CN111559960B - System and method for preparing anhydrous formaldehyde from methanol - Google Patents
System and method for preparing anhydrous formaldehyde from methanol Download PDFInfo
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Abstract
The invention discloses a system for preparing anhydrous formaldehyde from methanol, which comprises a dehydrogenation reactor, and a molten salt circulating unit, a methanol pretreatment unit and a product cooling unit which are connected with the dehydrogenation reactor; and the product cooling unit is respectively connected with the lava circulating unit and the methanol pretreatment unit. The invention also provides a method for preparing anhydrous formaldehyde by methanol, the method for preparing anhydrous formaldehyde by direct dehydrogenation of methanol is a new method with obvious process advantages and economic benefits, can effectively solve the problems of long flow and large investment in the industrial synthesis process of polymethoxy dimethyl ether, makes up technical air and short boards in the formaldehyde industry, and promotes the development of coal chemical industry and petrochemical industry to high-efficiency energy-saving green chemistry.
Description
Technical Field
The invention relates to the technical field of chemical synthesis, in particular to a system and a method for preparing anhydrous formaldehyde from methanol.
Background
Polyoxymethylene dimethyl ether (PODE) is a novel environment-friendly diesel oil oxygen-containing component capable of reducing oil consumption and reducing tail gas pollution, has excellent intersolubility with diesel oil, and can improve the combustion performance of the diesel oil and reduce the emission of the automobile tail gas pollution by over 50 percent. However, the polyoxymethylene dimethyl ethers synthesis process is demanding on raw materials, and requires formaldehyde or anhydrous formaldehyde with a concentration of 75% or more. Meanwhile, formaldehyde has active chemical properties and can react with a plurality of substances, and engineering plastics, urotropine and other medicines with excellent synthetic performance have increasingly increased requirements on formaldehyde with the concentration of over 75 percent and anhydrous formaldehyde. However, at present, formaldehyde with a concentration of 75% or more and anhydrous formaldehyde are obtained by removing water from industrial formaldehyde aqueous solutions by various methods, and it is necessary to directly prepare formaldehyde with a concentration of 75% or more and anhydrous formaldehyde.
However, the existing mature formaldehyde synthesis methods include a methanol silver catalytic method, a methanol iron molybdenum catalytic method and the like, the produced formaldehyde contains a large amount of water, the vapor pressure of the formaldehyde aqueous solution is low, and the formaldehyde and the water can easily form an azeotrope, so that the separation and purification of the formaldehyde are very difficult, and the energy consumption is high, and the cost is high.
Therefore, how to prepare anhydrous formaldehyde is a problem to be solved urgently by the technical personnel in the field.
Disclosure of Invention
In view of the above, the present invention provides a system and a method for preparing anhydrous formaldehyde from methanol, wherein the obtained formaldehyde and the byproduct hydrogen are easy to separate, no water is generated, the separation of formaldehyde aqueous solution is avoided, the investment of rectification equipment and the cost of operation are effectively saved, and the byproduct hydrogen is hydrogen; meanwhile, the reaction does not corrode equipment, and is beneficial to the stabilization and purification of the formaldehyde solution.
In order to achieve the purpose, the invention adopts the following technical scheme:
a system for preparing anhydrous formaldehyde from methanol is characterized by comprising a dehydrogenation reactor, and a molten salt circulating unit, a methanol pretreatment unit and a product cooling unit which are connected with the dehydrogenation reactor; and the product cooling unit is respectively connected with the lava circulating unit and the methanol pretreatment unit.
The beneficial effects of the preferred technical scheme are as follows: compared with a silver-catalyzed methanol excess method or an iron-molybdenum-catalyzed air excess method, the system for preparing anhydrous formaldehyde from methanol disclosed by the invention has the advantages of short process flow, less equipment investment, low operation and maintenance cost and low energy consumption, and the reaction product does not contain water or trace water and is more favorable for product application.
