JPS644964B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is obtained by decomposing heavy oil, coal, etc.
This paper relates to a method for separating extremely high-purity CO from a mixed gas consisting mainly of H ₂ and CO using a gas separation membrane. In particular, we aim to provide a particularly advantageous method when extracting high-purity CO from a portion of a mixed gas consisting mainly of H ₂ and CO and using this CO for the production of acetic acid or oxalic acid using the methanol method. be. It is already known that a gas is separated from a mixed gas using a gas separation membrane, and it is also used industrially. (Reference CEP, Oct1982, pages 27-32)
However, all of these techniques mainly focus on separating components that easily permeate (H ₂ in the case of the present invention), and are superior in terms of separating components that are difficult to permeate (CO in the case of the present invention) as in the method of the present invention. There were no other suggestions. Generally, when a gas separation membrane is used, the gas permeation rate in the membrane follows the following equation (1) for each component gas. Q = (p ₁ - P ₂ )K・S...(1) Q: Gas permeation rate (cm ³ (STP)/sec) p ₁ : Partial pressure of permeate component on raw gas side (cmHg) p ₂ : Permeate side 〃 〃 ( 〃 ) K: Permeability of the permeable component through the membrane (cm ³
(STP)/cm ² , sec, cmHg) S: Membrane area (cm ² ) As is clear from equation (1), in the process of separation in the membrane, a component gas that permeates quickly (H ₂ in the case of the present invention)
is lost from the raw gas side, and p ₁ decreases. On the other hand, on the permeate side, conversely, the component gas that permeates faster (H ₂ in the case of the present invention) increases, so p ₂ becomes a value close to the total pressure on the permeate side. Therefore, as the concentration of the component gas that permeates slowly (in the case of the present invention, CO) increases on the raw gas side, p ₁ − _{p 2}
The value of becomes low, and removal of the component gas (H ₂ in the case of the present invention), which permeates faster than the original gas, becomes difficult to proceed.
To solve this problem, in addition to increasing _p1 , that is, increasing the pressure, the pressure on the permeate side is reduced, or the permeate side is purged with a gas other than the component gas to be permeated (in the case of the present invention, purging with CO etc. ) and other measures will be taken. However, the former requires extra power and increases the cost due to the high pressure of the process. In the latter case, the concentration of the permeate component gas (H ₂ in the case of the present invention) on the permeate side decreases, and additional gas is added, which increases costs. The present invention is a method devised to solve these problems.It is a method that has been devised in order to solve these problems.At the stage when the component gas to be permeated ( _H2 in the case of the present invention) has descended on the raw gas side,
The solution is to use a membrane with low separation (in the present case H ₂ /CO separation). In other words, two or more membrane modules are used, and a membrane with high H ₂ /CO separation is used at a stage when the H ₂ concentration in the raw gas (mixed gas consisting mainly of H ₂ and CO) is high, and when the H ₂ concentration is lowered. At the stage H ₂ /
The solution is to use a membrane with low CO separation. The details of the present invention will be further explained using Examples and Comparative Examples. Example 1 is a case in which the method of the present invention is implemented using a mixed gas of H ₂ and CO with a relatively high CO concentration among cracked gases such as heavy oil, and Comparative Examples 1 and 2 are known methods. 1 is a membrane with high H ₂ /CO separation (Example 1)
In the case of Comparative Example 2, a membrane with a lower H ₂ /CO separation degree was used (the membrane used for the second and third stage modules in Example 1) was used. An example using a membrane with the same resolution as the membrane used in this study is shown below. From these results, it can be seen that when trying to obtain gas with a purity of 98% CO, Example 1 using the method of the present invention obtained the maximum amount of gas. That is, in other words, when trying to obtain the same amount of gas with a 98% CO concentration, the method of the present invention provides the smallest membrane area. In the case of Comparative Example 2, a value quite close to that of Example 1 of the method of the present invention was obtained, but the H ₂ concentration on the permeation side was low;
Furthermore, the amount of permeation is large, which is disadvantageous compared to the method of the present invention. Example 2 is a case in which the method of the present invention is implemented using a mixed gas of H ₂ and CO with a relatively low CO concentration among cracked gases such as heavy oil, and Comparative Examples 3 and 4 are conventional methods. 3
In this case, a membrane with high H ₂ /CO separation (1
In the case of Comparative Example 4, a membrane with a lower H ₂ /CO separation degree (the same membrane used for the second stage module in Example 2) was used. An example using a membrane with high resolution is shown below. It can be seen that in these cases, as in the case of Example 1, Example 2 of the method of the present invention is the most excellent. Example 1 This example shows a case in which the method of the present invention is implemented using a mixed gas of H ₂ and CO with a relatively high CO concentration among cracked gases such as heavy oil. FIG. 1 shows a schematic diagram of a flow sheet implementing the method of the invention. A, B, and C indicate membrane modules, each filled with 3000 hollow fiber polyimide membranes prepared by the method described in JP-A-57-157435 or JP-A-57-15819. . The size of the module is 2 cmφ x 20 cml. A module has a separation membrane with H ₂ /CO separation degree of 120,
That is, a polyimide separation membrane having a H ₂ permeability (K _H2 ) of 9.0×10 ⁻⁶ and a CO permeability (K _CO ) of 7.5×10 ⁻⁸ was used.
For the B and C modules, a separation membrane with an H ₂ /CO separation degree of 15, that is, a polyimide separation membrane with an H ₂ permeability (K _H2 ) of 9.0×10 ⁻⁶ and a CO permeability (K _CO ) of 6.0×10 ⁻⁷ was used. . The H ₂ and CO mixed gas passes through an acid gas removal device.
It is sent to the A module from conduit 1. At this time, the pressure was 31Kg/cm ² (gauge) and the temperature was room temperature. In module A, the permeate gas flows from the outside to the inside of the hollow fiber membrane and exits through the flow conduit 3. The pressure at this time was 1 Kg/cm ² (gauge). Non-permeable gas flows along the outside of the hollow fiber membrane, exits through conduit 2, and is fed into the B module. In the B module, as in the A module, the permeate gas flows from the outside to the inside of the hollow fiber membrane and exits through the flow conduit 5. The non-permeate gas flows along the outside of the hollow fiber membrane, exits through conduit 4 and enters the C module. In the C module, as in the A and B modules, the permeate gas flows from the outside to the inside of the hollow fiber membrane and then flows out through the flow conduit 8. Non-permeable gas flows along the outside of the hollow fiber membrane;
It flows out from the conduit 7. Flow rate at inlet, outlet and other points, H ₂ ,
The CO composition is shown in Table 1. Comparative Example 1 In this example, H ₂ /
CO separation degree 120 or H ₂ permeability (K _H2 ) 9.0×10 ^-6 ,
The same procedure as in Example 1 was conducted except that a polyimide separation membrane with a CO permeability (K _CO ) of 7.5×10 ⁻⁸ was used. The results are shown in Table 1. Comparative Example 2: A, B, (modules both contain H ₂ /CO
The same procedure as in Example 1 was carried out except that a polyimide separation membrane having a separation degree of 15, that is, a H ₂ permeability (K _H2 ) of 9.0×10 ⁻⁶ and a CO permeability (K _CO ) of 6.0×10 ⁻⁷ was used. The results are shown in Table 1.

