Preparation method of sodium citrate pentahydrate

Abstract

The invention provides a preparation method of sodium citrate pentahydrate, and relates to the technical field of citrate production. According to the method, sodium carbonate and anhydrous citric acid are used as raw materials, a sodium citrate solution is obtained through a microreactor, and then a finished product of sodium citrate pentahydrate is obtained through filtration, evaporation, crystallization and drying. According to the preparation method, sodium carbonate and citric acid reactants can be rapidly and uniformly mixed in the micro-channel, so that the mass transfer efficiency is greatly improved, and the reaction is more sufficient and rapid; according to the preparation method, the reaction temperature can be accurately controlled, side reaction caused by the temperature problem is prevented, and the product purity and yield are guaranteed; risks such as harmful gas leakage can be reduced, and production safety is guaranteed; the continuous feeding of reactants and the continuous discharging of products can be realized, the production efficiency is improved, the labor cost is reduced, automatic control is convenient to realize, and the stability and the consistency of the product quality can be ensured during the large-scale production of sodium citrate.

Description

Technical Field

[0001] The invention relates to the technical field of citrate production, in particular to a method for preparing sodium citrate pentahydrate. Background Art

[0002] Sodium citrate pentahydrate is used as an acidity regulator, flavoring agent, and stabilizer in the food and beverage industry; as an anticoagulant, expectorant, and diuretic in the pharmaceutical industry; and as an additive for non-toxic detergents in the detergent industry, it can replace sodium tripolyphosphate. It is also used in brewing, injections, photographic drugs, and electroplating. With the development of these industries, the market demand for sodium citrate pentahydrate continues to increase, and higher requirements are also placed on its quality and performance.

[0003] When sodium citrate pentahydrate is produced in a traditional batch reactor, the mass and heat transfer efficiency is low, the material mixing is uneven, and the reaction time is long, resulting in unstable product quality and large differences between batches. At the same time, it is difficult to accurately control the reaction conditions such as temperature, pressure, material ratio, etc. in the traditional production process, which is prone to side reactions and reduces the yield and purity of the product. In addition, the production process has high energy consumption and large wastewater discharge, which does not meet environmental protection requirements.

[0004] In recent years, microreactor technology has developed rapidly. Microreactors have a large specific surface area, can achieve efficient heat and mass transfer, can accurately control reaction parameters such as temperature, pressure, flow, residence time, etc., and also have the advantages of small footprint, high safety performance, and continuous production. These advantages make microreactors more and more widely used in the fields of chemical industry, medicine, materials, etc., and provide new technical means for the production of sodium citrate pentahydrate.

[0005] With the enhancement of environmental awareness and the popularization of green chemistry concepts, chemical production needs to develop in the direction of high efficiency, energy saving and environmental protection. The production of sodium citrate pentahydrate using microreactors can reduce energy consumption, reduce the emission of pollutants such as wastewater and waste gas, and improve the utilization rate of raw materials. It meets the requirements of green chemistry and sustainable development and helps promote the green transformation of the sodium citrate pentahydrate production industry. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention provides a method for preparing sodium citrate pentahydrate, which uses a microreactor as a reaction device for producing sodium citrate pentahydrate. It can achieve efficient heat and mass transfer, accurately control reaction parameters such as temperature, pressure, flow rate, residence time, etc., and has the advantages of small footprint, high safety performance, and continuous production. It provides a new technical means for the production of sodium citrate pentahydrate.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for preparing sodium citrate pentahydrate, the specific steps are as follows: (1) Raw material preparation: Sodium carbonate and anhydrous citric acid are prepared into aqueous solutions of a certain concentration using pure water, filtered through precision filters and stored in their respective storage tanks; (2) Microreactor reaction: Sodium carbonate solution and citric acid solution are delivered to the microreactor through a metering pump at a precise flow ratio, and are fully mixed and reacted in the microreactor; (3) Product separation and purification: After the reaction mixture flows out of the microreactor, it is first subjected to vacuum distillation and other operations to remove part of the water so that the sodium citrate pentahydrate reaches a supersaturated state, and then cooled and crystallized; the crystals are separated from the mother liquor by centrifugation, and the obtained crystals are then washed with an appropriate amount of organic solvent or deionized water to remove surface impurities; (4) Drying and packaging: The washed sodium citrate pentahydrate crystals are dried at low temperature to remove residual moisture to obtain the finished sodium citrate pentahydrate product, which is then packaged.

