Impurity removal method for producing low-chlorine monopotassium phosphate through organic extraction of crude phosphoric acid

Abstract

The invention relates to an impurity removal method for producing low-chlorine monopotassium phosphate by organic extraction of crude phosphoric acid. The method comprises the following steps of: arranging 1 # to 4 # extraction tanks which are sequentially connected, a filter press connected with each extraction tank, a phosphorus-potassium compound fertilizer storage tank connected with the filter press, a pre-extraction tank and an organic phase regeneration tank which are respectively connected with the 4 # extraction tank, and a lean organic phase tank connected with the 1 # extraction tank; the mixed extraction agent in the lean organic phase tank is fed into a 1 # extraction tank and then sequentially flows into a 2 # extraction tank, a 3 # extraction tank and a 4 # extraction tank to be extracted step by step, and an organic phase with the hydrochloric acid content gradually increased is obtained; the monopotassium phosphate water phase enters a 4 # extraction tank from the pre-extraction tank and then sequentially flows into a 3 # extraction tank, a 2 # extraction tank and a 1 # extraction tank, a monopotassium phosphate water phase with the hydrochloric acid content gradually reduced is obtained, and finally the refined monopotassium phosphate water phase is obtained. The hydrochloric acid extraction rate reaches 98% or above, and the chlorine ion content of the product is low. The technological process is simple, and the purity of the monopotassium phosphate product can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of potassium dihydrogen phosphate production processes, and particularly relates to a method for removing impurities applicable to a process for producing low-chloride potassium dihydrogen phosphate by organic extraction of crude phosphoric acid. Background Art

[0002] The production of potassium dihydrogen phosphate by the extraction method is a relatively economical production method. In the traditional process, wet-process crude phosphoric acid and potassium chloride are mixed, and a tertiary amine extractant is added. Hydrochloric acid enters the extraction phase. Since the hydrochloric acid content in the aqueous phase of potassium dihydrogen phosphate decreases and the pH increases, about 50% of the metal cations introduced by the crude phosphoric acid will precipitate out. After filtration, the aqueous phase of potassium dihydrogen phosphate is purified, and the aqueous phase is further concentrated to obtain a potassium dihydrogen phosphate product. This method has the following characteristics: (1) Tertiary amine extractants are mostly used as extractants. Tertiary amine extractants have a strong extraction ability for metal cations, which easily leads to a low product purity. (2) Single-stage extraction is used for hydrochloric acid extraction, and the single-stage extraction rate of hydrochloric acid is only 60%. (3) Metal cations are removed by two impurity removal steps. First, impurity removal is carried out by the neutralization method once. After extracting hydrochloric acid, the pH of the aqueous phase of potassium dihydrogen phosphate increases, and precipitation occurs for secondary impurity removal. (4) The main content of potassium dihydrogen phosphate produced by the extraction method is less than 96%, the chloride ion content is above 0.3%, and the metal cation content is above 0.03%. It can only meet the industrial grade standard and is restricted in the application in the field of food additives.

[0003] In order to obtain a potassium dihydrogen phosphate product with a lower chloride ion content and higher purity, a more effective method for removing impurities in the potassium dihydrogen phosphate production process needs to be provided. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and provide a method for removing impurities in a potassium dihydrogen phosphate production process with a high extraction rate of hydrochloric acid, a low extraction rate of metal cations introduced by phosphoric acid, and capable of obtaining a lower chloride ion content and higher product purity.

