Development of sodium diacetate

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Development of sodium diacetate: Sodium diacetate, with the chemical name monosodium diacetate, is abbreviated as SDA. It is a white crystalline substance with an acetic acid odor; it is highly soluble in water (100 g/100 mL of water), and acetic acid is released during dissolution. The pH of its 10% aqueous solution is 4.5–5.0, its melting point is 96°C, and it decomposes when heated above 150°C; it is also flammable. Sodium diacetate is a new type of broad-spectrum preservative and antifungal agent. Compared with other preservatives, it has the following advantages: 1) Nutritional value: Increasing the nutritional value of feed is a unique feature of sodium diacetate. Feeding animals with feed supplemented with sodium diacetate can reduce the feed-to-meat ratio, increase the lean meat percentage in pigs and the milk fat percentage in dairy cows, thereby improving the feed efficiency ； It is used for preserving forage through silaging, and can improve the utilization rate of protein in forage. 2) Applicability: The acidic taste of sodium diacetate can mask the unpleasant odors of synthetic drugs and various trace elements added to feed. Many livestock and poultry prefer to eat compound feed containing sodium diacetate, which increases their feed intake and daily weight gain, **thereby improving the cost-efficiency. 3) Economic efficiency: Compared with benzoic acid, propionic acid, sorbic acid and their corresponding salts, sodium diacetate requires less usage, has lower costs, and offers significant economic benefits. 4) Safety: Sodium diacetate has low toxicity and causes no side effects in humans or animals; international organizations and some developed countries consider it to be a completely safe food ingredient. Sodium diacetate is a new type of additive that is efficient, capable of preventing mold and corrosion, preserving freshness, enhancing nutrition, and offering a wide range of applications. Its main uses include: 1) as a mildew inhibitor for grains. Through preservation tests on rice, wheat, peanuts, beans, etc., sodium diacetate has been shown to effectively inhibit the growth of molds, thereby serving to prevent spoilage and maintain freshness. For example, by adding 0.1%-0.8% sodium diacetate to wet grains with a moisture content of 21.5%, their shelf life can be extended from 90 days to over 200 days, without the need for drying. This saves time and effort, and reduces losses due to mold and spoilage during storage and distribution. 2) Feed preservatives: When sodium diacetate is added to feed, it can reduce the water activity in bacteria, causing the bacterial proteins to denature and thereby leading to the dehydration and death of the bacteria, thus serving as a preservative. 3) Preservatives for various foods, fruits, meats, fish, shrimp, etc., can not only extend their shelf life but also improve the flavor of these foods. 4) Veterinary drugs. In addition, sodium diacetate is also used as a chelating agent in the pharmaceutical industry: and as a homogenizing agent in the chemical industry ； Buffer ； Mordants in the dye industry ； Electroplating additives for the machinery industry ； And it can be used to prepare acidulants and synthesize coumarins, etc. 1. Experimental Section 1.1 Reagents Soda ash: food-grade, Na2CO3 ≥ 98.5% ； Glacial acetic acid: food grade, HAC≥99.5% ； Additive: homemade. 1.2 Reaction principle: Glacial acetic acid reacts with soda ash at a certain temperature to produce sodium diacetate, which is then obtained as a product after cooling, crystallization, and drying. The reaction equation is as follows: 4HAC + Na2CO3 → 2NaAC·HAC + H2O + CO2. 1.3 Experimental procedure: For the reaction, a four-necked round-bottom flask is equipped with a stirrer, a thermometer, and a reflux condenser. Glacial acetic acid is added to the four-necked flask, and the stirrer is turned on; the measured amount of soda ash is then added in batches while stirring. The reaction proceeds slowly and the temperature rises. After all the soda ash has been added, the additives are introduced, and the heater is activated to maintain the temperature at 110–120°C. The reaction comes to an end once the contents in the four-necked flask have become a uniform transparent liquid. Cooling: Pour the solution obtained from the reaction into a beaker while it is still hot to allow it to cool; crystals form slowly and eventually turn into solid crystals, which are then crushed using a glass rod. Drying: The powdered crystals are placed in a constant-temperature drying oven to be dried and dehydrated, resulting in white crystals. Analysis shows that the mass fraction of acetic acid is 38%-40%, the mass fraction of sodium acetate is 56%-58%, and the mass fraction of moisture is 2%-5%, which meets the product standards. 2. Test Results and Discussion 2.1 Effect of Material Ratio on the Reaction By keeping the reaction time and temperature constant and varying the molar ratio of glacial acetic acid to sodium carbonate, a series of products were obtained; the analysis results are shown in Table 1. As can be seen from Table 1, the range that ensures the acetic acid content in the product is within acceptable limits is (3.8–4.2):1, while the range for sodium acetate content to be within acceptable limits is (3.8–4.3):1. Therefore, the common range for both parameters to be within acceptable limits is (3.8–4.2):1, meaning that the optimal ratio of glacial acetic acid to soda ash is (3.8–4.2):1. Table 1 Effect of material ratios on the reaction
n(HAC)/n(Na2CO3) w(HAC)/% w(NaAC)/% w(H2O)/%
3.8:1 38.67 58.24 3.09
4.0:1 39.39 57.93 2.68
4.2:1 39.51 57.05 3.44
4.3:1 41.60 56.20 2.20
4.4:1 41.90 55.74 2.36

