CN103086810A - Method for preparing urea gypsum by taking desulfurized gypsum as raw material and using solution crystallization method - Google Patents
Method for preparing urea gypsum by taking desulfurized gypsum as raw material and using solution crystallization method Download PDFInfo
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- CN103086810A CN103086810A CN2013100260273A CN201310026027A CN103086810A CN 103086810 A CN103086810 A CN 103086810A CN 2013100260273 A CN2013100260273 A CN 2013100260273A CN 201310026027 A CN201310026027 A CN 201310026027A CN 103086810 A CN103086810 A CN 103086810A
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Abstract
The invention discloses a method for preparing urea gypsum by taking desulfurized gypsum as a raw material and using a solution crystallization method. The method comprises the following steps: (1) preparing a saturated urea aqueous solution, and putting desulfurized gypsum and urea into the saturated urea aqueous solution so as to form slurry; (2) at normal temperature and pressure, uniformly mixing the slurry, then carrying out crystallization reaction on the slurry so as to obtain urea gypsum slurry; and (3) carrying out solid-liquid separation on the urea gypsum slurry, and then drying a solid phase obtained after solid-liquid separation so as to obtain urea gypsum. According to the method disclosed by the invention, desulfurized gypsum and urea are taken as raw materials, the investment is few, the operation is convenient, and the prepared urea gypsum is regular in crystal form, uniform in particle size, accurately adjustable in purity on a large scale, and stable in quality.
Description
Technical field
The invention belongs to large solid waste desulfurated plaster recycling field, also belong to chemical fertilizer and make the field, be specifically related to a kind ofly take desulfurated plaster and urea as raw material, utilize solution crystal process to prepare the method for urea gypsum.
Background technology
Chemical fertilizer is China's agricultural one of key element that supports of relying.China's agrochemical amount of application increased by 34% than 2000 in 2010, reached 5,561 ten thousand tons, and wherein nitrogenous fertilizer is the highest, was 2,354 ten thousand tons, accounted for 42.3% of chemical fertilizer total amount.But, the low phenomenon of China's chemical fertilizer ubiquity utilization ratio, take nitrogenous fertilizer as example, Apparent Availability only has 30-50%, and prolific area is even below 30%.Chemical fertilizer utilization ratio is low causes serious environmental problem, and for example, the chemical fertilizer that does not utilize flows into river, lake, and account for and flow into 60% of nitrogen total amount, be the major reason of body eutrophication.In addition, global anthropogenic discharge N
2The 60-90% of O is directed to farmland nitrogen application, N
2O is one of three large greenhouse gases of listing in Kyoto Protocol, and its warming effect is maximum, and GWP (Greenhouse effect potential) is CO
2150-200 doubly.Slow release fertilizer can make the available nutrient in fertilizer slowly discharge, and not only improves chemical fertilizer utilization ratio, and also can significantly reduce Rural Plane Source Pollution, reduce agriculture production cost, increase farmers' income, be also the useful technology of mitigation of climate change.
The nitrogenous fertilizer of most of developed countries is almost urea entirely, and Chinese nitrogenous fertilizer 60% is approximately urea.The solubleness of urea is easy to dissolving up to 108g/100ml (20 ℃) after fertilising, farm crop can't absorb rapidly, cause a large amount of losses.According to statistics, urea agricultural use rate is 30-40%, and in other words, the urea of 60-70% is with the form harm environment of Rural Plane Source Pollution.If urea is converted into the urea gypsum with stable molecule structure, its nitrogen content is 30%, solubleness is 3.67g/100g (30 ℃), water-soluble than approximately 30 times of urea reductions, the slow release of urea has improved the efficient that absorbs of crop, thereby significantly reduces pollution of area source amount and the greenhouse gas emission that causes due to loss.
At present, the method for modifying of slow released urea can be divided into: (1) organic synthesis method, and for example urea and aldehydes condensation form urea aldehyde; (2) pack, for example organic membrane coated urea, calcium magnesium phosphorus coated urea and sulphur clothing bag urea; (3) urea granules that the preparation particle diameter is large, intensity is high; (4) mixed grinding method: the gypsum of different ratios and urea mix, grinding obtains the urea gypsum, then adds additive to improve its intensity and adhesive property.These methods can access slow-release carbamide, organic synthesis method and packing method technique are more complicated, although the mixed grinding method is simple, but need additive to improve intensity and performance, be difficult to obtain all even stable urea products of quality, for example publication number is that the disclosed gypsum sphere of Chinese invention patent of CN 101798240A grinds the standby method of making the urea gypsum of fertilizer.
