CS224675B1 - Method of preparation a gas moxture comprising alcohol and air for aldehyde production on metallic catalysts - Google Patents

Description

SUMMARY OF THE INVENTION The present invention provides a process for the preparation of an alcohol-air mixture for the production of aldshyds by oxidative dehydrogenation of alcohols with air in the gas phase on metal catalysts.

The production of formaldehyde or higher aldshydols from methanol or the corresponding higher alcohols is carried out by gas-phase oxidative dehydrogenation on metal catalysts, preferably on silver, or by gas-phase air oxidation on oxide catalysts, preferably on molybdenum and iron oxides.

In the process for the production of formaldehyde from methanol using the oxide catalyst (USSR pat * 408 504) at 530-650 K, the rollers of the rollers run:

CH ₃ OH + (5.5 0 ₂ * CH ₂ O + H ₂ G -158.3 kO mol

CH ₂ O + (5,5 0 ₂ -HCOOH resp. CO + H ₂ 0 _Δ Η = -215 kO mol ¹

In a process for the production of formaldehyde from methanol using a silver catalyst in a different form and a different deposition / USSR Pat. 167 763, USSR Pat. 175 043, USSR Pat. 358,310, German Pat.

£ 1,231,222 I, German Pat. 1 285 995 / saba reaction in progress: CH _? OH w ^H 2 _δ Η «85.3 kOmol ¹  * CHgU + CHjOH + (5.5 0 ₂ - - * CH ₂ 0 + h ₂ o _{Δ Η} · ~ 155.3 truncated ^{1 H} 2 + <5.5 0 ₂ - H ₂ 0 aHu-243 comol ¹ CHjOH + 1,5 0 ₂ - - * C0 ₂ + 2 H ₂ 0 δΗβ-674 kOmol ¹ ck ₂ o + ° 2 - —C0 ₂ + h ₂ o _{Δ Η} «-519 truncated" ¹ ck ₂ o + <5.5 0 ₂ - - * HCOOH rssp.CO + h ₂ o δΗ «-215 kOmol ¹ ch ₂ o δ = ^ CO + h ₂ dHa 12.5 kMol

- 2,224,675

The combined process uses a silver catalyst in the first reactor, and, after adding air to the converted mixture, uses a second catalyst in the second reactor / US Pat, 2,519,788,

U.S. Pat. No. 3,987,107.

The silver catalyst production process is generally carried out by passing a methanol-air mixture, optionally inert, heated to 360-390 K through a heated immobilized catalyst at a temperature of 820-970 K and at a pressure of 50-200 kPa with a methanol concentration in the air above upper explosion limit. The converted gas is cooled immediately downstream of the catalyst bed, next to a condenser where some of the formaldehyde, methanol and water are condensed. The solution obtained and the gas is fed to an absorber where formaldehyde and methanol are scrubbed from the gas with countercurrent water. By controlling the amount of water in the absorber, the concentration of formaldehyde in the final product is adjusted.

In the process using an air-methanol mixture with the addition of water, the methanol is completely converted to a formaldehyde concentration in water of up to 42%, but a small portion of the unreacted methanol remains in the product.

In a process using an air-methanol mixture with an excess of methanol where incomplete methanol conversion takes place, a rectification column is used as the absorber to separate unreacted methanol. The distilled methanol is recycled to the process. This gives a solution of up to 50% formaldehyde in water with a methanol concentration below 1%,

Preparation of the methanol-water-air mixture for complete methanol conversion processes is performed in a rectifier column-type saturator, consisting of an evaporator and a rectifier part (PIR Pat, 54 939, NSR Pat, 2 323 758), a mixture of methanol-water of the specified composition mixed in the sand filter, it is fed to the upper deck and overflows into the evaporator. Air is supplied below the evaporator and is saturated with methanol and water by passing through the trays. On the bottom of the evaporator, which is heated by steam, the sludge is collected, which is essentially water with a small amount of methanol. The sludge is used to absorb formaldehyde. * By controlling the temperature in the saturator, the amount of air, methanol-water and sludge methanol-water-air and their constant concentrations.

224 875

Preparation of the methanol-air mixture according to the incomplete methanol conversion process is carried out in an air-bubbling saturator, return methanol is supplied from the rectification column for product treatment, fresh methanol and air under methanol hose, methanol circulation through a condenser. extracts some of the methanol to evaporate the methanol and some of the heat is obtained by heating with a water furnace, the amount of return methanol from the rectification column for the product treatment, cradle, depending on the conversion of methanol to the catalyst bed and mode of operation of the rectification column. The amount of fresh methanol is controlled to compensate for variations in the amount of recovered methanol. The desired methanol concentration in air is achieved by controlling the air flow, the methanol level in the saturator and its temperature. The disadvantage of this process is that the recovered methanol contains formaldehyde, which, after evaporation, gets in the methanol-air mixture on the catalyst bed. The formaldehyde coming in the gas mixture is converted to carbon oxides and water, thereby increasing the chemical losses of methanol while reducing the methanol conversion formaldehyde. The optional sludge from this apparatus is essentially methanol with about 5% by weight of formaldehyde and 10% by weight of water and is led to absorption.

