CN114315650A - Method and system for continuously producing dimethyl urea - Google Patents
Method and system for continuously producing dimethyl urea Download PDFInfo
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- CN114315650A CN114315650A CN202111502354.2A CN202111502354A CN114315650A CN 114315650 A CN114315650 A CN 114315650A CN 202111502354 A CN202111502354 A CN 202111502354A CN 114315650 A CN114315650 A CN 114315650A
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- MGJKQDOBUOMPEZ-UHFFFAOYSA-N N,N'-dimethylurea Chemical compound CNC(=O)NC MGJKQDOBUOMPEZ-UHFFFAOYSA-N 0.000 title claims abstract description 74
- 238000000034 method Methods 0.000 title claims abstract description 42
- BAVYZALUXZFZLV-UHFFFAOYSA-N Methylamine Chemical compound NC BAVYZALUXZFZLV-UHFFFAOYSA-N 0.000 claims abstract description 118
- XGEGHDBEHXKFPX-UHFFFAOYSA-N N-methyl urea Chemical compound CNC(N)=O XGEGHDBEHXKFPX-UHFFFAOYSA-N 0.000 claims abstract description 85
- 238000006243 chemical reaction Methods 0.000 claims abstract description 66
- 239000007788 liquid Substances 0.000 claims abstract description 47
- XSQUKJJJFZCRTK-UHFFFAOYSA-N Urea Chemical compound NC(N)=O XSQUKJJJFZCRTK-UHFFFAOYSA-N 0.000 claims abstract description 35
- 239000004202 carbamide Substances 0.000 claims abstract description 35
- 238000012546 transfer Methods 0.000 claims abstract description 12
- 238000002309 gasification Methods 0.000 claims abstract description 9
- 238000002156 mixing Methods 0.000 claims abstract description 9
- 238000003860 storage Methods 0.000 claims abstract description 7
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 47
- 238000012856 packing Methods 0.000 claims description 33
- 230000008569 process Effects 0.000 claims description 26
- 238000001816 cooling Methods 0.000 claims description 15
- XGEGHDBEHXKFPX-NJFSPNSNSA-N methylurea Chemical compound [14CH3]NC(N)=O XGEGHDBEHXKFPX-NJFSPNSNSA-N 0.000 claims description 15
- 238000010521 absorption reaction Methods 0.000 claims description 9
- 238000007599 discharging Methods 0.000 claims description 9
- 238000010438 heat treatment Methods 0.000 claims description 9
- 238000010924 continuous production Methods 0.000 claims description 7
- 238000001914 filtration Methods 0.000 claims description 6
- 238000004806 packaging method and process Methods 0.000 claims description 6
- 229910001220 stainless steel Inorganic materials 0.000 claims description 6
- 239000010935 stainless steel Substances 0.000 claims description 6
- 238000002425 crystallisation Methods 0.000 claims description 4
- 230000008025 crystallization Effects 0.000 claims description 4
- 230000015572 biosynthetic process Effects 0.000 claims description 3
- 239000000945 filler Substances 0.000 claims description 3
- 239000007787 solid Substances 0.000 claims description 3
- 238000004519 manufacturing process Methods 0.000 abstract description 10
- 239000007791 liquid phase Substances 0.000 abstract description 3
- 239000002994 raw material Substances 0.000 abstract description 3
- 239000000155 melt Substances 0.000 abstract 1
- 239000007789 gas Substances 0.000 description 21
- 239000000047 product Substances 0.000 description 17
- 238000007039 two-step reaction Methods 0.000 description 9
- 239000006227 byproduct Substances 0.000 description 6
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 6
- 239000002699 waste material Substances 0.000 description 5
- 238000005265 energy consumption Methods 0.000 description 4
- 239000013067 intermediate product Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 230000007246 mechanism Effects 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 239000006200 vaporizer Substances 0.000 description 4
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 3
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 3
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 3
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 3
- XEKOWRVHYACXOJ-UHFFFAOYSA-N Ethyl acetate Chemical compound CCOC(C)=O XEKOWRVHYACXOJ-UHFFFAOYSA-N 0.000 description 3
- 238000003786 synthesis reaction Methods 0.000 description 3
- 239000002918 waste heat Substances 0.000 description 3
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- ROSDSFDQCJNGOL-UHFFFAOYSA-N Dimethylamine Chemical compound CNC ROSDSFDQCJNGOL-UHFFFAOYSA-N 0.000 description 2
- -1 amide compounds Chemical class 0.000 description 2
- 229910052799 carbon Inorganic materials 0.000 description 2
- 230000008878 coupling Effects 0.000 description 2
- 238000010168 coupling process Methods 0.000 description 2
- 238000005859 coupling reaction Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000009826 distribution Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 229910000069 nitrogen hydride Inorganic materials 0.000 description 2
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- 238000004886 process control Methods 0.000 description 2