[0008] Preferably, the filtration accuracy of the precision filter in step (1) is not less than 10 microns. The purpose is to ensure the purity of the reaction raw materials, because impurities may affect the reaction and product quality, such as causing the product to turn yellow, reduce purity, etc.; secondly, to prevent clogging. The channel of the microreactor is small, and it is necessary to prevent solid impurities or insoluble substances that may be produced during the reaction from clogging the channel.

[0009] Preferably, the certain concentration in step (1) is the saturated solution concentration of sodium carbonate and anhydrous citric acid in pure water at 40° C. (68.6% and 32.9%, respectively), and the concentration and temperature of both should be strictly controlled.

[0010] Preferably, the microreactor described in step (2) is a micro-mesh type microreactor with a channel size of 300 microns. Its appearance is a cylindrical tank structure with an insulation layer or cooling jacket on the outside. There are multiple pipe interfaces on the tank body for the input and output of reactants, the entry and exit of cooling media, and gas discharge, etc.; the interior is composed of a dispersion chamber and a cross-flow channel, and a steel sheet engraved with micropores is placed between the two as a dispersion microstructure, which can be approximately regarded as a T-type microchannel. After entering the dispersion chamber, the reactants are dispersed into tiny droplets through the microporous steel sheet, and then enter the cross-flow channel to mix and react with other reactants. The design of the cross-flow channel can increase the contact area and contact time between the reactants and improve the reaction efficiency.

[0011] Preferably, the molar ratio of the reactants in step (2) is sodium carbonate: citric acid = 3:2. In actual production, it can be slightly adjusted according to the situation, such as a slight excess of sodium carbonate to ensure that the citric acid reacts fully. Before the reaction, the flow rate of each feed should be calculated according to the concentration of the sodium carbonate solution and the citric acid solution.

[0012] Preferably, the reaction temperature in step (2) is generally controlled in the range of 40-60° C. Too high a temperature may cause sodium citrate pentahydrate to lose its crystal water, while too low a temperature may result in a slow reaction rate.

[0013] Preferably, the residence time of the material in step (2) in the microreactor is usually controlled to be 2-5 minutes, which needs to be optimized according to factors such as the size of the microreactor, the flow rate of the feed and the reaction rate.

[0014] Compared with the prior art, the present invention provides a method for preparing sodium citrate pentahydrate, which has the following beneficial effects: 1. The preparation method of sodium citrate pentahydrate enables the solution of sodium carbonate and anhydrous citric acid to achieve efficient mixing and mass transfer, greatly increases the contact area and collision probability between reactants, thereby significantly shortening the reaction time and improving production efficiency; can quickly and accurately control the reaction temperature, avoid the occurrence of local overheating or supercooling, and make the reaction proceed under more ideal temperature conditions; can accurately control the reaction conditions, such as the ratio of reactants, reaction temperature, residence time, etc., reduce the occurrence of side reactions, thereby improving the purity of sodium citrate pentahydrate; the reaction process is stable, highly repeatable, and is not affected by human factors and the external environment, so that high-quality sodium citrate pentahydrate products can be stably produced to ensure the consistency of product quality.

[0015] 2. The preparation method of sodium citrate pentahydrate can achieve efficient mixing and mass transfer of sodium carbonate and anhydrous citric acid solution by using a microreactor for reaction, greatly increase the contact area and collision probability of reactants, significantly shorten the reaction time, and improve production efficiency.

[0016] 3. The preparation method of sodium citrate pentahydrate can accurately control parameters such as reaction temperature, reactant ratio, residence time, etc. By controlling the reaction temperature at 40-60°C, sodium citrate pentahydrate is prevented from losing crystal water and the reaction rate is prevented from being too slow; precise flow control ensures that the reactants react at a suitable molar ratio (sodium carbonate: citric acid = 3:2, which can be fine-tuned according to the situation), reduces the occurrence of side reactions, and improves product purity.

[0017] 4. The preparation method of sodium citrate pentahydrate has a stable reaction process, strong repeatability, is not affected by human factors and the external environment, and can stably produce high-quality sodium citrate pentahydrate products with good quality consistency. The physical and chemical indicators of the products produced in different embodiments all meet the GB 1886.25-2016 standard, and the indicator fluctuation is small.

