RU2171706C1 - Method of cleaning of industrial gaseous effluents - Google Patents

Abstract

FIELD: environmental control; applicable in gas cleaning. SUBSTANCE: method of cleaning of industrial gaseous effluents containing more than 1 vol. % of aliphatic compounds (including methanol) alongside with aromatic hydrocarbons (including hydroperoxides) includes passing of effluents at temperature of 240-290 C in presence of oxygen through catalytic composition of hard contact agent with specific surface of 0.2- 1.0 sq.m/g preliminarily calcined at temperature of 800-1350 C and catalyst containing 0.1-3.0% of palladium in aluminum oxide carrier, for instance, on active aluminum oxide. Use is made of hard contact agent including oxides of aluminum, iron, magnesium, calcium, potassium, sodium titanium (IV) and silicon. EFFECT: highly efficient cleaning of gaseous effluents (with conversion of organic compounds in amount of 99% and above) for prolonged time with no resinous accumulations on catalyst. 3 cl, 1 tbl

Description

 The invention relates to the field of environmental protection and can be used to clean industrial gas emissions, including aromatic and oxygen-containing products that cause gum formation.

 When the content of organic impurities in gas emissions in small quantities (less than 0.5 vol.%) Isothermal mode is used, for the implementation of which heat is supplied to the reaction mass in significant quantities. When the content of organic compounds in the gas stream is 1.0 vol.% And higher, the process is carried out in an adiabatic mode, accompanied by the release of heat, the amount of which depends on the concentration of organic components. As industrial contacts, various catalytic systems are used. Some contain oxides of base metals, for example, chromium, cobalt, zirconium (Russian patent N 2050976, class B 01 J 23/86, 21/06, publ. 12/27/1995), magnesium (US Pat. US N 4673558, class B 01 D 053/34, publ. 06/16/1987), manganese, copper (patent application of Russia N 95102026, CL B 01 D 053/86, publ. 05/27/1996). Other catalysts contain noble metals, for example platinum (US Pat. US N 5702836, class H 01 M 4/88, publ. 12/30/1997), palladium and silver (US Pat. US N 4673556, class B 01 D 53/36, publ. .16.06.1987). Recently, catalytic systems representing noble metals on complex oxide supports (Pat. U.S. N 5585083, class C 07 C 11/24, publ. 12/17/1996), in particular Group VIII metals on titanium and cerium oxides, US Pat. No. 4,716,859, class F 02 B 43/08, publ. 5.01.1988) or, for example, palladium and rhodium on cerium oxide (US Pat. No. 4919903, class B 01 D 53/36, publ. 24.04 .1990).

The most universal method for cleaning gas emissions from C ₃ hydrocarbons and oxygen-containing compounds (including inorganic ones) is described in the patent (US Pat. No. 5,292,991, class C 07 C 7/152, publ. 08.03.1994) by which the process is carried out at a temperature of 600 ^o C in the presence of platinum and palladium, applied together on a zeolite type ZSM, modified with oxides of zirconium and titanium; the conversion of hydrocarbons is 98.1%. The disadvantage of this method is the need to heat gas-vapor streams, enriched, as a rule, with nitrogen and water vapor, to a high temperature, as well as the ability to clean only light hydrocarbons that do not cause catalyst tarring.

In order to reduce the cost of heating steam and gas streams, as a rule, they strive to use less unified systems, developing catalytic compositions containing noble metals to neutralize specific organic compounds. For example, a method of low-temperature purification of gas emissions from organobromine compounds is known, which uses a catalyst containing platinum group metals on oxides of zirconium, manganese, cerium and cobalt (US Pat. No. 5653949, class C 01 B 007/00, publ. 5.08. 1997). To reduce the heating temperature of the gas stream when cleaning it from methanol and formaldehyde, it is recommended to use a palladium-rhodium catalyst on cerium oxide (US Pat. USA N 4950476, class B 01 D 053/36, publ. 21.08.1990). This method allows to reduce the reaction temperature to 150 ^o C. In order to further reduce the temperature of the gas purification from methanol to 85-120 ^o C, it is proposed to use a catalyst containing platinum in an amount of 0.05-0.5% on a carrier - high-silicon zeolite HZSM- 5 with a binder of silicon oxide (Pat. Russia N 2155093, CL B 01 D 53/86, publ. 02/10/1999). The disadvantage of both of these methods is the ability to purify gas emissions only from specific compounds: from methanol and formaldehyde in the first case and from methanol in the second. In the presence of aromatic hydroperoxides in the gas stream, which cause the resinification of the catalyst, these methods are not effective.