- 230000035484 reaction time Effects 0.000 description 2
- 230000009467 reduction Effects 0.000 description 2
- YBBLOADPFWKNGS-UHFFFAOYSA-N 1,1-dimethylurea Chemical compound CN(C)C(N)=O YBBLOADPFWKNGS-UHFFFAOYSA-N 0.000 description 1
- PHTSTUUPYUUDES-UHFFFAOYSA-N 1,3-dimethylurea Chemical compound CNC(NC)=O.CNC(NC)=O PHTSTUUPYUUDES-UHFFFAOYSA-N 0.000 description 1
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 230000002378 acidificating effect Effects 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 230000005587 bubbling Effects 0.000 description 1
- 230000008859 change Effects 0.000 description 1
- 238000012824 chemical production Methods 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 239000000498 cooling water Substances 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
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- 239000003960 organic solvent Substances 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
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Abstract
The application discloses a method and a system for continuously producing dimethyl urea. This application uses urea and monomethylamine as raw materials, divides two steps reaction, adopts the continuous reaction mode of tower series connection, and urea gets into the liquefaction jar from the storage tank, melts back through the pump sending to first packed tower upper end, and in liquid monomethylamine gasification back got into first packed tower from packed tower bottom, molten urea and gaseous monomethylamine gas-liquid contact countercurrent mixing, and both react and generate monomethylurea. The monomethyl urea enters the upper end of the second packed tower through a heater, the monomethyl amine is extracted from a gasification tank and then is heated, the monomethyl amine enters the tower from the bottom of the second packed tower, and gas-liquid phases are in full contact reaction in the packed tower to generate liquid dimethyl urea. Compared with the traditional intermittent multi-kettle series mode, the invention adopts two tower reactors, greatly reduces the equipment space, has continuous and automatic production process, advanced production process, good mass transfer performance, high heat transfer efficiency, quick reaction, improved yield and high safety.
Description
Technical Field
The invention relates to the technical field of chemical production, in particular to a method and a system for continuously producing dimethyl urea.
Background
Dimethyl urea (dimethylurea) belongs to amide compounds and is also called as homodimethyl urea and N, N-dimethylurea. CAS number 96-31-1, English name N, N' -Dimethyl urea, chemical formula C3H8N2O, molecular weight 88.11 g/mol. The pure product is in a gray-white thin sheet crystal state, the melting point is 101 ℃, and monomethylamine gas is easily generated by decomposition under the acidic or alkaline condition. Dimethyl urea has high solubility in water, is easily soluble in organic solvents such as acetone, benzene, ethyl acetate and ethanol, and is insoluble in gasoline and diethyl ether.
The national intellectual property office in 1988, 9.21 discloses a utility model patent with publication number CN87211457U entitled "continuous countercurrent four-stage series connection dimethyl urea manufacturing device", which adopts four reaction kettles connected in series as a reaction synthesis device, and has large occupied space and low space utilization rate; the gas monomethylamine is contacted with the liquid urea in a countercurrent mode, and excessive gaseous monomethylamine can cause more raw material waste; the gas phase and the liquid phase react in a bubbling contact mode, the contact area of the gas phase and the liquid phase is small, the reaction of the monomethylamine and the urea is insufficient, the mass transfer and heat transfer effects are not ideal, the reaction rate is reduced, the reaction time is long, and the production efficiency is low.
The national intellectual property office discloses a utility model patent with publication number CN205965801U entitled "tower reactor for dimethyl urea synthesis reaction" in 2017, 2.22.2017, and although gas-liquid mass transfer is increased, the tower equipment is complicated and bulky.
At present, no relevant continuous dimethyl urea preparation process is reported. Therefore, it is an urgent need to overcome the technical problems of providing a system and a production method for continuously preparing dimethylurea.
Disclosure of Invention
The invention aims to provide a method and a system for continuously producing dimethylurea, which are used for solving the technical problems that a plurality of reaction kettles are connected in series to serve as a reaction synthesis device in the prior art, the reaction device occupies large space, the space utilization rate is low, the reaction time is long, and the production efficiency is low.
