JPH0143730B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for producing 3,5-dimethylphenol by catalytically condensing acetone to isophorone and converting it to 3,5-dimethylphenol in one reaction step. Regarding. It is known to prepare isophorone by condensation of acetone using various catalysts. For example, this reaction is described in US Pat. No. 2,183,127 using CaO, Ca(OH) ₂ or CaC ₂ . Belgian Patent No. 612135, US Patent No. 2148103 and US Patent No.
According to No. 3337633, the condensation is carried out in the presence of an alkali. GB 610,752 describes the use of a catalyst prepared by suspending an oxide and depositing it on a steel billet. One of these mixtures consists of 94% magnesium oxide and 6% vanadium pentoxide. The catalyst according to US Pat. No. 3,155,730 consists of calcined bluestone-like limestone. The catalytic conversion of isophorone to 3,5-dimethylphenol is likewise known from numerous patent specifications, in which case different catalysts are described in each case. According to German Patent No. 1538224, the conversion is carried out using a catalyst consisting of iron oxide and an alkali, and German Patent Application No. 154388
No. 2,529,773 describes aluminum oxide catalysts mixed with various heavy metal oxides, such as cobalt oxide, molybdenum oxide or chromium oxide. According to German Patent No. 1768875, the conversion takes place in the presence of a chromium-nickel steel alloy as a catalyst. The direct synthesis of 3,5-dimethylphenol from acetone is described in DE-A-2316576. According to this publication, acetone is reacted in the vapor phase at a temperature of 371 to 510°C and a pressure of 0.
React over the catalyst at ~100 bar. The main products produced are 3,5-dimethylphenol, isophorone and mesityl oxide in different yields depending on the choice of reaction conditions. The intermediate products isophorone and mesityl oxide are separated and fed back to the reaction mixture. The catalyst used consists essentially of magnesium oxide, ie preferably commercially available magnesium oxide. According to DE 2316576 A1, the magnesium oxide catalyst may also contain small amounts, for example up to 10%, of other oxides, such as chromium trioxide, iron oxide, molybdenum trioxide. confirmed. However, this is not recommended since, although the conversion of acetone is increased, the selectivity for 3,5-dimethylphenol and isophorone is significantly reduced. It is clear that further undesired by-products are formed. This adverse effect of metal oxides is illustrated in the fed Cr ₂ O ₃ example of Example 1, and commercially available magnesium oxide is likewise shown to be the catalyst of choice. Unfortunately this result can only be reproduced in a glass reactor. If this process is carried out in a steel reactor, clearly poorer yields and selectivities are obtained, as shown in the comparative example below.
A possible explanation for this is that catalytic decomposition of acetone or acetone condensate occurs in the steel reactor under the given conditions. However, this direct synthesis has not hitherto been carried out industrially, since it is difficult to imagine a glass reactor for large-scale reactions at temperatures close to 500° C. and pressures up to 10 bar. Therefore, there was a problem to develop a method for directly producing 3,5-dimethylphenol from acetone with good yield and selectivity even using steel reactors that are advantageously used in the chemical industry. The solution to this problem is to react at a reaction temperature of 370 to 510 in the gas phase.
C and a pressure of 1 to 10 bar using a catalyst containing magnesium oxide;
reacted in a circulating process over a catalyst consisting of up to 60% by weight and 10% by weight of chromium oxide () and at 180 °C
The reaction products, isophorone and dimethylphenol, having a boiling point above , are removed from the product cycle, separated and purified. The problem is therefore solved both by the development of new catalyst systems and by technological changes in the process. In an attempt to speed up the reaction rate in the direct synthesis of 3,5-diphenylphenol from acetone, a catalyst made from magnesium oxide, silicon dioxide or silicates, and the additive chromium oxide (2000) was surprisingly used in West Germany. Patent Application Publication No. 2316576
It was observed that higher space-time yields of 3,5-dimethylphenol and isophorone were achieved with the catalysts described in the patent. Similarly, using this new catalyst system and coupled with the following cyclic operation method, reactions with good space-time yields and high selectivity to 3,5-dimethylphenol and isophorone can also be carried out in steel reactors. It was unexpectedly hot. Contrary to the above ideas, it was found that it is precisely the oxidized heavy metal center that catalyzes the reaction step of isophorone to 3,5-dimethylphenol, and that a favorable catalytic effect is achieved only at a certain degree of distribution of chromium oxide. did. It is important that this amount of chromium oxide is concentrated in the outer periphery of the particles, with the amount being less than 10%. Particularly good results have been obtained by adding silicic acid and silicates by high-temperature methods, which act as carriers for the other components. The catalyst is preferably prepared in a wet process by partially dissolving a charge of suspended, sparingly soluble silicate and partially dissolving likewise other suspended components, e.g. Concentrate sequentially with magnesium, magnesium oxide, magnesium carbonate, chromium acetate and other ingredients and then granulate. The mechanical stability of extrudates and tablets is improved by binders, such as water glass. The catalyst produced in this way is a magnesium oxide catalyst, for example "Harshaw Mg 0601 T" described in German Patent Application No. 2316576.
