DE4223847C1 - Regenerating catalytic metal filler bodies used in gas phase cleavage of urethane - by treating at elevated temp. with hydrogen contg. gas - Google Patents

Abstract

Process for activating or regenerating the catalytic properties of metal filler bodies for reactors for gas phase cleavage of urethanes, made of steel with an Fe content of at least 50 wt.% or copper bronzes with a Cu content of 60-96 wt.%, comprises treating the filler bodies in a first stage at a temp. of above 200 deg.C. with an oxygen-contg. gas, esp. air, or with hydrogen or a hydrogen-contg. gas mixt., and opt., when an oxygen-contg. gas was used in the first stage, post-treating the filler bodies at a temp. of above 200 deg. with hydrogen or a hydrogen-contg. gas mixt.. USE/ADVANTAGE - The process gives good regeneration of activity of Fe- and Cu-contg. catalysts used in fixed bed catalyst reactors used for gas phase cleavage of urethanes of formula R1 (NHCOOR2)n into the corresp. isocyanates of formula R1(NCO)n and alcohols of formula R2OH, in which R1 = n-valent 1-18C, esp. 6-13C (cyclo)aliphatic hydrocarbon gp. or 6-13C aromatic hydrocarbon gp., R2 = 1-18C, esp. 1-16C aliphatic hydrocarbon gp. or phenyl gp. and n = 1 or 2, esp. 2. The regeneration is technically simple to carry out, can be conducted with the catalyst in situ in the reactor, and does not use corrosive treatments.

Description

The invention relates to a method for activation or regeneration of the catalytic properties of metallic packing elements for gas phase reactors Cleavage of urethanes for the production of the Isocyanates corresponding to urethanes, and the ver the activated or regenerated packing in such gas phase fission reactors.

The thermal cleavage of urethanes under selective Condensation of the iso cyanate represents a well known method for phosgene free Production of organic isocyanates (see e.g. DE-OS 19 44 719, 24 10 505, 29 42 543, 32 27 748, 32 48 018 and 33 25 185 and U.S. Patent 4,330,479), in which publications the question of a possible catalysis of the cleavage reaction is not clearly answered by metals.  

As has now been found, iron or copper disfigure holding metal alloys actually effective Kataly sensors for thermal urethane cleavage, so that appropriate packing in the cleavage reactors at the same time represent effective fixed bed catalysts.  

However, to optimize the catalytic effect activation of the catalysts or regeneration tion of the used catalysts necessary because otherwise the catalytic effect is very low remains.

The object underlying the invention now existed in it, a new method of activation or rain the catalytic properties of metallic Packings for fission reactors for polyurethanes To provide which without great technical effort and can be done without corrosive treatment.

The solution to this problem found according to the invention consisted of a packing at above 200 ° C Gas treatment of the type described in more detail below to undergo.

The subject of the invention is the method according to claim 1.  

The invention also relates to the use of the invention activated or regenerated packing according to claim 2.

Suitable metallic, catalytically active according to the invention same packing can be in any shape, for example in the form of irregular sheet metal chipping, turning, planing or pipe chips, wire mesh spiral, wire coil, Raschig rings, Intos rings, Pall rings, Prym rings, Berl saddle, Super saddle, Inter pack, intalox, twin body, lattice body, rays body, balls and Sulzer packs.

The metallic fillers consist of, for example galvanized sheet steel or steel, such as. B. ferritic steels, martensitic-ferritic steels, martensitic steels, austenitic steels, austeni table-ferritic steels, austenitic Cr Ni and austenitic Cr Ni Mo steels and precipitation hardenable Steels. The steels can also contain alloys parts such as aluminum, cobalt, niobium, tantalum, titanium, Tungsten, lanthanum, zircon, hafnium, yttrium, phosphorus,  Manganese, copper, silicon, zinc, tin, Indium, gallium, boron, arsenic, antimony, cadmium, vanadium, Ruthenium, palladium, silver, cerium, molybdenum, chromium, Contain lead, bismuth, selenium or tellurium. Especially Chromium and others may be well suited Iron-nickel alloys containing elements with a Iron content of at least 50, preferably at least 70% by weight., Or copper bronzes with a copper content of 60 to 96% by weight.

For those used for activation or regeneration Gases are either oxygen-containing Gas mixtures or ent or hydrogen holding gas mixtures.