Preferably, the molten salt circulating unit comprises a molten salt kettle, a molten salt pump, a molten salt heat conduction oil heat exchanger and a molten salt furnace; the upstream of the molten salt kettle is connected with the dehydrogenation reactor, and the downstream of the molten salt kettle is connected with the molten salt heat conduction oil exchanger through the molten salt pump; the downstream of the fused salt heat conduction oil exchanger is connected with the fused salt furnace, and the fused salt furnace is connected with the dehydrogenation reactor.
The beneficial effects of the preferred technical scheme are as follows: the invention utilizes the molten salt circulating unit to completely realize the closed cycle of the heat exchange process, fully utilizes the energy and is beneficial to accurately controlling the reaction temperature.
Preferably, the methanol pretreatment unit comprises a methanol vaporizer and a methanol heat-conducting oil heat exchanger, wherein the methanol vaporizer vaporizes the methanol and is connected with the dehydrogenation reactor through the methanol heat-conducting oil heat exchanger.
The beneficial effects of the preferred technical scheme are as follows: the heat of reaction is removed through heat exchange of the heat conducting oil, and meanwhile, the methanol vaporization is completed, so that the removal of the heat of reaction can be completed, the energy required by the methanol vaporization can be completed, and the energy can be fully utilized.
Preferably, the product cooling unit comprises a quencher, a condenser, a steam generator, a vacuum pump and a heat-conducting oil storage tank; the upper stream of the quencher is connected with the dehydrogenation reactor, and the lower stream of the quencher is connected with the condenser; the condenser is circularly connected with the steam generator, and the downstream of the condenser is connected with the vacuum pump; and the heat conducting oil storage tank is respectively in circulating connection with the quencher, the molten salt heat conducting oil heat exchanger and the methanol heat conducting oil heat exchanger.
The beneficial effects of the preferred technical scheme are as follows: the chiller is used for primary heat exchange, the condenser is used for secondary heat exchange, and the primary heat exchange and the secondary heat exchange are mutually matched, so that the phenomenon that equipment leakage is caused due to the fact that the temperature difference of a single heat exchanger is too large and thermal stress is generated can be effectively avoided; the residual heat is used for exchanging heat with the steam generator to generate steam, so that the energy can be more effectively utilized; the vacuum system is used for reducing the retention time of reaction products in the catalyst, reducing side reactions and improving the reaction rate.
Preferably, the formaldehyde absorption unit comprises a first absorption tower and a second absorption tower;
the tower kettle of the first absorption tower is connected with the vacuum pump, anhydrous formaldehyde is output from the tower bottom, and the tower top is connected with the second absorption tower;
the tower kettle of the second absorption tower is connected with the tower top of the first absorption tower, the tower bottom of the second absorption tower is connected with a downstream device or a collecting device, and a hydrogen outlet is formed in the tower top;
the inside of first absorption tower with the second absorption tower sets gradually multilayer sieve and multilayer packing layer from top to bottom, every layer the top of packing layer is provided with liquid distributor, and the bottom is provided with liquid catch tray, liquid catch tray pass through pump, formaldehyde cooler with liquid distributor is connected.
The beneficial effects of the preferred technical scheme are as follows: the invention adopts two towers to respectively absorb, the first absorption tower can efficiently recover formaldehyde without water, and the second absorption tower adopts refined water to absorb, so that formaldehyde which is not absorbed by the first absorption tower can be completely recovered, and the discharged hydrogen can be washed by water to obtain more pure hydrogen. Meanwhile, the sieve plate and the filler are combined in the first absorption tower and the second absorption tower, so that respective advantages of the sieve plate and the filler can be fully exerted, and the optimal absorption effect is achieved.
Preferably, the formaldehyde cooler comprises a chilled water heat exchanger and a circulating water heat exchanger, the first layer of the packing layer is correspondingly provided with the chilled water heat exchanger, and the rest of the packing layers correspond to the circulating water heat exchanger.
The beneficial effects of the preferred technical scheme are as follows: the invention adopts the chilled water and the circulating water as heat exchange media, not only can achieve the heat exchange effect, but also can achieve the purpose of energy saving, and can effectively control the generation of formaldehyde scales.
