CN1762928A - Combined process of hydration + membrane + cryogenic separation for separation of ethylene cracking gas - Google Patents

Abstract

The present invention proposes one method of separating ethylene cracking gas and is one combined separation process including hydrating separation, cryogenic separation and membrane separation for separating hydrogen, methane and C2 component in the cracked gas. The combined separation process includes the first contact of the cracked gas with water containing liquid in hydrating separation unit for C2 component to form hydrate prior and for the cracked gas to be separated into methane + hydrogen flow and methane + C2 flow; dewatering hydrogen flow and methane + C2 flow, cooling and separating in cryogenic methane eliminating tower into methane and C2 component; dewatering methane + hydrogen flow, separating in membrane separator into methane and hydrogen, and pre-cooling and expanding methane to provide the methane eliminating tower with cold. The said process has low power consumption.

Description

Combined process of hydration + membrane + cryogenic separation for separation of ethylene cracking gas

technical field

The invention relates to a separation method for ethylene cracking gas, in particular to a combined process method for separating ethylene cracking gas by combining a hydration separation process, a cryogenic separation process and a membrane separation process, and belongs to the technical field of chemical industry.

Background technique

As a pillar industry of the petrochemical industry, the ethylene industry has always played an important role in the national economy.

With the development and requirements of various aspects, most of the existing ethylene plants are under the pressure of capacity expansion and efficiency enhancement. The most complicated part of the ethylene cracking and separation process is the cryogenic demethanization section, especially the cryogenic demethanizer, which is commonly used at present, is the bottleneck of the entire device's capacity expansion and efficiency enhancement.

In the separation process of cryogenic demethanization, there are two key links, one is the demethanizer, and the other is the cold box. Since the demethanizer requires the lowest temperature, it is the place where the cooling capacity is consumed the most, and the process operation is complicated. For the separation of various small molecule gases, the conventional distillation method needs to be realized at a very low temperature, such as the separation of methane and hydrogen. The separation needs to be carried out at about -160°C, and the separation of methane and ethane needs to be carried out at about -110°C, resulting in the largest proportion of cooling energy consumption in the raw material precooling and demethanizer system in the entire separation process. Some data suggest that the cooling capacity of the demethanizer system accounts for 42% of the total consumption of the separation process. Because the operating temperature of the cold box is very low (-160°C), the material requirements are very strict, the manufacturing cost is high, and it may cause an explosion due to the formation of blue ice. Therefore, the cold box and the demethanizer have become the bottleneck of the expansion and transformation of existing equipment, and it is also the reason for the high investment in the construction of new ethylene production plants. Therefore, seeking a more energy-saving and efficient process for separating hydrogen, methane and C2 components (ethylene and ethane) has important practical significance for reducing the energy consumption of separating ethylene cracking gas process in the ethylene industry and improving economic benefits.

Hydrate is a cage-type substance formed by water and small molecular gases (CH ₄ , C ₂ H ₆ , CO ₂ , N _{2 ,} etc.) Cage, the gas molecules are in the cage to maintain the stability of the cage). Since different gases have different degrees of difficulty in forming hydrates, the gas components that are easy to form hydrates can be preferentially entered into the hydrate phase through the method of forming hydrates to realize the separation of gas mixtures. As a well-known common sense, in general, only small molecular gases can form hydrates, so the hydrate method is usually only suitable for the separation of low-boiling point gas mixtures, and the biggest advantage of the hydrate method is that it can achieve low-boiling point gas mixtures above 0 °C. It is more effective to separate the mixture with not very low boiling point by conventional rectification.

The current research and application of hydrate technology is more on the storage and transportation of gas. How to combine hydrate technology with other operations such as gas separation has not been reported yet.

Contents of the invention

The present invention proposes a process for separating ethylene cracking gas which is different from the traditional technology. It combines hydration separation, membrane separation and cryogenic separation of methane. While obtaining high-purity C2 components, it can save the step-by-step process in the traditional process. Stage condensing section and cold box, and reduce the cooling load at the top of the demethanizer, thereby reducing the production energy consumption and cost input of the ethylene industry, and improving production efficiency.