The oxygen-containing gas mixtures contain up to to 60 vol .-%, preferably up to 40 vol .-% and esp preferably 10 to 25 vol .-% oxygen and in addition especially nitrogen, and possibly traces Carbon dioxide and / or noble gases. Oxygen / rare gas Mixtures are technically conceivable, but are out of the question largely due to price reasons. Especially before added gas mixture containing oxygen is air. When Gas mixture containing hydrogen come from mixtures Hydrogen with up to 90, preferably up to 80% by volume, based on the total mixture, of inert gases such as for example nitrogen, noble gases or gaseous Hydrocarbons such as methane or ethane into consideration.  

The gas treatment takes place above 200 ° C., preferably at 300 to 550 ° C and particularly preferably at 350 to 500 ° C, at a pressure of 1 to 10,000 mbar, preferably 5 to 7000 mbar and particularly preferably 10 to 5000 mbar, for a period of 0.1 to 40 h, preferably 0.5 up to 30 h and particularly preferably 1 to 24 h instead. Before The gas treatment is preferably carried out with packings filled reactor before starting up the reactor (Activation) or after interrupting the splitting process by interrupting the dosage of the to be split Urethane (regeneration) instead. The amount of gas is generally per liter empty reactor volume less than 1200 Nl / h, preferably 1000 to 2 Nl / h and particularly preferably 500 to 10 Nl / h, both in the Gas treatment in the first stage as well as in the optional aftercare in the second procedure level.

According to a preferred embodiment of the invention according to the method using an oxygen containing gas in the first stage of the process and Hydrogen or a gas containing hydrogen in the second stage of the process becomes acidic at the transition gas stream containing hydrogen to begin with dosed only one inert gas (e.g. nitrogen) and the Hydrogen concentration slowly up to 100 vol .-% increased or the reactor by evacuation less than 200 mbar, preferably less than 100 mbar and particularly preferably less than 20 mbar, of oxygen exempted and then with hydrogen or a hydrogen-containing gas back to the desired pressure brought up to 10,000 mbar.  

In a further embodiment, both the tem temperature and / or the amount of oxygen or the water the amount of fabric is slowly or gradually increased.

In a further embodiment, during the Activation of the pressure of z. B. 10,000 mbar slowly or can be reduced in stages to the subsequent gap pressure.

In a further embodiment, during the Activation of temperature, pressure and acid substance or hydrogen concentration can be varied.

In a further embodiment, during the Activation of pressure increased slowly or in stages be from z. B. 10 mbar up to 10,000 mbar.

As already indicated, when using an acidic substance-containing gas mixture in the first process stage the second stage of the process is only optional, because by treatment with the oxygen-containing gas alone a clear activation or Regeneration of the catalytically active packing is possible is, however, as well as the following Take examples by post-treatment with Hydrogen or a gas containing hydrogen mixture can still be improved.

As also indicated above, a be special embodiment conceivable, which is preferred for fresh packing (activation) is applied, and which is exclusively in a treatment with hydrogen or a hydrogen-containing gas mixture.  

The activated or regenerated according to the invention metallic packing have a much higher catalytic activity as the corresponding, unbe dealt in packing. They also tend to invent filler treated according to the invention is significantly less Deactivation. The activation or Regeneration also leads to repeated repetitions no corrosion in the reactor or on the metal fillers.

Fission reactors, the metal treated according to the invention Containing fillers are suitable for cleavage any urethane. Preferably in the gap reactors, the packing treated according to the invention contain urethanes of the general formula

R ₁ (NHCOOR ₂ ) _n

into the corresponding isocyanates of the formula

R ₁ (NCO) _n

and the corresponding alcohols of the formula

R ₂ OH

split.

Stand in these formulas
R ₁ for an n-valent (cyclo) aliphatic hydrocarbon radical with 1 to 18, preferably 6 to 13 carbon atoms or an n-valent aromatic hydrocarbon radical with 6 to 13 carbon atoms,
R ₂ for an aliphatic hydrocarbon radical having 1 to 18, preferably 1 to 6 carbon atoms or a phenyl radical and
n for 1 or 2, preferably for 2.

