A purification process for organic solvents and solid contents in raffinate acid

Abstract

The present invention relates to a purification process for organic solvents and solid contents in raffinate acid, comprising the following steps: (1) pretreating wet-process phosphoric acid raffinate acid through a process of cooking and steam stripping, and separating the lower-layer pretreated raffinate acid A after standing and layering; (2) filtering the pretreated raffinate acid A through a ceramic membrane to obtain a filtered clear liquid B and a filtered concentrated liquid C. The present invention preliminarily reduces the contents of organic solvents and solid contents in raffinate acid by means of stripping in a reaction kettle, and realizes better removal of the organic phase and suspended substances in raffinate acid through the hydrophilic and oleophobic advantages of the ceramic membrane and its retention effect with a small filtration pore size. The present invention can effectively remove organic solvents and solid contents in raffinate acid. The purification process is a pure physical separation process, and no other impurities are introduced throughout the process, improving the quality of the raffinate acid product.

Description

Technical Field

[0001] The invention relates to the technical field of phosphoric acid purification, and in particular to a purification process for organic solvents and solids in raffinate acid. Background Art

[0002] With the increasing maturity of my country's solvent extraction purification of wet-process phosphoric acid production technology, the industrial application of wet-process phosphoric acid has gradually replaced thermal phosphoric acid. Solvent extraction purification of wet-process phosphoric acid to produce industrial phosphoric acid has become the main development direction of the wet-process phosphoric acid processing industry structure adjustment. The core technology of solvent extraction purification of wet-process phosphoric acid is to extract and separate wet-process phosphoric acid with high impurity content through organic solvent to obtain industrial-grade phosphoric acid. 2 O 5 The extraction rate is generally 50% to 70%, and the byproduct residual acid contains P 2 O 5 and phosphoric acid with high impurities of iron, aluminum and magnesium.

[0003] At present, the industrialization of solvent extraction purification of wet-process phosphoric acid production technology has developed rapidly, and the utilization of residual acid in China is limited to the production of low-nutrient agricultural fertilizers such as monoammonium phosphate (MAP) and diammonium phosphate (DAP). 3+ 、Al 3+ Mg 2+ Various complex salts are formed during the ammonia neutralization reaction in the production of fertilizers, such as MgNH 4 PO 4 、AlNH 4 HPO 4 F 2 、FeNH 4 (HPO 4 ) 2 The presence of these complex salts will have a great impact on the quality and appearance of ammonium phosphate products produced by raffinate acid. In recent years, due to the overcapacity of high-concentration phosphate compound fertilizers and market price fluctuations, the efficient and clean utilization of raffinate acid has become a technical problem for phosphorus chemical companies. The high-value utilization of a large amount of by-product raffinate acid is directly related to the sustainable development of the wet phosphoric acid purification industry. At the same time, it has practical significance for solving the balanced production of raffinate acid and fertilizers. Summary of the invention

[0004] The purpose of the present invention is to overcome the above technical deficiencies, provide a purification process for organic solvents and solids in raffinate acid, and solve the technical problem in the prior art that raffinate acid contains more impurities, thereby limiting the scope of application.

[0005] In order to achieve the above technical purpose, the technical solution of the present invention provides a purification process for organic solvents and solids in raffinate acid, which comprises the following steps:

[0006] (1) Pretreat the raffinate acid of wet-process phosphoric acid through a process of cooking and steam stripping. After standing and stratifying, separate the lower-layer pretreated raffinate acid A.

[0007] (2) Filter the pretreated raffinate acid A through a ceramic membrane to obtain a filtered clear liquid B and a filtered concentrated liquid C.

[0008] Further, in step (1), the process of cooking and steam stripping is to cook the reaction kettle filled with the raffinate acid of wet-process phosphoric acid, and at the same time, introduce steam into the raffinate acid of wet-process phosphoric acid for stripping.

[0009] Further, the reaction kettle adopts a double-layer reaction kettle, and cooking is to introduce steam into the interlayer of the double-layer reaction kettle.

[0010] Further, the cooking temperature is 100 - 150 °C.

[0011] Further, the steam flow rate during stripping is 0.01 - 0.05 m 3 / h, and the cooking and stripping time is 60 - 120 min.

