CN212894525U - Device for preparing trioxymethylene by taking methanol as raw material - Google Patents

Abstract

The invention discloses a device for preparing trioxymethylene by taking methanol as a raw material, which consists of 4 systems, wherein a formaldehyde reactor and a formaldehyde absorption tower form a concentrated formaldehyde preparation working section; a trioxymethylene reactor, a trioxymethylene concentrating tower and a dealcoholization reaction rectifying tower form a concentrated trioxymethylene synthesis section; a membrane dehydration unit, a light component removal tower and a heavy component removal tower form a trioxymethylene separation and purification section; the dilute aldehyde recovery reaction rectifying tower and the trioxymethylene recovery rectifying tower are dilute aldehyde recovery working sections.

Description

Device for preparing trioxymethylene by taking methanol as raw material

Technical Field

The disclosure provides a device for preparing trioxymethylene by taking methanol as a raw material, and belongs to the field of chemical production processes.

Background

Polyoxymethylene (POM), also known as acetal resin and polyoxymethylene, is a thermoplastic engineering plastic with excellent comprehensive properties, is one of five major engineering plastics, is the closest metal material in mechanical properties of engineering plastics, and is known as "super steel" or "steel race". The main key monomer for producing polyformaldehyde is Trioxymethylene (TOX), a stable anhydrous formaldehyde polymer form, has wide application, can be used for preparing engineering plastic polyformaldehyde, and can also be used for replacing formaldehyde to prepare clean fuels, chemicals and fine chemicals.

According to the traditional trioxymethylene synthesis method, 50-65% of concentrated formaldehyde is used as a raw material, and trioxymethylene is synthesized under the action of a sulfuric acid catalyst. The reaction is a rapid reversible reaction, but the reaction equilibrium constant is small, the conversion rate of formaldehyde is low, and only trioxymethylene with the equilibrium composition of about 3% is obtained in the reaction liquid, so that the reaction conversion rate is improved by adopting reaction rectification. However, trioxymethylene, water, formaldehyde can form the lowest azeotrope, e.g., at 100 kPa, the azeotropic composition is trioxymethylene 69.5 wt%, formaldehyde 5.4 wt%, water 25.1 wt%. The azeotrope is separated by azeotropic distillation, and an entrainer is added in the azeotropic distillation process, so that trioxymethylene, water, formaldehyde and the entrainer form a new minimum azeotrope, and when the azeotropic distillation is carried out, the new azeotrope is evaporated out at the top of the tower, and the solution with higher purity of trioxymethylene is obtained at the bottom of the tower. The commonly used entrainers are benzene and dichloroethane, and the entrainer is recycled in production. The extraction and rectification are used for breaking through the azeotropic composition to extract the content of the trioxymethylene, and then refining is carried out through the working sections of dealcoholization and extraction agent removal, and the trioxymethylene is obtained.

The traditional trioxymethylene synthesis process mainly has the following problems: the sulfuric acid catalyst has serious corrosion to equipment, the product is difficult to separate from the catalyst, and the product is complicated to separate; the continuous production stability of the formaldehyde synthesis and formaldehyde concentration units is poor, the full-load operation is difficult, and the energy consumption is high; the trioxymethylene monomer reaction system has low conversion rate, a recovery system has large load, the extraction effect is poor, the steam consumption is large, and the impurity content exceeds the standard. For this reason, continuous improvements are being made in the relevant manufacturing enterprises and research institutions.

The pan-tilt plastics corporation in the patent CN1078591C (published 2002, 1/30) uses a substance having ion exchange ability to remove metal impurities in an aqueous formaldehyde solution, and then carries out trioxymethylene synthesis using a solid acid catalyst. The catalytic process replaces the traditional trioxymethylene synthesis catalyst with sulfuric acid with extremely strong corrosiveness.

In order to solve the difficulty that the separation difficulty of the trioxymethylene, water and formaldehyde azeotropic system is large, different patents adopt different separation schemes.

Trioxymethylene is obtained by separation by a crystallization separation process in both a patent CN100528861C (2009, 8, 19 days) of yunnan chemical corporation and a patent CN1273462C (2006, 9, 6 days) of basf corporation.

A process for producing trioxymethylene by pan-plastics corporation, CN1046717C (published Japanese 1994, 6/15), by an extraction separation process, and a synthetic separation process using a solvent having a boiling point lower than that of trioxymethylene and not forming an azeotrope with trioxymethylene as an extractant.