[0005] The technical solution adopted by the present invention is as follows: A method for removing impurities in the production of low-chloride potassium dihydrogen phosphate by organic extraction of crude phosphoric acid, the method is as follows: First, a 1# extraction tank, a 2# extraction tank, a 3# extraction tank, and a 4# extraction tank are sequentially connected by pipelines. A filter press is respectively connected to the bottom aqueous phase precipitation outlets of the 1# extraction tank, the 2# extraction tank, the 3# extraction tank, and the 4# extraction tank through pipelines. A phosphorus-potassium compound fertilizer storage tank is connected to the filter press through a feeding hopper. A pre-extraction tank and an organic phase regeneration tank are respectively connected to the 4# extraction tank through pipelines. A lean organic phase tank connected to the 1# extraction tank and an extractant storage tank for supplying extractant to the lean organic phase tank; the organic phase regeneration tank is connected to the lean organic phase tank through a pipeline; The extractant component in the extractant storage tank is an unsaturated ketone with 1-2 carbon-carbon unsaturated double bonds. In the lean organic phase tank, the extractant from the extractant storage tank and the recycled extractant from the organic phase regeneration tank are mixed evenly and then enter the No. 1 extraction tank for extraction reaction. Then, it flows from the No. 1 extraction tank to the No. 2 extraction tank, No. 3 extraction tank, and No. 4 extraction tank in sequence for step-by-step extraction, and the primary organic phase, secondary organic phase, tertiary organic phase, and quaternary organic phase with gradually increasing hydrochloric acid content are obtained step by step. The main component of each organic phase is the evenly mixed extractant, and the hydrochloric acid content loaded in each stage is different; the potassium dihydrogen phosphate aqueous phase stored in the pre-extraction tank is a mixed solution of crude phosphoric acid and potassium chloride. The potassium dihydrogen phosphate aqueous phase enters the No. 4 extraction tank from the pre-extraction tank, and then flows reversely from the No. 4 extraction tank to the No. 3 extraction tank, No. 2 extraction tank, and No. 1 extraction tank in sequence, and the primary potassium dihydrogen phosphate aqueous phase, secondary potassium dihydrogen phosphate aqueous phase, tertiary potassium dihydrogen phosphate aqueous phase, and refined potassium dihydrogen phosphate aqueous phase with gradually decreasing hydrochloric acid content are obtained step by step. At the same time, primary aqueous phase precipitation, secondary aqueous phase precipitation, tertiary aqueous phase precipitation, and quaternary aqueous phase precipitation are formed at the bottoms of the No. 1 extraction tank, No. 2 extraction tank, No. 3 extraction tank, and No. 4 extraction tank respectively; the obtained quaternary organic phase is sent to the organic phase regeneration tank to remove the hydrochloric acid in the organic phase and then returned to the lean organic phase tank; The primary aqueous phase precipitation, secondary aqueous phase precipitation, tertiary aqueous phase precipitation, and quaternary aqueous phase precipitation are respectively sent to a filter press for solid-liquid separation. The obtained solid phase is phosphorus-potassium compound fertilizer, which is sent to the phosphorus-potassium compound fertilizer storage tank for storage; the obtained liquid phase is the semi-finished potassium dihydrogen phosphate aqueous phase, which is returned to any one of the No. 1-4 extraction tanks for continuous extraction; The obtained refined potassium dihydrogen phosphate aqueous phase is sent for the production of low-chlorine potassium dihydrogen phosphate.

[0006] Furthermore, the unsaturated ketone is one of ketene, butenone, and isopropylidene acetone (4-methyl-3-penten-2-one).

[0007] Furthermore, the number of hydrochloric acid extraction stages can be 4 to 8 stages.

