Methods for Preparing 2-Hydroxyphosphonoacetic acid (HPAA)
2-Hydroxyphosphonoacetic acid is a good scale inhibitor. Its appearance is dark brown liquid with a molecular formula of C2H5O6P and a relative molecular mass of 156.03. The preparation method generally has the following three methods.
16.3 parts (0.11 mol/L) 50% aqueous solution of dihydroxyacetic acid (hydrated glyoxylic acid) and 8.2 parts (0.1 mol/L) of phosphorous acid were heated at 98~100 °C for 24 hours with stirring. 24.5 parts of a 60% aqueous solution of HPAA. 150 parts of this solution were subjected to distillation under reduced pressure (2 kPa) to obtain 104 parts of a brown viscous oily liquid.
From dimethyl phosphite and butyl glyoxylate, under the catalysis of sodium methoxide, according to the ratio of the amount of 1:(0.95~1), react at 25~120 °C for several hours. The phosphinyl hydroxyacetate can be used to prepare HPAA in three different routes.
A simpler route is to carry out a saponification reaction of dimethoxyphosphinyl hydroxyacetate with hydrochloric acid under the following conditions: The ratio of the amount of the dimethoxyphosphinyl hydroxyacetate butyl acetate to the hydrochloric acid is 1: (8~15), temperature 90~110 °C, reaction time 10~20 hours.
The di-sodium salt of phosphonoformaldehyde is formed by synthesizing dimethoxymethanephosphonic acid and sodium hydroxide solution at 80-90 °C for 1~3 hours. Then, it is reacted with hydrocyanic acid at 25~30 °C for 0.25~3 hours to form a disodium salt of phosphonohydroxyacetonitrile. Hydrolysis with hydrochloric acid gives HPAA.
Hydroxyphosphono Acetic Acid Product Properties
The 2-hydroxyphosphonoacetate product is present in [HPAA]2- and [HPAA]3- in water at pH 7-9. It forms a protective film on the metal surface with a chelate formed by Ca2+ and Zn2+. Its solubility product is ZnHPAA
2-Hydroxyphosphonoacetic acid has good compatibility and synergy with some commonly used water stabilizers. For example, when 2-hydroxyphosphonoacetate is combined with Zn2+, it only needs to add 5-10 mg/L, Zn2+ 1~ 2mg/L can provide good corrosion inhibition in different water systems.
In addition, the phosphorus content of hydroxyphosphonoacetic acid corrosion inhibitor is lower than that of conventional organic phosphorus water stabilizers, and meets the requirements of environmentally friendly “low phosphorus”. At the same time, its thermal stability is good, and it can be measured by differential scanning calorimeter up to 160 °C.
Even at a high temperature of 200 °C, the decomposition rate is only 8%, so it fully meets the requirements of heat exchange equipment in the steel, petrochemical, electric power, medicine, and other industries. Hydroxyphosphono acetic acid products have low toxicity, compared with traditional scale inhibition. Corrosion inhibitors are more acceptable for environmental protection.
In summary, the 2-hydroxyphosphonoacetic acid product is a cathodic corrosion inhibitor widely used in ferrous metals in water treatment and is especially suitable for low-hardness water quality and high-temperature heat exchangers.