Issue 33, 2012 - Research Progress in the Application and Preparation of CPAM

Polyacrylamide (PAM) has been developed in the laboratory for more than 100 years since 1893, and has obtained cationic polyacrylamide (CPAM), anionic polyacrylamide (APAM), amphoteric polyacrylamide (AmPAM) and nonionic polyacrylamide (NPAM)
with molecular weights ranging from thousands to tens of millions.
The dosage forms of various ionic polyacrylamide industrial products include four types: hydrosol, powder, emulsion and water dispersion, which are widely used in water treatment, petroleum, papermaking, medicine, mineral metallurgy and other industries
.
PAM is mainly used in petroleum, water treatment, papermaking three major industries in China, has a wide range of application prospects, and CPAM has higher application efficiency and application value because of its higher density of cationic charge, has been a research hotspot
for the majority of scientific researchers.

First, the application of CPAM

1.

With the diversification of pollutants in wastewater, especially the content of negatively charged organic matter, it is difficult to achieve satisfactory results
using conventional water treatment agents.
CPAM flocculant with positively charged active groups on the molecular chain has excellent turbidity removal and decolorization properties, which can destabilize negatively charged colloidal particles, and can also react with negatively charged dissolved substances to generate insoluble substances, so that particles flocculate and precipitate, and the total carbon content in water is reduced
.
CPAM can be used in surface water, coking wastewater, pharmaceutical wastewater, coal washing wastewater, Yellow River high turbidity water, landfill leachate, etc.
, among which it is the most widely
used in printing and dyeing wastewater treatment.

Europe, the United States and Japan have widely used CPAM in the water treatment industry, and the market share has reached more than
80% of the total polyacrylamide flocculants.
However, China is relatively lagging behind, only 20% of polyacrylamide flocculants are cationic types, and most of them are of poor quality, which has become a "bottleneck"
restricting the development of China's water treatment industry.

2.
Although polyacrylamide in the petroleum industry reduces the surface tension of water a lot, there are active groups in the molecule, which can change the interface state after adsorption at the interface, and has been used as a thickener, water loss agent, flocculant, dispersant, resistance reducer, scale inhibitor, flow control agent for the petroleum industry
for many years, so as to improve drilling fluid fluidity and oil recovery, and reduce fluid resistance
。 CPAM is used for water injection, acid injection, fracturing and drilling fluid, which can inhibit the expansion, dispersion and transfer of clay hydration, prevent the collapse of the well wall and the damage of the injection fluid to the oil and gas layer, it is suitable for various PH values, and long-term stability
.
In addition, it can also be used for flocculation and deoiling of oilfield sewage, and the treated sewage can be recycled as oilfield reinjection water
.

3.
Paper industry In the paper industry
, CPAM, which has a relatively low molecular weight, can be used as a paper reinforcing agent
.
The amide group of CPAM has a strong intermolecular interaction with the hydroxyl group on the surface of the fiber and is bound
by hydrogen bonding.
At the same time, the positive charge of CPAM and the negative charge of the paper fiber are combined by electrostatic attraction, and the two effects strengthen the force between the fibers, thereby improving the strength
of the paper.

CPAM, which has a relatively medium molecular weight, can be used as a retention and filter aid
.
When used as a retention aid, the charge attraction and bridging of the positively charged group carried on the CPAM molecular chain and the envelope of the floc make the fine fibers or particles form larger flocs and remain on the filter cloth, so that the retention rate of fillers, paper fibers, etc.
is greatly improved, so as to reduce the loss of fibers and fillers and reduce the pollution load
.
At present, the retention aid has been developed from the CPAM one-dimensional retention system to the binary retention system and the CPAM/particulate retention and filtration aid system
.
When used as a filter aid, the positive charge neutralization of CPAM reduces the charge on the surface of paper fiber or filler, which in turn reduces the wetting and directional arrangement performance of water molecules on the surface of filler and paper fiber, while particles such as filler and paper fiber condense to a certain extent make it lower than the surface, thereby improving its dehydration.

If CPAM is combined with aluminum sulfate, the retention and filtration effect can be further improved
.

CPAM, which has a relatively high molecular weight, can be used as a flocculant, and the flocculation and precipitation such as paper fibers and fillers lost in the discharge water can be recycled through the effect of adsorption bridging and electrical neutralization
.

4
.
The application of polyacrylamide in the field of mining and metallurgy in other industries
mainly involves mining, mineral processing and metallurgy.
As a dehydrating agent in the beneficiation process, it is mainly used for flotation of refined coal, very fine muddy sedimentation, circulating water purification and tailings water treatment in coal preparation operations, the use of PAM can not only improve the production capacity of filtration equipment, reduce the loss of solid particles in the filtrate and increase the selected yield, but also reduce the moisture of
the filter cake.
Because PAM reduces the sludge content of circulating water, it has become an important means to
prevent black water pollution.