A known method of purification of industrial gas emissions containing aldehydes, alcohols and ketones with the number of carbon atoms up to 5, at a low temperature (not higher than 150 ^o C) on a catalytic system comprising at least two noble metals in an amount of up to 22% on a special hydrophobic carrier ( U.S. Patent No. 5009872, CL B 01 D 53/56, publ. 04/23/1999). This method provides purification of the stream from ethanol by 90% and from formaldehyde by 93%. The disadvantage of this method is the limited ability to purify gas emissions only from organic compounds (methanol, ethanol, acetone, formaldehyde) that do not condition the resinification of the catalyst.

 The closest way to purify gas emissions from oxygen-containing organic compounds to the proposed one is the method by which gas emissions are passed over a catalyst representing 0.003-3.0% of palladium supported on an alumina carrier (US Pat. No. 4,450,244, class B 01 J 023/04, 021/04, 023/10, publ. 05.22.1984 - prototype).

According to the prototype, the process is carried out in the presence of oxygen at a temperature of 350-400 ^o C, which provides purification from various organic oxygen-containing compounds at a level of 88 - 96% at 350 ^o C and at a level of 98-100% at 400 ^o C. The advantage of this method is reduced the content of precious metals compared with the previous patent and a higher degree of purification from organic oxygen-containing compounds.

 The disadvantages of the prototype method are: 1) the Need to heat the gas stream to an elevated temperature, and 2) The limited ability to clean the gas stream only from organic compounds that do not lead to the resinification of the catalyst. When cleaning gases from aromatic hydroperoxides under the indicated conditions, the catalyst is ground in tar.

 The task was to develop a method for cleaning industrial gas emissions, including various oxygen-containing organic compounds, including aromatic hydroperoxides, without gumming on the catalyst.

 In order to simplify the process technology by lowering the temperature of purification of gas emissions, including aromatic hydroperoxides, cumene, and formic acid, the process is proposed as follows.

The initial gas stream, including aromatic and aliphatic oxygen-containing and non-oxygen-containing compounds, for example cumene, cumene hydroperoxide, methanol, formic acid, is passed through a catalytic system in the presence of oxygen, consisting of: I - solid contact with a specific surface area of 0.2 - 1.0 m ² / g, pre-calcined at 800-1350 ^o C and II - palladium catalyst containing 0.1-3% palladium on active alumina. The ratio of catalysts I: II is 0.5: 1 - 2: 1. After initiating the reaction on both catalysts maintain the process temperature of 240 - 290 ^o C.

The solid contact after calcination contains oxides of aluminum, iron (II), magnesium, calcium, potassium, sodium, titanium (IV), silicon in the following ratio, wt.%:
Alumina - 5.0-30
Iron (II) oxide - 0.1-5.0
Magnesium Oxide - 0.1-5.0
Calcium oxide - 0.1-5.0
Potassium oxide - 0.1-3.0
Sodium oxide - 0.1-3.0
Titanium oxide IV - 0.1-3.0
Silica - Else
Salient features of the proposed method for purifying gas emissions from aromatic and aliphatic hydrocarbons (including those containing methanol more than 1 vol.%) Are: the use of the catalytic composition of the indicated compositions I and II and the process at a temperature of 240 - 290 ^o C
When carrying out the process at a temperature above 290 ^o C on the specified catalytic composition, the palladium catalyst is rapidly deactivated, because at a temperature of more than 300 ^o C, palladium loses its catalytic activity. At temperatures below 240 ^o C, the conversion of hydrocarbons does not provide a sufficient degree of gas purification.

 The proposed method allows the purification of industrial gas emissions from harmful substances (e.g. methanol, cumene) with a degree of destruction of not less than 97-98% in the presence of compounds (e.g., aromatic hydroperoxides) that cause gum formation on other catalytic compositions.

