JPH0299114A - Dehumidifying method - Google Patents

Abstract

PURPOSE:To perform dehumidification in an industrially extremely advantageous manner by using a polymer membrane having specific permselectivity and permeation speed and bringing a gaseous mixture into contact with said membrane under a specific condition. CONSTITUTION:A gaseous mixture containing steam is brought into contact with a polymer membrane wherein the permeation speed of steam is at least 2.5X10<-3>cm<3>(STP)/cm<2>, sec, cmHg, that of methane is 1X10<-7>-2.5X10<-5>cm<3>(STP)/ cm<2>, sec, cmHg and the selective separation capacity of steam is 500 or more. The pressure of the steam-containing gas on the supply side of the membrane is held to 20kg/cm<2> or more and that on the permeation side thereof is held to 0.5-20cmHg. By this method, the sharp reduction of the membrane area and the sharp increase in treatment quantity become possible and, especially, natural gas is dehumidified in low cost.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for dehumidifying gas mixtures containing water vapor. Specifically, the present invention relates to a method of dehumidifying water vapor by contacting a gas mixture containing water vapor with a hollow fiber separation membrane having a specific performance under specific conditions to separate the water vapor in the mixture. .

[Conventional technology and its problems]

Gases, especially hydrocarbon gases such as natural gas, blanket gases on oil reservoirs, gases obtained from the separation of gas/oil mixtures, and gases generated in petroleum refining, need to be dehumidified.

In other words, the presence of moisture in hydrocarbon gas poses the danger of formation of solid hydrates due to freezing and corrosion of containers and piping in the presence of carbon dioxide and/or hydrogen sulfide; It is important to keep the water content to an extremely low value when transporting, supplying to the next process such as liquefaction, or commercially selling.

Traditionally, gas dehumidification methods include dehumidification by cooling, dehumidification by contact with glycol, dehumidification by adsorption to silica gel, etc., but these methods require large equipment and dehumidification. For example, glycol method dehydration equipment is extremely expensive in terms of safety, weight and size of the equipment, and its use has been limited to special cases. As an alternative to such dehumidification methods such as absorption and adsorption methods, a gas separation module with a built-in gas separation membrane is used to remove mixed gas from the viewpoint of downsizing, weight reduction, ease of maintenance, and safety. Dehumidification or drying methods have been proposed. That is, as a dehumidification method, (a) a method of dehumidifying a mixed gas by using a polymer membrane with specific performance and reducing the pressure on the permeation side of the gas separation membrane (JP-A-Sho!;'!-/! f21, No. 79) (b)
The permeability of methane gas, which is the main component of the supplied gas, is relatively high, and (QCH4 is / x 1o-5J (sTP)/cm +
sec + crnHg or more) and a method of dehumidifying a mixed gas using a gas separation membrane having a water vapor selectivity of 200-'100 for methane gas (JP-A-Sho!; 9-/
9313! ) (C) Method of dehumidifying a mixed gas by supplying a large amount of purge gas to the permeation side of a gas separation membrane to lower the partial pressure of the permeated water vapor (JP-A-5O-26-1I) (d) Method for dehumidifying a mixed gas by purging the permeate side of a gas separation membrane with 10 volumes or less of dry gas (moisture 500 ppm or less) against the mixed gas (JP-A-Sho/,
2-4' 2? =3) are known.

However, in method (a), the water vapor permeation rate of the membrane is low, so in order to dehumidify a predetermined amount of water, the degree of vacuum on the permeation side must be high, and a large membrane area is also required. As a result, the device becomes larger and more expensive, and it has not been put into practical use to date.

In method (b), it is difficult to produce a gas separation membrane with gas separation performance compatible with this method, and a large amount of useful gas (for example, methane), which is the main component of the mixed gas, is lost. I can't say it's advantageous.

In addition, method (C) consumes a considerably large amount of purge gas, and method (d) also requires a dehumidifying device for purge dry gas in addition to the separation membrane dehumidifying device because of the need to produce dry gas. Therefore, it cannot be said that it is advantageous.

Industrially separating water vapor from gas in this way
This is particularly important in the dehumidification of natural gas, and there are great expectations for the dehumidification method using a separation membrane method. However, in the conventional dehumidification method using a separation membrane process, the water vapor permeation rate of the membrane is low, so for industrial use the membrane area is extremely large and the equipment is large-scale, and there is also a loss of useful gas in the mixed gas. Due to its large size, it can be a method that is significantly more economical than existing dehumidification processes that do not involve desorption, but none of these methods have been put into practical use industrially.