However, this improvement in activity is not only due to an increase in active surface area, but also due to the addition of additional components, in particular hyperthermal silicon dioxide and Due to calcium silicate, the product ratio is 3,5-
There is a shift in favor of enhanced dimethylphenol formation. In a variant of the process, 3,5-dimethylphenol and isophorone are removed from each circulation, and in a recirculating process in which exclusively low-boiling intermediate products and starting material acetone are returned, particularly advantageous product fractionation and high space-time yields are achieved. was found to be achievable. Simultaneously returning the intermediate product isophorone is 3,5
It was found that -dimethylphenol did not contribute to an increase in yield, since isophorone did not convert exclusively to 3,5-dimethylphenol under these reaction conditions, but to a significant extent to the low-molecular-weight acetone condensation product, For example, it is converted into mesityl oxide. The simultaneous production of 3,5-dimethylphenol and isophorone is therefore an economical solution, especially since isophorone is also a useful intermediate product. That is, a reaction implementation that takes into consideration the optimum yield of 3,5-dimethylphenol and isophorone is proposed. If it is desired to also convert the isophorone obtained into dimethylphenol, a separate reaction using known methods is recommended. The main features of the reaction implementation according to the invention are that the high-boiling product isophorone produced from acetone and 3,
5-dimethylphenol is removed from each cycle by partial condensation at about 180° C. and the used product acetone and low-boiling intermediates are returned to the new conversion in the reactor. The following circular operating procedure is thus obtained: the starting mixture is fed into an evaporator and from there into a reaction tube filled with catalyst pellets, where the condensation takes place. The product mixture is then depressurized and subjected to partial condensation at approximately 180°C. The high-boiling products are worked up to purify 3,5-dimethylphenol and isophorone. The starting material acetone and other intermediates and by-products are condensed in a condenser downstream of the first condenser. The condensate separates into two phases. The heavy phase mainly contains acetone in addition to water;
After distilling off the water, the acetone is returned to the storage vessel together with the light phase. The amount of material not returned is replenished with fresh acetone. The composition of the charge mixture is adjusted by discharging by-products and replenishing acetone so that the following concentration range is maintained: Acetone 60-90% by weight Mesityl oxide 5-15 Water 10-15 Mesitylene 5-10 〃 Others 0-10 〃 As expected, in this method, the space-time yield of the intermediate product isophorone increases as the throughput increases. Surprisingly, this increase does not impair the space-time yield of 3,5-dimethylphenol. Rather 3,5
It is another advantage of the process of the invention that the space-time yield of dimethylphenol remains constant or even increases slightly in the range of 1 to 5 throughputs per catalyst per hour. Next, the present invention will be explained in detail with reference to examples. All "%" are "% by weight". Example 1 Fixed bed reactor composition: magnesium oxide 69%,
Sodium silicate 12.5%, chromium oxide () 1.5%,
Fill with 100 ml of 17% calcium silicate catalyst produced by high-temperature method. The catalyst pellet has a diameter of 4 mm and a length of 5
Exists as a cylindrical extrusion of ~10 mm. The fixed bed of catalyst has a temperature of 470°C. The acetone and low-boiling intermediates in the charge mixture are passed in circulation. Isophorone and 3,5-dimethylphenol are separated from each cycle by partial condensation. The liquid flow rate is 100ml/h. The reaction is carried out at a pressure of 5 bar. After 8 hours the reaction is complete and the catalyst is regenerated with an air/nitrogen mixture. The analysis and material balance are as follows: Space-time yield: 3,5-dimethylphenol
65 g/.h Isophorone 66 g/.h Example 1a (Comparative Example) Other conditions were the same as in Example 1, using magnesium oxide catalyst "Harshaw 0606 T". Space-time yield: 3,5-dimethylphenol
16 g/・h Isophorone 26 g/・h Example 2 Composition: Calcium silicate 51%, chromium oxide () 7.8%, magnesium oxide 41.2% catalyst by hyperthermal method using acetone under the conditions described in Example 1, but with a liquid flow rate of 360 ml/h React at h. Space-time yield: 3,5-dimethylphenol
100g/・h Isophorone 165g/・h Example 2a (comparative example) Pure magnesium oxide catalyst (Harshaw 0601
The acetone is reacted as in Example 1 using T) at a flow rate of 360 ml/h of the initial mixture. Space-time yield: 3,5-dimethylphenol
20g/・h Isophorone 60g/・h Example 3 Composition: Magnesium oxide 69%, sodium silicate
12.4% of acetone, 17% of aluminum silicate and 1.6% of chromium () oxide under the conditions described in Example 1, but with a liquid flow rate of 360 ml/h. Space-time yield: 3,5-dimethylphenol
55g/・h Isophorone 155g/・h Example 4 A catalyst of 50% calcium silicate, 41% magnesium oxide, and 9% chromium oxide (2) was prepared by high-temperature method, and pellets made from calcium silicate and magnesium oxide were mixed with chromium acetate (2) solution. put in,
It is then dried and manufactured by scorching heat. Using this preferably surface-doped catalyst with chromium oxide, acetone is reacted under the conditions described in Example 1, varying the liquid flow rate in the various tests. The following table shows the space-time yield (RZA) achieved at various liquid flow rates. 【table】

Claims (1)

[Claims] 1. Reaction temperature in the gas phase of 370 to 510°C and pressure 1.
In a process for producing 3,5-dimethylphenol by converting acetone using a catalyst containing magnesium oxide at ~10 bar, acetone is converted to 25-80% by weight of magnesium oxide and 20-60% of silicon dioxide or silicate. reacted in a circulation process with a catalyst consisting of up to 10% by weight of chromium oxide () and the reaction products isophorone and dimethylphenol with a boiling point above 180°C are removed from the product circulation, separated and purified. A method for producing 3,5-dimethylphenol from acetone, the method comprising: 2. Process according to claim 1, in which the silicon dioxide and the silicate are present in highly dispersed, hyperthermally obtained form. 3 Chromium oxide is concentrated on the catalyst surface,
A method according to claim 1 or 2. 4. The method according to any one of claims 1 to 3, wherein the high boiling point reaction product is separated by partial condensation. 5 The throughput of the reaction mixture is adjusted to between 1 and 7 per catalyst per hour.
4. The method according to any one of items 4 to 4.