CN112568303A

CN112568303A - Instant tea preparation process based on microfiltration-reverse osmosis technology

Info

Publication number: CN112568303A
Application number: CN202011413509.0A
Authority: CN
Inventors: 施世照; 汤秋江; 颜才印; 黄依群
Original assignee: HANGZHOU KAIJIE MEMBRANE SEPARATION TECHNOLOGY CO LTD
Current assignee: HANGZHOU KAIJIE MEMBRANE SEPARATION TECHNOLOGY CO LTD
Priority date: 2020-12-03
Filing date: 2020-12-03
Publication date: 2021-03-30
Anticipated expiration: 2040-12-03
Also published as: CN112568303B

Abstract

The application relates to the technical field of instant tea preparation, and particularly discloses an instant tea preparation process based on microfiltration-reverse osmosis technology. The application provides an instant tea preparation process adopting microfiltration-reverse osmosis technology, which comprises the following steps: 1) soaking tea leaves, extracting, centrifuging, and coarsely filtering to obtain tea soup stock solution A; 2) filtering the tea soup stock solution A by a microfiltration membrane to obtain a tea soup clarified solution B; 3) concentrating the tea soup clear solution B through a reverse osmosis membrane to obtain a tea soup concentrated solution C; 4) removing heavy metal ions from the tea soup concentrated solution C by an electrodialysis membrane group to obtain a tea soup concentrated solution D; 5) and drying the tea soup concentrated solution D to obtain the tea soup. The instant tea prepared by the preparation process has the advantages of low content of heavy metal and impurities and high drinking safety.

Description

Instant tea preparation process based on microfiltration-reverse osmosis technology

Technical Field

The application relates to the technical field of instant tea preparation, in particular to an instant tea preparation process based on microfiltration and reverse osmosis technologies.

Background

The Chinese tea has long culture source and has a history of over five thousand years, and the tea contains a plurality of beneficial components such as tea polyphenol, crude protein, a plurality of amino acids, cellulose and the like, and has a good health-care function for human bodies. With the acceleration of the pace of life of people, the traditional tea drinking mode is not suitable for the fast-paced life mode, and the instant tea has the characteristics of simple brewing, convenient carrying and the like and is rapidly loved by young people. The instant tea is prepared by tea leaves through a series of processes of extraction, filtration, drying, packaging and the like, but with the rapid development of modern industry, the atmosphere and soil pollution is serious, so that the content of heavy metals such as lead, chromium, arsenic and the like in the tea leaves is greatly increased compared with the content of the heavy metals in the prior art, and after people drink the instant tea prepared from the tea leaves with high content of the heavy metals, the harmful heavy metal elements can be gradually accumulated in the body, and the health of the people is harmed.

In order to solve the problems, the chinese patent with application publication number CN104642614A discloses a method for reducing heavy metal ions in instant tea, including arsenic and lead, wherein tea leaves are subjected to extraction, centrifugation, filtration, concentration and other processes to prepare a concentrated solution with a mass concentration of 5-15%, the concentrated solution is subjected to adsorption of tea polyphenols by a resin column filled with LX-8 macroporous adsorption resin, the column-passing solution is subjected to adsorption of heavy metal ions such as arsenic and lead by a resin column filled with chelate resin LSA-100, an eluent of LX-8 resin and the column-passing solution of LSA-100 resin are collected, uniformly mixed, concentrated and dried to prepare instant tea powder with low heavy metal content.

Aiming at the method for reducing the heavy metal ions including arsenic and lead in the instant tea, the inventor thinks that the resin column has low adsorption efficiency and capacity for the heavy metals and the removal rate of the metal ions in the instant tea is low.

Disclosure of Invention

In order to reduce the content of heavy metal ions in the instant tea, the application provides an instant tea preparation process based on microfiltration-reverse osmosis technology

In a first aspect, the application provides a process for preparing instant tea by microfiltration-reverse osmosis technology, which adopts the following technical scheme:

a preparation process of instant tea by microfiltration-reverse osmosis technology comprises the following steps:

1) soaking tea leaves, extracting, centrifuging, and coarsely filtering to obtain tea soup stock solution A;

2) filtering the tea soup stock solution A by a microfiltration membrane to obtain a tea soup clarified solution B;

3) concentrating the tea soup clear solution B through a reverse osmosis membrane to obtain a tea soup concentrated solution C;

4) removing heavy metal ions from the tea soup concentrated solution C by an electrodialysis membrane group to obtain a tea soup concentrated solution D;

5) and drying the tea soup concentrated solution D to obtain the tea soup.

By adopting the technical scheme, the tea soup stock solution A is filtered by adopting the microfiltration membrane, so that macromolecular particle impurities in the tea soup stock solution A are removed, the mass fraction of active ingredients in the tea soup stock solution A is further improved, and the probability of precipitates in the prepared instant tea is reduced; then, the tea soup clear liquid B further removes the contained water through a reverse osmosis membrane, so that the content of effective components in the tea soup concentrated liquid C is improved, and in addition, compared with a heat source type concentration process, the working temperature of the reverse osmosis process is lower, so that the beneficial components in the instant tea cannot be damaged; and then removing harmful heavy metals in the tea soup concentrated solution C through an electrodialysis membrane group, reducing the content of the heavy metals in the tea soup concentrated solution D, and finally enabling the instant tea obtained by drying the tea soup concentrated solution D to have the effects of low content of the heavy metals and better drinking safety.

Preferably, the electrodialysis membrane group comprises two polar liquid chambers, an anode electrode plate and a cathode electrode plate are respectively arranged in the two polar liquid chambers, a plurality of membrane pairs A are arranged between the two polar liquid chambers, each membrane pair A consists of a cation exchange membrane and an anion exchange membrane, a partition plate is arranged between every two adjacent anion exchange membranes and every adjacent cation exchange membranes at intervals, a plurality of material liquid chambers and receiving chambers are formed between every two adjacent anion exchange membranes and between every two adjacent cation exchange membranes, polar liquid circulates in the polar liquid chambers, tea soup concentrated liquid C circulates in the material liquid chambers, and receiving liquid circulates in the receiving chambers.

By adopting the technical scheme, when the tea soup concentrated solution C circulates in the material liquid chamber, harmful anions such as fluoride ions, nitrate radicals and the like in the tea soup concentrated solution C migrate towards the anode electrode plate under the action of an electric field force and enter the receiving chamber through the anion exchange membrane, and meanwhile, sodium ions, potassium ions and partial heavy metal ions in the tea soup concentrated solution C migrate towards the cathode electrode plate under the action of the electric field force and enter the receiving chamber through the cation exchange membrane and are combined with the fluoride ions and the nitrate radicals to maintain the charge balance in the electrodialysis membrane group, so that the harmful anions in the tea soup concentrated solution C can be removed, and the drinking safety of the prepared instant tea is good.

Preferably, the receiving liquid comprises a sodium chloride solution and an adsorbent, the adsorbent is at least one of polymeric ferric sulfate, chitosan and activated alumina, and the adsorbent is composed of polymeric ferric sulfate, chitosan and activated alumina according to a mass ratio of (2-3) to (1-2) to (0.5-1.5).

