JPS627604A - Method for recovering decomposed gas from methanol - Google Patents

Abstract

PURPOSE:To recover purified gaseous mixture consisting of H2 and CO by washing decomposed gas from methanol with aq. alkali, and passing, if necessary, through an adsorption tower contg. active carbon after washing with water to remove contained impurities. CONSTITUTION:Methanol 1 as feed is fed to a cracking reactor 2 packed with catalyst such as CuO, Cr2O3, MnO2, etc. being heated in a circulating line 3 of heat medium. Thus, the methanol is decomposed to H2 and CO. Since, in this stage, impurities such as CO2, unreacted methanol, dimethyl ether, etc., are contained in the mixture of H2 and CO, CO2 among the impurities is first removed by absorbing in aq. alkali by passing the gas through a washing tower 5 contg. aq. alkali such as NaOH. Then the gas is washed, if necessary, in a water washing tower 7 to remove unreacted methanol. Finally, dimethyl ether is removed by adsorption to active carbon packed in an active carbon adsorption tower 11. Thus, gaseous mixture 12 of H2 and CO contg. small amt. of impurities is obtd.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for purifying methanol decomposition gas, and more specifically, methanol decomposition gas obtained by a methanol decomposition reaction is washed with an alkali, and then optionally washed with water. The present invention relates to a method for purifying methanol cracked gas, which recovers hydrogen and carbon monoxide from methanol cracked gas in high yield by adsorption on activated carbon, and reduces the content of impurities to a desired level by a simple means.

[Prior Art] Conventionally, a methanol decomposition method has been known as a method for producing hydrogen and carbon monoxide from a methanol raw material. The decomposition method of methanol is a method carried out by the decomposition reaction shown below, and the methanol decomposition gas obtained by this method can be prepared by, for example, adjusting the content ratio of hydrogen and carbon monoxide as appropriate, or by adjusting the content ratio of hydrogen and carbon monoxide as necessary.・1taal
i #'s-s°' GL I 9 / )Lt @
IJt,.

It is used as a raw material, etc.

l・CH30H→ 2H2+co
1. .

-22 kcal/methanol (1 wol) In addition to hydrogen and carbon monoxide, methanol decomposition gas usually contains reaction by-products such as carbon dioxide and dimethyl ether, and impurities such as unreacted methanol. These impurities exhibit undesirable behavior when methanol decomposition gas is used in the acetic acid synthesis process mentioned above, and can clog heat exchangers when methanol decomposition gas is further separated into hydrogen and carbon monoxide using a cryogenic separator. It is harmful and must be removed by some method. In order to prevent such problems, carbon dioxide should be 5 vol, ppm or less, and unreacted methanol should be 3 vol. ppm or less, dimethyl ether at 3vol. It is necessary to reduce the amount to below ppm.

[Problems to be solved by the invention] A method for separating and removing such impurities is the PSA method (Pressure 5Win).
ion method) is known. The PSA method is a method in which methanol decomposition gas is introduced into an adsorption tower filled with an adsorbent such as zeolite, and the pressure is varied to continuously purify the methanol while repeating adsorption and desorption. According to the PSA law, carbon dioxide,
Unreacted methanol, dimethyl ether, etc. can both be removed to the order of ppm.

However, the PSA method has the disadvantage that the recovery rate of carbon monoxide is low, at most 70% or less, usually 50 to 6%.
It is 0%. If a cryogenic separator is installed after the PSA system to separate hydrogen and carbon monoxide, the carbon monoxide recovery rate of a normal cryogenic separator will be below 90%, so -
The recovery rate of carbon oxide will further decrease.

Under these circumstances, there is a need for a method for purifying methanol cracked gas that can recover hydrogen and carbon monoxide in methanol cracked gas with a high yield and also remove impurities such as carbon dioxide.

The present invention was made to solve the above-mentioned problems, and it recovers hydrogen and carbon monoxide in high yield from methanol decomposition gas obtained by a methanol decomposition method, and also removes impurities by a simple means. The purpose of the present invention is to provide a method for purifying methanol cracked gas that can reduce the content of slag to a desired level, and in particular, the methanol cracked gas purified by the present invention is suitable as a raw material gas for acetic acid synthesis or ethanol synthesis. used.

[Means for Solving the Problems and Effects] The present invention is a method for purifying methanol cracked gas, which is characterized by washing the methanol cracked gas with an alkali, then washing with water if desired, and then adsorbing the gas with activated carbon.

Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 1 is a process sheet showing a preferred embodiment of the present invention.