In order to achieve the above object, one embodiment of the present invention provides a method for continuously producing dimethylurea, comprising the steps of: a step of preparing methyl urea, wherein urea is molten and then conveyed to the upper end of a first packed tower, and is uniformly distributed on a filler in the first packed tower through a liquid distributor; heating monomethylamine to be in a gaseous state, then feeding the gaseous monomethylamine into a packed tower from the bottom of the first packed tower, carrying out mutual countercurrent mixing on molten urea and the gaseous monomethylamine, and carrying out sufficient gas-liquid contact and reaction on the surface of a packing to generate monomethylurea; the method comprises the following steps of (1) extracting liquid-state methylurea from the lower end of a first packed tower, conveying the extracted liquid-state methylurea to the upper end of a second packed tower, and uniformly distributing the liquid-state methylurea on a filler in the second packed tower through a liquid distributor; heating monomethylamine to be in a gas state, then entering the packed tower from the bottom of the second packed tower, mixing liquid monomethylurea and gaseous monomethylamine in a mutually countercurrent mode, and carrying out sufficient gas-liquid contact and reaction on the surface of the packing to generate dimethylurea.
Further, in the step of preparing the monomethylurea, the urea and the monomethylamine enter the first packed tower in a molar ratio of 1:1, and the temperature in the first packed tower is controlled at 140 ℃ of 135-.
Further, in the step of preparing the dimethyl urea, the monomethyl urea and the monomethyl amine enter the second packed tower in a molar ratio of 1:1, and the temperature in the second packed tower is controlled at 160-170 ℃.
Further, in the step of preparing the monomethylurea, ammonia gas is also generated in the process of generating the monomethylurea; in the step of preparing the dimethylurea, ammonia gas is also generated in the process of generating the dimethylurea; correspondingly, the step of preparing the monomethylurea and the step of preparing the dimethylurea also comprise the step of discharging ammonia gas, and the ammonia gas generated by the reaction is extracted from the upper end of the first packed tower or the second packed tower and enters an ammonia gas absorption device after exchanging heat with the monomethylurea.
Further, after the step of preparing the dimethyl urea, the method also comprises the following steps: and packaging a finished product of the dimethyl urea, namely cooling the dimethyl urea generated by the reaction, conveying the cooled dimethyl urea into a dryer through a pump for cooling crystallization, and conveying the crystallized solid to a finished product unit for packaging.
The present application also provides a system for continuously producing dimethyl urea, comprising: the upper end of the first packed tower is provided with a first inlet and a first outlet which are correspondingly arranged, the bottom of the first packed tower is provided with a second inlet and a second outlet, and the middle of the first packed tower is filled with packing; the first inlet is used for inputting molten urea, the second inlet is used for inputting gaseous monomethylamine, the first outlet is used for filtering and discharging ammonia gas, and the second outlet is used for filtering and discharging monomethylurea; the upper end of the second packed tower is provided with a third inlet and a third outlet which are correspondingly arranged, the bottom of the second packed tower is provided with a fourth inlet and a fourth outlet, and the middle of the second packed tower is filled with packing; the third inlet is communicated with the second outlet and is fed with methylurea, the fourth inlet is fed with gaseous monomethylamine, the third outlet filters and discharges ammonia gas, and the fourth outlet filters and discharges dimethylurea.
Further, the packing in the first packed tower and the second packed tower is at least one of corrugated stainless steel structured packing or pall ring stainless steel bulk packing.
Further, the molten urea is uniformly distributed on the packing in the first packed tower through a liquid distributor; the liquid-state methylurea is uniformly distributed on the packing in the second packed tower through a liquid distributor; the liquid distributor comprises a fluted disc type liquid distributor; and/or gaseous monomethylamine is conveyed through a gas distributor, the gas distributor comprising a loop gas distributor; and/or the ammonia gas is extracted from the first outlet or the third outlet through a wire mesh demister, enters a heat exchanger for cooling and then enters an ammonia gas absorption device.
Further, the front end of the first inlet also comprises a urea storage tank, a liquefaction tank and a first delivery pump which are connected in sequence; the front end of the second inlet and/or the fourth inlet further comprises a methylamine storage tank, a second delivery pump and a gasification tank which are connected in sequence.
Further, a heat exchanger, a dryer and a finished product unit which are connected in sequence are further included after the fourth outlet.