[Failure to solve the problem]

As a result of intensive research into a practical dehumidification method that eliminates the drawbacks of the above-mentioned "mixed gas dehumidification method using a gas separation membrane," the inventor has developed a hollow separation membrane with specific membrane performance. The present inventors have discovered that a scale can be used to dehumidify moisture in a mixed gas, especially natural gas, under specific conditions, which is industrially extremely advantageous, and has completed the present invention.

That is, the gist of the present invention is to provide a dehumidification method in which water vapor is separated from a gas containing water vapor using a polymer membrane, in which the water vapor permeation rate (QH20) of the polymer membrane is 2. j X
/ 0-3cm"(STP)/a++' +sec
+cmHg or more, the methane permeation rate (QCH4) is /
X / (f'~JJ X / 0-5cm3 (STP
)/z2+ seC+cy++Hg The selective separation performance of water vapor (QH20/QCH4) is above 5ooy, the pressure of the gas containing water vapor on the supply side, which is one side of the membrane, is 20K97cm2 or more, and the pressure on the other permeation side is 20K97cm2 or more. The dehumidification method is characterized in that the pressure is maintained at 0-j ctnHg -2□cm Hg.

The present invention will be explained in detail below.

The method of the present invention uses a polymer membrane with excellent water vapor permselectivity and permeation rate to realize a practical method for dehumidifying a mixed gas for the first time.
By passing a raw material gas containing water vapor at a pressure of 20 Kf7 cm2 or more and maintaining the pressure on the permeate side at 0.3 to 20 cmHg, a dehumidification method excellent in the following points is provided.

(1) The amount of permeation of water vapor is large, and the surface area of the separation membrane built into the gas separation device can be reduced, making the device compact and reducing costs.

(2) Since it has a polymer membrane with suitable water vapor permselectivity, it has the advantage of significantly reducing loss of products (for example, methane).

Furthermore, the aromatic polyimide and aromatic polyamideimide used in the present invention have excellent durability, heat resistance, chemical resistance, moist heat resistance, etc., and can stably dehumidify mixed gas for a long period of time. It can be implemented.

The mixed gas dehumidification device according to the present invention has an inlet hole for a feed gas supply, an outlet hole for a dehumidified product gas, and an outlet hole for a permeate gas separated from the feed gas by a separation membrane having selective permeability. A mixed gas containing water vapor is supplied under pressure to the inlet of the supply section, the permeate gas side is maintained at a reduced pressure, and the gas containing more water is drawn out from the permeate gas side.
This is a method for dehumidifying the moisture in the raw material gas.

Water vapor transmission rate (QH20) is 2. ! ;X/0
-3cn? (STP)/cm” + sec, cW
less than IHg, or the methane permeation rate (QCH4) is /X/0-'>"(STP)/cm'+s
If it is less than ec + cynHg, the membrane area required for dehumidification increases significantly, which is not preferable.

Also, the permeation rate of methane is s, tX/o-5,::
(STP) /♂, Sec, if it exceeds cmHg, or water vapor selective permselectivity (QH20/QCH4)
If is less than soo, methane loss with respect to the raw material methane gas increases, which is extremely disadvantageous in terms of economic efficiency.

Furthermore, the pressure of the raw material gas supplied to the separation membrane is 20K9/
If the pressure on the permeate side is less than ♂ or exceeds 20 cmHg, the difference in water vapor partial pressure, which is the driving force for water vapor permeation, is small, and the water vapor permeation rate is small. This is disadvantageous as it requires an increase in

Also, the pressure on the permeate side is 0. ! If it is less than r cmHg, production costs such as the capacity, power, and weight of the vacuum device will increase, which is undesirable.

For the above reasons, the present invention has a water vapor permeation rate of
/ 0-3cr2 (STP)/cm” + se
c + cmHg or more, preferably yo x/θ-3 (M?
(STP)/, l? + sec + cmHg or more,
The permeation rate of methane is /, ox y o-7~x, s
x t o-','(STP)/cm" + sec
, cmHg% preferably! ;×10-' ~/×10
-5cm” (STP)/z”! sec, ff
i) (g, particularly preferably /×/ f' ~/
X/0-51: (STP)/m”, sec
, crnHg % Water vapor and methane permeation rate ratio Q
Water vapor selective permselectivity expressed as H20/QCH4 is 200
The above is preferably ioo.

As mentioned above, most preferably a separation membrane of 2oθθ or more is used.

