Method for recovering triethylamine and NaHS from thiourea wastewater
By adjusting the pH value and adding Na2S seed crystals in the thiourea production wastewater, the recovery rate of triethylamine and NaHS is successfully improved, and the Na2S content is reduced, which solves the problems of difficult and high cost in the prior art. Efficient treatment of wastewater and low energy consumption process.
Patent Information
- Application Number
- CN202411395053.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-08
- Publication Date
- 2025-01-10
AI Technical Summary
The prior art is difficult to effectively recover triethylamine and NaHS in thiourea production wastewater, and the Na2S content in NaHS is high, resulting in high processing difficulty and high cost, and complex process, which poses the risk of secondary pollution.
By adding NaOH solution to the thiourea wastewater, adjust the pH to 13-13.5, performing atmospheric distillation and separating triethylamine, then heating and distillation, adding Na2S seed crystal filtration to obtain NaHS, further cooling and cooling to obtain by-product NaHS solid, optimize the process To improve recovery and reduce Na2S content.
The triethylamine recovery rate is greater than 98%, the Na2S content in NaHS is less than 1.5%, the wastewater COD, TN and TS indicators are reduced, the process is simple, the energy consumption is less, and there is no secondary pollution, which reduces operating costs.
Smart Images
Figure BDA0005073542820000011 
Figure BDA0005073542820000061 
Figure BDA0005073542820000071
Abstract
Description
Technical Field
[0001] The invention belongs to the technical field of pesticide wastewater treatment and relates to a method for recovering triethylamine and NaHS from thiourea wastewater, and specifically relates to a method for recovering by-product triethylamine from thiourea production wastewater and recovering by-product NaHS from thiourea wastewater after recovering by-product triethylamine. Background Art
[0002] Methylthiosemicarbazide (abbreviated as thiourea) is synthesized from methylamine, triethylamine, CS 2 , hydrazine hydrate as raw materials, the reaction equation and reaction principle are as follows:
[0003]
[0004] Reaction mechanism: First, methylamine reacts with carbon disulfide to generate methylaminothiocarboxylic acid triethylamine salt under the action of triethylamine. The salt reacts with hydrazine hydrate to generate methylthiosemicarbazide (MTSC), hydrogen sulfide and triethylamine. The raw material carbon disulfide added during the synthesis process will generate 1 molecule of H 2 S, this part H 2 S mainly exists in the reaction fraction and filtered mother liquor in the form of triethylamine hydrogen sulfide salt. If it is not treated, it will not only cause a waste of triethylamine, but also cause high COD, TN, and TS contents in the wastewater, making wastewater treatment difficult and increasing wastewater treatment costs.
[0005] The main source of thiourea synthesis wastewater is the combined wastewater of the concentrated fraction of thiourea synthesis mother liquor and the thiourea synthesis fraction. There is a large amount of triethylamine hydrogen sulfide salt in the wastewater, which makes it difficult to generate by-product NaHS through tail gas absorption. It is difficult to accurately control the amount of NaOH added in the process flow, resulting in excessive NaOH being added during the absorption of H 2 S is easily converted into Na 2 S, resulting in Na 2 The S content is high and the purity of the generated NaHS is low. Summary of the invention
[0006] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for effectively improving the recovery rate of by-product triethylamine and NaHS and reducing the Na in the recovered NaHS. 2 The invention discloses a method for recovering triethylamine and NaHS from thiourea wastewater, which has the advantages of low S content, simple process, low energy consumption, low operating cost and no secondary pollution.
[0007] In order to solve the above technical problems, the present invention adopts the following technical solutions.
