JPS5843132B2 - It's hard to understand why it's so difficult to understand. - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel and industrially advantageous method for removing organic sulfur compounds such as carbon disulfide, carbonyl sulfide, thiophene, mercaptans, etc. from carbon dioxide-containing gas. A hydrocarbon oil solution of a secondary amine is used as the absorption liquid, and the absorbed carbon dioxide gas is removed by volatilization in the first step and the absorbed organic sulfur compound is removed in the second step, while the absorption liquid is recovered in each step. This relates to the method of reusing the product.

In the present invention, gas refers to a gas containing an organic sulfur compound, such as carbonized coal gas, oil cracked gas, petroleum refinery waste gas, natural gas, synthetic gas, or industrial waste gas.

Conventional methods for removing organic sulfur compounds from gas include
The method of US Pat. No. 2,490,840 is known.

In this method, (a) the operation of removing organic sulfur compounds from the gas using a hydrocarbon oil solution of a secondary amine as an absorption liquid in the first step is the same as in the case of the present invention; 2
In the process, the absorption reaction liquid is brought into contact with a secondary amine aqueous solution, and the reaction product in the former is substantially transferred into the latter, and the raw absorption liquid is recovered and reused (secondary amine is also replenished). ←) The aqueous solution transferred in the third step is taken out, and after acid decomposition, free organic sulfur compounds are heated and removed, and by-product salts in the aqueous solution are decomposed with an alkali and steam distilled to obtain secondary This method combines the various operations of recovering and reusing the amine aqueous solution.

However, in this method, when carbon dioxide gas is contained in the gas, acid and alkali are also required to recover secondary amines from the reaction product with carbon dioxide gas, so the removal rate of organic sulfur compounds is limited. Increasing the secondary amine concentration in the absorbing liquid for the purpose of improving the absorbing liquid has the disadvantage that the amount of carbon dioxide absorbed and therefore the amount of acid and alkali consumed also increases.

Furthermore, since the solubility of secondary amines is originally higher in water than in hydrocarbon oil, in order to increase the absorption liquid phase concentration of the amine, it is necessary to further increase the aqueous phase concentration, but in this case, On the other hand, there is a drawback that mutual separation between the two layers becomes poor and water intrusion into the absorption liquid inhibits the selective absorption ability of organic sulfur compounds.

Therefore, in practice, the secondary amine concentration in the absorption liquid is only 1.0.
The amount is kept below 5% by weight, and in order to improve the removal rate, it is necessary to increase the scale of the absorption tower.

As the inventor of the present invention repeatedly conducted research to improve these drawbacks of the conventional method, he realized that the drawback of the conventional method was that an aqueous solution was mainly used to treat the absorption reaction liquid.
A method for recovering secondary amines without adding any water was sought.

As a result, the present inventor found that when the absorption reaction solution is heated as it is in the first step gently below 100°C, there is no substantial change (irreversible decomposition) in the reaction product between the secondary amine and the organic sulfur compound. Regardless of whether or not the reaction product of the secondary amine and carbon dioxide gas is selectively thermally decomposed, the secondary amine is regenerated (free carbon dioxide gas is volatilized) and the absorption reaction It has been discovered that the reaction product of a secondary amine and an organic sulfur compound, which is poorly soluble and precipitates mostly in solid or viscous liquid form, can be separated from the liquid, so that the absorption liquid can be recovered and reused.

Furthermore, as a second step, the present inventor has searched for a means to regenerate free secondary amines from the reaction product (reversible decomposition type) of the secondary amines and organic sulfur compounds separated as described above. When the reaction product is heated at a high temperature of about 100°C or more in hydrocarbon oil or other many organic solvents, irreversible decomposition occurs to some extent, making it impossible to regenerate the secondary amine as expected. Regardless of the above, when heating under reflux in an aliphatic or alicyclic alcohol having a carbon number of 4 to 10 (outside this range, the regeneration effect is poor), exceptionally, irreversible decomposition by-products and It has been discovered that the secondary amine can be recovered by distillation and regenerated while extremely effectively volatilizing the organic sulfur compound without recombining the volatile organic sulfur compound or the secondary amine.

That is, the present invention is a novel method that realizes the recovery and reuse of secondary amines in the absorption liquid by combining both the first and second steps, which no one has thought of yet.

Moreover, unlike conventional methods, the present invention does not use water to regenerate secondary amines, so not only does it not require any acid or alkali, but also contact between the absorption liquid and the aqueous solution (i.e., extraction separation).
Because there is no water contamination in the recovered secondary amine due to operations,
Desulfurization is extremely effective, and it has the great advantage of being able to increase the secondary amine concentration in the absorption liquid and improve the gas desulfurization rate in a normal-sized absorption tower for the first time.

The secondary amines used in the present invention include, for example, hyperidine, morpholine, pyrrolidine, hexamethyleneimine, N-methylaminoethanol, N-aminoethylpiperazine, N-(2-aminoethyl)-1. Examples include 3-propanediamine, jetanolamine, diimpropaturamine, dibutylamine, diisobutylamine, and diphenylamine.

The present invention will now be described in more detail with reference to the flowcharts shown in the accompanying drawings.

The gas to be treated enters the absorption tower 2 through conduit 1 and is discharged from the top of the tower through conduit 3.