Furthermore, the pressure of the raw material gas supplied to the membrane is θKf/crI
? The above is preferably 4' OKf/u or more, and the permeation pressure of the membrane is O,S~-〇αHg, preferably /4Mh~/θc
mHg, most preferably /fathom~! rcmHg.

In order to reduce the capacity of the device for reducing the pressure on the secondary side (permeation side) in the present invention, it is preferable to cool the water vapor in the permeate gas with a refrigerant through a heat exchanger and condense it before the pressure reduction device. .

Furthermore, the number of separation membrane modules in the dehumidification device can be arbitrarily determined depending on the amount of mixed gas to be processed, the moisture concentration of the source gas and product gas, and the dehumidification conditions such as the downstream pressure and negative side pressure. However, it is preferable to use several stages or more of modules arranged in series.

In this case, it is preferable to set the membrane area so that the amount of moisture removed in the seven stages is 374 to 1/6 of the moisture content of the supplied gas, in order to increase the permeation flow rate of water vapor.

The polymer membrane used in the present invention may be any polymer membrane as long as it satisfies the permeation performance of the present invention, and polyimide, polyamideimide, polyether, polysulfo/, polyethersulfone, and polyamide can be used. It will be done.

Furthermore, aromatic polyimide, aromatic polyamideimide, polyphenylene oxide, etc., which have excellent heat resistance, chemical resistance, and mechanical strength and are soluble in solvents, are preferable.

The shape of the polymer membrane may be flat, cheap, spiral, or hollow fiber, but hollow fiber membranes are particularly industrially advantageous because they have a large membrane area per unit volume.

The smaller the membrane thickness, the higher the permeation rate, which is advantageous, and thinning can be achieved by using a so-called asymmetric membrane formed by a mixed membrane forming method, or a composite membrane in which a support is coated with a thin film serving as a separation layer.

Therefore, the membrane of the present invention is particularly preferably a hollow fiber asymmetric membrane or a composite membrane.

Water permeability coefficient is /X/0-7cm3(STP)
・cm/cm", sec, cmHg or higher polymers include polyimide, polyamideimide, polydimethylphenylene oxide, polybutadiene, ethyl cellulose, cellulose nitrate, polycarbonate, polyethyl methacrylate, polystyrene, polyaminourethane copolymer, Examples include soluble polyamide.

As for membrane formation, the asymmetric hollow fiber membrane has a polymer concentration of 1O-1.
A dope solution consisting of an IO% solution is spun into a hollow fiber shape, then immersed in a coagulation solution to form a coagulation film, the solvent and coagulation solution are washed from the coagulation film, and the film is formed by thoroughly drying. Can be done.

A particularly preferable composite hollow fiber separation membrane is an asymmetric porous hollow fiber membrane made of polyimide or polyamideimide using a wet process, and has a water vapor permeability coefficient P) (20!; x/0-
7crI? (STP)・cm/cm” + SeC+
Examples include composite hollow fiber separation membranes coated with a dilute solution of polyoxydimethylphenylene, ethyl cellulose, soluble polyamide, polyimide, etc. having a crnHg or higher and PH20/PCH, ≧200 and dried.

〔Effect of the invention〕

In conventionally proposed dehumidification methods using membranes, the moisture concentration of the product can be reduced by bringing a mixed gas containing water vapor into contact with the membrane, as shown in examples, but the water concentration per membrane area can be reduced. In industries where the amount of mixed gas to be processed is small, and the amount of gas to be processed is large, the membrane area becomes significantly large and the equipment becomes large-scale.

Furthermore, there is a large loss of useful products (for example, methane gas) in the mixed gas, so it has not been industrialized due to economic considerations.

The dehumidification method according to the present invention enables a drastic reduction in membrane area, a drastic increase in throughput, and a drastic reduction in the loss of useful products, and has been adopted as the current dehumidification method for natural gas, for example. Since this method is more economical than the conventional glycol absorption method, it is widely expected to be used in the industrial world for dehumidifying water vapor in mixed gases.

〔Example〕

The present invention will be explained in more detail below with reference to Examples, but the present invention is not limited by the Examples.

Manufacture Reference Example/3. According to the procedure described in Example q of U.S. Pat. No. 370gIIkg. ．． 3',ll,II'-benzophenone tetracarboxylic anhydride and gθ molar tolylene diisocyanate (2,q-isomer approximately go molar and 2
．． A - a mixture of about 10 mol of isomers) and 20 mol of 9. A copolyimide was polymerized from a mixture containing K'-diphenylmethane diincyanate. Polymerization solvent is N+
A copolyimide solution with a resin concentration of 25% by weight was obtained using N'-dimethylformamide.

