KR102827947B1 - Reactor and Production Facilities for 1,3,5-trioxane in Polyoxymethylene Manufacturing Process - Google Patents

Abstract

The present invention relates to a reactor for efficiently reacting formalin to produce 1,3,5-trioxane in a process for producing polyoxymethylene, and a trioxane production facility including the reactor.
The trioxane reactor (10) according to the present invention maintains high pressure and temperature and increases the mixing efficiency of formalin and a catalyst to produce trioxane with a high yield in terms of space and time, reduces side reactions to increase the production amount of trioxane, and prevents local overheating in the reboiler (12) and suppresses clogging of the tube, enabling continuous operation for a long period of time.
In addition, the trioxane production facility (100) suppresses the catalyst in the trioxane reactor (10) from leaking to the next stage, thereby reducing corrosion of the facility, and the low-temperature, high-concentration formalin supplied from the formalin supply source (S1) and the high-temperature, low-concentration formalin recovered from the trioxane distillation tower (20) are combined with the reaction mixture circulating through the main body (11) and reboiler (12) of the trioxane reactor (10) and supplied to the trioxane reactor (10), thereby enabling the production of trioxane at an optimal reaction concentration and temperature.

Description

{Reactor and Production Facilities for 1,3,5-trioxane in Polyoxymethylene Manufacturing Process}

The present invention relates to a reactor for efficiently reacting formalin in a process for producing polyoxymethylene to produce 1,3,5-trioxane (hereinafter referred to as “trioxane”), and a trioxane production facility including the reactor.

Polyoxymethylene (POM), also known as polyacetal, is a type of engineering plastic that is widely used in automobile interior materials, key components of various electrical appliances, construction materials, toys, etc.

Polyoxymethylene is a polymer in which formaldehyde (CH ₂ O) molecules are continuously linked. If the polymer is made up of only formaldehyde molecules, it is a homopolymer ((-CH ₂ -O-)n), and if co-monomers with strong C-C bonds between formaldehyde molecules are randomly dispersed, it is a copolymer ((-CH ₂ -O-CH _{2 -CH 2 -O} -CH ₂ -O-)n).

Since the raw material formaldehyde is difficult to separate from impurities such as water and methanol, trioxane ((CH ₂ O) ₃ ) is produced by combining three formaldehyde molecules in a ring shape in the presence of an acid catalyst, and then the impurities are removed. Then, a crude polymer is formed by polymerizing with a co-monomer using a catalyst, and this is stabilized to obtain a polyoxymethylene copolymer.

In industrial sites, there are various processes including a formalin concentration process that concentrates 45% formalin to produce high-concentration formalin of 65-75%, a monomer process that heats high-concentration formalin in a trioxane reactor with an acid catalyst such as sulfuric acid to synthesize and purify trioxane, a polymerization process that polymerizes the purified trioxane with a comonomer such as dioxolane to produce a crude polymer, and a stabilization process that adds additives to stabilize the polymer terminals because the polymer has unstable terminal groups, and changes the chemical and physical properties appropriate to demand, before turning it into a product through a pellet process.

Among these processes, the process for synthesizing trioxane, a monomer of polyoxymethylene, is particularly important in terms of the production yield and purity of polyoxymethylene, and accordingly, research on methods for producing trioxane has been intensively conducted in conventional polyoxymethylene production technologies.

For example, in Korean Patent Publication No. 0893693, in order to improve the purity of trioxane, trioxane is synthesized by reacting 50-60% formalin with dichloroethane as an extraction solvent, DOP as a reaction buffer, and concentrated sulfuric acid as a catalyst, and in U.S. Patent Publication No. 3637751, in order to prevent clogging of a reboiler tube due to precipitation of paraformaldehyde, trioxane is manufactured by distilling an aqueous formaldehyde solution under the action of an acid catalyst in the presence of a monohydric alcohol and a diester of o-phthalic acid as an oil phase, and in U.S. Patent Publication No. 3310572, in order to improve the reactivity of trioxane, sulfuric acid as an acid catalyst and paraffinic oil as a stabilizer are added to 60-80% formalin. Mixing and distillation are used to manufacture trioxane, and in U.S. Patent Publication No. 3,732,252, in order to increase the conversion rate of trioxane, an soluble organic compound such as an alcohol, ether or ester having a dielectric constant of less than 40 is added to an aqueous formaldehyde solution in the presence of an acid catalyst of 25 to 80% and heated to synthesize trioxane, and in U.S. Patent Publication No. 4,110,298, in order to increase the conversion rate of trioxane, a monobutyl ether oily liquid of polyoxypropylene glycol is added to an aqueous formaldehyde solution in the presence of an acid catalyst to manufacture trioxane.