[0018] 5. The preparation method of sodium citrate pentahydrate meets the requirements of green chemistry and sustainable development. Compared with traditional processes, it can reduce energy consumption, reduce the emission of pollutants such as wastewater and waste gas, and improve the utilization rate of raw materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the process flow of the present invention. DETAILED DESCRIPTION

[0020] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] A method for preparing sodium citrate pentahydrate comprises the following steps: Step (1) raw material preparation: sodium carbonate and anhydrous citric acid are respectively prepared into aqueous solutions of a certain concentration using pure water, filtered through precision filters and stored in respective measuring tanks; Step (2) microreactor reaction: sodium carbonate solution and citric acid solution are delivered to the microreactor by a metering pump at a precise flow ratio, and are fully mixed and reacted in the microreactor; Step (3) separation and purification of the product: after the reaction mixture flows out of the microreactor, it is first subjected to vacuum distillation and other operations to remove part of the water so that the sodium citrate pentahydrate reaches a supersaturated state, and then cooled and crystallized; the crystals are separated from the mother liquor by centrifugation, and the obtained crystals are then washed with an appropriate amount of organic solvent or deionized water to remove surface impurities; Step (4) Drying and Packaging: The washed sodium citrate pentahydrate crystals are dried at low temperature to remove residual water to obtain the finished sodium citrate pentahydrate product, which is then packaged.

[0022] The precision filter in step (1) has a filtration accuracy of not less than 10 microns to ensure the purity of the reaction raw materials and prevent solid impurities or insoluble substances that may be produced during the reaction from clogging the channel.

[0023] The certain concentrations in step (1) are the saturated solution concentrations of sodium carbonate and anhydrous citric acid at 40°C.

[0024] The microreactor in step (2) is a micro-mesh type microreactor with a channel size of 300 microns; Its appearance is a cylindrical tank structure with an insulation layer or cooling jacket on the outside. There are multiple pipe interfaces on the tank body for the input and output of reactants, the inlet and outlet of cooling media, and gas discharge. The interior consists of a dispersion chamber and a cross-flow channel. A steel sheet with micropores is placed between the two as a dispersion microstructure. This structure can be roughly regarded as a T-type microchannel. After entering the dispersion chamber, the reactants are dispersed into tiny droplets through the microporous steel sheet, and then enter the cross-flow channel to mix and react with other reactants; The design of the cross-flow channel can increase the contact area and contact time between the reactants and improve the reaction efficiency.

[0025] The ratio of reactants in step (2) is sodium carbonate: citric acid = 3:2. In actual production, it can be slightly adjusted according to the situation, such as slightly excessive sodium carbonate to ensure sufficient reaction of citric acid.

[0026] The reaction temperature in step (2) is generally controlled at about 40-60°C. Too high a temperature may cause sodium citrate pentahydrate to lose its crystal water, while too low a temperature may result in a slow reaction rate.

[0027] The residence time of the material in step (2) in the microreactor is usually controlled at 2-5 minutes, which needs to be optimized according to factors such as the size of the microreactor, flow rate and reaction rate.

[0028] Example 1

[0029] (1) Raw material preparation: Sodium carbonate and anhydrous citric acid were prepared with pure water into saturated solutions at a temperature of 40°C and with mass concentrations of 68.6% and 32.9%, respectively, and stored in dedicated measuring tanks for standby use.

[0030] (2) Microreactor reaction: Based on the mass concentrations of sodium carbonate solution and citric acid solution (68.6% and 32.9%, respectively) and the molar ratio of the reactants (sodium carbonate: citric acid = 3:2), the raw material feed amount was reversed and the flow rates of each feed were calculated. Then, the sodium carbonate solution and citric acid solution were delivered to the microreactor through a metering pump at a precise flow ratio, where they were fully mixed and reacted.

[0031] The reaction temperature is controlled within the range of 40-45°C. Too high a temperature may cause sodium citrate pentahydrate to lose its crystal water, while too low a temperature may result in a slow reaction rate. The residence time of the material in the microreactor is controlled within 5 minutes.