[0008] A method for recovering triethylamine and NaHS from thiourea wastewater comprises the following steps:
[0009] (1) Recovering by-product triethylamine: adding NaOH solution to thiourea wastewater to adjust the pH value to 13-13.5, and then distilling at atmospheric pressure to a temperature of 101° C.-102° C. to obtain a first fraction and a first distillation residue, wherein the first fraction is an azeotrope of triethylamine and water, and the first fraction is separated to obtain a lower layer of a water layer containing triethylamine and an upper layer of a recovered triethylamine layer;
[0010] (2) Recovering the by-product NaHS solution: The first distillation residue is further heated and distilled to a temperature of 120° C. to 130° C. to obtain a second fraction and a second distillation residue. The second distillation residue is cooled to 70° C. to 80° C., and Na 2 S seed, then cool to 0℃~5℃, let stand, filter, and obtain Na 2 S crystals and filtrate, wherein the filtrate is a by-product NaHS solution;
[0011] (3) Recovering by-product NaHS solid: The filtrate obtained in step (2) is further distilled to a temperature of 160° C. to 170° C. to obtain a third fraction and a third distillation residue, and the third distillation residue is cooled and sliced to obtain a by-product NaHS solid.
[0012] In the above method for recovering triethylamine and NaHS from thiourea wastewater, preferably, in step (2), the Na 2 The amount of S seed crystal added is 0.05% to 0.1% of the mass of the second distillation residue.
[0013] In the above method for recovering triethylamine and NaHS from thiourea wastewater, preferably, in step (2), the standing time is 2 h to 4 h.
[0014] In the above method for recovering triethylamine and NaHS from thiourea wastewater, preferably, in step (3), the temperature is cooled to 70° C. to 90° C.
[0015] In the above method for recovering triethylamine and NaHS from thiourea wastewater, preferably, in step (1), the thiourea wastewater is a mixture of two wastewaters: a fraction obtained by distilling mother liquor to 130° C. to 150° C. during thiourea synthesis and a thiourea synthesis fraction.
[0016] The above method for recovering triethylamine and NaHS from thiourea wastewater preferably comprises: 2 S crystals are added to the next batch of thiourea wastewater, and then NaOH solution is added to adjust the pH value to 13.0-13.5, and the subsequent steps are repeated to continue to recover triethylamine and NaHS solids.
[0017] In the prior art, thiourea synthesis fraction can be obtained by the following method, but not limited thereto: 1 mol of methylamine aqueous solution and 1.16 mol of triethylamine are mixed, and 1 mol of CS is added at 25°C. 2 , stir and react below 25°C for 3 hours, add hydrazine hydrate, raise the temperature to 78°C and reflux for 2.5 hours, then distill to a top temperature of 100°C to obtain a thiourea synthesis fraction, and filter out the thiourea product after cooling the mother liquor of the distillation residue. The mother liquor filtrate is further concentrated to obtain a thiourea synthesis mother liquor distillation and concentration fraction.
[0018] Compared with the prior art, the advantages of the present invention are:
[0019] (1) The present invention treats thiourea production wastewater (mainly containing hydrogen sulfide salt of triethylamine) to recover by-product triethylamine and improve the recovery rate of triethylamine, while recovering and preparing by-product NaHS and reducing Na 2 The present invention adds excessive NaOH to a pH value of 13 to 13.5, separates triethylamine from the wastewater, and further concentrates it, adds Na 2 S seed crystallization filters out most of the Na in the NaHS byproduct 2 S, the triethylamine content is greater than 98%, and the NaHS byproduct Na 2 S content is less than 1.5%, NaHS content is greater than 70%, which greatly reduces the Na content in NaHS by-product 2 The content of S is reduced, and the COD of the wastewater after the triethylamine and NaHS are recovered is less than 10000mg / L, TN is less than 1000mg / L, and TS is less than 10mg / L, which can be used in thiourea synthesis, thereby achieving effective treatment of wastewater. The method of the invention has the advantages of simple process, low energy consumption, low operating cost, and no secondary pollution.
[0020] (2) The present invention filters out Na 2 S can be used in the alkali addition of the next batch of triethylamine recovery, which can not only effectively remove this part of Na 2 S is converted into NaHS, and the amount of NaOH added can be reduced by 35%-46%, and the recovery rate of triethylamine reaches more than 95%. 2 S<1.5%.