The output of China's desulfurated plaster is huge and increase is rapid, reached the fifty-five million ton to 2010 annual emissions, but comprehensive utilization ratio is only 40-50%, is mainly used in cement additire, soil improvement and preparation plaster of Paris.A large amount of desulfurated plasters are still stacked processing, become the famous large industrial solid castoff of China, not only occupy a large amount of soils, and secondary pollution are serious.
Summary of the invention
The invention provides a kind of method of utilizing solution crystal process to prepare the urea gypsum, take desulfurated plaster and urea as raw material, accurately adjustable, steady quality, slow-releasing are good on a large scale for less investment, easy to operate, the urea gypsum crystal formation rule for preparing, epigranular, purity.
A kind of method of utilizing solution crystal process to prepare the urea gypsum comprises the following steps:
(1) prepare saturated aqueous solution of urea, add desulfurated plaster and urea in described saturated aqueous solution of urea, form slurries;
(2) under normal pressure and temperature, carry out crystallization reaction after described slurries are mixed, obtain the urea gypsum slurries;
(3) described urea gypsum slurries is carried out solid-liquid separation, the solid phase after solid-liquid separation gets the urea gypsum after drying.
Utilize desulfurated plaster for raw material prepares urea gypsum large solid waste of both having dissolved, embodied again recycling value, also produced slow-release nitrogen fertilizer.Not only solved the improper disposal of desulfurated plaster from the source and stored up environmental pollution and the potential safety hazard of bringing, and having improved the utilization ratio of urea, having reduced the loss of N element, having alleviated body eutrophication and Agricultural greenhouse gas N
2The discharging of O.
The principle of institute of the present invention foundation is as follows:
The desulfurated plaster main component is terra alba (CaSO
42H
2O), CaSO in desulfurated plaster (butt)
42H
2The content of O is 90-95%.In the mixing saturated solution of desulfurated plaster and urea, desulfurated plaster is sloughed two crystal water, is combined with four urea molecules, transforms to generate urea gypsum (CaSO
4.4CO (NH
2)
2).
Process represents to be expressed as with reaction equation:
Saturated aqueous solution of urea in step (1) provides medium for crystallization reaction, in reaction process replenish after the urea dissolving that added of the urea in used up saturated aqueous solution of urea, remain that reaction medium is saturated aqueous solution of urea, the carrying out that is conducive to the crystallization reaction of desulfurated plaster and urea namely impelled desulfurated plaster and urea reaction and is converted into the urea gypsum.In the present invention, by the ratio of controlling desulfurated plaster and urea, the purity of urea gypsum is reached more than 98%, the dihydrate gypsum in desulfurated plaster and urea all are converted into the urea gypsum basically.
The desulfurated plaster that adds in step (1) is with CaSO
42H
2The O meter is 1.0 with the ratio of the molality of the urea that adds: (0.5～7.0).According to the purity of the gypsum of urea described in product, control the molality ratio of desulfurated plaster and urea, for preparing highly purified urea gypsum, more preferably 1.0: (2.0～5.0).
Described crystallization reaction preferably carries out in crystallization reactor, continues uniform stirring in the crystallization reaction process, obtains good mass transfer.Be to simplify reaction unit, reduce the running cost that heats up and produce, as preferably, described in step (2), the temperature of crystallization reaction is 10-100 ℃; More preferably 20-50 ℃.Temperature of reaction is too low, and speed of reaction descends thereupon, thereby has reduced the production capacity of reactor; Temperature of reaction is too high, although be conducive to improve speed of reaction, energy consumption increases, and might increase product cost.
As preferably, the time of crystallization reaction described in step (2) is 1-10h; For the assurance feed stock conversion is high, and obtain the high urea gypsum of purity, enhance productivity simultaneously, more preferably 2-6h.Reaction times is too short, may cause feedstock conversion incomplete; Reaction times is oversize, and production capacity decline, energy consumption increase.
As preferably, temperature dry described in step (2) is 40-105 ℃.Drying residencing time is 3s-15min, dry adopts a kind of in the modes such as pneumatic dryer, fluidized bed dryer.