During this time, the gas comes into contact with the absorption liquid supplied from the conduit 4 to the absorption tower 2VC, organic sulfur compounds are removed, and a portion of the coexisting carbon dioxide gas is also absorbed.

The absorption liquid enters the cushion tank 6 via the conduit 5 from the bottom of the column.

The absorption liquid enters the mixer 8 from the cushion tank 7 via the conduit 7, and is recycled as an absorption column overhead feed liquid.

The absorption liquid in the hold of the reaction product corresponding to the amount of the reaction product of the secondary amine and the organic sulfur compound produced by the one-pass absorption in the absorption tower 2 is supplied to the first regeneration tower 10 via the conduit 9. The reaction product of the secondary amine and carbon dioxide gas in the absorption liquid is decomposed by being gently heated at 100°C or less by the heater 11, and the generated carbon dioxide gas is passed from the top of the column to the conduit 1.
It is discharged after 2 steps.

In order to facilitate the discharge of carbon dioxide gas, it is effective to introduce a small amount of entrained gas through the conduit 12.

The absorption liquid whose secondary amine has been regenerated in the first regeneration tower 10 is
It enters the solid-liquid (or liquid-liquid) separator 15 through the conduit 14, and after separating the precipitated reaction product between the secondary amine and the organic sulfur compound, it passes through the cooler 16 in pure liquid form and is transferred to the mixer 8. supply and reuse.

The separated reaction product is supplied to the mixing tank 1, and the aliphatic solvent as a regeneration solvent is mixed with an alicyclic alcohol, and the mixture is supplied to the second regeneration tower 19 through a conduit 18.

In the second regeneration tower 19, the mixed liquid is heated by a tower bottom heater 20 and maintained at the boiling point temperature of the alcohol.

The organic sulfur compounds (gaseous) separated and liberated in the second regeneration tower 19 by this heating are discharged from the conduit 23b through the condenser 22 at the top of the tower. It is effective to introduce a small amount of entrained gas from the

The mixed liquid of secondary amine and alcohol from the second regeneration tower 19 is supplied from the bottom of the tower through a conduit 24 to a rectification tower 25, and the secondary amine separated by rectification here is passed through a conduit 26. The absorber feed liquid is supplied to a mixer 8.

The alcohol is supplied from the bottom of the rectification column 25 to the mixing tank 17 through the conduit 2T and is used for circulation.

Regarding the combination of secondary amine and alcohol used, if the alcohol has a higher boiling point, the secondary amine will be distilled out from the top of the column as shown in the figure, so the heating load on the rectification column will be small. Economically advantageous.

Next, reference examples and examples of the present invention will be shown to further clarify the characteristics of the present invention.

Reference example Carbon disulfide 150 ■ 5 lNd, carbony sulfide #5 o
my-S/NTIr, thiophene 80☆ - ρS/N- and a gas containing 2.5 vol.
Gas-liquid countercurrent contact was made with an absorption liquid having the composition shown in the table.

The removal efficiency of each component contained in the gas is shown in Table 2.

Example 1st step Absorption liquid from the absorption tower obtained in the reference example /161 to /16
No. 13 was heat-treated in the first regeneration tower under the conditions shown in Table 3 below.

The results are shown in Table 4. In addition, in Table 4, “Al
For comparison, 1 indicates the result when ml of the absorption liquid from the absorption tower was heat-treated at 120°C.

2nd step: After the completion of the 1st step, the reaction product of the secondary amine and the organic sulfur compound is separated from each liquid, and the reaction product is purified using each solvent shown in Table 6 under the conditions shown in Table 5. 2. The mixture was heated to reflux in a regeneration tower.

The results are shown in Table 6.

In addition, in Table 6, "B tt," Cn and "D" are /1
The results of using a solvent other than alcohol in place of cyclohexanol in Example 61 are shown for comparison.

[Brief explanation of the drawing]

The accompanying drawings are flowcharts illustrating an example of apparatus used to carry out the present invention. In the figure, thick solid lines indicate liquid-based routes, thin solid lines indicate gas or vapor-based routes, and broken lines indicate solid- or mucus-based routes. 2... Absorption tower, 6... Cushion tank, 8... Mixer, 10... Regeneration tower,
11... Heater, 15... Solid-liquid (or liquid-liquid) separator, 16... Cooler, 17...
...Mixing tank, 19...Second regeneration tower, 20
... Heater, 22 ... Condenser, 25.
...Rectification tower.

Claims (1)

[Claims] 1. In a method for removing 9 organic sulfur compounds in a carbon dioxide-containing gas by absorbing them into a hydrocarbon oil solution of a secondary amine,
In order to recover and reuse the secondary amine from the reaction product of the secondary amine, organic sulfur compound, and carbon dioxide generated in the absorption liquid, as a first step, the absorption liquid containing the reaction product is
By heating gently below 0°C, the reaction product of the secondary amine and carbon dioxide gas is selectively thermally decomposed to dissolve and recover the secondary amine, and the remaining precipitated secondary amine and organic The reaction product with the sulfur compound is separated from the absorption liquid, and then, as a second step, the reaction product is thermally decomposed in an aliphatic or alicyclic alcohol having 4 to 10 carbon atoms to volatilize the organic sulfur compound. A method for removing organic sulfur compounds from carbon dioxide-containing gas, which comprises heating the alcohol solution and recovering the secondary amine by distillation.