Combustible gas recovery method

Abstract

To provide a combustible gas collection method for more easily adsorbing and collecting a combustible gas, from an accompanying gas, especially, a gas including a combustible gas and steam.SOLUTION: There is provided a collection method of a combustible gas, the method comprises: a step for generating a mixed gas including, the combustible gas and steam, from a solution in which the combustible gas is dissolved; a step for bringing the mixed gas into contact with a combustible gas adsorption collection material, for adsorbing selectively the combustible gas to the combustible gas adsorption collection material; and a step for decompressing, for collecting the combustible gas adsorbed to the combustible gas adsorption collection material. The combustible gas adsorption collection material is formed of mainly, particles whose particle diameter is less than 1.0 mm, and the particles include at least one kind of a polymer selected from: at least one rubber selected from, a diene rubber, and silicon rubber and a cured object of the rubber.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to a method for recovering a combustible gas. [Background technology]

[0002] It is known that associated gas produced in the extraction of oil and natural gas, and gas produced by the treatment of produced water (hereinafter referred to as "associated gas, etc.") contain flammable gases such as propane.

[0003] As an apparatus for recovering combustible gas from such associated gas, Patent Document 1 describes "an LPG fraction recovery apparatus comprising: a compressor for pressurizing all or a part of surplus gas containing propane and butane generated in the production of crude oil, a de-ethanizer for bringing the pressurized surplus gas into gas-liquid contact with sponge oil to dissolve the propane and butane contained in the surplus gas into the sponge oil and for separating gas having a carbon number of 2 or less from the surplus gas, a sponge oil transfer pipe for discharging the sponge oil in which the propane and butane are dissolved from the de-ethanizer, a debutanizer that is connected to the de-ethanizer via the sponge oil transfer pipe and separates the propane and butane from the sponge oil, an LPG fraction discharge pipe for discharging a fraction containing propane and butane from the debutanizer, and a sponge oil return pipe for discharging the sponge oil from the debutanizer and returning the sponge oil to the de-ethanizer." [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2012-116981 A Summary of the Invention [Problem to be solved by the invention]

[0005] According to the LPG fraction recovery apparatus of Patent Document 1, it is possible to separate and recover propane and butane dissolved in sponge oil using a debutanizer, but the apparatus tends to be large-scale and the energy cost is high. Furthermore, since the gas generated by the produced water treatment contains a large amount of water vapor, there is a problem that condensation water is generated by compression.

[0006] In view of the above problems, the present invention aims to provide a combustible gas adsorption and recovery material capable of more easily adsorbing and recovering combustible gas from associated gases, particularly gases containing combustible gas and water vapor. Another object of the present invention is to provide a method for recovering combustible gas. [Means for solving the problem]

[0007] As a result of intensive research into achieving the above object, the present inventors have found that the above object can be achieved by the following configuration. [1] A method for recovering flammable gas, comprising: generating a mixed gas containing the flammable gas and water vapor from the aqueous solution in which the flammable gas is dissolved; contacting the mixed gas with a combustible gas adsorption and recovery material to selectively adsorb the combustible gas onto the combustible gas adsorption and recovery material; and a step of reducing pressure to recover the flammable gas adsorbed in the flammable gas adsorption and recovery material. The method for recovering flammable gas, wherein the flammable gas adsorption and recovery material is mainly composed of particles having a particle diameter of less than 1.0 mm, and the particles contain at least one type of rubber selected from the group consisting of diene rubber and silicone rubber, and at least one type of polymer selected from the group consisting of cured products of the rubber. [2] The method according to [1], wherein the aqueous solution contains 20 ppm to 10,000 ppm of the combustible gas. [3] The method according to [1] or [2], wherein the aqueous solution is produced water associated with the mining of petroleum or natural gas. [4] The method according to any one of [1] to [3], wherein the particles contain at least one polymer selected from the group consisting of silicone rubber and cured products of silicone rubber. [5] The method for recovering a flammable gas according to any one of [1] to [4], wherein the flammable gas adsorption recovery material is placed in a bag made of woven or nonwoven fabric. [6] The method according to any one of [1] to [5], wherein the contact is carried out for a period of 60 minutes or more and 20 hours or less. [7] The method according to any one of [1] to [6], wherein the pressure reduction is carried out for a period of 20 minutes or more and 40 minutes or less. [8] The method according to any one of [1] to [7], wherein the pressure reduction is performed using a vacuum pump. [9] The method of [8], wherein the recovery is performed using a cooler located upstream of the pressure reducing pump or a compressor located downstream of the pressure reducing pump.

[10] The method according to any one of [1] to [9], wherein the recovery is carried out while heating the combustible gas adsorption and recovery material.

[11] The method according to any one of [1] to

[10] , wherein the particles are made of crushed waste tires.

[12] The method for recovering a combustible gas according to any one of [1] to

[11] , wherein the combustible gas is a hydrocarbon having three or more carbon atoms in one molecule.

[13] The method for recovering a flammable gas according to any one of [1] to

[11] , wherein the flammable gas is selected from the group consisting of methane, ethane, propane, pentane, hexane, benzene, toluene, and xylene.

