CN110790647A - Production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol - Google Patents
Production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol Download PDFInfo
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- C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
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- C07C41/56—Preparation of compounds having groups by reactions producing groups by condensation of aldehydes, paraformaldehyde, or ketones
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Abstract
The invention discloses a production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol, belonging to the technical field of compound preparation, wherein the process comprises the steps of S1, taking methanol as a raw material, obtaining a low-concentration formaldehyde solution through oxidation and recovery, and obtaining a light formaldehyde solution through absorption of unrefined formaldehyde mixed gas through an absorption tower; s2, taking methanol and a low-concentration formaldehyde solution as raw materials, and sequentially processing the raw materials by a resin reactor, a reaction tower, a rectifying tower and a cooler to obtain methylal; s3, in the step S1, the low-concentration formaldehyde solution is subjected to secondary evaporation and concentration to obtain a high-concentration formaldehyde solution, and the high-concentration formaldehyde solution is subjected to vacuum drying to obtain polyformaldehyde; and S4, taking liquid ammonia as a raw material, reacting with the weak aldehyde solution in S1 after vaporization, evaporating, crystallizing, centrifuging and drying to obtain hexamethylenetetramine. The production system can improve the effective utilization of resources such as raw materials, reduce the emission of pollutants, reduce the pollution to the environment, effectively reduce the production cost of enterprises and improve the economic benefit.
Description
Technical Field
The invention relates to preparation of formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine, in particular to a production system for preparing the substances by taking methanol as a raw material, and belongs to the technical field of compound preparation.
Background
Formaldehyde, of the formula HCHO or CH O, with the formula weight of 30.03, is also called formaldehyde. Colorless gas, pungent smell, and has stimulating effect on eyes and nose. The formaldehyde belongs to a popular chemical product with wide application, simple production process and sufficient raw material supply, is the main stem of a downstream product tree of the methanol, the annual output of the world is about 2500 million tons, and about 30 percent of methanol is used for producing the formaldehyde. However, formaldehyde is a low-concentration aqueous solution, and is inconvenient for long-distance transportation from the economic point of view, so that plants are generally arranged near the main consumer market, and the import and export trade is very little. The methanol oxidation method and the natural gas direct oxidation method are mainly adopted in industry.
The low polymerization degree paraformaldehyde replaces the common industrial formaldehyde aqueous solution, and can reduce the energy consumption of dehydration and greatly reduce the wastewater treatment capacity in various formaldehyde downstream products such as synthetic pesticides, synthetic resins, coatings, fumigation disinfectants and the like, thereby being a green and environment-friendly project benefiting the nation and the people. Because the low polymerization degree paraformaldehyde is solid particles with higher effective components than industrial formaldehyde, the low polymerization degree paraformaldehyde is beneficial to chemical synthesis in chemical industry, pharmacy and other industrial fields and has wide application particularly in the aspect of synthesis requiring anhydrous formaldehyde as a raw material. It can also be used as disinfectant, bactericide, fumigant and herbicide, and for producing resin and artificial ivory.
The methylal is colorless, clear, volatile and combustible liquid and has chloroform smell and pungent smell. The methylal can be used as a solvent in an insecticide formula, can be used as a stabilizer in a leather polishing agent and an automobile polishing agent formula, can promote the dissolution of essence in an air freshener formula, and has wide application, the methylal is obtained by reacting methanol and a formaldehyde solution in a synthesis tower under the action of a catalyst, the generated methylal is distilled off from the top of the tower, the temperature of the top of the tower is controlled to be 41.5-42 ℃, unreacted methanol is separated from a product for recycling, and the methylal with the content of more than 85 percent can also reach the content of more than 99.9 percent.
Hexamethylenetetramine is white hygroscopic crystalline powder or colorless glossy rhombohedral crystals, and is combustible; it is mainly used as curing agent for resin and plastics, catalyst and foaming agent for aminoplast, and can be used for producing chloromycetin and producing pesticide, etc., and can be obtained by reaction of formaldehyde solution and liquid ammonia.
