JPS59130520A - Diaphragm gas separtion - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION BACKGROUND OF THE INVENTION The present invention relates to a method for separating gases by means of a membrane that is selective for the permeation of one or more gases in a gas mixture. In particular, it is a method for selectively separating acidic gases such as carbon dioxide and/or hydrogen sulfide from hydrocarbon gases such as methane by gas diffusion or permeation, without changing the characteristics of the membrane used. Concerning ways in which the separation efficiency of the stage can be improved.

Recently, gas separation membranes have been developed to separate many gases from mixtures with many other gases or vapors.

Gas separation by membranes, whether by diffusion or permeation through the membrane material, relies on large differential pressures being maintained on either side of the membrane. This pressure problem is quite different from that required when liquid substances are separated by semipermeable membranes.

Generally, the flow of one or more gases through a semipermeable membrane increases as the differential pressure across the membrane increases. However, such pressure increases are generally limited in practice by the strength of the membrane used, whether in flat film or hollow fiber form.

Moreover, the cost of compressing gases and gas mixtures through repeated separation stages, such as cascade separation steps or stages, quickly reaches economic limits. Such cascade separation stages are described, for example, in U.S. Pat. No. 2,540,152;
．． No. 713.271; No. 4,104.037 and No. 4.312.755; and European Patent Publication No.
, No. 029,600A1.

In particular, U.S. Pat. No. 4,119,417 discloses a pair of diaphragm separators connected in series and a number of reservoirs for supplying permeate and non-permeate gas from the two separators to other parts of the system. Discloses one having a piping structure. Although the diaphragms used in this gas separator system have a separation factor of about 4-5, the patentee has achieved higher separation factors by implementing these separators while recompressing the gas between the stators. trying to get .

If the diaphragm exhibits high selectivity for hydrogen permeability compared to slow permeation, then the slow permeation removes a remote permeate gas such as hydrogen from a gas mixture containing gas in a single stage. can be efficiently recovered by diaphragm gas separation. In this regard, see US Pat. No. 4,180,553 and US Pat. No. 4,172,885. See also US Pat. No. 4,180,552 for achieving separation with two permeator stages in series. Although hydrogen can be recovered with relatively high purity and high recovery, the non-permeable gas is often not of high purity in either component. U.S. Pat. No. 4,130,403 discloses the use of a pair of separators in series, where the low pressure permeate gas from the second separator is recompressed into the sixth separator. The non-permeable gas is recycled into a flow bridging the series pair separators. Excessive numbers of separation and recompression stages are generally economically unattractive.

A simple, efficient, and economical method for separating both permeate and nonpermeate gases at relatively high levels of recovery and purity without increasing the differential pressure across the membrane would be advantageous and desirable. .

For purposes of describing the present invention, a particularly convenient analytical characteristic of gas permeable polymeric membranes is the permeability of the membrane to a particular gas through the membrane. The permeability (pa/z) of a diaphragm to gas a in a gas mixture through membrane thickness t is defined as is the volume of membrane-permeating gas at standard temperature and pressure (STP). One way to express permeability is diaphragm surface area cm
Partial pressure difference ICInI (g
cIn3(STP) [i.e. cm3(S T
P)/crn2-8e (!-cmHg).Unless otherwise specified, all transmittances in this application are at 15°C.
temperature and pressure of 1 atm. Permeability is measured in gas permeation units (GPU), or cm3 (S T P )/
cm2-Bec-cmHgXl 06, so the IGPU is I
P)/cm2-sea-cm Hg. Another relationship useful for expressing gas permeation properties is the separation factor. The separation coefficient αa/b of a diaphragm for a given pair of gases a and b is the permeability of a diaphragm of thickness t for gas a in the gas mixture (Pa/z) versus the permeability of the same diaphragm for gas b (Pb/z). z).

In fact, the separation coefficient of a given diaphragm for a pair of given gases can be determined by a number of techniques that provide sufficient information to calculate the permeability for each gas. Some of the many techniques available for determining permeability and separation factors are described by Wang et al., Techniques Op Chemistry, Volume 7, Separation Diaphragms (John Wiley & Sons, 1974). It is disclosed in Chapter 16, pages 296-622.

