CS258698B1 - Process for producing formaldehyde by oxidized methanol dehydrogenation - Google Patents

Abstract

The purpose is to solve the production of formaldehyde on a silver catalyst with recycling of unreacted methanol with improved separation of unreacted methanol from the product. The stated purpose is achieved by treating a separated mixture of methanol, formaldehyde and water containing from 12 to 33% by weight of methanol, at an absolute pressure of from 10 to 101.3 kPa with gas in an amount of from 3.3. . 10 ~4 to 0.33 Nm3 per kilogram of unreacted methanol separated into the process and recycled.

Description

258698 3

The present invention provides a process for the preparation of formaldehyde by oxidative dehydrogenation of methanol with a silver catalyst.

Formaldehyde, an important raw material for the production of various organic synthesis products, can be produced by the reduction of carbon monoxide by oxidation of methane, possibly higher hydrocarbon or methanol (Walker, F .: Formaldehyde, 3 ed. New York 1964). world production of formialdehyde suggests that formaldehyde is currently produced in predominant methanol from methanol. It is preferably carried out by oxidizing the gas containing the oxygen in the gaseous phase on the oxide catalysts preferably on the molybdenum and iron oxides or the oxidizing dehydrogenated oxygen-containing gas in the gaseous phase 4 on the metal catalysts (Diem H., Hllt A .: Ullmans Encykl.Techn Chem., 4 Aufl., B. 11, 1967, 687).

In the process for the production of formaldehyde from methanol using an oxide catalyst (CS 139 407, CS 175 449, CS 182 499, SU 403 508, DE 2 442 311, DE 2 450 931, DE 2 608 823, DE 2 747 578, DE 2) 747,581), the reaction is carried out at a temperature of 500 to 670 K with excess oxygen to methanol, wherein the concentration of methanol is below the lower explosion limit of the reaction mixture. The process is carried out isothermally in heat exchange tube reactors in a catalytic layer. Reaction. heat is used to produce heat. Mainly the reaction of methanol oxidation: CH 2 O + H 2 O H = -156.3 kj / κ t "

This process has a conversion of 98-99% and a yield of 91-95%. Formaldehyde is extracted from the reaction gases by absorption into water, forming a solution of formaldehyde with insignificant amounts of methanethanol.

A classical process for the production of formaldehyde by methanol using a silver catalyst (DE 228 687), or another metal catalyst (DE 2 525 174, DE 2 627 421, US 4 354 945), may be a mixed catalyst (DE 3 213 227). in one step (DE1294 340) or in two stages (US 3,959,383; US 4,076,754; US 4,450,301). The silver catalyst is used in various forms. In addition to the silver mesh, it uses silver on a support (CS No. 167 763, SU 175 043, U.S. Pat. No. 4,382,149, U.S. Pat. No. 4,474,996, EP 0 091165, Muchlenov IP, Dobrinova is I., Derjúžkin v. I., Sořóko V. It is: Catalyst Technology, SNTL Praha1985, 175), sponge silver (JP 56'6 720), silver alloys (SU 358 310, PL 122 783, US4 418 215, US 4,424,397, EP 0 003 384), silver surface modified (PL 117 567, GB 2 121 787, US 1 968 552, DE 3 143 704, EP 0 079 490) and especially crystalline silver (GB1 337 783, DE 1 231 229, DE 1 285 995, DE 1 294 360, DE 2 201 434, DE 2 232 757, CS No 219 · 193). . .

The reaction is carried out at a temperature of 823 to 1023 K with an excess of methanol to the oxygen, wherein the concentration of methanol is the upper explosion limit of the reaction mixture. The process is carried out adiabatically with the heat exchange behind the catalyst layer. Methanol-de-hydrogenation reaction is carried out in the main: c 2 -CH 2 O 2 + h 2 and the oxidation reaction of methanol: 0.5 O 2 -> CH 2 O-i - - 156.3 kJ / mol 258698 deeper oxidation by-products resulting in carbon oxides and formic acid. The reaction is carried out at such concentration levels of oxygen, methanol and diluents that the overall thermal effect of the reaction is slightly positive, sufficient to compensate for heat loss of the roundhouse and to heat the raw materials, which ensures an autothermal regime. In the presence of a substantial amount of water vapor at 873 to 1023 K, a conversion of 83 to 98% and a yield of 82 to 89% is achieved, with the unreacted methanol remaining in the product.

Without the presence of a substantial amount of water vapor at 823-923 K, a conversion of 45-87% and a yield of 88-92% is achieved, with the unreacted methanols recycled to the process after separation by rectification.

