Application of propionic acid and propionate in feed
Propionic acid and propionate are important feed preservatives. Propionic acid is a colorless liquid and is volatile. Propionate mainly refers to calcium propionate, sodium propionate, zinc propionate, potassium propionate, ammonium propionate, etc., mostly white granules or powder, odorless or slightly odorous, soluble in water. Compared with other preservatives, propionic acid and its salts have many incomparable advantages, so it has become one of the most widely used preservatives in feed.
1 The preservative mechanism of propionic acid and propionate
The active ingredients of propionic acid and propionate to play the role of antiseptic and mildew are propionic acid molecules. It is generally believed that propionic acid exerts anti-corrosion and anti-mildew effects through the following ways: 1) The non-dissociated propionic acid active molecules form a high osmotic pressure outside the cells such as mold or bacteria, which dehydrates the mold cells and loses the ability to reproduce; 2) Propionic acid Active molecules can penetrate the cell walls of molds, etc., and inhibit the enzyme activity in the cells, thereby preventing the reproduction of molds.
2 Application and safety of propionic acid and propionate in feed
2.1 Application of propionic acid in feed
As a volatile liquid, the propionic acid vapor produced by the continuous volatilization of propionic acid during the storage process of the feed is in full contact with the surface of the feed, and has a uniform, extensive and efficient bacteriostatic effect. Studies have shown that propionic acid has a good inhibitory effect on Aspergillus flavus, some aerobic Bacillus, Salmonella and yeast (Kwon and Panda, 1999). At present, the main components of commercially available Lubaosi, Kemeiba, Wanlubao, etc. are propionic acid. However, there are also some problems in directly using propionic acid as a preservative: 1) The thermal stability is not good. According to reports, the volatilization of propionic acid can reach 1% during the granulation process at 80 °C; 2) The propionic acid loses rapidly during the storage process of the feed, and the duration of the drug effect is short, which is not conducive to the long-term preservation of the feed; 3) The propionic acid is easily destroyed by Calcium salts or proteins in the feed are neutralized, thereby reducing or inactivating. In view of this, people have developed a variety of propionate formulations.
2.2 Application of propionate in feed
Propionate has the advantages of high temperature resistance, non-volatile, not affected by other ingredients in the feed, low corrosiveness, less irritation, and suitable for long-term storage of feed. The main components of Kemeiling, Difendi and Chumoujing produced in my country are propionate. Among them, ammonium propionate, sodium propionate and calcium propionate are mainly used as silage preservatives and are widely used in cattle, sheep and poultry feed. Propionate can only be effective when converted into propionic acid, and the conversion process is affected by conditions such as moisture and pH. The weak basicity formed after propionate dissociation may also hinder its further dissociation. In addition, since propionate does not have a fumigation effect, the uniformity of feed mixing is required to be high. Excessive propionate dosage may also affect the palatability of the feed.
2.3 Safety of propionic acid and propionate Propionic acid is safe for humans and animals. The World Health Organization (WHO) and the United Nations Food and Agriculture Organization (FAO) have approved the use of calcium propionate as a food preservative internationally. At present, propionic acid (salt) has been widely used in the anti-corrosion and mildew prevention of bread, cereals, etc. Theoretically, after propionic acid enters the human or animal body, it can be converted into propionyl-CoA, D-methylmalonyl-CoA, L-methylmalonyl-CoA and succinyl-CoA in turn. Succinyl-CoA can not only enter the tricarboxylic acid cycle for complete oxidative decomposition, but also enter the gluconeogenesis pathway to synthesize glucose or glycogen. In fact, bacteria in the rumen of some ruminants (such as cattle) can ferment sugars (such as cellulose) into propionic acid, but because these propionic acids can enter lipid metabolism and sugar metabolism through the above-mentioned pathways, they are not suitable for ruminants. damage to health.
3 The production process of propionic acid The production methods of propionic acid include chemical synthesis and microbial fermentation. At present, propionic acid is mainly produced by chemical synthesis in industry. Propionaldehyde oxidation method, Rapa method and light hydrocarbon oxidation method are the most commonly used methods in propionic acid production industry. In addition, the acrylonitrile method, the ethanol carbonyl method, the n-propanol oxidation method, the propane (butane, paraffin) liquid phase oxidation method, etc. can also be used for the production of propionic acid, but due to the large investment in equipment and other reasons, they have not yet been adopted in practice. .
