Step-by-step washing production process of food-grade phosphoric acid by hydrochloric acid method

Abstract

The invention relates to the technical field of preparation of food-grade phosphoric acid, and discloses a step-by-step washing production process of food-grade phosphoric acid by a hydrochloric acid method. The process at least comprises a step-by-step washing step, and the step-by-step washing step comprises the following steps: primary washing: adding sulfuric acid into a washing solution, and carrying out 2-4-stage countercurrent washing in a phase ratio of (3-10): 1; secondary washing: adding reverse extraction acid into the washing solution, and carrying out countercurrent washing with the phase ratio of (10-20): 1, 2-4 levels; the reverse extraction acid is a phosphoric acid solution obtained in the reverse extraction step. According to the technology, the removal efficiency of calcium ions in the washing step in the hydrochloric acid method food-grade phosphoric acid preparation process is improved, and scaling of pipelines and equipment caused by calcium phosphate precipitates formed in the follow-up procedures is avoided.

Description

Technical Field

[0001] The present application relates to the technical field of food-grade phosphoric acid preparation, and more specifically, to a step-by-step washing production process for food-grade phosphoric acid produced using the hydrochloric acid method. Background Art

[0002] Phosphoric acid is an important chemical raw material, widely used in the fertilizer, food, water treatment, electronics, and coatings industries, among other sectors. Food-grade phosphoric acid is also an inexpensive acidulant, widely used as a food additive in the production of dairy, meat, aquatic products, and various beverages. While food-grade phosphoric acid is in high demand both domestically and internationally, its preparation methods remain relatively underdeveloped.

[0003] In the prior art, Chinese Patent Publication No. CN102515134A discloses a hydrochloric acid process for producing food-grade phosphoric acid. The process includes raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. However, in actual applications, it has been found that the traditional single-stage washing process has limited efficiency in removing calcium ions, resulting in the formation of calcium phosphate precipitation in subsequent steps, causing scaling of pipelines and equipment. Summary of the Invention

[0004] The invention of the present application aims to improve the efficiency of removing calcium ions in the washing step during the preparation of food-grade phosphoric acid by the hydrochloric acid method, thereby avoiding the formation of calcium phosphate precipitation in subsequent processes and causing scaling of pipes and equipment.

[0005] In order to achieve the above-mentioned invention object, the present application provides a step-by-step washing production process for food-grade phosphoric acid using the hydrochloric acid method, which adopts the following technical solutions:

[0006] A step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process comprises at least a step-by-step washing step, wherein the step-by-step washing step is:

[0007] Primary washing: add sulfuric acid to the washing liquid, compared with (3~10): 1, 2~4 levels of countercurrent washing;

[0008] Secondary washing: adding stripping acid to the washing liquid, compared with (10~20): 1, 2~4 levels of countercurrent washing;

[0009] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0010] Furthermore, in the one washing step, the washing liquid is a mixed solution containing 10-20 wt % phosphoric acid and 49-98 wt % sulfuric acid.

[0011] Furthermore, in the one-time washing step, the washing liquid further comprises a complexing agent, and the complexing agent is any one or more of tetrasodium glutamate diacetate, triammonium citrate and sodium gluconate.

[0012] Furthermore, the complexing agent is a mixture of triammonium citrate and sodium gluconate, and the weight ratio of the triammonium citrate to sodium gluconate is 1:(0.4-0.6).

[0013] Furthermore, the complexing agent is a mixture of triammonium citrate and sodium gluconate, and the weight ratio of the triammonium citrate to the sodium gluconate is 1:0.5.

[0014] Furthermore, in the one washing step, the washing temperature is 40-60°C.

[0015] Furthermore, in the secondary washing step, the phosphoric acid concentration of the stripping acid is 10-20 wt %.

[0016] Furthermore, in the secondary washing step, the washing temperature is 40-60°C.

[0017] In summary, this application has the following beneficial effects:

[0018] 1. The process of the present application improves the efficiency of removing calcium ions in the washing step during the preparation of food-grade phosphoric acid using the hydrochloric acid method, thereby avoiding the formation of calcium phosphate precipitation in subsequent processes that causes scaling of pipes and equipment.

[0019] 2. The washing step of the present application uses the phosphoric acid solution obtained in the stripping step for secondary washing, thereby realizing the reuse of the stripped acid.