Typical examples of urethanes which can be thermally split according to the invention are:
Methoxycarbonylamino-benzene, ethoxycarbonyl-benzene, 2,4- and 2,6-bis- (ethoxycarbonylamino) -toluene, 2,2′-, 2,4′- and 4,4′-bis- (methoxycarbonylamino) -diphenylmethane, n-octyloxycarbonylamino-methane, hexyloxycarbonylamino methane, dodecyloxycarbonylamino-ethane, 1,6-bis- (n-butoxycarbonylamino) -hexane, 1,6-bis- (ethoxycarbonyl-amino) -hexane, 1,6-bis- (n-butoxycarbonylamino) -2,2,4- trimethyl-hexane, 1,4-bis- (methoxycarbonylamino) -cyclo hexane, 1- (ethoxycarbonylamino) -3- (ethoxycarbonylamino methyl) -3,5,5-trimethyl-cyclohexane or 1- ( Phenoxycar bonylamino) -3- (phenoxycarbonylaminomethyl) -3,3,5-tri methyl-cyclohexane. The urethanes based on C ₁ -C ₄ -alkanols and monoisocyanates such as p-toluyl isocyanate, 3,4-dichlorophenyl isocyanate, stearyl isocyanate, cyclohexyl isocyanate or phenyl isocyanate can also be thermally split using the metallic filler treated according to the invention.

The thermal cleavage of the urethanes takes place according to the methods known per se. The urethanes can  in solid, liquid or gaseous form (e.g. as Powder, melt, steam), as a solution or suspension in the cleavage reactor or an upstream if necessary th pre-evaporator.

Will the urethane cleavage in the presence of a solution carried out by means of or suspending agent, so suitable all thermo stable compounds which are inert to the reaction or Mixtures of these compounds. Those are preferred to apply, whose boiling point between those of the ent speaking isocyanates and alcohol or one have a higher boiling point. Examples are ge called: aliphatic hydrocarbons, such as the alkanes, Cycloalkane, heptane, octane, nonane, decane, undecane, Dodecane, tridecane, tetradecane, pentadecane, hexadecane, Heptane decane, decalin, tetralin, liquid paraffin, alicyclic hydrocarbons, such as petroleum fractions of Naphtha row; optionally also substituted aromatic hydrocarbons such as naphthalene, 1- and 2-methylnaphthalene, 1-ethylnaphthalene, phenylnaphthalene, Benzylnaphthalene, benzene, toluene, 1,2-, 1,3- and 1,4-dimethylbenzene, 1,2,4- and 1,3,5-trimethylbenzene, 1,2,3,5- and 1,2,4,5-tetramethylbenzene, 1,3,5-triethylbenzene, Hexyl, heptyl, octyl, nonyl, Decylbenzene, hexaethylbenzene, diphenyl, 4,4'-dimethyldiphenyl, dibenzyl, diphenylmethane and 4,4'-dimethyl-diphenylmethane, halogen-substituted aromatic hydrocarbons such as B. chlorobenzene, 1,2- and 1,4-dichlorobenzene, 1,2,3,4-, 1,2,3,5-tetrachlorobenzene, Pentachlorobenzene, ethers, such as. B. Dioxane, tetrahydrofuran, diethylene glycol dimethyl ether,  Diethylene glycol diethyl ether, diisoamyl ether, di-n- amyl ether, dibenzyl ether, diphenyl ether, α-methyl naphthyl ether and β-ethylnaphthyl ether.

Alkanes such as cyclohexane are particularly preferred. Heptane, octane, nonane, decane, undecane, dodecane, tridecane, Tetradecane, pentadecane, hexadecane, heptadecane, tetralin and decalin, optionally substituted aromatic Hydrocarbons such as benzene, toluene, 1,2-, 1,3- and 1,4-dimethylbenzene, 1,2,4- and 1,3,5-trimethylbenzene, 1,2,3,5- and 1,2,4,5-tetramethylbenzene, 1,3,5-triethyl benzene, hexyl, heptyl, octyl, nonyl, decylbenzene, Ethers such as B. dioxane, tetrahydrofuran, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diisoamyl ether, di-n-amyl ether, since they are pure substance or have proven particularly successful as mixtures.

The concentration of the solvent or suspending agent and where appropriate their mixtures are smaller than 50% by weight, preferably less than 30% by weight and particularly preferably less than or equal to 20% by weight.