[14] The method according to any one of [1] to

[13] , wherein the particle diameter is in the range of 1.0 μm or more and 400 μm or less.

[0008] The configuration of a reference embodiment of the present invention will be described below. [1] A combustible gas adsorption and recovery material whose main component is particles having a particle diameter of less than 1.0 mm, said particles containing at least one type of rubber selected from the group consisting of diene rubbers and silicone rubbers, and at least one type of polymer selected from the group consisting of cured products of the above rubbers. [2] The flammable gas adsorption and recovery material according to [1], wherein the particles contain at least one polymer selected from the group consisting of silicone rubber and cured products of silicone rubber. [3] The combustible gas adsorption and recovery material according to [1], wherein the particles are made of crushed waste tires. [4] The combustible gas adsorption and recovery material according to any one of [1] to [3], which is used for recovering a combustible gas from a mixed gas containing the combustible gas and water vapor. [5] The combustible gas adsorption and recovery material according to any one of [1] to [4], which is used for recovering hydrocarbons having 3 or more carbon atoms in one molecule. [6] A method for recovering a flammable gas, comprising contacting a mixture containing a flammable gas and water with the flammable gas adsorption and recovery material described in any one of [1] to [5], selectively adsorbing the flammable gas onto the flammable gas adsorption and recovery material, and then reducing the pressure to recover the flammable gas. Effect of the Invention

[0009] According to the present invention, there is provided a combustible gas adsorption and recovery material capable of more simply adsorbing and recovering combustible gas from a gas containing combustible gas and water vapor. Also, according to the present invention, there is provided a method for recovering combustible gas. [Brief description of the drawings]

[0010] [Figure 1] The images show a sheet of cured silicone rubber before immersion in hexane (left), and the same cured material as above after immersing in hexane for 20 minutes (right). [Diagram 2] This is an image of a small piece of vulcanized rubber before immersion in hexane (left), and a similar piece of vulcanized rubber after immersion in hexane for 30 minutes (right). [Diagram 3] 1 is a scanning electron microscope image of particles containing a cured product of polydimethylsiloxane. [Figure 4] 1 shows the adsorption isotherm of hexane onto particles containing a cured polydimethylsiloxane. [Diagram 5] 1 shows the absorption isotherm of hexane into activated carbon at 30° C. [Figure 6] This is the adsorption isotherm of hexane onto NBR (acrylonitrile butadiene rubber) particles. [Figure 7] 1 is a curve showing the desorption rate of hexane from particles containing a cured material of polydimethylsiloxane. [Figure 8] FIG. 1 is a schematic diagram of an experimental apparatus for adsorption and recovery of hexane from a colloidal dispersion. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The present invention will be described in detail below. The following description of the components may be based on a representative embodiment of the present invention, but the present invention is not limited to such an embodiment. In this specification, a numerical range expressed using "to" means a range that includes the numerical values ​​before and after "to" as the lower and upper limits.

[0012] In the description of groups (atomic groups) in this specification, the description that does not indicate whether substituted or unsubstituted includes both those that have no substituents and those that have a substituent, within the scope that does not impair the effects of the present invention. For example, "alkyl group" includes not only alkyl groups that have no substituents (unsubstituted alkyl groups), but also alkyl groups that have a substituent (substituted alkyl groups). This also applies to each compound.

[0013] [Combustible gas adsorption and recovery material] The combustible gas adsorption and recovery material according to an embodiment of the present invention (hereinafter also referred to as "the present combustible gas adsorption and recovery material") is a combustible gas adsorption and recovery material whose main component is particles having a particle diameter of less than 1.0 mm (hereinafter also referred to as "specific particles"), and which contains at least one type of rubber selected from the group consisting of diene rubber and silicone rubber, and at least one type of polymer selected from the group consisting of cured products of the above rubber (hereinafter, the polymer consisting of the above rubber and the cured product will be referred to as "rubber, etc.").

[0014] Although the mechanism by which the problem of the present invention can be solved by the above is not necessarily clear, the present inventors speculate as follows: Note that the mechanism below is merely speculation, and even if the problem of the present invention is solved by a mechanism other than the mechanism below, it is still within the scope of the present invention.

[0015] Activated carbon has traditionally been used to adsorb combustible gases. Combustible gases with small molecular sizes, such as methane and / or ethane, are weakly adsorbed by activated carbon and are easily desorbed. However, when the molecular size is larger than that of propane, desorption becomes difficult. Furthermore, activated carbon strongly adsorbs water, making it difficult to adsorb combustible gases under high humidity conditions (in other words, when the target gas contains water vapor).

[0016] In addition to activated carbon, hydrophobic polymeric porous bodies obtained from crosslinked monomers such as divinylbenzene, as well as inorganic adsorbents such as zeolite and silica gel, are also known. However, these also strongly adsorb water and cannot be used as combustible gas adsorption and recovery materials.

[0017] The present inventors have conducted extensive research into a material capable of selectively recovering a combustible gas from a mixed gas containing the combustible gas and water vapor, and have found that a combustible gas adsorption and recovery material containing specific particles as a main component satisfies the desired characteristics, thereby completing the present invention.

