CS214341B1 - Method and apparatus for the production of acetaldehyde - Google Patents

Abstract

The production of acetaldehyde is carried out by oxidation and / or dehydrogenating ethanol to a silver catalyst at 340 to 640 ° C. The catalyst is mainly electrolytic silver or silver on carrier especially on zeolites. The catalyst can be still diluted with inert substances / carrier alone metal or glass balls and the like /. On the the catalyst is fed a mixture of a pair of ethanol, water, air, possibly also diethyl ether and acetals, as the main components, above the top explosion limit, generally in the case of moles ratio of 0.5 to 2.5. At the same time, the pairs come out from the reaction zone quickly cool down temperature 340 ° C (200 to 50 ° C). Then continue they are cooled, condensed, acetaldehyde is isolates and unconverted ethanol and some impurities is recirculated. The device consists of on the one hand, the apparatus used to make formalin from methanol, supplemented with a partitioning system consisting of at least one pressure of the rectification column to a pressure of 0.1 - 0.3 MPa and one atmospheric column and respective containers and intermediate containers.

Description

The invention relates to the production of acetaldehyde from petrochemical and / or fermentation ethanol, which generally contains, in addition to water, admixtures of by-products, which is carried out on a modified, readily available apparatus, using air or oxygen-containing gas as the oxidizing agent.

Known processes for the preparation of acetaldehyde from ethanol involve dehydrogenation to form hydrogen or oxidation to produce water in addition to acetldehyde. In the case of dehydrogenation processes, platinum, silver, medium and nickel based catalysts are used, the medium and its oxides based catalysts with a variety of different promoters and carriers / US Pat. No. 1,977,750), as well as agents that inhibit the dehydration of ethanol to ethylene, such as alkali (U.S. Pat. No. 2,861,106, German Pat. 1,044,791 /. For oxldation, platinum metals and silver are actively supported, both in the form of metal particles and deposited on supports / NSR pat. 1,913,311 /. However, the disadvantage is lower selectivity to acetaldehyde. The oxidation of ethanol to acetaldehyde

CH ₃ GH ₂ OH + 1/2 O ₂ = CH ₃ CHO + H ₂ O + 169.7 kJ oxygen can be catalyzed by similar catalysts to dehydrogenation, but silver and honey / German pat. 422,729 and 590,099, respectively. a combination of speckled spikes of these two metals / US Pat. 1,956,440, 2,482,742 and 2,682,560]. Since the reaction proceeds at relatively high temperatures, dehydrogenation also takes place alongside the oxidation.

Thus, exothermic oxidation (169.7 to 203.5 kJ / mol) can be completely or partially compensated by endothermic (-82.5 kJ / mol) dehydrogenation. However, as long as the temperature is not controlled, respectively. Controlled, low selectivity is achieved since there is a significant degree of total oxidation to carbon monoxide, carbon dioxide and water, as well as oxidation to acetic acid and decomposition of acetaldehyde to methane and carbon monoxide. In addition, ethyl acetate / Denis E.T., Mickevic I.N., Agabek V.E .; Mechanizm Židkofaznogo okislenija kislorodsoderžaščich soedinenij. Izdateť Nauka i technika, Minsk 1975 /. For temperature control, external cooling of tubes containing catalyzing meshes / Swedish pat has been proposed. 171,059 and U.S. Pat. Or the use of an air to ethanol ratio such that exothermic and endothermic reactions just equalize (Faith W. L., Keyes D. B., Clark R. L., Ritual Chemicals, p. 1 J. Wiley, New York 1950, 2 ed. 1957} Kirk-Othmer: Encyclopedia of Chemical Technology, 2nd Ed., Volume 1, p. 77. J. Wiley, New York 1963; Encyclopedia of Chemical Processing and Design, ed. McKetta J.J., Vol. 1, p. 114, Deckker, New York 1976]. Ethanol with conc. 50-95%, even very dilute, as obtained by direct hydration of ethylene / FRG pat. 1,913,311 /. The obvious disadvantage, however, is the energy intensity, since it is necessary to evaporate significant amounts of water together with ethanol.