2.2 Effect of temperature on the reaction
According to literature, the boiling point of acetic acid is 117°C, while the melting point of sodium diacetate is 96°C and its decomposition temperature is 150°C. In experiments, it was found that when the reaction temperature is below 100°C, the sodium diacetate formed crystallizes rapidly, causing the reaction mixture to become turbid and eventually turn into a paste-like substance; in such conditions, the stirrer is unable to mix all the materials properly, preventing the reaction from proceeding completely. As a result, some sodium carbonate remains in the product. When the reaction temperature exceeds 130°C, acetic acid boils, and the reaction rate increases significantly. A large amount of acetic acid vaporizes and enters the condenser, increasing the reflux volume and thus the load on the condenser. Therefore, after considering all these factors, the reaction temperature is set between 110–120°C. 2.3 Effect of time on the reaction: Samples were prepared with a material ratio of n(HAC):n(NaCO3) = 4.0:1, at a reaction temperature of 110–120°C, and for reaction times of 50, 100, and 150 minutes. The samples were then dried at 80°C for the same duration; the results are shown in Table 2. Table 2 Effect of time on the reaction Sequence Reaction time/min w(HAC)/% w(NaAC)/% 1 50 39.76 56.80 2 100 39.45 58.34 3 150 36.62 60.57 Note: The time required to ensure that all product parameters are within acceptable limits is 80–100 minutes. (The moisture content is within acceptable limits, so it is not listed.) 2.4 The influence of time and temperature on drying: During the drying process, the moisture that is bound to sodium diacetate through hydrogen bonds is removed during cooling and crystallization; however, the HAC bound to NaAC does not escape. This requires that the drying temperature not be too high and the drying time not be too long. Two temperature levels, 70°C and 80°C, were selected for drying experiments, and the results are shown in Tables 3 and 4. The moisture content decreases slowly over time; 3–7 hours at 70°C and 2–4 hours at 80°C meet the requirements. Table 3 Effect of time on drying at 70°C. Drying time/h, Moisture/%: 3, 4.40; 4, 3.57; 5, 3.53; 7, 2.88; 15, 1.12. Table 4 Effect of time on drying at 80°C. Drying time/h, Moisture/%: 2, 3.92; 3, 3.41; 4, 2.62; 7, 1.88; 2.5. Pilot plant results for a plant with an annual production capacity of 500 t. Based on the results obtained from pilot tests, a pilot plant for the production of sodium diacetate with an annual output of 500 t was designed; the process flow is shown in Figure 1 (omitted). The established process control conditions are: a reaction material ratio of 4.4:1, a reaction temperature of 125±5°C, and a reaction time of 1–2 hours. Drying conditions: inlet air temperature of 100°C, outlet air temperature of 80°C. Production is organized in accordance with the selected conditions; the equipment operates properly, and the products manufactured meet quality requirements. The pilot test results are shown in Tables 5 and 6. Table 5: Pilot-scale reaction data
Serial number | n(HAC)/n(Na2CO3) | Reaction temperature/°C | Reaction time/h | Analysis results (before drying) | w(HAC)/% | w(NaAC)/%
1 | 3.85:1 | 140 | 1 | 20.62 | 57.35
2 | 4.40:1 | 125 | 2 | 36.29 | 52.68