[0012] Further, in step (2), the ceramic membrane adopts a silicon carbide ceramic membrane.

[0013] Further, the pore size of the silicon carbide ceramic membrane is 30 - 50 nm.

[0014] Further, in step (2), during filtration, the membrane operating pressure is 0.3 - 0.5 MPa, the temperature of the pretreated raffinate acid A is 50 - 70 °C, and the average flux of the pretreated raffinate acid A is 300 - 500 L / (m 2 ·h).

[0015] Further, in step (2), when the solid content in the filtered concentrated liquid C is greater than 20%, it is in a qualified state; if it is not qualified, it is refluxed to the raffinate acid of wet-process phosphoric acid, and steps (1) and (2) are repeated until it is qualified; the qualified filtered concentrated liquid C is acidified with dilute sulfuric acid, and after filtration, it is used for the production of superphosphate.

[0016] Further, the mass concentration of the dilute sulfuric acid is 5%; the volume ratio of the filtered concentrated liquid C to the dilute sulfuric acid is 1:(0.1 - 0.15); the reaction temperature for acidification treatment is 110 - 130 °C, and the reaction time is 0.5 - 1 h.

[0017] Even further, 0.5 μm silicon carbide ceramic membrane is adopted for filtration.

[0018] Compared with the prior art, the beneficial effects of the present invention include:

[0019] The present invention preliminarily reduces the content of organic solvents and solid contents in the raffinate acid by stripping in a reaction kettle, and realizes better removal of the organic phase and suspended matter in the raffinate acid through the hydrophilic and oleophobic advantages of the ceramic membrane and its retention effect with a small filtration pore size. The present invention can effectively remove the organic solvents and solid contents in the raffinate acid, and the purification process is a pure physical separation process. No other impurities are introduced during the whole process, improving the quality of the raffinate acid product. The present invention effectively utilizes the raffinate acid generated in the wet-process phosphoric acid extraction process, turning waste into treasure, and no substances harmful to the environment are generated during the process, having high social and economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic structural diagram of the reaction kettle adopted by the present invention;

[0021] Figure 2 It is a schematic structural diagram of the device adopted by the process of the present invention;

[0022] Figure 3 It is a sampling comparison diagram of the process flow of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] In order to make the purpose, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0024] The present invention deeply purifies the by-product raffinate acid generated in the wet-process phosphoric acid extraction process, and the obtained product acid meets the industrial and wet-process phosphoric acid standards, realizing the high-value utilization of the raffinate acid. This technology has important research significance in the field of acid purification such as phosphoric acid purification.

[0025] Specifically, the present invention provides a membrane purification process dedicated to the wet-process phosphoric acid raffinate acid, and the purification process steps include three-step phosphoric acid purification treatment processes:

[0026] (1) Raffinate acid pretreatment process; the wet-process phosphoric acid raffinate acid is pretreated by a process of high-temperature cooking and steam stripping using a double-layer stainless steel reaction kettle to appropriately reduce the content of organic solvents and solid contents in the raffinate acid; among them, the pretreatment process is specifically: the wet-process phosphoric acid raffinate acid is first cooked at high temperature in a double-layer stainless steel reaction kettle, and then high-pressure steam is introduced for stripping. By directly contacting the raffinate acid with water vapor, the activity of the organic solvents dissolved in the raffinate acid increases and is driven upward by the steam, which is beneficial to the diffusion of the organic solvents in the raffinate acid into the upper layer liquid of the raffinate acid and better stratification with the phosphoric acid liquid in the raffinate acid, so as to achieve the purpose of separating the organic solvents from the raffinate acid. After standing, the pretreated raffinate acid A can be obtained from the lower discharge port;

[0027] (2) Raffinate acid ultrafiltration purification process; the pretreated raffinate acid A is filtered through a silicon carbide ceramic membrane. By utilizing the hydrophilic and oleophobic properties, the retention effect of the small pore size, and the acid and alkali resistance of the silicon carbide ceramic membrane, organic solvents and solid contents in the raffinate acid can be completely removed to obtain the silicon carbide ceramic membrane filtered clear liquid B and the silicon carbide ceramic membrane filtered concentrate C.