The method and the system for continuously producing the dimethylurea have the advantages that the characteristic of a typical two-step reaction process in the dimethylurea generation process is fully utilized, the reaction principle and the physicochemical property of intermediate products at different temperatures are respectively utilized, and a specific gas-liquid reaction and gas-gas reaction mechanism is combined, so that the two-step reaction is creatively provided for replacing the traditional one-step countercurrent reaction. The invention overcomes the defects of low continuity level, serious back mixing, long operation time, great waste of human resources, large occupied space of a reaction device and low space utilization rate of the traditional reaction kettle series connection process. Two tower reactors are adopted, so that the equipment space is greatly reduced, the mass transfer performance is good, the heat transfer efficiency is high, the reaction is rapid, the yield is improved, and the safety is high. The process has the advantages of simple operation, easy control, less by-products and the like. The reaction process is systematically divided in the reaction essence, so that the equipment investment is reduced, the reaction efficiency is improved, the generation of byproducts is reduced, the energy consumption is reduced, a process basis is provided for segmented intelligent control, and the obvious path advantages of a new process are revealed as follows.
(1) The reaction is changed from the traditional multi-kettle series-connection type countercurrent operation into the two-step operation of a double-packed tower, so that the equipment investment is saved, the yield of the target product is improved, and the flow foundation is provided for continuous production.
(2) The continuous two-step reaction fully utilizes a mechanism that the temperature plays a decisive role in the reaction process, starts from controlling the temperature, ensures the two reactions to be orderly carried out by respectively applying the two temperatures, and fundamentally solves the problems of energy waste and a large amount of byproducts caused by uneven heat distribution.
(3) The continuous two-step reaction also fully utilizes the influence rule of the material ratio on the reaction, urea in the first step of reaction and monomethylamine in the second step of reaction are respectively and slightly excessive (the excessive amount is not more than 3 percent) consciously, and the high-efficiency generation of intermediate products and final products is ensured. The high purity of the target product is realized by accurately controlling the circulation amount of the excessive materials.
(4) After the production process of the dimethyl urea is purposefully divided into two processes according to the reaction principle, the process control is more refined and purposeful, the fuzzy dilemma that one reactor is a black box and the internal control cannot be realized is fundamentally avoided, and the continuity of the process is realized from the intrinsic safety.
(5) By utilizing an advanced heat exchange network pinch point technology, heat generated in the cooling process of ammonia gas, monomethylamine gas, ammonia gas and dimethyl urea liquid is respectively coupled with heat required in the processes of urea melting liquefaction and monomethylamine gasification, so that energy is saved to the maximum extent, and contribution is made to carbon emission reduction of a factory.
(6) Energy can be theoretically not wasted completely through heat coupling and accurate control, and residual heat can be completely provided by air, so that zero heat loss in the system is really realized.
Drawings
The technical solution and other advantages of the present application will be presented in the following detailed description of specific embodiments of the present application with reference to the accompanying drawings.
Fig. 1 is a schematic structural diagram of a system for continuously producing dimethyl urea provided in an embodiment of the present application.
FIG. 2 is a flow chart of a process for the continuous production of dimethyl urea as provided in the examples herein.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. It is to be understood that the embodiments described are only a few embodiments of the present application and not all 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 application.
In the description of the present application, it is to be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; may be mechanically connected, may be electrically connected or may be in communication with each other; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.
Specifically, referring to fig. 1, the embodiment of the present application provides a system for continuously producing dimethylurea, in which urea and monomethylamine are used as raw materials, and a continuous reaction mode of series-connected towers is adopted, such that first step is to prepare and generate monomethylurea, and second step is to utilize the reaction of monomethylurea and monomethylamine to generate dimethylurea. The two-step reaction generates methylurea and dimethylurea and simultaneously generates ammonia gas, and the ammonia gas is directly removed to the ammonia gas absorption device; cooling the dimethyl urea by a heat exchanger, and crystallizing to obtain a finished product. Compared with the traditional intermittent multi-kettle series mode, the two tower reactors are adopted, the equipment space is greatly reduced, the production process is continuous and automatic, the production process is advanced, the mass transfer performance is good, the heat transfer efficiency is high, the reaction is rapid, the yield is improved, and the safety is high.
The total reaction formula is H2NCONH2+2CH3NH2→CH3NHCONHCH3+2NH3。
The first reaction step is represented by the formula H2NCONH2+ CH3NH2→CH3NHCONH2+ NH3。
The second reaction formula is CH3NHCONH2+ CH3NH2→CH3NHCONHCH3+NH3。
In the embodiment of the application, the system for continuously producing the dimethyl urea comprises a first packed tower 8 and a second packed tower 11.