Used as a fabric post-treatment agent in the textile industry, it can generate a protective layer that is smooth, wrinkle-proof and mildew-proof, reducing the yarn breakage rate during spinning and preventing static electricity
in the fabric.
It is used as a printing and dyeing auxiliary in the printing and dyeing industry, which can increase the adhesion fastness of dyes and improve the vividness
of colors.
In the construction industry, it can be used as a decorative binder, cement additive, fireproof glass and ceramic dispersant
.
In the agriculture and forestry industry, PAM can be widely used as a soil conditioner and seed culture agent
because it has the functions of soil preservation, water preservation, fertilizer preservation and yield increase.

At present, the research and development of new fields of CPAM application mainly focus on composite materials, including: intercalation composites prepared by montmorillonite and PAM as humidifiers, acrylamide/graphite oxide and polyacrylamide/graphite oxide nanocomposite flame retardant materials, metal-based composite coating technology doped at the molecular level of PAM polymers, and the development
of functional sidechain liquid crystal polyacrylamide.
Among them, liquid crystal polymer has controllable liquid crystal phase transition temperature and good photoelectric properties, which is a new functional polymer
with great application prospects.

Second, the preparation method of CPAM

At present, the commonly used synthesis methods of CPAM mainly include cation modification method and monomer copolymerization method
.
The cation modification method has been rarely used
because of its low controllability of cation degree and molecular weight and poor production economy.
The main monomer copolymerization methods used include aqueous solution polymerization, reversed-phase emulsion polymerization, reversed-phase suspension polymerization, water dispersion polymerization and other processes
.

1.
Aqueous solution polymerization aqueous solution polymerization
method is the oldest method of PAM production, which can produce polyacrylamide colloids and powdered products
.
Polyacrylamide colloids are generally directly polymerized by 8%~10% acrylamide aqueous solution under the action of initiator; Dry powder is mostly polymerized with 25%~30% acrylamide solution, and polyacrylamide colloid is granulated, kneaded, dried and crushed to obtain a powdered product
.
This method has the advantages of production safety, simple process equipment, no need to recover solvents and low production costs, and is currently a commonly used method
in China.

2.
Reversed-phase emulsion polymerization Reversed-phase emulsion polymerization
is an emulsification system
with non-polar hydrocarbon solvents as a continuous phase, water-soluble monomers dissolved in water as a dispersed phase, and under the action of lipophilic emulsifiers, oil-water (W/O) monomer droplets and monomeric swelling micelles are formed.
In reversed-phase emulsion polymerization, the initiation of nucleation polymerization sites is the core problem
of emulsion polymerization mechanism.

3.
Reversed-phase suspension polymerization Reversed-phase suspension polymerization is an ideal method
for realizing the industrial production of water-soluble polymers
developed in the past ten years.
Reversed-phase suspension polymerization is a polymerization reaction
in which an aqueous monomer solution is suspended in an organic solvent in the form of small liquid beads.
In the reversed-phase suspension polymerization of acrylamide, the sorbitan monostearate (Span60), inorganic ammonia, C12~C18 fatty acid sodium or butyl acetate fiber are used as the suspension agent (dispersion stabilizer), and the acrylamide aqueous solution forms a stable suspension system in gasoline, xylene or tetrachloroethylene, and the polymerization reaction
is initiated by the initiator.
When water-soluble emulsifiers and paraffin oil phase media are used, the hydrophilic and lipophilic balance value (HLB value) of the emulsifier is generally greater than 8
.

4.
Dispersion polymerization and dispersion polymerization usually refers to the monomer dissolved in organic solvents, polymerized into insoluble polymers
in the presence of stabilizers and dispersed in the continuous phase to form a colloidal stable dispersion system
.
The dispersion polymerization system is composed of
four basic components: initiator, monomer, stabilizer (dispersant) and dispersion medium.
Sometimes for special needs, cross-linking agents, comonomers, surfactants, inorganic salts and other components can be added
.

3.
Future research directions

China's fresh water resources are scarce, so it is imperative to rationally use water resources and improve sewage treatment capacity, and CPAM has broad
prospects in the future.
In the future, its research direction should mainly focus on the following points: (1) Develop new, efficient and inexpensive cationic monomers, diversify, non-toxic and functionalize cationic flocculants,
and actively develop their applications
in different fields.
Such as N,N-dimethacrylamide and other highly effective, hydrolysis-resistant, wide range of application flocculents
.

(2) Seek efficient and non-toxic comonomers, such as DDMAC, DMC, MBDAC and other cationic monomers with high efficiency and non-toxicity, high positive charge density, low price and so on
.
Optimize the synthesis process to make DADMAC fully linear polymerization and avoid cross-linking, so as to achieve the purpose of
fully controlling the relative molecular mass and cation degree.

(3) Seek suitable polymerization methods and processes
according to different application requirements.