heater, or a medium-pressure steam heater. Those skilled in the art can select the temperature of the secondary preheating according to the actual operating conditions, as long as the feedstock after primary preheating can be heated to the reaction temperature.

[0092] It is understandable that during the initial start-up phase of the reaction, the feedstock can be directly heated to the isomerization reaction temperature via secondary preheating. During continuous reaction operation, primary preheating is used to exchange heat between the n-butane feedstock and hydrogen and the isomerization reaction products, followed by secondary preheating to further heat the n-butane feedstock and hydrogen to the isomerization reaction temperature. Adopting this preferred implementation method helps to further reduce reaction energy consumption and process costs.

[0093] According to the present invention, preferably, the method further includes: separating and purifying the contacted product, wherein the separated n-butane is used to provide at least a portion of the n-butane feedstock. The separation and purification can be carried out using any method known in the art, as long as isobutane can be separated from the product. Preferably, the separation and purification includes: separating the contacted product by distillation to obtain light and heavy components, wherein the light components include C1-C3 hydrocarbons and H2, and the heavy components include C4 hydrocarbons. + Hydrocarbons; then isobutane products are separated from the heavy components by an isobutane removal column.

[0094] A second aspect of the present invention provides a system for producing isobutane by isomerization of n-butane, the system comprising: a feeding unit, a preheating device, a reactor 4, a light component separation device 5, and an isobutane removal tower 6;

[0095] The feeding unit is connected to the feed inlet of the preheating device, and n-butane raw material and hydrogen are fed into the preheating device for preheating.

[0096] The outlet of the preheating device is connected to the feed inlet of the reactor 4, and the preheated raw material is fed into the reactor 4 to contact the catalyst.

[0097] The catalyst includes an active matrix and an active metal component supported on the active matrix;

[0098] The active matrix includes the acidic active component SO4. 2- / ZrO2, an all-silica molecular sieve with an MFI structure, and alumina; the active metal component is selected from at least one noble metal element;

[0099] In the catalyst, the density of strong acid centers is 0.1-1 μmol / m³. 2 ;

[0100] The light component separation device 5 is used to separate the reaction products from reactor 4, recover the obtained light components, and send the obtained heavy components to the isobutane removal tower 6; wherein, the light components include C1-C3 hydrocarbons and H2, and the heavy components include C4 hydrocarbons. + hydrocarbon;

[0101] The isobutane removal tower 6 is used to separate isobutane products and n-butane, and the separated n-butane is returned to the feed unit.

[0102] According to some preferred embodiments of the present invention, the feeding unit includes a n-butane feedstock supply device and a hydrogen supply device.

[0103] Preferably, the n-butane feedstock supply device includes a feed pump 1, through which the n-butane feedstock is transported to a preheating device for preheating.

[0104] Preferably, the preheating device includes a heat exchanger 2 and a heater 3.

[0105] The heat exchanger 2 is used to exchange heat between the reaction product from the reactor 4 and the n-butane feedstock and hydrogen from the feed unit. The reaction product after heat exchange is sent to the light component separation device 5, and the n-butane feedstock and hydrogen are sent to the heater 3.

[0106] The heater 3 is used to heat the n-butane feedstock and hydrogen from the heat exchanger 2 to the isomerization reaction temperature, and then feed them into the reactor 4.

[0107] The present invention will be described in detail below through embodiments.

[0108] In the following examples, the bulk structure of the catalyst was analyzed and detected using a Rigaku D / MAX-3A XRD instrument. The analysis conditions were: CuKα target as the X-ray source, Ni filter, scanning range of 5°-70°, and step width of 0.02°.

[0109] The Pt content of the catalyst was determined using a Lambda 35 UV-Vis spectrophotometer. The sample was first dissolved in hydrochloric acid and then complexed with stannous chloride. The Pt content was then determined by colorimetry.

[0110] The Pd content of the catalyst was determined by ICP-AES. The sample was first nitrated with aqua regia, then diluted and brought to a constant volume. The Pd content was determined by atomic absorption spectrometry and compared with a standard curve.

[0111] The composition of the active matrix was characterized and analyzed using an XRF-1800 wavelength dispersive X-ray fluorescence spectrometer. Based on the intensity of the elements present in the sample obtained from the scanning and the pure substance sensitivity of these elements in the instrument, the content of each element in the sample was obtained through theoretical calculation and mathematical correction.

