MXPA97006920A - Catalyst and procedure for the catalytic cleaning of exhaust gases in the process - Google Patents

Abstract

The present invention relates to a catalyst for the process of cleaning exhaust gases under pressure, as they occur after the oxidation of paraxylene, (px) with air in liquid phase, during the production of dimethylterephthalate (DMT), which contains as components a) at least one titanium oxide and b) at least one element of the secondary group VIII of the Periodic Element System in metallic and / or oxidic form, to a process for obtaining a catalyst, wherein component b) is applied on molded bodies, which contains at least component a), individually or in admixture, by impregnation by immersion and / or by spraying, and to a process for cleaning exhaust gases under pressure, as they occur after the oxidation of paraxylene (px) with air in liquid phase, during the production of dimethylterephthalate (DMT), where the exhaust gas under pressure, which contains oxygen, from oxidation, is passed through by a condensation of one or several stages, an absorption of one or several stages and, if necessary, by oxygen feed, by a subsequent catalytic incineration operated under pressure, where, for the subsequent catalytic incineration, it is used the present catalyzed

Description

CATALYST AND PROCEDURE FOR THE CATALYTIC CLEANING OF EXHAUST GASES IN THE DMT PROCESS The invention relates to a catalyst for the process of cleaning exhaust gases under pressure, as they occur after the oxidation of para-xylene (px) with air in liquid phase during the production of dimethylterephthalate (DMT), to a process for obtaining said catalyst and for a process for cleaning exhaust gases under pressure, as they occur after the oxidation of para-xylene (px) with air in liquid phase during the production of dimethylterephthalate (DMT), wherein the Oxidation exhaust gas, under pressure, containing oxygen, is first passed through a condensation of one or several stages, by an absorption of one or several stages and then, if necessary adding oxygen, by a catalytic incineration further operated under pressure. It is known that the current Witten-DMT process basically contains the steps - oxidation of para-xylene (px) and methyl ester of para-toluyl acid (p-te), usually with cleaning of the exhaust gas connected later, - esterification with methanol from the reaction products of oxidation, - separation of the ester that formed, called crude ester (crude DMT) in a fraction rich in p-te, which is commonly fed back to oxidation, a crude DMT fraction, which in general it contains more than 85% by weight of DMT, and a residual fraction of difficult boiling, if necessary its processing, for example by a methanolysis or thermolysis connected later, and a subsequent recovery of the catalyst, - cleaning of the crude DMT fraction , for example by washing, recrystallization and distillation, ("Terephtalsauredimetilester", Ullmann Vol. 22, 4th edition, pp. 529-533; EP 0 464 046 Bl; DE-OS 40 26 733). It is also known DMT, ie fractions particularly rich in DMT, or, pure DMT, obtain terephthalic acid of corresponding quality by a specific hydrolysis. The oxidation of a mixture of para-xylene (px) and methyl ester of para-toluyl acid (p-te or pt-ester) is generally carried out with oxygen from the air, in the presence of a heavy metal catalyst (DE-PS 20 10 137), at a temperature of about 140 to 1802C and under a pressure of about 4 to 8 bar abs., In the liquid phase. From the oxidation step results a reaction mixture containing mostly monomethylterephthalate (MMT), p-toluyl acid (p-ta) and terephthalic acid (ta) dissolved, or suspended in p-te, which is esterified with methanol at a temperature of approximately 250 to 2802C and under a pressure of 20 to 25 bar abs .. Furthermore, oxidation produces an exhaust gas which, depending on pressure and temperature, is largely saturated with aliphatic compounds and aromatics. Thus, the exhaust gas, in addition to usable products, also contains secondary products of the reaction, to which belong, among others, low-boiling compounds acetaldehyde, formaldehyde and the corresponding methylacetals, dimethyl ethers, acetic acid and formic acid, as well as as its methyl esters. In addition to these organic components, the exhaust gas contains from the oxidation basically nitrogen of the air, a residual oxygen content of 0.5 to 4% by weight, C0 with 1 to 3% by weight and 0.3 to 2.0% by weight of CO. In the Witten-DMT process, normally the exhaust gas is first cooled in several stages, the high and medium boiling products being removed in stages by condensation. The usable products that remain in the exhaust gas, especially methanol and p-x, are then removed from the same to their traces in a multi-stage absorption, with the usable products being fed back to the process with which the absorption agent is enriched. In many countries, due to legal requirements, organic carbon compounds and CO must be removed from gases and exhaust air.