The upper end of the first packed tower 8 is provided with a first inlet and a first outlet which are correspondingly arranged, the bottom of the first packed tower is provided with a second inlet and a second outlet, and the middle of the first packed tower is filled with packing; the first inlet is used for inputting molten urea, the second inlet is used for inputting gaseous monomethylamine, the first outlet is used for filtering and discharging ammonia gas, and the second outlet is used for filtering and discharging monomethylurea.
The upper end of the second packed tower 11 is provided with a third inlet and a third outlet which are correspondingly arranged, the bottom of the second packed tower is provided with a fourth inlet and a fourth outlet, and the middle of the second packed tower is filled with packing; the third inlet is communicated with the second outlet and is fed with methylurea, the fourth inlet is fed with gaseous monomethylamine, the third outlet filters and discharges ammonia gas, and the fourth outlet filters and discharges dimethylurea.
Wherein, the packing in the first packed tower 8 and the second packed tower 11 is at least one of corrugated stainless steel structured packing or pall ring stainless steel bulk packing.
Wherein the molten urea is distributed evenly over the packing in the first packed tower 8 by means of a liquid distributor; the liquid-state methylurea is uniformly distributed on the packing in the second packed tower 11 through a liquid distributor; the liquid distributor comprises a fluted disc type liquid distributor; and/or gaseous monomethylamine is conveyed through a gas distributor, the gas distributor comprising a loop gas distributor; and/or the ammonia gas is extracted from the first outlet or the third outlet through a wire mesh demister, enters a heat exchanger for cooling and then enters an ammonia gas absorption device.
The front end of the first inlet further comprises a urea storage tank 1, a liquefaction tank 2 and a first delivery pump 3 which are connected in sequence; the front end of the second inlet and/or the fourth inlet further comprises a methylamine storage tank 4, a second delivery pump 5, a heat exchanger 6 and a gasification tank 7 which are connected in sequence.
Wherein, a heat exchanger 12, a dryer 13 and a finished product unit (not shown) are sequentially connected after the fourth outlet. The dryer 13 comprises a drum scraper dryer.
It can be understood that, for heating or cooling, the present application can be implemented by using a heat exchanger structure. Specifically, the heat exchanger 6 is disposed at the first outlet and the third outlet, the heat exchanger 9 is disposed between the second outlet and the third inlet, and the heat exchanger 10 is disposed between the gasification tank 7 and the third inlet.
Understandably, the heat exchanger structure can be used for repeatedly utilizing waste heat, energy consumption is saved, the ammonia gas and the monomethylamine liquid discharged from the first outlet and the third outlet are subjected to preliminary heat exchange through the heat exchanger 6, the discharged ammonia gas is cooled and then enters the ammonia gas absorption device, the waste heat in the ammonia gas can be effectively utilized, and the ammonia gas cooling speed can be increased. Therefore, the heat exchanger 6 can be used for exchanging heat with ammonia gas, waste heat in the ammonia gas is effectively utilized for preheating the monomethylamine liquid, the monomethylamine liquid is further gasified by the gasification tank 7 to reach the use temperature, and the gasified heating energy consumption of the monomethylamine is saved. A heat exchanger 9 is included between the first packed column 8 and the second packed column 11, for the purpose of raising the temperature of the monomethylurea exiting from the first packed column 8 to 160-170 ℃. Thus, the heat exchanger 6, the heat exchanger 9, the heat exchanger 10 and the heat exchanger 12 can be arranged as a device, and the temperature transmission direction can be adjusted by the temperature controller.
Referring to fig. 2, based on the above-mentioned system for continuously producing dimethyl urea, the present application also provides a method for continuously producing dimethyl urea, comprising steps S1-S3.
S1, preparing the monomethylurea, namely melting the urea, conveying the urea to the upper end of a first packed tower, and uniformly distributing the urea on the packing in the first packed tower through a liquid distributor; heating monomethylamine to be in a gas state, then feeding the gas-state monomethylamine into the packed tower from the bottom of the first packed tower, mixing molten urea and the gas-state monomethylamine in a mutually countercurrent manner, and carrying out sufficient gas-liquid contact and reaction on the surface of the packing to generate the monomethylurea. The urea and the monomethylamine enter the first packed tower in a molar ratio of 1:1, the temperature in the first packed tower is controlled to be 135-140 ℃, and the maximum temperature is not more than 140 ℃, so that the side reaction of the urea is avoided.