[0018] The flammable gas adsorption and recovery material according to the embodiment of the present invention contains specific particles as a main component. The specific particles contain rubber or the like, and therefore have high hydrophobicity and can selectively adsorb the flammable gas in the mixed gas. In addition, the specific particles can capture condensable (the definition of condensable will be described later) flammable gases, in other words, dissolve and retain the flammable gases in the polymer network. The specific particles swell in volume by absorbing flammable gases, so the amount of flammable gas adsorbed per unit mass tends to increase.

[0019] It has long been known that rubber and other materials swell when they absorb condensable flammable gases (e.g., hexane, etc.). However, this was considered to be a sign of the rubber's "deterioration," and it had never been used to absorb flammable gases. The inventors believe there are two reasons for this. One is that the adsorption and desorption rates of flammable gas are slow, making it difficult to design a separation process based on adsorption and desorption. The other is that in a collection container filled with rubber or the like, when the rubber or the like absorbs flammable gas, the volume increases isotropically, and pressure is applied to the inner surface of the lower part of the collection container, preventing further volume expansion (swelling), and thus a sufficient amount of adsorption cannot be obtained.

[0020] On the other hand, since the main component of this combustible gas adsorption and recovery material is specific particles with a particle diameter of less than 1.0 mm, it is presumed that this increases the specific surface area and enables faster adsorption and desorption of combustible gases. In addition, since the particle diameter is less than 1.0 mm, it is presumed that the specific particles have better fluidity and can easily reduce the volume change caused by swelling. The composition of this combustible gas adsorption and recovery material will be described in detail below.

[0021] [Specific particles] The present combustible gas adsorption and recovery material contains specific particles as a main component (the component with the largest content by mass). The content of the specific particles in the present combustible gas adsorption and recovery material is not particularly limited, but is generally preferably 50 to 100 mass% based on the total mass of the combustible gas adsorption and recovery material, in that a combustible gas adsorption and recovery material having a more excellent effect of the present invention can be obtained. The present combustible gas adsorption and recovery material may contain one type of specific particles alone, or may contain two or more types. When the present combustible gas adsorption and recovery material contains two or more types of specific particles, it is preferable that the total content is within the above numerical range.

[0022] The specific particles are particles having a particle diameter of less than 1.0 mm. In this specification, the particle diameter means the sphere-equivalent diameter if the particle has a sphere-equivalent structure, and means the shortest distance between opposing faces if the particle has a rectangular parallelepiped structure.

[0023] When the particle diameter of the particles is less than 1.0 mm, the specific surface area becomes larger and the volume change due to swelling can be easily alleviated.

[0024] Now, let's consider the swelling of rubber. For example, if there is a 1 cm cube of rubber, it will swell when it absorbs a flammable gas (such as hexane), but for this to happen, the flammable gas must dissolve inside the rubber. When the concentration of hexane in the gas phase is high, the flammable gas will diffuse and dissolve inside the rubber, but this does not immediately lead to swelling. This is because even if the surface tries to swell, the inside prevents this. Therefore, the swelling time of rubber and other materials can be considered to be determined almost entirely by the time it takes for flammable gas to reach the inside.

[0025] Therefore, the particle size of the specific particles needs only to be less than 1.0 mm, and may be appropriately determined depending on the diffusion speed of the flammable gas to be collected.

[0026] The particle size of the specific particles may be less than 1.0 mm, but in order to enable rapid recovery by reducing pressure, the particle size is preferably 100 μm or less, and more preferably 30 μm or less. There is no particular lower limit, but a lower limit of 1.0 μm or more is preferred in terms of superior handling properties. The specific particles may be used as they are, or may be placed in a bag made of woven or nonwoven fabric that is permeable to the mixed gas.

[0027] The specific particles contain at least one rubber selected from the group consisting of diene rubber and silicone rubber, and at least one polymer selected from the group consisting of the cured products of the rubber. In this specification, rubber means a polymer (polymer compound) that is in a rubbery state at room temperature and normal pressure and has not been subjected to chemical curing treatment (typically vulcanization, crosslinking, etc.). The specific particles may contain one type of rubber, etc. alone or two or more types. When the specific particles contain two or more types of rubber, etc., it is preferable that the total content is within the above numerical range, that is, 50 to 100 mass %.

[0028] The diene rubber is not particularly limited, but examples thereof include butadiene rubber, isoprene rubber, chloroprene rubber, natural rubber, styrene-butadiene rubber, styrene-isoprene rubber, and styrene-isoprene-butadiene rubber.

[0029] The silicone rubber is not particularly limited, but examples thereof include compounds represented by the following average composition formula: R a SiO (4-a) / 2 In the above formula, R a R may be the same or different and are unsubstituted or substituted monovalent hydrocarbon groups having 1 to 10 carbon atoms, and a is a positive number of 1.9 to 2.1. a Examples of R are not particularly limited, and include alkyl groups (methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, hexyl, cycloalkyl groups (cyclohexyl, etc.), alkenyl groups, vinyl groups (allyl, propenyl, isopropenyl, butenyl, and hexenyl), aryl groups (phenyl, tolyl, etc.), and groups in which some or all of the hydrogen atoms in these groups have been substituted with halogen atoms or cyano groups (chloromethyl, trifluoropropyl, cyanoethyl, etc.). Among these, R a is preferably a methyl group.