The combined process uses a silver catalyst in the first reactor and an oxide catalyst in the second reactor (U.S. Pat. No. 2,519,788, U.S. Pat. No. 3,987,107).

The oxidative dehydrogenation of methanol utilizing the metal catalyst is generally realized in several stages. The preparation of the gaseous mixture for the reaction with almost complete conversion of methanol is carried out in a saturator of a type-certification column consisting of a vaporizer and a rectification section (PL 54 9 9, DE 2 323 758). The methanol-water mixture of the specified composition is fed to the top of the rectification section, and an oxygen-containing gas is fed to the evaporator most frequently below the surface, which is saturated with methanol and water through the rectification portion. The conversion of the methanol is largely dependent on the concentration ratios of methanol, water and methanol respectively. other dilutants in the air (FR No. 1 487 093, SU 363 688, US 2 465 498]. The energy for evaporating methanol and water is supplied directly by water vapor in the evaporator, if only the methanol is fed to the saturator. then the gas is directly supplied by water vapor The preparation of the gas mixture for incomplete methanol conversion is carried out in a vaporizer of the evaporator type with the bubbling of gas in the volume of methanol and the energy to evaporate the fresh and recycled methanol is it obtains the circulation of the vaporized liquid through a process stage where condensation or absorption of the condensable components is carried out and also indirectly by means of water vapor. improved process of preparing the gas mixture is carried out in several stages, preferably in the first stage. in the flow direction of the gas under adiabatic conditions. The circulation of the liquid through the heat sources from the processor takes place in adiabatic stages and the required amount of energy is supplied to the gas mixture in its last stages (CS 242 270).

The methanol used can be crude, which can be purified by distillation removal of dimethyl ether, methyl ester of iron and pentacarbonyl iron. Purification of methanol by distillation improves the additional alkanol or alkyl ether (DE 2 201 434, DE 2 201 865). Chemically the methanol is treated, in particular with peroxide and metal hydroxide (DE 2 205 196). It is known to purify the mixture by ion exchange (DE 3 110 723, EP 0 061 057). -genogen-containing compound (US 4,198,351).

Preferably, the gaseous mixture prepared in the saturation plant is freed from mechanical impurities or drops (DE 2 114 370) to a temperature of 360 to 390 K and a catalytic bed of 823 to 1023 Kelvina. The catalyst can be placed in a contact basket (DE 2 173 938, DE 2 545 104, US 2 745 722) or on a metal substrate directly on the tube plate of a heat exchanger (DE 1 642 955, CS 225 301, CS 227 155). The deposition of the catalytic bed on the tube sheet can be quantified by indicating the weight of the catalyst and the permeable transition area of the converted gases (CS number 219 600). The catalyst loading can be quantified by giving the weight of methanol per catalyst area per time (US 2,462,413, DE 1,231,229, DE 1,294,380, DE 2,034,532, CS221880) the volume of the reaction mixture per catalyst volume per unit time (US 4 Or the weight of the methanol to the weight of the catalyst per unit time (CS 221 721).

Cooling of the converted gas is carried out immediately after the catalyst bed directly with water or solution. absorption system (DE 2 011 676, CS no. 184 646). Indirectly, by water for steam generation (GB 1 567 921, DE 2 002 789, DE 2 546 104, SU 929 624, SU 946 640], or by vaporized methanol-led process (SU 536 158, CS 184 646), the finished product utilizing the heat to distill off methanol from the absorbent solution.

At a temperature of -420 to 450 K, the cooled converted gases are either fed directly to the absorption stage or are condensed in a condenser to condense part of the condensable components. Cooling is carried out directly by the product and indirectly in processes with almost complete conversion of methanol or in processes with incomplete methanol directly by the solution obtained in absorption (CS 245 086) and by the indirect liquid containing the methanol, by circulating it between the saturator and the condenser. by using condensation heat, preparing the reaction mixture (CS 242 270), with a portion of the condensed components in form 7 258695 of the solution being fed to the unreacted methanol-product separation stage (CS 244587) and part of the solution together with the gaseous degree is brought to the degree of absorption.