[0032] (3) Product separation and purification: After the reaction mixture flows out of the microreactor, it is first subjected to vacuum distillation and other operations to remove part of the water so that the sodium citrate pentahydrate reaches a supersaturated state, and then cooled and crystallized. The crystals are separated from the mother liquor by centrifugation, and the obtained crystals are then washed with an appropriate amount of deionized water to remove surface impurities.

[0033] (4) Drying and packaging: The washed sodium citrate pentahydrate crystals are dried at low temperature to remove residual moisture to obtain the finished sodium citrate pentahydrate product, which is then packaged.

[0034] The physical and chemical indicators of sampling and testing are: Sodium citrate content (based on dry matter): 99.5%, light transmittance: 96.0%. Water: mass fraction: 10.8%, sulfate: 0.008 / %, iron salt: 4.2mg / kg, oxalate: 0.006%, calcium salt: 0.015%.

[0035] Carbonizable matter: 0.06, chloride: 0.003%, lead: 1.0 mg / kg, arsenic: 0.5 mg / kg.

[0036] It complies with GB 1886.25-2016 "National Food Safety Standard Food Additive Sodium Citrate" standard.

[0037] Example 2

[0038] (1) Raw material preparation: Sodium carbonate and anhydrous citric acid were prepared with pure water into saturated solutions at a temperature of 40°C and with mass concentrations of 68.6% and 32.9%, respectively, and stored in dedicated measuring tanks for standby use.

[0039] (2) Microreactor reaction: Based on the mass concentrations of sodium carbonate solution and citric acid solution (68.6% and 32.9%, respectively) and the molar ratio of the reactants (sodium carbonate: citric acid = 3:2), the raw material feed amount was reversed and the flow rates of each feed were calculated. Then, the sodium carbonate solution and citric acid solution were delivered to the microreactor through a metering pump at a precise flow ratio, where they were fully mixed and reacted.

[0040] The reaction temperature is controlled within the range of 45-50°C. Too high a temperature may cause sodium citrate pentahydrate to lose its crystal water, while too low a temperature may result in a slow reaction rate. The residence time of the material in the microreactor is controlled within 3 minutes.

[0041] (3) Product separation and purification: After the reaction mixture flows out of the microreactor, it is first subjected to vacuum distillation and other operations to remove part of the water so that the sodium citrate pentahydrate reaches a supersaturated state, and then cooled and crystallized. The crystals are separated from the mother liquor by centrifugation, and the obtained crystals are then washed with an appropriate amount of deionized water to remove surface impurities.

[0042] (4) Drying and packaging: The washed sodium citrate pentahydrate crystals are dried at low temperature to remove residual moisture to obtain the finished sodium citrate pentahydrate product, which is then packaged.

[0043] The physical and chemical indicators of sampling and testing are: Sodium citrate content (based on dry matter): 99.6%, light transmittance: 95.0%. Moisture: 10.8%, sulfate: 0.008%, iron salt: 4.1mg / kg, oxalate: 0.005%, calcium salt: 0.013%.

[0044] Carbonizable matter: 0.07, chloride: 0.003%, lead: 1.0 mg / kg, arsenic: 0.5 mg / kg.

[0045] It complies with GB 1886.25-2016 "National Food Safety Standard Food Additive Sodium Citrate" standard.

[0046] Example 3

[0047] (1) Raw material preparation: Sodium carbonate and anhydrous citric acid were prepared with pure water into saturated solutions at a temperature of 40°C and with mass concentrations of 68.6% and 32.9%, respectively, and stored in dedicated measuring tanks for standby use.

[0048] (2) Microreactor reaction: Based on the mass concentrations of sodium carbonate solution and citric acid solution (68.6% and 32.9%, respectively) and the molar ratio of the reactants (sodium carbonate: citric acid = 3:2), the raw material feed amount was reversed and the flow rates of each feed were calculated. Then, the sodium carbonate solution and citric acid solution were delivered to the microreactor through a metering pump at a precise flow ratio, where they were fully mixed and reacted.

[0049] The reaction temperature is controlled within the range of 50-60°C. Too high a temperature may cause sodium citrate pentahydrate to lose its crystal water, while too low a temperature may result in a slow reaction rate. The residence time of the material in the microreactor is controlled within 2 minutes.