The invention also provides a method for preparing anhydrous formaldehyde from methanol, which adopts the system and specifically comprises the following steps:
(1) Introducing nitrogen into the methanol dehydrogenation unit; introducing methanol into a methanol pretreatment unit, introducing the vaporized methanol into a dehydrogenation reactor, controlling the dehydrogenation reaction temperature through a molten salt circulation unit, and carrying out dehydrogenation reaction on the methanol under the action of a catalyst;
(2) Vacuumizing by a vacuum pump, and cooling the reaction gas by a quencher and a condenser in sequence;
(3) Introducing the cooled reaction gas into a first absorption tower, and absorbing by absorption liquid to obtain anhydrous formaldehyde; and introducing the residual gas into a second absorption tower to be absorbed by the refined water, discharging the residual hydrogen from the top of the tower, and collecting the residual hydrogen at the bottom of the tower to obtain the formaldehyde water solution.
The beneficial effects of the preferred technical scheme are as follows: the invention prepares the formaldehyde by methanol dehydrogenation, and obtains the anhydrous formaldehyde by absorption of the absorption liquid, and adopts reasonable process steps, thereby not only achieving high-quality products, but also achieving short process, less investment and low operation cost.
Preferably, the oxygen concentration in step (1) is <1000ppm; the vaporization temperature is 65-320 ℃; the temperature of the dehydrogenation reaction is 350-750 ℃, and the catalyst is a silver-loaded nano-grade rare metal catalyst.
The beneficial effects of the preferred technical scheme are as follows: under the action of the silver-loaded nano-scale rare metal catalyst, the invention effectively reduces the reaction temperature and fully utilizes the temperature difference of two media to increase the vaporization temperature of the methanol.
Preferably, the vacuumizing pressure in the step (2) is-1 kPa to-99 kPa, and the cooling is carried out to 80-120 ℃.
The beneficial effects of the preferred technical scheme are as follows: the invention can improve the reaction rate and reduce the generation of side reaction by vacuumizing and controlling under the negative pressure condition.
Preferably, the absorption liquid in the step (3) is refined water, methanol or methylal; the temperature of the top of the first absorption tower is 20-70 ℃, the temperature of the bottom of the first absorption tower is 50-130 ℃, and the pressure of the first absorption tower is 30-800 kPa; the temperature of the top of the second absorption tower is 20-30 ℃, the temperature of the bottom of the second absorption tower is 60-90 ℃, and the pressure of the second absorption tower is 30-70 kPa.
The beneficial effects of the preferred technical scheme are as follows: within the temperature and pressure range limited by the invention, the emission loss of organic components at the top of the tower can be effectively controlled, and the generation of formaldehyde scales can be effectively inhibited.
According to the technical scheme, compared with the prior art, the invention discloses a system and a method for preparing anhydrous formaldehyde from methanol, and the system and the method have the following beneficial effects:
(1) The system for preparing anhydrous formaldehyde from methanol disclosed by the invention is simple in structure, short in production process flow and low in investment;
(2) The system and the method disclosed by the invention have the advantages of high conversion rate and yield of the anhydrous formaldehyde, simple product separation and low production cost;
(3) The product obtained by the method disclosed by the invention is a mixed gas of formaldehyde and hydrogen, wherein the byproduct is easy to separate and is generated without water, the separation of a formaldehyde aqueous solution is avoided, the investment of rectification equipment and the operation cost thereof are effectively saved, and the byproduct is hydrogen; meanwhile, the reaction does not corrode equipment, and is beneficial to the stabilization and purification of the formaldehyde solution.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a schematic flow chart of a system for preparing anhydrous formaldehyde from methanol according to example 1 of the present invention.