Various waste gases, waste liquids and the like are generated in the production process of the substances, for example, formaldehyde obtained by the reaction of methanol and air in the formaldehyde production process can not be completely absorbed, formaldehyde exists in components which are not recovered, and if the formaldehyde is directly discharged to the outside, not only can the environment be polluted, but also the utilization efficiency of raw materials and the waste of resources can be reduced; for another example, in the production process of methylal, a large amount of cooling water is generated when the finished methylal is obtained by cooling, and the cooling water with heat is discharged out of the system to cause heat waste. Therefore, a new production system needs to be developed, so that the resources in each production link are utilized most effectively to the maximum extent, and the production cost of enterprises is reduced.
Disclosure of Invention
The technical problem to be solved by the invention is to provide a production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylene tetramine from methanol, which can comprehensively and effectively utilize materials of each unit in the production process, thereby reducing the production cost of enterprises, improving the economic benefit, improving the material utilization rate and reducing the environmental pollution.
In order to solve the technical problems, the technical scheme adopted by the invention is as follows:
a production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol comprises the following processes:
s1, using methanol and air as raw materials, oxidizing to obtain formaldehyde mixed gas, recovering the formaldehyde mixed gas to obtain a low-concentration formaldehyde solution, and absorbing the unrecovered formaldehyde mixed gas by an absorption tower to obtain a light formaldehyde solution and waste gas;
s2, taking methanol and the low-concentration formaldehyde solution obtained in the process S1 as raw materials, and sequentially processing the raw materials by a resin reactor, a reaction tower, a rectifying tower and a cooler to obtain methylal;
s3, in the process S1, the low-concentration formaldehyde solution is evaporated and concentrated for the second time to obtain a high-concentration formaldehyde solution, and the high-concentration formaldehyde solution is dried in vacuum to obtain paraformaldehyde;
s4, reacting vaporized liquid ammonia with the weak aldehyde solution in the process S1 to obtain hexamethylenetetramine through evaporative crystallization, centrifugation and drying.
The technical scheme of the invention is further improved as follows: s1 includes the following processes:
A. mixing methanol and air in a multifunctional evaporator and evaporating the mixture into mixed steam, and transferring the mixed steam into a methanol oxidizer for oxidation reaction to obtain formaldehyde mixed gas;
B. the obtained formaldehyde mixed gas is subjected to desalted water recovery to obtain a low-concentration formaldehyde solution, the formaldehyde in the mixed gas is converted into a light formaldehyde solution by the unrecycled formaldehyde mixed gas sequentially passing through a first absorption tower and a second absorption tower, waste gas enters a burner with a heat collecting pipe to be burned, and the heat collecting pipe collects heat.
The technical scheme of the invention is further improved as follows: the process A is a process for preparing formaldehyde by a silver method formaldehyde production process; in the process A, air is treated by an air filter, a Roots blower and an air washing tower in sequence and then enters the multifunctional evaporator, and methanol sequentially enters the multifunctional evaporator from a methanol storage tank through a methanol head tank and a filter tank.
The technical scheme of the invention is further improved as follows: the concentration of the low-concentration formaldehyde solution is 50-55%, and the concentration of the weak formaldehyde solution is 20-30%; and in the process B, the heat collected by the heat collecting tube returns to the multifunctional evaporator for utilization.
The technical scheme of the invention is further improved as follows: the heat collected by the heat collecting tube in the process B is returned to the resin reactor and the reaction tower for utilization in the process S2.
The technical scheme of the invention is further improved as follows: the secondary evaporation and concentration process in the S3 is that the low-concentration formaldehyde solution sequentially passes through a first-effect evaporation and concentration tower and a second-effect evaporation and concentration tower to obtain a high-concentration formaldehyde solution, wherein the concentration of the high-concentration formaldehyde solution is 70-85%; in S3, the drying is performed by a rake dryer.
The technical scheme of the invention is further improved as follows: the desiccator is adopted in the drying, the desiccator includes the barrel and wears to locate the inside hollow shaft of barrel still includes a plurality of hollow tubes and a plurality of baffle, and is a plurality of the baffle is with inside the dividing into a plurality of inner spaces of most hollow shafts, every two adjacent inner space by at least one the hollow tube intercommunication.
The technical scheme of the invention is further improved as follows: the hollow pipe comprises two vertical pipes and a transverse pipe, one ends of the two vertical pipes are fixedly communicated with the two ends of the transverse pipe, and the other ends of the two vertical pipes are communicated with the two adjacent inner spaces.