[0021] (3) In the present invention, the amount of NaOH solution added is based on adjusting the pH value of the thiourea wastewater to 13-13.5. The applicant found that when the pH value is adjusted to 12, although the H 2 S is converted to NaHS, but at this pH value, some H 2 S will escape with the distillate, and the distillate will be obviously yellow. When the pH value is adjusted to 13-13.5, the distillation process H 2 S is converted to Na2 The S and NaHS remain in the distillation residue and are not easily separated out with the distillate, and the NaOH solution reaches the appropriate dosage. DETAILED DESCRIPTION
[0022] The present invention is further described below in conjunction with specific preferred embodiments, but the protection scope of the present invention is not limited thereby. The materials and instruments used in the following embodiments are all commercially available. Unless otherwise specified, the processes used in the following embodiments are conventional processes, the equipment used is conventional equipment, and the data obtained are all average values of more than three tests.
[0023] The treatment object in the following embodiments is thiourea wastewater. The wastewater used in each batch of experiments is wastewater generated by 1 mol of thiourea synthesis, including about 90 g of a fraction obtained by distilling about 120 g of thiourea mother liquor generated in the thiourea synthesis process to 130-150 ° C and about 250 g of a thiourea synthesis fraction. The two wastewaters are mixed to a total of about 340 g. The wastewater contains a large amount of triethylamine and triethylamine hydrogen sulfide salt. Taking the total mass of the thiourea wastewater as 100%, the triethylamine hydrogen sulfide salt in the thiourea wastewater accounts for 29.8% to 30.6%, and the free triethylamine accounts for 11.51% to 12.10%. During the synthesis reaction, the amount of triethylamine added to synthesize 1 mol of thiourea is 117 g.
[0024] Example 1
[0025] A method for recovering triethylamine and NaHS from thiourea wastewater of the present invention comprises the following steps:
[0026] (1) Recovery of by-product triethylamine: 340 g of thiourea wastewater was added to a 1000 mL four-necked flask, stirred, and 80 g of NaOH solution (mass fraction 50%) was added to adjust the pH to 13.5. The mixture was distilled at atmospheric pressure to a temperature of 102° C. to obtain 132.5 g of the first fraction and 287.3 g of the first distillation residue. The first fraction was an azeotrope of triethylamine and water. The first fraction was separated to obtain a lower layer of 22.3 g of water layer containing triethylamine and an upper layer of 109.5 g of triethylamine layer, with a loss of 0.7 g. The lower water layer containing triethylamine can be used to treat the next batch of thiourea wastewater to recover triethylamine.
[0027] (2) Recovery of by-product NaHS solution: The first distillation residue was heated and distilled to 120°C to obtain 146.2 g of the second fraction and 141.0 g of the second distillation residue. The second distillation residue was cooled to 70°C and 0.1 g Na 2 S seed, moved into an ice machine, cooled to 5 ° C, stood for 2 h, filtered, and obtained Na 2 S crystals 28.1g and filtrate 112.5g, the filtrate is the by-product NaHS solution.
[0028] (3) Recovery of by-product NaHS solid: 112.5 g of the filtrate obtained in step (2) was further distilled to 160° C. to obtain 69.8 g of a third fraction and a third distillation residue. The third distillation residue was cooled to 70° C. and poured out. After cooling, the residue was sliced to obtain 42.7 g of by-product NaHS solid.
[0029] Through the above scheme, 109.5 g of triethylamine was recovered, with a content of 98.70% and a recovery rate of 92.37%. 42.7 g of NaHS was recovered, and Na 2 The S content is 1.21%, and the NaHS content is 70.12%.
[0030] Comparative Example 1
[0031] A method for recovering triethylamine and NaHS from thiourea wastewater comprises the following steps:
[0032] (1) Recovery of by-product triethylamine: 340 g of thiourea wastewater was added to a 1000 mL four-necked flask, stirred, and 80 g of NaOH solution (mass fraction 50%) was added to adjust the pH to 13.5, and distilled at normal pressure to a temperature of 102° C. to obtain a first fraction of azeotropic mixture of triethylamine and water, 132.5 g in total, and a first distillation residue, 287.3 g. The first fraction was separated to obtain a lower layer of a water layer containing triethylamine, 22.3 g (entering the next batch of thiourea wastewater treatment to recover triethylamine), and an upper layer of a triethylamine layer, 109.5 g, with a loss of 0.7 g.