EP 0 544 729 Bl discloses a process for cleaning an oxidation exhaust gas that comes from an atmospheric oxidation of xylene and which is under a pressure of 5 to 50 bar, being largely removed first, in a low wash exhaust gas pressure, at least xylene by absorption with an ester, for example para-toluyl acid methyl ester (p-te) or benzoic acid methyl ester (BME) or a mixture of esters, for example from p- tea and BME. A condensation stage may also be connected before the absorption. Furthermore, the oxidizable substances that are still in the exhaust gas after the absorption cleaning must be incinerated under pressure and the exhaust gas under pressure must be used to obtain energy in a vacuum turbine. Such incineration units necessary for the incineration of exhaust gases under pressure are complicated and expensive, both in the installation and in the operation. In addition, the adequate pressure incineration chambers are practically no longer available in the market. EP 0 544 726 Bl mentions in this respect the possibility of catalytically incinerating under pressure the oxidizable components found in the exhaust gas, the exhaust gas being incinerated by incineration, after washing by absorption, usually saturated with steam of water.

Guideline VDl 3476, "Catalytic procedure for exhaust gas cleaning", Manual VDl "Reinhaltung der Luft", Volume 6 (June 1990), describes, among other things, the removal of CO, hydrocarbons and NOx from the exhaust gases of Cars using Pt / Rh / Pd on ceramic carriers, at temperatures of 300 to 950sc. Suitable carrier materials for the exhaust gas cleaning catalysts are, inter alia, metals such as formed sheets (expanded metal), fabrics, networks, molded bodies of metal oxides, such as AI2O3, SiO2, Ti0, Zr0, MgO. as well as natural and synthetic minerals, such as pumice, mullite, cordierite, steatite or zeolites. Also for removing CO and vapors of organic compounds from industrial exhaust gases, noble metal catalysts or metal oxides are generally used on ceramic carriers, surface-rich carrier catalysts or integral contacts. EP 0 664 148 A1 teaches a method for cleaning exhaust gases under pressure by subsequent catalytic incineration, at a working temperature between 250 and 800 ° C and pressures between 2 and 20 bar, in particular using catalysts with Platinum and / or palladium on oxide? of aluminum. The tests show that these catalysts, under the conditions of work in exhaust gases of the oxidation of para-xylene in the obtaining of DMT, are deactivated even after a short time of operation, and, therefore, it is no longer reached the reduction of toxic substances required. Therefore, the invention was based on the objective of making available a catalytic system that would satisfy the requirements for the cleaning of the exhaust gases that occur in the oxidation during the production of DMT. Another objective of the present invention was to include said exhaust gas cleaning measures in the DMT process also under economic aspects. The stated objective is achieved according to the invention according to the specifications of the claims. It has now been found that a catalyst, which contains at least one titanium oxide and at least one element of the secondary group VIII of the Periodic Element System in metallic and / or oxidic form, is extraordinarily suitable for the gas cleaning process of Exhaust under pressure that comes from the oxidation of para-xylene (px) with air in liquid phase, in the obtaining of dimethylterephthalate (DMT), because even after a comparatively long operating time, no deactivation worth mentioning was observed, it was possible to maintain the required exhaust gas values and thus, it is also characterized by excellent industrial activity times.