The technical scheme of the invention is further improved as follows: the baffle comprises an upper baffle and a lower baffle, one end of the upper baffle is connected to the inner side wall of the upper part of the hollow shaft, one end of the lower baffle is connected to the inner side wall of the lower part of the hollow shaft, and free end parts of the upper baffle and the lower baffle are overlapped together to form a sealing structure; the upper baffle and the lower baffle are elastic bodies.
The technical scheme of the invention is further improved as follows: and the heat collected by the heat collecting pipe in the process B returns to the drying section in the process S3 for utilization.
Due to the adoption of the technical scheme, the invention has the technical progress that:
the production system can improve the effective utilization of resources such as raw materials, reduce the emission of pollutants, reduce the pollution to the environment, effectively reduce the production cost of enterprises and improve the economic benefit.
The invention collects the residual formaldehyde in the residual tail gas of the recovered formaldehyde in the formaldehyde production process, is convenient for subsequent purification and other uses, reduces the loss of the formaldehyde, and reduces the pollution of direct emission to the environment; and the hydrogen in the tail gas can be recycled, so that the comprehensive recovery treatment of the tail gas is realized, and the requirements of environmental protection and economy are met.
According to the design of the dryer structure in the production process of paraformaldehyde, the hollow pipe is used for replacing the original rake teeth, and the baffle is used for separating the interior of the hollow shaft, so that steam can be forced to pass through the interior of the hollow pipe, and the steam can smoothly flow through each part of the internal stirring device, and the heat exchange efficiency in the dryer is improved.
According to the invention, the heat collected by tail gas treatment in the formaldehyde production process is recycled to the formaldehyde synthesis process, the formaldehyde concentration process, the paraformaldehyde drying process, the methylal production process and the like, so that the comprehensive utilization of heat is realized, the production cost of enterprises is reduced, the maximum utilization of resources is realized in the whole production system process, the emission of pollutants is reduced, and the green and environment-friendly production is realized.
Drawings
FIG. 1 is a schematic structural view of a treatment apparatus for a mixed gas of residual formaldehyde after recovery of formaldehyde in a formaldehyde production process according to the present invention;
FIG. 2 is a schematic view showing the structure of a dryer used in the drying section of the paraformaldehyde production process of the present invention;
FIG. 3 is a detailed view of a hollow shaft of the dryer of the present invention;
FIG. 4 is a detail view of a baffle structure in the dryer of the present invention;
FIG. 5 is a flow diagram of a formaldehyde production process of the present invention;
FIG. 6 is a flow chart of the methylal production process of the present invention;
FIG. 7 is a flow chart of a process for producing paraformaldehyde according to the present invention;
FIG. 8 is a flow diagram of a hexamethylenetetramine production process according to the invention;
wherein, 11-formaldehyde production room, 12-first absorption tower, 13-second absorption tower, 14-burner, 15-water storage tank, 16-circulating pump, 17-spray device, 18-spray main pipe, 19-spray head, 110-gas-liquid separator, 111-weak aldehyde storage tank, 112-combustion head, 113-cracker, 114-heat collecting pipe, 115-gas conveying pipe, 116-air conveying pipe, 117-ignition head, 51-cylinder, 511-feed inlet, 512-vacuum pipe, 513-discharge outlet, 52-hollow shaft, 521-hollow pipe, 5211-horizontal pipe, 5212-vertical pipe, 5213-extension plate, 522-baffle, 5221-upper baffle, 5222-lower baffle, 523-inner space, 524-first rotary joint, 525-second rotary joint.
Detailed Description
The present invention will be described in further detail with reference to the following examples:
a production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol comprises the following processes:
s1, using methanol and air as raw materials, oxidizing to obtain formaldehyde mixed gas, recovering the formaldehyde mixed gas to obtain a low-concentration formaldehyde solution, and absorbing the unrecovered formaldehyde mixed gas by an absorption tower to obtain a light formaldehyde solution and waste gas;
s2, taking methanol and the low-concentration formaldehyde solution obtained in the process S1 as raw materials, and sequentially processing the raw materials by a resin reactor, a reaction tower, a rectifying tower and a cooler to obtain methylal;
s3, in the process S1, the low-concentration formaldehyde solution is evaporated and concentrated for the second time to obtain a high-concentration formaldehyde solution, and the high-concentration formaldehyde solution is dried in vacuum to obtain paraformaldehyde;
s4, reacting vaporized liquid ammonia with the weak aldehyde solution in the process S1 to obtain hexamethylenetetramine through evaporative crystallization, centrifugation and drying.