[0033] (2) Recovery of by-product NaHS solid: 287.3 g of the first distillation residue was taken and continued to be heated and distilled to a temperature of 160° C. to obtain 218.5 g of the second fraction and 68.8 g of the second distillation residue. The second distillation residue was cooled to 70° C., poured out, cooled, and sliced to obtain 68.6 g of NaHS by-product.
[0034] In the scheme of this comparative example, step (2) of Example 1 was not performed, and step (3) thereof was directly adopted. After measurement, the amount of triethylamine recovered was 109.0 g, the content was 98.90%, and the recovery rate was 92.14%. 68.2 g of NaHS was recovered, and the Na in the recovered NaSH was 2 The S content is 25.91%, and the NaHS content is 44.09%.
[0035] Example 2
[0036] A method for recovering triethylamine and NaHS from thiourea wastewater of the present invention comprises the following steps:
[0037] (1) Recovery of by-product triethylamine: 340 g of thiourea wastewater was added to a 1000 mL four-necked flask, stirred, and 68.5 g of NaOH solution (mass fraction 50%) was added to adjust the pH to 13.0, and distilled at normal pressure to a temperature of 102° C. to obtain a first fraction of azeotropic mixture of triethylamine and water, totaling 131.7 g, and a first distillation residue of 276.5 g. The first fraction was separated to obtain a lower layer of a water layer containing triethylamine, 22.0 g, and an upper layer of a triethylamine layer, 109.2 g, with a loss of 0.5 g.
[0038] (2) Recovery of by-product NaHS solution: Take 276.5 g of the first distillation residue and continue heating and distilling to a temperature of 120°C to obtain 146.8 g of the second fraction and 130.0 g of the second distillation residue. Cool the second distillation residue to 70°C and add 0.1 g Na 2 S seed, moved into an ice machine, cooled to 5 ° C, stood for 2 hours, filtered, and obtained Na 2 S crystals 12.50g and filtrate 117.1g, the filtrate is the by-product NaHS solution.
[0039] (3) Recovery of by-product NaHS solid: 117.1 g of the filtrate obtained in step (2) was further distilled to 160° C. to obtain 63.7 g of a third fraction and a third distillation residue. The third distillation residue was cooled to 70° C., poured out, cooled, and sliced to obtain 53.1 g of by-product NaHS solid.
[0040] Through the above scheme, 109.2 g of triethylamine was recovered, the content was 98.20%, and the recovery rate was 91.65%. 53.1 g of NaHS was recovered, and the Na 2 S content is 1.05%, NaHS content is 70.30%.
[0041] Comparative Example 2
[0042] A method for recovering triethylamine and NaHS from thiourea wastewater comprises the following steps:
[0043] (1) Recovery of by-product triethylamine: 340 g of thiourea wastewater was added to a 1000 mL four-necked flask, stirred, and 68.5 g of NaOH solution (mass fraction 50%) was added to adjust the pH to 13.0, and distilled at normal pressure to a temperature of 102° C. to obtain a first fraction of azeotropic mixture of triethylamine and water, 131.5 g in total, and a first distillation residue, 276.8 g. The first fraction was separated to obtain a lower layer of a water layer containing triethylamine, 22.0 g, and an upper layer of a triethylamine layer, 108.7 g, with a loss of 0.5 g.
[0044] (2) Recovery of by-product NaHS solid: The first distillation residue after the triethylamine is evaporated is heated and distilled to 160° C. to obtain 212.3 g of the second fraction and 64.5 g of the second distillation residue. The second distillation residue is cooled to about 70° C., poured out, cooled, and sliced to obtain 64.5 g of NaHS by-product.
[0045] Through the above scheme, 108.7 g of triethylamine was recovered, the content was 98.1%, the recovery rate was 91.14%, 64.5 g of by-product NaHS solid was recovered, and Na 2 The S content is 12.19%, and the NaHS content is 57.81%.
[0046] Example 3
[0047] A method for recovering triethylamine and NaHS from thiourea wastewater of the present invention is substantially the same as that of Example 1, except that in step (2), Na 2 After S seeding, transfer to ice machine, cool to 0℃, stand for 4h, filter and obtain Na 2 S crystals 28.5g, filtrate 112.0g; in step (3), 112.0g of the filtrate can be distilled out at 160°C to produce 70.0g of the third fraction, the third distillation residue is cooled to 70°C, poured out, cooled, and sliced to obtain 42.0g of by-product NaHS solid.