Measurements can be carried out either by pure gas permeation or by blended gas permeation. However, it has been experimentally shown that the permeability of a diaphragm for a specific gas is measured to be higher for pure gas permeation than for blended gas permeation. Generally, the permeability and separation coefficient more accurately predict the actual gas separation performance characteristics of the diaphragm, so it is desirable to determine the gas permeation characteristics for plain gas.

A gas separation method has been discovered that improves the recovery of nonpermeate product gas(es) without requiring repeated gas recompression between separation stages as required in cascade separation schemes. This method also does not require the use of a secondary separation system to further separate the components of the recycle stream. This new method is applicable to the separation of gas mixtures which can be separated by permeation through a membrane or by diffusion, but where the necessary recovery of the non-permeated product gas cannot be effected by the use of known single permeation stages. The method uses a membrane that exhibits a reasonable separation factor for at least 2' of gases in a gas mixture required to concentrate one gas to a permeate product gas and the other gas to a non-permeate product gas. It is particularly advantageous when used. The separation factor of a diaphragm, denoted .alpha., is the ratio of the diaphragm's permeability for a fast-permeating gas substance (substance 1) to its permeability for a slow-permeating gas substance (substance j). This reasonable separation factor ranges from about 8 to about 60.

The novel process of the invention is particularly advantageous for separating acid gases such as carbon dioxide and/or hydrogen sulfide from gas mixtures containing acid gases and hydrocarbon gases such as methane. In particular, the diaphragm has a separation coefficient for carbon dioxide/methane.Summary of the Invention The present invention provides a method for separating impermeable gases enriched in at least one gas from mixtures containing at least one gas and at least one other gas. In a diaphragm gas separation method for recovering a (b) supplying the mixture at a permeate pressure to a separator; provided that the primary separator has a predetermined primary separator diaphragm surface area; (b) the permeation of the at least one gas also The nonpermeable gas from the primary separator is transferred to at least two secondary separators having membranes that are selective to the permeation of the species gas, provided that the secondary separator is and the ratio of said predetermined primary separator diaphragm surface area to said predetermined secondary separator diaphragm surface area is at least 0.6; (d) removing a non-permeate gas enriched in at least one gas from said secondary separator; and (θ) recirculating permeate gas from said secondary separator. The method is characterized in that the volume of the at least one gas recovered in the non-permeable gas is increased by removing and returning at least a portion of it to the mixture.

This process is particularly advantageous when using a separator which exhibits selectivity for the permeation of acid gas components such as carbon dioxide and/or hydrogen sulfide and has a membrane in the range 8 to 60 for carbon dioxide/methane. It is.

This method converts the hydrocarbon gas mixture into lower hydrocarbon gases such as methane, ethane, propane, but/isobutane,
Effective for pemethane, isopentane, and mixtures thereof. This method is particularly effective when the hydrocarbon gas consists of methane. This process is preferably used to separate a mixture of feed gas and recycled permeate gas containing about 30 to about 70 moles of methane and about 60 to about 70 moles of carbon dioxide. This method is particularly advantageous when the methane-rich nonpermeate gas comprises at least about 90 moles of methane and at least 90 moles of total methane in the feed gas.

In this method, the diaphragm has a diaphragm of 8 to 3
This is particularly effective when exhibiting selectivity with a coefficient in the range of 0.

That is, this diaphragm has a gas separation coefficient α in the range of 8 to 60.

In such a method, the primary separator comprises a plurality of separators having a predetermined primary separator diaphragm surface area, and the secondary separator comprises a plurality of separators having a predetermined secondary separator diaphragm surface area, and It is often desirable that the ratio of the predetermined primary separator diaphragm surface area to the predetermined secondary separator diaphragm surface area be at least 0.6.