Wherein, as shown in fig. 5, S1 includes the following processes:
A. the process A is a process for preparing formaldehyde by a silver method formaldehyde production process, air is treated by an air filter, a Roots blower and an air washing tower in sequence and then enters a multifunctional evaporator, methanol sequentially enters the multifunctional evaporator from a methanol storage tank through a methanol head tank and a filter tank, the treated methanol and the air are mixed in the multifunctional evaporator and evaporated into mixed steam, and the mixed steam is transferred to a methanol oxidizer for oxidation reaction to obtain formaldehyde mixed gas;
B. the obtained formaldehyde mixed gas (mainly formaldehyde generated by reaction, hydrogen generated by side reaction and excessive air) is subjected to desalination (prepared by desalting fresh water) to recover low-concentration formaldehyde solution, the formaldehyde mixed gas (tail gas, mainly comprising water vapor, and some formaldehyde and hydrogen which are not adsorbed in the water vapor) which is not recovered passes through a first absorption tower and a second absorption tower in sequence to convert formaldehyde in the mixed gas into light formaldehyde solution, waste gas enters a burner with a heat collecting pipe to be combusted, and the heat collecting pipe collects heat; the concentration of the low-concentration formaldehyde solution is 50-55%, the low-concentration formaldehyde solution can be supplied to customers needing the low-concentration formaldehyde solution for use, and the concentration of the light formaldehyde solution is 20-30%; and in the process B, the heat collected by the heat collecting tube returns to the multifunctional evaporator for utilization, and the multifunctional evaporator can also be used in other working sections requiring heat in other processes for utilization.
As shown in fig. 1, the treatment process of the formaldehyde mixed gas (tail gas) which is not recovered in the process B specifically comprises the following steps: tail gas (mainly containing formaldehyde which is not collected and hydrogen generated by side reaction) is sequentially treated by a first absorption tower 12, a second absorption tower 13 and a burner 14, and the bottoms of the first absorption tower 12 and the second absorption tower 13 are communicated with a water storage tank 15 through pipelines; the bottoms of the first absorption tower 12 and the second absorption tower 13 are also communicated with a spray device 17 arranged above the corresponding absorption tower through pipelines, each pipeline is provided with a circulating pump 16, and the spray device 17 comprises a spray main pipe 18 and a spray head 19 arranged on the spray main pipe 18; the upper end of the first absorption tower 12 is communicated with the bottom of the second absorption tower 13 through a pipeline, and the bottom parts of the first absorption tower 12 and the second absorption tower 13 are respectively communicated with the diluted aldehyde storage tank 111 through pipelines; the burner 14 comprises a burner head 112 at the bottom end inside the burner, and a heat collecting pipe 14 (heat medium water or heat medium gas can be introduced into the inside of the burner head 112) above the burner head 112, wherein a gas conveying pipe 115, an air conveying pipe 116 and an ignition head 117 penetrating through the burner head 112 are arranged in the burner head 112, and the heat collecting pipe 114 is communicated with the formaldehyde production room 11 through a pipeline. The upper end of the second absorption tower 13 is communicated with a gas-liquid separator 110 through a pipeline, and the gas-liquid separator 110 is also respectively communicated with a dilute aldehyde storage tank 111 and a burner 14 through pipelines; a cracker 113 is provided in the burner 14 to promote the sufficient progress of combustion, the cracker 113 being located above the combustion head 112 and below the heat collecting pipe 114; the nozzle 19 is an atomizing nozzle, each pipeline is provided with a valve (as a switch or adjusting flow), the outer part of the burner 14 is provided with a heat-insulating layer, the cracker 113 is a high-temperature-resistant wire mesh, and the preferable high-temperature-resistant wire mesh is a titanium steel wire mesh.