In CN10055426C (published 2009, 1 month and 28 days), basf corporation proposed a pressure swing distillation technology to separate trioxymethylene based on the residual curve of water, trioxymethylene and formaldehyde system. In addition, the basf company has made a great deal of effort in removing formic acid, and in US 2010/0270140 a1 (CN 101896478B), a process for removing formic acid by physical (adsorption) or chemical means (such as addition of tertiary amine or imine, conversion of formic acid into salt by catalyst, and removal of the formed salt at the bottom of the rectification column) is added to the conventional pressure swing distillation process.

Meanwhile, researchers continuously optimize the full-process synthesis process of trioxymethylene, the technology of Yizhenpurization science and technology Limited in Ordos, CN106317012A (published as 2017, 1, 11) discloses that one of methanol or methylal and paraformaldehyde are used as raw materials, under the action of a solid acid catalyst, part of depolymerized paraformaldehyde participates in a reaction to generate polymethoxy dimethyl ether, the unreacted part produces trioxymethylene, and then the purified trioxymethylene is obtained through extraction, rectification and separation. The method has the advantages of low equipment corrosion, low equipment material requirement and less side reaction.

JP2014024754A (published as 2014, 2.6.d) by Baoli plastics discloses a process for preparing trioxymethylene from anhydrous formaldehyde in gas phase, which comprises reacting aqueous formaldehyde solution with higher alcohol to obtain hemiacetal, separating and dehydrating the hemiacetal, thermally decomposing the hemiacetal to obtain anhydrous formaldehyde in gas phase, and preparing trioxymethylene by using a solid acid catalyst.

A technology for preparing trioxymethylene by using an extraction catalytic tower is disclosed by Kery environmental protection science and technology, Inc. in CN109180636A (1/11 in 2019), methylal, methanol or dimethyl ether and air are oxidized to generate high-concentration formaldehyde, the high-concentration formaldehyde is reacted and separated by using the extraction catalytic tower to obtain a trimerization product, and the trimerization product is extracted, separated and rectified in sequence to obtain the trioxymethylene.

An apparatus and method for continuously preparing trioxymethylene including a reaction and concentration system, a crystallization system and a refining system is disclosed in CN106749164A (published 2017, 5-31), by suzhou double-lake chemical technology ltd. Under the action of a catalyst, reacting the raw material concentrated formaldehyde to generate trioxymethylene, and concentrating the trioxymethylene into a 63% trioxymethylene solution through a concentration tower; the crystallization system is used for concentrating 63% trioxymethylene solution into 93% trioxymethylene solution by a crystallization method; the refining system has the main function of refining 93 percent trioxymethylene solution into 99.9 percent trioxymethylene solution.

The above has the following problems:

first, due to the low equilibrium conversion for trioxane synthesis, a large amount of free formaldehyde is present in the trioxane solution during the separation. Free formaldehyde will condense and polymerize with water, methanol and formaldehyde itself to form hemiacetals, acetals and formaldehyde polymers. The relative volatility of partial hemiacetal, acetal, polymer of formaldehyde and trioxymethylene are similar and cannot be separated by common separation methods. The prior art generally adopts crystallization or extraction method to carry out primary separation on a synthetic product, and refining by rectification, but trioxymethylene with ultra-purity or nearly 100% purity still cannot be obtained, and simultaneously, new solvent is introduced into the extraction process, so that the separation system is more complicated, the energy consumption and the dilute aldehyde recovery are difficult, and a separate dilute aldehyde recovery unit is often needed for recovery.

Secondly, for the existing and the above-mentioned trioxymethylene preparation processes, the difficulties of large amount of dilute formaldehyde and high recovery energy consumption exist, for example, about 15% of dilute formaldehyde of about 4 tons can be generated when 1 ton of trioxymethylene is produced, 7-8 tons of steam can be consumed when 1 ton of trioxymethylene is produced, and the steam used for recovering the dilute formaldehyde accounts for more than 70%.

Since formaldehyde has a high affinity for water, in an aqueous formaldehyde solution, which exists mainly in the form of formaldehyde hydrate, formaldehyde is first combined with a polar solvent in water to produce methylene glycol.

In the aqueous formaldehyde solution, the mutual conversion between the methyl glycol and various multi-formaldehyde hydrates with different polymerization degrees is carried out.