The invention further provides at least two primary separators having diaphragms exhibiting selectivity for the permeation of at least one other gas compared to the permeation of at least one other gas.
at least two secondary separators having diaphragms exhibiting selectivity for the permeation of said acid gas as compared to the permeation of said gas, said at least said acid gas and said at least one other gas; means for feeding a mixture containing the above at permeate pressure into the primary separator; means for flowing the non-permeable gas from the primary separator to the secondary separator; means for removing enriched permeate gas, means for removing from said secondary separator a nonpermeate gas enriched in said at least one other gas, means for removing recirculated permeate gas from said secondary separator, and said recirculation. A diaphragm gas separation device comprising means for returning at least a portion of the permeate gas to the mixture supply means.

In a preferred embodiment of the apparatus of the present invention, said primary separator has a predetermined primary separator diaphragm surface area, said secondary separator has a predetermined secondary separator diaphragm surface area, and said 1
The ratio of the secondary separator diaphragm surface area to the secondary separator diaphragm surface area is at least 0.3.

Furthermore, preferred embodiments of the present invention provide for contacting a gas mixture containing carbon dioxide and/or hydrogen sulfide and methane with one side of a membrane that is more permeable to carbon dioxide than methane to remove the acid gas. This method separates acidic gases such as carbon dioxide and/or hydrogen sulfide from methane by allowing the gas to pass through the other side of the diaphragm. Permeate gas is removed from the other side of the membrane and divided into a recovery stream and a recycle stream, with the recycle stream being returned to contact one side of the membrane.

The membrane has a separation factor of at least about 8 for carbon dioxide/methane.

Detailed description of the invention The invention will be described in detail with reference to the drawings. FIG. 1 schematically illustrates an apparatus useful for carrying out the method of the invention. A feed gas containing hydrocarbon gases such as methane and acid gases such as carbon dioxide is provided by line 1, which mixes with the recycled permeate gas in line 12 to form a mixture and 1 by 5
Next, it is sent to the separator 7. The primary separator 7 has a diaphragm 8 that is selective to the permeation of methane and carbon dioxide.

This mixture is pumped at a permeate pressure such that the carbon dioxide-rich gas selectively permeates the membrane.

The permeate gas rich in carbon dioxide is transferred from the primary separator 1 to the line 2.
The non-permeable gas is transferred from the primary permeator 7 via line 6 to the secondary permeator 9 while being removed at reduced pressure by the . 2
The secondary permeator has a diaphragm 10 that is selective to the permeation of methane and to the permeation of carbon dioxide. Since the carbon dioxide selectively permeates through the diaphragm 1°, a non-permeable gas rich in methane is produced, and this non-permeable gas is taken out from the secondary PIi vessel 9 via line 3 under reduced pressure. The permeate gas from the secondary separator 9 is sent to the compressor 11 via line 4 and is fed back at permeate pressure via line 12 as recirculated permeate gas.

Membranes 8 and 10 exhibit selectivity for the permeation of hydrocarbons, such as methane, as well as acid gas components, such as carbon dioxide, such that the membranes have a separation factor for carbon dioxide/methane of at least about 8. characterized as. Although the separation coefficient may be in the form of a flat sheet, it is preferably in the form of hollow polymeric fibers. Diaphragms generally consist of multiple bundles of hollow fiber membranes. Preferred hollow fiber membranes include multicomponent membranes such as those disclosed in US Pat. No. 4,230,463. Examples of various effective separator designs include U.S. Pat. No. 3,616,928;
No. 539,341; No. 3.422,008; No. 3,5
No. 28,553; No. 3,702,658; and No. 4
, No. 315,819.

FIG. 6 discloses an alternative system in which the feed gas is supplied at low pressure and therefore must be compressed to permeate pressure. The permeate gas from secondary separator 9A is sent by line 4A as recycle permeate gas and mixes with the low pressure feed gas stream in line 1. These produce a low pressure gas mixture which is sent by line 12A to compressor 11A, which converts it into a mixture at permeate pressure.

Operation as shown in FIG. 3 is advantageous because both the recycle permeate gas and the feed gas are compressed to permeate pressure by the compressor. This saves significant amounts of capital equipment, equipment costs, and labor costs.

Of course, the separators 7.9 and 7A% of FIGS. 1 and 3
9A should be understood to represent a single separator or multiple separators so that the membrane surface area on each side of the separator is most economical depending on the membrane surface area required for the desired separation.