As preferably, step can be added Al in (2)
3+Accelerate the process of crystallization reaction, the selected Al that contains
3+Salt can be AlCl
3Or Al
2(SO
4)
3Can also add organic carboxyl acid and improve crystalline form, selected organic carboxyl acid can be citric acid or succinic acid.
As preferably, the liquid phase in step (3) after solid-liquid separation is returned to step (1).Unreacted urea soln recycle in crystallization reactor can not cause urea waste and environmental pollution.
Solid-liquid separation adopts filter plant, a kind of as in vacuum band-type filter machine, plate-and-frame filter press, centrifugal filter etc.
Compare with existing organic synthesis method, coating method, mixed grinding method and granular urea method and have following advantage:
(1) prepare the urea gypsum take desulfurated plaster as raw material, large industrial solid wastes of both having dissolved, protected environment, produced again slow-release nitrogen fertilizer, belong to Resource Recovery of Industrial Solid Waste and recycling economy.
(2) method of the present invention is to produce the urea gypsum under the normal pressure and temperature condition, and equipment is simple, investment is little, working cost is low, easy to operate, maintenance is simple, very suitable for mass production.
(3) the present invention produces the urea gypsum by aqueous solution crystalgrowing method, has fixing molecular structure and crystalline structure, crystalline form rule, epigranular, purity accuracy controlling, steady quality on a large scale.
(4) unreacted urea soln returns recycle in crystallization reactor, can not cause urea waste and environmental pollution.
To sum up, the invention provides the technology that a kind of less investment, the solution crystal process that easy to operate, cost is low are produced the urea gypsum, products obtained therefrom purity is adjustable, steady quality on a large scale, for extensive recycling desulfurated plaster provides new way, also provides a kind of slow-release nitrogen fertilizer for agricultural.
Description of drawings
Fig. 1 is the process flow sheet of the inventive method.
Fig. 2 a is the crystalline form figure of desulfurated plaster.
Fig. 2 b is the crystalline form figure of urea.
Fig. 2 c is the crystalline form figure of urea gypsum.
Fig. 3 a is the crystal structure model figure of desulfurated plaster.
Fig. 3 b is the crystal structure model figure of urea gypsum.
Fig. 4 is the XRD figure of desulfurated plaster, urea and urea gypsum.
Fig. 5 is the fourier infrared figure of desulfurated plaster, urea and urea gypsum
Embodiment
Process flow sheet of the present invention adds urea and water as shown in Figure 1 in the with slurry groove, prepare saturated aqueous solution of urea, adds by a certain percentage urea and desulfurated plaster in aqueous solution of urea, can add additive in case of necessity; Pump into after mixing and carry out crystallization reaction in crystallization reactor, continue uniform stirring in the crystallization reaction process, crystallization control temperature of reaction and reaction times, obtain the urea gypsum slurries after reaction is completed; With the urea gypsum slurries in filter plant as filtering in vacuum band filter; Liquid phase after filtration is returned to reuse in the with slurry groove, and the solid phase after filtration is delivered to and carried out drying in fluidized bed dryer, obtains the urea gypsum after drying, carries out the packing of product after detection purity.The desulfurated plaster that uses in following examples (butt) is CaSO wherein
42H
2The content of O is 95%.
Embodiment 1
By technical process shown in Figure 1, under 20 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated aqueous solution of urea, and the interpolation molality is 10
-4The AlCl of M
3As additive.Add the quality mol ratio in the saturated aqueous solution of urea and be the desulfurated plaster of 2.0: 1.0 (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 20 ℃, and residence time 6.0h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea gypsum slurries is pumped to vacuum band-type filter machine and carries out solid-liquid separation.It is dry under 55 ℃ that solid phase is delivered to fluidized bed dryer, and drying residencing time 10min obtains purity and be 35.5% urea gypsum, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
By technical process shown in Figure 1, under 40 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated urea soln.Adding the quality mol ratio in the saturated urea soln is that 1.0: 1.0 desulfurated plasters are (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 40 ℃, and residence time 8.0h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea gypsum slurries is pumped to vacuum band-type filter machine and carries out solid-liquid separation.It is dry under 105 ℃ that solid phase is delivered to fluidized bed dryer, and 10s, obtained purity and be 55.4% urea gypsum time of drying, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
Embodiment 3
By technical process shown in Figure 1, under 60 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated urea soln.Adding the quality mol ratio in the saturated urea soln is that 1.0: 2.0 desulfurated plasters are (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 60 ℃, and residence time 6.0h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea gypsum slurries is pumped to centrifugal filter and carries out solid-liquid separation.It is dry under 70 ℃ that solid phase is delivered to fluidized bed dryer, and 2min, obtained purity and be 80.5% urea gypsum time of drying, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
Embodiment 4
By technical process shown in Figure 1, under 80 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated urea soln.Adding the quality mol ratio in the saturated urea soln is that 1.0: 3.0 desulfurated plasters are (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 80 ℃, and residence time 4.0h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea gypsum slurries is pumped to automatic plate frame press filter and carries out solid-liquid separation.It is dry under 85 ℃ that solid phase is delivered to pneumatic dryer, and 1min, obtained purity and be 90.8% urea gypsum time of drying, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
By 7 batches of above condition duplications of production, the product purity scope is 88.9-91.2%.