Thus, the object of the present invention is a catalyst for a process for cleaning exhaust gases under pressure, as they occur after the oxidation of para-xylene (px) with air in liquid phase during the production of dimethylterephthalate (DMT). ), which is characterized in that it contains as components a) at least one titanium oxide and b) at least one element of the secondary group VIII of the Periodic Element System in metallic and / or oxidic form. Preferably, the catalyst according to the invention contains, respectively based on the weight of the catalyst: component a) in quantities of 50 to 99% by weight and component b) in quantities of 0.01 to 5% by weight, wherein component b) is calculated in sum and as metal. More suitably, the titanium oxide or a precursor compound for component a) comes from the so-called sulphate process, so that the catalyst according to the invention preferably contains sulfate as another component c), and may contain it in particular in amounts of 0.1 to 10% by weight, based on their weight. The sulphate as component c) can be present in the catalyst according to the invention as such or, for example, also as hydrogensulfate or oxidosulphate or oxidosulfate containing water, of a corresponding metal or as a sulfuric acid fixed or adhered to an oxidic compound of metal. The sulfate may also be present simultaneously in several of the aforementioned forms. In the catalyst according to the invention, component a), more suitably, is present as titanium dioxide, for example as rutile. Preferably, however, in the catalyst according to the invention component a) is predominantly in the form of anatase. But titanium oxides with lack of oxygen or oxides containing water, oxides hydroxides or hydroxides or sulfates may also be present, including hydrogen sulfates, for example, sulfates of oxide or sulfates of titanium oxide containing water, or oxides of titanium with sulfuric acid fixed or adhered. Component b) can also be proportionally present in a sulphatic form. More suitably, the catalyst according to the invention can contain as additional components barium sulfate and / or tungsten oxides and / or vanadium oxides and / or zirconium oxides and / or corresponding sulfates and / or phosphates, including the hydrogen phosphates , and / or silicon oxides and / or silicates. The structure of the catalyst according to the invention can be spherical, rod-shaped, tubular, annular or in the form of a ridge or a honeycomb. The catalysts according to the invention generally have around 200 to 2'000 2/3 of geometric surface, preferably it is bar extrudates, for example with a diameter of 4 mm. The catalysts according to the invention can also have a honeycomb structure, in particular those in which the hydraulic diameter (4a / U = dh with a = clear surface of the channel cross section, U = periphery of the clear surface of the cross section of channel and d ^ = hydraulic diameter) of each channel cross section of the honeycomb channels with flow is in the range of 1.5 mm to 6.5 mm. The present invention also provides a method for obtaining a catalyst according to claims 1 to 9, characterized in that component b) is applied individually or in a mixture by impregnation by immersion and / or by spraying. molded bodies, which contain at least component a). A process for the production of carriers molded on a titanium oxide base, also called shaped bodies, is disclosed in DE-PS 26 85 569. For the preparation of a catalyst according to the invention, generally molded bodies are used. a base of titanium oxide, as can be obtained, among other ways, by the preparation and extrusion of masses containing titanium oxide, a subsequent drying and calcination of the molded bodies, and more suitably a BET surface between 10 and 200 μg, as well as a pore volume of between 0.1 and 0.6 cm / g. The molded bodies, to improve the mechanical characteristics, can be reinforced, for example, with glass fibers. As a rule, the component b) of the catalyst according to the invention is applied to the carrier by means of a so-called impregnation, the molded bodies generally coming into contact with a solution, which suitably contains component b) in the form of salts dissolved. In the process according to the invention, for the impregnation of the moldings, a solution is used, for the preparation of which component b) is preferably used as nitrate. In this case it may be necessary to adjust the pH of the solution in a suitable manner, such as by adding an organic or inorganic acid, such as nitric acid, or a bleach, or also adding a complex former or stabilizer, for example for Stabilization of a noble metal solution. The impregnation can be effected by spraying one or several times of the molding body with a solution or by one or several times immersion of the molded body in a solution. More suitably, the impregnated moldings, preferably with air access, are dried in a temperature range of 30 to 650 ° C and subsequently calcined, that is to say, further treated with heat. When using nitrates it is a particular advantage of the manufacturing process according to the invention that component b) can be fixed to the molded body by a simple heat treatment of the molded body impregnated in metallic and / or oxidic form and without further residues, such as example halides. In addition, costly and time-consuming work steps can be saved in this way, as required, for example, in the "wash-coating" or a reduction step with hydrogen in the gas phase. Preferably, in the catalyst according to the invention, component b) is mostly present in the area of the surface of the molded body with a catalyst, that is to say, a so-called layer impregnation is preferred here. As component b), the catalyst according to the invention preferably contains platinum and / or rhodium. Particularly preferred are the catalysts according to the invention with a platinum content in the range of 0.05 to 0.5% by weight, very particularly 0.1 to 0.2% by weight Pt, based on the weight of the catalyst. It is also the object of the present invention a method for the cleaning of exhaust gases under pressure, as they occur after the oxidation of para-xylene (px) with air, in liquid phase, during the production of dimethylterephthalate (DMT), making passing the exhaust gas from the oxidation under pressure, which contains oxygen, first by a condensation of one or several stages, by an absorption of one or more stages and, if necessary adding oxygen, by a subsequent catalytic incineration operated under pressure, which is characterized in that, for the subsequent catalytic incineration, a catalyst according to claims 1 to 13 is used. In general, in the exhaust gas cleaning process according to the invention, the oxidation exhaust gas from an atmospheric oxidation of px, the usable products contained in the exhaust gas, basically px, p-te, DMT, benzoic