3.1 Propionaldehyde oxidation method The early production process includes two steps: propionaldehyde production and propionaldehyde oxidation. Propionaldehyde is usually produced by the hydroformylation of ethylene. Including cobalt catalyst high pressure carbonylation process and rhodium or titanium catalyst low pressure carbonylation process. In the production process of the high-pressure carbonylation method, the yield of propionaldehyde is reduced due to the partial hydrogenation of propionaldehyde to form propanol; while in the low-pressure carbonylation method, the aldehydes can be directly distilled from the reaction mixture. The propionic acid yield of the method is higher than that of the former. Then, under the mild conditions of 40～50℃ and 0.3～0.7MPa, propionaldehyde undergoes radical oxidation reaction with manganese as catalyst to generate propionic acid. This process has the advantages of high selectivity, high conversion, low corrosion and no need for high pressure equipment. At present, propionic acid is prepared by hydroformylation of ethylene under the catalysis of cobalt carbonyl or rhodium carbonyl using ethylene, carbon monoxide and hydrogen as raw materials in industrial production. This reaction is carried out under the conditions of 110 to 180° C. and 20 to 35 MPa. Due to the high selectivity of carbonyl rhodium catalyst to linear isomers and mild reaction conditions, it has become the main catalyst for the production of carbonyl aldehydes and carbonyl alcohols. Nevertheless, the cobalt carbonyl catalyst has not been withdrawn from the practice of propionic acid production, mainly due to its very low cost. In addition, chromium carbonyl, nickel, etc. can also be used as catalysts.
The propionaldehyde oxidation process is mature and is currently the largest production method of propionic acid. The main disadvantage of this method is that the technological process is complex, the equipment is numerous, and the requirements for equipment and pipeline materials are high.
3.2 Rapa method
The Repper method, also known as the ethylene oxo synthesis method, is a patent of the German BASF company. It takes ethylene as raw material and reacts with carbon monoxide and water under the catalysis of nickel carbonyl to generate propionic acid. The reaction is carried out at 250 to 320° C. and 10 to 30 MPa. Carbonyl complexes of cobalt, iron, rhodium, iridium, platinum, palladium, ruthenium, molybdenum-nickel, tungsten-nickel, etc. can also be used as catalysts. The Rapa method has the characteristics of low cost of raw materials, simple process flow, high conversion rate, good selectivity, and simple operation. However, due to the severe corrosion of propionic acid under high temperature and high pressure, it is necessary to use a silver-lined reactor. In view of this, many foreign companies have made many improvements to this law. In 1975, the successful research and development of low-pressure synthesis of butyraldehyde from propylene greatly promoted the development of the technology for the synthesis of propionic acid by direct carbonylation of ethylene. This new process has the potential to be the best method for propionic acid production.
3.3 Light hydrocarbon oxidation method
Until the 1960s, light hydrocarbon oxidation was the dominant method for propionic acid production in the world. At present, some manufacturers still use this method. The light hydrocarbon oxidation method uses light naphtha, liquefied natural gas or alkanes (such as n-butane) with a boiling point below 100 ° C as raw materials, and uses oil-soluble salts such as manganese naphthenate as catalysts. The oxidation reaction is carried out under the following conditions to generate acetic acid, and by-products formic acid, propionic acid and a small amount of other carboxylic acids. Compared with butane, naphtha is a more suitable feedstock, which is inexpensive and can be used for oxidation reactions at lower temperatures and pressures. However, the naphtha oxidation process is too dependent on experience.
3.4 Acetic acid homologation method
Under the catalysis of acetyl acetyl rhodium and methyl iodide, acetic acid can undergo a homologous carbon increase reaction with syngas, mainly generating propionic acid, and by-producing butyric acid and valeric acid.
3.5 Ethanol carbonylation
The ethanol carbonylation method was first adopted by DuPont in the United States. Under the conditions of 180～400℃ and 35.5～70.9MPa, the halides of boron trifluoride, carbon tetrachloride, copper acetate, manganese or aluminum, nickel, cobalt, iron, chromium, molybdenum, tungsten acid, etc. As a catalyst, propionic acid is synthesized in an acidic medium. British BP Company uses carbonylation reactants (such as ethanol) or derivatives (such as ethyl propionate) as raw materials to synthesize propionic acid in the presence of catalyst iridium, promoter rhodium or osmium halide.
3.6 Acrylonitrile method
The acrylonitrile method uses the sulfides of metals from Groups VI to VIII on the periodic table or their mixtures as catalysts, and reacts acrylonitrile with hydrogen and water to generate propionic acid at 130-200 ° C and 5.07 MPa. The method has high propionic acid yield and high feasibility.
3.7 Acrylic acid hydrogenation method
Acrylic acid hydrogenation method adopts copper-palladium series compound as catalyst to hydrogenate acrylic acid under normal temperature and pressure to generate propionic acid, and the amount of catalyst is O of acrylic acid quality. 1%. The reaction conditions of this method are mild, the technological process is simple, and the investment is low; the disadvantage is that the price of acrylic acid is relatively high, so it is not suitable for large-scale production.