[0112] The zirconium hydroxide powder used was purchased from Changling Catalyst Company, with a zirconium oxide content of 78.5% by weight.

[0113] The all-silica MFI molecular sieve Si-1 used was purchased from Changling Catalyst Co., Ltd., with a silica content of 99.7% by mass and a specific surface area of ​​444.6 m². 2 / g, XRD characterization as follows Figure 1 As shown.

[0114] The boehmite powder was purchased from Sasol GmbH, Germany, with an alumina content of 75% by mass.

[0115] The following preparation examples illustrate the preparation of the catalyst in this invention.

[0116] Preparation Example 1

[0117] (1) 38.2 g of zirconium hydroxide powder and 4.4 g of all-silica MFI molecular sieve Si-1 were mixed evenly, and 48.0 g of 5% by mass sulfuric acid aqueous solution was added. The mixture was impregnated at 40 °C for 4 h, and the impregnated solid was dried at 60 °C for 12 h and then at 120 °C for 12 h. The dried solid was ground into fine powder, passed through a 100-300 mesh sieve, and mixed evenly with 10.6 g of pseudoboehmite powder. A 5.0% by mass nitric acid aqueous solution was added for gelation. The ratio of the nitric acid aqueous solution to the total mass of the fine powder and the alumina precursor was 0.6:1. After kneading evenly, the mixture was extruded into strips. The wet strips were dried at 120 °C for 10 h and calcined at 680 °C for 4 h to obtain the active matrix SSiZA-1. The XRD characterization results of the active matrix SSiZA-1 are shown in […]. Figure 2 ,Depend on Figure 2 Characteristic peaks of all-silica MFI molecular sieves can be seen in the image, and the composition is shown in Table 1.

[0118] (2) Take 10.0g of active matrix SSiZA-1 and add it to 5.0g of aqueous solution containing 0.0266g of chloroplatinic acid and 0.1g of nitric acid. Impregnate at 25℃ for 3h. Dry the impregnated solid at 120℃ for 10h and calcine at 550℃ for 4h to obtain catalyst CAT-1. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0119] Preparation Example 2

[0120] (1) Take 38.2g of zirconium hydroxide powder and 7.8g of all-silica MFI molecular sieve, mix them evenly, add 48.0g of 5% sulfuric acid aqueous solution, impregnate at 40℃ for 4h, and dry the impregnated solid at 60℃ for 12h and 120℃ for 12h. Grind the dried solid into fine powder, pass it through a 100-300 mesh sieve, mix it evenly with 10.6g of pseudoboehmite powder, add 5.0% nitric acid aqueous solution for gelation, the ratio of the nitric acid aqueous solution to the total mass of the fine powder and the alumina precursor is 0.5:1, knead evenly, extrude into strips, dry the wet strips at 120℃ for 10h and calcine at 680℃ for 4h to obtain the active matrix SSiZA-2. The XRD characterization results of the active matrix SSiZA-2 are shown in the figure. Figure 2 The composition is shown in Table 1.

[0121] (2) Take 10.0g of active matrix SSiZA-2 and add it to 5.0g of aqueous solution containing 0.0266g of chloroplatinic acid and 0.1g of nitric acid. Impregnate at 25℃ for 3h. Dry the impregnated solid at 120℃ for 10h and calcine at 550℃ for 4h to obtain catalyst CAT-2. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0122] Preparation Example 3

[0123] (1) 38.2 g of zirconium hydroxide powder and 14.3 g of all-silica MFI molecular sieve Si-1 were mixed evenly, and 48.0 g of 5% by mass sulfuric acid aqueous solution was added. The mixture was impregnated at 40 °C for 4 h, and the impregnated solid was dried at 60 °C for 12 h and then at 120 °C for 12 h. The dried solid was ground into fine powder, passed through a 100-300 mesh sieve, and mixed evenly with 3.4 g of pseudoboehmite powder. A 5.0% by mass nitric acid aqueous solution was added for gelation. The ratio of the nitric acid aqueous solution to the total mass of the fine powder and the alumina precursor was 0.7:1. After kneading evenly, the mixture was extruded into strips. The wet strips were dried at 120 °C for 10 h and calcined at 680 °C for 4 h to obtain the active matrix SSiZA-3. The XRD characterization results of the active matrix SSiZA-3 are shown in […]. Figure 2 ,Depend on Figure 2 Characteristic peaks of all-silica MFI molecular sieves can be seen in the image, and the composition is shown in Table 1.

