DD299354A7 - METHANOL WATER MIXTURES FOR THE FORMALDEHYDE MANUFACTURE IN CYCLES - Google Patents

Abstract

The invention relates to a process for the evaporation of methanol-water mixtures without interfering enrichment of impurities. The technical object of the invention is to develop a process which prevents the evaporation of methanol-water mixtures, the enrichment of low-volatility impurities without unwanted by-products or wastewater incurred. According to the invention, the object is achieved in that a part of the bottom product of the evaporator is constantly withdrawn by means of a pump and pressed by means of a suitable filter, with all the suspended solids being retained. The majority of the filtrate is returned to the sump, a small part in the absorption system of formalin plant. The process enables a stable evaporation of methanol-water mixtures for a working period of at least 2,000 hours without disturbing enrichment of volatile volatiles and without the production of liquid waste products. FIG {evaporation; Multicomponent mixture; methanol; Water; Circulation; Filter; Pollution; By-product; Enrichment; Sewage}

Description

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Field of application of the invention

The invention relates to a process for the evaporation of methanol-water mixtures for the production of formaldehyde in circulating evaporators without disturbing accumulation of impurities.

Characteristic of the known state of the art It is known that the silver crystal catalyst is sensitive to formalin production Impurities in the starting product is methanol. Further disturbing impurities can be removed from the process air and the Process water come. Heavy volatile impurities are rich in the evaporation of methanol or methanol Water mixtures in the evaporator sump. This can lead to disturbances in the evaporator, e.g. by encrusting the Heating surfaces, by increased corrosion or by changing the process parameters. As the concentration of contaminants increases, so does the risk of entraining these contaminants

and to the silver crystal contact. In order to limit these side effects, it is customary in such cases to withdraw a certain proportion of the evaporator sump contents continuously or discontinuously. This limits the accumulation to a certain value. The withdrawn liquid is either worked up or forms an undesirable

By-product. Another possibility (J. Fischer, CAV 71, H. 8, p. 47/48) is to pass a portion of the bottom product unfiltered in the bypass

passing the reactor into the absorption system of the formalin plant. As a result, however, the methanol content of the

Formalins increased. The bypass current is therefore limited to an acceptable level, so that no sufficient reduction in the Solids content is achieved. Arn end of the driving period, the end product is therefore increasingly with solid from this Bypass current contaminated. According to DE-AS 1294359 and DE-AS 2114 370 it is known impurities in the starting products (air and / or Methanol) for the production of formaldehyde, i.a. by distillation, separation and separation. In a further DE-AS 2126798 a method is described in which the evaporator operates as a distillation stage. In this case, a portion of the methanol is driven by passing air, the rest, which Verunrelnigungervhälthält becomes

completely removed and worked up separately.

Ee is well known that the impurities in the starting products of formaldehyde production after the Silver crystal process interfere with the catalyst and / or the parts of the apparatus. The in the aforementioned publications

However, solutions described only lead to partial results. So they are to achieve a much longer

Operating time of the evaporator and the catalyst is not suitable. Object of the invention

The object of the invention is to develop a process for the evaporation of Me'.hanol-water mixtures for formaldehyde production in circulation evaporators, which allows a long operating time of both the evaporator and the catalyst of a Formalinaniage the silver crystal process without ec by low volatility Impurities in the raw materials to noticeable loss of effectiveness comes.

Explanation of the essence of the invention

The technical object of the invention is to develop a process for the evaporation of methanol-water mixtures for formaldehyde production in circulation evaporators, which limits the accumulation of heavy or nichtflücl.tiger impurities in the evaporator for methanol or methanol-water mixture and entrainment prevents harmful amounts of these impurities in the reactor of a formalin plant.

According to the invention, this object is achieved in that a portion of the bottom product of the evaporator is constantly withdrawn by means of a pump and pressed through a suitable filter, wherein all suspended solids are retained. The

Main amount of the filtered bottoms product gets into the sump lurück, while a small amount in the absorber system

the formalin plant is transferred. In this case, the insoluble constituents are removed by the filtration and with the

Feed the small amount of filtrate into the absorption system to remove the low-volatility impurities in the methanol

limited harmless content.

In the case of sodium evaporators, the filtration system is operated in the bypass of the natural circulation, whereby the partial flow to be filtered

should not exceed 10% of natural circulation. In forced circulation evaporators either the filter is installed in forced circulation or a separate circuit with pump and filter created.

The filtration reduces the required amount which must be conveyed as a bypass into the absorption system. The Degree of reduction depends on the nature of the impurities. The amount should not exceed 1% of the evaporation

included amount of methanol.

The supply of this small amount according to the invention exerts no adverse effect on the quality of the product

reduces the seizure of volatile waste products in addition to the expenditure on equipment and energy. The average

Methanol content is not increased because the additional feed by improving the degree of conversion and thus

lower content of methanol in the reaction gas is compensated.

embodiment The invention will be explained below by way of example. The accompanying drawing shows a flow chart of the

inventive method.

The evaporator is in this example a circulation evaporator with natural circulation. The separator 11st over the Circulation line 3 connected to the circulation evaporator 2. From the head of the circulation evaporator 2, the line 4 leads into the Separator 1 back. The vapors pass via line 5 to the reactor Formalinanlage after mixed via line 6, the reaction air

has been. About feed 7 is constantly fed methanol-water mixture. From the circulation line 3 is a

Partial flow by means of pump 8 is pressed through the filter 9 and passes back via line 10 in the circulation line 3. A

small amount passes via line 11 into the absorption system of the formalin plant.

In the evaporation of 3000kg methanol-water mixture (67% methanol) are 9OmVh liquid in circulation. With

of the pump 8 are pressed from it 2.5 m '/ h over the filter for cleaning. Of the purified mixture 0.025m ³ to 0.050m ^{3 get} into the absorption system, the main part in the circulation back. From the methanol plant used so reach 6 to 12 kg, this corresponds to 0.3 to 0.6%, past the reactor in the absorption system. During a working period of 2000h.

There were no disturbances due to accumulation of impurities.

Claims (2)

A process for the evaporation of methanol-water mixtures for the production of formaldehyde in circulating evaporators, characterized in that the evaporator bottom product is withdrawn by means of pump (G), forced through a filter (9) and the main portion of the filtered mixture is returned to the circulation line (3), while a small amount, which may not contain more than 1% of the amount of methanol coming to evaporate, is fed to the absorption system of the formalin plant. 2. The method according to claim 1, characterized in that in natural circulation evaporators of the partial stream to be filtered should not exceed 10% of the calculated natural circulation, so as not to affect the latter.