acid methyl ester (BME) and meta nol, in a condensing unit, if necessary also in a washing or absorption unit connected afterwards, are mostly removed and fed back into the process appropriately. Condensation is usually carried out at temperatures in the range of 15 to 80 seconds and pressures of 3 to 20 bar abs. The gas under pressure that comes from the condensation first heats up more adequately in a heat exchanger of opposite flow, for example from about 252C to about 1202C, at pressures of 3 to 20 bar abs., and then carried to a washing unit. The absorption unit can be composed of several washing steps, for example, first an exhaust gas cleaning with BME or a mixture of esters can take place. Figure 1 shows a preferred embodiment of the method according to the invention, see legend. According to an absorption unit like this, the exhaust gas, more adequately, can be saturated with the exhaust water (100) produced in the process, the so-called process water containing in general organic components. Usually, a so-called saturator (AS) is used for this. The process water is preferably circulated through a pump (Pl) and a heat exchanger (Wl) heated with low pressure steam and delivered to the saturator head (AS). In general, the exhaust gas is saturated with water and the components contained in the original process water, basically volatile organic compounds. To prevent the saturator (AS) from becoming clogged by enrichment of solids as well as high boiling components, which generally occur at the bottom of the saturator, a small part of the exhaust water (120) can be removed from the bottom of the saturator (AS) and, for example, feedback at a suitable place in the process. The exhaust gas leaving the absorption unit, preferably the saturator (AS), usually contains secondary products that are produced in the DMT process, such as CO and low-boiling compounds, such as acetaldehyde, formaldehyde, methylacetate. , dimethyl ether, acetic acid and formic acid, as well as their methyl esters. In order to eliminate these secondary products in the least harmful way to the environment, the exhaust gas under pressure can now be brought to a subsequent catalytic incineration. For the subsequent catalytic incineration (KNV) the catalyst according to the invention is used here. The reactor of the subsequent catalytic incineration is usually formed as a fixed bed reactor and can receive both stirring catalysts and also monolithic catalysts. Suitably, monoliths in the form of honeycomb are used, which are generally characterized by a very low pressure loss, which in the exhaust gas cleaning process according to the invention has a positive effect particularly in energy recovery by an exhaust gas turbine. In the process according to the invention, the subsequent catalytic incineration is preferably carried out at pressures between 2 and 20 bar abs, particularly preferred 5 to 10 bar abs., And at a working temperature between 160 and 6502C, particularly preferred between 200 and 5502C. In the process according to the invention, the subsequent catalytic incineration is preferably carried out at a space velocity (GHSV) of 10000 h-1 to 50,000 h.l, particularly preferred in the range of 5,000 h.l. up to 30'000 h-1 (GHSV = VN / VCat [Nm3 / m3xh], with VN = volume flow in the normal [Nm / h] and VCat = catalyst volume [m]). For the first reactor operation (KNV), process air (141) is usually first heated through an electrically operated heat exchanger (W4) and passed through the reactor (KNV) until it has reached its Prescribed operating temperature, which guarantees the initiation of the catalyst. The reactor can then be supplied with exhaust gas. Suitably, the subsequent catalytic incineration then proceeds thermally to a large extent in an autarkic manner. In the process according to the invention, the exhaust gas before the catalyst normally contains water vapor in amounts of 0.04 to 2.8 kg / N 3, in particular 0.1 to 0.4 kg 3 of water per Nm of exhaust gas. Preferably, the flow of exhaust gas to be cleaned (150), before entering the catalyst area, it is preheated (160, 161, 171) counter-flowed with the exhaust gas (pure gas) (180) leaving the reactor, by means of a suitable arrangement of heat exchangers (W2, W3). The oxidation in the DMT process is generally adjusted in such a way that the oxygen required for the catalytic incineration is already present in the exhaust gas before it enters the reactor. The oxygen content in the exhaust gas (130), if necessary, can be raised by applying pressurized air (140). Usually, in this way, the organic compounds and CO that are found in the exhaust gas are transformed almost completely into carbon dioxide and water. The content of oxygen in the pure gas (180, 190) is preferably adjusted to a value between 0.5 and 2% by volume. For the recovery of the compression energy, the pure gas (190) can be reduced in its pressure through an exhaust gas turbine (TU) to obtain mechanical or electrical energy. For the recovery of energy by means of a vacuum turbine, in general, those flows of pure gas which are under a pressure of, preferably, more than 3 bar abs are used. As the exhaust gas usually meets the requirements now, be discarded by a chimney (210). The temperature for this effect, if necessary by adding unheated exhaust gas, can be controlled in such a way that the pure gas leaving the exhaust gas turbine possesses a temperature of approximately 125 c. In the process according to the invention, the flow of pure gas can also be bifurcated, at least in part, before the turbine, after the corresponding drying, it can be cooled to temperatures below 40 C (W5) and, appropriately, it can then be used as an inert gas, for example for "blanketing" in the process (200). The particular advantages of the process according to the invention are, in addition to the good industrial lifetime achieved of the catalyst, also the simultaneous use of the exhaust water that is produced, the incineration of all the products obtained in the oxidation and which pass to the Exhaust gas and the minimization of CO contents in pure gas to values that, with the measuring devices, are often no longer detectable in daily operation. The invention is illustrated in more detail with the following examples: Examples: Example 1: - obtaining a catalyst for the cleaning of the exhaust gas from the oxidation in the Witten-DMT process. 2 000 g of a commercial catalyst carrier, in the form of a bar, is placed in a rotary drum. in Ti02 (type H9050 from Hüls AG) and heated to 1102C by a flow of hot gas. Upon reaching the temperature, they are sprayed for approximately 20 minutes, at 1102C, 500 ml of an aqueous solution of Pt-nitrate with w (Pt) = 5.2 g / 1. The solvent evaporates and the metal precipitates in a thin marginal zone on the carrier. The material is then removed and calcined in an air flow for 4 hours at 450 ° C.