[0030] The molecular chain of the silicone rubber is preferably linear. The average degree of polymerization of the silicone rubber is not particularly limited, but is preferably 1,500 to 10,000. The degree of polymerization is determined as the number average degree of polymerization in terms of polystyrene by gel permeation chromatography (GPC).

[0031] When the specific particles contain the above-mentioned cured rubber, the curing method is not particularly limited, but examples thereof include a method of curing using a known vulcanizing agent, curing agent, and the like. As the vulcanizing agent, organic peroxides such as dicumyl peroxide, benzoyl peroxide, t-butyl hydroperoxide, and 2,4-dichlorobenzoyl peroxide can be used. A known vulcanization accelerator can also be used in combination. Examples of known vulcanizing agents include sulfur and 4,4'-dithiodimorpholine dimorpholine, etc. Examples of sulfur include powdered sulfur, precipitated sulfur, highly dispersible sulfur, surface-treated sulfur, insoluble sulfur, etc.

[0032] Examples of the curing agent include an addition reaction curing agent consisting of a combination of an organohydrogenpolysiloxane and a platinum group metal catalyst, and the above-mentioned organic peroxides.

[0033] Examples of the platinum group metal catalyst include platinum element alone, platinum compounds, platinum complexes, chloroplatinic acid, alcohol compounds of chloroplatinic acid, aldehyde compounds of chloroplatinic acid, ether compounds of chloroplatinic acid, complexes with various olefins, etc. The platinum group metal catalyst may be used alone or in combination of two or more kinds.

[0034] The molecular structure of the organohydrogenpolysiloxane may be a straight chain, a cyclic, a branched chain, or a three-dimensional network structure (resinous). Examples of organohydrogenpolysiloxanes include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetrahydrogen-1,3,5,7-tetramethylcyclotetrasiloxane, and 1-propyl-3,5,7-trihydrogen-1,3,5,7-tetramethylcyclotetrasiloxane. The organohydrogenpolysiloxane may be used alone or in combination of two or more kinds.

[0035] The diffusion rate of gas in rubber etc. has a large effect on the adsorption and desorption rate. There is no data available on the diffusion rate of flammable gases with relatively large molecular weights, such as hexane, but it is known that polydimethylsiloxane rubber is 22 times more permeable to small molecules, such as oxygen, than natural rubber. In comparison, the gas permeability of butadiene rubber is about 0.8 times that of isoprene rubber, and the gas permeability of isoprene rubber is about the same as that of natural rubber.

[0036] That is, from the viewpoint of the adsorption / desorption speed, rubbers containing polyorganosiloxane (particularly polydimethylsiloxane) are particularly superior. In some cases, polydimethylsiloxane rubbers have gas permeability 100 times or more higher than rubbers containing acrylonitrile-butadiene rubber (NBR). On the other hand, even if it is NBR, excellent adsorptive properties can be obtained if the sphere-equivalent diameter is 30 μm or less.

[0037] Combustible gases contained as components of petroleum and natural gas are generally hydrophobic. For this reason, rubber and the like are preferably hydrophobic. Rubber and the like are generally water permeable, and those that are not sufficiently dried during the manufacturing process contain several percent of water. Natural rubber in particular has a high water content.

[0038] It is preferable to use a material for adsorbing and recovering flammable gas from which water has been removed by a conventional drying method. However, even if the material contains some moisture, the moisture inside will decrease as the material repeatedly adsorbs and desorbs flammable gas, and the rubber material itself will become hydrophobic.

[0039] Among them, rubbers containing polyorganosiloxanes (especially polydimethylsiloxanes) can have a moisture content of 1% or less, and are highly resistant to water. Particles containing polydimethylsiloxane as the main component are more expensive than particles containing natural rubber as the main component, but the price is expected to fall as production volume increases.

[0040] It is also preferred that the particles are pulverized waste tires. There are no particular limitations on the crushed waste tire material, but crushed waste tires containing cured diene rubbers (polybutadiene, polyisoprene, etc.) used in trucks and private cars can be used. The crushed waste tires are preferably obtained by removing reinforcing materials such as bead wires, metal materials such as steel cords, and fibrous materials such as polyester cords from waste tires and crushing them. By removing the reinforcing materials, the amount of flammable gas adsorbed is increased. Typically, metallic and resinous reinforcing materials are often removed using a magnet or a blowing method.

[0041] When the particles are made of ground waste tires, the mechanism by which the more excellent effects of the present invention are obtained is not necessarily clear, but the present inventors speculate as follows. The ground waste tires contain carbon black, which is presumably what gives the ground waste tires excellent adsorption performance. Carbon black is often used to increase the mechanical strength of tires, which makes it easy to pulverize to sizes less than 1.0 mm using techniques such as roll grinding. In addition, the inclusion of carbon black allows the diene rubber to maintain its shape even when the degree of cure is low. In other words, the inclusion of carbon black allows the diene rubber, which is flexible and easily absorbs flammable gases, to be pulverized, resulting in particles with excellent flammable gas absorption and recovery performance.

[0042] The particles containing rubber including polybutadiene and polyisoprene may be made from crushed waste tires.