By adopting the technical scheme, the ionic radius of the fluoride ions is smaller, free diffusion is easier to occur, when the concentration of the fluoride ions in the material liquid chamber is smaller than that of the fluoride ions in the receiving liquid, the fluoride ions overcome the electric field force under the action of concentration difference and migrate again to the material liquid chamber through the anion and cation membranes, ferric sulfate, chitosan and active alumina can form a ligand with the fluoride ions, the ionic radius of the ligand is larger, the steric hindrance is large, and migration is not easy to occur, so that the lower content of the fluoride ions in the tea soup concentrated liquid C in the material liquid chamber can be maintained.

Preferably, a complexing agent is further added into the receiving liquid, the complexing agent is at least one of aminopolycarboxylic acid, amino acid and phosphate, and the complexing agent is composed of the aminopolycarboxylic acid, the amino acid and the phosphate according to the mass ratio of (2-5) to (1-3) to (1-2).

By adopting the technical scheme, calcium, magnesium, zinc and other ions in the material liquid migrate into the receiving liquid under the action of the electric field force, aminopolycarboxylic acid, amino acid and phosphate in the receiving liquid can be complexed with calcium, magnesium, zinc and other ions, the reverse migration of the calcium, magnesium, zinc and other ions is reduced, the content of the calcium, magnesium, zinc and other ions in the material liquid is reduced, the hardness of the tea soup concentrated solution C is reduced, and the prepared instant tea has better taste.

Preferably, the step 4) further comprises a bipolar membrane electrodialysis membrane group, the bipolar membrane electrodialysis membrane group comprises two polar liquid chambers, a plurality of membrane pairs B are arranged between the two polar liquid chambers, each membrane pair B is composed of a cation exchange membrane, an anion exchange membrane and a bipolar membrane in sequence, a partition plate is arranged between the anion exchange membrane, the cation exchange membrane and the bipolar membrane, adjacent membrane pairs B are also separated by the partition plate, a plurality of material liquid chambers, acid liquid chambers and alkali liquid chambers are formed between adjacent anion exchange membranes, the bipolar membrane and the cation exchange membrane, a material liquid chamber is arranged between adjacent anion exchange membranes and the bipolar membrane, an alkali liquid chamber is arranged between adjacent anion exchange membranes and the bipolar membrane, an acid liquid chamber is arranged between adjacent cation exchange membranes and the bipolar membrane, a tea soup concentrated solution C circulates in the bipolar membrane, and polar liquid circulates in the polar liquid chamber.

By adopting the technical scheme, heavy metal ions such As Hg, As, Pb, Cu, Cr, Cd and the like remaining in the tea soup concentrated solution C continuously migrate into the alkali liquor chamber under the action of the electric field force, so that the heavy metal content in the tea soup concentrated solution C is further reduced.

Preferably, an intermediate membrane is further arranged between the adjacent anion exchange membrane and the bipolar membrane in the membrane pair B, a partition plate is arranged between the intermediate membrane and the anion exchange membrane as well as between the intermediate membrane and the bipolar membrane, an intermediate chamber is arranged between the adjacent intermediate membrane and the bipolar membrane, and a sodium chloride solution is circulated in the intermediate chamber.

By adopting the technical scheme, the cation barrier layer can be formed between the acid chamber and the feed liquid chamber by the intermediate liquid chamber, so that the probability that heavy metal ions such As Hg, As, Pb, Cu, Cr, Cd and the like are transferred into the feed liquid chamber again through the anion exchange membrane after passing through the bipolar membrane is reduced, and the heavy metal content in the tea soup concentrated solution C is further reduced.

Preferably, the alkali liquor is internally circulated with a sodium chloride solution, the sodium chloride solution is added with a complexing agent, the complexing agent is at least one of dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyethyleneimine xanthate, sodium trithiocyanate and gamma-sodium polyglutamate, and the complexing agent is composed of dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyethyleneimine xanthate, sodium trithiocyanate and gamma-sodium polyglutamate according to the mass ratio of (1-2): (0.5-1.5): (0.5-1.5): (0.1-0.5): (0.5-1): 0.2-0.5).

By adopting the technical scheme, dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyminoxanthate, sodium trithiocyanate, gamma-polyglutamate and part of Hg, As, Pb, Cu, Cr, Cd and other heavy metal ions form stable cross-linked reticular chelate, the other part of Hg, As, Pb, Cu, Cr, Cd and other heavy metal ions are combined with hydroxide radical dissociated from the bipolar membrane to form heavy metal hydroxide with extremely small particle fineness, and meanwhile, the heavy metal hydroxide cannot be deposited on the bipolar membrane or a cation exchange membrane under the continuous circulation of alkali liquor, the normal operation of the bipolar membrane electrodialysis membrane group is ensured while the heavy metal ions are removed, the reverse migration amount of the Hg, As, Pb, Cu, Cr, Cd and other heavy metal ions after matching and combination is greatly reduced, and the heavy metal content in the prepared instant tea is further improved.

Preferably, the gamma-polyglutamic acid sodium is subjected to crosslinking modification treatment.

By adopting the technical scheme, the poly-sodium glutamate forms a polymeric macromolecular substance after being subjected to crosslinking modification, the capture area of-COO-reactive groups on a molecular chain of the gamma-poly-sodium glutamate is increased, the system viscosity of alkali liquor is increased to a certain extent, the adsorption and binding capacity to heavy metal ions is improved, the removal capacity of the bipolar membrane electrodialysis membrane group to the heavy metal ions in the tea soup concentrated solution C is further improved, and the heavy metal content in the tea soup concentrated solution C is reduced.

Preferably, the microfiltration membrane in the step 2) is one of polyolefins, polysulfones, cellulose esters, fluorine-containing materials and polycarbonates.

By adopting the technical scheme, the microfiltration membrane can intercept particles of which the particle size is 0.1-1 micron, and can filter suspended matters, bacteria and macromolecular colloidal substances in the tea soup stock solution A, so that the obtained tea soup stock solution A is clear and transparent and has no precipitate; the microfiltration membranes of polyolefins, polysulfones, cellulose esters, fluorine-containing materials and polycarbonates have high chemical stability, long service life and good process stability.

Preferably, the reverse osmosis membrane in the step 3) is one of cellulose acetate, polyamide and composite membrane.

By adopting the technical scheme, the reverse osmosis membrane can intercept dissolved salts and organic molecules with the molecular weight larger than 100, and water molecules pass through the reverse osmosis membrane, so that water in the tea soup concentrated solution C can be removed, the mass fraction of the effective content in the tea soup concentrated solution C is improved, the process adopts pressure difference as the power for separating the water molecules, the original flavor of the instant tea can be kept, beneficial components in the tea soup concentrated solution C are prevented from being damaged in a long-time high-temperature environment, and in addition, the reverse osmosis membrane of cellulose acetate, polyamide and composite membranes has better chemical stability, higher mechanical strength and longer service life.