FIG. 2 schematically illustrates an alternative apparatus for carrying out another aspect of the method of the invention. A gas mixture containing, for example, methane and carbon dioxide is supplied by line 42, which is combined with the feed gas by line 41 and by line 6.
Consisting of recirculated permeate gas from 6. This gas mixture is fed at permeate pressure to a plurality of primary separators 43, 47 and 51 in series. Each primary separator has membranes 44.48 and 52 that are selective for the permeation of carbon dioxide so that the carbon dioxide-rich permeate gas leaves the separator in line 45.49.
and 53. The nonpermeate gas passes through each primary separator in series with minimal permeate pressure drop, for example by lines 46, 50 and 54. The number of primary separators in series depends on factors such as the total gas flow rate, the separation required, and the economical membrane surface area that can be provided in a single separator. The opaque gas from the primary separators is fed by line 5G to the secondary separators, while line 56 carries the opaque gas to secondary separators 59 and 61 arranged in parallel, for example by lines 57 and 58. into the injected gas stream. The secondary separators 59 and 61 have diaphragms 60 and 62 that are selective to the permeation of carbon dioxide, so that the permeate gas rich in carbon dioxide is passed through lines 64 and 62, respectively, rather than the gas supplied to the secondary separators. It can be taken out from 65. The permeate gas stream can be combined as recycled permeate gas and is conveyed by line 66 to be combined with the feed gas in line 41. The non-permeate gas from the secondary separator is substantially methane-rich and flows through line 6.
8 and 61 from the secondary separator. The number of secondary separators also depends on variables such as the amount of gas to be processed, the separation required and the amount of membrane surface area that can be provided in a single separator.

Depending on the separation to be performed, the primary separator e.g. 43.4γ
and 51 may be in series as shown in FIG. 2, or may be in parallel or in a series/parallel combination.

Similarly, the array of secondary separators, e.g. 59 and 61,
It may be in parallel as shown in the figure or in a series or series/parallel arrangement.

FIG. 4 schematically depicts an apparatus useful for carrying out aspects of the method of the present invention with a single membrane separator. For example, a gas mixture of carbon dioxide and methane is supplied to the compressor 11
1 through a line 112 to a separator 1 having a diaphragm 114 more permeable to methane than to carbon dioxide.
Sent to 13.

The carbon dioxide permeates selectively from one side of the diaphragm to the other, resulting in a carbon dioxide-rich permeate gas stream in line 1.
16 from the separator 113. Non-permeable gas is removed from separator 113 through line 104; this gas stream is a methane-rich recycle stream. line 1
A portion of the carbon dioxide-rich permeate gas stream passing through 16 is removed from this line and sent by line 103 to compressor 111
is recirculated to the suction side of the diaphragm 114 and fed back into contact with one side of the membrane 114.

The remaining permeate gas stream is removed as a carbon dioxide-enriched recovery stream 105. The amount of carbon dioxide-rich permeate gas stream returned to the inlet side of the electrical divider 113 is about 10-50%.

A large amount of diaphragm permeation data has been accumulated as a result of a large number of diaphragm gas separation operations, and computer simulations of diaphragm gas separation can be used to predict diaphragm gas separator performance with reasonable accuracy. . Such diaphragm separation data may be, for example, dicarbon dioxide 21.8
A feed gas containing molt and 76.9 moles of methane,
When contacted with a gas separation membrane that is highly permeable to carbon dioxide, a permeate gas containing 78.6 moles of carbon dioxide was removed. The nonpermeate gas was concentrated to 79.0 moles of methane. The same membrane was contacted with a substantially carbon dioxide-rich feed gas containing 79.8 moles of carbon dioxide and only 16.9 moles of methane and operated under similar conditions of temperature, pressure, and flow rate. In this case, the permeate gas was concentrated to 94.4 moles of carbon dioxide. However, the nonpermeate gas was only concentrated to 19.2 molar parts of methane.

The examples below are based on computer simulations of membrane gas separation of gas mixtures containing carbon dioxide and methane. The metric units of measurement used in the following examples are the units of measurement commonly used in the United States converted using the following conversion factors.

