DE19858505A1 - Selective oxidation and the preparation of aromatic compounds containing hydroxyl groups - Google Patents

Abstract

The invention relates to a process for the preparation of aromatic compounds containing hydroxyl groups by catalytic oxidation.

Description

The invention relates to the one-step preparation of a hydroxyl group containing aromatics by selective, catalytic oxidation of an aromatic Hydrocarbon.

To aromatic compounds containing hydroxyl groups such as. B. too So far it has not been possible to get phenol directly by selective benzenes Oxidation in one step and in high yields in corresponding Convey hydroxy compounds. Either the aromatic ring not at all attacked by the oxidizing agent or it was attacked by this destroyed. Mainly carbon dioxide and coke were formed.

From an economic point of view, it was previously only over several intermediate stages possible to introduce a hydroxyl group into the aromatic system.

Technically established for the production of phenols from benzene has the cumene process. This is usually the case with benzene and propene produced cumene peroxidized and then the oxidation product in phenol and Split acetone.

Furthermore, starting from toluene, the benzoic acid process is in use, the Benzoic acid made from toluene can be decarboxylated to phenol. Of the Decarboxylation step, i. H. the loss of an organically bound carbon, however already consumes a possible price advantage of toluene compared to benzene this level. The process is therefore only interesting if the target product Benzoic acid is used and free capacity for the production of phenol become.  

Other methods of making phenol e.g. B. over chlorobenzene (chlorination or oxychlorination of benzene) or the sulfonation process (production of Benzenesulfonic acid) have proven to be uneconomical. Reasons were e.g. T. the unsatisfactory selectivity, corrosion problems and the occurrence of undesirable By-products.

The cyclohexanol process (hydration of cyclohexene in the 1st stage) is also not economical. The process has too many stages to go to Target product to get phenol.

For this reason, the largest proportion of phenol in the world is above mentioned Cumolroute produced. However, since this also produces acetone, the Economics of this process from the market prices for phenol and acetone dependent.

To avoid dependency on the co-product acetone, concentrate many attempts to selectively oxidize benzene or benzene derivatives. For example, U.S. Patents No. 5,055,623, No. 5,672,777 and No. 5,110,995 the oxidation of benzene with nitrous oxide on suitable Catalysts.

The oxidizability of benzene on vanadium / molybdenum / tungsten oxide catalysts with nitrous oxide has been known since 1982 (Iwamoto). Zeolite catalysts of the type ZSM-5 have been used for the direct oxidation of benzene discovered with nitrous oxide in 1988 (Gubelmann, Rhone-Poulenc). The mode of action of zeolites is fundamentally on their microporous Channel system with pore dimensions in the size of the molecules to be oxidized returned.  

The use of iron-containing zeolite catalysts of the type ZSM-5 for the Oxidation of benzene with nitrous oxide is described in J. Phys. Chem. 1994, 98, 7548- 7550 by Volodin, Bolshov and Panov.

Oxidation on zeolites, in particular type ZSM-5, is also described in the following documents:
3rd World Congress on Oxidation, 1997 Elsevier Science BV, RK Graselli et al. (Editors),
M. Haafele et al. (University of Erlangen-Nuremberg) and
GI Panov et al., Applied Catalysis A: General, 98 (1993) 1-20.

The reaction of is considered to be the most technologically advanced Nitrous oxide on acidic zeolites of type ZSM-5 and ZSM-11 with various metal additives (e.g. iron). The reaction temperature will Usually carried out under normal pressure at temperatures of 300-450 ° C.

A disadvantage of zeolites is that due to the completely crystalline structure Varying the pore size does not change the molecule to be oxidized can be adapted, but only depending on the type of crystal is gradually possible. This means that zeolites relate to each Do not have the oxidation problem specifically adjusted. Also the surface polarity, certain reaction mechanisms are conceivable via their setting Zeolites hardly variable. The literature, such as. B. U.S. Patent No. 5,110,995 or No. 5,055,623, describe a zeolite type (the Pentasile ZSM-5 and ZSM-11) for the production of many phenol derivatives. Zeolites or acidic zeolites can be used different metals can be modified. However, this can be described At best improve the problem, but do not solve it in principle. For example an exchange of a hydrogen atom by a sodium atom in an acid one Zeolites are made. There was no loss of activity in the iron-containing zeolite observed, while the activity of replacing iron with aluminum  when a hydrogen atom is replaced by a sodium atom. Overall, however, sales and selectivity are still unsatisfactory.