In summary, the present application has the following beneficial effects:

1. according to the application, the microfiltration-reverse osmosis-electrodialysis process is combined, macromolecular particles and colloids in the tea soup stock solution A are filtered, and then heavy metal ions in the tea soup concentrated solution C are removed through the electrodialysis membrane group, so that the prepared instant tea has a good drinking safety effect.

2. Electrodialysis-bipolar membrane electrodialysis combination is adopted in the application, the removal rate of heavy metal ions in the tea soup concentrated solution C is further improved, and the prepared instant tea is low in heavy metal content.

Detailed Description

The present application will be described in further detail with reference to examples.

The application provides an instant tea preparation process based on microfiltration-reverse osmosis technology, which comprises the following steps:

4) separating the tea soup concentrated solution C by an electrodialysis membrane component, and removing heavy metal ions to obtain a tea soup concentrated solution D;

5) and drying the tea soup concentrated solution D to obtain the tea soup.

Preferably, the step 1) of soaking, extracting, centrifuging and roughly filtering the tea leaves to obtain the tea soup stock solution A is to extract the tea leaves in boiling water for 3-5 times, then centrifuge the tea leaves for 5-15min by a butterfly centrifuge at the rotating speed of 5000-. Preferably, the tea leaves in the step 1) are soaked, extracted, centrifuged and coarsely filtered to obtain the tea soup stock solution A, and the tea leaves are extracted for 3 times in boiling water and then centrifuged at the rotating speed of 6500r/min for 10 min.

Preferably, in the step 2), the tea soup stock solution A is filtered by a microfiltration membrane to obtain the tea soup clarified liquid B, the temperature range of the tea soup stock solution A in the storage tank a is controlled to be 1-45 ℃, the working pH value range is 2-11, then the tea soup stock solution A is fed into a microfiltration device by a booster pump, the initial flow is adjusted to be 0.1-0.15t/h, the water inlet pressure is 0.2MPa-0.5MPa, wherein the filtrate is discharged, the tea soup stock solution A is circulated in the storage tank a and the microfiltration device to obtain the tea soup clarified liquid B, and the tea soup clarified liquid B is stored in the storage tank B. Further preferably, the water inlet pressure is 0.3MPa to 0.4 MPa. Further preferably, impurities with the molecular weight of more than 5 ten thousand in the filtrate enter the butterfly centrifuge again for separation, and the supernatant is conveyed to the storage tank a.

Preferably, the tea soup concentrated solution C obtained by concentrating the tea soup clear solution B through the reverse osmosis membrane in the step 3) is obtained by feeding the tea soup clear solution B into a reverse osmosis device by using a high-pressure pump, adjusting the initial flow to be 3-6t/h and the water inlet pressure to be 0.55MPa-0.8MPa, discharging the filtrate, circulating the tea soup clear solution B in a storage tank B and the reverse osmosis device to obtain the tea soup concentrated solution C, and storing the tea soup concentrated solution C in the storage tank C.

Further preferably, the microfiltration membrane in the microfiltration equipment in the step 2) is one of polyolefins, polysulfones, cellulose esters, fluorine-containing materials and polycarbonates. Further preferably, the microfiltration membrane in the microfiltration device in the step 2) is a polyolefin hollow fiber membrane. More preferably, the pore size of the microfiltration membrane is 0.1 to 1 μm.

Preferably, the reverse osmosis membrane in the reverse osmosis equipment in the step 3) is cellulose acetatePolyamide and composite film. Further preferably, the reverse osmosis membrane in the reverse osmosis equipment in the step 3) is polyamide. Further preferably, the reverse osmosis membrane in the reverse osmosis equipment in the step 3) is an aromatic polyamide. More preferably, the reverse osmosis membrane has a water permeability of 22.7 to 41.6m³And d. More preferably, the reverse osmosis membrane has a water permeability of 37.9m³And d. Further preferably, the reverse osmosis membrane is a homogeneous membrane.

Further preferably, the operation mode of the microfiltration device of the application comprises the following steps:

description of the operation of the microfiltration apparatus

1) Opening a liquid inlet valve, a reflux valve and a filtrate outlet valve, and starting a booster pump;

2) observing the water outlet flow meter, adjusting the reflux valve to enable the initial flow to be 0.1-0.15t/h and the water inlet pressure to be 0.2-0.5 MPa, wherein the water outlet flow can be properly reduced along with the reduction of the water in the tea soup stock solution A in the operation process, and the reflux valve cannot be closed to increase the water outlet flow at the moment;

3) opening the discharge port after the operation is finished, and discharging the residual tea soup stock solution A in the microfiltration equipment;

description of the operation of microfiltration apparatus

1. External pressure type cleaning step

1) Filling clean water in the washing tank, and closing the liquid inlet valve, the discharge valve, the chemical cleaning reflux valve, the filtrate outlet valve and the backwashing inlet valve;

2) and opening a cleaning liquid inlet valve, a water washing tank outlet valve and a drain valve, and opening a cleaning pump to perform external pressure type cleaning for 3-10min, wherein the cleaning time is based on the clear outlet water of a drain outlet.

2. Chemical cleaning step

1) Preparing a cleaning agent in the chemical cleaning box, and closing the liquid inlet valve, the emptying valve, the blowdown valve, the reflux valve, the filtrate outlet valve and the backwashing inlet valve;

2) and opening an outlet valve of the cleaning box, a cleaning liquid inlet valve and a chemical cleaning liquid return valve, then opening a cleaning pump to perform chemical circulation cleaning, wherein the circulation time is 30-60min, and as the cleaning agent can be heated in the inner circulation process, the cleaning pump is stopped for 15min to wait for the chemical cleaning liquid to be cooled to below 40 ℃, cleaning is performed, the inner circulation is accumulated for 30-60min, and in addition, the chemical cleaning agent can be soaked in the microfiltration equipment for 12 h.

3) Preparing a chemical agent, namely using 2-5% of hydrogen hydroxide solution to clean organic pollution of the microfiltration membrane; 0.5-2% hydrochloric acid solution is used for cleaning the microfiltration membrane to pollute inorganic salt precipitate (insoluble precipitate such as calcium, magnesium and the like).

3. Water backwash

1) Filling deionized water or RO produced water in the water washing tank, and closing the liquid inlet valve, the cleaning liquid inlet valve, the discharge port, the chemical cleaning liquid reflux valve, the reflux valve and the filtrate outlet valve;

2) opening an outlet valve and a blow-off valve of the cleaning tank, opening the degree of a backwashing inlet valve 1/5-1/4 or temporarily closing the backwashing inlet valve completely, then opening a cleaning pump, slowly opening the backwashing inlet valve and observing a pressure gauge at the same time, controlling the water inlet pressure to be about 0.15-0.2Mpa and the cleaning time to be 3-10min, and taking the clarity of the water outlet of a blow-off outlet as the standard, and in addition, the backwashing water inlet pressure is required to be less than 0.23 Mpa.