The absorption system may be one component (RO 65 503, CS 181 239) or multiple cameras (US 3 606 732, GB 970 855, PL number 63 227, PL 87 884), wherein the heat absorption may also be used to prepare the gas mixture into the reaction (DD 151 547). Low form aldehyde, methanol and water non-condensable gases may be combusted non-catalytically to produce water vapor due to the hydrogen content of 16 to 21% by volume. Their catalytic combustion (EP 0 068 377) and the possible recycling process are also possible (CS 238 445, CS239 192, CS 239 592). By adjusting the amount of the absorption, the formaldehyde concentration in the commercial product is adjusted (SU411071). If the absorption medium, except water, can be used in a solution containing urea or ammonia, the solution obtained in the crystallization evaporation in the production of hexamethylenetetramine (CS 257 817), in particular in the case of special determination of the use of the product, may be used. . In processes with almost complete methanol conversion, an aqueous solution with a formaldehyde content of 36 to 42% by weight is obtained in the condensation absorption system. and methanol from 2 to 8% by weight, which is directly to the commercial product. A reduction in the amount of methanol in the product can be achieved by incorporating into the process of a further depletion column in which an inert gas (U.S. Pat. No. 4,385,188, EP 0 068 840) or degassing process (U.S. Pat. , EP 0 079 322) separates a portion of the methanol. After its removal by the next condenser, the methanol, formaldehyde and water solution obtained is recycled to the process. The depleting column leaves the finished product with a methanol content ranging from 1.1 to 1.5% by weight. The process using the depletion column is quantified, in addition to the weight ratio of gas to the aqueous solution leaving the depletion column, in the range from 0.5 to 2.5 by other parameters. In incomplete meta-transformation processes, an aqueous solution containing 20 to 38% by weight of formaldehyde is obtained in the condensation absorption system. and methanol from 12 to 333 wt. By including the rectification stage in the process (U.S. Pat. No. 3,174,911, PL No. 88,884), the unreacted methanol is preferably separated off by pressure and recycled to the reaction. A step of rectifying the separation of unreacted methanol from an aqueous solution of formaldehyde having 3 to 15 theoretical plates, at a temperature of 308 to 373 K, a pressure of 10 to 101.3 kPa and a reflux ratio of 2 to 6 separates said solution into distillate, formaldehyde methanol from 1.3 to 5 wt. and from about 4 to about 15 wt. and a distillation residue, an aqueous solution containing formaldehyde from 36 to 50% by weight. and methanol to 1 wt. The distillate is recycled to the reaction and the desilatory residue is a commercial product. The advantage of this procedure over the previous one is the achievement of a higher yield and the possibility of producing a product with a higher concentration of formaldehyde. The disadvantage is more energy-intensive performance

SUMMARY OF THE INVENTION The present invention relates to a process for producing formaldehyde by oxidative dehydrogenation of methanol on a silver catalyst with the recycling of unreacted methanol, characterized in that, in the step of rectifying the unreacted methanool product, the methanol, formaldehyde, and water are separated. with a methanol content of from 12 to 33% by weight, at an absolute pressure of from 10 to 101.3 kPa, a gas quantity of from 3.3. recycle unreacted methanol process.

The gas may be air or another substance which is an inert condition for the dispersed mixture to work the methanol rectification step and is non-condensable under said pressure. It is advantageous if it can, after the condensation separation of the methanol, be added to the absorption stage or to the stage of preparation of the gas mixture. An advantage of the process of the present invention is to increase the efficiency of the work of the rectification stage of methanol separation from the product. Depending on the mode of operation of this stage, reducing its energy intensity or reducing the energy intensity of the step of preparing the gaseous mixture can be reduced, while increasing the selectivity of methanol to formaldehyde conversion. These advantages can be illustrated with the aid of the above mentioned example of a possible process according to the invention. Example 1 [Comparative]

514 kilograms / h of fresh methanol and 2 071 kilograms / h of recycled methanol are introduced into the saturation device with a water content of 5.85% by weight. and formaldehyde of 1.45 wt. This mixture is gasified by air at a temperature of 316 K, passed through a process process of 3,888 kg / h. The evaporation energy is obtained by circulating the liquid through the condenser of the reaction plants and supplied directly by means of water vapor in the saturator. The energy consumption in the form of steam is 0.62 GJ / h. The resulting gaseous mixture is passed through a crystalline silver catalyst at 863 K. The reaction mixture is cooled down in the reactor indirectly by a liquid circulating reactor downstream of the catalytic bed and the rectification separation of unreacted methanol from the product. At 415 K, the cooled reaction mixture passes through the reaction product condenser

Claims (1)