[0020] 3. The food-grade phosphoric acid obtained by the process of the present application has a low calcium ion content and high phosphoric acid purity, thereby improving product quality. DETAILED DESCRIPTION

[0021] The technical solutions and effects of the present application are further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the invention, rather than to limit the invention.

[0022] The applicant's prior patent application (CN102515134A) describes a hydrochloric acid method for producing food-grade phosphoric acid, comprising the following steps: taking 200 grams of poor phosphate rock containing about 20% P2O5, crushing it to a size of more than 20 mesh, and then adding it to a beaker; adding 400 ml of 23 wt% hydrochloric acid and a portion of water, reacting them under stirring for 20 minutes, and then adding 14 ml of 6 wt% Na2S solution for pre-removal of impurities, and then adding 10 ml of 0.1 wt% flocculant. The precipitate was condensed and then filtered with filter paper; the filtrate was extracted with a mixed solvent of N235: isooctyl alcohol: kerosene = 15%: 15%: 70% by volume to remove iron, the extraction temperature was 20-30°C, the extraction phase: aqueous phase = 1:1, and the resulting residual aqueous phase was the iron-removed dilute phosphoric acid; then, a ten-stage extraction of the iron-removed dilute phosphoric acid was performed using a mixed solvent of tributyl phosphate and kerosene as an extractant, the extraction temperature was 20-30°C, the volume ratio of tributyl phosphate: kerosene = 1:1, and the water phase was extracted. The organic phase obtained by extraction is subjected to five-stage washing with a 15wt% dilute phosphoric acid solution, and the aqueous phase: organic phase ratio is 1:25 during washing; then, the organic phase is subjected to five-stage back extraction with 1wt% dilute hydrochloric acid, and the aqueous phase obtained by back extraction is the dilute phosphoric acid solution, and the aqueous phase: organic phase ratio is 1:10 during back extraction. The organic phase after back extraction is then subjected to five-stage back extraction with pure water, so that the organic phase can be returned to the extraction process for recycling, and the aqueous phase: organic phase ratio when back extraction with pure water is 1: 10; Next, 4 ml of a 6 wt % Na2S solution was added to the dilute phosphoric acid solution for impurity removal; 5 g of activated carbon was added to the dilute phosphoric acid and stirred to remove organic matter; the solution was filtered using filter paper; 1 ml of 30 wt % hydrogen peroxide was added to remove easily oxidizable substances from the dilute phosphoric acid; the dilute phosphoric acid solution was evaporated and concentrated at an evaporation temperature of 158°C; 1 g of activated carbon was added to the dilute phosphoric acid cooled to room temperature and stirred for decolorization, and then filtered using a sand core funnel to obtain 56.4 g of colorless, transparent finished phosphoric acid.

[0023] The four groups of finished phosphoric acid prepared above were measured for H3PO4 content by gravimetric method, F content by standard curve method, As and Pb content by ICP-MS, and oxidizable substances (calculated as H3PO3) content by titration. The specific data are as follows:

[0024] Finished product mass 56.5g; H3PO4 content 83.2%; F content 0.0005%; As content 0.00004%; Pb content 0.0004%; easily oxidized material content 0.007%.

[0025] Based on this patent, this application further improves the washing step in the process. By adopting a step-by-step washing method, the efficiency of removing calcium ions in the washing step during the preparation of food-grade phosphoric acid using the hydrochloric acid method is improved, thereby avoiding the formation of calcium phosphate precipitation in subsequent processes and causing scaling of pipes and equipment.

[0026] The washing process of this application is:

[0027] Primary washing: add sulfuric acid to the washing liquid, compared with (3~10): 1, 2~4 levels of countercurrent washing;

[0028] Secondary washing: adding stripping acid to the washing liquid, compared with (10~20): 1, 2~4 levels of countercurrent washing;

[0029] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0030] In the primary washing step, the washing solution is a mixed solution containing 10-20wt% phosphoric acid and 49-98wt% sulfuric acid. As a preferred embodiment, in the primary washing step, the washing solution also includes a complexing agent, and the complexing agent is any one or more of glutamic acid diacetate tetrasodium, triammonium citrate and sodium gluconate. Further, the complexing agent is a mixture of triammonium citrate and sodium gluconate, and calculated by weight, triammonium citrate: sodium gluconate is 1:(0.4-0.6). Further, the complexing agent is a mixture of triammonium citrate and sodium gluconate, and calculated by weight, triammonium citrate: sodium gluconate is 1:0.5. Further, in the primary washing step, the washing temperature is 40-60°C. In the secondary washing step, the phosphoric acid concentration of the stripping acid is 10-20wt%. Further, in the secondary washing step, the washing temperature is 40-60°C.