According to the invention, the process for the production of acetaldehyde by partial oxidation and / or dehydrogenation of ethanol on a silver catalyst at a temperature of 340 to 640 ° C is carried out such that the silver catalyst, preferably consisting of electrolytically prepared crystalline silver and / or supported silver, preferably on the zeolite as a carrier, a mixture of ethanol, water and oxygen-containing gas, preferably air, optionally diethylether and monoethyl and diethyl acetal, as the main components, is fed, the molar ratio of organic to oxygen-containing gas, preferably air being above the upper limit of explosives, typically at a molar ratio of 0.5 to 2.5, the vapors of the crude product leaving the reaction zone being rapidly cooled below 340 ° C, preferably to 200 to 50 ° C, then further cool and condense, preferably by sprinkling with an aqueous solution of ethanol and the acetaldehyde formed is separated, the unconverted ethanol with some water, acetals and possibly also ethers is recirculated.

The apparatus for producing acetaldehyde according to the present invention, consisting of a choke, reactor, condenser, columns, reservoirs, pumps, exchangers, piping, valves and fittings, is an original formalin plant consisting of a choke, a reactor and an absorption section for formaldehyde is added. by a separation system of at least one pressure rectification column for separating acetaldehyde from the higher-boiling liquid fractions and, as a rule, one atmospheric column, as well as feedstock, intermediate and product containers.

The process according to the invention is feasible using the equipment used for the production of formaldehyde, respectively. formalin by the oxidation of methanol, which is a technically and investment-intensive addition of the equipment and relatively easy modification and modification of the technology taking into account the kinetics, thermodynamics and physico-chemical properties of acetaldehyde as the final product and aqueous ethanol solution, usually with admixtures of acetaldehyde, diethyl ether and acetals as the raw material. An advantage of the process according to the invention is the high selectivity of oxidation to acetaldehyde, a possibility of oxidation. In recirculation, use also by-products, used ¹ after minor technical modifications and additions to equipment previously used for the production of formalin. Further, the possibility of ^one used ^one as a starting raw material, not only ethanol, the direct hydration of ethylene, but also a fermentation ethanol obtained and the sulfitovných liquor, which does not need a high concentration, which may be below the concentration of the azeotrope of ethanol and water, thus saving the consumption of steam distillation , respectively. rectification. At the same time, expensive ethanol refining is not required. Like raw material, ethanol, resp. water. ethanol solution contain ¹ as by-products or admixtures acetaldehyde, acetals, diethyl ether, ethyl acetate, acetic acid, vinylethyl ether and the like. Preferably, synthetic ethanol obtained by direct hydration of ethylene, distillation concentrated to 88-92% ethanol and containing by-products of the hydration process, i.e. diethyl ether, acetaldehyde, acetals, crotonaldehyde, butnols and the like. These by-products do not interfere with the conversion of ethanol, they are also partially oxidized and do not provide acetaldehyde, unless the oxidation products are removed from the process with the effluent gas or the effluent water from the separation column.

The silver catalyst may form a scaffold silver catalyst, e.g. Raney silver, other electrolytically prepared crystalline silver, carrier silver / e.g. alphaalumina, gamma-alumina, pumice, ceramic particles /, generally prepared by impregnating inorganic solar silver carriers or silver complexes, especially! silver on synthetic or natural zeolites. In order to avoid overheating of the catalyst bed as well as its higher utilization, it is suitable, especially in the case of silver catalysts with a higher specific surface area (e.g. silver on zeolites / or also electrolytic silver, by diluting it with the carriers themselves, or with metal or glass beads, rollers, etc., which furthermore help to a more uniform, i.e. better, temperature distribution, or even heat dissipation.