In the figure: 101 is a dish-type dehydrogenation reactor, 102 is a molten salt kettle, 103 is a molten salt pump, 104 is a molten salt heat transfer oil heat exchanger, 105 is a methanol vaporizer, 106 is a molten salt furnace, 107 is a methanol heat transfer oil heat exchanger, 108 is a heat transfer oil storage tank, 109 is a heat transfer oil storage tank, 110 is a quencher, 111 is a condenser, 112 is a steam generator, 113 is a vacuum pump, 114 is a first absorption tower, 115 is a second absorption tower, 116 is a chilled water heat exchanger, 117 is a chilled water heat exchanger, 118 is a circulating water heat exchanger, and 119 is a circulating water heat exchanger.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Example 1
A system for preparing anhydrous formaldehyde by using methanol comprises a dehydrogenation reactor, and a molten salt circulating unit, a methanol pretreatment unit and a product cooling unit which are connected with the dehydrogenation reactor; and the product cooling unit is respectively connected with the lava circulating unit and the methanol pretreatment unit.
The molten salt circulating unit comprises a molten salt kettle, a molten salt pump, a molten salt heat conduction oil heat exchanger and a molten salt furnace; the upper stream of the fused salt kettle is connected with a dehydrogenation reactor, and the lower stream of the fused salt kettle is connected with a fused salt heat conduction oil exchanger through a fused salt pump; the lower reaches of the fused salt heat conduction oil exchanger are connected with a fused salt furnace, and the fused salt furnace is connected with the dehydrogenation reactor.
The methanol pretreatment unit comprises a methanol vaporizer and a methanol heat-conducting oil heat exchanger, wherein the methanol vaporizer vaporizes methanol and is connected with the dehydrogenation reactor through the methanol heat-conducting oil heat exchanger.
The product cooling unit comprises a quencher, a condenser, a steam generator, a vacuum pump and a heat-conducting oil storage tank; the upper stream of the quencher is connected with the dehydrogenation reactor, and the lower stream of the quencher is connected with the condenser; the condenser is circularly connected with the steam generator, and the downstream of the condenser is connected with a vacuum pump; the heat conducting oil storage tank is respectively connected with the quencher, the molten salt heat conducting oil heat exchanger and the methanol heat conducting oil heat exchanger in a circulating manner.
The formaldehyde absorption unit comprises a first absorption tower and a second absorption tower;
the tower kettle of the first absorption tower is connected with a vacuum pump, anhydrous formaldehyde is output from the tower bottom, and the tower top is connected with the second absorption tower;
the tower kettle of the second absorption tower is connected with the tower top of the first absorption tower, the tower bottom is connected with a downstream device or a collecting device, and a hydrogen outlet is arranged at the tower top;
the inside of first absorption tower and second absorption tower sets gradually multilayer sieve and multilayer packing layer from top to bottom, and the top of every layer of packing layer is provided with liquid distributor, and the bottom is provided with liquid catch tray, and liquid catch tray passes through pump, formaldehyde cooler and is connected with liquid distributor.
The formaldehyde cooler comprises a chilled water heat exchanger and a circulating water heat exchanger, the chilled water heat exchanger is correspondingly arranged on the first packing layer, and the other packing layers correspond to the circulating water heat exchanger.
Principle of operation
The gas in the whole system is replaced by nitrogen in the using process to ensure O in the system 2 ％<0.1% (1000 ppm), then conveying the molten salt in the molten salt kettle to a molten salt heat transfer oil heat exchanger through a molten salt pump, heating the molten salt to 350-750 ℃ through a molten salt furnace, and returning the heated molten salt to the molten salt kettle to form circulation after passing through the shell pass of the butterfly-shaped dehydrogenation reactor, thereby achieving the purpose of controlling the temperature of the butterfly-shaped dehydrogenation reactor. Conveying raw material methanol to a methanol vaporizer through a pump, controlling the vaporization temperature of the methanol to be 280-320 ℃ during initial start-up, controlling the vaporization temperature of the methanol to be 65-320 ℃ during normal start-up, conveying the methanol to a methanol heat conducting oil heat exchanger after the vaporization temperature of the methanol reaches the standard, carrying out heat exchange, conveying the methanol to a disc-type dehydrogenation reactor, contacting with a silver loaded nanoscale rare metal catalyst filled in the reactor, and simultaneously controlling the dehydrogenation reaction temperature of the methanol to be 350-750 ℃ through controlling the temperature of molten salt to carry out dehydrogenation reaction; pumping out the reacted gas through a vacuum pump, controlling the vacuum pressure to be-1 to-99 kpa, moving the reacted gas away through heat conducting oil of a shell layer of a quencher, enabling a heat conducting oil gas phase of the shell layer of the quencher to pass through a heat conducting oil tank to a molten salt heat conducting oil heat exchanger to exchange heat with a methanol heat conducting oil heat exchanger, enabling the heat conducting oil gas phase to become liquid phase heat conducting oil after heat exchange to return to the heat conducting oil tank through gravity, then returning to the shell layer of the quencher to form circulation, and enabling the reacted gas to be in a circulating stateThe body gets back to the condenser after through the quench cooler quenching, and steam generator is carried to hot water, and steam generator's lower cauldron hot water gets back to the condenser and carries out the heat exchange and produce steam, and the steam that produces shifts out through steam generator, carries first absorption tower through the vacuum pump after the reaction gas heat exchange.