SUMMARY OF THE INVENTION The present invention provides a process for preparing an alcohol-air mixture for the production of aldehydes by oxidative dehydroganization of alcohols in gas phase on metal catalysts, preferably on crystalline silver. It is characterized in that part of the fresh alcohol 6 in an amount of from i to 70%, preferably from 2 to 40% of the total fresh alcohol 3, is fed to the choke device supplied with a constant inlet, preferably at the temperature of the alcohol in the choke device. 2 to the first to n-1 choke feeders downstream of the gaseous mixture, preferably to the central part thereof, as shown in the Annex,

The saturation device for the preparation of an alcohol-air mixture consists of a vaporizer part 1 and a rectification part 2, by regulating the temperature of the alcohol, its height above the air inlet 5, the saturating part 5 of the device, the inlet of fresh alcohol 3 compensating for the irregular inlet of the porter. 5, the required amount and concentration parameters are achieved

By regulating the inflow of part of the fresh alcohol 6 into the rectifier part 2 of the choke device and by controlling the amount of sludge 7 from the choke device, an alcohol-air gas mixture with a reduced amount of high-boiling, undesired components is prepared for the reaction process. Advantageously, the rectification part 2 is formed by cap trays having a number of from three to seven, preferably from three to five. The sludge 7 from the choke is discharged to the absorption column.

The advantage of this process is the preparation of a gaseous mixture of alcohol with a small amount of substances boiling above the boiling point of the alcohol, which has a beneficial effect on the conversion and selectivity of the air oxidative dehydrogenation of the air to the corresponding aldehyde, as follows:

Example 1

Into the saturation device of the evaporator type with bubbling

X 3 X air is supplied with 10.26x10 kg s of fresh, 8.12x10.0 kg with ~ -3 3 -1 return methanol and 14.11x10 ms air, 0.43x10 kg of s methanol is blown from the choke device, The resulting mixture is superheated to 370 J < tb &gt; &lt; tb &gt; &lt; tb &gt; &lt; tb &gt; &lt; / RTI &gt; over a kilogram of 850 K silver catalyst. and after partial condensation in a condenser, it is fed to an absorption column into which 12.5 * 10 * kg of water is injected into * 3 ** X for the absorption of formaldehyde and methanol from the gas.

8.12x10 kg with methanol returning to the process and 3 3 —1

24,52x10 kg with 36% formaldehyde,

0.7 wt% methanol and 63.3 wt% water.

Example 2

A saturation device consisting of an air bubbling evaporator 1 and a rectification column 2 is fed with «2 and ** · χ 4

11,29x10 “kg s” fresh 3, 7,09x10 “kg s” of porter methanol 4 and 14,11x10 “ms” of air 5, Of which air 5, return me “-3 -1 ^- tanol 4 and 9,032x10 kg s fresh methanol 2 ^is fed to the -3 -3 evaporator part 1, and 2.258x10 kg with fresh methanol 6 is fed to the center of the rectifier part 2 of the choke device as shown in the annex.

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0.43x10 &quot; kg s &quot; of methanol 7, which is fed to an absorption column. The resulting mixture is superheated to 370 K and passed at a pressure of 0.138 MPa to one kilogram of silver catalyst at 850 K. it feeds into an absorption column into which it injects 13.83 x 1 * ⁵ kg s ^{-1 of} water to absorb formaldehyde and methanol from the gas. Rectification of the resulting liquid mixture is obtained

-3 -1

7.09x10 kg with methanol 4 returning to the process and 26.97x10 ³ with ¹ product of 36 wt.%, Formaldehyde, 0.7 wt. % methanol and 63.3 wt. water.

Claims (1)

A process for the preparation of an alcohol-air mixture for the production of aldehydes by oxidative dehydrogenation of alcohols with air in the gas phase on metal catalysts, preferably on crystalline silver, characterized in that the recoverable alcohol and part fresh from 30 to 99% of the total fresh alcohol supplied are gasified the air mixture and the resulting gaseous mixture are scrubbed with a portion of fresh alcohol in an amount of from 1 to 70% of the total fresh alcohol fed into the process, the portion of fresh alcohol being introduced into the central portion of the liquid-gas contact zone.