Under different formaldehyde concentrations and temperatures, the distribution of the multi-formaldehyde hydrates with different polymerization degrees has a certain amount of long-chain multi-formaldehyde hydrates even in a low-concentration formaldehyde solution, and a 30% formaldehyde aqueous solution can be turbid when stored at room temperature, because the multi-formaldehyde hydrates with large polymerization degrees are easy to precipitate. Therefore, dehydration of the formaldehyde solution is a complex physical and chemical process, which results in great energy consumption of the scheme for recovering the dilute aldehyde by rectification.

Thirdly, the aqueous formaldehyde solution undergoes a disproportionation reaction (Cannizzaro) in the presence of a catalyst to produce methanol and formic acid.

Formaldehyde may also form methyl formate in one step by the Tischenko reaction.

Therefore, by-products such as methanol, formic acid, methyl formate and the like exist in the synthesis process of the trioxymethylene, particularly, hemiacetal is easily formed between the methanol and the formaldehyde, the separation difficulty is high, but if the methanol is not separated, the methanol is accumulated in a system, and the production rate of the trioxymethylene is reduced.

Fourthly, when the technology of recovering the dilute aldehyde by adopting the rectification method is adopted, the formaldehyde solution is continuously heated, so that the formaldehyde is subjected to disproportionation reaction (Cannizzaro) to generate methanol and formic acid, and the formic acid has extremely strong corrosivity to cause equipment corrosion, so that the rectification tower for recovering the dilute aldehyde cannot be used for a long time.

In summary, the prior patent technology is only optimized and improved from the aspects of catalysts, separation processes and preparation processes, and still cannot solve the key problems of large recovery amount of dilute aldehyde, more byproducts, difficult recovery and utilization, high energy consumption, high requirement on equipment materials and the like which restrict the trioxymethylene production for a long time.

Disclosure of Invention

The present disclosure is directed to overcoming the above problems in the prior art and providing an apparatus for preparing trioxymethylene using methanol as a raw material. The method utilizes multiple reaction rectification and combines multiple internal circulation process routes, can reduce the yield of dilute aldehyde, reduce the separation energy consumption, reduce the impurity content of trioxymethylene, and convert the dilute aldehyde and byproducts into formaldehyde to generate raw materials through catalysis, and circulate the raw materials to a formaldehyde synthesis unit, thereby improving the utilization rate of the raw materials, simultaneously carrying out catalytic conversion, reducing the types of the byproducts, leading no byproducts to be sent out except water in the whole process, and realizing the green, environment-friendly and long-period stable operation of the trioxymethylene production.

In order to achieve the above object, the present disclosure provides a device for preparing trioxymethylene, comprising a concentrated formaldehyde preparation section, a concentrated trioxymethylene synthesis section, a trioxymethylene separation and purification section, and a dilute aldehyde recovery section, wherein:

(1) concentrated formaldehyde preparation: comprises a formaldehyde reactor and a formaldehyde absorption tower;

(2) concentrated trioxymethylene synthesis section: comprises a trioxymethylene synthesis reactor, a trioxymethylene concentration tower and a dealcoholization reaction rectifying tower;

(3) a trioxymethylene separation and purification section: comprises a membrane dehydration unit, a light component removal tower and a heavy component removal tower;

(4) a dilute aldehyde recovery section: comprises a dilute aldehyde recovery reaction rectifying tower and a trioxymethylene recovery rectifying tower.

In a preferred embodiment, in the concentrated formaldehyde preparation section, the discharge port of the formaldehyde reactor is connected with the feed port of the formaldehyde absorption tower, and the discharge port of the formaldehyde absorption tower is connected with the feed port of the trioxymethylene synthesis reactor.

The formaldehyde reactor may use an oxidation catalyst in which the effective metal element is one or more of iron, molybdenum, bismuth, chromium, tungsten, cobalt, nickel, which oxidizes one or a mixture of methanol or methylal to formaldehyde.

In a preferred embodiment, in the concentrated trioxymethylene synthesis section, the discharge port of the trioxymethylene synthesis reactor is connected with the feed port of a trioxymethylene concentrating tower; the trioxymethylene concentrating tower is provided with two discharge ports, one is connected with a feed port of the membrane dehydration unit, and the other is connected with a feed port of the dealcoholization reaction rectifying tower.

In a preferred embodiment, in the concentrated trioxymethylene synthesis section, the trioxymethylene synthesis reactor is a separate tank reactor or a fixed bed reactor or a fluidized bed reactor, and is integrated with the rectifying tower and is arranged in the rectifying tower tank or the rectifying tower.