When the device is used, part of water is added into the first absorption tower 12 and the second absorption tower 13 from the water storage tank 15 through a pipeline, then tail gas discharged from the formaldehyde production room 11 is introduced to the bottom of the first absorption tower 12 through a pipeline, a circulating pump 16 of the first absorption tower 12 is started to send water in the towers to a spray main pipe 18 through a pipeline, and then the tail gas is downwards sprayed to gas overflowing from the bottom water through a spray nozzle 19 (the formaldehyde is easily dissolved in the water, the formaldehyde in the tail gas is dissolved by the water sprayed by the spray nozzle, and the formaldehyde is not dissolved by the hydrogen), the spraying is repeatedly and circularly performed, a detection port can be arranged on the pipeline of the absorption tower leading to the light aldehyde storage tank 111, the concentration of the light aldehyde solution in the towers can be detected at any time, and water can be supplemented or the light aldehyde solution is discharged into the light aldehyde storage tank 111 and then; the gas passing through the upper end of the first absorption tower 12 enters the second absorption tower 13 through the pipeline again for circular spraying, the gas overflowing through the second absorption tower 13 is basically hydrogen with water (the water may have a very small amount of residual formaldehyde), and can be directly introduced into the combustor 14 for combustion to collect heat, or the gas overflowing through the second absorption tower 13 is firstly separated from the hydrogen by the gas-liquid separator 110 and then enters the combustor 14 for combustion, the separated liquid is transported to the light aldehyde storage tank 111 through the pipeline, and the light aldehyde solution in the light aldehyde storage tank 111 can be concentrated and purified, and can also be used in other process production requiring the light aldehyde solution (such as synthesis process of hexamethylenetetramine in process S4); the hydrogen separated by the gas-liquid separator 110 enters the combustion head 112 and the combustor 14 through the gas delivery pipe 115, the ignition head 117 ignites, the air delivery pipe 116 delivers air to combust the hydrogen, the heat generated by the combustion is collected by the heat collection pipe 114, the cracker 113 can be arranged in the combustor 14, the combusted gas heats the cracker 113 to a higher temperature, the hydrogen which is not combusted passes through the silk-screen high-temperature cracker 113 and is fully combusted, the heat generated by the combustion heats the heat collection pipe 114 on the upper part of the combustor 14 (the heat collection pipe can be a heat-resistant pipe (the outside of which is connected with a water storage tank, not shown in the figure, the heat is contacted with the water in the heat collection pipe 114, the water absorbs heat and is heated to become hot water with high heat, and the hot water is circularly delivered to the place needing the heat from the pipe, the low-temperature water flows into the water storage tank to realize the full collection of heat; the heat collecting tube may be another device capable of collecting heat), so as to collect heat, the collected heat may be returned to the process S1 to heat air or methanol [ heat is transmitted through a pipeline communicating between the burner 14 and the formaldehyde production plant 11 ], or may be transmitted to another place where heat is needed through a pipeline, for example, the heat collected by the heat collecting tube is transmitted to the heating section in the processes S2 and S3 to be utilized, or transmitted to the paraformaldehyde drying section to be utilized. Alternatively, the tail gas from the formaldehyde production process can be fed directly to the burner 14 for combustion without being treated in an absorber.
As shown in fig. 6, the specific process of process S2 can be performed by the method of patent application CN 201910373473.9, and the improvement of the present invention is that the heat collected by the heat collecting tube of process B in process S1 is returned to the resin reactor and the reaction tower in process S2 for utilization; the cooling water produced by the cooler in the process S2 and the tower bottom wastewater produced by the reaction tower can be recycled, for example, the alcohol vapor produced by the tower bottom wastewater after being treated by the stripping tower is recycled into the reaction tower, the cooling water is condensed by the condenser and then is treated by the desalted water in the water washing tower, and the alcohol vapor obtained by the treated washing liquid through the stripping tower is recycled into the reaction tower.