Λ

The catalyst is typically placed in the reactor in a low and wide layer. The catalyst bed geometry is also important. With a circular diameter, the height to width ratio is 1: 6 to 1: 100. In such an arrangement, the heat exchange with the surroundings, and therefore the reactor walls, is small, so that the reactor operates practically adiabatically. The reaction heat generated by the oxidation of ethanol is partially compensated by the simultaneous dehydrogenation of ethanol and partly heats the reaction mixture. Therefore, it is preferable to add ¹ to the ethanol-oxygen-containing gas mixture, typically air, water vapor / resp. use ¹ dilute aqueous ethanol solution ( ¹ ), which receives part ^{1 of the} reaction heat. Although the catalyst layer is low, there is a significant temperature gradient over it. The reactor temperature regime should be controlled by selecting the composition of the feed mixture (ethanol vapor with water and air vapor admixtures), the inlet temperature upstream of the catalyst bed (180-330 ° C), and the catalyst loading so that the reaction mixture temperature is 340-640 °. C, preferably 440-560 ° C.

The oxygen-containing gas is diluted with nitrogen by oxygen, most often air, with ozone admixtures. Clean air is needed, so it is usually pre-refined from sulfur dioxide, hydrogen sulphide, hydrogen chloride, nitrogen oxides and any other impurities that may come from industrial exhalations and are a catalytic poison. Refining can be done e.g. by washing with a solution or by absorption or adsorption in a bed of solid material containing substances reacting with said acid gases.

The acetaldehyde production plant, the basic scheme of which is shown in the figure, is made of stainless steel or stainless steel. of aluminum and its alloys, consists of cage devices and apparatus, such as choke 1, reactor 3, and flow plant, washing machines, respectively. a condenser 5, an extraction column 8, a pressure column 13 and a column 17, cartridges 20, 24, saline valves, pumps, intermediate tanks, measuring and regulation technology.

Further details of the manufacturing process and equipment as well as the advantages are evident from the examples.

F

Example 1

A 7 cm catalyst consisting of silver on pumice as a 0.4 mm grain carrier is charged into a tubular reactor heated by a jacketed electric coil. After stabilizing the conditions, the reaction is carried out at an average temperature of 413 ° C with a mixture of air and ethanol with a mole ratio of air: ethanol - 1.11: 1. The product is cooled efficiently and the reaction gas passes through a scrubber to collect acetaldehyde residues in tetrahydrofuran. At a time coordinate W (F = 2.73) in gmol @ ^-1 and a catalyst loading of 259.8 mol.dm @ ^-1 h ^{@ 1} , the ethanol conversion (ethanol used) is 99% synthetic, produced by hydrating ethylene (50.7%) and the selectivity of acetaldehyde formation is 91.2%. In addition to ethanol and acetaldehyde, the reaction product also contains 2.4% acetaldehyde diethyl acetal and water (17.3% w / w).

Example 2 o

7 cm of silver catalyst prepared electrolytically and with a grain size of 0.4 to 2 mm are charged into a tubular reactor. After stabilizing the oxidation conditions at 425 ° C, with mol. air ratio of ethanol to 1.19: 1 and the catalyst zatíažení 239.3 mol.dmj _tat .h reaction was analyzed by gas chromatography. Ethanol conversion reached 54.1%, acetaldehyde formation selectivity 90.6%. The reaction product also contains 4.4 wt. acetal and water / 20.2%

214,341 w / w also formed by the reaction. Except nitrogen, the gases contain small amounts of carbon dioxide, hydrogen and oxygen.