(III) description of the normal operation of the reverse osmosis plant

1) Opening a liquid inlet valve, an adjusting valve and a clear water permeation valve;

2) starting the high-pressure pump, observing the water inlet pressure gauge A, the pressure gauge B, the pure water flowmeter and the concentrated water flowmeter, slowly closing the regulating valve to ensure that the initial flow of the pure water flowmeter is 3-6t/h, and paying attention to the pressure range of the pressure gauge A to be 0.55-0.8 Mpa.

(IV) cleaning description of reverse osmosis membrane equipment

The microfiltration and reverse osmosis concentration units must be cleaned as necessary after each batch operation is completed.

1. Physical cleaning

1) Closing all valves, filling pure water in the cleaning water tank, and then opening a cleaning liquid inlet valve, a water cleaning blowdown valve and a chemical cleaning liquid return valve;

2) and (3) starting the cleaning pump, circulating for 5-10min at a large flow rate, and discharging the cleaning liquid after closing the cleaning pump and all valves according to the cleanness degree of the discharged water to wait for the next operation.

And (4) storing the reverse osmosis membrane and the microfiltration membrane in a uniform wet state after cleaning, and strictly preventing water loss.

2. Chemical cleaning

2.1, cleaning Explanation

The reverse osmosis membrane module is chemically cleaned after the following conditions occur: a. under the condition of constant pressure, the initial water yield is reduced by 20% compared with that of the water produced after the last physical cleaning; b. under the condition of constant initial flow, the initial pressure is increased by 20 percent compared with the pressure after the last cleaning and the stop of reverse osmosis equipment exceeds 10 days; c. the system operating pressure is obviously increased; d. the reverse osmosis equipment has the continuous operation time of more than 5 d.

2.2 cleaning fluid selection and cleaning fluid formulation

Cleaning solution 1: citric acid 0.02% solution, adjusted to PH 4.0 with ammonium hydroxide and used at a temperature of less than 40 ℃.

Cleaning solution 2: the mixed solution of STTP sodium tripolyphosphate and NA-EDTA (STTP sodium tripolyphosphate content is 0.0197%, and NA-EDTA content is 0.00817%), and the pH is slowly adjusted to 10.0 with sulfuric acid or hydrochloric acid, and the use temperature is less than 40 ℃.

Cleaning solution 3: the mixed solution of STTP sodium tripolyphosphate and NA-DDBS (STTP sodium tripolyphosphate content 0.0199%, NA-DDBS content 0.00258%) is slowly adjusted pH 10.0 with sulfuric acid or hydrochloric acid, and the use temperature is less than 40 ℃.

Cleaning solution 4: 0.0017% hydrochloric acid solution, adjusted to PH 2.5 with ammonium hydroxide and used at a temperature of less than 35 ℃.

Cleaning solution 5: 0.01% sodium bisulfite solution, the pH was slowly raised with sodium bisulfite, and then adjusted to 11.5 with hydrochloric acid, the application temperature was less than 35 ℃.

Cleaning solution 6: the mixed solution of sodium hydroxide and SDS sodium dodecyl sulfate (sodium hydroxide content is 0.001%, SDS sodium dodecyl sulfate content is 0.00029%), the PH value is slowly increased by sodium hydroxide, hydrochloric acid is added to adjust the PH value to 11.5, and the using temperature is lower than 30 ℃.

Cleaning solution 7: 0.001% sodium hydroxide solution, the pH was slowly raised with sodium hydroxide, and then adjusted back to 11.5 with hydrochloric acid at a temperature of less than 30 ℃.

The water for preparing the cleaning solution is RO product water or deionized water, and free chlorine and hardness are avoided.

Cleaning solution selection instructions are shown in table 1:

TABLE 1 selection of chemical cleaning Agents

2.3 description of cleaning procedure

1) Selecting proper chemical cleaning liquid according to the pollution condition of the reverse osmosis membrane and the components in the tea soup concentrated solution;

2) preparing selected chemical cleaning liquid in a chemical cleaning water tank, opening a cleaning liquid inlet valve, a chemical cleaning feed back valve and a chemical cleaning permeate reflux valve, and closing the other valves;

3) starting a cleaning pump, circulating for 30-60min at a large flow rate, then closing the cleaning pump, and discharging the cleaning liquid;

4) adding deionized water or RO produced water into a cleaning water tank, and cleaning according to a physical cleaning method until the effluent is neutral.

Preferably, the electrodialysis membrane group comprises two polar liquid chambers, an anode electrode plate and a cathode electrode plate are respectively arranged in the two polar liquid chambers, a plurality of membrane pairs A are arranged between the two polar liquid chambers, each membrane pair A consists of a cation exchange membrane and an anion exchange membrane, a partition plate is arranged between every two adjacent anion exchange membranes and every two adjacent cation exchange membranes at intervals, a plurality of material liquid chambers and receiving chambers are formed between every two adjacent anion exchange membranes and between every two adjacent cation exchange membranes, polar liquid circulates in the polar liquid chambers, tea soup concentrated liquid C circulates in the material liquid chambers, and receiving liquid circulates in the receiving chambers.

Preferably, the polar solution is 0.1mol/L sodium chloride solution, and the receiving solution is 0.05mol/L sodium chloride solution.

Preferably, the anion exchange membrane in the electrodialysis membrane stack is a homogeneous anion exchange membrane. Further preferably, the cationic groups in the homogeneous anion-exchange membrane are quaternary ammonium type cationic groups. Further preferably, the anion exchange membrane has a permselectivity greater than 90%. More preferably, the anion exchange membrane is an anion exchange membrane produced by Asahi glass.

Preferably, the cation exchange membranes in the electrodialysis membrane stack are homogeneous cation exchange membranes. Further preferably, the anionic groups in the homogeneous cation exchange membrane are sulfonic acid type cationic groups. Further preferred, the homogeneous cation exchange membrane has a permselectivity greater than 90%. More preferably, the anion exchange membrane is a cation exchange membrane produced by Asahi glass.

Preferably, the bipolar membrane in the bipolar membrane electrodialysis membrane group is a homogeneous bipolar membrane. Further preferably, the bipolar membrane is a bipolar membrane produced by Tingrun China.