[0028] (3) Ultrafiltration concentrate treatment process; for the concentrate C, it is acidified with low-concentration dilute sulfuric acid, filtered, and then used for the production of single superphosphate.

[0029] The raw raffinate acid solution, reaction kettle (FB18044), and high-temperature steam used in the purification process are all provided by Yunnan Tian'an Chemical Co., Ltd.

[0030] Preferably, in step (1), the high-temperature cooking temperature of the double-layer stainless steel reaction kettle is 100 - 150 °C. After the temperature reaches, high-pressure steam is introduced for stripping. The steam flow rate control range is: 0.01 - 0.05 m 3 / h, and the temperature is controlled at 100 - 150 °C; the cooking and stripping time is 60 - 120 min. The reaction kettle material of the present invention is 316L, with strong corrosion resistance. In the present invention, too high cooking and stripping temperatures will cause the volatilization of phosphoric acid, affecting the quality of phosphoric acid, and too low temperatures will result in too low stripping efficiency of tributyl phosphate; when the stripping time continues to extend after 120 min, the separation effect of organic solvents does not change significantly.

[0031] See Figure 1 , the reaction kettle 1 of the present invention is of a double-layer structure, including an outer shell 2 and an inner tank 3, and there is an interlayer structure between the outer shell 2 and the inner tank 3; an inlet 4 is opened at the upper end of the reaction kettle 1, and several high-pressure steam pipes 5 are connected to the reaction kettle 1, preferably two; the lower ends of the high-pressure steam pipes 5 extend to the lower part of the inner tank 3 of the reaction kettle, which is beneficial for the full contact of steam with organic solvents; the inlet 4 is used as the feed inlet for wet-process phosphoric acid raffinate acid and can also be used as the steam outlet; a steam inlet 6 and a steam outlet are opened on the side wall of the outer shell 2 for steam to enter the interlayer structure and cook the inner tank 3; the lower part of the inner tank 3 is connected to a sewage outlet 7 and a discharge outlet 8, and the sewage outlet 7 and the discharge outlet 8 are located outside the outer shell 2; preferably, the sewage outlet 7 is located directly below the reaction kettle 1 (on the axis); the discharge outlet 8 can be optionally located directly below the reaction kettle 1 (in this case, the sewage outlet 7 can be omitted or the sewage outlet 7) or at the lower side.

[0032] Preferably, in step (2), the ultrafiltration membrane used in the deep purification system is a special silicon carbide ceramic membrane, specifically a silicon carbide ceramic membrane with a pore size of 30 - 50 nm. The membrane operating pressure is 0.3 - 0.5 MPa, the temperature of the raffinate acid is 50 - 70 °C, and the average flux of the membrane-purified raffinate acid is 300 - 500 L / (m 2 ·h).

[0033] Preferably, in step (3), for the raffinate acid concentrate C after being treated by the ultrafiltration system, its organic solvent content is greater than 4%, the solid content is greater than 20%, and 5% dilute H 2 SO 4 0.1 - 0.15 m 3 is added to each cubic meter of the filtered concentrate C for acidification reaction. The reaction temperature is 110 - 130 °C, the reaction time is 0.5 - 1 h, the reaction process is stirred at 50 r / min, and a small amount of HF will be generated in the accompanying reaction. The specific chemical reaction formula is as follows:

[0034] Ca 5 F(PO4) 3 + 5H 2 SO 4 + nH 2 O = 3H 3 PO 4 + HF + 5CaSO 4 ·nH 2 O

[0035] After the reaction is completed, it is filtered with a 0.5 μm silicon carbide ceramic membrane. The clear liquid after filtration is used to produce monoammonium phosphate (MAP) with low nutrients and is to be used for producing superphosphate or calcium magnesium phosphate fertilizer.

[0036] Taking the solid content in the filtered concentrate C being greater than 20% as the qualified state; if it is not qualified, it is refluxed to the raffinate acid of wet-process phosphoric acid, and steps (1) and (2) are repeated until it is qualified and then acidification treatment is carried out.