In the above inventions, it was estimated that the yield of trioxane, that is, the rate at which formaldehyde is converted into trioxane, is inversely proportional to the distillation rate. However, U.S. Patent Publication No. 3,470,208 states that the rate of decrease in yield is not as great as the rate of increase in distillation rate, and that the negative effect on the yield of trioxane due to the increase in distillation rate can be offset by recycling unreacted formaldehyde into the distillate.

Accordingly, in the above invention, a reaction mixture of trioxane and a nonvolatile strong acid catalyst is distilled to produce trioxane at a high productivity of about 150 g per hour or more per 1000 g of the mixture, and then the product is contacted with a basic compound such as an alkali metal carbonate, an alkaline earth metal oxide or an anion exchange resin, and impurities are removed through filtration, fractional distillation, etc. to recover high-purity trioxane at a high yield, and by increasing the distillation speed, the distillation yield decreases but the productivity of trioxane increases.

However, in order to increase the production of trioxane, the concentration of the reaction mixture, formalin and acid catalyst, must be kept as high as possible. High-concentration formalin precipitates and produces paraformaldehyde as a side reaction, which blocks the reboiler tube at the bottom of the trioxane reactor and hinders continuous operation. In addition, high-concentration acid catalyst increases side reactions and generates many impurities that hinder the polymerization reaction.

In addition, as the demand for polyoxymethylene increases day by day, it is essential to enlarge the production facilities for it, and among these, the trioxane reactor must be manufactured with an internal lining of acid-resistant glass to prevent corrosion by highly corrosive acid catalysts such as sulfuric acid, which increases the production cost. In addition, large-scale glass-lined reactors have many problems in transporting them from the manufacturing plant to the polyoxymethylene production facility, so several small reactors have to be installed in parallel, which increases the installation and operating costs at the production site.

Korean Patent Publication No. 10-2006-0043301: Continuous production method of 1,3,5-trioxane Korean Patent No. 10-1092220: Method for producing 1,3,5-trioxane

The present invention is intended to solve the above problems, and provides a method for continuously producing trioxane by reducing the installation and operation costs of a trioxane production facility in a polyoxymethylene manufacturing process, increasing the production yield, and preventing operation failures.

In order to solve the above problem, the present invention provides a trioxane reactor (10) including a main body (11) into which formalin and a catalyst are introduced and into which formalin is polymerized by heating to produce trioxane; a reboiler (12) which is installed integrally with the lower center of the main body (11) so as to be circulated and which heats a reaction mixture introduced from the main body (11) and returns it to the main body (11); a reboiler circulation pipe (L1) which has one end connected to the lower part of the main body (11) and the other end connected to the lower part of the reboiler (12) and which transports the reaction mixture of the main body (11) to the lower part of the reboiler (12); and a formalin recovery pipe (L2) which is connected to the reboiler circulation pipe (L1) and supplies high-concentration formalin and low-concentration formalin.

In addition, the present invention provides a trioxane production facility (100) including: the trioxane reactor (10); a trioxane distillation tower (20) in which gas flowing in from the upper portion of the main body (11) is separated into gas and liquid; a recovery pump (30) for transferring liquid from the lower portion of the trioxane distillation tower (20) to a formalin recovery pipe (L2); a cooler (40) for condensing gas discharged from the upper portion of the trioxane distillation tower (20); a reflux drum (50) for receiving a condensate condensed in the cooler (40); a reflux pump (60) for returning the condensate of the reflux drum (50) to the upper portion of the trioxane distillation tower (20); and a distillation tower upper pipe (L4) for transferring gas discharged from the upper portion of the trioxane distillation tower (20) to a crude polymerization process.

