The advantages of inorganic flocculants are relatively economical and simple to use; but they are large in dosage, low in flocculation effect, and have the disadvantages of high cost and strong corrosiveness. Organic polymer flocculant is a new type of wastewater treatment agent developed in the late 1960s. Compared with traditional flocculants, it can double the efficiency and the price is lower, so it has a tendency to gradually become the mainstream agent. Coupled with stable product quality, the production of organic polymer flocculants has accounted for 30% to 60% of the total flocculant output.

Certain natural polymer organics such as polysaccharides with more carboxyl groups and starches with more phosphate groups have flocculation properties. The introduction of active groups into macromolecules by chemical methods can improve this performance. For example, after a natural polysaccharide is etherified and introduced into active groups such as carboxyl groups and amide groups, the flocculation performance is better and can accelerate the sedimentation of cane juice.

Graft copolymerization of natural polymer materials such as starch, cellulose, chitosan, etc. with acrylamide, the polymer has good flocculation performance, or some special properties. Some domestically developed products are mainly used in sewage treatment and sludge dewatering.

Since most organic polymer flocculants themselves or their hydrolysis and degradation products are toxic, and acrylamide monomers used for synthesis are toxic and can anaesthetize the central nervous system of humans, their application areas are restricted to certain extent, forcing flocculants to be cheap, practical, non-toxic and efficient Direction development.

Variety classification

There are many varieties of organic flocculants. They are all macromolecular organic substances containing a large number of active groups, and there are three main categories:

1. It is made based on natural polymer organic matter and chemical treatment to increase its active group content.

2. Polyacrylamide series products synthesized by modern organic chemical methods.

3. It is made by grafting (or copolymerizing) natural raw materials and polyacrylamide.

Organic polymer flocculants are divided into two categories: natural polymer and synthetic polymer. From the chemical structure, it can be divided into the following three types:

(1) Polyamine type-low molecular weight cationic electrolyte;

(2) Quaternary ammonium type-wide range of molecular weight and high cationicity;

(3) The copolymer of acrylamide has a relatively high molecular weight, ranging from hundreds of thousands to several million or tens of millions. They are all sold in milky or powder form, which is inconvenient to use, but has good flocculation performance. According to the dissociation of different functional groups, the particles can be divided into three categories: cationic, anionic, and nonionic. The macromolecules of organic polymer flocculants can carry hydrophilic groups such as -COO-, -NH-, -SO3, -OH, etc., and have various structures such as chain and ring.

Because of its many active groups, high molecular weight, low dosage, low scum production, strong flocculation ability, easy separation of flocs, and good degreasing and suspended solids removal effects, it has good effects in treating oil refinery wastewater.

Polyacrylamide

The most widely used flocculant in domestic water treatment is a series of synthetic polyacrylamide products, mainly divided into anionic, cationic, nonionic and zwitterionic. Polyacrylamide (polyacrylamide), often abbreviated as PAM (in the past also abbreviated as PHP), various PAM used in water treatment, in essence, a certain proportion of acrylamide and sodium acrylate through copolymerization of polymer products, there are a series The product.

Polyacrylamide can be divided into ultra-high relative molecular weight polyacrylamide, high relative molecular weight polyacrylamide, medium relative molecular weight polyacrylamide and low relative molecular weight polyacrylamide according to its molecular weight. Ultra-high molecular weight polyacrylamide is mainly used for tertiary oil recovery in oil fields. High molecular weight polyacrylamide is mainly used as a flocculant, medium molecular weight polyacrylamide is mainly used as a dry strength agent for paper, and low molecular weight polyacrylamide is mainly used Make a dispersant.

Polyacrylamide is a high molecular polymer. Specializing in the treatment of various difficult-to-treat wastewater and the treatment of sludge dewatering. (Sludge dewatering generally uses cationic polyacrylamide) It is widely used in municipal sewage and sludge treatment in the paper-making printing and dyeing industry.

The molecular formula of acrylamide is: CH2 = CH－CONH2

The molecular formula of sodium acrylate is: CH2 = CH-COONa

Non-ionic organic polymer flocculant

Non-ionic organic polymer flocculants are mainly polyacrylamide. It is obtained by polymerization of acrylamide.

Anionic organic polymer flocculant

Polymers such as polyacrylic acid, sodium polyacrylate, calcium polyacrylate, and alkali hydrolyzate of polyacrylamide.

Copolymers of styrene sulfonate, lignosulfonate, acrylic acid and methacrylic acid.

Cationic organic polymer flocculant

Quaternized polyacrylamide cations are all obtained by methylolation and quaternization of -NH2, which can be divided into polyacrylamide cationization and cationization acrylamide polymerization.

Polyacrylamide (PAM) first reacts with aqueous formaldehyde solution to partially methylolate the amide group, then reacts with a secondary amine for alkylamidation, and then reacts with hydrochloric acid or an aminating reagent to quaternize the tertiary amine.

Under alkaline conditions, it first reacts with acrylamide and aqueous formaldehyde, then reacts with dimethylamine, and after cooling, it is quaternized with hydrochloric acid. The product is concentrated by evaporation and filtered to obtain a quaternized acrylamide monomer.

Cationic derivatives of polyacrylamide

Most of these products are obtained by the copolymerization of acrylamide and cationic monomers.

Amphoteric polyacrylamide polymer

Partially hydrolyzed polyacrylamide is added with appropriate amount of formaldehyde and dimethylamine to synthesize an amphoteric polyacrylamide flocculant with carboxyl group and aminomethyl group through Mannitz reaction.

Acrylamide graft copolymer

Because starch has a rich source of cheap price, it is also a polymer compound. It has a hydrophilic rigid chain. With this rigid chain as the skeleton, it is connected with flexible polyacrylamide branch chains. This kind of rigid and flexible network macromolecules can not only maintain In addition to the functions of the original polyacrylamide, it also has some more excellent properties.