[0031] Example 1

[0032] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0033] In the production process of this embodiment, the washing step is:

[0034] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0035] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0036] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0037] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0038] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0039] Example 2

[0040] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0041] In the production process of this embodiment, the washing step is:

[0042] Primary washing: add sulfuric acid to the washing liquid at a ratio of 6:1, and perform two-stage countercurrent washing;

[0043] Secondary washing: add stripping acid to the washing liquid, with a ratio of 15:1, and two-stage countercurrent washing;

[0044] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0045] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0046] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0047] Example 3

[0048] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0049] In the production process of this embodiment, the washing step is:

[0050] Primary washing: add sulfuric acid to the washing liquid at a ratio of 10:1, and perform 2-stage countercurrent washing;

[0051] Secondary washing: add stripping acid to the washing liquid, with a ratio of 20:1, and two-stage countercurrent washing;

[0052] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0053] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0054] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0055] Example 4

[0056] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0057] In the production process of this embodiment, the washing step is:

[0058] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform 4-stage countercurrent washing;

[0059] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and 4-stage countercurrent washing;

[0060] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0061] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0062] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0063] Example 5

[0064] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0065] In the production process of this embodiment, the washing step is:

[0066] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0067] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0068] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0069] In one washing step, the washing liquid is a mixed solution containing 15 wt % phosphoric acid and 70 wt % sulfuric acid, and the washing temperature is 50°C.

[0070] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 15 wt % and the washing temperature was 50°C.

[0071] Example 6

[0072] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0073] In the production process of this embodiment, the washing step is:

[0074] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0075] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0076] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0077] In one washing step, the washing liquid is a mixed solution containing 20 wt % phosphoric acid and 75 wt % sulfuric acid, and the washing temperature is 60°C.

[0078] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 20 wt % and the washing temperature was 60°C.

[0079] Example 7

[0080] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0081] In the production process of this embodiment, the washing step is:

[0082] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0083] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0084] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0085] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0086] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0087] In the first washing step, the washing liquid further comprises a complexing agent, which is tetrasodium glutamate diacetate.

[0088] Example 8

[0089] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0090] In the production process of this embodiment, the washing step is:

[0091] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0092] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0093] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0094] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0095] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0096] In the first washing step, the washing liquid further comprises a complexing agent, which is triammonium citrate.

[0097] Example 9

[0098] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0099] In the production process of this embodiment, the washing step is:

[0100] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0101] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0102] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0103] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0104] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0105] In the first washing step, the washing liquid also includes a complexing agent, which is a mixture of triammonium citrate and sodium gluconate, and the weight ratio of triammonium citrate to sodium gluconate is 1:0.4.

[0106] Example 10

[0107] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0108] In the production process of this embodiment, the washing step is:

[0109] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0110] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0111] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0112] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0113] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0114] In the first washing step, the washing liquid also includes a complexing agent, which is a mixture of triammonium citrate and sodium gluconate, and the weight ratio of triammonium citrate to sodium gluconate is 1:0.5.

[0115] Example 11

[0116] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0117] In the production process of this embodiment, the washing step is:

[0118] Primary washing: add sulfuric acid to the washing liquid at a ratio of 3:1, and perform two-stage countercurrent washing;

[0119] Secondary washing: add stripping acid to the washing liquid, with a ratio of 10:1, and two-stage countercurrent washing;

[0120] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0121] In one washing step, the washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0122] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0123] In the first washing step, the washing liquid also includes a complexing agent, which is a mixture of triammonium citrate and sodium gluconate, and the weight ratio of triammonium citrate to sodium gluconate is 1:0.6.

[0124] Comparative Example 1

[0125] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0126] In the production process of this embodiment, the washing step is:

[0127] Add sulfuric acid to the washing liquid at a ratio of 3:1, and perform 4-stage countercurrent washing;

[0128] The washing liquid is a mixed solution containing 10 wt % phosphoric acid and 49 wt % sulfuric acid, and the washing temperature is 40°C.

