JPS61151013A - Method of purifying carbon dioxide - Google Patents

Abstract

PURPOSE:To obtain high-quality CO2 suitable for Dry Ice, having no offensive smell, by subjecting Crude CO2 containing CH4 and hydrocarbons except CH4 to a contact reaction in the presence of an oxidizing catalyst under a specific condition, removing CH4, and purifying CO2. CONSTITUTION:The crude CO2:1 containing CH4 and hydrocarbons except CH4, such as C2H4, C4H10, aldehyde, etc. is sent through the valve 2 partially through the heat exchanger 3 and partially through the valve 4 at a desired temperature to the CO2 blender 5. On the other hand, an amount of O2 to burn completely the hydrocarbons except methane is calculated to give the O2:6, which is sent from the valve 7 to the blender 5 and blended with the crude CO2:1. Then, the mixed gas 8 is heated to >=temperature (200 deg.C) capable of starting a reaction, fixed depending upon the composition of the mixed gas, sent to the reactor 10 packed with the platinum catalyst 9 supported on gamma-Al2O3, the reactor is kept at a temperature (e.g., 400 deg.C) to oxidize the hydrocarbons except CH4 into CO2 completely but not to react with CH4 by controlling the valves 2 and 4, the gas is reacted, introduced to the methane separator 12, CH4 in the reaction gas is removed and carbon dioxide is purified.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method for purifying carbon dioxide.

[Prior technology] Carbon dioxide is used in the form of liquefied carbon dioxide gas or dry ice for preserving fish, butter, cheese, ice cream, etc., for low-temperature transportation, for cooling, for welding, for the foundry industry, and for the production of soft drinks. It is widely used as a fire extinguisher, etc.

Natural gas, fermentation gas, by-product gas from petroleum refining, by-product gas from ammonia synthesis process, etc. are used industrially as crude carbon dioxide raw material gas, which is the raw material for liquefied carbon dioxide gas and dry ice. The technology for producing highly pure carbon dioxide has already been established. For example, crude carbon dioxide produced as a by-product in the ammonia production process mainly contains impurities such as methane and hydrogen, and since these do not liquefy under the conditions for liquefying carbon dioxide, they are easily purified by distillation or the like.

[Problem that the invention seeks to solve]

On the other hand, when crude carbon dioxide produced as a by-product in the ethylene oxide manufacturing process is used as a carbon dioxide source, the crude carbon dioxide contains ethylene, acetaldehyde, etc. as impurities in addition to methane. Ethylene, acetaldehyde, and the like liquefy under carbon dioxide liquefaction conditions, so they remain in the liquefied carbon dioxide as impurities and are accompanied by an unpleasant odor.

Such liquefied carbon dioxide cannot be used for preserving or transporting foods, or as an additive for soft drinks, etc., not only because of its unpleasant odor but also because of its negative effects on the human body.

Furthermore, when used as dry ice, ethylene that remains as an impurity gasifies under the conditions used to manufacture dry ice (normal pressure, -78°C), so even if dry ice is compression molded, the molded product will explode. Otherwise, the strength of the molded product may be extremely reduced, causing it to break during handling.

From this perspective, the present invention provides a method for refining crude carbon dioxide containing methane and hydrocarbons other than methane, particularly crude carbon dioxide produced as a by-product in the ethylene oxide manufacturing process, into carbon dioxide of good quality that can be used in liquefied carbon dioxide gas and dry ice. This is what we are trying to provide.

Means for Solving Problem C] The present inventor has conducted extensive research in order to solve the above problems, and has completed the present invention.