[0124] (2) Take 10.0g of active matrix SSiZA-1 and add it to 5.0g of aqueous solution containing 0.0266g of chloroplatinic acid and 0.1g of nitric acid. Impregnate at 25℃ for 3h. Dry the impregnated solid at 120℃ for 10h and calcine at 550℃ for 4h to obtain catalyst CAT-3. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0125] Preparation Example 4

[0126] Following the method of Preparation Example 1, except that 10g of active matrix SSiZA-1 was added to 5.0g of an aqueous solution containing 0.0416g of palladium chloride and 0.1g of nitric acid, and impregnated at 25°C for 3h. The impregnated solid was then dried at 120°C for 10h and calcined at 550°C for 4h to obtain catalyst CAT-4. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0127] Preparation Example 5

[0128] (1) Take 38.2g of zirconium hydroxide powder, add 48.0g of sulfuric acid aqueous solution with a concentration of 5% by mass, soak at 40℃ for 4h, and dry the soaked solid at 60℃ for 12h and 120℃ for 12h.

[0129] The dried solid was ground into a fine powder and passed through a 100-300 mesh sieve. 4.4g of all-silica MFI molecular sieve and 10.6g of pseudoboehmite powder were added and mixed evenly. A 5.0% by mass nitric acid aqueous solution was added to dissolve the powder. The mass ratio of the nitric acid aqueous solution to the total mass of the fine powder, MFI molecular sieve and alumina precursor was 0.6:1. After kneading evenly, the mixture was extruded into strips. The wet strips were dried at 120℃ for 10h and calcined at 680℃ for 4h to obtain the active matrix SSiZA-4. The composition is shown in Table 1.

[0130] (2) Take 10.0g of active matrix SSiZA-4 and add it to 5.0g of aqueous solution containing 0.0266g of chloroplatinic acid and 0.1g of nitric acid. Impregnate at 25℃ for 3h. Dry the impregnated solid at 120℃ for 10h and calcine at 550℃ for 4h to obtain catalyst CAT-5. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0131] Preparation Example 6

[0132] The method of preparation example 2 is the same, except that the amount of chloroplatinic acid used in step (2) is 0.0106 g.

[0133] Catalyst CAT-6 was prepared. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0134] Preparation Example 7

[0135] The method is the same as in Preparation Example 2, except that nitric acid was not introduced into the impregnation solution in step (2) as a competing adsorbent.

[0136] Catalyst CAT-7 was prepared. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0137] Comparative Preparation Example 1

[0138] (1) Take 38.2g of zirconium hydroxide powder, add 48.0g of 5% sulfuric acid aqueous solution, and impregnate at 40℃ for 4h. Dry the impregnated solid at 60℃ for 12h and then at 120℃ for 12h. Grind the dried solid into a fine powder, pass it through a 100-300 mesh sieve, mix it evenly with 16.6g of pseudoboehmite powder, and add 5.0% nitric acid aqueous solution for gelation. The ratio of the nitric acid aqueous solution to the total mass of the fine powder and alumina precursor is 0.6:1. After kneading evenly, extrude the mixture into strips, dry the wet strips at 120℃ for 10h, and calcine at 680℃ for 4h to obtain the active matrix DSSiZA-1. The XRD characterization results of the active matrix DSSiZA-1 are shown below. Figure 2 As can be seen, catalyst DA1 does not contain the characteristic peaks of Si-1 in the all-silica MFI molecular sieve. The composition is shown in Table 1.

[0139] (2) Take 10.0g of the above active matrix DSSiZA-1 and add it to 5.0g of an aqueous solution containing 0.0266g of chloroplatinic acid and 0.1g of nitric acid. Impregnate at 25℃ for 3h. Dry the impregnated solid at 120℃ for 10h and calcine at 550℃ for 4h to obtain catalyst DCAT-1. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0140] Comparative Preparation Example 2

[0141] (1) Take 38.2g of zirconium hydroxide powder and 10.2g of all-silica MFI molecular sieve, mix them evenly, add 48.0g of 5% by mass sulfuric acid aqueous solution, and impregnate at 40℃ for 4h. Dry the impregnated solid at 60℃ for 12h and 120℃ for 12h. Grind the dried solid into fine powder, pass it through a 100-300 mesh sieve, add 5.0% by mass nitric acid aqueous solution to dissolve it, the mass ratio of nitric acid aqueous solution to the fine powder is 0.6:1, knead evenly, and then extrude it into strips. Dry the wet strips at 120℃ for 10h and calcine at 680℃ for 4h to obtain the active matrix DSSiZA-2. The composition of the active matrix DSSiZA-2 is shown in Table 1.

