CS240539B1 - Spós & b of catalytic combustion of gaseous mixtures of azalc or waste industrial gases containing hydrogen - Google Patents

Abstract

The purpose of the invention is a method for catalytic combustion of gas mixtures and/or industrial waste gases containing hydrogen as the main oxidizable component and a smaller amount of carbon monoxide, aliphatic alcohols and aliphatic aldehydes with a reduced consumption of inexpensive catalytic combustion catalysts. The stated purpose is achieved by a two-stage arrangement of the catalytic combustion process, whereby in the first stage combustion takes place at substoichiometric oxygen concentrations on metal catalysts and in the second stage, after the addition of oxygen, at superstoichiometric oxygen concentrations. It is particularly advantageous to use copper on supports as the first stage catalyst.

Description

The invention relates to a process for the catalytic combustion of gaseous mixtures and / or industrial waste gases containing hydrogen as the main oxidizable component, carried out in two stages, in an expedient arrangement of the oxygen concentration in both stages.

Gaseous mixtures and / or industrial waste gases containing oxidisable substances in low concentrations are catalytically combusted from environmental reasons to final oxidation products, carbon dioxide and water. Typically, the process is carried out in one step at an above-stoichiometric oxygen concentration to ensure complete combustion. The catalysts most commonly used are platinum or palladium deposited in small amounts on a support of alumina, ceramic or metal (Kirk-Othmer Encycl. Chem. Technol., 3rd ed., 9, 1980, p. 511). The disadvantage of these processes is the use of deficient and precious noble metals as catalysts.

In an effort to reduce the consumption of noble metals, the catalysts based on them are replaced by the less expensive oxide catalysts. A partial replacement of the precious metal is achieved by a combined oxide catalyst of the formula XO _y , wherein y is 1 to 3 and one or more noble metals (British Pat. 1 558 167). Another possibility of partially replacing the noble metals is to use a bilayer catalyst whose first layer contains Mn and Cu oxides and the second separate layer, a noble metal catalyst (German Pat. No. 3,042,843).

Often the oxides themselves are used as catalysts for catalytic combustion. It is known to use a catalyst comprising oxides of medium and chromium (USSR Pat. No. 386,667), chromium oxide and chromite media (USSR Pat. No. 882,592), cobalt oxide with the addition of one or more metals III. A groups (NSR Pat. 2,641,317), mixed oxides of Ag-Co-Mn (U.S. Pat. No. 4,302,360). A disadvantage of oxide catalysts is their relatively low catalytic activity compared to the platinum group metals, which requires a large volume of catalyst in the combustion reactor. This results in higher pressure drop over the gas flow through the catalyst bed, thereby greatly increasing the operating cost of the process.

The catalytic combustion of gaseous mixtures with a higher content of oxidizable components releases a considerable amount of heat, the use of which is economically advantageous. There are also frequent cases of composition of gaseous mixtures that the concentrations of pollutants present in them are low and are either below the level permitted by health regulations or only slightly higher. Catalytic combustion of such gas mixtures is not only motivated by ecological requirements, but mainly by the effort to exploit their potential energy content. In these mixtures, hydrogen is often the major oxidizable component. In addition, carbon monoxide, aliphatic alcohols such as methanol, ethanol, aliphatic aldehydes such as formaldehyde, acetaldehyde and some other substances are also present, mostly at lower concentrations.

The present invention relates to a process for the catalytic combustion of gaseous mixtures and / or waste industrial gases containing mainly hydrogen and also carbon monoxide, aliphatic alcohols, aliphatic aldehydes and some other substances, characterized in that the catalytic combustion is carried out in two stages; , downstream of the gaseous mixture, the process takes place at substoichiometric oxygen concentrations on the metal catalysts and in the second stage after the addition of oxygen or oxygen-containing gas at post-stoichiometric oxygen concentrations.