In a preferred embodiment, the bottom of the trioxymethylene synthesis reactor is provided with a discharge port which can discharge part of reactants to reduce the content of formic acid in the reactor; or partial deactivated cyclizing catalyst can be discharged, and a cyclizing catalyst replenishing port is arranged at the inlet of the trioxymethylene synthesis reactor. The cyclization catalyst is preferably an acidic catalyst, the acidic catalyst is preferably a solid acid catalyst, and the solid acid catalyst is one or a mixture of more of resin, a molecular sieve, a supported ionic liquid and alumina.

In a preferred embodiment, in the concentrated trioxymethylene synthesis section, the trioxymethylene concentration column is provided with a methanol feed inlet.

In a preferred embodiment, in the concentrated trioxymethylene synthesis section, the trioxymethylene concentration column is a plate column, a divided wall column, or a packed column.

In a preferred embodiment, in the concentrated trioxymethylene synthesis section, the dealcoholization catalyst of the dealcoholization reaction rectifying tower is one or a mixture of several of resin, molecular sieve, supported ionic liquid and alumina. The reactor of the dealcoholization reaction rectifying tower can be an independent kettle type reactor or a fixed bed reactor or a fluidized bed reactor, and is also combined with the rectifying tower into a whole to be arranged in the rectifying tower kettle or the rectifying tower.

In a preferred embodiment, in the trioxymethylene separation and purification section, the membrane dehydration unit has two discharge ports, one is connected with a feed port of a light component removal tower, and the other is connected with a feed port of a dilute aldehyde recovery reaction rectifying tower; the light component removal tower is provided with two discharge ports, one discharge port is connected with a feed port of the dilute aldehyde recovery reaction rectifying tower, and the other discharge port is connected with a feed port of the heavy component removal tower; the de-heavy tower is provided with two discharge ports, one discharge port is used for obtaining pure trioxymethylene material flow, and the other discharge port is connected with a feed port of the dilute aldehyde recovery reaction rectifying tower.

In a preferred embodiment, the light ends and heavy ends removal column is a tray column, a dividing wall column or a packed column.

In a preferred embodiment, in the trioxymethylene separation purification section, the membrane used in the membrane dehydration unit is a water-permeable molecular sieve membrane, a polymeric membrane or an organic-inorganic hybrid membrane.

In a preferred embodiment, in the trioxymethylene separation purification section, a methanol feed port is increased in the membrane dehydration unit.

In a preferred embodiment, in a dilute aldehyde recovery section, the discharge port of the dilute aldehyde recovery reaction rectifying tower is connected with a trioxymethylene recovery rectifying tower; the top of the trioxymethylene recovery rectifying tower is circulated to the feed inlet of the trioxymethylene concentrating tower, and part of the tower kettle is circulated to the formaldehyde absorption tower.

In a preferred embodiment, the reactor of the dilute aldehyde recovery reaction rectifying tower can be a separate kettle type reactor or a fixed bed reactor or a fluidized bed reactor, and is also integrated with the rectifying tower and is arranged in the kettle of the rectifying tower or the rectifying tower. When a kettle type device is adopted and the device is placed in a kettle of a dilute aldehyde recovery reaction rectifying tower, the dosage of the catalyst is 0.1-20% of the reaction liquid. A dilute aldehyde conversion catalyst is used in the dilute aldehyde recovery reaction rectifying tower, and preferably an acidic catalyst is used, wherein the acidic catalyst comprises one or a mixture of more of a molecular sieve, a supported ionic liquid, resin and alumina.

Adopt this disclosed advantage to lie in: multiple internal circulations are adopted, so that the utilization rate of raw materials is improved, and the aims of energy conservation, emission reduction and green synthesis are fulfilled.

The process of the application hardly produces zero emission, does not adopt any other solvent, only has methanol and air as feed materials, and has water and trioxymethylene as discharge materials, and the whole system does not discharge any by-products or wastes except partial water.

Drawings

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the disclosure and together with the description serve to explain the principles of the disclosure.