In the figure, raw methanol is supplied to a decomposition reactor 2 through a raw material supply line 1, and the above-mentioned methanol decomposition reaction is carried out in this decomposition reactor 2. The decomposition reactor 2 is kept at a predetermined temperature by a heat medium circulation line 3. As a decomposition catalyst, copper, chromium, manganese oxide catalyst (CuO, Cr20s, Mn
O2 catalyst) etc. are preferably used. These catalysts remove the precipitate formed by mixing chromate, dichromate or chromium salt solutions, manganese salt solutions and copper salt solutions with or without the addition of aqueous ammonia or caustic soda solution. It is obtained by washing and drying with water, heating it to around 350°C, and then reacting the obtained copper, chromium, and manganese oxides with an equivalent or less than the equivalent amount of chromic acid to prepare copper chromate as a binder.

The methanol decomposition gas obtained by the decomposition reaction is introduced into the alkali cleaning tower 5 through the decomposition reactor outlet gas line 4, where only carbon dioxide is adsorbed by the alkali and removed. The alkali used here is NaOH
A solution or the like is preferably used. The methanol cracked gas from which carbon dioxide has been removed is introduced into the water washing tower 7 through the water washing tower introduction line 6. In the water washing tower 7, unreacted methanol is absorbed by water and removed. The alkali washing tower 5 and the water washing tower 7 are provided with washing liquid circulation lines 9a and 9b via pumps 8a and 8b, respectively, to circulate alkali or water, respectively. In the present invention, if residual methanol in the methanol decomposition gas is small, the water washing tower 7 may not be provided and water washing may not be performed.

The methanol cracked gas from which carbon dioxide and unreacted methanol have been removed is introduced into the activated carbon adsorption tower 11 through the activated carbon adsorption tower introduction line 10 . In the activated carbon adsorption tower 11, reaction by-products other than carbon dioxide, such as dimethyl ether, are adsorbed and removed.

The methanol cracked gas from which reaction by-products and unreacted methanol have been removed in this way passes through the purified gas line 12 and is supplied to the subsequent process. In this case, if desired, a cryogenic separator may be installed on the purified gas line 12 to separate hydrogen and carbon monoxide, or a gas membrane separator may be installed to separate the gas into raw material gas for acetic acid synthesis, etc. Adjust the carbon oxide/hydrogen ratio. In addition, in the present invention, when a cryogenic separator is provided, since the content of impurities is at a low level, the accompanying molecular sieve adsorption tower can be simplified.

[Example] Hereinafter, the present invention will be specifically explained based on Examples.

EXAMPLE Using substantially the same process as shown in FIG. 1, methanol decomposition reaction and methanol decomposition gas were purified.

A methanol decomposition reactor filled with 80 kg of copper-based decomposition catalyst was used, and hot oil was used as a heat medium. Into this decomposition reactor, methanol 0.3Kmol/
hr was supplied, and the decomposition reaction was carried out under the reaction conditions of a reaction temperature of 330° C., a reaction pressure cuff, and 5 kO/iG. The gas composition of the methanol decomposition gas obtained in this way was
Shown in the table.

This methanol decomposition gas is subjected to alkali washing and water washing in a water washing tower/alkali washing tower according to FIG. Next, activated carbon adsorption was performed in an activated carbon adsorption tower to purify the methanol decomposition gas. Table 1 shows the composition of the activated carbon adsorption column outlet gas.

Table 1 As a result, as shown in Table 1, reaction by-products and unreacted methanol could be removed to an undetectable level in the activated carbon adsorption column outlet gas. In addition,
This gas flow rate was 19.4N TIi/hr.

Furthermore, when comparing the flow rates of hydrogen and carbon monoxide in the outlet gas of the decomposition reactor with those in the purified activated carbon adsorption tower outlet gas, the yields of both are 99.0%, respectively. It turns out.

[Effects of the Invention] As explained above, according to the method for purifying methanol cracked gas of the present invention, in which methanol cracked gas is washed with alkali, then washed with water if desired, and further adsorbed with activated carbon, hydrogen and carbon monoxide can be highly purified. In addition to recovering high yields, the content of impurities such as carbon dioxide, unreacted methanol, and dimethyl ether can be reduced to a desired level using simple means.

In addition, since the residual rate of these impurities can be extremely low, when using a cryogenic separation device to separate methanol decomposition gas into hydrogen and carbon monoxide, the molecular sieve adsorption tower required for the cryogenic separation device can be used. It can be simplified and costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a process sheet showing one embodiment of the present invention. 1... Raw material supply line, 2... Decomposition reactor, 3...
・Heating medium circulation line, 5...Alkali cleaning tower, 1...
・Washing tower, 8a, 8b...Pump, 9a, 9b...
Cleaning liquid circulation line, 11...activated carbon adsorption tower. □ FFtlliA B Fi mK*? k. Agent Patent attorney Tatsuo Ito 1 □

Claims (1)

[Claims] 1. A method for purifying methanol cracked gas, which comprises washing the methanol cracked gas with an alkali and then adsorbing it on activated carbon. 2. The method for purifying methanol cracked gas according to claim 1, wherein water washing is performed before the activated carbon adsorption.