As an evaporator for the urethane or urethane solution medium mixtures are suitable for all common evaporators, especially falling film evaporators and thin film evaporators steamer in a vacuum of less than 1000 mbar and be preferably 1 to 600 mbar and particularly preferably 2 to 300 mbar, at temperatures below 600 ° C, preferred 250 to 400 ° C and particularly preferably 280 to 350 ° C, operate.  

It proves to be particularly suitable and therefore preferred the dosage of the urethane or urethane solvent mixed in the cracking reactor when it is at 50 to 350 ° C and is preferably preheated to 150 to 250 ° C and over a distribution body, such as. B. slit diaphragms, screen plate metal sintered plates, nozzles, showers and distributors Soil in the reactor under negative pressure, for. B. by the Suction effect of the evacuated reactor or with a Overpressure of up to 300 bar, preferably 1 to 100 bar and particularly preferably 2 to 60 bar, in the vacuum gap reactor is metered.

To perform the cleavage, the ones to be cleaved Urethanes or their vapors in bulk or as a mixture with the above solution or Sus Pendiermittel metered into the gap reactor in which cleavage at a maximum temperature of 650 ° C, preferably from 300 to 550 ° C and particularly preferred 350 to 500 ° C, under a reduced pressure of maximum 1000 mbar, preferably 1 to 600 mbar and particularly preferably from 3 to 300 mbar.

The loading of the reactor with urethane or urethane Solvent mixture, based on that for the cleavage available reactor empty volume is 10 up to 10000 g / 1 h, preferably 40 to 5000 g / 1 h and especially preferably 100 to 2000 g / 1 h.

The cracking reactor is generally a vacuum-proof tube or tube bundle, the tube inner diameter preferably 15 to 500 mm and the Pipe lengths are 0.5 to 30 m. The fission reactor  can be any position between vertical and hori take zonally.

The cracked gases leaving the cracking reactor, consisting of the isocyanate, the alcohol and the possibly added inert solvent or suspending agent, are advantageously carried out, for. B. in a fractionation column or in a multi-stage condensation device for separate condensation of the cleavage products. The condensation is expediently carried out at the same pressure as the cleavage. For example, for the condensation of the cleavage products from 1,6-bis (n-butoxycarbonylamino) hexane (HDU) at a vacuum of 10 mbar,
in the first condensation stage for the removal of hexamethylene diisocyanate (HDI), a condensation temperature of 50 to 150 ° C. and in the second condenser stage for the condensation of the n-butanol and solvent or suspending agent a temperature of -20 to + 30 ° C. a.

These are used to clean the condensation products subjected to a fine distillation and can thus in the desired purity can be provided.  

The invention is illustrated below on the basis of the split of 1,6-bis (n-butoxycarbonylamino) hexane (HDU) explained.

The stated cleavage results were determined by freezing the cracked gases in an acetone / (CO ₂ cold trap and titrating the isocyanates. This method was chosen in order to eliminate the influence of fractional condensation on the urethane cleavage. In some cases, with the samples with 18 and 21 h running time, the fractional condensation was used to determine its influence on the cleavage result and the concentration of hexamethylene diisocyanate (HDI) and 1-isocyanate-6- (n-butoxycarbonylamino) hexane (HMI).

The indicated NCO yields were determined as follows:

The loading was carried out in the fractional condensation the yields for HDI and HMI are determined from the gas chromatographic Analyzes of the 1st condensation stage according to the following Formulas:

The NCO yields when using the fractionated Kon densation fell somewhat compared to the freezing method wrestle out because in the capacitors through recombination with which alcohol was lost isocyanate.

Comparative example

The splitting apparatus consisted of a tubular reactor 50 cm quartz with an empty volume of 100 ml, with 90 ml wire mesh helices (3 × 3 mm) Steel (steel alloy consisting of 18% by weight chromium, 11% by weight nickel, 2% by weight molybdenum, max. 0.07% by weight Carbon and 69 wt .-% iron) is charged. Of the The reactor inlet is with a heated metering unit direction and a gassing device for activation and regeneration of the catalysts. The con The fission gases are densified at a low temperature condensation stage or (switchable) with a fractional condensation stage consisting of two capacitors connected in series. Behind the Condensation stages is the reactor to a vacuum pump  connected. The reactor was heated to 400 ° C. The Condensation stage for condensing the entire gap gases were cooled to -78 ° C. The first capacitor for HDI deposition worked at 80 ° C, the second Condenser for the separation of n-butanol and decalin at approx. 0 ° C.