Due to the heavy pollution, high cost, high consumption of renewable resources (such as petroleum), and harsh operating conditions, chemical synthesis methods have made a lot of research on microbial fermentation methods (Zhang Huafeng and Katie, 2004). However, the microbial fermentation method still cannot completely replace the chemical synthesis method. The main reason is that the former has low yield and poor economic benefits. The author believes that in order to improve the economic benefits of microbial fermentation, in addition to technical aspects such as strains and fermentation processes, we must also pay attention to the reform of propionic acid production ideas: 1) Propionic acid fermentation and vitamin B12 fermentation can be reasonably integrated. Vitamin B12 is expensive. If the by-product propionic acid can be obtained in the fermentation of vitamin B12, the production cost of propionic acid will be greatly reduced; 2) propionic acid can be separated and extracted from the waste liquid of vitamin B12 fermentation. In this way, it can not only turn waste into treasure, but also be conducive to ecological environment protection, and both economic and social benefits are greater. Wang Jinyu et al. (2004) determined the process conditions for complex extraction of propionic acid from vitamin B12 fermentation waste. After four-stage cross-flow extraction, the extraction rate of propionic acid could reach more than 98%.
4 The production process of propionate
4.1 The production process of calcium propionate
4.1.1 Calcium propionate is prepared by using propionic acid and calcium hydroxide as raw materials. First, the two main raw materials, propionic acid and calcium hydroxide, are mixed evenly, and then pumped into a stainless steel reaction kettle, heated to 80-90 °C to accelerate the reaction, and the temperature should not exceed 130 °C to avoid propionic acid volatilization. Afterwards, it is evaporated and concentrated, and the heating temperature is ≥105°C. The obtained calcium propionate precipitate can be packaged into human library after drying, grinding and testing.
4.1.2 Calcium propionate is prepared from propionic acid and calcium carbonate. The propionic acid and calcium carbonate are placed in a reaction pot equipped with a stirring device, mixed evenly, and the temperature is maintained at 70-80°C. After the reaction is complete, use a plate and frame filter press to compress, filter out useless filter residues and impurities, make the compressed filtrate clear and transparent, and then suck the filtrate into a vacuum concentration tank for concentration until crystallization occurs, then put the tank to separate the crystals . The mother liquor is subjected to the next concentration (cycle concentration). Dry the concentrated crystals with hot air or vacuum dryer. Finally crushed, packed and inspected. The above two processes are simple, easy to operate, easy to obtain raw materials, low in cost, low in energy consumption, and of good quality. Mass production has now been achieved.
4.1.3 Calcium propionate was prepared from eggshells. The calcium carbonate content in eggshell is about 93%, which is a natural source of calcium. The preparation of calcium propionate from eggshells is safe and reliable, and can turn waste into treasure. The main process is as follows: First, the shell membrane separation is carried out. Then, the eggshells were washed, dried, and dried in a drying oven (the temperature was controlled at about 110° C.) to remove water. Then take out and calcined at 900°C for 135min in a muffle furnace to obtain white eggshell powder (CaO). Then, the eggshell powder is made into milk of lime and mixed with propionic acid to obtain calcium propionate solution. The solution is evaporated, concentrated, dried and dehydrated to obtain the finished product of calcium propionate (Chen Minzi, 1999).
4.2 The production process of sodium propionate
Put sodium carbonate into the neutralization reactor, add water and stir to dissolve it, and then slowly add propionic acid. After adding propionic acid, adjust the pH value of the reaction solution to 6.8-7.3, and heat to boiling. After cooling to below 60℃, add carbon powder to decolorize. . After washing with a small amount of anhydrous propionic acid and drying, the finished product of sodium propionate can be obtained, and the yield is about 89% (Wu Cuihong et al., 2003).
4.3 The production process of zinc propionate The preparation methods of zinc propionate are mainly calcium propionate method, zinc oxide method and zinc hydroxide method. Because the calcium propionate method has the advantages of short process route, quick and thorough reaction, and easy control of the preparation process, only the metathesis reaction method using calcium propionate as raw material is introduced here.
When using calcium propionate and zinc sulfate as raw materials to produce zinc propionate, the theoretical dosage of the two should be 1:1 (molar ratio), but in order to make the two react as completely as possible and the residual sulfate ions in the product do not exceed the standard , it is necessary to make an excess of calcium propionate. Wang Suilou and Ma Gengli (2002) thought that the ratio of calcium propionate:zinc sulfate 1.16:1 is more appropriate.