The reaction gas is conveyed to the tower kettle of a first absorption tower through a vacuum system for formaldehyde absorption, absorption liquid can be refined water, methanol and methylal, the absorption liquid is absorbed by refined water when producing hydrated formaldehyde, the absorption liquid is absorbed by methylal or methanol when producing Polyoxymethylene (PODE) or anhydrous formaldehyde, the addition amount of the absorption liquid is adjusted according to the required concentration of downstream products, the absorption liquid is added from a first layer sieve plate or a second layer sieve plate on the top of the tower, the number of the sieve plates on the top of the first absorption tower is 5-20, the tower is provided with 2-9 packing layers, the lower part of each packing layer is provided with a liquid collecting disc, the liquid on the liquid collecting disc is conveyed to a heat exchanger through a pump and then to a liquid distributor, the formaldehyde circulating through the first layer packing tower is cooled by a freezing water in a first hydrated formaldehyde cooler, the formaldehyde circulating through the second layer packing tower is cooled by a circulating water in a corresponding formaldehyde cooler, the anhydrous formaldehyde at the tower bottom of the first absorption tower is extracted to a storage tank or is conveyed to a downstream device, organic components and hydrogen which are not absorbed at the tower top return to the tower bottom of a second absorption tower for formaldehyde absorption again, the absorption liquid is refined water, the absorption liquid is added from a first layer of sieve plate or a second third layer of sieve plate at the tower top, the number of the sieve plates at the tower top is 5-20, 2-9 packing layers are arranged in the tower, a liquid collecting tray is arranged at the lower part of a liquid distributor at the upper part of each packing layer, the liquid on the liquid collecting tray is conveyed to a heat exchanger through a pump and then conveyed to a liquid distributor, the formaldehyde circulating through the first layer of packing tower is cooled by frozen water in a first hydrated formaldehyde cooler, the formaldehyde circulating through the packing tower below the second layer is cooled by circulating water in a corresponding formaldehyde cooler, and the hydrated formaldehyde at the tower bottom of the second absorption tower is conveyed to the storage tank or the downstream device through a tower bottom pump, the hydrogen washed on the top of the tower is delivered to a downstream device or an incinerator to be incinerated to generate steam, the temperature of the top of the first absorption tower is controlled to be 20-70 ℃, the temperature of the bottom of the first absorption tower is controlled to be 50-130 ℃, the tower pressure is controlled to be 30-800 kpa, the temperature of the top of the second absorption tower is controlled to be 20-30 ℃, the temperature of the bottom of the second absorption tower is controlled to be 60-90 ℃, and the tower pressure is controlled to be 30-70 kpa.