[0043] For example, particles containing silicone rubber (particularly polydimethylsiloxane) absorb hexane, a flammable gas, and swell in volume by 200% or more. The density of particles containing silicone rubber is about 0.93 to 1.0 g / ml, and the density of hexane is about 0.655 g / ml. For this reason, it can be assumed that particles containing silicone rubber will absorb about 1.5 times their mass in hexane, however, cured silicone rubber will absorb about 1.0 times its mass in hexane, and rubber with an even higher crosslink density will absorb about 0.5 times its mass in hexane. Generally, particulate rubber containing silicone rubber has a higher crosslink density, so the amount of hexane adsorbed is about 0.5 times its mass.

[0044] [Application] This combustible gas adsorption and recovery material selectively adsorbs combustible gas and can easily desorb and recover combustible gas. In general, when desorbing combustible gas from a combustible gas adsorption and recovery material, the heat of vaporization is required, so the temperature of the combustible gas adsorption and recovery material drops somewhat. However, even when the temperature drops, the drop in the desorption speed is only slight, and this combustible gas adsorption and recovery material can be used to adsorb and recover combustible gas.

[0045] On the other hand, when adsorbing and recovering combustible gas from a mixed gas of combustible gas and water vapor, adsorbing a large amount of water such as activated carbon, if the partial pressure of the combustible gas is low. When water is adsorbed, the water contained in the adsorbent freezes during desorption, so that desorption of water under reduced pressure becomes very slow, and as a result, water is often left behind in the combustible gas adsorption and recovery material.

[0046] The present combustible gas adsorption and recovery material is particularly useful for selectively recovering combustible gas from a mixed gas of combustible gas and water vapor. Such mixed gas is generated by blowing a combustible gas or a non-combustible gas into produced water containing tens to tens of thousands of ppm of combustible gas. By contacting this mixed gas with a combustible gas adsorption and recovery material, the combustible gas can be absorbed by the combustible gas adsorption and recovery material.

[0047] [How to recover flammable gas] A method for recovering flammable gas according to an embodiment of the present invention is a method for recovering flammable gas, which comprises contacting a mixed gas containing flammable gas and water with the flammable gas adsorption and recovery material already described, selectively adsorbing the flammable gas onto the flammable gas adsorption and recovery material, and then reducing the pressure to recover the flammable gas.

[0048] The time for contacting the mixed gas with the combustible gas adsorption and recovery material is not particularly limited, but may be appropriately determined depending on the content of combustible gas in the associated gas, etc. In general, the contact time is preferably within 20 hours, more preferably within 2 hours. If the contact time is 2 hours and the desorption time is 20 minutes, the adsorption and desorption operation can be performed about 10 times a day.

[0049] The combustible gas to be recovered by this recovery method is not particularly limited, and may be a combustible gas having one or more carbon atoms in one molecule. Among them, hydrocarbons having three or more carbon atoms in one molecule are preferable because they are easy to store and transport. In particular, hydrocarbons having five or more carbon atoms have high utility value as naphtha, and recovery of these gases allows for effective use as resources. The hydrocarbons include aliphatic hydrocarbons and aromatic hydrocarbons. The aliphatic hydrocarbons include ethane, propane, pentane, hexane, etc. The aromatic hydrocarbons include benzene, toluene, xylene, etc.

[0050] The flammable gas to be recovered is not particularly limited, but is preferably a pentane isomer that is liquid at room temperature and pressure, and a hydrocarbon having 6 or more carbon atoms in one molecule. However, under low temperature or high pressure conditions, the recovery method is also effective for recovering ethane, propane, and butane isomers, and under high temperature and / or low pressure conditions, it is also effective for recovering aromatic hydrocarbons such as BTX (benzene, toluene, xylene).

[0051] If hydrocarbons with three or more carbon atoms could be removed from combustible gases, the problem of clogging in PSA (pressure swing adsorption) technology using activated carbon, etc., or in gas separation processes using ceramic membranes would be solved, making long-term continuous operation possible. In addition, removing condensable hydrocarbons would make it easier to inject them underground, which would lead to a reduction in greenhouse gas emissions.

[0052] This flammable gas adsorption and recovery material uses specific particles as an adsorbent to recover flammable gas in the gas phase. Compared to conventional gas adsorbents such as activated carbon, this adsorbent has a weaker adsorption power, and is not only easy to regenerate but also can be used to recover flammable gas.

[0053] An example of the application of combustible gas recovery is produced water that contains combustible gas in a wide range from tens of ppm to tens of thousands of ppm. When this produced water is depressurized, it generates a mixed gas containing water vapor and combustible gas. Therefore, when the water is cooled, the water vapor is separated, but at the same time, combustible gas components with relatively high boiling points such as pentane and hexane are also condensed. This recovery method is suitable for recovering such condensable combustible gases (combustible gases that are difficult to separate from water). Note that the condensability here does not mean the condensability at normal pressure. Under low temperature and high pressure conditions, combustible gases such as methane, ethane, and propane are also condensed.

[0054] High-boiling flammable gases such as pentane and hexane are dispersed in the produced water after the pressure has been reduced to normal pressure, and these are removed by bubbling methane, nitrogen gas, etc. This recovery method is also suitable for recovering flammable gases from mixed gases containing water vapor and flammable gases generated in such processes.