The trioxane reactor (10) according to the present invention maintains high pressure and temperature and increases the mixing efficiency of formalin and a catalyst to produce trioxane with a high yield in terms of space and time, reduces side reactions to increase the production amount of trioxane, and prevents local overheating in the reboiler (12) and suppresses clogging of the tube, enabling continuous operation for a long period of time.

In addition, the trioxane production facility (100) suppresses the catalyst in the trioxane reactor (10) from leaking to the next stage, thereby reducing corrosion of the facility, and the low-temperature, high-concentration formalin supplied from the formalin supply source (S1) and the high-temperature, low-concentration formalin recovered from the trioxane distillation tower (20) are combined with the reaction mixture circulating through the main body (11) and reboiler (12) of the trioxane reactor (10) and supplied to the trioxane reactor (10), thereby enabling the production of trioxane at an optimal reaction concentration and temperature.

Figure 1 is a schematic diagram of a trioxane reactor and production facility according to the present invention.
Figure 2 is a conceptual drawing showing a formalin recovery pipe (L2) connected to two reboiler circulation pipes (L1a, L1b).
Figure 3 is a conceptual drawing showing a steam header pipe (L6) and a steam tube (L7) for insulating the reboiler circulation pipe (L1).
Figure 4 is a drawing conceptually showing a mist separator (13) installed in the upper part of the inside of the main body (11) of a trioxane reactor (10).

Hereinafter, the present invention will be described in detail with reference to the attached drawings.

When adding reference signs to components of each drawing, it should be noted that identical components are given the same signs as much as possible even if they are shown on different drawings.

In addition, when describing the present invention, if it is determined that a detailed description of a related known configuration or function may obscure the gist of the present invention, the detailed description is omitted.

In FIG. 1, a trioxane reactor according to one embodiment of the present invention is indicated by reference numeral 10.

A trioxane reactor (10) comprises a main body (11) into which formalin and a catalyst (hereinafter referred to as “reaction mixture”) are introduced and the formalin is polymerized by heating to produce trioxane; a reboiler (12) which is installed integrally with the lower center of the main body (11) so as to be circulated, and which heats the reaction mixture introduced from the main body (11) and returns it to the main body (11); and a reboiler circulation pipe (L1) which has one end connected to the lower part of the main body (11) and the other end connected to the lower part of the reboiler (12) and transfers the reaction mixture of the main body (11) to the lower part of the reboiler (12).

In addition, the trioxane reactor (10) includes a formalin supply source (S1) that supplies high-concentration formalin to the main body (11) and a heat source (S2) that supplies a heat medium to the reboiler (12). The formalin supply source (S1) is supplied to the main body (11) through the reboiler (12) via the reboiler circulation pipe (L1), and the heat source (S2) is supplied to the outer space (shell side) of a tube built into the reboiler (12). It is preferable to use steam as the heat medium of the heat source (S2).

It is preferable to use an acid catalyst such as sulfuric acid as the above catalyst, and the interior of the main body (11) may be lined with titanium or zirconium instead of the conventional glass lining to prevent corrosion by the acid catalyst, thereby preventing cracks or breakage due to external impact.

High concentration of formalin generates side products such as paraformaldehyde in the process of generating trioxane by a catalyst, and these side products can block the reboiler circulation pipe (L1) and the tubes built into the reboiler (12). Therefore, it is preferable to install two or more reboiler circulation pipes (L1) and arrange the multiple reboiler circulation pipes (L1a, L1b) to face each other symmetrically with the reboiler (12) as the center (see FIG. 2).

If the temperature of the reboiler circulation pipe (L1) is lower than that of the reaction mixture flowing inside, by-products such as paraformaldehyde precipitate and attach to the inner wall of the pipe, so the outside of the reboiler circulation pipe (L1) is insulated to prevent this.

Conventionally, a steam jacket is installed on the outside of a reboiler circulation pipe (L1) to insulate the pipe using the high-temperature steam flowing inside the steam jacket. However, if the steam condenses inside the steam jacket and the condensate is not discharged smoothly, a hammering phenomenon occurs. The hammering phenomenon gives a strong impact to the pipe, causing deformation or damage to the pipe, which may hinder the circulation of the reaction mixture.