Changing other parameters such as higher reaction temperatures (zeolites are considered to be temperature stable up to about 800 ° C) leads to higher benzene conversions, but also to lower selectivity and greater deactivation of the catalyst. If the partial pressure of N ₂ O is increased, the benzene conversion can also be increased, but this is also at the expense of the selectivity. A gradual improvement can only be achieved by increasing the partial pressure of benzene. The selectivity and the amounts of phenol obtained increase somewhat. Nevertheless, it is still desirable to further increase the selectivity and the degree of conversion.

The relatively rapid occurring at the temperatures usually used Coking the catalyst leads to a loss of activity and the catalyst must therefore be regenerated relatively often (about every 48 hours).

The process described above for the catalytic oxidation of benzenes The dinitrogen oxide used must have a very high degree of purity. Contaminants such as oxygen or hydrophilic gases such as water vapor or Ammonia can inactivate the zeolite catalyst to ineffectiveness. Only inert gases such as noble gases or nitrogen are tolerable as admixtures.

Various sources can be considered for nitrous oxide. The catalytic Decomposition of ammonium nitrate at 100-160 ° C with manganese, copper lead, Bismuth, cobalt and nickel catalysts deliver a mixture Nitrous oxide, nitrogen oxide and nitrogen dioxide so that the gas is not direct can be used for the oxidation of benzene.

The oxidation of ammonia with oxygen on platinum or bismuth oxide catalysts at 200-500 ° C and the conversion of nitrogen oxide with carbon monoxide on platinum catalysts are somewhat cheaper. In the first case, however, water is created as a by-product, in the second case carbon dioxide. The nitrous oxide produced in this way cannot be used directly for the benzene oxidation either. Likewise, the dinitrogen monoxide obtained in the production of adipic acid cannot be used directly for the oxidation, but must be subjected to a separate cleaning step. In particular, the oxygen and NO _x contained in the exhaust gas interfere.

The purity of the nitrous oxide can also be seen against the background that Zeolites absorb water, which reduces their catalytic effect. A few Zeolite structures can be made hydrophobic by dealumination, which This further limits the selection of suitable zeolites. The Deauminating is still an additional process step and leads to undesirable amorphous parts in the zeolite. In addition, the extent of Do not set the dealumination properly, so that with regard to the process of this must be determined empirically. That means fluctuating Oxidizing agent qualities such. B. different admixtures of Water vapor cannot be used.

The object of the present invention was therefore to provide an economical process for catalytic oxidation of aromatic compounds to the corresponding Hydroxy compounds with high selectivities even with low ones To provide nitrous oxide quality.

Surprisingly, it was found that porous glasses have catalytic oxidation from aromatic compounds to corresponding hydroxy compounds also at Excellent catalyst for the use of contaminated nitrous oxide can.

The present invention therefore relates to a method for the production Aromatic compounds containing hydroxyl groups by catalytic  Oxidation, the catalytic oxidation of the aromatic compound in Presence of a porous glass with a gas containing nitrous oxide a temperature of 100-800 ° C is carried out.

The method according to the invention can be used by using an appropriate porous glass to the respective operating conditions such. B. the quality of the dinitrogen monoxide to be used or the type of aromatic compound be optimally adjusted.

This was not to be expected as the specialist literature contributed to a high benzene turnover simultaneous high selectivity to phenol "special" zeolites z. B. from Pentasil Type such as ZSM-5 and ZSM-11 suggests.

These zeolites have a three-dimensional structure ("cage structure") and therefore a large surface. The pore system of the process according to the invention Porous glasses used is predominantly structured differently, so that they as a rule do not allow three-dimensional access to zeolites and therefore a (if any) significantly reduced catalytic effect should expect.

To what extent the duct system or the Composition of the porous glasses used in the present process The cause of their catalytic effect may be left open, that However, the inventive method also leads to the use of Low quality nitrous oxide at high sales with very good Selectivities.

A mixture of 5 to 100% by volume can be used as the gas containing nitrous oxide. Use dinitrogen monoxide and 0 to 95 vol .-% of another gas.  

The nitrous oxide content of that used in the process according to the invention Gases can also be between 80 and 100 vol .-%, combined with 0 to 20 vol .-% another gas.

Air, oxygen, nitrogen, noble gases, carbon dioxide, Steam or ammonia or their mixtures are used.