[0008] The chloride ions in the potassium dihydrogen phosphate aqueous phase will enter the organic phase. When the organic phase has already loaded a small amount of chloride ions, The present invention uses a novel unsaturated ketone extractant, which has a unique extraction ability for chloride ions and hardly extracts metal cations in wet-process phosphoric acid. The metal cations do not participate in the solvent circulation and do not accumulate, which is beneficial to improving the product purity. The potassium dihydrogen phosphate produced can reach the food grade. As long as there is a large concentration difference of chloride ions between the aqueous phase and the organic phase of potassium dihydrogen phosphate, the organic phase loaded with chloride ions can still extract chloride ions from the aqueous phase of potassium dihydrogen phosphate. The organic phase with the lowest chloride ion content in the 1# extraction tank is used to extract the aqueous phase of potassium dihydrogen phosphate with the lowest chloride ion content, and the organic phase with the highest chloride ion content in the 4# extraction tank is used to extract the aqueous phase of potassium dihydrogen phosphate with the highest chloride ion content. The present invention ingeniously designs different concentration gradients and multi-stage countercurrent extraction to improve the extraction rate of chloride ions. The extraction rate of hydrochloric acid by the method of the present invention is over 98%, and the removal rate of metal cations only needs to be decontaminated once and reaches over 96%. Due to the use of multi-stage countercurrent extraction, the extraction rate of chloride ions is extremely high, and the chloride ion content in the obtained potassium dihydrogen phosphate product can reach below 0.0003%, which is much lower than the chloride ion content of 0.3% in the products of traditional production methods. Due to the use of multi-stage countercurrent extraction and multi-stage decontamination, the removal rate of metal cations is extremely high, abandoning the neutralization method for decontamination in the traditional process and simplifying the process flow. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 It is a process schematic diagram of the method of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] The content of the present invention will be further described below in conjunction with the drawings of the specification and embodiments.

[0013] An impurity removal method for producing low-chloride potassium dihydrogen phosphate by organic extraction of crude phosphoric acid, as Figure 1 shown, first set up an impurity removal system, including a 1# extraction tank 1, a 2# extraction tank 2, a 3# extraction tank 3, and a 4# extraction tank 4 sequentially connected by pipelines, a filter press 5 respectively connected to the bottom aqueous phase precipitation outlets of the 1# extraction tank, the 2# extraction tank, the 3# extraction tank, and the 4# extraction tank by pipelines, a phosphorus-potassium compound fertilizer storage tank 6 connected to the filter press through a hopper, a pre-extraction tank 7 and an organic phase regeneration tank 8 respectively connected to the 4# extraction tank by pipelines, a lean organic phase tank 9 and an extractant storage tank 11 connected to the 1# extraction tank by pipelines; the organic phase regeneration tank 8 is connected to the lean organic phase tank 9 by a pipeline.

[0014] The extraction agent stored in the extraction agent storage tank 11 is an extraction agent, and the composition of the extraction agent is an unsaturated ketone containing 1-2 carbon-carbon unsaturated double bonds, such as vinyl ketone, butenone, isopropylidene acetone (4-methyl-3-penten-2-one), but not limited to these unsaturated ketones. In this embodiment, vinyl ketone is used. The extraction agent is pumped into the lean organic phase tank 9 by the extraction agent delivery pump 4. In the lean organic phase tank 9, the extraction agent is mixed evenly with the recycled extraction agent from the organic phase regeneration tank 8. The evenly mixed extraction agent enters the 1# extraction tank 1 from the lean organic phase tank 9 for extraction reaction, and then flows from the 1# extraction tank to the 2# extraction tank 2, 3# extraction tank 3 and 4# extraction tank 4 in sequence for step-by-step extraction, and the first-stage organic phase 3a, second-stage organic phase 3b, third-stage organic phase 3c and fourth-stage organic phase 3d with gradually increasing hydrochloric acid content are obtained step by step; the potassium dihydrogen phosphate aqueous phase enters the 4# extraction tank 4 from the pre-extraction tank 7, and then flows countercurrently from the 4# extraction tank to the 3# extraction tank 3, 2# extraction tank 2 and 1# extraction tank 1 in sequence, and the first-stage potassium dihydrogen phosphate aqueous phase 1a, second-stage potassium dihydrogen phosphate aqueous phase 1b, third-stage potassium dihydrogen phosphate aqueous phase 1c and refined potassium dihydrogen phosphate aqueous phase 10 with gradually decreasing hydrochloric acid content are obtained step by step. During the process of the countercurrent flow and mutual mixing of the lean organic phase and the potassium dihydrogen phosphate aqueous phase, the potassium dihydrogen phosphate aqueous phase is continuously purified, and at the same time, first-stage aqueous phase precipitation 2a, second-stage aqueous phase precipitation 2b, third-stage aqueous phase precipitation 2c and fourth-stage aqueous phase precipitation 2d are respectively formed at the bottoms of the 1# extraction tank, 2# extraction tank, 3# extraction tank and 4# extraction tank. The obtained fourth-stage organic phase 3d is sent to the organic phase regeneration tank 8 to remove the hydrochloric acid in the organic phase and then returned to the lean organic phase tank 9.