To solve this problem, steam tracing can be installed instead of a steam jacket. Steam tracing increases heat transfer efficiency by wrapping steam tubes, through which steam flows, so that they are in direct contact with the pipe, and the outside of the steam tubes is wrapped with insulating material to prevent heat from being lost to the outside. However, the steam temperature is high on the inlet side of the steam tracing where steam is supplied, so that the reboiler circulation pipes (L1a, L1b) are overheated, and as a result, the reaction mixture inside the pipe may evaporate due to local overheating. The evaporated steam interferes with the flow of the reaction mixture, which reduces the efficiency of the reboiler (12). On the outlet side where steam is discharged, the steam temperature is low, so that the insulating effect of the pipe is reduced, and by-products are precipitated and attached to the inner wall of the pipe, which interferes with the flow of the reaction mixture, thereby reducing the efficiency of the reboiler (12).

Accordingly, the outside of the reboiler circulation pipe (L1) is first wrapped with insulation material, and a ring type steam header pipe (L6) is installed on the outside of the insulation material, and several steam tubes (L7) are connected to the steam header pipe (L6) and wrapped around the outside of the insulation material, and then the outside of the steam tubes (L7) is wrapped again with insulation material to prevent the heat of the steam from being lost to the outside (see Fig. 3).

A steam header pipe (L6) is installed in each of a plurality of reboiler circulation pipes (L1a, L1b), and a plurality of steam header pipes (L6) can be installed above and below each reboiler circulation pipe (L1a, L1b). Steam in the steam header pipe (L6) is evenly supplied to the outside of the insulation material of the reboiler circulation pipe (L1a, L1b) through the steam tube (L7), so that local overheating or temperature drop of the reaction mixture in the reboiler circulation pipe (L1a, L1b) is prevented, enabling efficient operation of the reboiler (12).

In prior art documents, Korean Patent Publication No. 10-2006-0043301 and Korean Registration Patent No. 10-1092220, the reaction mixture of the trioxane reactor is transferred to the heating device through the lower pipe, heated, and then returned to the lower part of the reactor through the pipe. During the transfer and return process of the reaction mixture, paraformaldehyde precipitates and attaches to the inner wall of the pipe and the tube of the heating device, thereby hindering the continuous operation of the reactor. However, as described above, by installing the main body (11) and the reboiler (12) in contact with each other from above and below, the section in which the reaction mixture is transferred from the main body (11) to the reboiler (12) is reduced to the shortest distance, the section in which the reaction mixture is returned from the reboiler (12) to the main body (11) is eliminated, and the steam header pipe (L6) is used to prevent local overheating or temperature drop, thereby suppressing the precipitation of paraformaldehyde in the tube of the reboiler (12) and the reboiler circulation pipe (L1). Continuous operation is possible without interruption in the flow of the reaction mixture circulating through the main body (11) and the reboiler (12).

In the process of reacting formalin with trioxane, an acid catalyst such as sulfuric acid is generally used. During the operation of the trioxane reactor (10), some of this acid catalyst rises up the inner wall of the main body (11) in the form of small water droplets and flows out through the passage where the vapor is discharged at the top. The flowed out acid catalyst causes corrosion in unlined equipment of the subsequent process.

To prevent this, it is desirable to install a mist separator (13) at the inlet inside the main body (11) of the steam pipe (L3), which is the steam discharge passage of the main body (11) of the trioxane reactor (10).

The above mist separator (13) is a shape that combines a cylinder-1 (13-1) having the same size of both openings and a tapered cylinder-2 (13-2) having different sizes of both openings, the diameter of the wide opening of the cylinder-2 is larger than the diameter of the opening of the cylinder-1, one opening of the cylinder-1 is joined to the narrow opening of the cylinder-2 without a gap, and the other opening of the cylinder-1 is joined to the edge without a gap centered on the inlet of the steam pipe (L3) (see FIG. 4).

Accordingly, the wide opening of cylinder-2 is positioned downward, so that the acid catalyst that rises along the inner wall of the main body (11) flows downward along the outer walls of cylinders-1 and-2 of the mist separator (13) and naturally falls from the end of the wide opening of cylinder-2.

Additionally, in FIG. 1, a trioxane production facility according to one embodiment of the present invention is indicated by reference numeral 100.