[0142] (2) Take 10.0g of active matrix DSSiZA-2 and add it to 5.0g of aqueous solution containing 0.0266g of chloroplatinic acid and 0.1g of nitric acid. Impregnate at 25℃ for 3h. Dry the impregnated solid at 120℃ for 10h and calcine at 550℃ for 4h to obtain catalyst DCAT-2. The composition and physicochemical properties of the catalyst are shown in Table 2.

[0143] Comparative preparation example 3

[0144] The method was the same as in Example 2, except that an equal mass of ZSM-5 molecular sieve (denoted as Si-2, manufactured by Changling Catalyst Co., Ltd., with a silica / alumina molar ratio of 65) was used. XRD characterization is shown in [reference needed]. Figure 1 Replace the all-silica MFI molecular sieve.

[0145] The prepared active matrix is ​​designated DSSiZA-3. The composition of the active matrix DSSiZA-3 is shown in Table 1. The catalyst DCAT-3 was prepared, and its composition and physicochemical properties are shown in Table 2.

[0146] Table 1

[0147]

[0148] Table 2

[0149]

[0150] The following examples illustrate the method for producing isobutane by isomerization of n-butane in this invention.

[0151] The n-butane feedstock used in the following examples includes: 0.02% by mass propane, 0.66% by mass isobutane, 98.72% by mass n-butane, and 0.60% by mass pentane. The water content is 0.5 ppmw.

[0152] The following embodiments employ the following methods: Figure 3 The isomerization reaction is carried out in the system shown. Figure 3 As shown, the reaction system includes: a feeding unit, a preheating device, a reactor 4, a light component separation device 5, and an isobutane removal tower 6; the feeding unit includes a n-butane feedstock supply device and a hydrogen supply device, the n-butane feedstock supply device including a feed pump 1, and the preheating device including a heat exchanger 2 and a heater 3. The reactor 4 is loaded with catalyst, and the loading and reaction conditions are shown in Tables 3 and 4.

[0153] First, hydrogen gas is introduced to reduce the catalyst packed in reactor 4. The reduction conditions are: 260℃, gauge pressure 0.1MPa, gas-to-catalyst volume ratio 800, and reduction for 3 hours.

[0154] Then, the n-butane feedstock is fed into the feed line via feed pump 1, mixed with hydrogen, and then heated to the reaction temperature via heat exchanger 2 and heater 3. It is then fed into reactor 4 to contact the catalyst for isomerization. The resulting reaction product is fed into heat exchanger 2 to exchange heat with the mixture of isobutane and hydrogen. The heat-exchanged reaction product is then fed into light component separation unit 5. Light components, consisting of C1-C3 hydrocarbons and a small amount of H2, are separated at the top of the unit; C4 hydrocarbons are separated at the bottom. + The hydrocarbons are fed into isobutane removal column 6 for separation. Isobutane product is separated at the top of the column, and a small amount of C5 is separated at the bottom. +The heavy components are extracted via a side stream, and n-butane is recycled back to the feed unit. Product sampling and analysis method: A bypass with a sampling port is installed on the main outlet line of reactor 4. During sampling, the sampling cylinder is connected to the sampling port via a quick connector. Then, the valves before and after the sampling cylinder are opened, and the cylinder is purged with the product. After purging, the outlet valve of the sampling cylinder is closed. After a certain amount of the material to be analyzed is introduced, the inlet valve is closed, and the quick connector is disconnected. Sampling is then complete. The sample is sent to the laboratory for analysis of the reactor outlet product composition. The analysis results are listed in Tables 3 and 4.