Preferably, in the step 4), the tea soup concentrated solution D obtained by removing heavy metal ions from the tea soup concentrated solution C by the electrodialysis membrane group is: the electrodialysis membrane group comprises an electrode liquid tank, a material liquid tank m and a receiving tank, wherein the electrode liquid circulates between the electrode liquid tank and the electrode liquid chamber, the concentrated liquid C circulates between the material liquid tank m and the material liquid chamber, and the receiving liquid circulates between the receiving tank and the receiving chamber to obtain the tea soup concentrated liquid C1. More preferably, the electrodialysis process is to control the current density to be 500A/square meter, the voltage to be 150V and 200V, and the flow velocity of the feed liquid and the polar liquid to be 3-4m³H is used as the reference value. More preferably, the electrodialysis process is to control the current density to be 400A/square meter, the voltage to be 200V and the flow velocity of the feed liquid and the polar liquid to be 3.5m³/h。

Preferably, the adsorbent is at least one of polymeric ferric sulfate, chitosan and activated alumina. Further preferably, the adsorbent is composed of polyferric sulfate, chitosan and activated alumina according to the mass ratio of (2-3) to (1-2) to (0.5-1.5). Further preferably, the adsorbent is composed of polyferric sulfate, chitosan and activated alumina according to a mass ratio of 2.5:1.5: 1. Further preferably, the concentration of the adsorbent is 0.01 to 0.05 mol/L. Further preferably, the concentration of the adsorbent is 0.03 mol/L. It is further preferred that the polymeric ferric sulfate has an overall iron content of greater than 10% and a basicity of 8.0-16.0%. Further preferably, the chitosan is β -chitosan, and the average relative molecular mass is 10000. More preferably, the alumina trihydrate has an average surface area of 200 square meters per gram.

Preferably, the receiving liquid is further added with a complexing agent, and the complexing agent is at least one of aminopolycarboxylic acid, amino acid and phosphate. Further preferably, the complexing agent is composed of aminopolycarboxylic acid, amino acid and phosphate according to the mass ratio of (2-5) to (1-3) to (1-2). More preferably, the complexing agent is composed of aminopolycarboxylic acid, amino acid and phosphate according to the mass ratio of 3.5:2: 1.5. Further preferably, the concentration of the complexing agent is 0.01 to 0.02 mol/L. Further preferably, the concentration of the complexing agent is 0.015 mol/L. More preferably, the aminopolycarboxylic acid is triethylamine hexaacetic acid. The amino acid is L-leucine. Further preferably, the phosphate is potassium orthophosphate.

Preferably, the step 4) further comprises a bipolar membrane electrodialysis membrane group, the bipolar membrane electrodialysis membrane group comprises two polar liquid chambers, a plurality of membrane pairs B are arranged between the two polar liquid chambers, each membrane pair B is composed of a cation exchange membrane, an anion exchange membrane and a bipolar membrane in sequence, a partition plate is arranged between the anion exchange membrane and the cation exchange membrane, adjacent membrane pairs B are also separated by the partition plate, a plurality of material liquid chambers, acid liquid chambers and alkali liquid chambers are formed between the adjacent anion exchange membrane, the bipolar membrane and the cation exchange membrane, material liquid chambers are arranged between the adjacent anion exchange membrane and the adjacent cation exchange membrane, alkali liquid chambers are arranged between the adjacent anion exchange membrane and the bipolar membrane, acid liquid chambers are arranged between the adjacent cation exchange membrane and the bipolar membrane, tea soup concentrated solution C circulates in the material liquid chambers, and polar liquid circulates in the polar liquid chambers.

Preferably, the polar liquid is 0.1mol/L sodium chloride solution, the alkali liquid is 0.02mol/L sodium chloride solution, and the acid liquid is 0.01mol/L sulfuric acid solution.

Preferably, the bipolar membrane electrodialysis membrane group comprises an electrode liquid tank, a feed liquid tank n, an acid liquid tank, an alkali liquid tank and an intermediate liquid tank, wherein the electrode liquid circulates between the electrode liquid tank and an electrode liquid chamber, a concentrated solution C1 circulates between the feed liquid tank n and the feed liquid chamber, the acid liquid circulates between the acid liquid tank and the acid liquid chamber, the alkali liquid circulates between the alkali liquid tank and the alkali liquid chamber, and the intermediate liquid circulates between the intermediate liquid tank and the intermediate liquid chamber to obtain a tea soup concentrated solution D. Preferably, the bipolar membrane electrodialysis process comprises controlling the current density at 350A/square meter and the voltage at 100V and 150V, and controlling the flow rates of the feed liquid, the acid liquid, the alkali liquid and the polar liquidIs 1.5-2.5m³H is used as the reference value. More preferably, the bipolar membrane electrodialysis process is to control the current density to be 200A/square meter, the voltage to be 120V, and the flow velocity of feed liquid, acid liquid, alkali liquid and polar liquid to be 2m³/h。

Preferably, the intermediate chamber is circulated with a sodium chloride solution. Further preferably, 0.01mol/L sodium chloride solution circulates in the intermediate chamber. Further preferably, the intermediate membrane is an anion exchange membrane. Further preferably, the intermediate membrane has a permselectivity of greater than 90% for the anion exchange membrane. More preferably, the anion exchange membrane of the intermediate membrane is an anion exchange membrane produced by asahi glass.

Preferably, the alkaline liquor chamber is internally added with a complexing agent, and the complexing agent is at least one of dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyminoxanthate, sodium tripolyphosphate and gamma-sodium polyglutamate. More preferably, the complexing agent is composed of dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyminoxanthate, sodium trithiocyanate and gamma-polyglutamate according to the mass ratio of (1-2): (0.5-1.5): (0.5-1.5): (0.1-0.5): 0.5-1): 0.2-0.5. More preferably, the complexing agent is dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyminoxanthate, sodium tripolyphosphate and gamma-sodium polyglutamate according to the mass ratio of 1.5:1:1:0.3:0.7: 0.3. Further preferably, the concentration of the complexing agent is 0.02 to 0.08 mol/L. More preferably, the concentration of the complexing agent is 0.05 mol/L. Further preferably, the dithiocarbamate is sodium dithiocarbamate.

Preferably, the gamma-polyglutamic acid sodium is subjected to cross-linking modification treatment to form gamma-polyglutamic acid sodium molecules which are cross-linked with each other through chemical bonds under the action of a catalyst. Further preferably, the crosslinking degree of the gamma-polyglutamic acid sodium is 10-50%. More preferably, the degree of crosslinking of the gamma-polyglutamic acid sodium is 25%.

The main material information of the present application is shown in table 2:

table 2 main material information table of the present application

Example 1

The instant tea preparation process based on the microfiltration-reverse osmosis technology comprises the following steps:

step 1) extracting tea leaves in boiling water for 3 times, centrifuging for 10min at the rotating speed of 6500, filtering by polypropylene filter cloth of 500 meshes to obtain tea soup stock solution A, and storing the tea soup stock solution A in a storage tank a.

And 2) feeding the tea soup stock solution A in the storage tank a into a microfiltration device by using a booster pump, adjusting the initial flow to be 0.1t/h and the water inlet pressure to be 0.3MPa, wherein the filtrate is discharged, the tea soup stock solution A circulates in the storage tank a and the microfiltration device to obtain a tea soup clarified solution B, and the tea soup clarified solution B is stored in a storage tank B.

And 3) conveying the tea soup clear liquid B in the storage tank B into reverse osmosis equipment by using a high-pressure pump, adjusting the initial flow to be 3t/h and the water inlet pressure to be 0.55MPa, discharging the filtrate, circulating the tea soup clear liquid B in the storage tank B and the reverse osmosis equipment to obtain tea soup concentrated liquid C, and storing the tea soup concentrated liquid C into the storage tank C.

