JPS621283B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for treating exhaust gas generated in the process of producing methylphenols using methanol and phenol as raw materials.

Recently, 2.6, a type of alkylphenol,
-Xylenol is attracting attention as a raw material for new heat-resistant resins. The method of manufacturing by gas phase reaction (formula (1)) is being put into practical use on an industrial scale.

In addition, cresol was originally produced from heavy oil obtained by low-temperature carbonization of coal, but recently it has been produced using the reaction shown in equation (2). Synthesized from methanol and phenol.

Furthermore, 2,3,6-trimethylphenol, which is a raw material for pharmaceuticals, is also synthesized from methanol and phenol through the reaction shown in equation (3).

In the reactions shown in these formulas (1), (2), and (3), decomposition products and byproducts are produced in addition to the target product.

In other words, in any reaction, methanol is decomposed to produce hydrogen, carbon monoxide, methane, carbon dioxide, water, etc., although there are some differences depending on the performance of the catalyst used during the reaction process. .
Among these, water is also produced as a reaction product.

In addition, when the purpose is to produce 2,6-xylenol in the reaction represented by formula (1), cresols, anisole, 2,4- and 3,5-xylenol, 2,3,6- and 2,4・When 6-trimethylphenol etc. are produced as a by-product and the purpose is to produce O-cresol in the reaction shown by formula (2), m- and p-cresol, xylenols, 2.3.
6-trimethylphenol, 2,4,6-trimethylphenol, etc. are produced as by-products. Furthermore, 2.
Even in the production method for producing 3,6-trimethylphenol, it is no exception that cresols and xylates are produced as by-products. However, usually 2.
3,6-trimethylphenol can be obtained by separating a by-product during the production of cresol or 2,6-xylenol, and industrialization for the purpose of independent production has not been carried out.

In other words, in either method, the reaction product fluid includes hydrogen, hydrogen, and unreacted methanol and phenol.
Carbon monoxide, methane, carbon dioxide, water, cresols (o-, m-, p-forms), anisole, xylenol (2,4-, 2,6-, 3,5-forms)
Trimethyl-phenol (2,3,6-,
It is a multicomponent mixture containing 2-, 4-, 6-isomers, etc.

From such a multi-component mixture, the target components (in each method, the target o-cresol,
When obtaining 2,6-xylenol or 2,3,6-trimethylphenol, among the components other than the target product, low-boiling components become exhaust gas and high-boiling components become waste liquid and are separated. That is, hydrogen, carbon monoxide, methane, carbon dioxide, methanol, and water are low-boiling components, and therefore become exhaust gas components. Furthermore, other by-products, such as phenols, anisole, and cresols when producing 2,6-xylenol, and phenols and anisole when producing cresol, are contained in the exhaust gas.

Until now, no industrial treatment method for such exhaust gas from the alkylphenol production process has been known.

As a result of various studies on the treatment of process exhaust gas in the practical manufacturing process of methylphenols, the present inventors discovered a simple method that efficiently recovers the active ingredient and does not inhibit the catalytic reaction. Completed the invention.

That is, the method of the present invention is a multi-component mixture produced when methyl phenols are produced by subjecting phenol and methanol to a gas phase reaction in the presence of a metal oxide-containing catalyst, that is, methyl phenols, which are the target products, This process processes exhaust gas from which high-boiling components have been separated from a mixture of by-product methylphenols, methanol decomposition products, and unreacted raw materials.

The treatment method is to (1) wash the exhaust gas from which high-boiling components have been separated with an aqueous methanol solution having a boiling point higher than the treatment temperature under the treatment temperature and pressure, and then (2) wash this This method uses water to clean the waste gas.