S2, preparing dimethyl urea, namely extracting liquid-state monomethyl urea from the lower end of the first packed tower, conveying the liquid-state monomethyl urea to the upper end of a second packed tower, and uniformly distributing the liquid-state monomethyl urea on a packing in the second packed tower through a liquid distributor; heating monomethylamine to be in a gas state, then entering the packed tower from the bottom of the second packed tower, mixing liquid monomethylurea and gaseous monomethylamine in a mutually countercurrent mode, and carrying out sufficient gas-liquid contact and reaction on the surface of the packing to generate dimethylurea. The methylurea and the monomethylamine enter the second packed tower in a molar ratio of 1:1, and the temperature in the second packed tower is controlled at 160-170 ℃.
Wherein, in the step S1, ammonia gas is also generated in the process of generating the monomethylurea; in the step S2 of preparing dimethylurea, ammonia gas is also generated in the process of generating dimethylurea; correspondingly, the step S1 of preparing the monomethylurea and the step S2 of preparing the dimethylurea further comprise the step of discharging ammonia gas, and the ammonia gas generated by the reaction is extracted from the upper end of the first packed tower or the second packed tower and enters an ammonia gas absorption device after being subjected to heat exchange with the monomethylurea.
And S3, packaging the finished product of the dimethyl urea, namely cooling the dimethyl urea generated by the reaction to be in a liquid state, putting the liquid state into a dryer for cooling crystallization, and conveying the liquid state to a finished product unit for packaging.
The invention is further described with reference to the following figures and specific embodiments.
Taking 10000 tons of dimethylurea product produced annually as an example: the solid urea was added to the liquefaction tank at a mass flow rate of 790kg/h (same below), heated to a molten state (135 ℃) and pumped to the top of the first packed tower and uniformly dispersed on the packing by means of a liquid distributor. Meanwhile, liquid monomethylamine liquid is sent into a vaporizer at a mass flow of 817kg/h, the vaporizer takes air and warm water (35 ℃) as heating media, the proportion of the air and the warm water is gradually adjusted along with the change of seasons (more air and less warm water in summer, and the opposite is true in winter), and most of the warm water in the vaporizer is derived from cooling water during the crystallization and cooling of dimethylamine products. The outlet temperature of the vaporizer was controlled at 25 ℃, half of the monomethylamine gas entered the bottom of the first packed column, filled the column through a gas distributor, and reacted with urea in the first step on the pallapak 250Y structured packing. The temperature of the first packed column was controlled at 140 ℃ and the pressure at 2 bar. Ammonia gas generated in the first step of reaction is extracted from the first packed tower at the flow rate of 224kg/h and enters an ammonia gas cooler, and the methylurea is extracted from the bottom of the first packed tower at the flow rate of 974kg/h and enters a top liquid distributor of the second packed tower after being heated to 160 ℃ by a heat exchanger. Monomethylamine gas is heated from 25 ℃ to 150 ℃ by a heater at a rate of 408kg/h, then enters a second packed tower through a gas distributor, and the monomethylamine and the monomethylurea are contacted and reacted on a Mellapak250Y structured packing, the temperature in the second packed tower is controlled at 167 ℃, and the pressure is controlled at 2 bar. The generated ammonia gas enters an ammonia gas absorption device, and is absorbed by water to prepare ammonia water solution for sale or self-use. The product dimethyl urea enters a cooler at the flow rate of 1159kg/h, is cooled from 167 ℃ to 120 ℃, and then enters a roller scraper dryer in a liquid state to be cooled and crystallized to 25 ℃. Through the reaction process, the conversion rate of the urea is 99.4%, and the purity of the dimethyl urea is 99.5%.
The method and the system for continuously producing the dimethylurea have the advantages that the characteristic of a typical two-step reaction process in the dimethylurea generation process is fully utilized, the reaction principle and the physicochemical property of intermediate products at different temperatures are respectively utilized, and a specific gas-liquid reaction and gas-gas reaction mechanism is combined, so that the two-step reaction is creatively provided for replacing the traditional one-step countercurrent reaction. The invention overcomes the defects of low continuity level, serious back mixing, long operation time, great waste of human resources, large occupied space of a reaction device and low space utilization rate of the traditional reaction kettle series connection process. Two tower reactors are adopted, so that the equipment space is greatly reduced, the mass transfer performance is good, the heat transfer efficiency is high, the reaction is rapid, the yield is improved, and the safety is high. The process has the advantages of simple operation, easy control, less by-products and the like. The reaction process is systematically divided in the reaction essence, so that the equipment investment is reduced, the reaction efficiency is improved, the generation of byproducts is reduced, the energy consumption is reduced, a process basis is provided for segmented intelligent control, and the obvious path advantages of a new process are revealed as follows.