5OFHX O,0268= N m”/hrpsi
X 0.89 = kPa ft2x O, [l 929 = m”BHP Xo,
7457=kW (where FEOFH is the unit of flow expressed in standard cubic feet per hour; N 7713/hr is the unit of flow expressed in nominal cubic meters per hour; psi is the unit of flow expressed in nominal cubic feet per hour) kPa is the unit of pressure in kilopascals; ft” is the unit of area in square feet; TrL2 is the area in square meters is the unit of; BHP
is the unit of power in brake horsepower; and kW is the unit of power in kilowatts.

Example 1 This is a computer simulation to illustrate the separation of a known diaphragm, and proves that an increase in diaphragm area has a disadvantageous effect on methane recovery by a diaphragm gas separation method. This effect is such that as the diaphragm surface area increases, the purity of methane in the non-permeable gas increases, but the recovery of methane is slightly reduced. Carbon dioxide 44.0
A feed gas consisting of 55.0 molar parts of methane and 1.0 molar parts of nitrogen is supplied at a flow rate of 1115 Nm''/hr.

This gas has a permeation pressure of 3620 kPa and a membrane surface area of 1
1067 FL" separator. The permeate side of the diaphragm is maintained at 172 kPa.

The membranes of both separators have a carbon dioxide permeability of 35. Q GPU (
), characterized as having a methane permeability &2.5 GPU and a nitrogen permeability of 1.90 p U. Based on this carbon dioxide transport and the permeability of methane, the membrane exhibits a selectivity of 14 for the permeation of carbon dioxide over methane; i.e., carbon dioxide-rich gases are selectively permeated through the membrane. There will be. The permeate recovery gas is expected to have a composition of 69.1 molar carbon dioxide and 60.4 molar methane and a flow rate of 704 N771''/hr.

This permeate gas stream recovers 99.1% of the total carbon dioxide contained in the feed gas.

In addition, the non-permeable gas from the permeator has a composition of 1.1 molar carbon dioxide and 96.9 molar methane and has a flow rate of 416 N 77
13/hr. This non-permeable gas stream eliminates 65% of the total methane contained in the feed gas.
．． 1% will be recovered.

The simulation was repeated under the same conditions except that the membrane surface area was increased to 1236 m2. As the diaphragm surface area increases,
The non-permeable gas becomes methane concentrated to a level of 97.6 moles of methane. However, the recovery of methane by impermeable gas is such that the impermeable gas accounts for 60% of the total methane in the feed gas.
0. ．． It will probably drop to about 1%.

Furthermore, the simulation was repeated under the same conditions except that the membrane surface area was increased to 1384 m''.

Due to this increase in membrane surface area, the impermeable gas is 97.8
It is predicted that the methane will be concentrated to the level of molch. However, the recovery of methane by the nonpermeate gas will be further reduced to only 54.9% of the total methane in the feed gas.

Data related to this simulation are summarized in Table 1.

What's the size? + mouth glossy size to 0 size K) mute o-+old-o a:+-o size0i 00C1ffi +”-to ■
O dimensionu'')r C'J (a)α
℃ dimension L1'')F Examples 2 to 5 below are provided to explain the present invention in detail, and show that even if the total surface area of the diaphragm is increased, the recovery of methane by non-permeable gas is significantly improved.

Example 2 Feed gas consisting of 44.0 mole carbon dioxide, 55.0 mole methane and 1.0 mole nitrogen at a flow rate of 11
Co/computer simulation explains diaphragm gas separation supplied at 15 Nm”/hr. This gas is
Supplied at a permeation pressure of 0 kPa. This feed gas is combined with permeate recycle gas which is now compressed to F) 3620 kPa and is fed to a primary separator with a membrane surface area of 743 m2. The non-permeable gas from the primary separator is transferred to a secondary separator with a membrane surface area of 362 m2.

The diaphragms of both separators have a carbon dioxide permeability of 35.0 GPU (
), characterized as having a methane permeability of 2.5 GPU and a nitrogen permeability of 1.90 PU. Based on the permeability of carbon dioxide and methane, this membrane exhibits a selectivity of 14 for the permeation of carbon dioxide over the permeation of methane: i.e. 30.9% for carbon dioxide.
It is predicted that permeate recycle gas having a composition of 68.1% and 68.1% methane can be removed from the secondary separator at a flow rate of 'I 15 Nm''/hr and returned as permeate recycle gas to be mixed with the feed gas. Ru.

