DE102004006861A1 - Purification of off-gas from solid-phase condensation of polycondensates, e.g. polyamide or polyester, involves adding oxygen-containing gas and passing the mixture over a metal oxide-based catalyst - Google Patents

Abstract

A metal oxide-based catalyst (I) is used in a method for purifying a gas stream contaminated with organic compounds (II) by adding an oxygen-containing gas, passing it over (I) so that the gas leaving the catalyst unit has an oxygen content of 0-500 ppm, and using oxygen analyser(s) and/or Lambda probe(s) to monitor the ratio of oxygen to (II). An independent claim is also included for a system for carrying out this method, comprising a solid-phase condensation reactor (1), a line (7) for feeding gas from (1) into a catalyst unit (8) containing (I), a gas inlet (9) for O2-containing treatment gas, an outgoing line (24) from the unit (8), and O2 analyser(s) and/or Lambda probe(s) in at least one of the lines (11, 24) connected to (8).

Description

The The present invention relates to a method according to the preamble of claim 1 and to a plant according to the preamble of Claim 15.

method and plants of this type are known from US-A-5,547,652 or US-A-5,612,011 known. It is about the cleaning of the exhaust gases of the Process by means of a noble metal catalyst consisting of platinum or mixtures of platinum and palladium, or in other words the post-combustion (oxidation) of the impurities with a noble metal catalyst. It becomes the complete Oxidation an at least stoichiometric Quantity of oxygen so fed that the oxygen content after the catalyst in the first mentioned patent in a range of 0-10 ppmv / v lies. In the second mentioned patent, so much oxygen is fed in, that the oxygen content after the catalyst in a range from 0-250 ppmv / v lies. Here, however, there is the disadvantage that the noble metal catalysts used very expensive and subject to sharp price fluctuations. To comes that special chemical compounds or catalyst poisons such as Sb or Ge, which are discharged from the polycondensate, the Deactivate noble metal catalysts, thereby reducing the life of Noble metal catalysts is limited.

The EP 0 699 471 A1 describes a process for purifying the substantially oxygen-free process gases from the thermal solid-phase treatment of condensation polymers, wherein a maximum stoichiometric amount of oxygen is added for the catalytic oxidation of the oxidizable organic impurities. Here, the carbon monoxide content, which is related to the oxygen content, is determined at the outlet of the oxidation reactor, for example by means of a micro fuel cell, whereby the oxygen content can be determined indirectly. So much oxygen is fed in here that the carbon monoxide content after the catalyst is in the range of 10 to 1000 ppmv / v. In this method, however, there is the disadvantage that the use of CO as a controlled variable always takes place at least partially incomplete combustion. This leads increasingly to deposits on the catalyst material, whereby the life of the catalysts is limited.

Of the The present invention is based on the object, a method for cleaning a contaminated with organic compounds Gas stream to provide the disadvantages of the prior art avoids and works very efficiently.

The solution This object is achieved by the method according to claim 1 or by the Device according to Claim 15. According to the invention This process involves the purification of process gases that are mixed with organic compounds are contaminated with a catalyst material consisting of at least a metal oxide or mixtures containing at least one metal oxide contain.

advantage of this invention is that the active surface of the metal oxide catalysts many times bigger is as with noble metal catalysts. As a result, the material is less susceptible on catalyst poisons, e.g. Sb or Ge, which from the polycondensate be discharged.

Preferably is the metal underlying the metal oxide or metal oxides an element of the subgroup elements or transition metals, in particular the fourth period of the periodic table of the elements (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn), it being particularly advantageous has proven, if the catalyst material at least manganese oxide, Contains iron oxide, copper oxide or cobalt oxide.

Bevorzugteerweise contains the catalyst material at least 50%, in particular at least 65% the metal oxides described above, wherein, for example, in a Copper-manganese mixed oxide of manganese oxide at least 35%, in particular at least 40% and the copper oxide content at least 15%, in particular at least 20% or in the case of an iron-manganese mixed oxide, the iron oxide content at least 35%, in particular at least 40% and the manganese oxide content at least 15%, in particular at least 20%.