(1) The reaction is changed from the traditional multi-kettle series-connection type countercurrent operation into the two-step operation of a double-packed tower, so that the equipment investment is saved, the yield of the target product is improved, and the flow foundation is provided for continuous production.
(2) The continuous two-step reaction fully utilizes a mechanism that the temperature plays a decisive role in the reaction process, starts from controlling the temperature, ensures the two reactions to be orderly carried out by respectively applying the two temperatures, and fundamentally solves the problems of energy waste and a large amount of byproducts caused by uneven heat distribution.
(3) The continuous two-step reaction also fully utilizes the influence rule of the material ratio on the reaction, urea in the first step of reaction and monomethylamine in the second step of reaction are respectively and slightly excessive (the excessive amount is not more than 3 percent) consciously, and the high-efficiency generation of intermediate products and final products is ensured. The high purity of the target product is realized by accurately controlling the circulation amount of the excessive materials.
(4) After the production process of the dimethyl urea is purposefully divided into two processes according to the reaction principle, the process control is more refined and purposeful, the fuzzy dilemma that one reactor is a black box and the internal control cannot be realized is fundamentally avoided, and the continuity of the process is realized from the intrinsic safety.
(5) By utilizing an advanced heat exchange network pinch point technology, heat generated in the cooling process of ammonia gas, monomethylamine gas, ammonia gas and dimethyl urea liquid is respectively coupled with heat required in the processes of urea melting liquefaction and monomethylamine gasification, so that energy is saved to the maximum extent, and contribution is made to carbon emission reduction of a factory.
(6) Energy can be theoretically not wasted completely through heat coupling and accurate control, and residual heat can be completely provided by air, so that zero heat loss in the system is really realized.
In the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.
The above embodiments of the present application are described in detail, and specific examples are applied in the present application to explain the principles and implementations of the present application, and the description of the above embodiments is only used to help understand the technical solutions and core ideas of the present application; those of ordinary skill in the art will understand that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; such modifications or substitutions do not depart from the spirit and scope of the present disclosure as defined by the appended claims.
Claims (10)
1. A method for the continuous production of dimethyl urea, comprising the steps of:
a step of preparing methyl urea, wherein urea is molten and then conveyed to the upper end of a first packed tower, and is uniformly distributed on a filler in the first packed tower through a liquid distributor; heating monomethylamine to be in a gaseous state, then feeding the gaseous monomethylamine into a packed tower from the bottom of the first packed tower, carrying out mutual countercurrent mixing on molten urea and the gaseous monomethylamine, and carrying out sufficient gas-liquid contact and reaction on the surface of a packing to generate monomethylurea; and
a step of preparing dimethyl urea, in which liquid-state methyl urea is extracted from the lower end of the first packed tower and then is conveyed to the upper end of a second packed tower, and is uniformly distributed on the packing in the second packed tower through a liquid distributor; heating monomethylamine to be in a gas state, then entering the packed tower from the bottom of the second packed tower, mixing liquid monomethylurea and gaseous monomethylamine in a mutually countercurrent mode, and carrying out sufficient gas-liquid contact and reaction on the surface of the packing to generate dimethylurea.
2. The method for continuously producing dimethylurea according to claim 1, wherein in the step of preparing monomethylurea, the urea and the monomethylamine are fed into the first packed column at a molar ratio of 1:1, and the temperature in the first packed column is controlled at 135-140 ℃.
3. The method for continuously producing dimethylurea according to claim 1, wherein in the step of preparing dimethylurea, the monomethylurea and the monomethylamine are fed into the second packed column at a molar ratio of 1:1, and the temperature in the second packed column is controlled at 160-170 ℃.
4. The method for continuously producing dimethylurea according to claim 1, wherein in the step of preparing monomethylurea, ammonia gas is also generated during the formation of monomethylurea; in the step of preparing the dimethylurea, ammonia gas is also generated in the process of generating the dimethylurea; correspondingly, the step of preparing the monomethylurea and the step of preparing the dimethylurea also comprise the step of discharging ammonia gas, and the ammonia gas generated by the reaction is extracted from the upper end of the first packed tower or the second packed tower and enters an ammonia gas absorption device after exchanging heat with the monomethylurea.