The non-obviousness of the proposed method follows from the fact that the solid contact, proposed as catalyst I in the composition of the catalytic composition, was previously used for thermal decomposition: 1) by-products formed in the synthesis of 4,4-dimethyldioxane-1,3 (DMD), and 2 ) the pyran fraction obtained by the decomposition of DMD during the synthesis of isoprene from formaldehyde and isobutylene (Pat. Russia N 1695631, CL 07 07/11, 11/096, publ. 12/20/1996). Thermally decomposed products consist of compounds of the pyran and dioxane type, whose properties are very different from aromatic hydroperoxides contained in gas emissions. The use of a similar solid contact, previously calcined at a temperature of 800-1000 ^o C, for the above purposes, we do not know. Industrial applicability of the proposed method is illustrated by the following examples:
Example 1

12 ml of a palladium catalyst containing 0.1% metal on alumina and 6 ml of a solid contact consisting of (wt.%): Alumina 22.4, iron oxide (II) are sequentially loaded into a 2.26 cm cross-section glass reactor. 0.42, magnesium oxide 0.43, calcium oxide 0.67, potassium oxide 2.4, sodium oxide 1.2, titanium oxide (IV) 0.47, the rest is silicon oxide. The solid contact is preliminarily calcined at a temperature of 800 ^o C; while its specific surface is 1 m ² / g. A steam-gas stream is supplied to the reactor at a rate of 63.0 l / h. The composition of the stream (vol.%): Nitrogen 89.5, oxygen 6.0, water vapor 3.0, methanol 1.5, formic acid 0.002, cumene 0002, cumene hydroperoxide 0.002. The volumetric feed rate of the cleaned stream is 3500 h ^-1 . The reactor is heated by an electric furnace, providing an oxidation reaction initiation temperature of ~ 100 ^o . In addition to the initial vapor-gas stream, air is supplied in an amount necessary to maintain the reaction temperature at a level of 240 ^° C. During the oxidation process, the reactor electric furnace is switched off, since the reaction is carried out in an adiabatic mode with the release of a significant amount of heat. The experiment is carried out after 150 hours of operation of the catalyst for 4 hours. During this time, the composition of the gas-vapor stream serves (g): methanol 5.040, formic acid 0.00966, cumene 0.02520, cumene hydroperoxide 0.0319. The reaction products are sent to a system consisting of four series-connected traps (absorbers), cooled by a mixture of carbon dioxide and acetone (temperature -70 - -80 ^o C). The first and last traps are empty, and the second and third are filled with n-butyl alcohol. After completion of the experiment, the content of the reaction products is determined by GLC. The total amount of products in the absorbers in this experiment is (g): methanol 0.0353, formic acid 0.00000, cumene 0.00015, cumene hydroperoxide 0.00510, which corresponds to the following values of the conversion of substances (%): methanol 99.3, formic acid 100, cumene 99.4, cumene hydroperoxide 84.0. When unloading the catalyst, no tarring was detected,
Example 2

In the reactor described in example 1, load 3 ml of a palladium catalyst containing 3.0% metal on alumina, and on top of 6 ml of the solid contact described in example 1, but calcined at a temperature of 1350 ^o C. Moreover, its specific surface is 0.2 m ² / g. A steam-gas stream is supplied to the reactor at a rate of 90 l / h. The composition of the stream (vol.%): Nitrogen 88.5, oxygen 6.0, water vapor 3.0, methanol 2.5, formic acid 0.002, cumene 0.01, cumene hydroperoxide 0.01. The volumetric feed rate of the cleaned stream is 10,000 h ^-1 . The reactor electric furnace provides a preliminary temperature for heating the catalyst at a level of ~ 100 ^o C. In addition to the initial gas-vapor stream, air is supplied in an amount necessary to maintain the reaction temperature at a level of 290 ^o C. During the oxidation process, the reactor electric furnace is turned off, since the reaction is carried out in an adiabatic mode with the release of a significant amount of heat. During the four-hour balance experiment, conducted after 150 hours of catalyst operation, (g) is supplied: methanol 12.05, formic acid 0.0138, cumene 0.1803, cumene hydroperoxide 0.2283. The total content of products in the absorbers in this experiment is (g): methanol 0.06, formic acid 0.0000, cumene 0.0005, cumene hydroperoxide 0.00365, which corresponds to the following values of the conversion of substances (%): methanol 99.5, formic acid 100, cumene 99.7, cumene hydroperoxide 98.4. When unloading the catalyst, no tarring was detected.

