Views: 5 Author: Site Editor Publish Time: 2017-05-10 Origin: Site
Environmentally friendly chemistry, also known as green chemistry, is the use of chemical techniques and methods, to fundamentally reduce the appearance and application of raw material, solvent, reagent, products and by-products which are harmful to human health and the environment. Then under the environmental friendly chemical concepts, people put forward the concept of “environmental friendly water treatment chemicals”. It means those water treatment chemicals which manufacturing process is clean, using process is no toxicity to human health and the environment, and can be biodegradable, with no harm to the environment in the end. The new environmental friendly water treatment chemicals are the development direction of water treatment chemicals in 21th Century. They have high scale inhibition performance, good biodegradability, non toxicity, and are non phosphorus and nitrogen free.
1. Acrylic Copolymer
Polyacrylic Acid (PAA) series of water treatment chemicals have the advantages of low production cost, small using amount, good scale effect of calcium carbonate, no pollution to the environment, no nourishing bacteria and algae, and so on. They are the earlier polymer scale inhibitor dispersants. The acrylic acid/methyl acrylate copolymer was successfully developed in the middle of 1980s, which laid the foundation of water-soluble polymer water treatment chemicals in China. Nalco Water, Shandong Taihe Technologies, Shandong Thfine Chemical, Jianghai Environmental, etc., all developed and produced of acrylic acid/methyl acrylate copolymer, to be used as scale inhibitors and dispersants in oilfield water injection, industrial cooling water, boiler water and other systems. Its scale inhibition and dispersion performance is related to its molecular weight and molecular weight distribution.
2. Maleic Acid Copolymer
Maleic copolymer is developed successfully from maleic acid (anhydride) and styrene sulfonic acid by Chemed Company in 1970s for the first time. It has good heat resistance, and has good scale inhibition effect to CaCO3 scale, Ca3(PO4)2 scale and CaSO4 scale, and has obvious synergistic effect when using with organic phosphonic acid and polyvalent metal chelating agent, especially suitable for high temperature circulating cooling water system or medium low temperature boiler water system. The Maleic acid/ethylene glycol/acrylic acid terpolymer produced from maleic acid, oxalic ester, acrylic acid by Zhang Liangjun, has a large number of -COO-, with strong chelating ability to Ca2+, Mg2+, and can be used for high temperature resistant water treatment.
3. Polyepoxysuccinic Acid
At the beginning of 1990s, USA has developed the Polyepoxysuccinic Acid (PESA), then Japan and other countries also studied on PESA and its derivatives. Polyepoxysuccinic Acid (PESA) is a kind of non-phosphorus, nitrogen-free and biodegradable corrosion inhibitor, not only has the characteristics of good biodegradability, but also has advantages of a small using amount and good scale performance, with strong alkali resistance, high basicity, high hardness of water and its inhibition rate is obviously superior to the commonly used organic phosphonic acid. It has dual scale inhibition function, and has obvious synergistic effect with organic phosphonic acid compound. PESA has good compatibility with chlorine, and its scale and performance is not affected by the chloride concentration, and has good synergistic effect when compound used with phosphate, 2-Phosphonobutane-1,2,4-Tricarboxylic Acid (PBTCA) and other chemicals. If add PESA into the corrosion inhibitor which is based on orthophosphate, it can greatly reduce the consumption of orthophosphate, and make the emission concentration of phosphorus below 1mg·L-1.
Xiong Rongchun etc. used maleic anhydride as monomer to compound non-phosphorus, non-nitrogen and biodegradable green scale inhibitor Polyepoxysuccinic Acid (PESA), and got the optimum synthesis conditions, the range of molecular weight and infrared spectra of best scale inhibition. In the laboratory, Wu Xueqin etc. used maleic anhydride as raw material by catalytic polymerization to make Polyepoxysuccinic Acid. They set up 3 factors and 3 levels orthogonal experimental groups to determine the optimum polymerization conditions, according to the three synthesis condition(time, temperature and dosage of initiator) which can affect the corrosion and scale inhibition performance of PESA. When the dosage is 40mg·L-1, the scale inhibition efficiency of calcium ion concentration less than 500mg·L-1 reached 100%, and the scale inhibition efficiency of calcium ion concentration of 600~700mg·L-1 was more than 85%.
However, when PESA is used to treat calcium phosphate scale, calcium silicate scale and magnesium silicate scale, its effect is not significant, this is because the main molecular structure of Polyepoxysuccinic Acid is carboxyl group, and its single functional group also limits its ability to disperse iron. In recent years, there have been a lot of research on the modification of PESA, which is mainly the introduction of other functional groups on the basis of the original structure of PESA. Aiming at the deficiency of scale inhibition performance of PESA, Hu Xinggang made the modification study, and introduced the sulfonic acid group into its molecular structure, and made a new type of environmentally friendly scale inhibitor Polyepoxy Carboxylic Acid (PECS) by using two monomers: 3-chloro-2-hydroxy sodium sulfonate (CHPS) and epoxysuccinic acid (ESA) sodium.
4. Polyaspartic Acid
Polyaspartic Acid (PASP) was first proposed by the American Donlar company at the beginning of 1990s. It has excellent scale inhibition and dispersion performance, when used as scale inhibitor and dispersant, the calcium carbonate scale inhibition effect is the best, and already proved to have good corrosion inhibition performance in the oil field. Its molecule does not contain phosphorus, so it’s biodegradable. Xu Yaojun etc. used L-aspartic acid as monomer to synthesize Polyaspartic Acid by using pyrocondensation polymerizatiot method, and did research on its scale and corrosion inhibition and dispersion performance. And the results showed that PASP is a kind of water treatment agent with excellent performance. The inhibition rate is close to 100% under the addition quantity of 5.0mg·L-1. PASP is a kind of poly amino acids, which mainly includes Polyaspartic Acid, Polyaspartic Ester and Polyaspartic Acid Sodium Salt. PASP is resistant to high temperature, and has good thermal stability, not only can be biodegradable, but also has the function of chelation and dispersion. The best molecular weight range to chelate CaCO3 and BaSO4 is 3000~4000, and the best molecular weight range to chelat CaSO4 is 1000~2000. The synthesis, modification and application of PASP have become a hot research field in the developed countries, and it is necessary to seek a high performance, low cost and biodegradable polymer inhibitor to reduce environmental pollution.
In recent years, the research on environmental friendly polymer inhibitors in China has achieved great progress, however, in the study of environmental friendly water treatment agents, especially in the production of new polymer scale inhibitors, there is a certain gap with abroad. With the increase of environmental protection, developing low phosphorus or phosphorus free nitrogen, biodegradable multi-functional environmentally friendly water treatment agents will become the most mainstream research direction in the field of industrial water treatment. In the synthesis of new products, we need to break the existing ideas, starting from the green idea, pay attention to the influence to environment in production process, and improve the production technology of the water treatment agents.