Anything added to a polymer system that can increase the plasticity of the polymer system can be called a plasticizer.

The main function of plasticizer is to weaken the second valence bond between polymer molecules, that is, van der Waals force, so as to increase the fluidity of polymer molecular chain and reduce the crystallinity of polymer molecular chain, that is, to increase the plasticity of polymer, which is manifested by the decrease of hardness, modulus, softening temperature and brittleness temperature of polymer, while the increase of elongation, bending flexibility and flexibility.

Plasticizers can be divided into two types according to the mode of action, namely internal plasticizer and external plasticizer.

The internal plasticizer is actually a part of the polymer. Generally, the internal plasticizer is the second monomer introduced during the polymerization of polymers. Because the second monomer * * * is aggregated in the molecular structure of the polymer, the regularity of the polymer molecular chain decreases, that is, the crystallinity of the polymer molecular chain decreases. For example, a vinyl chloride-vinyl ester copolymer is softer than a vinyl chloride homopolymer. The use temperature range of internal plasticizer is relatively narrow, and it must be added in the polymerization process, so the internal plasticizer is used less.

The external plasticizer is a low molecular weight compound or polymer. Adding it to the polymer to be plasticized can increase the plasticity of the polymer. Plasticizers for external use are generally liquids with high boiling point and difficult volatilization or solids with low melting point, mostly ester organic compounds. Usually, they do not react chemically with polymers, and the interaction with polymers is mainly swelling at high temperature to form solid solutions with polymers. External plasticizer has comprehensive performance, convenient production and use, and wide application. Now people generally refer to plasticizers as external plasticizers. Dioctyl phthalate (DOP) and dibutyl phthalate (DBP) are both external plasticizers.

2. Classification and properties of plasticizers

There are many kinds of plasticizers, including more than 65,438+0,000 kinds in the research and development stage, but there are more than 200 kinds of plasticizers used in commercial production, and phthalate esters from petrochemical industry are the most.

Plasticizers can be classified in many ways. According to the size of molecular weight, it can be divided into monomer plasticizer and polymerization plasticizer; According to shape, it can be divided into liquid plasticizer and solid plasticizer; According to the performance, it can be divided into general plasticizer, cold-resistant plasticizer, heat-resistant plasticizer and flame-retardant plasticizer. It is a common classification method to classify plasticizers according to their chemical structures.

According to the chemical structure can be divided into:

(1) phthalate (such as DBP, DOP, DIDP)

(2) Aliphatic dibasic acid esters (such as dioctyl adipate DOA and dioctyl sebacate DOS).

(3) Phosphate esters (such as triphenyl phosphate TCP and tolyl diphenyl phosphate CDP)

(4) Epoxy compounds (such as epoxidized soybean oil and epoxidized butyl oleate)

(5) Polymer plasticizer (such as propylene adipate)

Polyester)

(6) Benzoate (e.g. 1, 2,4-triisooctyl trimellitic acid)

(7) Chlorine-containing plasticizers (such as chlorinated paraffin and methyl pentachlorostearate)

(8) Alkyl sulfonate

(9) polyol ester

(10) Other plasticizers

The ideal plasticizer should have the following properties: (1) good compatibility with resin; (2) high plasticizing efficiency; (3) stable to thermal light; (4) low volatility; (5) Low liquidity; (6) Water resistance and extractability to oil and organic solvents; (7) Good flexibility at low temperature; (8) Good flame retardancy; (9) Good electrical insulation; (10) is colorless, odorless and nontoxic; (1 1) has good mildew resistance; (12) has good anti-pollution ability; (13) Plasticized paste has good viscosity stability; (14) cheap.

Among plasticizers, the amount of phthalate plasticizers is the largest, accounting for about 80% of the total output of plasticizers. Dioctyl phthalate (DOP) and dibutyl phthalate (DBP) are the main plasticizers in China. Due to the limitation of raw material alcohol source, the yield of excellent varieties such as DHP, DIDP and DIOP is not large.

3. Reaction mechanism of phthalate esters

In the total output of plasticizers, phthalates account for more than 80% of the total output, and DOP and DBP are its leading products. Taking DBP as an example, the reaction mechanism of phthalate esters was introduced.

The production of DBP in China is mostly carried out under normal pressure, and the raw materials phthalic anhydride and n-butanol react in the presence of acidic catalysts (such as H2SO4). Acidic catalyst is a traditional esterification catalyst, which has the advantages of high activity, low price and easy availability, but the disadvantage is that it is easy to cause side reactions.