About the dosing device tempered to 180 ° C 40 g per hour of a mixture of 80 wt .-% HDU and 20% by weight of decalin in the reactor heated to 400 ° C fed in liquid. This corresponds to a burden of 400 g / 1 h. The pressure in the reactor was 10 mbar. The Cracked gases were temporarily in the end of the reactor arranged cold trap (-78 ° C) and at times frak tion condenses. With fractional condens sation condensed in the first condensation stage a mixture of HDI, HMI and decalin; in the second Condensation stage a mixture of n-butanol, decalin and HDI, which recombined to HDU.

The activity of the reactor was checked every 3 hours Sampling determined. The analyzes were carried out with the help of Gas chromatography and by NCO titration. In Table 1, the Er results compiled.  

Table 1

Splitting result depending on the service life, without catalyst activation (here and in the tables below, the figures refer to the yield in%, based on the theoretically expected yield)

The experiment was stopped after 24 hours because the Activity had decreased significantly.

example 1

The deactivated catalyst in the comparative example was in Leave the reactor at the reaction temperature (400 ° C) and treated with 15 l air / h for 14 h, the pressure in the Reactor was 1000 mbar.

Upon completion of the regeneration, the reactor was immediately evacuated again to 10 mbar and the dosage with  40 g / h of a mixture of 80% by weight HDU and 20% by weight Decalin continued. Table 2 shows the results compiled.

Table 2

Splitting result depending on the service life, after activation with air

As can be seen from Table 2, the coils were after the Treatment is not only regenerated, but also more active than before and, in addition, were less inclined to Deactivation.

Example 2

In the gap reactor used in the comparative example and example 1 90 ml of fresh, untreated stainless steel wire mesh coils the steel alloy specified in the comparative example filled. Then the catalyst  in an air flow of 15 l / h at the reaction temperature temperature of 400 ° C for 14 h. After the removal the air by briefly evacuating the reactor Catalyst by reducing with 15 l hydrogen / h 400 ° C and 1000 mbar activated for a further 3 h. in the Following this activation, the reactor was turned on Evacuated 10 mbar and with the dosage of 40 g HDU / decalin mixture started. In Table 3 they are Results compiled:

Table 3

Splitting results depending on the service life, after activation with air and additional activation with hydrogen

In contrast to the one regenerated with oxygen This catalyst was the catalyst from the start much more active and showed none over 24 Decrease in its activity.  

Example 3

As in Example 2, fresh, untreated wire mesh coils filled. In this However, trap 4 × 4 mm copper-bronze coils. After the under Example 3 described activation at 400 ° C was with the dosage of the HDU / decalin mixture at 10 bar fine. The results are summarized in Table 4 poses.

Table 4

Splitting results depending on the service life, after activation with air and additional activation with hydrogen

Like the stainless steel coils, the copper bronze also showed start from the beginning with constant activity, without tension sign of deactivation.

Claims (2)

1. A method for activating or regenerating the catalytic properties of metallic packing for reactors for gas-phase splitting of urethanes, which consist of steel with an iron content of at least 50 wt .-% or copper bronzes with a copper content of 60 to 96%, characterized in that the fillers are treated in a first process stage at temperatures above 200 ° C. with an oxygen-containing gas mixture, in particular air, or hydrogen or a hydrogen-containing gas mixture and, if appropriate, in the case of using an oxygen-containing gas mixture in the first process stage, in a second The process stage at temperatures above 200 ° C with hydrogen or a hydrogen-containing gas mixture aftertreated. 2. Use of the activated or regenerated packing according to claim 1 in reactors for gas phase splitting of urethanes with selective condensation of the gaseous isocyanates obtained as fission products, in particular in the splitting of urethanes of the general formula R ₁ (NHCOOR ₂ ) ₂ , in which
R ₁ for a divalent (cyclo) aliphatic carbon hydrogen radical with 6 to 13 carbon atoms and
R _{2 represents} a saturated aliphatic hydrocarbon radical having 1 to 6 carbon atoms.