As shown in fig. 7, in the process of the secondary evaporation and concentration in the process S3, the low-concentration formaldehyde solution sequentially passes through the first-effect evaporation and concentration tower and the second-effect evaporation and concentration tower to obtain the high-concentration formaldehyde solution, the concentration of the high-concentration formaldehyde solution is 70 to 85%, and the secondary evaporation is vacuum evaporation and concentration, specifically: free CH in aqueous formaldehyde solution at 60 DEG C2O accounts for 0.1 wt% of the total amount, and free CH in the aqueous formaldehyde solution at 100 DEG C2O accounts for 1% (wt) of the total amount. At 100 ℃ and 1atm, aldehyde and waterBoiling composition of middle CH2O content 21% wt, CH2The O composition increases with increasing temperature and pressure. Reduced temperature, reduced pressure, CH in azeotrope2The O content decreased and the azeotropic phenomenon disappeared when the pressure was lower than 26.6kPa (absolute) and the temperature was 65 ℃. The formaldehyde concentration adopts a vacuum concentration process to concentrate low-concentration formaldehyde into high-concentration formaldehyde solution with the concentration of 70-85% (the light formaldehyde solution obtained in the process S1 can also be subjected to vacuum concentration to obtain the formaldehyde solution with higher concentration), and the vacuum concentration process can effectively reduce the formaldehyde content in the aldehyde-water azeotrope and reduce the formaldehyde brought away by water evaporation.
The process S3, the drying is performed in a dryer, which may be a rake dryer, but is preferably an improved dryer of the present invention, as shown in fig. 2 and 3, including a horizontal cylinder 51 and a hollow shaft 52 penetrating the inside of the cylinder 51, a feeding port 511 for feeding materials and a vacuum pipe 512 for connecting to a vacuum pump are provided at the top of the cylinder 51, a discharging port 513 for discharging materials is provided at the bottom of the cylinder 51, a decelerating motor 53 is connected to one side of the hollow shaft 52, the decelerating motor 53 is used for providing power for rotating the hollow shaft 52, a first rotary joint 524 and a second rotary joint 525 are respectively connected to both ends of the hollow shaft 52, the first rotary joint 524 is used for introducing steam into the inside of the hollow shaft 52, the second rotary joint 525 is used for discharging steam from the inside of the hollow shaft 52, and a plurality of steam inlets and steam outlets (not shown) are further included for steam heating the interlayer provided in the inner wall of the cylinder 51, the above are all the prior arts, and no further description is given, so reference can be made to the chinese invention patent No. 201610129367.2. Compared with the rake dryer in the prior art, the invention has the advantages that the hollow pipe 521 replaces the hollow rake teeth used in the prior art, and in order to be matched with the hollow pipe 521, a plurality of baffles 522 are arranged in the hollow shaft 52 and are used for guiding the circulation of steam; as shown in fig. 3, the plurality of baffles 522 divide the interior of the hollow shaft 52 into a plurality of interior spaces 523, each two adjacent interior spaces 523 are fixedly communicated with each other by at least one hollow pipe 521, the hollow pipe 521 is made of hard metal, and the hollow pipe 521 also rotates simultaneously in the rotation process of the hollow shaft 52, so that the hollow pipe 521 can stir paraformaldehyde in the cylinder 51, and in the stirring process, due to the matching of the hollow pipe 521 and the baffles 522, steam can move along the track (the direction indicated by the arrow) shown in fig. 3, so that the steam can move more smoothly in the hollow pipe 521, and the phenomenon of steam blockage in the hollow rake teeth in the prior art is avoided, thereby increasing the heat exchange efficiency in the cylinder 51 and better increasing the heating efficiency of the formaldehyde solution; meanwhile, the hollow pipe 521 includes two vertical pipes 5212 and a horizontal pipe 5211, one end of the two vertical pipes 5212 is fixedly communicated with two ends of the horizontal pipe 5211, the other end of the two vertical pipes 5212 is communicated with two adjacent inner spaces 523, the length of the vertical pipe 5212 is slightly smaller than the radius of the cylinder body 51, and the extension plate 213 is arranged outside the horizontal pipe 5211 to increase the stirring efficiency of the hollow pipe 21 on the material. Furthermore, the cross tube 5211 and the vertical tube 5212 are connected by a sealing flange, which can be removed to replace the cross tube 5211 alone when the cross tube 5211 needs to be replaced after being worn.