5. The method for continuously producing dimethyl urea according to claim 1, further comprising, after the step of preparing dimethyl urea:
and packaging a finished product of the dimethyl urea, namely cooling the dimethyl urea generated by the reaction, conveying the cooled dimethyl urea into a dryer through a pump for cooling crystallization, and conveying the crystallized solid to a finished product unit for packaging.
6. A system for the continuous production of dimethyl urea, comprising:
the upper end of the first packed tower is provided with a first inlet and a first outlet which are correspondingly arranged, the bottom of the first packed tower is provided with a second inlet and a second outlet, and the middle of the first packed tower is filled with packing; the first inlet is used for inputting molten urea, the second inlet is used for inputting gaseous monomethylamine, the first outlet is used for filtering and discharging ammonia gas, and the second outlet is used for filtering and discharging monomethylurea; and
the upper end of the second packed tower is provided with a third inlet and a third outlet which are correspondingly arranged, the bottom of the second packed tower is provided with a fourth inlet and a fourth outlet, and the middle of the second packed tower is filled with packing; the third inlet is communicated with the second outlet and is fed with methylurea, the fourth inlet is fed with gaseous monomethylamine, the third outlet filters and discharges ammonia gas, and the fourth outlet filters and discharges dimethylurea.
7. The system for continuous production of dimethyl urea according to claim 1, wherein the packing in the first packed column and the second packed column is at least one of corrugated stainless steel structured packing or pall ring stainless steel loose packing.
8. The system for continuous production of dimethyl urea according to claim 1,
the molten urea is uniformly distributed on the packing in the first packed tower through a liquid distributor; the liquid-state methylurea is uniformly distributed on the packing in the second packed tower through a liquid distributor; the liquid distributor comprises a fluted disc type liquid distributor; and/or the presence of a gas in the gas,
gaseous monomethylamine is conveyed through a gas distributor, which comprises a loop gas distributor; and/or the presence of a gas in the gas,
and the ammonia gas is extracted from the first outlet or the third outlet through a wire mesh demister, enters the heat exchanger for cooling and then enters the ammonia gas absorption device.
9. The system for continuously producing dimethyl urea according to claim 1, further comprising a urea storage tank, a liquefaction tank and a first transfer pump connected in sequence at the front end of the first inlet; the front end of the second inlet and/or the fourth inlet further comprises a methylamine storage tank, a second delivery pump and a gasification tank which are connected in sequence.
10. The system for continuously producing dimethyl urea according to claim 1, further comprising a heat exchanger, a dryer and a finished product unit connected in sequence after the fourth outlet.
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| CN202111502354.2A CN114315650A (en) | 2021-12-10 | 2021-12-10 | Method and system for continuously producing dimethyl urea |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117138737A (en) * | 2023-10-26 | 2023-12-01 | 新华制药（寿光）有限公司 | Tower-type synthetic method of dimethylurea |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN87211457U (en) * | 1987-08-22 | 1988-09-21 | 山东新华制药厂 | Continuous, reverse flow, four-stage series device for preparing dimethyl urea |
| DE102009025135A1 (en) * | 2009-06-17 | 2010-12-23 | Emitec Gesellschaft Für Emissionstechnologie Mbh | Device for evaporating a urea-water solution |
| CN205965801U (en) * | 2016-06-08 | 2017-02-22 | 中国天辰工程有限公司 | A tower reactor for dimethyl urea building -up reactions |
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2021
- 2021-12-10 CN CN202111502354.2A patent/CN114315650A/en active Pending
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN87211457U (en) * | 1987-08-22 | 1988-09-21 | 山东新华制药厂 | Continuous, reverse flow, four-stage series device for preparing dimethyl urea |
| DE102009025135A1 (en) * | 2009-06-17 | 2010-12-23 | Emitec Gesellschaft Für Emissionstechnologie Mbh | Device for evaporating a urea-water solution |
| CN205965801U (en) * | 2016-06-08 | 2017-02-22 | 中国天辰工程有限公司 | A tower reactor for dimethyl urea building -up reactions |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117138737A (en) * | 2023-10-26 | 2023-12-01 | 新华制药（寿光）有限公司 | Tower-type synthetic method of dimethylurea |
| CN117138737B (en) * | 2023-10-26 | 2024-01-30 | 新华制药（寿光）有限公司 | Tower-type synthetic method of dimethylurea |
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