Example 2: Cleaning of the exhaust gas from the oxidation in the Witten-DMT process Figure 1 shows a preferred embodiment of the process according to the invention for the cleaning of exhaust gases under oxidation pressure in the Witten-DMT process. In this regard, tables 1 a + b show material flows, their composition and the respective operating conditions; see the legend. The quantities of exhaust gas and exhaust water and their compositions are typical for a DMT / PTA installation with a capacity of 240 kt / y. The exhaust gas produced after the condensation and absorption unit in the DMT / PTA installation and basically free of usable products, enters as material flow (110) with an amount of 70 * 768 kg / h and a temperature of 1202C at the lower part of the saturator (AS). In the upper part of it, the exhaust water (20O00 kg / h) (100) that comes from the DMT / PSA installation is received. The saturator is equipped either with valve bottoms or with structured packing. The exhaust water is circulated (121) by means of a circulation pump (Pl) through a heat exchanger (Wl) heated with low pressure steam. To avoid the enrichment with solids of the saturator and, with it, the possible problems of operation of the installation, a small part of the bottom product of the washing is locked to af rea (120) and fed back into the DMT / PTA process in a determinated place. To start the reactor (KNV) process air (141) is first passed through the electrically heated heat exchanger (W4) to the subsequent catalytic incineration, until a temperature is reached that guarantees the initiation of the reaction. The exhaust gas (130) washed and saturated with water and the organic contents of the exhaust water, with a temperature of 121.52c and a pressure of 7.1 bar, is heated to 2502C through the counterflow heat exchangers (150, 160 , 170) and is taken to the reactor of the subsequent catalytic incineration. The inlet temperature of the exhaust gas before the reactor can be adjusted both on arrival and also during normal operation by the flow of matter (161). The atmospheric oxygen necessary for incineration can be added additionally through the flow of matter (140). The reactor (KNV) is provided with catalyst time H 5922 from Hüls AG, see example 1, and is operated at a space velocity in the range of approximately 30,000 [Nm 3 / m 3 × h]. The incineration is complete and only relatively small excesses of oxygen are necessary. Conditioned by the heat of the reaction of the exothermic incineration process, the clean exhaust gas (pure gas) exits the reactor at a temperature of 40isc (180) and is delivered to the side of the jacket of the heat exchanger (W2, W3) for the heating of the exhaust gas, cooling the pure gas to a temperature of 2772C (190) and then, through the exhaust gas turbine (TU), its pressure is reduced to normal pressure (210) and Discarded through the chimney into the atmosphere. To obtain inert gas it is possible to cool the pure gas (190) partially under pressure and use it in the DMT / PTA installation as "blanketing" (200).