Manufacture Reference Example 3 The copolyimide solution obtained in Manufacture Reference Example/ is extruded at a constant flow rate from a hollow fiber manufacturing nozzle, and at the same time air is extruded at a constant flow rate into the center of the hollow fiber as a core gas.
It was introduced into a coagulation bath at 0° C., and then taken up continuously at a constant speed and wound around a skein. After this, it was immersed in water and dried day and night.

This hollow fiber was dried at 700°C for 3θ minutes and further dried for 22! r
It was dried at ℃ for 30 minutes. The hollow fiber had an inner diameter of 370μ and an outer diameter of qaoμ.

Production Reference Example 3 A hollow fiber separation membrane was produced under the same conditions as Production Reference Example 3, except that water was used as the core liquid and the drying temperature was set at θ°C.

Reference Production Example A hollow fiber separation membrane was produced under the same conditions as Reference Production Example G, except that the coagulation bath temperature was 20°C and the drying temperature was 3OO°C.

Manufacturing reference example! Production Reference Example/The copolymerized polyimide solution produced in N,
The solution was adjusted to a 71/71 weight imide solution with N dimethylformamide. Using this solution, hollow fibers were spun in the same manner as in Production Reference Example C, and then immersed in hot water at 100°C for 75 minutes.
The temperature was raised from 0°C to 500'C, and heat treatment was performed for 30 minutes.

This hollow fiber was immersed in a toluene solution containing polyoxydimethylphenylene/wt% for 1 minute, air-dried, and heated to 30°C at SO℃.
Drying was performed for a minute to produce a copolyimide composite membrane.

Production reference example 6 Production of the hollow fiber produced in production reference example 7 Polyimide dilution in which 75 parts of a solvent prepared by mixing dimethylformamide/dioxane at a ratio of 30,770 (weight ratio) was added to 70 parts of the polyimide solution polymerized in reference example 1. After soaking in the solution for 7 minutes and air drying, 27! A copolyimide composite membrane was produced by drying at r°C for 30 minutes.0 Production Reference Example 7 The copolyimide solution obtained in Production Reference Example/ was extruded from a hollow fiber production nozzle at a constant flow rate, and at the same time a core was placed in the center of the hollow fiber. Water and dimethylformamide as liquids! 0730
The hollow fibers formed by extruding a liquid mixed at a ratio of (weight ratio) at a constant flow rate are introduced into coagulated water consisting of water while being continuously drawn at a constant speed υ with an air gap of /σσ, and immersed in it. It was further washed in water. After this - After air drying day and night, dry at 100℃ for 30 minutes and then from 200℃ to 500℃
After raising the temperature to 500° C. for 73 minutes, heat treatment was performed at 500° C. for 77 minutes.

The obtained hollow fiber had an outer diameter of t, qoμ, and an inner diameter of 325μ.

Production Reference Example g A copolyimide composite membrane was produced using the hollow fiber produced in Production Reference Example 3 under the same conditions as Production Reference Example 6, except that it was dried at 310°C.

Production reference example Water/dimethylformamide as the cotton core liquid composition sh/qs
(weight ratio), airy? 7p 30111? FI-
v and heat treatment temperature to 37! A hollow fiber separation membrane was manufactured under the same conditions as the manufacturing reference example except that the temperature was changed to ℃.

Reference Example Gas Permeability Test Production Reference Example The hollow fiber separation membranes obtained in t to t were each bound with epoxy resin to produce a 30 m2 hollow fiber module. The 7th side (supply side) is placed in a water vapor atmosphere of go℃ioo%, the secondary side (permeation side) is sucked with a vacuum pump to a vacuum degree of /mmHg, and the permeated water vapor is trapped with liquid nitrogen. is cooled and collected to determine the water vapor transmission rate (QH
20) was calculated.

The permeation rate of methane (QCH4) is 3θ℃ on the seventh side.
g/crr? This was calculated from the amount of methane permeated by flowing methane gas and bringing the downstream side to atmospheric pressure.

The results are shown in Table-/.

Method for Evaluating Dehydration of Methane Production Reference Examples The hollow fiber separation membranes produced in λ to W were each bound with epoxy resin to produce a hollow fiber module of approximately 100♡.

Methane gas containing moisture at a pressure higher than atmospheric pressure on the 7th outlet side of the hollow fiber module? s (Nil/m), and the dehydration property of the membrane was tested by reducing the pressure to the 7th outlet side pressure or lower (reduced pressure).