Step 4) conveying the tea soup concentrated solution C in the storage tank C to a material liquid tank m by using a pump, then operating an electrodialysis membrane group to enable polar liquid to circulate between the polar liquid tank and a polar liquid chamber, circulating the tea soup concentrated solution C between the material liquid tank m and the material liquid chamber, circulating receiving liquid between a receiving tank and the receiving chamber, controlling the current density to be 400A/square meter, the voltage to be 200V, and controlling the flow velocity of the material liquid and the polar liquid to be 3.5m³H is used as the reference value. And finally obtaining the tea soup concentrated solution D. The receiving liquid is not added with an adsorbent and a complexing agent.

And 5) conveying the tea soup concentrated solution D into a pressure type spray tower for atomization through a high-pressure pump at the pressure of 15MPa, and drying for 15s under the conditions that the air inlet temperature is controlled to be 150 ℃ and the air outlet temperature is 80 ℃ to obtain the tea soup concentrated solution D.

Example 2

And 2) feeding the tea soup stock solution A in the storage tank a into a microfiltration device by using a booster pump, adjusting the initial flow to be 0.15t/h and the water inlet pressure to be 0.4MPa, wherein the filtrate is discharged, the tea soup stock solution A circulates in the storage tank a and the microfiltration device to obtain a tea soup clarified solution B, and the tea soup clarified solution B is stored in a storage tank B.

And 3) conveying the tea soup clear liquid B in the storage tank B into reverse osmosis equipment by using a high-pressure pump, adjusting the initial flow to be 5t/h and the water inlet pressure to be 0.7MPa, discharging the filtrate, circulating the tea soup clear liquid B in the storage tank B and the reverse osmosis equipment to obtain tea soup concentrated liquid C, and storing the tea soup concentrated liquid C into the storage tank C.

And 5) conveying the tea soup concentrated solution D into a pressure type spray tower for atomization through a high-pressure pump at the pressure of 20MPa, and drying for 15s under the conditions that the air inlet temperature is controlled to be 150 ℃ and the air outlet temperature is 80 ℃ to obtain the tea soup concentrated solution D.

Example 3

And 2) feeding the tea soup stock solution A in the storage tank a into a microfiltration device by using a booster pump, adjusting the initial flow to be 0.12t/h and the water inlet pressure to be 0.35MPa, wherein the filtrate is discharged, the tea soup stock solution A circulates in the storage tank a and the microfiltration device to obtain a tea soup clarified solution B, and the tea soup clarified solution B is stored in a storage tank B.

And 3) conveying the tea soup clear liquid B in the storage tank B into reverse osmosis equipment by using a high-pressure pump, adjusting the initial flow to be 6t/h and the water inlet pressure to be 0.8MPa, discharging the filtrate, circulating the tea soup clear liquid B in the storage tank B and the reverse osmosis equipment to obtain tea soup concentrated liquid C, and storing the tea soup concentrated liquid C into the storage tank C.

And 5) conveying the tea soup concentrated solution D into a pressure type spray tower for atomization through a high-pressure pump at the pressure of 18MPa, and drying for 15s under the conditions that the air inlet temperature is controlled to be 150 ℃ and the air outlet temperature is 80 ℃ to obtain the tea soup concentrated solution D.

Example 4

And 2) feeding the tea soup stock solution A in the storage tank a into a microfiltration device by using a booster pump, adjusting the initial flow to be 0.12t/h and the water inlet pressure to be 0.35MPa, wherein the filtrate is discharged, the tea soup stock solution A is circulated in the storage tank a and the microfiltration device to obtain a concentrated solution B, and the tea soup clear solution B is stored in a storage tank B.

Step 4) conveying the tea soup concentrated solution C in the storage tank C to a material liquid tank m by using a pump, then operating an electrodialysis membrane group to enable polar liquid to circulate between the polar liquid tank and a polar liquid chamber, circulating the tea soup concentrated solution C between the material liquid tank m and the material liquid chamber, circulating receiving liquid between a receiving tank and the receiving chamber, controlling the current density to be 400A/square meter, the voltage to be 200V, and controlling the flow velocity of the material liquid and the polar liquid to be 3.5m³H is used as the reference value. And finally obtaining the tea soup concentrated solution D. And adding an adsorbent into the receiving solution, wherein the adsorbent consists of polymeric ferric sulfate, beta-chitosan and active alumina trihydrate according to the mass ratio of 2.5:1.5: 1. The concentration of the adsorbent was 0.03 mol/L.

Example 5

Step 4) conveying the tea soup concentrated solution C in the storage tank C to a feed liquid tank by a pumpm, operating the electrodialysis membrane group to enable polar liquid to circulate between a polar liquid tank and a polar liquid chamber, circulating tea soup concentrated solution C between a material liquid tank m and a material liquid chamber, circulating receiving liquid between a receiving tank and a receiving chamber, controlling the current density to be 400A/square meter, the voltage to be 200V, and controlling the flow velocity of the material liquid and the polar liquid to be 3.5m³H is used as the reference value. And finally obtaining the tea soup concentrated solution D. And adding an adsorbent and a complexing agent into the receiving solution, wherein the adsorbent consists of polymeric ferric sulfate, beta-chitosan and trihydrate activated alumina according to the mass ratio of 2.5:1.5: 1. The complexing agent is composed of triethylamine hexaacetic acid, L-leucine and potassium orthophosphate in a mass ratio of 3.5:2: 1.5. The concentration of the adsorbent was 0.03 mol/L. The concentration of the complexing agent is 0.015 mol/L.

Example 6

Step 4) pumping the tea soup concentrated solution C in the storage tank C to a material liquid tank m, operating the electrodialysis membrane group to enable polar liquid to circulate between the polar liquid tank and the polar liquid chamber, and enabling the tea soup concentrated solution C to circulate in the material liquid tankm and the feed liquid chamber, receiving liquid circulates between the receiving tank and the receiving chamber, the current density is controlled to be 400A/square meter, the voltage is controlled to be 200V, and the flow velocity of the feed liquid and the polar liquid is controlled to be 3.5m³H is used as the reference value. Recycling to obtain tea soup concentrated solution C1. And adding an adsorbent and a complexing agent into the receiving solution, wherein the adsorbent consists of polymeric ferric sulfate, beta-chitosan and trihydrate activated alumina according to the mass ratio of 2.5:1.5: 1. The complexing agent is composed of triethylamine hexaacetic acid, L-leucine and potassium orthophosphate in a mass ratio of 3.5:2: 1.5. The concentration of the adsorbent was 0.03 mol/L. The concentration of the complexing agent is 0.015 mol/L.

Step 5) conveying the tea soup concentrated solution C1 obtained in the step 4) to a feed liquid tank n by a pump, operating a bipolar membrane electrodialysis membrane group to enable polar liquid to circulate between a polar liquid tank and a polar liquid chamber, circulating the tea soup concentrated solution C1 between the feed liquid tank n and the feed liquid chamber, circulating acid liquid between an acid liquid tank and an acid liquid chamber, circulating alkali liquid between an alkali liquid tank and an alkali liquid chamber, controlling the current density to be 200A/square meter, controlling the voltage to be 120V, and controlling the flow velocity of the feed liquid, the acid liquid, the alkali liquid and the polar liquid to be 2m³H is used as the reference value. Circulating to obtain tea soup concentrated solution D. The polar liquid is 0.1mol/L sodium chloride solution, the alkali liquor is 0.02mol/L sodium chloride solution, and the acid liquor is 0.01mol/L sulfuric acid solution.