That is, the present invention enables methane and crude carbon dioxide containing hydrocarbons other than methane to undergo a contact reaction with oxygen or an oxygen-containing gas in the presence of an oxidation catalyst to oxidize hydrocarbons other than methane to carbon dioxide. In the carbon dioxide purification method for removing carbon dioxide, the catalytic reaction is determined according to the type and content of methane and hydrocarbons other than methane in the crude carbon dioxide, and the hydrocarbons other than methane initiate an oxidation reaction. (b) The oxidation reaction is carried out at a temperature at which hydrocarbons other than methane in the crude carbon dioxide are completely oxidized to carbon dioxide, and methane does not substantially react. (c) the reaction temperature is controlled by the temperature and flow rate of the crude carbon dioxide, (d) the temperature of the crude carbon dioxide is controlled by the heat possessed by the catalytic reactants, and (e) and the reaction temperature is controlled by the temperature and flow rate of the crude carbon dioxide. This method of purifying carbon dioxide is characterized in that the amount of oxygen or oxygen-containing gas required for complete combustion of hydrocarbons other than methane in the crude carbon dioxide is a catalytic reaction.

In the present invention, hydrocarbons other than methane include not only saturated and unsaturated hydrocarbons such as ethylene and butane, but also aldehydes such as acetaldehyde, which are lower oxides of hydrocarbons, and fatty acids such as acetic acid.

In addition, the oxidation catalyst used in the present invention includes one or more components of oxides of metals in the fourth period of the periodic table, such as titanium, vanadium, chromium, manganese, iron, cobalt, nickel, and copper, or A catalyst consisting of one or more components of so-called platinum group metals of Group 8 of the fifth and sixth periods of the Table of Contents, or a catalyst in which these catalyst components are supported on a carrier such as alumina, is used.

In the present invention, first, methane and crude carbon dioxide containing hydrocarbons other than methane are catalytically reacted with oxygen or an oxygen-containing gas in the presence of an oxidation catalyst to oxidize hydrocarbons other than methane to carbon dioxide. At this time (11), this reaction is carried out while maintaining the catalyst bed inlet temperature at a temperature at which oxidation of hydrocarbons other than methane begins, and the temperature is controlled by the temperature of the crude carbon dioxide fed.

(The reaction temperature (measured at the outlet of the catalyst layer) increases due to the 21M reaction. In order to carry out this reaction at a reaction temperature where hydrocarbons other than methane are completely oxidized and methane is not substantially oxidized, The temperature is controlled by the inlet temperature of the catalyst layer and by the temperature of the crude carbon dioxide, and further controlled by the flow rate of the crude carbon dioxide fed into the reaction system as necessary.

(3) Setting the temperature at which oxidation of hydrocarbons other than methane begins and the reaction temperature at which methane is not substantially oxidized depends on the type and amount of methane and hydrocarbons other than methane in the crude carbon dioxide, the type of catalyst, etc. This is done based on information gathered in advance.

(4) The waste heat generated by this oxidation reaction is heat exchanged with a portion of the crude carbon dioxide and used to control the temperature of the crude carbon dioxide supplied to the reaction system.

(5) The amount of oxygen or oxygen-containing gas supplied to the reaction system is sufficient to completely burn hydrocarbons other than methane, which is calculated based on the flow rate of crude carbon dioxide and analytical information.

Furthermore, in the present invention, hydrocarbons other than methane are oxidized and removed to carbon dioxide through an oxidation reaction, and methane is separated from the crude carbon dioxide by conventional methods such as distillation and liquefaction to refine it into carbon dioxide of extremely high purity. .

〔Example〕

The present invention will be specifically explained below using examples.

FIG. 1 is a flow sheet showing an example of the purification method of the present invention.

Methane produced as a by-product during ethylene oxide production: 3,500pp
Crude carbon dioxide 1 containing m, 000 ppm of ethylene G and 500 ppm of acetaldehyde is supplied to valve 2.
25 Nn? /min.

A portion of the crude carbon dioxide is heated by the waste heat of the reaction gas in the heat exchanger 3, and a portion is bypassed through the valve 4, heated to a temperature necessary for the reaction, and sent to the oxygen mixer 5.

On the other hand, the amount of oxygen to completely burn ethylene and acetaldehyde is calculated based on the flow rate of crude carbon dioxide and analysis information, and 0.5Nrrf/min of oxygen 6 is supplied to valve 7.
It is sent through the oxygen mixer 5 and mixed with crude carbon dioxide.