Embodiment 5
By technical process shown in Figure 1, under 100 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated urea soln.Adding the quality mol ratio in the saturated urea soln is that 1.0: 4.0 desulfurated plasters are (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 100 ℃, and residence time 1.0h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea calcium plaster is pumped to centrifugal filter and carries out solid-liquid separation.It is dry under 105 ℃ that solid phase is delivered to pneumatic dryer, and 3s, obtained purity and be 98.9% urea gypsum time of drying, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
By 5 batches of above condition duplications of production, the product purity scope is 98.0-99.6%.
Embodiment 6
By technical process shown in Figure 1, under 60 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated urea soln.Adding the quality mol ratio in the saturated urea soln is that 1.0: 5.0 desulfurated plasters are (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 60 ℃, and residence time 5.5h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea gypsum slurries is pumped to centrifugal filter and carries out solid-liquid separation.It is dry under 98 ℃ that solid phase is delivered to pneumatic dryer, and 7s, obtained purity and be 95.5% urea gypsum time of drying, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
By 8 batches of above condition duplications of production, the product purity scope is 94.0-95.8%.
Embodiment 7
By technical process shown in Figure 1, under 85 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated urea soln.Adding the quality mol ratio in the saturated urea soln is that 1.0: 6.0 desulfurated plasters are (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 85 ℃, and residence time 3.6h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea gypsum slurries is pumped to centrifugal filter and carries out solid-liquid separation.It is dry under 89 ℃ that solid phase is delivered to pneumatic dryer, and 9s, obtained purity and be 79.7% urea gypsum time of drying, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
By technical process shown in Figure 1, under 90 ℃ of conditions, add urea and water in the with slurry groove, prepare saturated urea soln.Adding the quality mol ratio in the saturated urea soln is that 1.0: 7.0 desulfurated plasters are (with CaSO in desulfurated plaster
42H
2O counts) and urea (urea that adds), the slurries of formation desulfurated plaster and urea.Slurries pump in crystallization reactor, continue uniform stirring, and holding temperature is at 90 ℃, and residence time 2.5h completes desulfurated plaster and urea reaction and is converted into the urea gypsum slurries, and the urea gypsum slurries is pumped to centrifugal filter and carries out solid-liquid separation.It is dry under 70 ℃ that solid phase is delivered to pneumatic dryer, and 20s, obtained purity and be 72.6% urea gypsum time of drying, is the urea gypsum product after packing.Isolated liquid-phase reflux is to the with slurry groove.
The crystalline form of desulfurization of raw material gypsum and urea is as shown in Fig. 2 a and Fig. 2 b, and desulfurated plaster is oblique system, is irregular ellipsoid shape, sheet, particle diameter 20-50 micron; Urea is tetragonal system, is long column shape, minor axis 20-100 micron, major diameter 200-500 micron.The crystalline form of the urea gypsum that the present invention prepares is as shown in Fig. 2 c, be triclinic(crystalline)system, be tabular, short cylinder, minor axis 20-100 micron, major diameter 50-100 micron can find out from Fig. 2 c the urea gypsum epigranular that the present invention prepares, and has hardly desulfurated plaster and urea in Fig. 2 c, illustrate that desulfurated plaster and urea have been converted into the urea gypsum fully, in the urea gypsum product for preparing, the purity of urea gypsum is up to more than 98%.