[0037] See Figure 2 , the deep purification system of the present invention includes a raw material tank 9. The raw material tank 9 is connected to the discharge port 8 through a feed pipe 10; the bottom of the raw material tank 9 is connected to a membrane module 12 through a circulation pump 11. The membrane module 12 includes a silicon carbide ceramic membrane; the pretreated raffinate acid A is pumped into the membrane module 12 through the circulation pump 11, and the filtered clear liquid B and the filtered concentrate C are obtained through filtration by the silicon carbide ceramic membrane therein. If the filtered concentrate C is not qualified, it returns to the raw material tank 9 through the reflux pipeline 13 for cyclic treatment until it is qualified.

[0038] Preferably, to further ensure the solid content of the raffinate acid before entering the membrane, the time of the step of aging and clarification in the reaction kettle is increased. The preferred aging and clarification time is 6 - 8 h, and the temperature is maintained at 40 - 60 °C to ensure the stability of the operation of the silicon carbide membrane.

[0039] Preferably, to obtain higher-quality phosphoric acid, an organic nanofiltration step can be added. The preferred membrane material is an organic acid-resistant nanofiltration membrane with a pore size of 1 nm. The preferred operating pressure is 6 - 7 MPa, and the operating temperature is 60 - 70 °C; the content of metal cations in the acid solution is reduced, so as to meet the food-grade phosphoric acid standard.

[0040] The main mechanism of action of the present invention is:

[0041] (1) The purpose of the pretreatment process is to ensure an appropriate temperature before the raffinate acid enters the membrane, and to preliminarily reduce the organic solvent and solid content, so as to ensure the treatment flux of the silicon carbide ceramic membrane and the acid-resistant nanofiltration membrane and reduce the membrane system pressure.

[0042] (2) In the deep purification system, a circulating cross-flow filtration process is adopted. The ultrafiltration membrane used is a special silicon carbide ceramic membrane with a membrane pore size range of 30 - 50 nm, a membrane operating pressure of 0.3 - 0.5 MPa. The contact angle between the silicon carbide ceramic membrane and water is 0, which has the advantages of hydrophilic and oleophobic properties and the interception effect of small filtration pore size, and has a good effect of intercepting organic solvents, realizing better removal of the organic phase and suspended matter in the raffinate acid. This ceramic membrane can operate stably under strong acids and alkalis and has a strong impact resistance.

[0043] (3) Due to the process characteristics of the refined acid, its by-product raffinate acid contains a large amount of organic solvents (tributyl phosphate, sulfonated kerosene). The properties of organic solvents such as tributyl phosphate limit the utilization space of the raffinate acid. Using a special silicon carbide ceramic membrane can effectively remove the organic solvents in the raffinate acid and ensure the acquisition of a higher-quality purified acid front-end product.

[0044] (4) The present invention effectively utilizes the raffinate acid generated in the wet-process phosphoric acid extraction process. By using high-temperature steam stripping and a special nanoscale silicon carbide ceramic membrane, the organic solvents that are difficult to remove in the raffinate acid are effectively removed, improving the upper limit of the utilization of the raffinate acid. And no environmentally harmful substances are generated during the process, realizing the high-value utilization of the raffinate acid, and having high social and economic benefits.

[0045] The impurity components in the raffinate acid are complex, including both residual extractants and associated impurities and solid content enriched after extraction and back-extraction. Through testing, in the present invention, by mass percentage, the main content of wet-process phosphoric acid and some impurities are: P 2 O 5 ≤30%, MgO ≤ 3%, Fe 2 O 3 ≤2%, Al 2 O 3 ≤2%, Pb ≤ 70 ppm, Cd ≤ 2 ppm, TBP ≤ 4000 ppm, and the solid content is 10000 - 15000 mg / L.

[0046] The following examples further illustrate the present invention in combination with the process flow.