The gas containing nitrous oxide used can also contain organic or inorganic contaminants, e.g. B. from an oxidation process (z. B. N ₂ O production in situ or N ₂ O-containing exhaust gas from the production of adipic acid).

In a particular embodiment of the present invention, as aromatic compound uses benzene, but it is also the oxidation of others Aromatics such as toluenes, xylenes or halogenated benzenes and the oxidation multinuclear aromatics such as B. naphthalene possible.

It was also surprising when the porous surface was modified non-polar Glasses observed that the benzene conversion almost below 375 ° C (e.g. 350 ° C) is just as high as above 375 ° C. The selectivity increases with lower ones Temperatures as expected. With zeolite-catalyzed system falls Usually the benzene conversion drops sharply with falling temperature. Under Under comparable conditions, a zeolite behaves much less favorably.

The process according to the invention is preferred at temperatures of 200-700 ° C. carried out particularly preferably at 250-550 ° C.

The production of the porous glasses used in the process according to the invention or microporous amorphous mixed metal oxides can according to DE 195 06 843 A1 respectively.  

The porous glasses used in the inventive method are after Sol-gel process manufactured.

In one embodiment of the present invention, the porous glasses are made 50-100% by weight of oxides of elements from the 3rd main group, the 4th Main group, the 3rd subgroup or from the 4th subgroup of the Periodic table, including the lanthanoids and actinoids.

In another embodiment of the present invention, the Mixed metal oxide matrix of the porous glasses at least 50% by weight of compounds of the elements titanium, silicon, vanadium, aluminum, zircon or cerium and / or bis 50% by weight of one or more metal oxides in very fine to atomic Distribution from the group of metals molybdenum, tin, zinc, vanadium, manganese, Iron, cobalt, nickel, arsenic, lead, antimony, bismuth, ruthenium, rhenium, chromium, Tungsten, niobium, hafnium, lanthanum, cerium, gadolinium, gallium, indium, thallium, Silver, copper, lithium, potassium, sodium, beryllium, magnesium, calcium, Strontium and barium included.

The mixed metal oxide matrix of the porous glasses preferably contains at least one, particularly preferably at least two of the compounds from the group SiO ₂ , TiO ₂ , Al ₂ O ₃ , vanadium oxide, zirconium oxide, cerium oxide, spinel, mullite, silicon carbide, silicon nitride and titanium nitrite.

Furthermore, the mixed metal oxide matrix can additionally contain up to 10% by weight the metals platinum, rhodium, iridium, osmium, silver, gold, copper, nickel, Palladium and cobalt in highly disperse form in metallic or oxidized Condition included.

The porous glasses are available through acid or fluoride catalyzed linear Polymerization or polycondensation of hydrolyzable, soluble compounds above  named metals and oxides. Alkoxy are preferably mixed Alkoxyalkyl, alkoxyoxo or acetylacetonate derivatives of the metals described or metal oxides in the acid to neutral pH range in the sol-gel process used. This is followed by a gentle drying and slow calcination, whereby the end of the calcination temperature is 120-800 ° C.

An alternative production method for this type of connections is the Thermolysis processes (K.W. Terry et al., J. Am. Chem. Soc. 1997, 119, 9745- 9756). The disadvantage here, however, is reduced compared to the sol-gel process Possibility of variation in production, so that only a few in the end product Element relationships are possible.

The production of non-polar or hydrophobic porous glasses goes z. B from the patent DE 195 45 042 A1. The polarity of the inner and outer surface of porous glasses can be adjusted, for example, by copolycondensing alkyl or aryloxysilanes with non-hydrolyzable alkyl or aryl groups R 'of the R'-Si (OR) _{3 type} with the other components of the sol-gel process will.

R and R 'can be the same or different and are preferably aliphatic Hydrocarbon radicals with up to 6 carbon atoms such as methyl, ethyl or Isopropyl groups or phenyl radicals.

The metal oxide reacted with this non-hydrolyzable group comes from the list of metals mentioned above. The ligands used for the starting compound, ie the soluble metal compound, are preferably halides, alkoxides, oxyalkoxides, carboxylates, oxalates, nitrates, sulfates, sulfonates, acetylacetonates, glycolates or aminoalkoxylates. The base material is SiO ₂ , Al ₂ O ₃ , TiO ₂ or ZrO ₂ .

The use of hydrophobic porous glasses is particularly high Water content of the dinitrogen monoxide is an advantage because it maintains a constant high level Selectivity is guaranteed.