When the dryer of the invention is used, firstly, high-concentration formaldehyde solution is added into the cylinder 51 through the feed inlet 511, then steam is added into the hollow shaft 52 and the hollow pipe 521 through the first rotary joint 524 for preheating, and simultaneously, the interlayer arranged in the inner wall of the cylinder 51 is preheated through the steam inlet and the steam outlet (the heat collected by the heat collecting pipe in the process S1 can also be introduced for preheating), also refer to the Chinese invention patent with the patent number of 201610129367.2, after the preheating is finished, the vacuum pump is started, the vacuum pump continuously vacuumizes the inside of the cylinder 51 through the vacuum pipe 512, the speed reducing motor 53 is started at the same time, the speed reducing motor 53 drives the hollow shaft 52 to rotate, the hollow shaft 52 drives the hollow pipe 521 to rotate, the horizontal pipe 5211 and the extension plate 5213 arranged thereon stir the materials, in the stirring process, the steam can sequentially pass through the plurality of internal spaces 523 and the hollow pipe 521 along the, so through hollow tube 521, hollow shaft 52 cooperates the steam in the interlayer to implement stirring heating to the polyformaldehyde crude product, cooperate the negative pressure again and take away the moisture of evaporating, in addition can also condense the moisture of evaporating or solvent and retrieve, with this realization to the concentrated drying of formalin, after concentrated drying is accomplished, discharge the product through discharge opening 513, second rotary joint 525 cooperates the flow of control hollow shaft 52 and the inside steam of hollow tube 521 with first rotary joint 524 in the drying process, connect high compression pump with first rotary joint 524 at last, leading-in with the outside air, take away the moisture in hollow shaft 52 and the hollow tube 521, with this prevent that the comdenstion water from taking away in steam access inside accumulation, because the persistence of comdenstion water leads to preheating link energy consumption too high the condition when avoiding starting drive next time and take place.
In other preferred aspects, as shown in fig. 4, the barrier 522 includes an upper barrier 5221 and a lower barrier 5222, one end of the upper barrier 5221 being attached to the inside wall of the upper portion of the hollow shaft 52, one end of the lower barrier 5222 being attached to the inside wall of the lower portion of the hollow shaft, the free end portions of the upper and lower barriers 5221, 5222 overlapping together to form a seal, the upper and lower barriers forming a barrier seal against the hollow shaft 52. And the upper and lower barriers 5221 and 5222 are made of an elastic body, and when the steam pressure supplied reaches a certain level, the overlapped portion of the upper and lower barriers 5221 and 5222 is pushed open to form an opening, through which the steam moves in the axial direction of the hollow shaft 52, and since the upper and lower barriers 5221 and 5222 have elasticity, when the steam pressure is reduced, the upper and lower barriers are automatically restored to form a sealing structure again, and at this time, the steam circulation is continued in the state as shown in fig. 3. That is, when the steam pressure is small, the upper barrier 5221 and the lower barrier 5222 are overlapped at the free ends to form a sealing structure, and the steam is circulated as shown in fig. 3; when the steam pressure is high, the upper and lower barriers 5221 and 5222 form openings at free ends, and the openings are enlarged as the steam pressure increases, and the circulation path of the steam is increased along the hollow shaft 52 through the openings. In some cases, it is necessary to rapidly increase the circulation rate of the steam or supply the steam at a high pressure for a long time, and limitations of the circulation manner shown in fig. 3 may occur, and although the uniformity thereof can be secured, the circulation efficiency may not be satisfactory; in some cases, the connection position of the hollow shaft 52 and the hollow pipe 521 is easily blocked by external foreign matters due to the small connection port, so that the steam cannot flow, and at this time, the hollow shaft may need to be disassembled for maintenance.
The steam generated in the second evaporation and concentration in the process S3 is condensed by a condenser, and the condensed water is formaldehyde aqueous solution with the concentration of about 20 percent because of the residual formaldehyde in the steam; the water vapor evaporated during the drying of the dryer is also recycled by a cooling and recycling tower to obtain a 30% formaldehyde aqueous solution, and the formaldehyde aqueous solution can be concentrated and can also be used for the production process of hexamethylenetetramine in the process S4.
As shown in fig. 8, the specific process of the process S4 is to continuously stir and introduce vaporized liquid ammonia into a low-concentration formaldehyde solution (which may be a weak formaldehyde solution in the process S1, or a low-concentration formaldehyde solution obtained in the process S3), keep ammonia excess, react for about half an hour, control the end point at pH 9, and keep the temperature not lower than 80 ℃ (which may be heated by heat collected in the process S1, or by cooling water generated in a cooler in the process S2), react to obtain a hexamethylenetetramine solution, transfer the hexamethylenetetramine solution to an evaporative crystallizer to perform evaporative crystallization at 80 ℃, perform solid-liquid separation in a centrifuge after crystallization, return the obtained mother liquor to the evaporative crystallizer to perform crystallization, and dry the centrifuged solid in a dryer to obtain hexamethylenetetramine as a final product.