[0055] The method for reducing pressure to recover (desorb) the flammable gas is not particularly limited, but a method for reducing pressure with a vacuum pump can be applied. The degree of pressure reduction may be adjusted appropriately depending on the amount and / or vapor pressure of the flammable gas to be collected. For example, when the flammable gas is adsorbed at normal pressure, the pressure may be reduced to about 20 kPa.

[0056] The time required for desorption may be adjusted appropriately depending on the amount and / or vapor pressure of the combustible gas to be recovered. Specifically, it is preferably within 30 minutes, more preferably within 20 minutes. During recovery, the combustible gas adsorption and recovery material may be heated.

[0057] Incidentally, mixed gases containing combustible gases, water vapor, and non-combustible gas components such as carbon dioxide are generated not only in produced water treatment but also in various other processes. In chemical plants that use natural gas and / or associated gas, components are generally separated in various processes by decompression and compression, and a mixture of flammable gas and water (especially water vapor) is generated each time. The flammable gas adsorption and recovery material can also recover flammable gas from such a mixture.

[0058] For example, amine gas removal processes that separate carbon dioxide. Generally, amine-based liquid absorbents are used to separate methane and carbon dioxide, but in the process, water and coagulable flammable gases are also absorbed. When the absorbent is heated and depressurized to regenerate it, a mixed gas containing water vapor and flammable gas (which often also contains carbon dioxide) is generated. This flammable gas adsorption and recovery material can recover flammable gas from the above-mentioned mixed gas.

[0059] This flammable gas adsorption and recovery material can also be used for volatile gases generated from tankers, etc. It can also be used to recover VOCs (Volatile Organic Compounds) in chemical plants and organic solvents related to wastewater treatment. It can also be used to recover gasoline vapors at gas stations. Furthermore, this flammable gas adsorption and recovery material can be used as a filler for PSA (Pressure Swing Adsorption). EXAMPLES

[0060] The present invention will be described in more detail below based on examples. The materials, amounts, ratios, processing contents, processing procedures, etc. shown in the following examples can be appropriately changed without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be interpreted as being limited by the following examples.

[0061] [Reference example 1] In Reference Example 1, the degree of swelling and the swelling rate were evaluated to show that a cured product of polydimethylsiloxane absorbs hexane and swells significantly. The sample used was a sheet (1 mm x 100 mm x 100 mm) made of a hardened silicone rubber whose main component was polydimethylsiloxane. The above samples were cut to an appropriate size and immersed in hexane at room temperature to evaluate the degree of swelling. After 10 minutes of immersion in hexane, the long side of the 35 mm sheet became 49 mm, and after 20 minutes it became 51 mm, and thereafter, there was no change in size. Figure 1 shows images of the sheet before immersion and after 20 minutes of immersion in hexane. From the results in Figure 1, it was found that one side had increased by 1.457 times, and therefore the volume of the sample had increased by more than three times, meaning that the sample had swelled by more than 200%.

[0062] [Reference example 2] In Reference Example 2, to demonstrate that a cured product (vulcanized rubber) made from cured natural rubber absorbs hexane and swells significantly, rubber bands were cut into 1 mm cubes and immersed in hexane at room temperature for 30 minutes to evaluate the degree of swelling.

[0063] Figure 2 shows images of the rubber band before immersion and after 30 minutes in hexane. As shown in Figure 2, after 30 minutes of immersion in hexane, the volume occupied by the sample had more than doubled, and the sample had swelled by more than 100%. The swelling degree of the sample was measured at 1 kg / cm for each sample before and after immersion in hexane. 2The specimen is evaluated by applying a pressure of 1000 psi. When the specimen is immersed in hexane while under pressure, it only swells by about 10%. This is because as the specimen swells, pressure is applied to the inner wall of the cylinder, increasing frictional resistance. However, in the case of hardened natural rubber, this frictional resistance can be reduced by reducing the sphere-equivalent diameter.

[0064] [Experiment (I)] In experiment (I), to demonstrate that particles containing a cured polydimethylsiloxane ("KMP-598" manufactured by Shin-Etsu Chemical Co., Ltd., a cross-linked linear polydimethylsiloxane) absorb flammable gas and desorb it by reducing pressure, an adsorption experiment was carried out from the gas phase of hexane using particles containing a cured polydimethylsiloxane. Figure 3 shows an image of the above particles taken with a scanning electron microscope. The particles were nearly spherical, with a sphere-equivalent diameter in the range of 3 to 30 micrometers.

[0065] The adsorption isotherm of this sample for hexane at 25° C. is shown in FIG. In Figure 4, the amount of adsorption in each process of adsorption and desorption is plotted as a relative pressure from the saturated vapor pressure. For example, in the adsorption process, when the relative pressure is 0.9005, 1000 mg of rubber absorbs 457.6 mg of hexane. In the desorption process, when the relative pressure is 0.8814, 1000 mg of rubber absorbs 446.0 mg of hexane. This result shows that the above particles have excellent absorption properties for gaseous hexane.