[0015] The first-stage aqueous phase precipitation 2a, second-stage aqueous phase precipitation 2b, third-stage aqueous phase precipitation 2c and fourth-stage aqueous phase precipitation 2d are respectively sent to the filter press 5 for solid-liquid separation. The obtained solid phase is phosphorus-potassium compound fertilizer, which is sent to the phosphorus-potassium compound fertilizer storage tank 6 for storage. The obtained liquid phase is the semi-finished potassium dihydrogen phosphate aqueous phase 12, which is returned to any one of the 1#-4# extraction tanks for continuous extraction. In this embodiment, it is returned to the 4# extraction tank.

[0016] The unsaturated ketone type extraction agent used in the method of the present invention is an extraction agent with excellent performance. When it extracts hydrochloric acid, it hardly extracts metal cations. The extraction rate of hydrochloric acid is higher than that of traditional tertiary amine extraction agents, and it can avoid metal cations from participating in the solvent cycle, effectively preventing the reduction of the purity of the potassium dihydrogen phosphate product caused by the metal cations participating in the solvent cycle from entering the potassium dihydrogen phosphate aqueous phase.

[0017] In this embodiment, the total hydrochloric acid extraction rates of the 1#-4# extraction tanks are designed to be 60%, 80%, 95%, 99.9%, and the total removal rates of metal cations in the 4#-1# extraction tanks are designed to be 50%, 78%, 90%, 96%.

[0018] The analysis results of chloride ions in each stage of potassium dihydrogen phosphate aqueous phase in this embodiment are shown in the following table: Pre-extraction tank 1a 1b 1c 10 Chloride ion % 0.3000 0.1200 0.0600 0.0150 0.0003 The analytical results of metal cations in the aqueous phase of potassium dihydrogen phosphate at all levels in this embodiment are shown in the following table: Pre-extraction tank 1a 1b 1c 10 <![CDATA[Fe 2 O 3 %]]> 0.0140 0.0005 0.0014 0.0031 0.0070 The analytical results of chloride ions in the organic phase at all levels in this embodiment are shown in the following table: Lean organic phase tank 3a 3b 3c 3d Chloride ion % Not detected 0.0180 0.0240 0.0285 0.0300 In the organic phase regeneration tank, ammonia water reacts with hydrochloric acid in the organic phase to generate ammonium chloride. The ammonium chloride dissolves in water. Approximately 20% of the metal cations circulating in the organic phase will also enter the aqueous phase, and 80% of the metal cations return to the lean organic phase tank to participate in the solvent circulation. The organic phase from which hydrochloric acid has been removed is called the circulating extractant.

[0019] Each hydrochloric acid extraction tank is of the first stage. The number of hydrochloric acid extraction stages can be designed to be 4 - 8 according to process requirements. In the lean organic phase tank, the ratio of the extractant added from the extractant storage tank to the circulating extractant returned from the organic phase regeneration tank is 1:500 - 600.

[0020] Send the obtained refined potassium dihydrogen phosphate aqueous phase (10) for extraction to produce potassium dihydrogen phosphate with low chloride content. Potassium dihydrogen phosphate with a main content greater than 99%, a chloride ion content below 0.0003%, and a metal cation content below 0.0005% can be prepared.

[0021] Unless otherwise specified, the percentages mentioned in the present invention are all mass percentages.