The trioxane production facility (100) comprises a main body (11) and a reboiler (12), and includes a trioxane reactor (10) that polymerizes formalin into trioxane by heating; a trioxane distillation tower (20) in which gas flowing in from the upper portion of the main body (11) is separated into gas and liquid; a recovery pump (30) that transfers liquid from the lower portion of the trioxane distillation tower (20) to the reboiler (12); a cooler (40) that cools and condenses gas discharged from the upper portion of the trioxane distillation tower (20); a reflux drum (50) that receives the condensate condensed in the cooler (40); a reflux pump (60) that returns the condensate of the reflux drum (50) to the upper portion of the trioxane distillation tower (20); and a distillation tower upper pipe (L4) that transfers some of the gas discharged from the upper portion of the trioxane distillation tower (20) to a crude polymerization process (not shown).

A valve tray is built into the trioxane distillation tower (20) so that the vapor introduced from the trioxane reactor (10) is separated into gas and liquid. The separated gas at the top of the trioxane distillation tower (20) is transferred to a cooler (40) or a crude polymerization process through the upper pipe (L4) of the distillation tower, and the separated liquid at the bottom of the trioxane distillation tower (20) is returned to the trioxane reactor (10) through the recovery pump (30).

A formalin recovery pipe (L2) is installed at the discharge port of the above recovery pump (30) and connected to a reboiler circulation pipe (L1). The formalin recovery pipe (L2) is connected to a plurality of reboiler circulation pipes (L1a, L1b), and a formalin supply source (S1) for supplying high-concentration formalin to a trioxane reactor (10) is connected to the formalin recovery pipe (L2) (see FIG. 2).

A nitrogen supply pipe (L5) connected to a nitrogen supply source (S3) is connected to the upper pipe (L4) of the distillation tower, and a nitrogen supply valve (V1) is installed in the nitrogen supply pipe (L5). A pressure regulating device (PIC) is installed downstream of the connection portion of the nitrogen supply pipe (L5), and a pressure regulating valve (V2) is installed downstream of the pressure regulating device (PIC). The pressure regulating device (PIC) measures the pressure of the upper pipe (L4) of the distillation tower and controls the nitrogen supply valve (V1) and the pressure regulating valve (V2), thereby controlling the operating pressure in the trioxane distillation tower (20).

The trioxane reactor (10) and production facility (100) of the present invention configured as described above can be operated as follows.

First, as a preparatory step for a polyoxymethylene manufacturing process, formalin is concentrated in a formalin concentration process to manufacture high-concentration formalin, for example, high-concentration formalin of 65 to 75 wt% (not shown), and then the manufactured high-concentration formalin is supplied to the main body (11) of the trioxane reactor (10) via a formalin supply source (S1), a formalin recovery pipe (L2), a reboiler circulation pipe (L1a, L1b), and a reboiler (12), and an acid catalyst, preferably sulfuric acid, is supplied to the trioxane reactor (10) at an appropriate concentration of the reaction mixture, and a heat medium, preferably saturated steam of 160 to 170° C., is supplied from a heat source (S2) to the reboiler (12) to catalytically polymerize the formalin in the main body (11), thereby producing 1,3,5-trioxane as a reaction product.

High-concentration formalin is continuously supplied from a formalin supply source (S1), and the catalyst is replenished in the amount consumed during the reaction, so that the catalyst concentration of the reaction mixture in the main body (11) is always kept constant. The catalyst can be supplied through a pipe through which high-concentration formalin is supplied from the formalin supply source (S1).

Formalin inside the main body (11) descends to the lower chamber of the reboiler (12) through the reboiler circulation pipe (L1) by its own weight together with the catalyst, then passes upward through the tube of the reboiler (12), and while passing through the tube, is heated by the heat medium supplied to the outer space of the tube and circulated back to the main body (11).

The trioxane reactor (10) is operated at a pressure of 0.1 to 4.0 kg/cm2.g and a temperature of 102 to 115°C, and the formalin in the main body (11) is maintained at a concentration of 40 to 75 wt%, and the reaction mixture is composed of 90 to 98 wt% of formalin and 2 to 10 wt% of a catalyst, including side reactants, and it is preferable that the average residence time of formalin is about 60 minutes.