The main advantage of two-stage catalytic combustion with a substoichiometric oxygen concentration in the first stage by the process of the present invention is that a substantial part of the oxidizable components, mainly hydrogen, is catalytically burned in the first stage on metal catalysts where the reaction rate of oxidation is significantly higher based on metal oxides. This can be seen, for example, from the ratio of the initial reaction rates of hydrogen oxidation for gas mixtures containing 14 percent by volume. hydrogen and 5% vol. oxygen on the one hand and a gas mixture containing 4% vol. Hydrogen and 5% vol. oxygen on the other hand. At 250 ° C, the ratio of the initial reaction rates on the metallic to oxide form of the same supported copper catalyst is 8.8. With the process of the present invention, it is possible to achieve higher specific loads on the catalyst, thereby reducing both its consumption and reducing the operating costs of transporting the gases. Any metal may be used as the first-stage catalyst, and preference is given to using low-cost medium, cobalt, nickel and iron catalysts. Particularly preferred is the use of media applied at concentrations of 10 to 50% by weight. onto a suitable carrier.

In the second stage, either metal oxide catalysts or noble metal active ingredient catalysts can be used. Since a smaller proportion of oxidizable substances is catalytically burned in the second stage, the catalyst requirement in this stage is relatively low.

A preferred variant of the process according to the invention is the use of one commercially available Pxide-based catalyst in both stages. In the first step, such a catalyst, after prior reduction, is used as a metal catalyst, in the second step, in the original oxidized form.

The reaction rate of hydrogen with oxygen is sufficiently high on metal catalysts already at a temperature of 200 to 300 ° C, at which combustion can be carried out in a tubular re240539 actuator with cooled boiling water. The combustion heat is thus used to produce steam in the reactor jacket. Only the remainder of the hydrogen and any organic matter present are burned in the second stage in excess oxygen. The second step is preferably conducted at a higher temperature of 300 to 1000 degrees Celsius, which is achieved by adiabatic regimens.

When working with excess air throughout the catalytic reactor volume, only enough gases can be added to the air to prevent the formation of an explosive mixture; the hydrogen content in the air shall not exceed 4% vol. Therefore, the hydrogen-containing combusted gas is at a higher concentration, respectively. other flammable substances must be added gradually to the air and the reactor must be divided into several layers. For example, the off-gas from formaldehyde production containing 18 to 20 vol. hydrogen and a small amount of methanol, formaldehyde and carbon monoxide must be burned on four layers. Such a device is difficult to control. It is therefore an advantage of the invention to be able to burn most of the hydrogen in the first stage, since sufficient oxygen can be added here. For example, two layers are sufficient to burn off the waste gases from formaldehyde production.

The process according to the invention can advantageously be used for catalytic vision of gaseous mixtures and / or waste industrial off-gases, for example from methane steam reforming, coke oven and gasworks, oxidative dehydrogenated alcohol processes on metal catalysts, various chemical and petrochemical plants.

Example

One possible embodiment of the process of the invention is shown in FIG. Waste gas from the production of formaldehyde A in an amount of 7200 Nm ³ / h, containing 17.3% by volume of hydrogen, 0.4% by volume of hydrogen; of carbon monoxide, 0,05% vol. formaldehyde, 0.2% v / v of methanol, 0.1% by volume. Oxygen and the remainder of the inert component are fed via blower 1 through heat exchanger 3 to a tubular catalytic reactor 5 filled with 1.4 m ^{3 of} catalyst. The catalyst is CuO na supported on alumina in the form of 5X5 mm tablets. At a bath temperature of 200 ° C, the original copper oxide is reduced by the off-gas to metallic honey.

After reduction of the catalytic charge, air B is added to the waste gas A prior to entering the reactor at 2690 Nm ³ / h by blower 2 after being previously heated in heat exchanger 4. At a substoichiometric oxygen concentration, catalytic combustion of the major part of hydrogen present in the waste gas The return heat is used to produce 4 t / h of water vapor at a pressure of 1.8 MPa C from the water condensate D supplied to the jacket of the tubular reactor 5.

To the reaction gases from the first stage at 230 ° C, 860 Nm ³ / h of air are added and the resulting mixture is fed to an adiabatically operating second stage 6 with a stoichiometric oxygen concentration. For the catalytic combustion of the second part of the oxidizable substances in the reactor 6, 2 m ^{3 of} the same copper catalyst as in the first stage is used, except that it is in the original, oxidized form.