Legend of Figure 1 / Table 1 and the material flows Figure 1 shows a preferred embodiment of the method according to the invention for the cleaning of exhaust gases under oxidation pressure in the Witten-DMT process.

Flows of matter in figure 1 and in the tables and b: 100: Process water 110: Exhaust gas of the condensation or absorption unit 120: Bottom product, feedback to the process 121: Circuit of the saturator 130: Gas of exhaust from saturator 140: Pressurized air 141: Pressurized air to initialize reactor 142: Suction air 150: Exhaust gas, enriched with oxygen 160: Exhaust gas flow to heat exchangers W 2 + 3 161: Flow of exhaust gas for the regulation of the reaction temperature 170: Exhaust gas heated by counterflow heat exchanger, before reactor 180: Pure gas after reactor 190: Pure gas after the counterflow heat exchanger 200: Partial flow of pure gas cooled and under pressure, feedback as inert gas to the process 210: Flow of pure gas remaining, without tension before the chimney Parts of the installation in figure 1: AS: Saturator Pl: Pump Wl: Heat exchanger, steam operated W2 + 3: Counterflow heat exchangers KNV: Reactor for subsequent catalytic incineration W4: Heat exchanger, electrically operated W5: Heat exchanger TU: Depression turbine Legend of the tables la and b: Regarding figure 1, in tables la and b the flows of matter, its composition and the respective working conditions are shown.

Legend of the abbreviations p-x: para-xylene p-ta: para-toluyl acid p-te: methyl ester of para-toluyl acid (pT-ester) BME: methyl ester of benzoic acid HM-BME: methyl ester of hydroxymethylbenzoic acid MM-BME: methoxymethylbenzoic acid methyl ester DMT: crude DMT dimethylterephthalate: crude ester (raw DMT flow after esterification) crude DMT: dimethylterephthalate fraction after distillation of crude ester Pure DMT: pure dimethylterephthalate (DMT highly pure intermediate or final) DMO: dimethylortophthalic acid DMI: dimethyl isophthalic acid DMP: dimethyl phthalate = isomeric mixture of DMT, DMO and DMI MMT: monomethylterephthalate (monomethyl ester of terephthalic acid) TA: terephthalic acid MTA: terephthalic acid of medium purity PTA: high purity terephthalic acid PTA-p: terephthalic acid of very high purity, that is, the highest (content of MMT and p-TA of, overall, less than 50 ppm by weight) TAS: terephthalaldehyde acid (4-CBA) TAE: methyl ester of terephthalaldehyde acid Formaldehyde-DMA: formaldehydedimethylacetal Acetaidehyde-DMA: acetaldehydedimethylacetal Table Table la - Continuation Table Ib Table Ib - Continuation

Claims (13)

NOVELTY OF THE INVENTION Having described the foregoing invention, the content of the following is claimed as property: CLAIMS

1. A catalyst for the process of cleaning exhaust gases under pressure, as they occur after the oxidation of para-xylene (px) with air in liquid phase, during the production of dimethylterephthalate (DMT), characterized in that, as components, it contains a) at least one titanium oxide and b) at least one element of the secondary group VIII of the Periodic Element System in metallic and / or oxidic form.

2. A catalyst according to claim 1, characterized in that, as component b), it contains platinum and / or palladium and / or rhodium.

A catalyst according to claim 1 or 2, characterized in that it contains - component a) in amounts of 50 to 99% by weight and - component b) in amounts of 0.01 to 5% by weight where component b) it is calculated in sum and as metal, referred respectively to the weight of the catalyst.