Conveniently, the catalyst material is a porous material, so that a big active surface given is. It can be considered porous Catalyst solid material are present as a catalyst coating a porous one support material be applied or as porous Catalyst coating to be applied to a carrier material.

When the catalyst material is used in a form present as a solid material without carrier material, it may be present in the form of pellets, tablets, granules, extrudates or in the form of powder in a catalyst bed, wherein the pellets, tablets, granules or extrudates additionally sub such as a binder or dopants may contain.

If the catalyst material is used in a form in which it on a carrier material is applied, the coated with the catalyst material support material e.g. in the form of a grid, a braid, in the form of honeycomb cells and the like. Or in the form of a porous support matrix present, such as in the form of balls.

preferred support materials are e.g. Alumina, titania or zirconia. Here can be a synergetic interaction between the catalyst material and the carrier material result.

positive Effects are achieved if the catalyst material contains a doping, which contains, for example, cerium or zirconium.

The invention The polluted gas is purified by oxidation (catalytic Combustion) of the impurities on a solid catalyst from at least one metal oxide or mixtures containing at least contain a metal oxide, in particular copper-manganese oxides or iron-manganese oxides are used. Preferably the catalyst material as bulk material, either without carrier material, or as a coating on a substrate such as alumina balls as a so-called catalyst bed. The oxidation preferably takes place in a temperature range of 150 to 600 ° C, in particular from 170 to 350 ° C instead.

Preferably the temperature of the contaminated gas stream is in the range of 150 ° C - 600 ° C and in particular in the range of 170 ° C-350 ° C.

Preferably the contaminated gas stream comes from a reactor and is after the purification at least partially recycled to the reactor. at the reactor is e.g. around a reactor for the solid phase condensation a polycondensate, e.g. Polyamide, polycarbonate, polylactide or polyester, in particular polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) and their copolymers, wherein the Polycondensate also a recycled polycondensate, in particular a recycled PET (RPET).

Preferably becomes the normal operation described in the previous paragraphs or continuous operation by a temporary Heating the catalyst material above the operating temperature Normal or continuous operation changed. This can cause carbon deposits be "burned" on the catalyst material, whereby the catalyst material largely regenerated and thus its life extended can be.

Of the Contaminated gas stream may undergo further process steps prior to oxidation through, such as a filtration for the separation of solid impurities, an increase in pressure (conveying), a mixing with other gases, an adsorption for example of non-oxidizable Substances or catalyst poisons, as well as a warming to increase the temperature to a suitable oxidation temperature. The warming can to a constant temperature or alternatively periodically / cyclically increased to a further Temperature done. This allows the efficient effectiveness of the Catalyst material extended become.

It is possible, too, upon further heating of the contaminated gas upstream of the catalyst unit to dispense, if the process gas, the reactor with sufficiently high Temperature leaves and the oxidation temperature at the catalyst is sufficiently low. Optionally, the catalyst bed or the catalyst support directly be heated, for example by external heat sources or by the heat of combustion of the Impurities.

Of the contaminated gas stream can after oxidation further process steps go through, such as a cooling, a drying, a pressure increase (Advancement), a filtration, a heating and mixing with additives or other process gas streams.

at The process gas is essentially an oxygen-free one Gas, such as nitrogen or CO2, including gas mixtures or gases can be used with added additives. to Oxidation of the organic impurities becomes the process gas one suitable amount of oxygen in the form of at least one oxygen or ozone-containing gas such as air, oxygen or Ozone supplied.

Conveniently, the monitoring takes place of the relationship from oxygen to the impurities by means of at least one Oxygen analyzer and / or by means of at least one lambda probe before and / or after the catalyst, those of the oxygen analyzers and lambda probes emitted monitoring signals weighted before further processing. This can be used to control the oxygen supply.

Preferably is added only so much oxygen-containing gas that the after Oxygen content measured from the catalyst 0 to 500 ppmv / v, preferably 0 to 50 ppmv / v, and most preferably 0 to 20 ppmv / v. When oxygen-containing gas is e.g. Air or an ozone-containing gas used.