The combustion gases from the 450 ° C reactor S are cooled in heat exchangers 3, 4 and are discharged to a chimney E or used for suitable purposes by one of the known processes. They contain 2 ppm formaldehyde, 8 ppm methanol and 22 ppm carbon monoxide.

Claims (2)

240539 by a chilled water boiler. The heat of combustion is thus used to produce steam in the reactor shell. Only the remainder of the hydrogen and possibly the present organic substances are burned in a second stage in excess oxygen. The second stage is preferable to conduct at a higher temperature of 300 to 1,000 degrees Celsius, which is achieved by the adiabatic modes. When working with excess air in a full-scale catalytic reactor, only enough gases can be added to the air to avoid an explosive mixture; The hydrogen content of the air must not exceed 4% by volume of Pretose hydrogen-containing combustion gas at higher concentrations or higher. other flammable substances must add to the air gradually and the reactor needs to be divided into several layers. For example, off-gas from formaldehyde production containing 18-20% by volume of hydrogen and a small amount of methanol, formaldehyde and oxide-carbonate must be combusted in four layers. Such a device is difficult to regulate. It is therefore an advantage of the invention to be able to burn off most of the hydrogen in the first stage, since sufficient oxygen can be added here. The process according to the invention may advantageously be used for the catalytic combustion of gaseous mixtures and / or off-gas effluents, for example from steam methane reformation, from coke oven and gas plants, from alcohol oxidation dehydrogenation processes from metal catalysts, from various chemical and petrochemical supplies. Example One of the possible transformations of the process of the invention is shown in Fig. 1. Waste gas from the production of formaldehyde A in an amount of 7,200 Nm 3 / h, containing 17.3% by volume of hydrogen, 0.4% by volume of carbon monoxide, 0.05% by volume. of formaldehyde, 0.2% by volume methanol, 0.1% by volume. The oxygen catalyst and the rest of the inert component are fed via a blower 1 via a heat exchanger 3 to a tubular catalytic reactor 5 filled with 1.4 m3 of catalyst. The catalyst is CuO to be supported on alumina in the form of tablets of 5 x 5 mm diameter. At a bath temperature of 200 [deg.] C., the copper (II) oxide is reduced to a copper copper waste gas. After the catalytic charge has been reduced, air B is added to the exhaust gas A prior to entering the reactor with an amount of 2690 Nm 3 / h by blower 2 after previous heating in the heat exchanger 4. When the oxygen is under stoichiometric concentration, the catalytic combustion of the main hydrogen portion occurs. present in the off-gas in the reactor 5. The combustible heat is used to produce 4 t / h of water vapor of 1.8 MPa C from the aqueous condensate D fed to the tube of the tube reactor 5. To the reaction gases of the first a temperature of 230 ° C is added to 860 Nm 3 / h of air and the resulting mixture is fed to an adiabatic-processing second stage 6 with an overstoichiometric oxygen concentration. To catalytically burn a second portion of oxidizable fluxes in reactor 6, 2 m 3 of the same copper catalyst is used as in the first step, except that it is in a flooded, oxidized form. The combustion gases from the S-reactor at 450 ° C are cooled in the heat exchangers 3, 4a and are discharged to the chimney or used for some purpose by any of the known methods. They contain 2 ppm of formaldehyde, 8 ppm of methanol and 22 ppm of carbon monoxide. OBJECT A process for the catalytic combustion of gaseous mixtures and / or industrial and / or off-gas industrial gases, aliphatic alcohols and aliphatic aldehydes, characterized in that the catalytic combustion is carried out in two stages, the process being carried out in a first stage concentration at a first stage OXYGEN to the metal catalysts and in the second stage, after the oxygen or oxygen-containing gas has been added, at oxygen-concentration concentrations. 2. Catalytic combustion method according to claim 1, characterized in that copper on supports is used as the first stage catalyst. 1 sheet of drawings