4. A catalyst according to at least one of claims 1 to 3, characterized in that, as component c), it contains sulphate.

A catalyst according to claim 4, characterized in that it contains the component c) in amounts of 0.1 to 10.0% by weight, based on the weight of the catalyst.

6. A catalyst according to at least one of claims 1 to 5, characterized in that, as additional components, it contains barium sulfate and / or tungsten oxides and / or vanadium oxides and / or zirconium oxides and / or corresponding sulfates and / or phosphates and / or silicon oxides and / or silicates.

7. A catalyst according to at least one of claims 1 to 6, characterized in that it contains titanium oxide, which is mostly in the form of anatase.

8. A catalyst according to at least one of claims 1 to 7, characterized in that it has a honeycomb structure.

9. A catalyst according to at least one of claims 1 to 8, characterized in that the component b) is mostly in the surface area of the molded body of the catalyst.

10. A process for obtaining a catalyst according to claims 1 to 9, characterized in that component b) is applied to moldings containing at least component a), individually or as a mixture, by impregnation by immersion and / or by spraying.

11. A process according to claim 10, characterized in that molded bodies with a BET surface of between 10 to 200 m 2 / g and a volume of pores 3 of between 0.1 and 0.6 cm / g are used.

12. A process according to claim 10 or 11, characterized in that, for the impregnation of the molded articles, a solution is used, for the preparation of which component b) is used as nitrate. 13. A process according to at least one of claims 10 to 12, characterized in that the impregnated shaped bodies are then thermally treated under air access. 14. A procedure for the cleaning of exhaust gases under pressure, as they occur after the oxidation of para-xylene (px) with air in liquid phase, during the production of dimethylterephthalate (DMT), where the exhaust gas is low The pressure, which contains oxygen, of the oxidation, is first passed through a condensation of one or several stages, an absorption of one or several stages and, if necessary, under oxygen feed, by a subsequent catalytic incineration operated under pressure, characterized in that a catalyst according to claim 1 is used for the subsequent catalytic incineration.

13. 15. A process according to claim 14, characterized in that the subsequent catalytic incineration is operated in the temperature range between 160 and 6502C and at pressures from 2 to 20 bar abs .. 16. A method according to claim 14 or 15, characterized by operating the subsequent catalytic incineration at a space velocity (GHSV) in the range of 1 000 h "1 to 50 '000 h" 1. 17. A method according to at least one of claims 14 to 16, characterized in that, after the last stage of the absorption, water from the process, which contains organic components, is fed to the exhaust gas flow through a saturator. 18. A process according to at least one of claims 14 to 17, characterized in that the catalyst exhaust gas contains water vapor in amounts of 0.04 to 2.8 kg / Nm3. 19. A method according to at least one of claims 14 to 18, characterized in that the exhaust gas catalytically cleaned under pressure is reduced in pressure through a turbine to obtain mechanical or electrical energy. 20. A process according to claim 19, characterized in that the energy still contained is partially recovered from the exhaust gas under pressure, catalytically cleaned, reducing the pressure of the exhaust gas flow under a pressure of more than 3 bar abs. in a vacuum turbine to obtain mechanical and / or electrical energy. 21. A method according to at least one of claims 14 to 20, characterized in that the clean exhaust gas is used as an inert gas. SUMMARY The present invention relates to a catalyst for the process of cleaning exhaust gases under pressure, as they occur after the oxidation of paraxylene (px) with air in liquid phase, during the production of dimethylterephthalate (DMT), which contains as components a) at least one titanium oxide and b) at least one element of the secondary group VIII of the System Periodic of Elements in metallic and / or oxidic form, to a process for obtaining a catalyst, wherein component b) is applied on molded bodies, containing at least component a), individually or in a mixture, by impregnation by dipping and / or spraying, and a procedure for cleaning exhaust gases under pressure, as they occur after the oxidation of paraxylene (px) with air in liquid phase, during the production of dimethylterephthalate (DMT), where the Exhaust gas under pressure, which contains oxygen, from oxidation, is first passed through a condensation of one or several stages, an absorption of one or more stages and, if necessary, under oxygen supply, by incineration further catalytic operated under pressure, wherein, for the subsequent catalytic incineration, the present catalyst is employed.