The gas throughput or the space velocity (standard volume flow divided by the catalyst volume) is usually in the range from 1000 to 60000 h ^-1 , in particular from 5000 to 20000 h ^-1 . The greater the space velocity, the smaller the residence time of the gas to be cleaned in contact with the catalyst. As space velocity increases, there is a decrease in the rate of conversion of the impurities in the gas. The linear velocity or empty tube velocity (operating volume flow / catalyst bed cross section in the direction of the flow direction of the gas) is in a range of about 0.3 to 2.5 m / s.

The bulk density of the inventive catalyst material in the catalyst bed is in a range of about. 300 to 1500 kg / m ³ .

The grain size the catalyst material bed used is within a range about. 0.1 to 50 mm, in particular 1 to 10 mm.

Further Advantages, features and applications of the invention result from the following, non-limiting description an embodiment shown schematically in the drawing, in which:

1 a schematic representation of a first embodiment of an inventive system shows;

2 a schematic representation of a second embodiment of an inventive system shows; and

3 a schematic representation of a third embodiment of an inventive system shows.

4 shows a first type of catalyst material used.

5 shows a second type of catalyst material used.

First embodiment ( 1 )

A reactor ( 1 ) is intended for solid phase condensation of polyesters such as polyethylene terephthalate. It is conventional, so that a detailed description can be omitted, the supply and the discharge of polyesters via rotary valve ( 2 ) respectively. ( 3 ) he follows. The exhaust gas of the condensation process is via an exhaust pipe ( 4 ) first a filter ( 5 ) for removing particulate impurities. The gas from the filter is then fed via a supply line ( 7 ) via a heat exchanger ( 6 ) to a catalyst unit ( 8th ), as is in the heat exchanger ( 6 ) expediently the waste heat from the catalyst unit ( 8th ) used gas stream.

A gas feed ( 9 ) provides for the supply of a gas containing at least oxygen, ie either pure oxygen or a gas such as air, which contains only a corresponding proportion of oxygen. However, it is also possible to feed in a gas which contains ozone instead of oxygen. The oxygen or ozone is used to oxidize, in supply line ( 7 ) flowing through gas, impurities used and flows the supply line ( 7 ) just before the catalyst unit ( 8th ) too. The so in a collecting line ( 11 ) combined gas streams are expediently before the catalyst unit ( 8th ) with the aid of an electric heater ( 10 ) to an optimum temperature for those in the catalyst unit ( 8th ) taking place oxidation. This is conveniently in the range of 170 ° C to 350 ° C. Subsequently, the collecting line ( 11 ) in the catalyst unit ( 8th ) one. The catalyst unit ( 8th also points an output line ( 24 ), which via a heat exchanger ( 6 ) advantageous to the reactor ( 1 ) is recycled, in particular when, as is customary in polycondensation, the gas to be purified is an inert gas, such as nitrogen. In the return of the gas into the reactor ( 1 ) can be placed between the heat exchanger ( 6 ) and the reactor ( 1 ) optionally the following apparatuses are installed: radiator, blower, fan, gas dryer, filter and heater.

Just before entering the catalyst unit ( 8th ) is in the collecting line ( 11 ) a lambda probe is mounted, which measures the ratio of oxygen to impurities in the combined gas. According to this measurement, an electrical output signal via a line ( 12 ). Alternatively or additionally, a further lambda probe and / or an oxygen measuring cell can be attached to the outlet of the catalyst unit. The lambda probe at the outlet of the catalyst unit ( 8th ) can measure the result of the cleaning and a corresponding electrical signal via line ( 18 ) submit. The oxygen measuring cell at the outlet of the catalyst can control the oxygen content in the outlet line ( 24 ) after the catalyst unit ( 8th ) and send a corresponding signal via line ( 16 ) submit. If appropriate, it is also possible to use only one oxygen measuring cell at the outlet of the catalytic converter or one lambda probe at the inlet of the catalytic converter.

In the illustrated embodiment with three measurements lead the electrical lines ( 12 . 16 and 18 ) to a processor μ. The over the lines ( 12 . 16 and 18 ) incoming signals can also be weighted before they with a desired signal from a, preferably adjustable setpoint generator ( 20 ). The result of this comparison results in a deviation or control signal which is output from the output of the processor ☐ via a line (FIG. 21 ) to a controller ( 22 ) to be led. The regulator ( 22 ) advantageously changes in a corresponding manner a valve V in the gas feed ( 9 ).