The moisture content of the raw materials and products (methane gas that flows along the membrane and is dehydrated/next side) is measured using a Karl Fischer moisture meter (Model CA-03 manufactured by Mitsubishi Kasei Corporation), and the permeated water vapor is collected with liquid nitrogen. Then, the water concentration and water permeation rate (N, CC/-m) of the raw materials and products were calculated.

The methane permeation rate (N, CC/11111) was determined by measuring the amount of methane permeation at the secondary side under atmospheric pressure. In tests conducted with reduced pressure on the secondary side, the permeation rate of methane (N, cr
, 7m) was calculated using differential pressure.

Methane permeation rate JCH4 (cC/m)/water permeation rate JH20 (CC/
Chestnut) was used.

Small membrane area and less loss of useful products,
In order to achieve an economical dehumidification process with a high recovery rate, it is advantageous that the water permeation rate is high and the methane permeation rate/water permeation rate is small.

Example/-9 Dehumidification was performed using the hollow fiber separation membrane of Production Reference Example under the dehumidification conditions shown in Table 2, and the amount of permeated water (water permeation rate), product water concentration, Product loss (JCH4
/JH20) was measured.

The results are shown in Table-2.

Comparative Example/~6 Using the same hollow fiber as Example/-9, the dehumidification performance of methane was measured in the same manner as Example/~9 under the dehumidification conditions shown in Table-C, and the results are shown in Table-2. show.

Using the hollow fiber separation membrane of Manufacturing Reference Example 3, the dehumidification performance of methane was measured under the dehumidification conditions shown in Table 3 in the same manner as in Examples 70-1.

Comparative Examples 7-q Using the same hollow fiber separation membrane as in Examples 10-//, methane dehumidification performance was measured in the same manner as in Examples/-9 under the dehumidifying conditions shown in Table 3.

These results are shown in Table 3.

Example/Da~/S Production Reference Example Using the composite hollow fiber separation membrane described above, the methane dehumidification performance was measured under the dehumidification conditions shown in Table 5 in the same manner as in Example/~.

Comparative Examples 73 to 15 Using the composite hollow fiber separation membrane shown in Example/Dull/left, the dehumidification performance of methane was measured under the dehumidification conditions shown in Table 3 in the same manner as in Examples/~Wa.

These results are shown in Table-5.

Examples 7.2 to 3 Using the hollow fiber separation membrane of Production Reference Example D, the dehumidification performance of methane was measured under the dehumidification conditions shown in Table q in the same manner as in Examples 2 to 3.

Comparative Example/θ~7.2 Using the hollow fiber separation membrane of Examples/C~/3, the dehumidification performance of methane was measured under the dehumidification conditions shown in Table 9 in the same manner as in Examples/~D.

These results are shown in Table 1.

Comparative Example 76 - Production Reference Example 6 Using hollow fiber separation membranes of Ri, Za, Ri
The dehumidification performance of methane was measured under the dehumidification conditions of B in the same manner as in Examples/--I, and the results are shown in Table 6.

Claims (4)

[Claims] (1) In a dehumidifying method in which water vapor is separated from a gas containing water vapor using a polymer membrane, the water vapor permeation rate (QH_2O) of the polymer membrane is 2.5 x 10^-^3 cm^
3 (STP)/cm^2, sec, cmHg or more, methane permeation rate (QCH_4) is 1 x 10^-^7~2.
5×10^-^5cm^3(STP)/cm^2, se
c, cmHg and water vapor selective separation performance (QH_2O/
QCH_4) is 500 or more and the pressure of the gas containing water vapor on the supply side, which is one side of the membrane, is 20Kg/cm^2
The pressure on the other permeation side is 0.5 cmHg.
A dehumidifying method characterized by maintaining the humidity at ~20 cmHg (2) The dehumidification method according to claim 1, wherein the polymer membrane is a hollow fiber membrane having an asymmetric structure selected from aromatic polyimide, aromatic polyamideimide, and aromatic polyether. (3) The polymer membrane has a water permeability coefficient of 1×10^ on it.
-＾7cm＾3(STP)・cm/cm＾2, sec,
The dehumidification method according to claim 1, which is a composite hollow fiber separation membrane comprising a polymer layer having a thickness of 5 μm or less and having a high molecular weight of 5 μm or more. (4) QH_2O of polymer membrane is 5 x 10^-^3cm^
3(STP)/cm^2, sec, cmHg or more QCH
_4 is 1x10^-^6~1.0x10^-^5cm^
3(STP)/cm^2, sec, cmHg and QH_
2O/QCH_4 is 1500 to 25000, The dehumidification method according to claims 1, 2, and 3