The permeate gas from the primary separator has a composition of 78.1 molt carbon dioxide and 21.6 molt methane, and has a flow rate of 617 N m”7.
'hr. This permeate gas stream will contain 97.9% of the carbon dioxide contained in the feed gas.

In addition, the non-permeable gas from the secondary separator is carbon dioxide 2.0
Flow rate 499 N with a composition of molti and methane 96.1 molti
771"/hr. This non-permeable gas stream will recover 78.2% of the total feed methane in the feed gas.

The permeate gas stream will exit each permeator at a pressure of 1721 cPa. A compression power of 23 kw would be required to compress the permeate recycle gas to a permeate gas pressure of 3620 kPa.

Data related to the computer simulation of Example 2 are summarized in Table 2.

The examples serve to further illustrate computer simulations of membrane gas separation of gas mixtures containing carbon dioxide and methane.

The same feed gas used in the simulation of Example 2 can be separated by the method of the present invention in which the primary permeator has a membrane surface area of 539 m2 and the secondary permeator has a membrane surface area of 697 m''.

Other operating parameters are the same as in Example 2, except that the permeate recycle gas has a composition of 50.1 mole carbon dioxide and 49.2 mole methane and a flow rate of 300 Nm3/hr. This recirculated gas has a high capacity of 172 kP.
6 Q kW to compress from a to 3620 kPa
requires the power of

The permeate gas recovered from the primary separator contains 84% carbon dioxide.
Flow rate 566 with a composition of 6 molti and methane 15.2 molti
The permeate gas stream is expected to contain 97.3% of the total carbon dioxide in the feed gas.

The non-permeable gas from the secondary separator has a composition of 2.0 mol of carbon dioxide and 96.2 mol of methane, and a flow rate of 55 ONm.
It is expected to flow out in hr. Recovery of methane by this non-permeable gas is expected to be quite high at 85.7% of the total methane in the feed gas.

The relevant data of the computer simulation of this Example 6 are summarized in Table 2.

Example 4 This example further illustrates a computer simulation of membrane gas separation of a gas mixture containing carbon dioxide and methane.

In this embodiment, the diaphragm surface area of the primary separator is further reduced and the diaphragm surface area of the secondary separator is further increased. This allows the device to accommodate high volumes of recycle gas, thereby increasing methane recovery from the non-permeate gas stream recovered from the secondary permeator.

Primary separator with diaphragm surface area of 427 m” and diaphragm surface area of 95 m”
The same feed gas used in the simulation of Example 2 is separated by the method of the invention using a 7 m2 secondary separator. Other operating parameters are 520 N77
Same as Example 2 except that 13/hr of recycled permeate stream is returned for mixing with the feed gas. This high volume of recirculated permeate gas requires 102 kW of power to compress from 172 kPa to 3620 kPa.

Recovery of methane by nonpermeate gas from the secondary separator is expected to increase to 90.5% of the total methane in the feed gas.

The relevant data of this computer simulation of Example 4 are summarized in Table 2.

Example 5 This example serves to further illustrate a computer simulation of membrane gas separation of a gas mixture containing carbon dioxide and methane.

This example serves to illustrate the further improved recovery of methane in the nonpermeate gas from the secondary separator. This is accomplished by further adjusting the membrane surface area between the separators and further increasing the flow rate of the recycled permeate gas. The primary separator has a diaphragm surface area of 279 m2
and the secondary separator has a membrane surface area of 1551rrL
It has 2.

Other operating parameters are the same as Example 2 except that 1400 Nm3/hr of permeate recycle gas is returned for mixing with the feed gas. This volume of recirculated gas is 17
2 to compress from 2 kPa to 3620 k'Pa
It required 751w power.

Recovery of methane by nonpermeate gas from the secondary separator is expected to improve to 96.4% of the total methane in the feed gas.

The relevant data of the computer simulation of this Example 5 are summarized in Table 2.