Example 3

An electrolytically prepared silver of a similar type to that used to oxidize methanol to formaldehyde is charged into a stainless steel tubular reactor. Ethyl alcohol of 90.7% by weight, 0.1% by weight acetaldehyde, 0.05% by weight acetals and 0.2% by weight are injected into the reactor over a run-in period. diethyl ether, the remainder being water / mol. ratio of air -0.1 to ethanol - 1.21: 1). The catalyst loading is 244.5 mol.dm. .h. After the temperature has stabilized at 409 ° C, the oxidation products condense by efficient cooling. According to the composition of the reaction product, an ethanol conversion of 59.1% is achieved. Acetaldehyde is formed with a selectivity of 91.5%. Another component of the reaction product is a mixture of acetaldehyde monoethyl acetal and acetaldehyde diethyl acetal (2.4% w / w) and water (25.3% w / w).

Example 4

This example illustrates the effect of water on oxidation selectivity. The reaction is carried out on the apparatus of Example 3, with an 80.5% by weight aqueous ethanol solution being injected into the reactor. At a load of 277, 1 mol.dm ^-1 h ^-1 and mol. The ratio of air: ethanol-1: 07: 1, at an average temperature of 405 ° C, achieved an ethanol conversion of 52.4% and a selectivity to acetaldehyde of 99.1%. The acetals content of the product was 0.8% by weight. and water 33.1 wt.

Example 5

When ethanol with conc. 69.7 wt. under experimentally similar conditions as in Example 2 / temperature 401 ° C, load 271 mol.dm ^-1 .h ¹ , mol. air: ethanol ratio 1,09:

The conversion of ethanol was 54.4% and the selectivity of acetaldehyde formation was 92.7%. The product also contains 3.5 wt. % acetal and 40.8 wt. water.

Example 6

This example illustrates the effect of moles. ratio of air / oxygen / ethanol to the results of ethanol oxidation and dehydrogenation.

The reaction is carried out under similar conditions to that of Example 4 (temperature 402 ° C, loading 247 mol.dm.h ^-1 ) except that mol. poiper of air to ethanol 0.563: 1. Celt

Chromatographic analysis of the product composition shows an ethanol conversion of 26.4% and a selectivity of acetaldehyde formation of 94.4%. The product contains 2.3 wt. % acetal, 2.5 wt. diethyl ether and

II, 2 wt. water.

Example 7

A liquid mixture of composition (% w / w): 74.3 ethanol is injected into the stainless steel reactor at 400 ° C; 8.8 water, 13.8 acetals (acetaldehyde monoethyl acetal and acetaldehyde diethyl acetal) and 0.1 diethyl ether. At mol. ratio of air: ethanol + acetal - 1,1: 1a for —3 “1“ 1 catalyst loading 248,5 mol.dm _to fc.h / time coordinate W / F - 2,81 ghmol / gives product containing 0,8 % wt. acetal (conversion 94.2%). The ethanol conversion is 53.6%.

Example 8

Ethanol containing 2.1 wt.% Is injected into the stainless steel reactor at 400 ° C.

214,341 acetals and 10.2 wt. water. At mol. air: ethanol ratio - 1.12: 1 and a load of 252.1 mo.m · m · hr · h (time coordinate W (F = 2.75 g · h.mol)) yields a product with 1.1 wt. of acetals (which arise even when working without acetal in the feed). The ethanol conversion is 51.2%.

Example 9

A synthetic unrefined ethanol of 92.5% by weight containing small amounts of acetaldehyde, diethyl ether, higher alcohols (sec.-butyl alcohol) and the remainder to 100% water is injected into the stainless steel reactor at 520 ° C.

The feed conditions are adjusted to a time coordinate W / F = 1.1 gmol ¹ and mol. air to ethanol ratio 1.1: 1. Under the above conditions, ethanol conversion of 58.0 wt. and acetaldehyde formation selectivity 93.5%.

Example 10

This example illustrates the possibility ^{1 of} reducing the catalytic silver charge and its replacement or dilution with an inert charge with which the silver catalyst is mixed.