The Measurement of the oxygen content in ppmv / v range is carried out in a known Way with a commercial one Device, preferably continuously. An influence of the measured values by other gas components should be excluded. Proved suitable e.g. the measurement by means of an electrochemical sensor (Micro Fuel cell). The oxygen-laden gas diffuses through the Diaphragm of the analyzer into a thin electrolyte layer. there it comes to a redox reaction in which the resulting electron flow directly proportional to the concentration of oxygen in the sample gas is. It can However, other measurement principles are applied.

For measuring the ratio of oxygen to the impurities, as described above, a lambda probe described in US patent no EP 1 100 611 B1 used.

Second embodiment ( 2 )

The same descriptions apply as in embodiment 1 with the difference that the heat exchanger ( 6 ) is omitted in embodiment 1. Since the oxidation takes place in the catalyst in a temperature range of preferably 170-350 ° C, can for economic reasons to a heat exchanger ( 6 ) are waived. It is within the scope of this invention that the heater ( 10 ) in front of the catalyst either in continuous operation or periodically. Periodic operation has the advantage that it is more economical than a continuous operation, while the heater is turned on at certain intervals for a limited time to eliminate any deposits at elevated catalyst temperature.

Third embodiment ( 3 )

The same descriptions apply as in embodiment 1 with the difference that the heat exchanger ( 6 ) and the heater ( 10 ) fall in embodiment 1 before the catalyst. Due to the low combustion temperatures in a range of 170-350 ° C, heating of the gas flowing out of the reactor 1 is no longer necessary for economic reasons.

4 shows a first type of catalyst material used for gas purification. This is a mixed oxide catalyst, which is present in extruded form (pellets). As a mixed oxide, for example, iron-manganese oxide or copper-manganese oxide is used. These so-called "Vollextrudate" also have a binder.

5 shows a second type of catalyst material used for gas purification. This is a mixed oxide catalyst, which is applied to a support material (alumina beads). Here too, the mixed oxide used is, for example, iron-manganese oxide or copper-manganese oxide.

Example 1:

On a Cu-Mn oxide catalyst material and a Fe-Mn oxide catalyst materials at room velocity (RG) of 36000h ^-1 and at a gas temperature before the catalyst in a range of 180-320 ° C, the reaction of ethylene glycol (EG ) tested. In each case, the oxygen content, carbon monoxide content and the content of hydrocarbons after the catalyst were measured in volume fractions per total volume (ppmv / v). In this case, an air stream upstream of the catalyst was added to the nitrogen stream so that the content of oxygen and carbon monoxide downstream of the catalyst was, if possible, in each case in a range of 0-20 ppmv / v.

As From Table 1, the reaction was at temperatures from 280-320 ° C over 99%. The oxygen content was in this temperature range after the catalyst depending on gas temperature between 3 and 24 ppmv / v. The CO content was never higher at these temperatures as 7 ppmv / v. But even at temperatures of 180-260 ° C, the reaction was always over 93%.

Table 1 (overview of the experiments Example 1)

Example 2

Performance and conditions corresponded exactly to Example 1, but the experiments were carried out this time with a space velocity of 12000h ^-1 .

Table 2 shows that there is almost no difference in EC conversion at a space velocity of 12000h- ¹ . The EC implementation rates are all over 99.6%.

Table 2 (overview of the experiments Example 2)

Example 3

Performance and conditions were exactly as in Example 1. The reaction of ethylene glycol (EG) was tested on two Cu-Mn oxide catalyst materials. The first experiment was a solid material, in this case in extruded form ( 4 ). The extrudate had a diameter of about 1.2 mm and a length between 2 and 6 mm. In the second case it was an oxide on support material ( 5 ), the metal oxides were deposited on alumina balls. The diameter of the oxide material balls was about 2.5-4.5 mm.

Out Table 3 shows that the EG reaction rates on the material in extruded form, especially at lower temperatures between 200 and 260 ° C, are better than the oxide material on aluminum substrate.