Table 6: Pilot-scale drying test data
Serial number | Inlet air temperature/°C | Outlet air temperature/°C | Analysis results | w(HAC)/% | w(NaAC)/% | w(H2O)/%
1 | 20 | 20 | 36.00 | 57.12 | 6.75
2 | 60 | 40 | 36.68 | 56.66 | 4.38
3 | 70 | 50 | 37.48 | 56.36 | 4.11
4 | 80 | 60 | 39.15 | 57.54 | 2.40
5 | 100 | 80 | 39.13 | 57.65 | 1.87

3. Technical and economic evaluation
3.1 Technical evaluation
A new process was developed in this project for the production of a preservative and antifungal agent for food and feed—sodium diacetate. Products were produced on both pilot and scale-up levels, and the technical performance was evaluated from the following two aspects. 3.1.1 Raw materials: Currently, sodium diacetate is produced in China mainly through the liquid-phase method using acetic acid and sodium acetate, as well as the liquid-phase synthesis method using acetic acid and soda ash; organic or inorganic solvents need to be added during these reactions. The synthesis method we developed for acetic acid and soda ash requires only a small amount of additive, with no other solvents needed. In terms of raw material costs, sodium acetate is expensive, costing 6,500–7,000 yuan per ton, while soda ash is cheaper at 1,400–1,600 yuan per ton. There is an oversupply in China, so it is available at low prices with high yields, resulting in low overall costs. 3.1.2 Reaction process control and consumption: In the liquid-phase method using acetic acid and sodium acetate, 7 times as much ethanol as sodium acetate is required; the reaction time is as long as 5 hours, resulting in high energy consumption. The recovery of ethanol further increases costs. The final product has a low melting point and tends to decompose during drying, which affects product quality. Additionally, the process is lengthy and requires significant investment. The liquid-phase synthesis method using acetic acid and soda ash is simple in process, but the reaction time is as long as 5 hours; the mother liquor must be separated and concentrated for recovery, resulting in high energy consumption. The acidic nature of the mother liquor poses a strong corrosive threat to the equipment, requiring anti-corrosion measures that increase the cost of the equipment. The carbon dioxide gas produced during the reaction contains large amounts of acetic acid, which reduces the yield by about 80% and also leads to unstable product quality. The synthesis method using acetic acid and caustic soda requires specialized equipment, resulting in high investment costs; although the reaction time is only 2 hours, the process flow is short and the yield can exceed 90%. The synthesis method using acetic acid and liquid alkali involves a longer process, requires more equipment, is complex to operate; the mother liquor is acidic and highly corrosive to the equipment, necessitating anti-corrosion measures, and it results in high investment costs. The one-step synthesis method we have developed for the production of sodium diacetate features advantages such as readily available raw materials, a short process, simple equipment, easy operation, and low investment. In its production, the reaction temperature is low, the reaction time is short, less steam is consumed, and synthesis occurs in one step without the need for separation. For devices of the same scale, this method requires the least investment and operational costs, resulting in the lowest product cost. 3.2 Economic Evaluation 3.2.1 Basic Data for Calculation 3.2.1.1 Technical Data Based on the pilot plant results, the yield of this process (expressed in terms of glacial acetic acid) is 95.3%. Material ratio for the reaction: HAC:Na2CO3 = 4.4:1 (mole ratio). Glacial acetic acid contains 99.5% HAC, with a main mass fraction of soda ash at 99%. 3.2.1.2 Major Raw Materials and Prices of Water, Electricity, and Steam Table 7 of major raw materials and prices of water, electricity, and steam. Table 7 Prices of major raw materials and utilities
Items: Glacial acetic acid/(yuan·t-1), Soda ash/(yuan·t-1), Water/(yuan·t-1), Electricity/(yuan·t-1), Steam/(yuan·t-1)
Prices: 6,500, 1,500, 1.5, 0.5, 100