The procedure is similar to Example 2, except that 5 g of electrolytic silver is mixed with 7 ci? an inert filler such as natural zeolite-clinoptilolite or glass beads with a diameter of 0.5 mm (weight ^{1 of the} catalyst in Example 2 is 22.3 g). After loading into the reactor, ethanol (90.7% w / w) and air were injected. The molar ratio of air to ethanol = 1.22: 1 and the time coordinate was 2.91 g / mol ^Χ . Under these conditions, the conversion of ethanol is 65% and the selectivity of acetaldehyde formation is 92%.

Example 11

Mixture of ethanol and water, resp. The aqueous ethanol directly arriving from the ethanol production plant passes through the intermediate tank and via line 27 enters the choke 1, heated by steam and ring ring, to which also the regenerated ethanol with the addition of acetaldehyde, acetals and diethyl ether enters. Filtered air is supplied to the lower part of the choke 1 via line 26. The preheated air / water vapor / organic mixture consisting of ethanol and admixtures of acetaldehyde, acetals, diethyl ether and traces of ethyl acetate enters the oxidation reactor 3 together with the flushing line 2. The reactor is maintained at 445 + 20 ° C. The molar ratio of air to ethanol is 1.19:

And a catalyst load of ethanol of 240 mol.dm ^-1 h ^-1 . The oxide mixture is rapidly cooled to 150 to 100 ° C in the subsequent flow heat exchanger 28 of reactor 3, whereby the recovered heat is used to preheat the feedstocks in the choke 1. The cooled mixture enters the condenser 5 via line 4. 6 in ethanol solution. The liquid fraction from the condenser 5 is passed through lines 10 and 12 to the acetaldehyde column 13, in the case of lower purity requirements, via line 10 to column 17. Gases and vapors from the apparatus. The liquid phase passes through line 11 to an acetaldehyde column 13 operating at an overpressure of 0.11 to 0.17 MPa. The distillate-acetaldehyde is routed via a conduit 16 through a condenser, as a rule, to a container 24 and from there for distribution or further use. The depleted 1414 341 pieces from the bottom of column 13 are passed through route 15 to column 17, which is optionally sprinkled with fresh crude ethanol fed in via route 19. Distilled ethanol, optionally with admixtures of acetals and ethyl acetate, is passed through line 18 to intermediate tank 20 from ¹ to fresh feed. 27 to the choke 1. The residue from column 17 is passed through a route 21 for recovery 22 or separation of acetic acid residues, acetals and esters, optionally a waste water treatment plant and, as a rule, some waste water containing admixtures of by-products is passed through line 23 to the ethanol storage tank 20.

Claims (2)

OBJECT OF THE INVENTION Process for the preparation of acetaldehyde by partial oxidation and / or dehydrogenation of ethanol on a silver catalyst at a temperature of 340 to 640 ° C, characterized in that for a silver catalyst, preferably consisting of electrolytically prepared crystalline silver and / or supported silver, preferably on zeolite as carrier, a mixture of ethanol, water and oxygen-containing gas, preferably air, optionally diethyl ether and monoethyl of diethyl acetal, as the main components, is fed, wherein the molar ratio of organic to oxygen-containing gas, preferably air, is above the upper limit explosives, typically at a molar ratio of 0.5 to 2.5, wherein the vapors of the crude product leaving the reaction zone are rapidly cooled below 340 ° C, preferably to 200 to 50 ° C, after which they are further cooled and condensed, preferably by shaking with an aqueous ethanol solution, if necessary With water alone and the acetaldehyde formed, ethyl acetate and acetic acid are also separated, unconverted ethanol and some of the water, acetals and possibly also ethers are recirculated. A plant for the production of acetaldehyde according to Claim 1, comprising a choke, reactor, condenser, columns, reservoirs, pumps, exchangers, pipes, fittings and ancillary equipment, characterized in that the flood generating plant consists of a choke (1); of the reactor (3) and the absorption section (5 and 8) for formaldehyde are supplemented by a separation system with at least one pressure rectification column (13) for separating acetaldehyde from higher boiling fractions and generally one atmospheric column (17) as well as feedstock containers, intermediate and product.