FIG. 1 is a schematic view of an exemplary embodiment of an apparatus for preparing trioxymethylene according to the present disclosure;

reference numerals: v0101, an evaporator; r0101, a formaldehyde reactor; t0101, a formaldehyde absorption tower; r0201, a trioxymethylene synthesis reactor; t0201, a trioxymethylene concentrating tower; r0202, a dealcoholization reaction rectifying tower; m0301, a membrane dehydration unit; t0301, a light component removal tower; t0302, a heavy component removal tower; r0401, a dilute aldehyde recovery reaction rectifying tower; r0402, and a trioxymethylene recovery rectifying tower.

Detailed Description

The present disclosure will be described in further detail with reference to the drawings and embodiments. It is to be understood that the specific embodiments described herein are for purposes of illustration only and are not to be construed as limitations of the present disclosure. It should be further noted that, for the convenience of description, only the portions relevant to the present disclosure are shown in the drawings.

A device for preparing trioxymethylene comprises 4 systems, wherein a formaldehyde reactor R0101 and a formaldehyde absorption tower T0101 form a concentrated formaldehyde preparation working section; a concentrated trioxymethylene synthesis section is formed by a trioxymethylene reactor R0201, a trioxymethylene concentrating tower T0201 and a dealcoholization reaction rectifying tower R0202; the membrane dehydration unit M0301, the light component removal tower T0301 and the heavy component removal tower T0302 form a trioxymethylene separation and purification section; the dilute aldehyde recovery reaction rectifying tower R0401 and the trioxymethylene recovery rectifying tower R0402 are dilute aldehyde recovery sections.

In the preparation working section of the concentrated formaldehyde, a mixture of methanol and methylal is changed into a gas phase through an evaporator V0101, then enters a formaldehyde reactor R0101 and is mixed with air (material 1) with the mass flow of 1825Kg/h to generate the formaldehyde at the temperature of 280 ℃ and the normal pressure under the action of an iron-molybdenum oxidation catalyst, and a penetrating fluid material flow absorbs the formaldehyde in a formaldehyde absorption tower T0101 to obtain a concentrated formaldehyde water solution material flow with the formaldehyde concentration of 56.98%.

In the concentrated trioxymethylene synthesis section, a macroporous resin acid catalyst is pre-loaded in a trioxymethylene synthesis reactor R0201, and the acid catalyst is usedThe dosage of the agent is 10 percent of the mass of the reaction liquid, the reaction temperature is 105 ℃, the pressure is normal pressure, 60.50 percent of concentrated formaldehyde aqueous solution material flow quickly reaches the reaction balance under the action of an acid catalyst, and the reaction moves to the positive reaction direction because the concentration of trioxymethylene in heavy gas phase of the reactor is more than that of liquid phase trioxymethylene, and gas phase materials are extracted from an outlet. The gas phase material flow of the trioxymethylene synthesis reactor R0201 consists of methanol 0.83%, methylal 0.15%, CH₃O(CH₂O)₂CH₃Content 0.2%, CH₃O(CH₂O)₃CH₃0.1 percent of trioxymethylene, 18.47 percent of trioxymethylene, 37.22 percent of formaldehyde and 43.03 percent of water. Mixing the gas phase material flow of a trioxymethylene synthesis reactor R0201 and the trioxymethylene aqueous solution material flow, separating by a concentration tower T0201, wherein the number of tower plates of the concentration tower is 10, the reflux ratio is 2, and obtaining the material flow of concentrated trioxymethylene mixture trioxymethylene concentrated solution at the tower top, wherein the material flow comprises 1.40% of methanol, 0.42% of methylal and CH₃O(CH₂O)₂CH₃Content 0.45%, CH₃O(CH₂O)3CH₃0.06 percent of formaldehyde, 67.31 percent of trioxymethylene, 7.34 percent of formaldehyde and 23.01 percent of water. The aqueous formaldehyde solution is obtained in the bottom of the column and contains 0.46 percent of methanol and CH₃O(CH₂O)₂CH₃Content 0.06%, CH₃O(CH₂O)₃CH₃0.11 percent of formaldehyde 47.91 percent and 51.47 percent of water. The aqueous solution of formaldehyde flows through a dealcoholization reaction rectifying tower R0202, the number of tower plates of the dealcoholization reaction rectifying tower is 8, the reflux ratio is 1.5, the temperature is 110 ℃, the pressure is 0.05Mpa, and the catalyst is SiO₂/Al₂O₃ZSM-5 molecular sieve catalyst of 30, and a mixed material flow is obtained at the top of the tower, and the component of the mixed material flow is that the methylal content is 100.00 percent; part of dealcoholized formaldehyde aqueous solution obtained at the bottom of the tower is recycled to a trioxymethylene synthesis reactor R0201, the components of the dealcoholized formaldehyde aqueous solution are 48.04 percent of formaldehyde and 51.96 percent of water, and the rest dealcoholized formaldehyde aqueous solution material flow enters a dilute aldehyde recovery system.

