Progress in the synthesis and application of green chemical polyaspartic acid

Polyaspartic acid (sodium salt) , or sodium salt of polyaspartate is a green chemical with increasing global sales in recent years. It is a polyamino acid with a carboxylic acid side chain, which is completely biodegradable and environmentally friendly. In today's highly developed industry, environmental issues are increasingly attracting people's attention, and the synthesis and application of polyaspartic acid have attracted much attention from all countries.

Polyaspartic acid can change the crystal structure of calcium salts and is an excellent scale inhibitor and dispersant used in circulating cooling water systems, boilers and oil and gas field water treatment; polyaspartic acid has a good viscosity reduction effect; polyaspartic acid can promote plant growth as a fertilizer synergist; it also has excellent moisturizing properties and is used in the manufacture of daily cosmetics and health care products; super absorbent resins are prepared from polyaspartic acid; in addition, drug delivery carrier materials prepared from polyaspartic acid have been widely used in family planning, anti-tumor and other drugs.

Polyaspartic acid has a wide range of applications and a large market capacity. Its production and use will inevitably bring huge economic and social benefits. This article reviews the research progress in the synthesis and application of polyaspartic acid in recent years.

1 Synthesis of polyaspartic acid

There are two main types of raw materials for synthesizing polyaspartic acid, one is L-aspartic acid as a raw material, and the other is maleic anhydride and its derivatives as raw materials. The synthesis methods are described as follows.

1.1 L-aspartic acid as a raw material

The reaction equation for the thermal condensation of L-aspartic acid to synthesize polyaspartic acid is:

The results of nuclear magnetic resonance measurement show that the β body accounts for about 75% and the α body accounts for about 25%.

The process of thermally condensing polyaspartic acid using L-aspartic acid as a raw material is simple, and the reaction process does not pollute the environment except for the generation of a small amount of water vapor. Depending on the reaction conditions, the average molecular weight of the product can be in the range of 1000 to 200000.

1.1.1 Direct thermal condensation synthesis

Put a certain amount of L-aspartic acid in an oil bath or muffle furnace at 200 to 270 ° C, and thermally condense the aspartic acid to synthesize polysuccinimide (Polysuccinimide). Measure the weight loss at regular intervals and calculate its conversion rate. Table 1 shows the reaction results of 30g L-aspartic acid at 250 ° C.

Polysuccinimide is hydrolyzed into polyaspartic acid under alkaline conditions. The relative molecular weight of the product is measured by gel chromatography and is between 1000 and 5000.

1.1.2 Thermal condensation synthesis under acid catalysis

Add an appropriate amount of acid catalyst to L-aspartic acid, stir it into a homogeneous mixture, and place it in a constant temperature oven for reaction. The obtained product is washed with distilled water until neutral and hydrolyzed into polyaspartic acid.

The product obtained by the reaction is ground into powder and subjected to a secondary thermal condensation reaction to obtain polyaspartic acid with a mass average molecular weight of 100,000 to 200,000.

1.1.3 Catalytic polymerization in solvent

Aspartic acid is catalytically polymerized in a thioether solvent or a cyclic carbonate solvent. The solvents include: cyclopentane, methyl cyclopentane, dimethyl cyclopentane, dimethyl sulfone, methyl ethyl sulfone, propylene carbonate, ethylene carbonate, etc. The reaction temperature is 50 to 200 ° C, the reaction time is 0.15 to 12 h, and the mass average molecular weight of the sample is measured by gel chromatography.

1.2 Using maleic anhydride and its derivatives as raw materials

Use maleic anhydride and ammonia to generate polyaspartic acid

The synthesis of polyaspartic acid using maleic anhydride and its derivatives as raw materials has the advantages of easy availability of raw materials and low production cost, but the relative molecular mass of the obtained polymer product is low.

1.2.1 Reaction of maleic anhydride and ammonia in an autoclave

In the solvent, the molar ratio of maleic anhydride to ammonia is 1: 0.18-1: 1.12, the reaction temperature is 150-300 °C, the reaction pressure is 0.12-7.10 MPa, and the reaction time is 5-300 min. The solvent can be water, methanol, ethanol, n-propanol, isopropanol, etc., and the mass average relative molecular mass of the obtained product is 500-10,000.