[0050] (3) Product separation and purification: After the reaction mixture flows out of the microreactor, it is first subjected to vacuum distillation and other operations to remove part of the water so that the sodium citrate pentahydrate reaches a supersaturated state, and then cooled and crystallized. The crystals are separated from the mother liquor by centrifugation, and the obtained crystals are then washed with an appropriate amount of deionized water to remove surface impurities.

[0051] (4) Drying and packaging: The washed sodium citrate pentahydrate crystals are dried at low temperature to remove residual moisture to obtain the finished sodium citrate pentahydrate product, which is then packaged.

[0052] The physical and chemical indicators of sampling and testing are: Sodium citrate content (based on dry matter): 99.4%, light transmittance: 94.0%. Moisture: 10.3%, sulfate: 0.007%, iron salt: 3.8 mg / kg, oxalate: 0.006%, calcium salt: 0.012%.

[0053] Carbonizable matter: 0.09, chloride: 0.002%, lead: 0.09mg / kg, arsenic: content 0.3mg / kg.

[0054] It complies with GB 1886.25-2016 "National Food Safety Standard Food Additive Sodium Citrate" standard.

[0055] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing sodium citrate pentahydrate, characterized in that: The following steps are involved: Step (1) raw material preparation: sodium carbonate and anhydrous citric acid are respectively prepared into aqueous solutions of a certain concentration using pure water, filtered through precision filters and stored in respective measuring tanks; Step (2) microreactor reaction: sodium carbonate solution and citric acid solution are delivered to the microreactor by a metering pump at a precise flow ratio, and are fully mixed and reacted in the microreactor; Step (3) separation and purification of the product: after the reaction mixture flows out of the microreactor, it is first subjected to vacuum distillation and other operations to remove part of the water so that the sodium citrate pentahydrate reaches a supersaturated state, and then cooled and crystallized; the crystals are separated from the mother liquor by centrifugation, and the obtained crystals are then washed with an appropriate amount of organic solvent or deionized water to remove surface impurities; Step (4) Drying and Packaging: The washed sodium citrate pentahydrate crystals are dried at low temperature to remove residual water to obtain the finished sodium citrate pentahydrate product, which is then packaged.

2. A method for preparing sodium citrate pentahydrate according to claim 1, characterized in that: The precision filter in step (1) has a filtration accuracy of not less than 10 microns to ensure the purity of the reaction raw materials and prevent solid impurities or insoluble substances that may be produced during the reaction from clogging the channel.

3. A method for preparing sodium citrate pentahydrate according to claim 1, characterized in that: The certain concentrations in step (1) are the saturated solution concentrations of sodium carbonate and anhydrous citric acid at 40°C.

4. A method for preparing sodium citrate pentahydrate according to claim 1, characterized in that: The microreactor in step (2) is a micro-mesh type microreactor with a channel size of 300 microns; Its appearance is a cylindrical tank structure with an insulation layer or cooling jacket on the outside. There are multiple pipe interfaces on the tank body for the input and output of reactants, the inlet and outlet of cooling media, and gas discharge. The interior consists of a dispersion chamber and a cross-flow channel. A steel sheet with micropores is placed between the two as a dispersion microstructure. This structure can be roughly regarded as a T-type microchannel. After entering the dispersion chamber, the reactants are dispersed into tiny droplets through the microporous steel sheet, and then enter the cross-flow channel to mix and react with other reactants; The design of the cross-flow channel can increase the contact area and contact time between the reactants and improve the reaction efficiency.

5. A method for preparing sodium citrate pentahydrate according to claim 1, characterized in that: The ratio of reactants in step (2) is sodium carbonate: citric acid = 3:

2. In actual production, it can be slightly adjusted according to the situation, such as slightly excessive sodium carbonate to ensure sufficient reaction of citric acid.

6. A method for preparing sodium citrate pentahydrate according to claim 1, characterized in that: The reaction temperature in step (2) is generally controlled at about 40-60°C. Too high a temperature may cause sodium citrate pentahydrate to lose its crystal water, while too low a temperature may result in a slow reaction rate.

7. A method for preparing sodium citrate pentahydrate according to claim 1, characterized in that: The residence time of the material in step (2) in the microreactor is usually controlled at 2-5 minutes, which needs to be optimized according to factors such as the size of the microreactor, flow rate and reaction rate.

Images