[0155] Wherein, n-butane conversion rate (%) = ((mass of n-butane in feed - mass of n-butane in product) / mass of n-butane in feed) × 100%;

[0156] Isobutane selectivity (%) = ((mass of isobutane in product - mass of isobutane in feed) / (mass of n-butane in feed - mass of n-butane in product)) × 100%;

[0157] Isobutane yield (%) = ((mass of isobutane in product - mass of isobutane in feed) / mass of n-butane in feed) × 100%.

[0158] Table 3

[0159]

[0160] Table 4

[0161]

[0162] The results in Tables 3 and 4 show that the method for producing isobutane by isomerization of n-butane provided by this invention can efficiently produce isobutane from n-butane, while exhibiting high feed conversion and isobutane selectivity. A comparison of the results after 10 hours and 100 hours of reaction demonstrates that the method provided by this invention has high stability and can achieve long-term stable operation. Furthermore, in preferred embodiments, the method provided by this invention can balance high space velocity and conversion, achieving high product yield under mild reaction conditions, at low reaction temperatures and hydrogen-to-hydrogen ratios.

[0163] The preferred 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 combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for producing isobutane by isomerization of n-butane, characterized in that, The method includes: contacting n-butane feedstock with a catalyst under hydrogen-exposed conditions and under isomerization reaction conditions; The catalyst includes an active matrix and an active metal component supported on the active matrix; The active matrix includes the acidic active component SO4. 2- / ZrO2, an all-silica molecular sieve with an MFI structure, and alumina; the active metal component is selected from at least one noble metal element; In the catalyst, the density of strong acid centers is 0.1-1 μmol / m³. 2 .

2. The method according to claim 1, wherein, The density of strong acid centers is 0.2-0.7 μmol / m³. 2 .

3. The method according to claim 1, wherein, In the catalyst, the molar ratio of the strong acid to the weak acid is 4-8:

1.

4. The method according to claim 1, wherein, Based on the total mass of the catalyst, the content of the active matrix is ​​99-99.95 wt%; and based on elements, the content of the active metal component is 0.05-1 wt%.

5. The method according to claim 4, wherein, Based on the total mass of the catalyst, the content of the active matrix is ​​99.5-99.9 wt%; and based on elements, the content of the active metal component is 0.1-0.5 wt%.

6. The method according to claim 1, wherein, The active metal component is selected from Pt and / or Pd.

7. The method according to claim 1, wherein, The active matrix includes zirconium, silicon, aluminum and sulfur, respectively calculated as zirconium oxide, silicon oxide, aluminum oxide and SO3. Based on the total mass of the active matrix, the content of zirconium oxide is 30-90 wt%, the content of silicon oxide is 1-35 wt%, the content of aluminum oxide is 5-50 wt% and the content of SO3 is 1-10 wt%.

8. The method according to claim 7, wherein, Based on the total mass of the active matrix, the content of zirconium oxide is 50-80 wt%, the content of silicon oxide is 5-30 wt%, the content of aluminum oxide is 5-30 wt%, and the content of SO3 is 2-8 wt%.

9. The method according to claim 7, wherein, The mass ratio of SO3 to ZrO2 is (0.02-0.12):

1.

10. The method according to claim 9, wherein, The mass ratio of SO3 to ZrO2 is (0.03-0.08):

1.

11. The method according to claim 1, wherein, In the active matrix, the mass ratio of the acidic active component (calculated as ZrO2) to the mass ratio of the all-silica molecular sieve (calculated as SiO2) is 1:(0.1-1).

12. The method according to claim 11, wherein, In the active matrix, the mass ratio of the acidic active component (calculated as ZrO2) to the mass ratio of the all-silica molecular sieve (calculated as SiO2) is 1:(0.15-0.5).

13. The method according to claim 1, wherein, The isomerization reaction conditions include: a reaction temperature of 160-240℃; a pressure of 1-4 MPa; and a mass hourly space velocity (HHSV) of 0.5-10 h⁻¹ for the n-butane feedstock. -1 The hydrogen / hydrocarbon molar ratio is 0.02-0.

3.

14. The method according to claim 13, wherein, The isomerization reaction conditions include: a reaction temperature of 170-225℃; a pressure of 1.5-3.5 MPa; and a mass hourly space velocity (HHSV) of 1-5 h⁻¹ for the n-butane feedstock. -1 The hydrogen / hydrocarbon molar ratio is 0.03-0.

2.