[Table] Example 2 This example shows a case in which the method of the present invention is implemented using a mixed gas of H ₂ and CO with a relatively low CO concentration among cracked gases such as heavy oil. FIG. 2 shows a schematic diagram of a flow sheet implementing the method of the invention. A and B indicate membrane modules, which are disclosed in JP-A-57-157435 or JP-A-57-15819, respectively.
It is filled with 3000 hollow fiber polyimide membranes prepared by the method described in the publication. The size of the module is 2 cmφ x 20 cml.
The A module has the same H ₂ /CO separation as in Example 1.
120 separation membrane, i.e. H ₂ permeability (K _H2 ) 9.0×10 ^-6 ,
A polyimide separation membrane with a CO permeability (K _CO ) of 7.5×10 ^-8 was used. For the B module, a separation membrane with an H ₂ /CO separation degree of 20, that is, a polyimide separation membrane with an H ₂ permeability (K _H2 ) of 9.0×10 ⁻⁶ and a CO permeability (K _CO ) of 4.5×10 ⁻⁷ was used. The gas introduction method, pressure, temperature, etc. were all the same as in Example 1. The results are shown in Table 2. Comparative Example 3 In this example, both A and B modules were made of polyimide with an H ₂ /CO separation degree of 120, that is, a H ₂ permeability (K _H2 ) of 9.0×10 ⁻⁶ and a CO permeability (K _CO ) of 7.5×10 ⁻⁸ . The same procedure as in Example 2 was carried out except that a separation membrane was used. The results are shown in Table 2. Comparative Example 4 In this example, both the A and B modules were made of polyimide with an H ₂ /CO separation degree of 20, that is, a H ₂ permeability (K _H2 ) of 9.0×10 ⁻⁶ and a CO permeability (K _CO ) of 4.5×10 ⁻⁸ . The same procedure as in Example 2 was carried out except that a separation membrane was used. The results are shown in Table 2.

【table】

【table】 [Brief explanation of the drawing]

Figures 1 and 2 each represent a schematic diagram of a flow sheet for gas separation, where A, B, and C are modules;
1, 2, 3, 4, 5, 6, 7, 8, and 9 indicate conduits, respectively.

Claims (1)

[Claims] 1 H ₂ and CO obtained by decomposing heavy oil, coal, etc.
When separating high-purity CO from the main mixed gas using a gas separation membrane, two or more membrane modules are used, and when the _H2 concentration in the raw gas is high,
A membrane with a high H ₂ /CO separation is used, and a membrane with a low H ₂ /CO separation is used at the stage when _{the H 2 concentration} has decreased.
How to separate CO.