Examples 2-5 above illustrate embodiments of the process of the present invention for recovering hydrocarbon-rich non-permeable gases from mixtures containing hydrocarbon gases and acid gases. These examples illustrate the wide range of variables that can be manipulated to most effectively carry out the process depending on feed gas conditions, available membrane surface area, operating costs, and separation required.

The present invention utilizes recycle gas to increase hydrocarbon recovery from a mixture of hydrocarbon gas and acid gas to high levels without reducing hydrocarbon recovery as membrane surface area increases. Provided is a diaphragm gas separation method for improving the recovery of gas.

EXAMPLE The example describes a computer simulation of membrane gas separation according to the present invention using a single membrane separator. Table 6 summarizes the simulation results in which a feed gas of 55.0 molar methane and 45.0 molar carbon dioxide is combined with an impermeable gas stream of 95.0 molar methane and 78.0 molar methane.
It is anticipated that separation into a permeate gas stream of 0 molar carbon dioxide will be possible. This nonpermeate gas stream will recover 78.0% of the total methane in the feed gas. The permeate gas stream is not recycled. The pressure on the supply side of the diaphragm is 2520kP
The pressure on the permeate side of the diaphragm is 172 kpa.

Table 6 Nagarani★ 101 102 103 104 1
05 flow rate (103N7713/hr) 5.6
5.6 0 2.6 3.0 Composition (mol%) OH, 55,055,0-95,022,0002'
45.0 45.0 - 5.0 78.0
★Nagaraya corresponds to the flow of lines represented by the same ya in Figure 4.

Example 7 This example describes a computer simulation of gas separation using the same membrane as Example 6, except that 25.7% of the permeate gas stream is recycled to the gas mixture. Fourth
The simulations summarized in the table show that the supply is 95.
We predict that it can be separated into a nonpermeate gas stream of 0 molar methane and a permeate gas stream of 80.8 molar carbon dioxide. This impermeable soot stream will recover 81.5% of the total methane in the feed gas.

Table 4 Nagariya★ 101 102 103 104 1
05 flow rate (103Nm3/hr) 5.6 6.6
1.0 2.6 3.0 Composition (mol%) OH, 55,049,619,295,019,200
245,050,480,85,080,8★Nagare-ya corresponds to the flow of the line represented by the same-ya in FIG.

Example 8 This example describes a computer simulation of the same membrane gas separation as Example 7, except that 50% of the permeate gas stream is recycled to the gas mixture. The simulations summarized in Table 5 set the feed gas to 95.0
We predict that it will be possible to separate a non-permeate gas stream of 84.5 molar methane and a permeate gas stream of 84.5 molar carbon dioxide. This nonpermeate gas stream will recover 85.6% of the total methane in the feed gas.

Table 5 Nagariya★ 101 102 103 104 1
05 Flow rate (10”N@3/hr) 5.6 8.4
2.8 2.8 2.8 Composition (mol%) CjH455-041,715,595,015°5C
! 02 45.058.3 84.5 5.0
84.5★ Flowing Tomb corresponds to the flow of the line represented by the same lagoon in Figure 4.

Diaphragms suitable for use in this process often have a substantially high separation factor, ie, at least about 9, for hydrogen sulfide/methane as well as for carbon dioxide/methane.

Therefore, hydrogen sulfide or a mixture of hydrogen sulfide and carbon dioxide can be separated from methane with substantially the same efficiency as when carbon dioxide is separated from methane.

Although the invention has been described with respect to specific embodiments, it is not limited thereto. It should be understood that various modifications may be devised by those skilled in the art without departing from the spirit and scope of the invention.