Example 3 (for comparison)
In the reactor described in example 1, load 12 ml of a palladium catalyst containing 3.0% metal on alumina; solid contact do not load. A steam-gas stream of the composition shown in Example 1 is supplied to the reactor at a rate of 24 l / h. The volumetric feed rate of the cleaned stream is 2000 h ^-1 . In addition to the feed stream, air is supplied in an amount providing a reaction temperature of 290 ^° C. due to self-heating of the catalyst. During the four-hour balance experiment, conducted after 75 hours of catalyst operation, (g) are supplied: methanol 1.9200, formic acid 0.00368, cumene 0.009616, cumene hydroperoxide 0.01218. The total content of products in the absorbers in this experiment is (g): methanol 0.7430, formic acid 0.0000, cumene 0.00285, cumene hydroperoxide 0.00569, which corresponds to the following values of the conversion of substances (%): methanol 61.3, formic acid 100, cumene 70.4, cumene hydroperoxides 53.3. When unloading, it turned out that the palladium catalyst was more than half coated with resinous products.

Example 4 (for comparison)
In the reactor described in example 1, load 12 ml of solid contact prepared according to example 2; the palladium-containing catalyst is not charged. A steam-gas stream of the composition shown in Example 1 is supplied to the reactor at a rate of 90 l / h. The volumetric feed rate of the cleaned stream is 7500 h ^-1 . The reaction temperature provided by supplying an additional amount of air (with the electric heating of the reactor furnace turned off) is 290 ^o C. During the four-hour balance experiment, conducted after 150 hours of catalyst operation, (g) is supplied: methanol 7,200, formic acid 0,0138, cumene 0 , 1803, cumene hydroperoxides 0.2283. The total content of products in the absorbers in this experiment is (g): methanol 6.547, formic acid 0.0000, cumene 0.1554, cumene hydroperoxide 0.2011, which corresponds to the following values of the conversion of substances (%): methanol 9.07, formic acid 100, cumene 13.8, cumene hydroperoxides 11.9. When unloading a solid contact, no tarring was detected.

 The data of examples 1-4 are summarized in table.

An analysis of the data in the table indicates that the use of a catalytic composition using solid contact with a specific surface area of 0.2 - 1.0 m / g, calcined at a temperature of 800 - 1350 ^o C, and a palladium catalyst with a metal content of 0.1 - 3% provides effective cleaning of the gas-vapor stream containing organic impurities in an amount of more than 1.0 vol. %, in the presence of oxygen at a space velocity of 3500 - 10000 h ^-1 and a reaction temperature of 240 - 290 ^o C, due to the supply of an additional amount of air (in adiabatic mode, without supplying heat from the outside) for more than 150 hours; no resinification of the catalyst is observed. In the absence of solid contact, even with an increased palladium content (3%) at a reduced space velocity (2000 h ^-1 ) and an increased reaction temperature (290 ^o C), after 75 hours of operation, the catalyst is resinized and the efficiency of purification of the stream from organic compounds is significantly reduced. In the absence of palladium contact, even after a long run (150 hours), no solid contact is resinized. However, the conversion of harmful organic substances is insignificant and gas stream purification practically does not occur.

Claims (2)

1. The method of purification of industrial gas emissions from aromatic compounds, including hydroperoxides, and aliphatic compounds, including methanol, with a content of the latter of more than 1.0 vol.%, Which consists in transmitting gas emissions in the presence of oxygen through the catalytic system at 240 ° C - 290 ° C, and the catalytic system consists of solid contact with a specific surface area of 0.2 - 1.0 m ² / g, previously calcined at 800 - 1350 ° C, and a catalyst containing 0.1 - 3.0% palladium on alumina nose body. 2. The method according to p. 1, which consists in using a solid contact composition, wt.%:
Alumina - 5.0 - 30.0
Iron oxide (II) - 0.1 - 5.0
Magnesium Oxide - 0.1 - 5.0
Calcium oxide - 0.1 - 5.0
Potassium oxide - 0.1 - 3.0
Sodium oxide - 0.1 - 3.0
Titanium (IV) oxide - 0.1 - 3.0
Silica - Else
3. The method according to p. 1, which consists in the fact that the process is carried out in the presence of palladium supported on active alumina.

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