The crystalline structure of gypsum and urea gypsum is to such as shown in Fig. 3 a and Fig. 3 b, and gypsum is sandwich type, Ca
2+And SO
4 2-Alternative arrangement forms interlayer, and water molecules is in passage; Ca in the urea gypsum
2+And SO
4 2-Also be arranged alternately, four urea molecules are distributed in around it.
The XRD feature of desulfurated plaster, urea and urea gypsum as shown in Figure 4, the diffracted primary peak position of desulfurated plaster is at 11.6 °, 20.7 ° and 29.1 °; The peak position of urea is at 22 °; And the product diffracted primary peak position generation considerable change that generates is 12.0 °, 26.3 ° and 27.9 °.Software analysis shows that product is the urea gypsum.The infrared spectrum feature of desulfurated plaster, urea and urea gypsum as shown in Figure 5, from the left side of figure, first place's desulfurated plaster the first two absorption peak is H-O, urea two peaks are N-H, and product this position is a level and smooth peak; Second place's product does not have the sharp-pointed water peak of two of desulfurated plaster; The 3rd place is that product is identical with the peak of urea, is all the C-N peak.To sum up analyze desulfurated plaster and urea reaction and prepare the urea gypsum.
It is more than the characterization data of the product for preparing of embodiment 5.
molality by controlling desulfurated plaster and urea in the present invention is than the product that can prepare required purity in a big way, for example standby to obtain purity be 35.5% urea gypsum that to prepare purity to embodiment 5 be 98.9% urea gypsum by above-described embodiment system 1, in this scope, molality by controlling desulfurated plaster and urea is than stablizing the product that obtains required purity, for example duplication of production in embodiment 4～6, the product purity that obtains all is stabilized near a specific value, produce 5 batches as embodiment 5, the product purity scope is 98.0-99.6%, it can be said that bright preparation method of the present invention can stably prepare the product of required purity.
method of the present invention is first with material dissolution, carry out again crystallization reaction, in whole reaction process all take saturated aqueous solution of urea as reaction medium, reaction is carried out at molecular level, the product purity that obtains is high, steady quality, can reach 98.0-99.6% by the urea gypsum purity of the inventive method preparation is the highest, and ball-milling preparation method is automatic reaction, the impossible complete reaction of urea and desulfurated plaster, therefore the purity of product is difficult to improve, be that in the product that in the Chinese invention patent application of CN 101798240A, the gypsum ball milling method is prepared, its its purity of urea gypsum is the highest less than 90% as publication number, hence one can see that, relative ball-milling preparation method, method of the present invention can improve the purity of urea gypsum in product greatly, stabilized product quality.
Claims (6)
1. the solution crystal process take desulfurated plaster as raw material prepares the method for urea gypsum, it is characterized in that, comprises the following steps:
(1) prepare saturated aqueous solution of urea, add desulfurated plaster and urea in described saturated aqueous solution of urea, form slurries;
(2) under normal pressure and temperature, carry out crystallization reaction after described slurries are mixed, obtain the urea gypsum slurries;
(3) described urea gypsum slurries is carried out solid-liquid separation, the solid phase after solid-liquid separation gets the urea gypsum after drying.
2. the method for stating according to claim 1 is characterized in that, the desulfurated plaster that adds in step (1) is with CaSO
42H
2The O meter is 1.0: 0.5～7.0 with the ratio of the molality of the urea that adds.
3. method according to claim 1, is characterized in that, described in step (2), the temperature of crystallization reaction is 10-100 ℃.
4. method according to claim 1, is characterized in that, the time of crystallization reaction described in step (2) is 1-10h.
5. method according to claim 1, is characterized in that, temperature dry described in step (3) is 40-105 ℃.
6. method according to claim 1, is characterized in that, the liquid phase in step (3) after solid-liquid separation is returned to step (1).
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| CN107145679A (en) * | 2017-05-23 | 2017-09-08 | 成安金隅太行水泥有限公司 | It is a kind of to detect the method that desulfurated plaster saturated aqueous solution pH predicts cement setting time |
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| WO2022003564A1 (en) | 2020-07-01 | 2022-01-06 | Sabic Global Technologies B.V. | Methods for producing urea calcium sulfate from moist phosphogypsum |
| EP4183764A1 (en) * | 2021-11-18 | 2023-05-24 | SABIC Global Technologies, B.V. | Methods of making urea calcium sulfate (ucs) using high shear mixing |
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