[0047] Example 1

[0048] Step 1: Add the original raffinate acid solution into a double-layer stainless steel reactor, heat it with steam to 100 °C, and the heating time is 10 - 15 min. After heating, introduce high-pressure steam into the reactor for stripping. Control the steam temperature not to exceed 150 °C through flow control. The steaming and stripping time is 60 min, and age and clarify at this temperature for 60 min. After discharging the raffinate acid from the discharge port, obtain the pretreatment liquid A;

[0049] Step 2: Add the pretreatment liquid A into a silicon carbide ceramic membrane ultrafiltration system for ultrafiltration to obtain the silicon carbide ceramic membrane filtered clear liquid B and the silicon carbide ceramic membrane filtered concentrate C; the pore size of the ultrafiltration membrane is 40 nm, the inlet membrane pressure is 0.4 MPa, the temperature of the feed liquid is 70 °C, and the measured average flux is 500 L / (m 2 ·h), and the P 2 O 5 recovery rate is 96.3%;

[0050] Step 3: Take 0.1 m 3 of the ultrafiltration concentrate, add 10 L of 5% dilute sulfuric acid, react at 120 °C for 30 min. After the reaction is completed, filter with a 0.5 μm silicon carbide ceramic membrane, and respectively take the clear liquid D and the concentrate E. The ω(P 2 O 5 ) of the treated clear liquid is 20.32%, and the ω(P 2 O 5 ) of the concentrate is 21.41%.

[0051] The changes in the elemental content at each stage in the process are shown in Table 1 below.

[0052] Table 1 Changes in elemental content at each stage in Example 1 of the present invention

[0053]

[0054] Example 2

[0055] The operation steps are the same as those in Example 1, increase the aging time of the reactor to 6 h, use the filtered clear liquid B after ultrafiltration as the sample solution, add one nanofiltration step, select a 1 nm organic acid-resistant nanofiltration membrane for the membrane, preferably the operating pressure is 6 - 7 MPa, the operating temperature is 60 - 70 °C, and other process parameters in the process are the same as those in Example 1.

[0056] The comparison of the treated liquids obtained at each stage in Example 2 is as Figure 3 shown. From left to right, they are the original raffinate acid solution, the pretreatment liquid, the ultrafiltration clear liquid, the ultrafiltration concentrate, the nanofiltration clear liquid, and the nanofiltration concentrate. The turbidity of the original raffinate acid solution is the highest, and the turbidity of the ultrafiltration concentrate, the pretreatment liquid, and the nanofiltration concentrate decreases in turn. The ultrafiltration clear liquid is a light green transparent liquid, and the nanofiltration clear liquid is a colorless transparent liquid.

[0057] It is measured that the ultrafiltration P 2O 5 The yield is 95.9%, and for nanofiltration P 2 O 5 The yield is 55.2%. The changes in the element contents at each stage of the process are shown in Table 2 below.

[0058] Table 2 Changes in the element contents at each treatment stage in Example 2 of the present invention

[0059]

[0060] As can be seen from Table 1 and Table 2, after pretreatment, the organic solvent in the present invention is reduced to less than 600 mg / kg, and the solid content is reduced to less than 5000 mg / L. After ultrafiltration treatment, no organic solvent and solid content are detected in the raffinate acid clear liquid B, the removal rate is 100%, and the phosphorus yield is greater than 95%.

[0061] Comparative Example 1

[0062] Remove the steam cooking and stripping steps, and other conditions are the same as in Example 1.

[0063] In the process, there is no steam cooking and stripping step, and the stock solution directly enters the ultrafiltration system. Other conditions are the same as in Example 1. After verification: due to the high solid content and organic solvent content in the stock solution, the silicon carbide ceramic membrane is severely fouled, further resulting in too low clear liquid production. After measurement, the average flux is less than 100 L / (m 2 ·h).

[0064] Comparative Example 2

[0065] Set the steam flow rate to 0.07 m 3 / h, and other conditions are the same as in Example 1.

[0066] Increasing the steam flow rate in the process will lead to an increase in the stripping temperature to verify the stripping efficiency of the organic solvent. Other conditions are the same as in Example 1. After verification: with the increase in temperature, the separation efficiency of the organic solvent slightly increases, and the quality of the phosphoric acid after pretreatment decreases significantly due to the increase in the activity of associated ions. Therefore, the cooking and stripping temperatures should not be too high.