Table 3 (overview of the experiments Example 3)

Claims (20)

A process for purifying a gas stream with impurities formed by organic compounds, wherein an at least oxygen-containing gas is supplied to the contaminated gas stream and passed over a catalyst material, wherein the gas at the outlet of the catalyst unit has a content of 0 ppm up to 500 ppm oxygen, and wherein the monitoring of the ratio of oxygen to the impurities by means of at least one oxygen analyzer and / or by means of at least one lambda probe, which is connected to at least one of the line paths connected to the catalyst unit, is carried out, characterized in that in the catalyst unit, a catalyst material is used, which consists of at least one metal oxide or mixtures containing at least one metal oxide. Method according to claim 1, characterized in that that the underlying metal oxide or metal oxides Metal is an element of the subgroup elements or transition metals, especially the fourth period, the periodic table of the elements is. Method according to claim 2, characterized in that that the catalyst material used at least manganese oxide, iron oxide, Contains copper oxide or cobalt oxide. Method according to one of the preceding claims, characterized characterized in that the catalyst material in a without carrier material present form is used. Method according to one of the preceding claims, characterized characterized in that the catalyst material is used in a mold is at which the catalyst material on a support material is applied. Method according to one of the preceding claims, characterized characterized in that the temperature of the gas stream is in the range of 150 ° C-600 ° C and in particular is in the range of 170 ° C-350 ° C. Method according to one of the preceding claims, characterized characterized in that the contaminated gas in front of the catalyst unit is not heated further. Method according to one of the preceding claims, characterized characterized in that the contaminated gas stream from a reactor comes and after cleaning at least partially in the reactor is returned. Method according to one of the preceding claims, characterized characterized in that the contaminated gas from at least one reactor for the Solid-phase condensation a polycondensate, e.g. Polyamide, polycarbonate, polylactide or polyester, in particular polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polyethylene naphthalate (PEN) and their copolymers, is derived and / or that the contaminated gas from a reactor for the solid phase condensation a recycled polycondensate, in particular a recycled PET (RPET), is from. Method according to one of the preceding claims, characterized characterized in that the normal operation or continuous operation, in particular according to Claim 6, by a temporary Heating the catalyst material above the operating temperature Normal or continuous operation is changed. Method according to one of the preceding claims, characterized characterized in that the monitoring by means of at least one oxygen analyzer and / or by means of at least one lambda probe before and / or after the catalyst he follows. Method according to one of the preceding claims characterized characterized in that of the oxygen analyzers and lambda probes emitted monitoring signals weighted before further processing. Method according to one of the preceding claims characterized characterized in that as much oxygen-containing gas is added, the oxygen content measured after the catalyst is 0-500 ppm, preferably 0-50 ppm and most preferably 0-20 ppm. Method according to one of the preceding claims characterized characterized in that the oxygen-containing gas used is air, Oxygen or an ozone-containing gas. Arrangement for carrying out the method according to one of the preceding claims, with a reactor ( 1 ) for the solid phase condensation; a supply line ( 7 ) for contaminated, from the reactor ( 1 ) flowing gas to a catalyst unit ( 8th ); a gas feed ( 9 ) for an at least oxygen-containing gas for treating the effluent gas from the reactor; and at least one of the catalyst unit ( 8th ) leading outgoing line ( 24 ); wherein on at least one of the with the catalyst unit ( 8th ) connected lines ( 11 . 24 ) in each case at least one oxygen analyzer and / or at least one lambda probe is connected, characterized in that the catalyst material of the catalyst unit comprises at least one metal oxide or mixtures containing at least one metal oxide. Arrangement according to claim 15, characterized in that it measures the gas flows from the supply line ( 7 ) and the gas feed ( 9 ) and to the catalyst unit ( 8th ) leading collecting line ( 11 ) having. Arrangement according to claim 15 or 16, characterized the catalyst material is a porous material. Arrangement according to one of Claims 15 to 17, characterized that porous Catalyst material is a solid material. Arrangement according to one of Claims 15 to 17, characterized that the porous one Catalyst material on a carrier material is applied. Arrangement according to one of Claims 15 to 19, characterized the catalyst material has a doping.