[0066] In this adsorption experiment, the equilibrium time (i.e., the time assumed to reach adsorption equilibrium) was set to 1000 seconds. Since the adsorption rate of gaseous hexane to the particles becomes very slow near the adsorption equilibrium, the time of 1000 seconds was set to assume that the adsorption equilibrium was reached.

[0067] This indicates that if the equivalent sphere diameter is in the range of 3 to 30 micrometers, 0.45 wt% of hexane can be adsorbed in 17 minutes, indicating that the adsorption speed is within the range that can be used as an adsorbent. Furthermore, the adsorption isotherm in FIG. 4 shows that when the relative pressure in the desorption process was 0.2135, 38.5 mg of hexane was adsorbed, which is more than 400 mg less than when the relative pressure was 0.8814. This shows that hexane can be recovered by changing the relative pressure. The broad adsorption isotherm in Figure 4 indicates that the adsorption of gaseous hexane is Henry-type adsorption. In other words, the amount of adsorption increases as the pressure increases. Henry-type adsorption means that the particles are in a rubbery state, above their glass transition temperature at room temperature. This type of adsorption is completely different from the adsorption isotherms of conventional porous materials in a glass (solid) state.

[0068] [Reference example 3] As Reference Example 3, Figure 5 shows the absorption isotherm of hexane into activated carbon at 30°C. The horizontal axis of Figure 5 shows the relative pressure of hexane, and the vertical axis shows the amount of hexane adsorbed as the volume of hexane under standard conditions. When compared with Figure 4, it can be seen that the adsorption of hexane into activated carbon occurs at a very low relative pressure. This indicates that with activated carbon, hexane does not desorb unless the pressure is significantly reduced, and hexane cannot be recovered at room temperature.

[0069] [Experiment (II)] In experiment (II), we conducted an adsorption experiment of NBR (acrylonitrile butadiene rubber) particles ("PN30A" manufactured by JSR Corporation) from the gas phase of hexane to demonstrate that particles containing diene rubber absorb flammable gas and desorb it by reducing pressure. Note that NBR contains 35% acrylonitrile and is an oil-resistant rubber, so most of the butadiene is copolymerized with acrylonitrile. Observation with a scanning electron microscope revealed that the equivalent spherical diameter of the particles was 400 micrometers.

[0070] The adsorption isotherms of this sample for hexane at 25°C are shown in Figure 6. In the adsorption process, 1000 mg of rubber absorbs 59.0 mg of hexane when the relative pressure is 0.901. In the desorption process, 1000 mg of rubber absorbs 55.8 mg of hexane when the relative pressure is 0.8609. This result shows that NBR powder has the ability to absorb hexane in a gaseous state. However, the amount of adsorption is only about 12 to 13% compared to experiment (I).

[0071] The reason for the small amount of adsorption is that the particle diameter is larger by one order of magnitude or more, and the hexane is not sufficiently adsorbed in the equilibrium time of 1000 seconds (the time assumed to reach adsorption equilibrium). Another reason is that the particles are oil-resistant, and the degree of swelling with hexane is small. However, it is easy to predict that the absorption speed and amount will increase by increasing the polybutadiene content in the NBR and increasing the equivalent sphere diameter of the powder.

[0072] [Experiment (III)] In experiment (III), a hexane vapor adsorption experiment was conducted to demonstrate the flammable gas absorption characteristics of waste tire powder ("Rubber Powder #2500" manufactured by Toyo Rubber Chip Co., Ltd.) with a sphere-equivalent diameter of 400 micrometers. The crushed waste tires used contained at least 25% natural rubber by mass. When exposed to saturated hexane vapor at 25°C for 5 hours, 1g of crushed waste tires absorbed 487mg of hexane. This demonstrated that waste tires can be used as a hexane adsorbent. It is easy to predict that the absorption rate will increase if the sphere-equivalent diameter of the crushed waste tires is made smaller.

[0073] [Experiment (IV)] In experiment (IV), the adsorption and desorption rates were evaluated to show that particles containing hardened polydimethylsiloxane could be used to recover combustible gases. Particles with a sphere-equivalent diameter of 3 to 30 micrometers were used. First, the particles were exposed to saturated hexane vapor at 25°C for 2 hours. As a result, 107.88 g of particles absorbed 47.85 g of hexane. The amount absorbed per gram was 444 mg, which was slightly smaller than the amount absorbed in the previous experiment (III).

[0074] Figure 7 shows the amount of desorbed hexane when the particles absorbed 47.85 g of hexane were dried using an oil rotary pump with an effective displacement of 135 L / min. The amount of desorbed hexane was measured after reducing the pressure for 3 minutes. As a result, it was found that 90% or more by mass of the hexane adsorbed on the particles was desorbed within 30 minutes.

[0075] [Example 1] In Example 1, in order to demonstrate that combustible gas can be selectively adsorbed and recovered from a mixed gas of water vapor and a combustible gas, air was bubbled into a colloidal dispersion of hexane, and an adsorption experiment was conducted from the mixed gas of hexane and water vapor that evaporated into the gas phase.