[0022] The embodiments are only descriptions of the preferred modes of the present invention and do not limit the protection scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for removing impurities by organic extraction of crude phosphoric acid to produce low-chlorine potassium dihydrogen phosphate, characterized in that: Here’s how: First, a 1# extraction tank (1), a 2# extraction tank (2), a 3# extraction tank (3), and a 4# extraction tank (4) are sequentially connected through pipelines; a filter press (5) is connected to the bottom aqueous phase precipitation outlets of the 1# extraction tank, the 2# extraction tank, the 3# extraction tank, and the 4# extraction tank through pipelines, respectively; a phosphorus-potassium compound fertilizer storage tank (6) is connected to the filter press through a lower hopper; a pre-extraction tank (7) and an organic phase regeneration tank (8) are connected to the 4# extraction tank through pipelines, respectively; a lean organic phase tank (9) is connected to the 1# extraction tank through a pipeline; and an extractant storage tank (11) supplies an extractant to the lean organic phase tank (9); the organic phase regeneration tank (8) is connected to the lean organic phase tank (9) through a pipeline; The extractant component in the extractant storage tank (11) is an unsaturated ketone containing 1 to 2 carbon-carbon unsaturated double bonds. In the lean organic phase tank (9), the extractant from the extractant storage tank (11) and the circulating extractant from the organic phase regeneration tank (8) are mixed evenly and then enter the 1# extraction tank (1) for extraction reaction. Then, the extractant flows from the 1# extraction tank to the 2# extraction tank (2), the 3# extraction tank (3) and the 4# extraction tank (4) in sequence for extraction step by step, and a primary organic phase (3a), a secondary organic phase (3b), a tertiary organic phase (3c) and a quaternary organic phase (3d) with gradually increasing hydrochloric acid content are obtained step by step. The main component of each organic phase is the evenly mixed extractant, and the hydrochloric acid content loaded at each stage is different. The pre-extraction tank (7) stores a potassium dihydrogen phosphate aqueous phase, and the potassium dihydrogen phosphate aqueous phase is crude phosphoric acid. and a mixed solution of potassium chloride, the potassium dihydrogen phosphate aqueous phase enters the 4# extraction tank (4) from the pre-extraction tank (7), and then flows from the 4# extraction tank in reverse order to the 3# extraction tank (3), the 2# extraction tank (2) and the 1# extraction tank (1), and gradually obtains a primary potassium dihydrogen phosphate aqueous phase (1a) with a gradually decreasing hydrochloric acid content, a secondary potassium dihydrogen phosphate aqueous phase (1b), a tertiary potassium dihydrogen phosphate aqueous phase (1c), and a refined potassium dihydrogen phosphate aqueous phase (10). At the same time, a primary aqueous phase precipitate (2a), a secondary aqueous phase precipitate (2b), a tertiary aqueous phase precipitate (2c), and a quaternary aqueous phase precipitate (2d) are formed at the bottom of the 1# extraction tank, the 2# extraction tank, the 3# extraction tank, and the 4# extraction tank, respectively; the obtained quaternary organic phase (3d) is sent to the organic phase regeneration tank (8) to remove the organic phase hydrochloric acid and then returns to the lean organic phase tank (9); The first-stage aqueous phase precipitate (2a), the second-stage aqueous phase precipitate (2b), the third-stage aqueous phase precipitate (2c), and the fourth-stage aqueous phase precipitate (2d) are respectively sent to a filter press (5) for solid-liquid separation. The obtained solid phase is a phosphate-potassium compound fertilizer, which is sent to a phosphate-potassium compound fertilizer storage tank (6) for storage; the obtained liquid phase is a semi-finished potassium dihydrogen phosphate aqueous phase (12), which is returned to any one of the 1# to 4# extraction tanks for further extraction; The obtained refined potassium dihydrogen phosphate aqueous phase (10) is sent for extraction to produce low-chlorine potassium dihydrogen phosphate.

2. The impurity removal method for producing low-chlorine potassium dihydrogen phosphate by organic extraction of crude phosphoric acid according to claim 1, characterized in that: The unsaturated ketone is one of vinyl ketone, butenone and mesityl oxide (4-methyl-3-penten-2-one).

3. The impurity removal method for producing low-chlorine potassium dihydrogen phosphate by organic extraction of crude phosphoric acid according to claim 1 or 2, characterized in that: The hydrochloric acid extraction stage is 4 to 8.

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