The method for separating ethylene cracking gas proposed by the present invention adopts a combined process comprising hydration separation, cryogenic separation and membrane separation operation, mainly applying the new type of hydration separation to the separation process of ethylene cracking gas. First, C2 components are combined with Separation of a large amount of methane and hydrogen, that is, the separation of hydrogen, methane and C2 components (mainly a mixture of ethane and ethylene), and further separation of a small amount of methane that coexists with C2 components to improve the C2 components (especially ethylene), and the methane stream obtained in the separation process is pre-cooled and expanded as the cooling source of the demethanizer to meet the refrigeration requirements of the demethanizer, so that the whole process does not need external refrigeration operation.

The main difference between the method of the present invention and the traditional process of separating ethylene cracking gas is that the hydration technology is first used to make the C2 component form hydrate first, and then separate it from hydrogen and most of the methane gas. At this time, a small amount of methane and the C2 component will form hydrate at the same time Therefore, the methane content in the gas phase after hydrate decomposition is already very low, and the cooling load required for separation through the demethanization process is already very small. The aqueous liquid decomposed in the hydrate decomposer can be cooled and returned to the hydrate reactor for recycling.

Specifically, the combined process for separating ethylene cracked gas provided by the invention may include steps:

The cracked gas to be separated first enters the hydration separation unit and contacts with the water-containing liquid. The conditions for hydrate formation are controlled so that the C2 components in the cracked gas preferentially form hydrates, and the cracked gas is separated into methane + hydrogen stream and methane + C2 stream;

The methane + C2 stream obtained from the hydration separation process is dehydrated and cooled and then enters the cryogenic demethanizer to achieve fine separation of methane and C2 components. The obtained methane stream is expanded and refrigerated to provide cooling capacity for the demethanizer;

The methane + hydrogen stream obtained in the hydration separation process enters the membrane separator after dehydration, and the hydrogen and methane in it are separated. The obtained methane stream is pre-cooled and expanded and used as a cold source for the demethanizer to provide Cooling capacity.

In the method for separating ethylene cracked gas provided by the present invention, the cracked gas to be separated first enters the hydration separation unit, and is separated into two streams of methane+hydrogen and methane+C2 through the hydration reaction in the unit. Part of the C2 components and a small part of methane are converted into hydrates, that is, the hydration separation unit of the present invention undertakes the task of separating the C2 components in the cracked gas to a large extent. Specifically, the hydration separation unit includes two continuous processes of generating hydrate and decomposing hydrate, which are respectively undertaken by the hydration reactor (also called the hydration reaction tower in the present invention) and the hydrate decomposer, allowing the cracked gas to be separated to flow from the bottom Entering the hydration reaction tower, it is in continuous contact with the descending water-containing liquid during the upward process. During this process, more than 99% of the C2 components and a small part of methane in the cracked gas can be realized to form hydrates (slurries), and the hydrates from the hydration reaction The lower part of the tower comes out and enters the hydrate decomposer, and the mixed gas stream of methane + C2 components released after dissolution leaves the hydration separation unit, dehydrates, cools, and then enters the cryogenic demethanizer. The gas phase leaving the hydration reaction tower mainly contains hydrogen and methane, and the molar concentration of the C2 component in it is less than 1%. The gas phase components leave the hydration reactor and then enter the membrane separator to separate hydrogen and methane. The separated methane is directly It is pre-cooled and expanded for the cooling source of the demethanizer.

The combined process method for separating ethylene cracking gas provided by the present invention is to use the methane stream separated in its own system to perform expansion refrigeration to provide cooling capacity for the demethanizer. The entire process does not require additional low-temperature refrigeration, that is, no need at all The step-by-step condensation section and cold box in the traditional process. At the same time, since the methane in the mixed gas entering the demethanizer has been greatly reduced, the logistics load and cooling load of the demethanizer can be significantly reduced, thereby reducing the overall energy consumption of the process of separating ethylene cracking gas and improving economic benefits, which has important practical significance.