1.2.2 Reaction of maleic anhydride and its derivatives with nitrogen-containing compounds

Maleic anhydride, maleic acid, fumaric acid and its derivatives are fully mixed with urea, isourea, carbamic acid, ammonium bicarbonate, ammonium carbonate, etc. in a paddle dryer and fed into a screw extruder. The reaction temperature is 160-220°C and the reaction time is 110-60min. The mass average molecular weight of the obtained product is 1000-5000.

1.2.3 Two-step reaction of maleic anhydride and ammonia

First, maleic anhydride reacts with ammonia water at less than 150°C to form maleic acid ammonium salt. Then the reaction mixture is condensed at more than 200°C to synthesize polysuccinimide, which is hydrolyzed to polyaspartic acid under alkaline conditions. The mass average molecular weight of the product is 3000-12000.

2 Application of polyaspartic acid

Polyaspartic acid is a class of compounds. According to their different relative molecular weights, they can be used in scale inhibition, viscosity reduction, farmland and water-absorbing resin.

2.1 Green scale inhibitor

Polyaspartic acid is a non-toxic, non-polluting and degradable green scale inhibitor. Since the 1990s, it has become a research and development hotspot for major chemical companies in countries around the world, especially the United States, Germany and Japan. Since 1999, my country has successively published a number of related research reports. The results show that polyaspartic acid has good thermal stability, excellent scale inhibition performance and low dosage. The calcium carbonate scale inhibition performance of polyaspartic acid with a mass average molecular weight of about 4000 is better than that of polymaleic acid and polyacrylic acid; when the Ca2+ mass concentration is 1200mg/L, the calcium carbonate scale inhibition rate can still be maintained at nearly 50%; when the pH is 10.15 and the added agent mass concentration is 3mg/L, the scale inhibition rate can still reach more than 90%; when the temperature increases from 40℃ to 80℃, the scale inhibition rate decreases slightly with the increase of temperature. Therefore, polyaspartic acid is a water treatment agent that can be used in high temperature and high calcium ion concentration water systems.

2.2 Drilling fluid viscosity reducer

Polyaspartic acid can reduce the viscosity of drilling fluid. In bentonite mud, the greater the amount of polyaspartic acid added, the better the viscosity reduction effect. When the mass average molecular weight of polyaspartic acid is 12700, the viscosity reduction rate is 70.159% when the addition amount is 0.14%, which meets the requirements of viscosity reducers in oilfield chemistry. In standard mud, when the mass average molecular weight of polyaspartic acid is 17,000, the viscosity reduction rate is 70.151% when the addition amount is 0.11%; when the addition amount is 0.13%, the viscosity reduction rate is 79.149%. Polyaspartic acid also has good salt and calcium resistance.

2.3 Fertilizer synergist

Polyaspartic acid is neither a fertilizer nor a hormone. Applying it alone without fertilization has no obvious advantage for plant growth. When polyaspartic acid with a mass average molecular weight of 3,000 to 5,000 is supplied to plants (usually at the roots or leaves), it can enhance the plant's intake of fertilizers and enable plants to use nutrients more effectively, so it is called a fertilizer synergist. The results show that under the same fertilizer application amount, the use of polyaspartic acid 0.1015-3.16g/m2 can increase grain yield by 5%-30%; under the same grain yield, the fertilizer application can be reduced by 1/2-1/3, greatly improving the rural ecological environment. Therefore, the promotion and application of polyaspartic acid in agriculture has considerable economic benefits and significant social benefits.

3 Conclusion

Polyaspartic acid and its derivatives are increasingly valued because they are completely biodegradable and have chelating and dispersing functions. At present, domestic scientific researchers have carried out a lot of research on their scale inhibition performance, but there is still room for improvement in reducing costs and promoting their use; other application research of polyaspartic acid has been rarely reported in China, and there is a large gap with foreign countries. Research efforts should be increased to make green chemicals truly benefit the people.

Shandong Yuanlian Chemical Co.,ltd. is a famous manufacturer of Polyaspartic acid sodium salt (polyaspartate sodium) in China, any needs for MSDS, TDS, COA of MGDA, feel free to contact: [email protected]; Tel: +86 537 3739818