10 and the degree of absorption. In the condensation absorptive system, formaldehyde and unreacted methanol are washed with water of 2649 kilograms / h and separated from the off-gas which is exhausted by the turbocharger to the air. In condensation and absorption. The system yields 7,738 kg / h of a formaldehyde solution of 27.4% by weight and methanol of 25.7% by weight, resulting in a stepwise separation of unreacted methanol from the product. This technological stage consists of a cooker, a capsule column with eight theoretical equilibrium stages, a condensation-reflux device and a vacuum pump. The rectification is carried out at an absolute pressure of 45 kPa, measured at the outlet of the distillation vapors, into a condensation reflux device produced by the pump. At the above pressure and the reflux ratio of 4, the solution is divided into 2071 kilograms / h of methanol with a water content of 5.85% by weight. % of formaldehyde and 1.45% w / w to 5,637 kg / h of product with aldehyde content of 37% w / w. and methanol 0.94% wt. The residue of 30 kg / h is in the form of a pair of 26.5 Nm < 3 >, which passes through the pump to the absorption degree or to the stage of preparation of the gas mixture. The vacuum sucking to said plurality of vapors from the surrounding air regulates the air to the value of its vapor flow rate. The energy for operation of the step-by-step verification is obtained by circulating the vaporized solution between the column base and the reactors and is supplied in a steam boiler indirectly by steam. Energy consumption in the form of steam is 5.5 Gj / h. The consumption of methanol per tonne of product produced is 446 kg. EXAMPLE 2 2,572 kg / h of fresh methanol and 2,013 kg / h of recycled methanol with a water content of 3.72 are fed to a saturator. wt. and 0.9% by weight of formaldehyde. This mixture is gasified with air at 31 K to 3 888 kg / h. The energy to vaporise it is obtained by circulating the liquid through the reaction product condenser and is supplied indirectly by means of water vapor in the feed device. The energy consumption in the form of steam is 0.51 GJ / h. The resulting gaseous mixture is passed through a crystalline silver catalyst bed at 863 K. The reaction mixture is cooled down indirectly by the liquid circulating between the reactor and the degree of rectification separation of unreacted methanol from the product. At 415 K, the cooled reaction mixture passes through the condenser reaction gases and the degree of absorption. In a condensation absorption system, a water content of 2728 kg / h of unreacted methanol is washed out of the off-gas which is exhausted from the process to the atmosphere by means of a turbocharger. In the condensation absorption system, 7,871 kg / formaldehyde content of 27% by weight is obtained. and 25.4% by weight methanol, the availability of rectification separation of unreacted methanol is afforded. This technological step consists of a cooker, a column cell with a total of eight theoretical equilibrium stages, a condenser and a vacuum pump. The rectification takes place at an absolute pressure of 45 kPa, measured at the outlet of the distillation vapor to the condensation reflux device formed by the pump. At the indicated pressure, the liquid ratio was 3.5 and the solution was separated by 2,013 kg / l of methanol with a water content of 3.72 ppm. wt. % and formaldehyde 0.92% by weight and to 5,806 kg / h of a product with formaldehyde content of 37% by weight. and 0.91% by weight of methanol. The remainder of 52 kg / h is in the form of a vapor volume of 45.9 Nm 3 which passes through the pump to the absorption available or to the gas mixture preparation stage. The pump sucks 33.4 Nm < 3 > / l of the vapor and the condensation reflux device and the remainder of the control air throughput of the vapor flow. The energy for the operation of the rectification stage is obtained by circulating the vaporized solution between the fifth column and the reactor and supplying the cooker indirectly with steam. The energy consumption in the form of steam is 3.6 GJ / h. The consumption of methanol per tonne of product produced is 443 kg. It follows from the above examples that by displacing the gas at 1: 66.10 -2 Nm @ 3 in a 1 kilogram distribution of the dispersed mixture, the step of rectifying the recovered unreacted recycle methanol process takes place in the step of refining the energy in the stage to prepare a gaseous mixture of 0.11 GJ / h in the step of rectifying the unreacted methanol from the product at 1.9 GJ / h. Also, with regard to the lower formaldehyde content of the recycled methanol, the catalytic process selectivity increases by 3 kg of methanol consumption per tonne of product produced. OBJECT OF THE METHOD OF PRODUCING formaldehyde by oxidative dehydrogenation of methanol on a silver catalyst with the recycling of unreacted methanol, characterized in that in the step of separating unreacted methanol from the product, methanol, formaldehyde and water containing from 12 to 33% by weight of methanol are acted upon at an absolute pressure from 10 to 101.3 kPa, gas from 3.3. 10 ~ 4 to 0.33 Nm3 converted to one kilogram divided into the recycled unreacted methanol process.