In the trioxymethylene separation and purification section, in a membrane dehydration unit M0301, the material flow of the trioxymethylene concentrated solution passes through a NaA molecular sieve membrane permeation gasification membrane, the dehydration temperature is 120 ℃, the pressure of the retentate side is 0.2MPa, the pressure of the permeate side is-0.098 MPa, and the material flow is obtained at the permeate sideA stream of a highly concentrated trioxymethylene mixture having a composition of methanol 1.00%, methylal 0.23%, CH₃O(CH₂O)₂CH₃Content 0.60%, CH₃O(CH₂O)₃CH₃0.08 percent of formaldehyde, 85.71 percent of trioxymethylene, 4.34 percent of formaldehyde and 8.05 percent of water. On the retentate side, a permeate stream is obtained, based on water, with a composition of methanol 2.62%, methylal 1.01%, trioxymethylene 12.13%, formaldehyde 16.36%, and water 67.88%. Separating by a lightness-removing column T0301 to obtain a light boiling impurity material flow at the top of the column, wherein the light boiling impurity material flow comprises 3.33 percent of methanol, 0.75 percent of methylal and CH₃O(CH₂O)₂CH₃Content 1.60%, CH₃O(CH₂O)₃CH₃The content of 0.05 percent, the trioxymethylene 52.97 percent, the formaldehyde 14.47 percent, the water 26.83 percent, the number of tower plates of the light component removing tower is 12, and the reflux ratio is 1. The trioxymethylene material flow containing a small amount of heavy boiling impurities is obtained in the tower bottom, and the composition of the trioxymethylene material flow is CH₃O(CH₂O)₂CH₃Content 0.17%, CH₃O(CH₂O)₃CH₃The content is 0.09 percent, and the trioxymethylene is 99.74 percent. Separating with a de-heavy tower T0302 to obtain pure trioxymethylene material flow with 100% trioxymethylene content at the tower top and heavy boiling impurity material flow at the tower bottom, wherein the pure trioxymethylene material flow comprises the trioxymethylene 68.97% and CH₃O(CH₂O)₂CH₃Content 20.69%, CH₃O(CH₂O)₃CH₃The content is 10.34 percent, the tower plate number of the heavy component removing tower is 15, and the reflux ratio is 2.

In the dilute aldehyde recovery section, mixing material flow, formaldehyde water solution material flow, penetrating fluid material flow taking water as a main component, light boiling impurity material flow, heavy boiling impurity material flow and methanol material flow to obtain dilute aldehyde recovered material flow, passing through a dilute aldehyde recovery reactive distillation column R0401, wherein the number of tower plates of the reactive distillation column is 18, the reflux ratio is 2, the temperature is 120 ℃, the pressure is 0.05MPa, and the catalyst is SiO₂/Al₂O₃ZSM-5 molecular sieve catalyst at 10, yielded at the top a recycle stream of formaldehyde and methylal azeotrope (stream 16) with a composition of methylal content 88.00% and methanol content 12.00%. Obtaining a water material flow with the water content larger than that of trioxymethylene in the tower kettle, separating the water material flow by a trioxymethylene recovery rectifying tower R0402, and obtaining the trioxymethylene at the tower topAnd (3) circulating the trioxymethylene aqueous solution material flow with the formaldehyde content of 70% to an inlet of the T0201 trioxymethylene concentrating tower. 100 percent of water flow is obtained in the tower kettle, and part of the water flow is circulated to the formaldehyde absorption tower T0101.

Through the device, compared with the trioxymethylene prepared by the prior art, the purity of the trioxymethylene is obviously improved, the advancement of the trioxymethylene is also reflected in that the utilization rate of a methanol raw material reaches more than 98 percent, and no dilute aldehyde wastewater is generated.

In the description herein, reference to the description of the terms "one embodiment/mode," "some embodiments/modes," "example," "specific example," or "some examples," etc., means that a particular feature, structure, material, or characteristic described in connection with the embodiment/mode or example is included in at least one embodiment/mode or example of the application. In this specification, the schematic representations of the terms used above are not necessarily intended to be the same embodiment/mode or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments/modes or examples. Furthermore, the various embodiments/aspects or examples and features of the various embodiments/aspects or examples described in this specification can be combined and combined by one skilled in the art without conflicting therewith.