[0076] 8 is a schematic diagram showing the experimental method of Example 1. First, a 10,000 mass ppm dispersion of hexane colloid was prepared by ultrasonic irradiation, and diluted as necessary to prepare a hexane colloidal dispersion. On the other hand, a certain amount of particles containing a cured product of polydimethylsiloxane (similar to the above) was enclosed in the adsorbent column. Here, the experiment was carried out while the particles were wrapped in nylon cloth to prevent them from scattering.

[0077] In the adsorption process, the air in the adsorbent column was sent to a tank of colloidal dispersion liquid to bubble it, and the hexane and water vapor that had evaporated into the gas phase were returned to the adsorbent column. By performing this operation for a specified period of time, the hexane was adsorbed onto the particles. A diaphragm-type dry vacuum pump with an effective pumping speed of 60 L / min was used for bubbling.

[0078] After the hexane was adsorbed, the gas valve connected to the colloidal dispersion of hexane was closed, and the valve for the recovery process was opened to introduce hexane into the condenser, and the amount recovered was measured. One method of recovering hexane is to use a vacuum pump to reduce the pressure in the adsorbent column and capture the volatile hexane in a "cooler" placed before the vacuum pump. Another method of recovering hexane is to use a vacuum pump to reduce the pressure in the adsorbent column and liquefy the volatile hexane in a "compressor" installed after the vacuum pump. In Example 1, since the amount of hexane recovered was small, the amount of hexane that could be recovered by the adsorbent was evaluated by capturing it in the former cooler (liquid nitrogen trap in this case). The results are shown in Table 1.

[0079] [Table 1]

[0080] In experiment number 1 in Table 1, the hexane concentration was 10,000 ppm, and the hexane recovery efficiency was 74.3% (both on a mass basis). In this experiment, a small water tank (6.5 L) was used because the hexane concentration was high. In the small water tank, the distance between the water tank and the adsorbent column was short, and water contamination (0.5 g) was confirmed in the adsorbent column. On the other hand, in experiments 2 to 5 in Table 1, a large water tank was used, and in these cases, no water was recovered at all. In other words, selective recovery of hexane was possible. In experiment 2, the adsorption tank was leaked without closing the valve connected to the large water tank, so some of the adsorbed hexane was desorbed, lowering the recovery efficiency. In experiment number 3, an experiment was conducted without adding the adsorbent, and in this case, hexane was not recovered. Recovery from 50 ppm and 20 ppm hexane colloidal solutions was also examined using a large water tank, and the recovery efficiencies were 33.0% (experiment number 4) and 18.3% (experiment number 4), respectively. The fact that hexane was recovered even with a hexane concentration of 20 ppm, and no water was recovered, indicates that this flammable gas adsorption and recovery material can selectively recover flammable gas even from water containing low concentrations of flammable gas. The recovery rate of hexane can be improved by improving the recovery system shown in Figure 8, and the data in Table 1 shows only one example. For example, recovery efficiency can be increased by improving the sealing method of the colloidal dispersion tank, the airtightness of the material (PVC tube, etc.) used to transport the hexane-containing gas, the volume of the colloidal dispersion, and the hexane volatilization method.

Claims

1. A method for recovering a flammable gas, comprising: generating a mixed gas containing the flammable gas and water vapor from the aqueous solution in which the flammable gas is dissolved; contacting the mixed gas with a combustible gas adsorption and recovery material to selectively adsorb the combustible gas onto the combustible gas adsorption and recovery material; and a step of reducing pressure to recover the flammable gas adsorbed in the flammable gas adsorption and recovery material. The flammable gas is a volatile hydrocarbon having 5 or more carbon atoms, The combustible gas adsorption and recovery material is mainly composed of particles having a particle diameter of 1.0 μm or more and less than 1.0 mm, The method for recovering flammable gas, wherein the particles contain at least one polymer selected from the group consisting of cured natural rubber, cured linear polydimethylsiloxane, and acrylonitrile butadiene rubber, or crushed waste tires.

2. The method according to claim 1, wherein the aqueous solution contains 20 ppm to 10,000 ppm of the combustible gas.

3. 3. The method according to claim 1, wherein the aqueous solution is produced water associated with the mining of petroleum or natural gas.

4. The method according to any one of claims 1 to 3, wherein the particles contain a cured product of the linear polydimethylsiloxane.

5. The method according to any one of claims 1 to 4, wherein the flammable gas adsorption and recovery material is placed in a bag made of woven or nonwoven fabric.

6. The method according to any one of claims 1 to 5, wherein the contact is carried out for a period of 60 minutes to 20 hours.

7. The method according to any one of claims 1 to 6, wherein the pressure reduction is performed using a pressure reduction pump.

8. The method according to claim 7 , wherein the recovery is performed using a cooler located in a stage preceding the decompression pump or a compressor located in a stage following the decompression pump.

9. The method according to any one of claims 1 to 8, wherein the recovery is performed while heating the combustible gas adsorption recovery material.

10. The method according to any one of claims 1 to 3, wherein the particles are pulverized waste tires.

11. The method according to any one of claims 1 to 10, wherein the flammable gas is selected from the group consisting of pentane, hexane, benzene, toluene, and xylene.

12. The method according to any one of claims 1 to 11, wherein the particle diameter is in the range of 1.0 µm to 400 µm.

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