[Brief explanation of the drawing]

1, 2, 6, and 4 are schematic illustrations of the apparatus used in carrying out the method of the present invention. Primary separator・・・・・・・・・7.7A% 43
．． 4L 51 Secondary separator・・・・・・・・・・・・L
9A% 5L 61 single separator・・・・・・・・・
・・・113 Diaphragm・・・・・・・・・・・・・・・・・・
・・・・・・・・・・・・8.10.44.48.52.6
0.62.114 Compressor・・・・・・・・・・・・・・・・・・1
1.11A, 111 Fang 3 Figure O 1 Procedural amendment (method) % formula % 1, Indication of the case Patent Application No. 190613 of 1982 2, Title of the invention 3, Person making the amendment Relationship with the case 1t 'Applicant address 4, agent January 31, 1980 6, number of inventions increased by amendment 7, subject of amendment/--\\

Claims (9)

[Claims] (1) In a diaphragm gas separation method for recovering an impermeable gas enriched in at least one gas from a mixture containing at least one gas and at least one other gas, (a) said mixture at permeate pressure to at least two primary separators having diaphragms exhibiting selectivity for the permeation of said at least one other gas relative to the permeation of said at least one gas; provided that the primary separator has a predetermined primary separator diaphragm surface area: (b) the permeation of the at least one other gas in the bundle is greater than the permeation of the at least one gas in the bundle; 1 to at least two secondary separators having diaphragms exhibiting selectivity for
transfer nonpermeate gas from a secondary separator, provided that the secondary separator has a predetermined secondary separator membrane surface area, and the predetermined primary separator membrane surface area versus the predetermined secondary separator membrane surface area; (c) withdrawing from said primary separator a permeate gas enriched in said at least one other gas; (d) withdrawing said at least one bundle from said secondary separator; a nonpermeate gas enriched in one gas; and (θ) recovered in the nonpermeate gas by removing recycled permeate gas from the secondary separator and returning at least a portion of it to the mixture. A method characterized in that the capacity of at least one gas in the bundle is increased. 2. The method of claim 1, wherein at least one gas in said bundle contains a hydrocarbon gas and said at least one other gas is an acidic gas. (3) The diaphragm having a selectivity for the permeation of at least one other gas as compared to the permeation of at least 1 ai gases in the bundle has a separation coefficient α in the range of 8 to 60. The method according to the second term of the scope. (4) The method according to claim 6, wherein the hydrocarbon gas is methane. (5) The method according to claim 4, wherein the acidic gas comprises carbon dioxide. 6. The method of claim 5, wherein said mixture comprises said recycled permeate gas and a feed gas containing about 60 to about 70 moles of methane and about 60 to about 70 moles of carbon dioxide. 7. The method of claim 6, wherein said non-permeable gas enriched with said at least one gas comprises at least 90 moles of methane and at least 90q6 of the total methane in said feed gas. (8) A method for separating an acid gas from a gas mixture containing a hydrocarbon gas, wherein the hydrocarbon gas is also permeable to the acid gas and has a separation factor for carbon dioxide/methane of at least about 8. (b) removing a non-permeable gas stream from the one side of the membrane; (C) removing a permeate gas stream from the other side of the membrane; and (d) returning a portion of the permeate gas to the gas mixture as a recycle stream. 9. The method of claim 8, wherein 10-50% of said permeate gas stream is returned to said gas mixture. 10. The method of claim 9, wherein said gas mixture consists of a feed gas containing 20 to 80 volumes of methane and said recycle stream. 11. The method of claim 10, wherein the αυ impermeable gas stream contains at least 90 volumes of methane. Q2. The method of claim 11, wherein a sufficient amount of said permeate stream is returned as a recycle stream such that said non-permeate gas stream contains at least 80% of the methane in said feed gas. α) at least two primary separators having diaphragms exhibiting selectivity for the permeation of at least one other gas compared to the permeation of at least one other gas; at least two secondary separators having diaphragms exhibiting selectivity for the permeation of said gases as compared to said gases; means for feeding the non-permeate gas from the primary separator to the secondary separator; means for removing from the primary separator at least the gas-enriched permeate gas; means for removing a non-permeate gas enriched in at least one other gas from the separator; means for removing recycled permeate gas from the secondary separator; and means for supplying at least a portion of the recycled permeate gas to the mixture. A diaphragm gas separation device consisting of means for returning the gas to α→ The primary separator has a predetermined primary separator diaphragm surface area, the secondary separator has a predetermined secondary separator diaphragm surface area, and the primary separator diaphragm surface area versus the 2 17. The apparatus of claim 16, wherein the ratio of secondary separator membrane surface areas is at least 0.6.