15. The method according to claim 14, wherein, The isomerization reaction conditions include: a mass hourly space velocity (MSV) of 1.2-4 h⁻¹ for the n-butane feedstock. -1 .

16. The method according to claim 1, wherein, The n-butane feedstock includes n-butane and optional impurity components.

17. The method according to claim 16, wherein, The n-butane content in the n-butane raw material is not less than 80 wt%.

18. The method according to claim 17, wherein, The n-butane content in the n-butane raw material is not less than 90 wt%.

19. The method according to claim 18, wherein, The n-butane raw material contains 95-100 wt% n-butane.

20. The method of claim 16, wherein, The impurity component is selected from at least one of C1-C3 alkanes, isobutane, C5+ alkanes, water, and sulfur.

21. The method according to claim 20, wherein, The content of C1-C3 alkanes in the n-butane feedstock is less than 1 wt%.

22. The method according to claim 21, wherein, The content of C1-C3 alkanes in the n-butane feedstock is less than 0.5 wt%.

23. The method of claim 20, wherein, The content of C5+ alkanes in the n-butane feedstock is less than 1.5 wt%.

24. The method according to claim 23, wherein, The content of C5+ alkanes in the n-butane feedstock is less than 1 wt%.

25. The method according to claim 20, wherein, The isobutane content in the n-butane feedstock is less than 2 wt%.

26. The method according to claim 25, wherein, The isobutane content in the n-butane feedstock is less than 1 wt%.

27. The method of claim 20, wherein, The water content in the n-butane feedstock is less than 5 ppmw.

28. The method according to claim 27, wherein, The water content in the n-butane feedstock is less than 3 ppmw.

29. The method according to claim 20, wherein, The sulfur content in the n-butane feedstock is less than 10 ppmw.

30. The method according to claim 29, wherein, The sulfur content in the n-butane feedstock is less than 5 ppmw.

31. The method according to claim 1, wherein, The method further includes: preheating the n-butane feedstock and hydrogen to the isomerization reaction temperature before contacting them with the catalyst.

32. The method according to claim 31, wherein, The preheating includes primary preheating and secondary preheating. The primary preheating method includes exchanging heat between the product of the isomerization reaction and the n-butane feedstock and / or hydrogen.

33. The method according to claim 1, wherein, The method further includes: separating and purifying the product of the contact, wherein the separated n-butane is used to provide at least a portion of the n-butane raw material.

34. A system for producing isobutane by isomerization of n-butane, characterized in that, The system includes: a feeding unit, a preheating device, a reactor (4), a light component separation device (5), and an isobutane removal tower (6). The feeding unit is connected to the feed inlet of the preheating device, and n-butane raw material and hydrogen are fed into the preheating device for preheating. The outlet of the preheating device is connected to the feed inlet of the reactor (4), and the preheated raw material is fed into the reactor (4) to contact the catalyst. The catalyst includes an active matrix and an active metal component supported on the active matrix; The active matrix includes the acidic active component SO4. 2- / ZrO2, an all-silica molecular sieve with an MFI structure, and alumina; the active metal component is selected from at least one noble metal element; In the catalyst, the density of strong acid centers is 0.1-1 μmol / m³. 2 ; The light component separation device (5) is used to separate the reaction products from the reactor (4), recover the obtained light components, and send the obtained heavy components to the isobutane removal tower (6); wherein, the light components include C1-C3 hydrocarbons and H2, and the heavy components include C4 hydrocarbons. + hydrocarbon; The isobutane removal tower (6) is used to separate isobutane products and n-butane, and the separated n-butane is returned to the feed unit.

35. The system according to claim 34, wherein, The feeding unit includes a n-butane feedstock supply device and a hydrogen supply device.

36. The system according to claim 35, wherein, The n-butane feedstock supply device includes a feed pump (1), through which the n-butane feedstock is transported to a preheating device for preheating.

37. The system according to claim 36, wherein, The preheating device includes a heat exchanger (2) and a heater (3). The heat exchanger (2) is used to exchange heat between the reaction product from the reactor (4) and the n-butane feedstock and hydrogen from the feed unit. The reaction product after heat exchange is sent to the light component separation device (5), and the n-butane feedstock and hydrogen are sent to the heater (3). The heater (3) is used to heat the n-butane feedstock and hydrogen from the heat exchanger (2) to the isomerization reaction temperature and then feed them into the reactor (4).

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