According to the method of the present invention, the exhaust gases resulting from the gas phase reaction step of phenol and methanol, i.e., mainly low-boiling components resulting from the decomposition of methanol, such as hydrogen, carbon monoxide, methane, carbon dioxide, and The reaction methanol, water, and by-product methyl phenols contained in a small amount corresponding to the vapor-liquid equilibrium partial pressure are removed by the by-product methylated phenols in the washing step (1) above, and the by-product methylated phenols are removed in the washing step (2). Methanol is removed and discharged during the process. (2)
The washed liquid obtained in the washing step (1) is an aqueous methanol solution, which is used in the washing step (1) after adjusting the concentration as necessary. In the method of the present invention, the exhaust gas from the methylphenol production process, which is washed with an aqueous methanol solution and then water, is extracted by cooling the fluid flowing out from the reaction tube of the methylphenol production process, and mainly contains hydrogen, carbon monoxide, It is a gas phase containing methane, carbon dioxide, methanol, water, and small amounts of cresols, xylenols, trimethylphenols, anisole, phenols, etc. corresponding to the vapor-liquid equilibrium partial pressure.

That is, in the 2,6-xylenol manufacturing process, the fluid flowing out from the reaction tube is in a gas state at a temperature of 10 kg/cm ² (G) or less and 350 to 550°C, although it varies depending on the reaction conditions. This gaseous fluid is cooled to a temperature of 40 to 150°C by first performing heat recovery during the separation process.

In this step, components with a boiling point above anisole are condensed into a liquid phase, while hydrogen, carbon monoxide, methane, carbon dioxide, methanol, and water are removed as a gas phase. Of the components forming the liquid phase, a small amount corresponding to the vapor-liquid equilibrium partial pressure is also contained in the gas phase.

In addition, some of the components that become the gas phase remain dissolved in the liquid phase. The gas phase removed here is treated according to the method of the invention.

On the other hand, the components that become the liquid phase are supplied to a purification process consisting of several concentration columns, distillation columns, crystallization tanks, etc.
Although the target product is obtained, the gas discharged from these concentration columns, distillation columns, etc. or the condensers attached thereto can also be treated by the method of the invention. That is, in the production process of methylphenols, the gas treated by the method of the present invention is discharged from two or more locations.

In the treatment of the exhaust gas from the alkylphenol production process according to the method of the present invention, first (1) the exhaust gas after heat recovery is washed with an aqueous methanol solution in a gas cleaning tower.

The upper limit of the methanol concentration of the methanol aqueous solution used for this washing is the concentration at which the temperature of the exhaust gas to be treated reaches the boiling point. That is, the treatment is performed with a methanol aqueous solution having a methanol concentration having a boiling point higher than the temperature of the exhaust gas to be treated. For example, if the exhaust gas is discharged at atmospheric pressure and the temperature is 80℃, the methanol concentration
Since the boiling point is reached at 23.5 mol%, the upper limit of the methanol aqueous solution concentration used for washing is 23.5 mol%. Furthermore, if the exhaust gas temperature is lower than 64.6°C at normal pressure, 100 mol% methanol can be used. However, in a methanol aqueous solution with a methanol concentration of 10 mol% or less, anisole, phenol,
This is not preferable because cresols and the like become difficult to dissolve in the liquid. Therefore, when the exhaust gas temperature to be treated is 90℃ or higher, methanol concentration must be added to 10% to obtain a cleaning effect.
Even if a methanol aqueous solution of mol % or higher is used, if the methanol concentration exceeds the upper limit, the cleaning liquid itself will boil and the cleaning effect will be lost. Therefore, it is usually preferable to perform heat recovery or cooling so that the temperature of the exhaust gas is 90° C. or lower.

Next, (2) the exhaust gas washed with the methanol aqueous solution is led to a second washing tower, where it is washed with water. It is preferable that the water used be at room temperature, but
Can be used at temperatures below ℃.

The gas discharged from the second washing tower is discharged to the atmosphere through a stack, a combustion device, etc.