And 6) conveying the tea soup concentrated solution D into a pressure type spray tower for atomization through a high-pressure pump at the pressure of 18MPa, and drying for 15s under the conditions that the air inlet temperature is controlled to be 150 ℃ and the air outlet temperature is 80 ℃ to obtain the tea soup concentrated solution D.

Example 7

Step 4) conveying the tea soup concentrated solution C in the storage tank C to a material liquid tank m by using a pump, then operating an electrodialysis membrane group to enable polar liquid to circulate between the polar liquid tank and a polar liquid chamber, circulating the tea soup concentrated solution C between the material liquid tank m and the material liquid chamber, circulating receiving liquid between a receiving tank and the receiving chamber, controlling the current density to be 400A/square meter, the voltage to be 200V, and controlling the flow velocity of the material liquid and the polar liquid to be 3.5m³H is used as the reference value. Recycling to obtain tea soup concentrated solution C1. And adding an adsorbent and a complexing agent into the receiving solution, wherein the adsorbent consists of polymeric ferric sulfate, beta-chitosan and trihydrate activated alumina according to the mass ratio of 2.5:1.5: 1. The complexing agent is composed of triethylamine hexaacetic acid, L-leucine and potassium orthophosphate in a mass ratio of 3.5:2: 1.5. The concentration of the adsorbent was 0.03 mol/L. The concentration of the complexing agent is 0.015 mol/L.

Step 5) pumping the tea soup concentrated solution C1 obtained in the step 4) into a feed liquid tank n, operating a bipolar membrane electrodialysis membrane group to enable polar liquid to circulate between a polar liquid tank and a polar liquid chamber, circulating the tea soup concentrated solution C1 between the feed liquid tank n and the feed liquid chamber, circulating acid liquid between an acid liquid tank and an acid liquid chamber, circulating alkali liquid between an alkali liquid tank and an alkali liquid chamber, circulating intermediate liquid between an intermediate liquid tank and an intermediate liquid chamber, controlling the current density to be 200A/square meter, controlling the voltage to be 120V, and controlling the flow rate of the feed liquid, the acid liquid, the alkali liquid and the polar liquid to be 2m³H is used as the reference value. Circulating to obtain tea soup concentrated solution D. The polar liquid is 0.1mol/L sodium chloride solution, the alkali liquor is 0.02mol/L sodium chloride solution, and the acid liquor is 0.01mol/L sulfuric acid solution. The intermediate solution is 0.01mol/L sodium chloride solution.

Example 8

Step 4) conveying the tea soup concentrated solution C in the storage tank C to a material liquid tank m by using a pump, then operating an electrodialysis membrane group to enable polar liquid to circulate between the polar liquid tank and a polar liquid chamber, circulating the tea soup concentrated solution C between the material liquid tank m and the material liquid chamber, circulating receiving liquid between a receiving tank and the receiving chamber, controlling the current density to be 400A/square meter, the voltage to be 200V, and controlling the flow velocity of the material liquid and the polar liquid to be 3.5m³H is used as the reference value. Recycling to obtain tea soup concentrated solution C1. And adding an adsorbent and a complexing agent into the receiving solution, wherein the adsorbent consists of polymeric ferric sulfate, beta-chitosan and trihydrate activated alumina according to the mass ratio of 2.5:1.5: 1. The complexing agent is composed of triethylamine hexaacetic acid, L-leucine and potassium orthophosphate in a mass ratio of 3.5:2: 1.5. The concentration of the adsorbent was 0.03 mol/L. The concentration of the complexing agent is 0.015 mol/L. A complexing agent is added in the alkali liquor chamber, and the concentration of the complexing agent is 0.05 mol/L. The complexing agent is composed of sodium dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyminoxanthate, sodium trithiocyanate and gamma-sodium polyglutamate according to the mass ratio of 1.5:1:1:0.3:0.7: 0.3.

Step 5) pumping the tea soup concentrated solution C1 obtained in the step 4) into a feed liquid tank n, operating a bipolar membrane electrodialysis membrane group to circulate the polar liquid between a polar liquid tank and a polar liquid chamber, and collecting the tea soup concentrated solution C1 circulating between a feed liquid tank n and a feed liquid chamber, circulating an acid liquid between an acid liquid tank and an acid liquid chamber, circulating an alkali liquid between an alkali liquid tank and an alkali liquid chamber, circulating an intermediate liquid between an intermediate liquid tank and an intermediate liquid chamber, controlling the current density to be 200A/square meter and the voltage to be 120V, and controlling the flow velocity of the feed liquid, the acid liquid, the alkali liquid and the polar liquid to be 2m³H is used as the reference value. Circulating to obtain tea soup concentrated solution D. The polar liquid is 0.1mol/L sodium chloride solution, the alkali liquor is 0.02mol/L sodium chloride solution, and the acid liquor is 0.01mol/L sulfuric acid solution. The intermediate solution is 0.01mol/L sodium chloride solution.

Example 9

Step 4) pumping the concentrated tea soup liquid C in the storage tank C to a liquid feed tank m, operating an electrodialysis membrane group to enable polar liquid to circulate between a polar liquid tank and a polar liquid chamber, circulating the concentrated tea soup liquid C between the liquid feed tank m and the liquid feed chamber, circulating receiving liquid between a receiving tank and a receiving chamber, controlling the current density to be 400A/square meter and the voltage to be 200V,the flow rate of the feed liquid and the polar liquid is 3.5m³H is used as the reference value. Recycling to obtain tea soup concentrated solution C1. And adding an adsorbent and a complexing agent into the receiving solution, wherein the adsorbent consists of polymeric ferric sulfate, beta-chitosan and trihydrate activated alumina according to the mass ratio of 2.5:1.5: 1. The complexing agent is composed of triethylamine hexaacetic acid, L-leucine and potassium orthophosphate in a mass ratio of 3.5:2: 1.5. The concentration of the adsorbent was 0.03 mol/L. The concentration of the complexing agent is 0.015 mol/L. A complexing agent is added in the alkali liquor chamber, and the concentration of the complexing agent is 0.05 mol/L. The complexing agent is composed of sodium dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyminoxanthate, sodium trithiocyanate and gamma-sodium polyglutamate according to the mass ratio of 1.5:1:1:0.3:0.7: 0.3. The degree of crosslinking of the gamma-polyglutamic acid sodium is 25%.