Platinum catalyst supported on γ-alumina XC-140-2-0
A heated mixed gas 8 of crude carbon dioxide and oxygen is fed into a reactor 10 filled with 62 (trade name manufactured by Toyo CCI) 9, and the inlet temperature of the catalyst layer is controlled by the amount of heat contained in the mixed gas. The temperature was set to 200°C.

This temperature of 200° C. is set in advance based on the composition of the crude carbon dioxide accumulated and the type of catalyst used. That is, in this case, using a mixed gas of crude carbon dioxide and oxygen having the same composition as above, using the same catalyst 50 m 12, the crude carbon dioxide was reacted with 8201/H1 oxygen at a flow rate of 3 ON/H,
The relationship between the reaction temperature and the removal rate of ethylene, acetaldehyde and methane was investigated and the results shown in Figure 2 were obtained. As a result, it was found that ethylene decomposition started at 160°C, and acetaldehyde decomposed at an even lower temperature.Therefore, 200°C was set as the temperature for starting the reaction, that is, the inlet temperature of the catalyst layer.

When the reaction was carried out with the catalyst layer inlet temperature set at 200°C, the reaction temperature became 400°C due to the oxidation reaction. Second
As is clear from the figure, it has been found that at this temperature, ethylene and acetaldehyde in the crude carbon dioxide are completely oxidized, and methane is not substantially oxidized, so the reaction temperature was maintained at 400° C. thereafter.

The reaction temperature is maintained by controlling the catalyst bed inlet temperature within the temperature range in which ethylene is completely oxidized, and the temperature is controlled by changing the flow rate ratio of crude carbon dioxide passing through the heat exchanger 3 and the bypass with a valve 4. and further control the flow rate of crude carbon dioxide 1 supplied to the reaction system through valve 2 as necessary.

After the reaction, the crude carbon dioxide 11 exchanges heat with a portion of the crude carbon dioxide in the heat exchanger 3, and is sent to the methane separator 12-.

Methane in crude carbon dioxide after reaction is 3.380pp
m, and ethylene and acetaldehyde were not detected.

Methane 13 is separated from the crude carbon dioxide thus obtained by a conventional method such as liquefaction, and the purity is 99.97%.
14 of purified carbon dioxide could be obtained.

〔Effect of the invention〕

According to the method of the present invention, high-purity carbon dioxide containing no ethylene or acetaldehyde can be reliably produced from crude carbon dioxide containing impurities such as hydrocarbons other than methane, such as ethylene and acetaldehyde. It can be safely used for storage, transportation, and as an additive for soft drinks, etc., and can produce extremely high quality carbon dioxide that will not be destroyed even when made into dry ice.

[Brief explanation of drawings]

FIG. 1 is a flow sheet showing an example of the purification method of the present invention. FIG. 2 is a diagram showing the relationship between reaction temperature and removal rate of ethylene, acetaldehyde, and methane.

Claims (1)

[Claims] After catalytically reacting crude carbon dioxide containing methane and hydrocarbons other than methane with oxygen or an oxygen-containing gas in the presence of an oxidation catalyst to oxidize hydrocarbons other than methane to carbon dioxide, In a carbon dioxide purification method for removing methane, the catalytic reaction is determined according to the type and content of methane and hydrocarbons other than methane in the crude carbon dioxide, and hydrocarbons other than methane undergo an oxidation reaction. Crude carbon dioxide heated above the starting temperature is fed into the reaction system, and (b) the oxidation reaction is such that hydrocarbons other than methane in the crude carbon dioxide are completely oxidized to carbon dioxide, and methane does not substantially react. (c) The reaction temperature is controlled by the temperature and flow rate of the crude carbon dioxide, (d) The temperature of the crude carbon dioxide is controlled by the heat possessed by the catalytic reactants, and (e) and supplied to the catalytic reaction system. A method for purifying carbon dioxide, characterized in that the amount of oxygen or oxygen-containing gas used is the amount necessary for complete combustion of hydrocarbons other than methane in crude carbon dioxide.