In addition to porous glasses, additives can also be used. Support systems or mixtures based on SiO ₂ or Al ₂ O _{3 are also} to be understood as such. The use of a combination of porous glasses and (crystalline) zeolites is also possible, as shown in the examples, without conversion and loss of selectivity.

What is important is the pore size and the total surface of the glasses used. Of the Average pore size should be between 0.1 and 1.0 nm, determined according to Horvath and Kawazoe (J. Chem. Eng. Jpn. 16 (1983) 470 ff).

The total surface area of the porous glasses in the dried state is preferably at least 50 m ² / g, particularly preferably 50-5000 m ² / g, very particularly preferably 75-1500 m ² / g, each determined by the BET method according to WF Maier et al ., Tetrahedron 51 (1995) 3787 ff.

Examples 1. Manufacture of porous glasses 1.1 Zirconia-silica glass

1 ml of tetrabutoxyzirconium, 10 ml of tetraethoxysilane and 8 ml of ethanol are successively dissolved in one another and 2 ml of 8N hydrochloric acid are added with stirring. After gel formation, the material is heated to 65 ° C with a heating rate of 0.5 ° C / min, held at 65 ° C for 3 hours, heated to 250 ° C with a heating rate of 0.2 ° C / min and calcined for a further 3 hours at this temperature. The product shows a monomodal pore distribution.
BET: 500 m ² / g
Pore diameter: 0.74 nm

1.2 Alumina-zirconia-silica glass

0.45 ml of triisobutylaluminum, 2.01 ml of tetra-n-propoxyzirconium, 27.5 ml of tetraethoxysilane and 25 ml of ethanol are successively dissolved in one another and 4.5 ml of 0.4N hydrochloric acid are added with stirring over a period of 10 minutes. The temperature rises to 55 ° C. After gel formation has taken place and slow predrying at room temperature, the material is heated to 65 ° C. at a heating rate of 0.5 ° C./min, kept at 65 ° C. for 3 hours and at a heating rate of 0.2 ° C./min Heated 300 ° C and calcined for a further 3 hours at this temperature. The product shows a monomodal pore distribution.
BET: 290 m ² / g
Pore diameter: 0.69 nm

1.3 Zirconia-silica glass

1 ml of tetrabutoxyzirconium, 10 ml of tetraethoxysilane and 8.4 ml of ethanol are successively dissolved in one another and 2 ml of 2N hydrochloric acid are added with stirring. After gel formation, the material is heated to 65 ° C with a heating rate of 0.5 ° C / min, held at 65 ° C for 3 hours, heated to 250 ° C with a heating rate of 0.2 ° C / min and calcined for a further 3 hours at this temperature. The product shows a monomodal pore distribution.
BET: 250 m ² / g
Pore diameter: 0.65 nm

1.4 Vanadium oxide-silicon dioxide glass

1.2 g of vanadylacetylacetonate, 10 ml of tetraethoxysilane and 8 ml of ethanol are successively dissolved in one another and 2 ml of 8N hydrochloric acid are added with stirring. After gel formation, the material is heated to 65 ° C with a heating rate of 0.5 ° C / min, held at 65 ° C for 3 hours, heated to 250 ° C with a heating rate of 0.2 ° C / min and calcined for a further 3 hours at this temperature. The product shows a monomodal pore distribution.
BET: 550 m ² / g
Pore diameter: 0.66 nm

1.5 Iron-containing silicon dioxide glass

1.2 g of iron acetylacetonate, 10 ml of tetraethoxysilane and 8 ml of ethanol are successively dissolved in one another and 2 ml of 8N hydrochloric acid are added with stirring. After gel formation, the material is heated to 65 ° C with a heating rate of 0.5 ° C / min, held at 65 ° C for 3 hours, heated to 230 ° C with a heating rate of 0.2 ° C / min and calcined for a further 5 hours at this temperature. The product shows a monomodal pore distribution.
BET: 520 m ² / g
Pore diameter: 0.62 nm

1.6 Titanium dioxide-silicon dioxide glass

0.14 ml of tetraethoxytitanium, 10 ml of tetraethoxysilane and 8 ml of ethanol are successively dissolved in one another and 1.8 ml of 8N hydrochloric acid are added with stirring. After gel formation, the material is heated to 65 ° C with a heating rate of 0.5 ° C / min, held at 65 ° C for 3 hours, heated to 250 ° C with a heating rate of 0.2 ° C / min and calcined for a further 3 hours at this temperature. The product shows a monomodal pore distribution.
BET: 480 m ² / g
Pore diameter: 0.67 nm