3 mol (mol) of formaldehyde reacts to produce 1 mol of trioxane, and the higher the formalin concentration, catalyst concentration, pressure, and temperature in the trioxane reactor (10), the higher the production amount of trioxane.

However, if the formalin concentration is high, the production of trioxane can be increased, but there is a high possibility that paraformaldehyde, a side reaction product, will be generated and precipitated, which reduces the heat exchange efficiency of the reboiler (12), thus reducing the production of trioxane. In severe cases, the reboiler (12) tube may become clogged, requiring the operation to be stopped and the reboiler (12) to be cleaned.

In addition, a high catalyst concentration increases the production of trioxane, but relatively, side reactions also increase, which generates a lot of impurities that interfere with the polymerization reaction, thus increasing the load rate of the post-process and decreasing the yield. In addition, a high methanol concentration in the reaction mixture also generates a lot of these impurities, which is not desirable.

Therefore, as shown in Fig. 1, by installing two or more reboiler circulation pipes (L1a, L1b) so that the reaction mixture can easily circulate through the tubes of the reboiler (12), and connecting the formalin recovery pipe (L2) to the reboiler circulation pipes (L1a, L1b) so that low-concentration formalin recovered from the trioxane distillation tower (20) is directly supplied to the reboiler (12), the formalin concentration inside the reboiler (12) tubes is lowered, which reduces the production of paraformaldehyde and reduces the occurrence of scale adhering to the tube walls, thereby enabling long-term operation of the trioxane reactor (10) and the trioxane production facility (100).

In addition, since the reaction mixture and the recovered formalin are combined and then pass through the tube of the reboiler (12) to enter the lower part of the trioxane reactor (10), the flow velocity inside the tube becomes fast, which further reduces scale adhesion, and the fast flow velocity quickly flows the reaction mixture inside the trioxane reactor (10) to increase the mixing efficiency of formalin and the catalyst, and as a result, the trioxane polymerization reaction is promoted, so that more trioxane can be produced per unit time and volume, and in addition, there is no need to install a separate stirring facility in the main body (11).

Trioxane produced in the trioxane reactor (10) is transferred to the bottom of the trioxane distillation tower (20) through the vapor pipe (L3) at the top of the trioxane reactor (10) in the form of vapor together with unreacted formalin, reacted trioxane, water, etc., and then rises up the trioxane distillation tower (20) equipped with a valve tray, whereby the concentration of trioxane in the vapor increases, and low-concentration formalin containing water and some trioxane is collected at the bottom of the trioxane distillation tower (20).

Low-concentration formalin at the bottom of the trioxane distillation tower (20) is recovered to the trioxane reactor (10) via the formalin recovery pipe (L2), the reboiler circulation pipe (L1), and the reboiler (12) by the recovery pump (30), and a formalin supply source (S1) that supplies high-concentration formalin is connected to the formalin recovery pipe (L2) so that it participates in the trioxane reaction again together with the high-concentration formalin.

In the formalin concentration process, which is a pre-process, the concentrated high-concentration formalin has a low temperature of about 70°C, and if directly injected into the trioxane reactor (10) operated at over 100°C, it may have a negative effect on the trioxane polymerization reaction due to the temperature difference. However, as described above, the low-temperature, high-concentration formalin is mixed with the high-temperature, low-concentration formalin whose flow rate is four times or more than its own, so that the temperature rises first and the formalin concentration is adjusted to the optimal reaction concentration. Then, as it passes through the reboiler (12), the temperature is raised a second time by the heat medium, so that the formalin temperature is adjusted to the optimal reaction temperature. Therefore, the formalin can participate in the reaction after being adjusted to the optimal reaction concentration and temperature.

Normally, a highly corrosive acid catalyst is used as a catalyst used in trioxane polymerization reaction, so there is a problem that the catalyst included in the reaction mixture circulating through the main body (11) and the reboiler (12) corrodes the tube of the reboiler (12), thereby shortening the operating life of the reboiler (12).

Since the high-concentration formalin supplied from the formalin supply source (S1) does not contain a catalyst or contains a small amount of catalyst, the mixture of high-concentration formalin and low-concentration formalin has a lower catalyst concentration than the reaction mixture, and as described above, by connecting the formalin recovery pipe (L2) to the reboiler circulation pipe (L1) and allowing the mixture with a low catalyst concentration to pass through the reboiler (12) together with the reaction mixture with a high catalyst concentration, the catalyst concentration of the reaction mixture passing through the tube of the reboiler (12) is lowered, so that corrosion of the tube can be suppressed.