It should be pointed out that the design idea of the technology of the present invention is to allow the C2 components in the cracked gas to generate hydrates prior to methane in the hydration reaction tower, so as to improve the primary separation efficiency of methane and C2 components. Usually contain more C3 (propane, propylene) and above components in the cracking product that comes from cracking furnace, and their existence has side effect to the separation effect of methane and C2 component, therefore adopts the inventive method to require to enter the hydration reaction tower The stream should be a light stream (that is, mainly containing hydrogen, methane, ethane, ethylene, etc.) after most of the heavy components of C3 and above are separated from the cracked product, and the content of heavy components of C3 and above is best controlled within Less than 2% molar concentration. At the same time, the hydration reaction system should not contain substances that are conducive to the formation of hydrates from methane, such as propane, propylene, butane, cyclopentane, tetrahydrofuran, etc. The applicant of this case has a previous patent that records this content, patent number ZL02129611.1, in which cyclopentane, tetrahydrofuran and other substances are used as thermodynamic accelerators with certain selectivity to promote the formation of hydrates from methane and inhibit the formation of hydrates from C2 the goal of.

In the present invention, in order to improve the separation effect of methane and C2 in the hydration process and increase the hydrate formation rate, in addition to avoiding the above-mentioned unfavorable factors, one of the following measures can also be taken to increase the selectivity of the hydration process to the C2 component: (1) The aqueous liquid adopts an aqueous solution containing an additive that can solubilize the C2 component (especially ethylene). There are many choices for the additive, which can be an anionic surfactant, especially an anionic surface active agent Higher fatty alcohol sulfates in active substances, such as sodium lauryl sulfate (also known as "sodium lauryl sulfate"), sodium cetyl sulfate (also known as "sodium cetyl sulfate"), octadecyl sulfate Sodium sulfate (also known as "sodium stearyl sulfate"), etc.; it can also be vinyl lactam monomers, polymers, water-soluble or water-dispersible polymers of mixtures; or some ionic compounds, such as NaF, MgF ₂ , SrF ₂ , BaF ₂ , NaCl, CaCl ₂ , MgCl ₂ , CaSO ₄ , Na(ClO ₄ ), NaH ₂ PO ₄ , Na ₂ HPO _{4 ,} etc.; The concentration in the water is preferably controlled at 300 to 1000 mg/liter; (2) the aqueous liquid adopts an emulsion (emulsion) formed by water and a hydrocarbon liquid, and the hydrocarbon liquid is pure alkanes or mixed hydrocarbons above C6 or C6 ( Such as gasoline, kerosene, diesel oil, etc.), the hydrocarbon liquid can preferentially dissolve the C2 component after forming an emulsion with water, so that it has more opportunities to preferentially contact with water to form hydrate, and the oil-water volume ratio is 1:1～ 4:1. Appropriate emulsifiers, such as Span series, can be used when preparing emulsions.

In the process flow of the present invention, the specific conditions for forming and dissolving hydrates are within the grasp of those skilled in the art, and there have been many studies. In general, the temperature in the hydration reaction tower should be controlled between -15 and 10°C, and the pressure should be controlled between 1 and 8 MPa, so as to facilitate the formation of hydrates by the C2 component (a small amount of methane will form hydrates at the same time), According to the nature of the mixed gas and the requirement of separation accuracy, when the operating temperature in the hydration reaction tower is below 0°C, the aqueous liquid in the hydration reaction system is preferably an emulsion formed by water and hydrocarbon liquid. The temperature in the hydrate dissolver should be controlled between 15 and 50°C, and the pressure should meet the operating requirements of the cryogenic demethanizer (generally greater than 3.0MPa).

Through the above-mentioned hydration separation unit, although the cracked gas can be separated to a large extent, the purity of the ethylene obtained after the separation still cannot meet the requirements, and a small part of methane is also entrained, which requires further separation and purification. The specific steps include: the methane+C2 mixed gas stream released from the hydrate decomposer of the hydration separation unit is dehydrated and cooled, and then enters the cryogenic demethanizer, and the fine separation of methane and C2 components is realized in the demethanizer Separation, the operating conditions in the demethanizer are the same as the traditional process, and are well known to those skilled in the art. In the present invention, the methane gas stream separated in the demethanizer is expanded and refrigerated to directly provide part of the cooling capacity for the demethanizer.