It will be understood by those skilled in the art that the foregoing embodiments are merely for clarity of illustration of the disclosure and are not intended to limit the scope of the disclosure. Other variations or modifications may occur to those skilled in the art, based on the foregoing disclosure, and are still within the scope of the present disclosure.

Claims (10)

1. The device for preparing trioxymethylene is characterized by comprising a concentrated formaldehyde preparation working section, a concentrated trioxymethylene synthesis working section, a trioxymethylene separation and purification working section and a dilute formaldehyde recovery working section, wherein:

(1) concentrated formaldehyde preparation: comprises a formaldehyde reactor (R0101) and a formaldehyde absorption tower (T0101);

(2) concentrated trioxymethylene synthesis section: comprises a trioxymethylene synthesis reactor (R0201), a trioxymethylene concentrating tower (T0201) and a dealcoholization reaction rectifying tower (R0202);

(3) a trioxymethylene separation and purification section: comprises a membrane dehydration unit (M0301), a lightness-removing tower (T0301) and a heavies-removing tower (T0302);

(4) a dilute aldehyde recovery section: comprises a dilute aldehyde recovery reaction rectifying tower (R0401) and a trioxymethylene recovery rectifying tower (R0402).

2. The apparatus according to claim 1, wherein in the concentrated formaldehyde preparation section, the outlet of the formaldehyde reactor (R0101) is connected to the inlet of a formaldehyde absorption column (T0101), and the outlet of the formaldehyde absorption column (T0101) is connected to the inlet of a trioxymethylene synthesis reactor (R0201).

3. The apparatus according to claim 1, characterized in that in the concentrated trioxymethylene synthesis section, the discharge port of said trioxymethylene synthesis reactor (R0201) is connected to the feed port of the trioxymethylene concentration column (T0201); the trioxymethylene concentrating tower (T0201) is provided with two discharge ports, one discharge port is connected with a feed port of the membrane dehydration unit (M0301), and the other discharge port is connected with a feed port of the dealcoholization reaction rectifying tower (R0202).

4. The apparatus according to claim 1, characterized in that in the concentrated trioxymethylene synthesis section, the trioxymethylene synthesis reactor (R0201) is a separate tank reactor or a fixed bed reactor or a fluidized bed reactor.

5. The apparatus according to claim 1, characterized in that in the concentrated trioxymethylene synthesis section, the trioxymethylene concentrating column (T0201) is provided with a methanol feed inlet.

6. The apparatus according to claim 1, characterized in that in the concentrated trioxymethylene synthesis section, the trioxymethylene concentrating column (T0201) is a plate column, a dividing wall column or a packed column.

7. The plant according to claim 1, characterized in that in the trioxymethylene separation and purification section, the membrane dehydration unit (M0301) has two discharge ports, one connected to the feed port of the lightness-removing column (T0301) and the other connected to the feed port of the dilute aldehyde recovery reaction rectification column (R0401); the light component removal tower (T0301) is provided with two discharge ports, one discharge port is connected with a feed port of the dilute aldehyde recovery reaction rectifying tower (R0401), and the other discharge port is connected with a feed port of the heavy component removal tower (T0302); the de-heavy tower (T0302) has two discharge ports, one of which obtains pure trioxymethylene material flow, and the other of which is connected with the feed port of the dilute aldehyde recovery reaction rectifying tower (R0401).

8. The apparatus according to claim 1, wherein in the trioxymethylene separation purification section, the membrane used in the membrane dehydration unit (M0301) is a water-permeable molecular sieve membrane, a polymeric membrane or an organic-inorganic hybrid membrane.

9. The apparatus according to claim 1, characterized in that in the trioxymethylene separation purification section, a methanol feed inlet is added in the membrane dehydration unit (M0301).

10. The apparatus according to claim 1, characterized in that in the dilute aldehyde recovery section, the discharge port of the dilute aldehyde recovery reaction rectifying column (R0401) is connected with a trioxymethylene recovery rectifying column (R0402); the top of the trioxymethylene recovery rectifying tower (R0402) is circulated to the feed inlet of the trioxymethylene concentrating tower (T0201), and the bottom of the tower is partially circulated to the formaldehyde absorption tower (T0101).

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