The reaction mixture inside the main body (11) boils upwards as formalin is synthesized into trioxane by heating in the reboiler (12), and at this time, some of the catalyst rises along the inner wall of the main body (11) in the form of small water droplets. However, the catalyst droplets are recovered into the main body (11) by the mist separator (13) installed at the inlet of the steam pipe (L3) and prevented from flowing out to the trioxane distillation tower (20).

The vapor with a high trioxane concentration at the top of the trioxane distillation tower (20) is condensed by cooling water in a cooler (40), transferred to a reflux drum (50), and then returned to the top of the trioxane distillation tower (20) by a reflux pump (60). The upper and lower temperatures of the trioxane distillation tower (20) can be controlled by adjusting the discharge flow rate of the reflux pump (60). For example, the upper temperature can be set to 89 to 99° C. and the lower temperature can be set to 97 to 107° C. Accordingly, the trioxane concentration of the vapor discharged to the top of the trioxane distillation tower (20) can be controlled.

Since the polymerization reaction of formalin progresses in a forward reaction as the reaction pressure increases, and thus the productivity of trioxane increases, a pressure control device (PIC) is installed in the upper pipe (L4) of the distillation tower (20) to increase the pressure within the system, and the temperature of the trioxane reactor (10) can also be easily controlled through pressure control.

The pressure regulating device (PIC) measures the pressure inside the distillation column upper pipe (L4) and controls the nitrogen supply valve (V1) and the pressure regulating valve (V2). When the pressure inside the system drops, the nitrogen supply valve (V1) is opened to supply nitrogen from the nitrogen source (S3), thereby increasing the pressure. When the pressure inside the system is high, the pressure regulating valve (V2) is opened to control the pressure of the trioxane production process.

The conventional trioxane distillation tower maintains the upper part in a vacuum state, but in a vacuum state, outside air is easily drawn in, so there is a constant possibility that trioxane may come into contact with oxygen in the air, become unstable, and be oxidized to change into formic acid and formaldehyde. However, if the trioxane production facility (100) is maintained at a constant pressure, for example, 5 to 7 kPa, as described above, this phenomenon can also be prevented.

A portion of the trioxane vapor flowing through the upper pipe (L4) of the distillation tower is transferred to a polymerization process, which is a post-process, and is manufactured into polyoxymethylene. The trioxane vapor can be purified into pure trioxane through a trioxane absorption tower and an extraction tower (not shown) and then transferred to a crude polymerization process for manufacturing polyoxymethylene.

The above trioxane vapor contains approximately 55 wt% of trioxane, 18 wt% of formaldehyde, 26 wt% of water, and trace amounts of methylal, methyl formate, polyoxymethylene dimethoxide, paraformaldehyde, etc. as by-products. The formaldehyde conversion rate is approximately 75.7%, and the space-time yield (based on the amount of reacted formaldehyde) is approximately 550 g of trioxane per hour per 1 kg of formaldehyde, which can achieve higher productivity compared to conventional trioxane production facilities.

The above description is not intended to limit the technical idea of the present invention, but is merely an example, and various substitutions and equivalent modifications and variations are possible within the scope that does not depart from the technical idea of the present invention, and the protection scope of the present invention should be interpreted by the claims below, and all technical ideas within the equivalent scope should be understood to be included in the scope of the rights of the present invention.