[0129] Comparative Example 2

[0130] This embodiment discloses a step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid process, comprising the steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, washing, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration. The steps of raw material preparation, acid hydrolysis, pre-impurity removal, filtration, extraction and iron removal, extraction, stripping, impurity removal, oxidation, evaporation and concentration, and decolorization and filtration are consistent with those in Chinese Patent Publication No. CN102515134A and are not further described here.

[0131] In the production process of this embodiment, the washing step is:

[0132] Add stripping acid to the washing liquid, the ratio is 10:1, and 4-stage countercurrent washing;

[0133] The stripping acid is the phosphoric acid solution obtained in the stripping step.

[0134] In the secondary washing step, the phosphoric acid concentration of the stripping acid was 10 wt % and the washing temperature was 40°C.

[0135] Performance testing

[0136] Test 1:

[0137] Determine the H3PO4 content in the finished phosphoric acid obtained in the above examples and comparative examples;

[0138] Determine the calcium ion content before and after washing, and calculate the calcium ion removal rate:

[0139] Removal rate (%) = (1-C 初 / C 终 )*100%;

[0140] Among them, C 初: initial calcium ion concentration in the process liquid after acid hydrolysis (ppm);

[0141] C 终 : calcium ion concentration in the organic phase after secondary washing (ppm);

[0142] The results are recorded in the following table:

[0143] <![CDATA[Content percentage of H3PO4]]> Calcium ion removal rate% Example 1 85.1 99.4 Example 2 85.3 99.5 Example 3 85.2 99.3 Example 4 86.2 99.6 Example 5 86.1 99.5 Example 6 86.0 99.4 Example 7 87.3 99.7 Example 8 87.2 99.6 Example 9 87.6 99.8 Example 10 87.9 99.9 Example 11 87.7 99.8 Comparative Example 1 81.5 88.3 Comparative Example 2 80.1 84.8

[0144] Test 2:

[0145] The pilot production line (running continuously for 3 months using the process of Example 10) had a calcium ion removal rate of 99.6%.

[0146] From the above data, it can be seen that the process of the present application improves the efficiency of removing calcium ions in the washing step during the preparation of food-grade phosphoric acid by the hydrochloric acid method, avoiding the formation of calcium phosphate precipitation in subsequent processes and causing scaling of pipes and equipment.

[0147] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A step-by-step washing production process for food-grade phosphoric acid using the hydrochloric acid method, characterized in that: At least comprising a step-by-step washing step, wherein the step-by-step washing step is: Primary washing: add sulfuric acid to the washing liquid, compared with (3~10): 1, 2~4 levels of countercurrent washing; Secondary washing: adding stripping acid to the washing liquid, compared with (10~20): 1, 2~4 levels of countercurrent washing; The stripping acid is the phosphoric acid solution obtained in the stripping step.

2. The step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid method according to claim 1, characterized in that: In the one-time washing step, the washing liquid is a mixed solution containing 10-20 wt % phosphoric acid and 49-98 wt % sulfuric acid.

3. The step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid method according to claim 2, characterized in that: In the one-time washing step, the washing liquid further comprises a complexing agent, and the complexing agent is any one or more of tetrasodium glutamate diacetate, triammonium citrate and sodium gluconate.

4. The step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid method according to claim 3, characterized in that: The complexing agent is a mixture of triammonium citrate and sodium gluconate, and the weight ratio of the triammonium citrate to the sodium gluconate is 1:(0.4-0.6).

5. The step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid method according to claim 4, characterized in that: The complexing agent is a mixture of triammonium citrate and sodium gluconate, and the weight ratio of the triammonium citrate to the sodium gluconate is 1:0.

5.

6. The step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid method according to any one of claims 2 to 5, characterized in that: In the one washing step, the washing temperature is 40-60°C.

7. The step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid method according to claim 1, characterized in that: In the secondary washing step, the phosphoric acid concentration of the stripping acid is 10-20 wt %.

8. The step-by-step washing production process for food-grade phosphoric acid produced by the hydrochloric acid method according to claim 1 or 7, characterized in that: In the secondary washing step, the washing temperature is 40-60°C.