Examples 2 to 7
Embodiments 2 to 7 of the present invention further provide a method for preparing anhydrous formaldehyde from methanol, where the system for preparing anhydrous formaldehyde from methanol disclosed in embodiment 1 specifically includes the following steps, where each specific technical parameter is as shown in table 1 below:
(1) Introducing nitrogen into the methanol dehydrogenation unit, and controlling the oxygen concentration to be less than 1000ppm; introducing methanol into a methanol pretreatment unit, and introducing the vaporized methanol into a dehydrogenation reactor, wherein the vaporization temperature is 65-320 ℃; controlling the dehydrogenation reaction temperature to be 350-750 ℃ through a molten salt circulating unit, and carrying out dehydrogenation reaction on methanol under the action of a silver-loaded nanoscale rare metal catalyst;
(2) Vacuumizing by a vacuum pump to-1 kPa to-99 kPa, and cooling the reaction gas to 80-120 ℃ by a quencher and a condenser in sequence;
(3) Introducing the cooled reaction gas into a first absorption tower, absorbing the reaction gas by refined water, methanol or methylal, introducing a mixed solution of anhydrous formaldehyde or methylal into a storage tank or a downstream device, introducing the residual gas into a second absorption tower, absorbing the residual gas by the refined water, discharging the residual hydrogen from the top of the tower, and collecting the residual hydrogen at the bottom of the tower to obtain hydrated formaldehyde; the temperature of the top of the first absorption tower is controlled to be 20-70 ℃, the temperature of the bottom of the first absorption tower is controlled to be 50-130 ℃, the pressure of the first absorption tower is controlled to be 30 kPa-800 kPa, the temperature of the top of the second absorption tower is controlled to be 20-30 ℃, the temperature of the bottom of the second absorption tower is controlled to be 60-90 ℃, and the pressure of the second absorption tower is controlled to be 30 kPa-70 kPa.
TABLE 1
The above methods of examples 2 to 6 were respectively used to calculate the conversion rate of methanol during dehydrogenation, and the selectivity of formaldehyde, carbon dioxide and dimethyl ether in the product was calculated, and the results are shown in table 2.
TABLE 2
It is obvious from the above table that the conversion rates of methanol are all above 94% by using the methods disclosed in the embodiments 2 to 6 of the present invention, especially the conversion rates of the embodiments 4 to 6 can be as high as 100%, which indicates that the raw material utilization rate is high, and the raw material cost is effectively saved; the selectivity of formaldehyde in the product is above 81%, wherein the selectivity of formaldehyde in example 5 is even as high as 100%, the content of byproducts and impurities in the product is low, and the yield of the formaldehyde product is high.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. The device disclosed by the embodiment corresponds to the method disclosed by the embodiment, so that the description is simple, and the relevant points can be referred to the method part for description.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. The device for preparing anhydrous formaldehyde from methanol is characterized by comprising a dehydrogenation reactor, and a molten salt circulating unit, a methanol pretreatment unit and a product cooling unit which are connected with the dehydrogenation reactor; the product cooling unit is respectively connected with the molten salt circulating unit and the methanol pretreatment unit;
the molten salt circulating unit comprises a molten salt kettle, a molten salt pump, a molten salt heat conduction oil heat exchanger and a molten salt furnace; the upper stream of the molten salt kettle is connected with the dehydrogenation reactor, and the lower stream of the molten salt kettle is connected with the molten salt heat conduction oil exchanger through the molten salt pump; the lower stream of the fused salt heat conduction oil exchanger is connected with the fused salt furnace, and the fused salt furnace is connected with the dehydrogenation reactor.
2. The apparatus of claim 1, wherein the methanol pretreatment unit comprises a methanol vaporizer and a methanol heat transfer oil exchanger, the methanol vaporizer vaporizes the methanol and is connected to the dehydrogenation reactor through the methanol heat transfer oil exchanger.
3. The apparatus for preparing anhydrous formaldehyde from methanol according to claim 2, wherein the product cooling unit comprises a chiller, a condenser, a steam generator, a vacuum pump and a heat transfer oil storage tank; the upper stream of the quencher is connected with the dehydrogenation reactor, and the lower stream of the quencher is connected with the condenser; the condenser is circularly connected with the steam generator, and the downstream of the condenser is connected with the vacuum pump; the heat conducting oil storage tank is respectively connected with the quencher, the molten salt heat conducting oil heat exchanger and the methanol heat conducting oil heat exchanger in a circulating manner.