[0067] The present invention discloses a deep purification process for organic solvents and solid contents in raffinate acid. The process includes a three-step phosphoric acid purification treatment process, including a raffinate acid pretreatment process, a raffinate acid ultrafiltration membrane purification process, and a treatment process for ultrafiltration concentrate. The raffinate acid pretreatment process: includes pretreatment with a double-layer stainless steel reaction kettle + steam stripping, aiming to remove part of the organic solvents and solid contents through high-temperature cooking and stripping in the reaction kettle, and preliminarily reduce the contents of organic solvents and solid contents in the raffinate acid; the ultrafiltration purification process: includes a set of silicon carbide ceramic membrane treatment system, aiming to utilize the hydrophilic and oleophobic characteristics and tiny filtration pore diameter of the silicon carbide ceramic membrane to completely remove the organic solvents (such as tributyl phosphate, sulfonated kerosene, etc.) in the raffinate acid; the concentrate treatment process: the concentrate generated by the silicon ceramic membrane, because it contains a large amount of solid contents and organic solvents, and the contents of other impurity ions remain unchanged. This part of the acid solution is treated with sulfuric acid and used for the production of superphosphate, and finally the high-value utilization of wet-process phosphoric acid raffinate acid can be realized.

[0068] Advantages of the present invention: The organic solvent purification treatment technology can effectively remove the organic solvents and solid contents in the raffinate acid. The purification process is a pure physical separation process, and no other impurities are introduced throughout the process, improving the quality of the raffinate acid product; the present invention effectively utilizes the raffinate acid generated in the wet-process phosphoric acid extraction process, turning waste into treasure, and no substances harmful to the environment are generated during the process, having high social and economic benefits.

[0069] The specific embodiments of the present invention described above do not constitute a limitation on the protection scope of the present invention. Any other corresponding changes and deformations made according to the technical concept of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A purification process for organic solvents and solid contents in raffinate acid, characterized in that, it comprises the following steps: (1) Pretreat the wet-process phosphoric acid raffinate acid through a process of steaming and steam stripping. After static stratification, separate the lower-layer pretreated raffinate acid A; the impurities contained in the wet-process phosphoric acid raffinate acid include MgO, Fe 2 O 3 , Al 2 O 3 and TBP; (2) Filter the pretreated raffinate acid A through a ceramic membrane to obtain a filtered clear liquid B and a filtered concentrated liquid C; In step (1), the cooking and steam stripping process involves cooking the reaction kettle containing wet-process phosphoric acid raffinate, and simultaneously introducing steam into the wet-process phosphoric acid raffinate for stripping; the cooking temperature is 100 - 150 °C; the steam flow rate during stripping is 0.01 - 0.05 m 3 / h, and the cooking and stripping time is 60 - 120 min; In step (2), the ceramic membrane is a silicon carbide ceramic membrane; In step (2), when the solid content in the filtered concentrated liquid C is greater than 20%, it is in a qualified state; if not qualified, it is refluxed to the raffinate acid of wet-process phosphoric acid, and steps (1) and (2) are repeated until qualified; the qualified filtered concentrated liquid C is acidified with dilute sulfuric acid, and after filtration, it is used for the production of superphosphate.

2. The purification process for organic solvents and solid contents in raffinate acid according to claim 1, characterized in that, The reaction kettle adopts a double-layer reaction kettle, and steam is introduced into the interlayer of the double-layer reaction kettle during cooking.

3. The purification process for organic solvents and solid contents in raffinate acid according to claim 1, characterized in that, The pore size of the silicon carbide ceramic membrane is 30 - 50 nm.

4. The purification process for organic solvents and solid contents in raffinate acid according to claim 1, characterized in that, In step (2), during filtration, the membrane operating pressure is 0.3 to 0.5 MPa, the temperature of the raffinate acid A after pretreatment is 50 to 70 °C, and the average flux of the raffinate acid A after pretreatment is 300 to 500 L / (m 2 ·h).

5. The purification process for organic solvents and solid contents in raffinate acid according to claim 1, characterized in that, The mass concentration of the dilute sulfuric acid is 5%; the volume ratio of the filtered concentrated liquid C to the dilute sulfuric acid is 1:(0.1 - 0.15); the reaction temperature for acidification treatment is 110 - 130 °C, and the reaction time is 0.5 - 1 h.

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