By the above-mentioned washing treatment according to the method of the present invention, the liquid after washing in the first washing tower becomes a solution of water, methanol, anisole, phenol, and cresol. When the liquid phase from which exhaust gas is separated in the alkyl phenol production process is treated in a distillation column, concentration column, or crystallization tank, and the exhaust gas discharged is treated, there is only a very small amount of it in the washing liquid obtained from the first column. However, o-cresol or xylenol is included.

Anisole, phenol, cresol, and xylenol have limited solubility in water, whereas their solubility in aqueous methanol solution is much higher than that in water. Furthermore, if the solid is in water, it will not be in the form of crystalline particles, but in the form of sticky lumps, and once it has precipitated, it will be extremely difficult to handle. Therefore, the above-mentioned components in the exhaust gas can be recovered very efficiently by using an aqueous methanol solution as a washing liquid, and can be handled stably without any appearance of solid precipitation. Moreover, the recovered liquid does not contain any substances that would inhibit the synthesis of the target methylphenols, so after adjusting the concentration of water or methanol, it can all be supplied to the reaction process. .

The liquid after washing in the second washing tower contains methanol, and depending on the concentration and temperature, it can be used as the washing liquid in the first tower. Generally, the concentration of methanol is adjusted and used as the washing liquid in the first washing tower.

Incidentally, the exhaust gas discharged from two or more places during the production of alkylated phenol may be washed individually, or may be collected and then washed in the first washing tower and the second washing tower.

The type of washing tower used here is not particularly determined, and any type may be used as long as it allows good contact between the exhaust gas and the washing liquid. For example, a packed column type, tray column type, spray tower type, stirring tank type, or submerged injection type may be used. Further, the methanol aqueous solution obtained from two or more locations after washing may be supplied individually to the washing or reaction step, or may be supplied collectively.

Hereinafter, the present invention will be further explained in detail with reference to the drawings.

Figure 1 shows an example of the exhaust gas cleaning process. 1st
Exhaust gas is introduced into the scrubbing tower 1 from the bottom of the tower through a conduit 2. An aqueous methanol solution for washing is supplied to the top of the column through conduit 8. At this time, the upper limit of the methanol concentration of the methanol aqueous solution is supplied at a concentration such that the temperature of the exhaust gas introduced from the bottom of the column reaches the boiling point. In practice, it is supplied at a concentration below that concentration or at a temperature lower than the exhaust gas temperature. While the exhaust gas ascends through the first washing tower 1, effective components other than methanol are recovered and taken out from the conduit 3 as a methanol solution. The exhaust gas that has ascended from the first washing tower 1 passes through the conduit 4 from the top of the tower.
It enters the bottom of the second washing tower 5. Water is supplied from conduit 10. Since methanol, one of the active ingredients, remains in the gas passing through the conduit 4, it is collected by the water flowing down while rising in the second washing tower 5, and is passed through the conduit 6 from the bottom of the tower to diluted methanol. It is extracted as a methanol aqueous solution. Methanol is supplied through the conduit 7, and the aqueous solution made to a predetermined concentration in the concentration adjustment tank 13 passes through the pump 12 and the heat exchanger 11, where the temperature is lower than the temperature of the exhaust gas entering the first washing tower. Supply the tower. The active ingredients are recovered in the second washing tower 5, and the exhaust gas containing only inert gas components is exhausted through the conduit 9.

FIG. 2 shows an example of an exhaust gas cleaning process different from that shown in FIG. 1.

In this case, since it is not a tower type but a tank blowing type, the first washing tank 1 and the second washing tank 5 are shown.

The exhaust gas is blown into the first washing tank 1 through the conduit 2. If the temperature inside the tank is high, the amount of active ingredients recovered will decrease, so in order to adjust the temperature inside the tank, a cooling coil 11 is provided to allow cooling water to pass through.