[0048] Through the above scheme, 109.9 g of triethylamine was recovered, the content was 98.52%, the recovery rate was 92.53%, 42.0 g of NaHS was recovered, and the Na in the recovered NaSH was 2 The S content is 0.56%, and the NaHS content is 70.42%.
[0049] Example 4
[0050] A method for recovering triethylamine and NaHS from thiourea wastewater of the present invention is basically the same as that of Example 1, except that: in step (2), the first distillation residue is heated and distilled to 130°C to obtain 151.2 g of the second fraction and 136.1 g of the second distillation residue. The second distillation residue is cooled to 70°C, 0.1 g of Na 2 S seed, moved into an ice machine, cooled to 5 ° C, stood for 2 hours, filtered, and obtained Na 2 S crystals 28.4g and filtrate 107.9g; in step (3), 107.9g of the filtrate is further distilled to 160°C to obtain 65.4g of the third fraction and the third distillation residue, the third distillation residue is cooled to 70°C, poured out, cooled, and sliced to obtain 42.5g of by-product NaHS solid.
[0051] Through the above scheme, the amount of triethylamine recovered was 109.0 g, the content was 98.75%, and the recovery rate was 91.97%. 42.5 g of NaHS was recovered, and the Na 2 S content is 1.01%, NaHS content is 70.73%.
[0052] Example 5
[0053] A method for recovering triethylamine and NaHS from thiourea wastewater according to the present invention is basically the same as that of Example 1, except that: in step (3), the filtrate obtained in step (2) is further distilled to 170° C. to obtain 73.0 g of a third fraction and a third distillation residue, and the third distillation residue is cooled to 70° C., poured out, cooled, and sliced to obtain 39.5 g of by-product NaHS solid.
[0054] Through the above scheme, the amount of triethylamine recovered was 109.0 g, the content was 98.8%, and the recovery rate was 92.04%. 39.5 g of NaHS was recovered, and the Na 2 The S content is 1.32%, and the NaHS content is 75.7%.
[0055] Example 6
[0056] A method for recovering triethylamine and NaHS from thiourea wastewater of the present invention is substantially the same as that of Example 1, except that: the water layer containing triethylamine and NaHS in the previous batch is washed with water and the mixture is stirred for 2 hours. 2 S crystals were applied, that is, 22.3 g of the aqueous layer containing triethylamine obtained in step (1), 28.1 g of Na obtained in step (2) 2 S crystals are added to the next batch of 340 g of thiourea wastewater, 43.2 g of NaOH solution (50 wt%) is added to adjust the pH to 13.5, and step (1) of distilling to 102° C. and separating the first fraction, as well as step (2) and step (3) are repeated.
[0057] Through the above scheme, the amount of NaOH solution (50wt%) was reduced by 46%, the amount of triethylamine recovered was 113.5g, the content was 98.81%, and the recovery rate was 95.85%. 61.6g of NaHS was recovered, and the Na in the recovered NaSH was 2 S content is 1.05%, NaHS content is 70.12%.
[0058] Example 7
[0059] A method for recovering triethylamine and NaHS from thiourea wastewater of the present invention is substantially the same as that of Example 2, except that: the water layer containing triethylamine and NaHS in the previous batch is washed with water and the mixture is stirred for 2 hours. 2 S crystals were applied, that is, 22.0 g of the aqueous layer containing triethylamine obtained in step (1), 12.50 g of Na obtained in step (2) 2S crystals are added to the next batch of 340 g of thiourea wastewater, 44.5 g of NaOH solution (50 wt%) is added to adjust the pH to 13.0, and step (1) of distilling to 102° C. and separating the first fraction, as well as step (2) and step (3) are repeated.
[0060] Through the above scheme, the NaOH solution (50wt%) was reduced by 35.0%, the amount of triethylamine recovered was 112.7g, the content was 98.53%, and the recovery rate was 95.00%. 61.6g of NaHS was recovered, and the Na in the recovered NaHS was 2 S content is 1.00%, NaHS content is 70.12%.