1.7 Hydrophobicized titanium dioxide-silicon dioxide-methyl silicon sesquioxide glass

0.133 ml of tetraisopropoxytitanium, 8 ml of tetraethoxysilane, 1.8 ml of methyltriethoxysilane and 7.9 ml of ethanol are successively dissolved in one another and 1.98 ml of 8N hydrochloric acid are added with stirring. After the gel has formed and the gel has hardened, it is heated under protective gas to 65 ° C. at a heating rate of 0.2 ° C./min, kept at 65 ° C. for 3 hours and at a heating rate of 0.2 ° C./min Heated to 250 ° C and calcined for a further 3 hours at this temperature. The product shows a monomodal pore distribution.
BET: 540 m ² / g
Pore diameter: 0.70 nm

1.8 Hydrophobicized iron-containing silicon dioxide-methyl silicon sesquioxide glass

8 ml of tetraethoxysilane, 1.8 ml of methyltriethoxysilane, 0.5 g of iron acetylacetonate and 8 ml of ethanol are successively dissolved in one another and 2 ml of 8N hydrochloric acid are added with stirring. After the gel has formed and the gel has hardened, it is heated under protective gas to 65 ° C. at a heating rate of 0.2 ° C./min. Maintained at 65 ° C for 3 hours, heated to 230 ° C at a heating rate of 0.2 ° C / min, and calcined at this temperature for a further 5 hours. The product shows a monomodal pore distribution.
BET: 420 m ² / g
Pore diameter: 0.61 nm

2. Implementation of the catalysts with benzene and Nitrous oxide / associated gas 2.1 Test conditions

2 cm ^{3 of} catalyst are introduced into a tubular reactor with an inner diameter of 8 mm. The catalyst is previously ground to a grain size of 500-1000 microns. The reaction space is heated to the specified temperature. The temperature is controlled via a thermocouple. The amount of benzene and the gas are continuously added in gaseous form, the gas flow being set to 60 cm ³ / min. The pressure is in the range of 760 torr. The molar ratio of benzene to oxidizing agent in the gas space is 5: 1. Nitrogen is used as the carrier gas for the laboratory tests. The gas composition is analyzed using a GC / MS system. Fe-ZSM-5 from UOP and ZSM-5 (iron-free) from VAW are used as zeolites.

2.2 results

Claims (12)

1. A process for the preparation of hydroxyl group-containing aromatic compounds by catalytic oxidation, characterized in that the catalytic oxidation of the aromatic compound is carried out in the presence of a porous glass with a gas containing nitrous oxide at a temperature of 100-800 ° C. 2. The method according to claim 1, characterized, that benzene is used as the aromatic compound. 3. The method according to any one of claims 1 or 2, characterized, that the gas containing nitrous oxide contains 5 to 100% by volume Nitrous oxide and 0 to 95 vol .-% of another gas contains. 4. The method according to any one of claims 1 or 2, characterized, that the gas containing nitrous oxide contains 80 to 100% by volume Nitrous oxide and 0 to 20 vol .-% of another gas contains. 5. The method according to any one of claims 3 or 4, characterized, that the other gas from air, oxygen, nitrogen, noble gases, carbon dioxide, Water vapor or ammonia or mixtures thereof.   6. The method according to any one of claims 1 to 5, characterized, that the average pore size of the porous glass is between 0.1 and 1.0 nm lies. 7. The method according to any one of claims 1 to 6, characterized, that the catalytic oxidation at a temperature of 200-700 ° C is carried out. 8. The method according to claim 7, characterized, that the catalytic oxidation at a temperature of 250-550 ° C is carried out. 9. The method according to any one of claims 1 to 8, characterized in that the total surface of the porous glass in the dry state is at least 50 m ² / g. 10. The method according to claim 9, characterized in that the total surface of the porous glass in the dry state is 50-5000 m ² / g. 11. The method according to claim 9, characterized in that the total surface of the porous glass in the dry state is 75-1500 m ² / g. 12. The method according to any one of claims 1 to 11, characterized, that the porous glass is produced by the sol-gel process and to at least 50% by weight of oxides of elements from the 3rd main group, the 4th main group, the 3rd subgroup or the 4th subgroup of the Periodic table, including the lanthanoids and actinoids.