4. The apparatus for preparing anhydrous formaldehyde from methanol according to claim 3, further comprising a formaldehyde absorption unit, wherein the formaldehyde absorption unit comprises a first absorption tower and a second absorption tower;
the tower kettle of the first absorption tower is connected with the vacuum pump, anhydrous formaldehyde is output from the tower bottom, and the tower top is connected with the second absorption tower;
the tower kettle of the second absorption tower is connected with the tower top of the first absorption tower, the tower bottom of the second absorption tower is connected with a downstream device or a collecting device, and a hydrogen outlet is formed in the tower top;
the interior of the first absorption tower and the interior of the second absorption tower are sequentially provided with a plurality of layers of sieve plates and a plurality of layers of packing layers from top to bottom, the top of each layer of packing layer is provided with a liquid distributor, the bottom of each layer of packing layer is provided with a liquid collecting disc, and the liquid collecting discs are connected with the liquid distributors through pumps and formaldehyde coolers.
5. The device for preparing anhydrous formaldehyde from methanol according to claim 4, wherein the formaldehyde cooler comprises a chilled water heat exchanger and a circulating water heat exchanger, the first layer of the packing layer is correspondingly provided with the chilled water heat exchanger, and the rest of the packing layers are correspondingly provided with the circulating water heat exchanger.
6. A method for preparing anhydrous formaldehyde by using methanol is characterized by adopting the device as claimed in any one of claims 1 to 5, and specifically comprising the following steps:
(1) Introducing nitrogen into the methanol dehydrogenation unit; introducing methanol into a methanol pretreatment unit, introducing the vaporized methanol into a dehydrogenation reactor, controlling the dehydrogenation reaction temperature through a molten salt circulation unit, and carrying out dehydrogenation reaction on the methanol under the action of a catalyst;
(2) Vacuumizing by a vacuum pump, and cooling the reaction gas by a quencher and a condenser in sequence;
(3) Introducing the cooled reaction gas into a first absorption tower, and absorbing by absorption liquid to obtain anhydrous formaldehyde; and introducing the residual gas into a second absorption tower to be absorbed by the refined water, discharging the residual hydrogen from the top of the tower, and collecting the residual hydrogen at the bottom of the tower to obtain the formaldehyde water solution.
7. The method for preparing anhydrous formaldehyde from methanol according to claim 6, wherein in the step (1), nitrogen is introduced into the methanol dehydrogenation unit, and the oxygen concentration is controlled to be less than 1000ppm; the vaporization temperature is 65-320 ℃; the temperature of the dehydrogenation reaction is 350-750 ℃, and the catalyst is a silver-loaded nano-scale rare metal catalyst.
8. The method for preparing anhydrous formaldehyde from methanol according to claim 6, wherein the vacuum is applied at a pressure of-1 kPa to-99 kPa in the step (2), and the cooling is performed to 80-120 ℃.
9. The method for preparing anhydrous formaldehyde from methanol according to claim 6, wherein the absorption liquid in step (3) is methanol or methylal; the temperature of the top of the first absorption tower is 20-70 ℃, the temperature of the bottom of the first absorption tower is 50-130 ℃, and the pressure of the first absorption tower is 30-800 kPa; the temperature of the top of the second absorption tower is 20-30 ℃, the temperature of the bottom of the second absorption tower is 60-90 ℃, and the pressure of the second absorption tower is 30-70 kPa.
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| CN106397147A (en) * | 2016-08-19 | 2017-02-15 | 新疆天智辰业化工有限公司 | Technology for producing formaldehyde through iron-molybdenum method |
| CN109557964A (en) * | 2018-12-27 | 2019-04-02 | 南通江天化学股份有限公司 | A kind of dcs of high-concentration formaldehyde production line |
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| CN106397147A (en) * | 2016-08-19 | 2017-02-15 | 新疆天智辰业化工有限公司 | Technology for producing formaldehyde through iron-molybdenum method |
| CN109557964A (en) * | 2018-12-27 | 2019-04-02 | 南通江天化学股份有限公司 | A kind of dcs of high-concentration formaldehyde production line |
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