On the other hand, the methane+hydrogen gas phase stream obtained from the hydration separation process is dehydrated and then enters the membrane separator for separation to obtain low-pressure hydrogen and high-pressure methane. After the methane stream obtained in the membrane separation process is pre-cooled and expanded to refrigerate, it is used as the main cooling source of the demethanizer to provide cooling capacity for the demethanizer. The membrane separation technology is also a well-known technology in the art, and its operating conditions should be grasped by those skilled in the art, and are not the focus of the present invention.

In summary, the combined process method of the present invention combining hydration separation, cryogenic separation and membrane separation can be applied to transform the existing ethylene cracking gas separation process, including sequential separation process and front depropanization (C3 component) Separation process. The cut-in point is selected from the cracked product where most of the C3 and above components have been removed, and the hydration separation technology is mainly used to realize the preliminary separation of hydrogen, methane and C2 in the ethylene cracking gas, so that a large amount of methane entering the demethanizer Reduction, significantly reducing the logistics load and cooling load of the demethanizer; and using the methane stream obtained in the separation process to provide the cooling capacity required by the demethanizer after pre-cooling and expansion, so that the traditional step-by-step condensation section and cooling can be eliminated. Box, improve economic benefits. In order to improve the effect of hydration separation, it is preferable to give appropriate compression to the cracked gas which is cut into the process of the present invention, for example, to adjust the pressure of the cracked gas to about 3.6-5.0 MPa. At the same time, due to the adoption of the traditional rectification method to realize the fine separation of methane and C2 (a mixture of ethane and ethylene), high-purity products can be obtained. In other words, the combined process of the present invention not only avoids complex refrigeration and heat exchange procedures, saves energy consumption, but also enables products to meet requirements, and has superior advancement and practicability.

Description of drawings

Figure 1 is a schematic diagram of the combined process flow of the present invention.

Detailed ways

The present invention will be described in more detail below in conjunction with the accompanying drawings and specific embodiments, but it does not constitute any limitation to the applicable scope of the present invention.

Please refer to shown in Fig. 1, the method for separating ethylene cracking gas of the present invention is to adopt the combined process that comprises hydration separation, cryogenic separation and membrane separation operation, and its main technological process is:

The stream of light components (hydrogen, methane, C2 (mixture of ethane+ethylene), etc.) of the cracked product after separating the heavy components above C3 enters the hydration reaction tower 1 from the lower part, and in the upward process, it is mixed with the downward aqueous liquid Continuous contact generates gas hydrate; as long as the hydration conditions of methane are controlled, the C2 components (ethane, ethylene) in the mixed gas will preferentially form hydrates, and together with a small amount of methane hydrate, they will become hydrate slurry, which will be released from the lower part of the reaction tower and enter the hydration process. Decomposer 2, hydrogen and methane can be concentrated in the gas phase.

The hydrate slurry obtained from the hydration separation process enters the hydrate decomposer 2 and is decomposed to become a mixed gas of ethane and ethylene containing a small amount of methane. After dehydration, it enters the cryogenic demethanizer 3 to realize the fine separation of methane and C2 components. separate. High-purity C2 (a mixture of ethylene and ethane) is collected as the final product, and the finely separated methane stream is pre-cooled and expanded by the expansion refrigeration mechanism 5 (the part inside the dotted line box in the figure). After the heat exchange process, it is Subsequent cryogenic demethanization provides cooling. The water-containing liquid decomposed in the hydrate decomposer 2 can also be returned to the hydrate reactor 1 for recycling after cooling down.

During the hydration separation process, the concentrated gas phase flow is dehydrated and enters the membrane separator 4 for separation operation to obtain hydrogen gas and methane gas respectively. The hydrogen is recovered, and the methane stream is expanded and refrigerated by the pre-cooling and expansion refrigeration mechanism 5 (the part in the dotted line in the figure), and also provides the cooling source for the demethanization operation of the demethanizer 3, and the whole process may not require additional low-temperature refrigeration equipment and processes.