Comparative example 1

The preparation process of the instant tea based on the microfiltration-reverse osmosis technology comprises the following steps:

And 3) conveying the tea soup clear liquid B in the storage tank B into reverse osmosis equipment by using a high-pressure pump, adjusting the initial flow to be 3-6t/h and the water inlet pressure to be 0.55-0.8MPa, discharging the filtrate, circulating the concentrated liquid B in the storage tank B and the reverse osmosis equipment to obtain tea soup concentrated liquid C, and storing the tea soup concentrated liquid C into the storage tank C.

And 4) conveying the tea soup concentrated solution C into a pressure type spray tower for atomization through a high-pressure pump at the pressure of 18MPa, and drying for 15s under the conditions that the air inlet temperature is controlled to be 150 ℃ and the air outlet temperature is 80 ℃ to obtain the tea soup concentrated solution C.

Performance test

The content of heavy metal elements in the instant tea obtained in the same mass in the examples 1 to 9 is tested according to the method for measuring the content of lead, arsenic, cadmium, copper and iron in the import and export tea leaves of SN/T2056-:

table 3 examples 1-9 and comparative example 1 the heavy metal content per gram of instant tea

As can be seen by comparing examples 1-3 with comparative example 1 and combining Table 3, the content of heavy metal ions and fluoride in the instant tea is greatly reduced by the electrodialysis membrane stack, and the drinking safety of the instant tea is improved.

Comparing examples 1-3 and example 4 with Table 3, it can be seen that the adsorbent adsorbs heavy metal ions, further reducing the content of heavy metals in the instant tea.

As can be seen by comparing examples 1 to 3 and examples 4 to 5 with table 3, the complexing agent reduces back migration of heavy metal ions in the electrodialysis received solution and maintains a low heavy metal content in the tea soup concentrate C.

Comparing examples 1-3, examples 4-5, example 6 and in combination with table 3, it can be seen that bipolar membrane electrodialysis further reduced the heavy metal content of instant tea.

As can be seen by comparing examples 1 to 3, examples 4 to 6 and example 7 with table 3, the intermediate solution reduces the back migration of heavy metal ions, and maintains the content of heavy metal ions in the concentrated tea soup C1 in the feed solution chamber to be low.

Comparing examples 1-3, examples 4-7, example 8 and in combination with table 3, it can be seen that the adsorbent further reduced the heavy metal content of the instant tea.

Comparing examples 1 to 3, examples 4 to 8 and example 9 with table 3, it can be seen that sodium γ -polyglutamate having a crosslinking degree of 25% has a better capturing effect on heavy metal ions, further reducing the reverse migration amount of heavy metals.

In conclusion, the heavy metal content in the instant tea is greatly reduced through the synergistic effect of the bipolar membrane electrodialysis, the intermediate chamber, the complexing agent and the adsorbent, so that the drinking safety of the instant tea is higher.

The present embodiment is only for explaining the present application, and it is not limited to the present application, and those skilled in the art can make modifications of the present embodiment without inventive contribution as needed after reading the present specification, but all of them are protected by patent law within the scope of the claims of the present application.

Claims

1. An instant tea preparation process based on microfiltration-reverse osmosis technology is characterized by comprising the following steps:

5) and drying the tea soup concentrated solution D to obtain the tea soup.

2. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 1, characterized in that: the electrodialysis membrane group comprises two polar liquid chambers, an anode electrode plate and a cathode electrode plate are respectively arranged in the two polar liquid chambers, a plurality of membrane pairs A are arranged between the two polar liquid chambers, each membrane pair A consists of a cation exchange membrane and an anion exchange membrane, a partition plate is arranged between every two adjacent anion exchange membranes and every two adjacent cation exchange membranes at intervals, a plurality of material liquid chambers and receiving chambers are formed between every two adjacent anion exchange membranes and between every two adjacent cation exchange membranes, polar liquid circulates in the polar liquid chambers, tea soup concentrated liquid C circulates in the material liquid chambers, and receiving liquid circulates in the receiving chambers.

3. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 2, characterized in that: the receiving liquid comprises a sodium chloride solution and an adsorbent, wherein the adsorbent is at least one of polymeric ferric sulfate, chitosan and activated alumina, and the adsorbent consists of the polymeric ferric sulfate, the chitosan and the activated alumina according to a mass ratio of (2-3) to (1-2) to (0.5-1.5).

4. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 3, characterized in that: the receiving liquid is also added with a complexing agent, the complexing agent is at least one of aminopolycarboxylic acid, amino acid and phosphate, and the complexing agent is composed of the aminopolycarboxylic acid, the amino acid and the phosphate according to the mass ratio of (2-5) to (1-3) to (1-2).

5. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 1, characterized in that: the step 4) further comprises a bipolar membrane electrodialysis membrane group, the bipolar membrane electrodialysis membrane group comprises two polar liquid chambers, a plurality of membrane pairs B are arranged between the two polar liquid chambers, each membrane pair B is composed of a cation exchange membrane, an anion exchange membrane and a bipolar membrane in sequence, partition plates are arranged between the anion exchange membrane, the cation exchange membrane and the bipolar membrane, adjacent membrane pairs B are also separated by the partition plates, a plurality of material liquid chambers, acid liquid chambers and alkali liquid chambers are formed between the adjacent anion exchange membrane, the bipolar membrane and the cation exchange membrane, material liquid chambers are arranged between the adjacent anion exchange membrane and the adjacent cation exchange membrane, alkali liquid chambers are arranged between the adjacent anion exchange membrane and the bipolar membrane, acid liquid chambers are arranged between the adjacent cation exchange membrane and the bipolar membrane, tea soup concentrated solution C circulates in the material liquid chambers, and polar liquid circulates in the polar liquid chambers.

6. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 5, is characterized in that: an intermediate membrane is further arranged between the adjacent anion exchange membrane and the bipolar membrane in the membrane pair B, partition plates are arranged between the intermediate membrane and the anion exchange membrane as well as between the intermediate membrane and the bipolar membrane, an intermediate chamber is arranged between the adjacent intermediate membrane and the bipolar membrane, and a sodium chloride solution is circulated in the intermediate chamber.

7. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 5, is characterized in that: the alkali liquor indoor circulation sodium chloride solution is characterized in that a complexing agent is added in the sodium chloride solution, the complexing agent is at least one of dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyethyleneimine xanthate, sodium tripolyphosphate and gamma-sodium polyglutamate, and the complexing agent is composed of dithiocarbamate, polyacrylamide, sodium hypophosphite, sodium polyethyleneimine xanthate, sodium tripolyphosphate and gamma-sodium polyglutamate according to the mass ratio of (1-2): (0.5-1.5): (0.5-1.5): (0.1-0.5): (0.5-1): 0.2-0.5).

8. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 7, is characterized in that: the gamma-polyglutamic acid sodium is subjected to crosslinking modification treatment.

9. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 1, characterized in that: the microfiltration membrane in the step 2) is one of polyolefins, polysulfones, cellulose esters, fluorine-containing materials and polycarbonates.

10. The instant tea preparation process based on microfiltration-reverse osmosis technology according to claim 1, characterized in that: the reverse osmosis membrane in the step 3) is one of cellulose acetate, polyamide and composite membrane.