Claims (10)
1. A production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol is characterized by comprising the following processes:
s1, using methanol and air as raw materials, oxidizing to obtain formaldehyde mixed gas, recovering the formaldehyde mixed gas to obtain a low-concentration formaldehyde solution, absorbing the unrecovered formaldehyde mixed gas by an absorption tower to obtain a light formaldehyde solution, and discharging waste gas;
s2, taking methanol and the low-concentration formaldehyde solution obtained in the process S1 as raw materials, and sequentially processing the raw materials by a resin reactor, a reaction tower, a rectifying tower and a cooler to obtain methylal;
s3, in the process S1, the low-concentration formaldehyde solution is evaporated and concentrated for the second time to obtain a high-concentration formaldehyde solution, and the high-concentration formaldehyde solution is dried in vacuum to obtain paraformaldehyde;
s4, reacting vaporized liquid ammonia with the weak aldehyde solution in the process S1 to obtain hexamethylenetetramine through evaporative crystallization, centrifugation and drying.
2. The production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol according to claim 1, wherein S1 comprises the following steps:
A. mixing methanol and air in a multifunctional evaporator and evaporating the mixture into mixed steam, and transferring the mixed steam into a methanol oxidizer for oxidation reaction to obtain formaldehyde mixed gas;
B. the obtained formaldehyde mixed gas is subjected to desalted water recovery to obtain a low-concentration formaldehyde solution, the formaldehyde in the mixed gas is converted into a light formaldehyde solution by the unrecycled formaldehyde mixed gas sequentially passing through a first absorption tower and a second absorption tower, waste gas enters a burner with a heat collecting pipe to be burned, and the heat collecting pipe collects heat.
3. The production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol according to claim 2, wherein the process A is a process for preparing formaldehyde by a silver formaldehyde production process; in the process A, air is treated by an air filter, a Roots blower and an air washing tower in sequence and then enters the multifunctional evaporator, and methanol sequentially enters the multifunctional evaporator from a methanol storage tank through a methanol head tank and a filter tank.
4. The production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol according to claim 3, wherein the concentration of the low-concentration formaldehyde solution is 50-55%, and the concentration of the weak aldehyde solution is 20-30%; and in the process B, the heat collected by the heat collecting tube returns to the multifunctional evaporator for utilization.
5. The system for producing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol according to claim 2, wherein the heat collected by the heat collecting tube in the process B is returned to the resin reactor and the reaction tower in the process S2 for use.
6. The production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol according to claim 1, wherein the secondary evaporation concentration process in S3 is that the low-concentration formaldehyde solution sequentially passes through a primary evaporation concentration tower and a secondary evaporation concentration tower to obtain a high-concentration formaldehyde solution, and the concentration of the high-concentration formaldehyde solution is 70-85%; in S3, the drying is performed by a rake dryer.
7. The production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol according to claim 1, wherein a dryer is used for drying, the dryer comprises a cylinder body, a hollow shaft penetrating through the inside of the cylinder body, a plurality of hollow pipes and a plurality of baffles, the plurality of baffles divide the inside of most hollow shafts into a plurality of internal spaces, and each two adjacent internal spaces are communicated by at least one hollow pipe.
8. The system of claim 7, wherein the hollow tube comprises two vertical tubes and a horizontal tube, one end of each vertical tube is fixedly connected to two ends of the horizontal tube, and the other end of each vertical tube is connected to two adjacent internal spaces.
9. The production system of claim 7, wherein the baffle comprises an upper baffle and a lower baffle, one end of the upper baffle is connected to the inner side wall of the upper part of the hollow shaft, one end of the lower baffle is connected to the inner side wall of the lower part of the hollow shaft, and the free end parts of the upper baffle and the lower baffle are overlapped to form a sealing structure; the upper baffle and the lower baffle are elastic bodies.
10. The production system for preparing formaldehyde, paraformaldehyde, methylal and hexamethylenetetramine from methanol according to claim 2, wherein the heat collected by the heat collecting tube in the process B is returned to the drying section in the process S3 for utilization.
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