100: Trioxane production facility, 10: Trioxane reactor, 11: Main body, 12: Reboiler, 13: Mist separator, 13-1: Cylinder-1, 13-2: Cylinder-2, 20: Trioxane distillation tower, 30: Recovery pump, 40: Cooler, 50: Reflux drum, 60: Reflux pump
L1/L1a/L1b: reboiler circulation pipe, L2: formalin recovery pipe, L3: steam pipe, L4: distillation tower top pipe, L5: nitrogen supply pipe, L6: steam header pipe, L7: steam tube
S1: formalin source, S2: heat source, S3: nitrogen source
PIC:Pressure regulator, V1:Nitrogen supply valve, V2:Pressure regulating valve

Claims (7)

A body (11) into which formalin and a catalyst are introduced and the formalin is polymerized by heating to produce trioxane;
A reboiler (12) installed integrally with the lower center of the main body (11) so as to be circulated, and heats the reaction mixture introduced from the main body (11) and returns it to the main body (11);
A reboiler circulation pipe (L1) having one end connected to the lower part of the main body (11) and the other end connected to the lower part of the reboiler (12) to transfer the reaction mixture of the main body (11) to the lower part of the reboiler (12); and
A trioxane reactor (10) including a formalin recovery pipe (L2) connected to the above reboiler circulation pipe (L1) and supplying high-concentration formalin and low-concentration formalin. In claim 1,
A trioxane reactor (10) characterized in that two or more reboiler circulation pipes (L1) are installed, and a plurality of reboiler circulation pipes (L1a, L1b) are arranged symmetrically facing each other with the reboiler (12) as the center. In claim 1,
A trioxane reactor (10) characterized in that the above reboiler circulation pipe (L1) is wrapped with insulating material on the outside of the pipe, a ring-type steam header pipe (L6) is installed on the outside of the insulating material, several steam tubes (L7) are connected to the steam header pipe (L6) to wrap around the outside of the insulating material, and then the outside of the steam tubes (L7) is wrapped again with insulating material. In claim 1,
A steam pipe (L3) for discharging steam is installed on the upper part of the main body (11), and a mist separator (13) is installed at the inlet of the steam pipe (L3) inside the main body (11).
The above mist separator (13) is a trioxane reactor (10) characterized in that it is a shape that combines a cylinder-1 (13-1) having the same size of both openings and a tapered cylinder-2 (13-2) having different sizes of both openings, the diameter of the wide opening of the cylinder-2 is larger than the diameter of the opening of the cylinder-1, one opening of the cylinder-1 is joined to the narrow opening of the cylinder-2 without a gap, and the other opening of the cylinder-1 is joined to the edge without a gap centered on the inlet of the steam pipe (L3). In claim 1,
A trioxane reactor (10) characterized in that the interior of the main body (11) is lined with glass, titanium or zirconium. A trioxane reactor (10) including a main body (11) into which formalin and a catalyst are introduced and the formalin is polymerized by heating to produce trioxane, a reboiler (12) which is installed integrally with the lower center of the main body (11) so as to be circulated and which heats a reaction mixture introduced from the main body (11) and returns it to the main body (11), a reboiler circulation pipe (L1) which has one end connected to the lower part of the main body (11) and the other end connected to the lower part of the reboiler (12) and which transports the reaction mixture of the main body (11) to the lower part of the reboiler (12), and a formalin recovery pipe (L2) which is connected to the reboiler circulation pipe (L1) and supplies high-concentration formalin and low-concentration formalin;
A trioxane distillation tower (20) in which gas flowing in from the upper part of the main body (11) is separated into gas and liquid;
A recovery pump (30) that transfers the liquid at the bottom of the above trioxane distillation tower (20) to a formalin recovery pipe (L2);
A cooler (40) that condenses the gas discharged from the upper portion of the trioxane distillation tower (20);
A reflux drum (50) that receives the condensate condensed in the above cooler (40);
A reflux pump (60) that returns the condensate of the above reflux drum (50) to the upper part of the trioxane distillation tower (20); and
A trioxane production facility (100) including a distillation tower upper pipe (L4) for transporting gas discharged from the upper portion of the trioxane distillation tower (20) to a crude polymerization process. In claim 6,
A trioxane production facility (100) characterized in that a nitrogen supply pipe (L5) connected to a nitrogen supply source (S3) is connected to the upper pipe (L4) of the distillation tower, a nitrogen supply valve (V1) is installed in the nitrogen supply pipe (L5), a pressure regulating device (PIC) is installed downstream of the connection portion of the nitrogen supply pipe (L5), and a pressure regulating valve (V2) is installed downstream of the pressure regulating device (PIC), and the pressure regulating device (PIC) measures the pressure of the upper pipe (L4) of the distillation tower and controls the nitrogen supply valve (V1) and the pressure regulating valve (V2).

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