Wherein cryogenic demethanization, membrane separation hydrogen and methane, and methane precooling expansion process and device are all conventional technologies for gas separation and ethylene cracking gas demethanization, and the described hydration reaction tower (or reactor) refers to There is no special requirement for the reaction device in which raw material gas and water-containing liquid can be fully contacted to form hydrate. For example, it can be a pressure-resistant reactor. In actual production, tower-type hydration reactors can be used to achieve multi-stage separation. The tower-type hydration reactor is not specially designed, and its internal structure can be similar to that of a multi-stage rectification tower, which is more conducive to the full contact and separation of gas and liquid.

Example 1. Analysis of the separation effect and energy consumption of ethylene cracking gas in the combined process of hydration separation + membrane separation + cryogenic separation

In this embodiment, the simulated ethylene cracking gas is separated according to the combined process flow of the present invention, the separation effect data is recorded, and the heat energy consumption in the process is analyzed.

Simulated ethylene cracking gas (feed gas) stream composition (mol%):

_H2 , 19.85%; _CH4 , 42.78%; _{C2H4 ,} 33.78%; _C2H6 , _{2.41 %} ; _C3H6 , 0.35%.

Specific process flow:

The cracked gas stream to be separated (the pressure of the cracked gas at this moment is about 3.6MPa) is first sent into the hydration reactor 1, which is a hydration reaction tower capable of multi-stage separation in this embodiment. The operating conditions of the hydration reaction tower are: temperature 1°C, pressure 5MPa, the water-containing liquid is water+diesel oil emulsion, the oil-water volume ratio is about 2:1, and the gas-liquid volume ratio is about 75:1.

After the above hydration separation, two streams are formed: the gas phase stream after multi-stage separation is hydrogen + methane gas mixture (H ₂ (60.06%) + CH ₄ (39.94%)), and the separated liquid phase slurry is decomposed Vessel 2 is re-decomposed into the gas phase (in the decomposer after heating up and depressurizing properly) to form a mixed gas of methane, ethane, ethylene and propylene (CH ₄ (10.01%)+C ₂ H ₄ (78.56%)+C ₂ H ₆ (9.34%) + C ₃ H ₆ (2.09%)). The aqueous liquid is sent back to the hydration reactor 1 for recycling.

The mixed gas from the dissolver enters the cryogenic demethanizer 3 to realize the separation of methane from C2 and above components. The test results show that the yield of ethylene can reach 99.8%, and the methane gas is expanded and refrigerated to the demethanizer. Provide cold source.

The gaseous phase stream (mixed gas of hydrogen and methane) separated from the hydration reaction tower enters the membrane reactor 4 under the conditions of 50°C and 5MPa (the membrane module adopts 16 pieces of Dg200 (area 5600m ² ) silicone rubber-polysulfone composite hollow fiber membrane) to obtain concentrated hydrogen and methane, wherein the concentration of hydrogen can be concentrated to more than 97%. The methane gas is pre-cooled and expanded to provide a cooling source for the demethanizer.

Through the above process, hydrogen, C2 gas (ethylene, ethane and a small amount of propylene) and methane gas can be obtained respectively.

Below is the energy consumption analysis and comparison of the traditional front depropanization cryogenic separation process flow and the combined process of the present invention:

Analytical standard - feed gas stream composition (H ₂ , 19.85%; CH ₄ , 42.78%; C ₂ H ₄ , 33.78%; C ₂ H ₆ , 2.41%; C ₃ H ₆ , 0.35%), feed gas flow rate 1290Kmol /h;

The traditional pre-depropanization cryogenic separation process refers to the current conventional process for ethylene gas production, and here only the energy consumption is measured, without a more detailed description of the process.

①Using the traditional pre-depropanization cryogenic separation process:

Total energy consumption = cold box heat load (2mmkcal/h) + total heat load outside the cold box (2.08mmkcal/h) + demethanizer top condensation load (1.64mmkcal/h) + demethanizer bottom reboil load (1.6 mmkcal/h) = 7.32mmkcal/h;

2. adopt the combined technological process of the embodiment of the present invention 1:

Total energy consumption = heat load of hydration reactor (2.10mmkcal/h) + power required for cracking gas to be compressed from 3.6MPa to 5MPa (0.30mmkcal/h) + energy consumption of membrane separation (0.77mmkcal/h) + removal Methane overhead condensation load (0.48mmkcal/h) = 3.65mmkcal/h

Note: The above calculation includes the energy consumption of compressing cracked gas, but this step is to improve the separation efficiency and is not necessary. If the incoming raw material gas is directly hydrated and separated, the total energy consumption will be lower than the above calculation.