[0061] It can be seen from the above examples 1-7 and comparative examples 1-2 that the by-product NaHS recovery process of the present invention can make the NaHS content>70%, Na 2 S content <1.5% (Industrial NaHS by-product requires Na 2 S is less than 3%), meeting industrial standards.
[0062] It can be seen from the above-mentioned Example 6 and Example 7 that after application, the triethylamine recovery rate of the present invention can reach more than 95%, and the 50wt% NaOH solution can achieve a reduction of 35%-46%.
[0063] The second fraction and the third fraction produced in the process of recovering the by-product NaHS solid in Examples 1 to 7 were combined to analyze the water quality COD, TN (total nitrogen), and TS. The results are shown in Table 1 below.
[0064] Table 1 Test results after combining the second fraction and the third fraction in Example 1-7
[0065]
[0066]
[0067] As shown in Table 1, the by-product triethylamine and by-product NaHS recovery process of the present invention has COD < 10000 mg / L, TN < 1000 mg / L, and TS < 10 mg / L in the wastewater after triethylamine and NaHS are recovered, and the wastewater can be used in the thiourea synthesis step, thereby achieving effective treatment of the wastewater and reducing the burden of the subsequent wastewater pretreatment process.
[0068] The above is only a preferred embodiment of the present invention and does not limit the present invention in any form. Although the present invention has been disclosed as above in the preferred embodiment, it is not used to limit the present invention. Any technician familiar with the art can make many possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and technical solution of the present invention, or modify it into an equivalent embodiment of equivalent changes. Therefore, any simple modification, equivalent replacement, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention, still fall within the scope of protection of the technical solution of the present invention.
Claims
1. A method for recovering triethylamine and NaHS from thiourea wastewater, characterized in that: The following steps are involved: (1) Recovering by-product triethylamine: adding NaOH solution to thiourea wastewater to adjust the pH value to 13-13.5, and then distilling at atmospheric pressure to a temperature of 101° C.-102° C. to obtain a first fraction and a first distillation residue, wherein the first fraction is an azeotrope of triethylamine and water, and the first fraction is separated to obtain a lower layer of a water layer containing triethylamine and an upper layer of a recovered triethylamine layer; (2) Recovering the by-product NaHS solution: continuing to heat and distill the first distillation residue to a temperature of 120° C. to 130° C. to obtain a second fraction and a second distillation residue, cooling the second distillation residue to 70° C. to 80° C., adding Na2S seed crystals, and then cooling to 0° C. to 5° C., standing, and filtering to obtain Na2S crystals and a filtrate, wherein the filtrate is the by-product NaHS solution; (3) Recovering by-product NaHS solid: The filtrate obtained in step (2) is further distilled to a temperature of 160° C. to 170° C. to obtain a third fraction and a third distillation residue, and the third distillation residue is cooled and sliced to obtain a by-product NaHS solid.
2. The method for recovering triethylamine and NaHS from thiourea waste water according to claim 1, characterized in that: In step (2), the amount of the Na2S seed crystals added is 0.05% to 0.1% of the mass of the second distillation residue.
3. The method for recovering triethylamine and NaHS from thiourea waste water according to claim 1, characterized in that: In step (2), the standing time is 2 h to 4 h.
4. The method for recovering triethylamine and NaHS from thiourea waste water according to claim 1, characterized in that: In step (3), the temperature is lowered to 70°C to 90°C.
5. The method for recovering triethylamine and NaHS from thiourea wastewater according to any one of claims 1 to 4, characterized in that: In step (1), the thiourea wastewater is a mixture of two wastewaters: a fraction obtained by distilling the mother liquor to 130° C. to 150° C. during the thiourea synthesis process and a thiourea synthesis fraction.
6. The method for recovering triethylamine and NaHS from thiourea wastewater according to any one of claims 1 to 4, characterized in that: The water layer containing triethylamine obtained in step (1) and the Na2S crystals obtained in step (2) are added to the next batch of thiourea wastewater, and then NaOH solution is added to adjust the pH value to 13.0-13.5, and the subsequent steps are repeated to continue to recover triethylamine and NaHS solids.