The exhaust gas from which active ingredients have been recovered in the first washing tank 1 enters the second washing tank 5 via a conduit 4. 1st washing tank 1
The methanol aqueous solution from which the active ingredients were recovered is transferred to conduit 3.
taken out from An aqueous methanol solution for washing is supplied from a conduit 8. Water is supplied to the second washing tank 5 through a conduit 10, and methanol in the exhaust gas led through the conduit 4 is recovered. A dilute methanol aqueous solution is taken out from the conduit 6, and methanol for concentration adjustment is supplied from the conduit 7 to the concentration adjustment tank 13. The exhaust gas, in which the effective components have been recovered and is now composed only of inert gas components, is exhausted from the conduit 9.

The method of the present invention will be further explained below with reference to Examples.

Example 1 Methanol 0.37Kg/hr and phenol in a test equipment for the purpose of producing 2,6-xylenol
0.63Kg/hr was passed through the catalyst layer and reacted under conditions of a temperature of 420°C and a pressure of 1000mmHg (gauge). When the gas after the reaction was cooled at 70℃ in a condenser, components with boiling points higher than anisole were condensed, and noncondensable gases such as hydrogen, carbon monoxide, methane, and carbon dioxide were
74.55%, methanol 13.54%, water 11.88%, anisole 0.01%, phenol 0.02% (all vol.
%) was obtained as exhaust gas at 0.55 Kg/hr. This gas was washed in a packed column type washing tower consisting of two columns exactly as shown in Figure 1, in which the first column was washed with a 40 mol% methanol aqueous solution at 25°C, and the second column was washed with methanol-free water at 28°C. . The washing liquid obtained from the second column was supplied to the first column after adjusting its concentration and temperature. 1st
The gas coming out from the top of the towers is 89.5% noncondensable gas, 8.3% methanol, 2.2% water, 10 ppm anisole, and 5 ppm phenol (all by volume).
The gas discharged from the tower was 97.5% noncondensable gas, 0.02% methanol, and 2.5% water, with no detectable anisole or phenol. The washing liquid taken out from the bottom of the first column was a homogeneous solution.

Example 2 The condensate obtained in Example 1, most of which consists of components having a boiling point higher than anisole, was
It was fed at a rate of 0.5 Kg/hr to a continuous distillation column operated at 40 Torr and a bottom still temperature of 135°C. The gas coming out of the top of the tower was led to a water-cooled condenser and condensed at 50°C, but uncondensed gas was still discharged at about 80/HR. This gas also consisted of 0.25% of noncondensable gases such as methane and carbon dioxide dissolved in the liquid, 48.5% of methanol, and 51.2% of water (both vol%). Anisole, phenol, and cresol were observed, albeit in small amounts. This gas is added to the second
The material was guided to the same tank-type washing device as shown in the figure and washed. 1st
The washing tank was washed with a methanol aqueous solution, and the second washing tank was washed with water. Further, both the first and second chambers were maintained at a temperature of 35°C. As a result, the gas exhausted through the second layer is 94.2% noncondensable gas, 0.01% methanol, and 5.8% water.
Anisole, phenol, cresol, etc. were not detected.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the steps necessary to carry out the method of the present invention, and is a diagram in the case where a column-type washing device is used. FIG. 2 is a diagram showing a case where a tank-type cleaning device is used. 1...First washing tower (tank), 2...Exhaust gas inflow conduit, 3...Methanol solution outflow conduit, 5...Second
Washing tower (tank), 7...methanol supply conduit for adjustment, 9...exhaust gas outflow conduit, 10...water supply conduit, 13...methanol concentration adjustment tank.

Claims (1)

[Claims] 1. The exhaust gas from the methylphenol manufacturing process is washed with a methanol aqueous solution having a concentration of 10 mol% or more in a first washing step, then washed with water in a second washing step, and then washed with water in a second washing step. A method for treating exhaust gas in a process for producing methylphenols, characterized in that an aqueous methanol solution obtained in the washing step is used as an aqueous methanol solution in the first washing step. 2 The temperature of the exhaust gas treated with methanol aqueous solution is
The method according to claim 1, wherein the temperature is 90°C or less.