Therefore, energy can be saved by at least 50% when the combined process of the present invention is used to separate ethylene cracked gas.

From the preliminary technical and economic analysis in this example, it can be known that after adopting the combined process flow of the present invention to separate the ethylene cracking gas, the methane flow rate in the demethanizer drops by more than 70%, and the C2 content at the top of the hydration tower is less than 0.8-1.0 %, the separation of methane and hydrogen adopts the membrane separation method, the hydrogen has a good recovery rate, and the expensive cold box is removed. Compared with traditional cryogenic separation, adopting the combined process of the present invention to separate ethylene cracked gas can save more than 50% of the energy consumption of cryogenic separation; in addition, simply using the hydration separation method can achieve a large degree of separation of cracked gas , but the purity of ethylene can not meet the requirements, and adopt the present invention, let the hydration separation take on most of the separation tasks, realize the fine separation of methane and C2 (ethane and ethylene) with the method of traditional rectification, obtain the high-purity product. Such a combination not only avoids complex refrigeration and heat exchange procedures, saves energy consumption, but also makes the product meet the requirements. The ethylene recovery rate can reach 99.8%, and the purity can also meet the requirements. At the same time, because the methane entering the demethanizer is greatly reduced, the logistics load and cooling load of the demethanizer can be significantly reduced, so it has revolutionary significance.

Embodiment 2, the single-stage hydration separation of the water liquid separation ethylene cracking gas containing SDS (500ppm)

Hydration reaction conditions: T=275.15K, P=3MPa, gas-water volume ratio is 75:1

Experimental method: The cracked gas mixture to be separated and the water-containing liquid are contacted in a high-pressure reactor to form hydrates. During the reaction process, the reaction temperature and pressure were kept constant, and when the reaction reached equilibrium, the composition of the gas phase and the composition of the gas released after the dissolution of the hydrate were analyzed respectively.

The gas composition released after the hydrate is dissolved is the dry basis composition of the hydrate phase (the gas composition after deducting the amount of water).

Table 1. Single-stage hydration separation effect of water-liquid separation of ethylene cracking gas containing SDS (500ppm) component name Raw gas composition (mol%) Gas phase composition (mol%) Hydrate phase composition (dry basis, mol%) H2 18.27 60.25 10.65 CH4 30.33 25.16 30.42 C2H4 35.88 10.36 41.14 C2H6 5.0 1.68 5.12 C3H6 10.48 2.55 12.67

Embodiment 3, the single-stage hydration separation of ethylene cracking gas separation when the aqueous liquid adopts the emulsion of water+diesel

Hydration reaction conditions: T=274.15K, P=5MPa, oil-water volume ratio is 2:1, emulsifier Span 20 is used to make a water-in-oil emulsion system, and the gas-liquid volume ratio entering the hydration reaction tower is 75:1;

The experimental method is the same as in Example 2.

Table 2. The single-stage hydration separation effect of separating ethylene cracking gas when the aqueous liquid adopts water+diesel oil emulsion component name Raw gas composition (mol%) Gas phase composition (mol%) Hydrate phase composition (dry basis, mol%) H2 18.27 65.35 9.78 CH4 30.33 24.18 31.44 C2H4 35.88 8.37 40.84 C2H6 5.0 1.08 5.71 C3H6 10.48 1.02 12.21

Embodiment 4, the single-stage hydration separation of the water liquid separation ethylene cracking gas containing poly-N-vinyllactam (650ppm)

Hydration reaction conditions: T=275.15K, P=3MPa, gas-water volume ratio is 75:1;

The experimental method is the same as in Example 2.