3.2.1.3 Average wage and benefits for workers: 15,000 yuan per person per year; total workforce: 15 people. 3.2.1.4 Cost coefficients – Depreciation expense: 14.14% of the original value of fixed assets ； Management fee: 5% of sales revenue ； Sales expense: 1% of sales revenue. 3.2.2 Investment Situation 3.2.2.1 Pilot-scale investment amount: The investment cost for a 500t/a sodium diacetate production facility is shown in Table 8. Table 8 Investment Amounts: Project, Amount in 10,000 yuan – Equipment investment: 16; Civil engineering: 15; Electrical and instrumentation equipment: 5; Installation and piping work: 10; Total: 46. 3.2.2.2 Cost calculation of sodium diacetate: The cost calculation for sodium diacetate is shown in Table 9. Table 9 Cost Calculation for Sodium Diacetate
Name | Raw Material Cost | Energy Cost | Glacial Acetic Acid/(t•t-1) | Soda Ash/(t•t-1) | Water (t•t-1) | Electricity/(kW•h/t-1) | Steam/(t•t-1)
Consumption Standard | 0.9 | 0.38 | 10 | 150 | 0.8 |
Amount/(Yuan•t-1) | 5850.0 | 570.00 | 15 | 75 | 80.0

Continued from Table 9
Name | Packaging Materials | Wages and Benefits | Maintenance Costs | Administrative Costs | Sales Costs | Total Factory Cost
Plastic Bags (pieces•t-1) | Consumption Standard | 40 | Amount/(Yuan•t-1) | 60 | 450 | 300 | 500 | 100 | 800

3.2.2.3 Investment Analysis
The market price of sodium diacetate fluctuates between 10,000 and 13,500 yuan per ton; here it is assumed to be 10,000 yuan per ton. The profit and loss situation is shown in Table 10. Table 10: Profit and Loss Overview Item Sales Revenue Factory Costs Sales Profit Amount in 10,000 yuan 500 400 100 It can be seen that the payback period for the investment is less than 1 year. 4 Conclusions In summary, through pilot and scale-up studies, this project has not only demonstrated its economic viability but also established the process for producing sodium diacetate by reacting glacial acetic acid with soda ash. The conclusions are as follows: 4.1 Optimal process conditions for the reaction The optimal pilot-scale conditions are as follows: the material ratio is n(HAC):n(Na2CO3) = (3.8–4.2):1, the reaction temperature is 110–120°C, and the reaction time is 80–100 minutes. Optimal pilot-scale process conditions: material ratio n(HAC):n(Na2CO3) = 4.4:1, reaction temperature 125±5°C, time 2 hours, and self-made additive at 1%-5%. 4.2 Optimal drying process: Optimal pilot-scale process conditions: temperature of 70–80°C, time of 2–7 hours. Optimal pilot-scale process conditions: inlet air temperature of 100°C, outlet air temperature of 80°C. This process method is relatively advanced, with a rational design, a short process flow, lower equipment investment, and stable pilot production. This post was last edited by zxh6267 on 2009-2-6 07:10.]