Table 3, the single-stage hydration separation effect of the water-liquid separation ethylene cracking gas containing poly-N-vinyllactam (650ppm) component name Raw gas composition (mol%) Gas phase composition (mol%) Hydrate phase composition (dry basis, mol%) H2 19.85 44.58 0.98 CH4 42.78 48.31 38.86 C2H4 33.78 6.52 54.64 C2H6 2.41 0.26 3.72 C 3H6 1.18 0.33 1.80

From the results listed in Table 2, it can be seen that when the water-containing liquid is an emulsion of water+diesel oil, most of the C2 will be transferred to the hydrate phase after the first separation, while the methane will be concentrated in the gas phase, and almost all the hydrogen will remain in the gas phase. , indicating that the hydration separation effect is very good. In addition, Table 2 lists the separation effect of single balance stage. The hydration separation process in the tower type hydration reactor adopted in the present invention is a multi-stage separation process, and the effect is much better than single-stage separation.

From the comparison of the results listed in Table 2 and Table 3, when the C3 content is more, the separation effect of methane and C2 is significantly reduced. The aqueous liquid adopts the emulsion composed of water and other hydrocarbon liquids (such as n-heptane, n-octane, kerosene, etc.), and similar results can be obtained.

Claims (10)

1, a kind of combination process that is used for separating ethene cracking gas comprises the combination of hydration separation, low temperature separation process and membrane sepn operation, can realize that hydrogen in the splitting gas, methane separate with the C2 component, and this combination process process comprises:

Splitting gas to be separated at first enters the hydration separation unit, and contacts with liquid, aqueous, and the control hydrating condition makes the C2 component in the splitting gas preferentially form hydrate, and splitting gas is separated into the methane+C2 logistics of methane+hydrogen gaseous stream and hydrate forms;

Methane+C2 logistics enters the deep cooling demethanizing tower after dissolving, dewater, cooling off, realize the fine separation of methane and C2 component, and methane stream is carried out swell refrigeration, for demethanizing tower provides cold;

Methane+the hydrogen gas stream that obtains in the hydration separation process enters membrane separation apparatus after dehydration, wherein hydrogen is separated with methane, to the methane stream that obtains carry out precooling, the cold source of back of expanding as demethanizing tower.

2, the described combination process of claim 1, wherein, the unitary operation of described hydration separation comprises makes splitting gas to be separated and liquid, aqueous reverse the contact, wherein C2 component and part methane generate hydrate in hydration reactor, and make that the slurries of this hydrate and gas phase separation are laggard goes into hydrate and dissolve device and be decomposed and discharge the process of C2 component and methane.

3, claim 1 or 2 described combination procesies, wherein, described splitting gas to be separated is the lightweight stream feed gas that has separated after most of C3 and the above heavy constituent, C3 wherein and above component concentration are lower than 2% volumetric molar concentration.

4, the described combination process of claim 2, wherein, described hydrate is dissolved liquid, aqueous that decomposition obtains in the device and return hydrate reactor after cooling, recycles.

5, each described combination process of claim 1～4, wherein, take one of following measure to increase hydro-combination process to the C2 components selection: (1) is adopted and is contained additive liquid, aqueous that the C2 component is had solublization, and the concentration of additive is controlled at 300～1000mg/ liter; (2) emulsion that formed by water and hydrocarbon liquids of liquid, aqueous employing, described hydrocarbon liquids are C6 or above pure alkane or the hydrocarbon mixture of C6.

6, the described combination process of claim 5, wherein, the described additive that C2 is had a solublization is selected from anionic surface active substances, the polymkeric substance of the water-soluble or water dispersible of vinyl lactam monomer, polymkeric substance, mixture, or ionic compound; Described hydrocarbon mixture with water formation emulsion is gasoline, kerosene or diesel oil, and the profit volume ratio is 1: 1～4: 1.

7, each described combination process of claim 1～4, wherein, operating in the hydration reactor of described formation hydrate finished, and service temperature is between-15～10 ℃, and pressure is between 1～8MPa.

8, the described combination process of claim 5, wherein, operating in the hydration reactor of described formation hydrate finished, and service temperature is between-15～10 ℃, and pressure is between 1～8MPa.

9, each described combination process of claim 1～4, wherein, described hydrate is dissolved the interior service temperature of device between 15～50 ℃, and pressure is greater than 3.0MPa.

10, each described combination process of claim 1～4, wherein, described splitting gas to be separated is before entering the hydration separation unit, and pressure is 3.6～5.0MPa.

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