In the esterification reaction, firstly, phthalic anhydride molecules and alcohol molecules form butyl phthalate. The reaction is exothermic without catalyst, and generally tends to be carried out at 120℃.

It's done.

The reaction formula is as follows:

Monobutyl ester reacts with alcohol molecules under the action of H+ to produce dibutyl ester, and the reaction of producing monobutyl ester is irreversible, while the reaction of producing dibutyl ester from monobutyl ester is equilibrium and reversible.

The reaction formula is as follows:

The total reaction formula is:

This reaction is an equilibrium reaction, so increasing the concentration of alcohol or decreasing the concentration of water and taking away the heat of reaction are beneficial to the formation of dibutyl acid. In practical production, in order to increase the concentration of dibutyl ester, the appropriate temperature should be controlled at 140 ~ 145℃, so that butanol can be properly excessive and the water generated by the reaction can be removed in time.

4. Production technology

4. 1 mass production process

Intermittent production equipment, the so-called "universal" production equipment, a set of production equipment of American Reichhold Chemical Company is a typical example of this "universal" production equipment. The device can handle more than 60 kinds of raw materials, besides ordinary phthalates, it can also produce other kinds of plasticizers, such as aliphatic dibasic esters.

The process conditions of mass production of phthalate esters are similar, but slightly different with the properties of raw materials and products. Taking the production of DBP as an example, phthalic anhydride and n-butanol are esterified in the presence of acidic catalyst (such as H2SO4). In order to make the equilibrium reaction beneficial to the formation of DBP, the water generated by esterification reaction can be continuously removed during the reaction, and an appropriate amount of n-butanol can be added.

After esterification, an appropriate amount of NaOH solution was added to neutralize H2SO4, and the wastewater was delaminated and dealcoholized, and unreacted n-butanol was removed under reduced pressure. Then activated carbon is added for decolorization, and the final product DBP is obtained after decolorization and filtration. The block diagram of DBP production process is shown in figure 1, which includes five production processes: esterification, neutralization, dealcoholization, decoloration and filtration. The five processes of batch production process are all batch operations.

Advantages and disadvantages of batch production:

Advantages 1) Less investment and faster construction.

2) product switching is easy, and various plasticizers can be produced.

3) The technology is simple and the quality of personnel is easy to meet.

Disadvantages 1) The product quality fluctuates greatly and is unstable.

2) backward technology and high labor intensity.

3) High energy and material consumption

Intermittent production is suitable for small-scale production of various plasticizers, with less investment and quick results.

4.2 Continuous production process

Due to the huge demand for DOP and DBP plasticizers, the continuous production process based on DOP and DBP has been widely used. At present, the maximum single-line capacity of DOP in China is 50,000 tons/year, and the maximum single-line capacity of DBP is 20,000 tons/year.

In continuous production, esterification reactors can be divided into two categories: tower reactors and cascade reactors. When using acidic catalyst, it is reasonable to choose tower esterifier; When a non-acidic catalyst is used or no catalyst is used, it is more suitable to use a stepped series reactor because of the long residence time of the reaction mixture.

The five processes of esterification, neutralization, dealcoholization, decoloration and filtration in DBP continuous production process are all continuous operations.

Advantages and disadvantages of continuous production:

Advantages: 1) The product quality is good and stable.

2) Low energy and material consumption and good economic benefits.

3) Advanced technology and high labor productivity.

4) High automation level and low labor intensity.

Disadvantages 1) Long construction period and large one-time investment.

2) The main equipment is difficult to manufacture and process.

3) It is difficult to switch products, and it is not suitable for producing various plasticizers.

4) High quality requirements for workers.

Continuous production is suitable for large-scale production, the source of raw materials is guaranteed, the production management level is high, and the quality of personnel is high.

4.3 Semi-continuous production process

The so-called semi-continuous production means that the esterification process is intermittent, and the processes after esterification (neutralization, dealcoholization, decoloration and filtration) are continuous. Semi-continuous production process is a transitional stage from batch production process to continuous production process. Most of the main phthalate plasticizers DOP and DBP in China are produced by semi-continuous production process. Its scale is generally 1 ~ 20000 tons/year.

Advantages and disadvantages of semi-continuous production:

Advantages 1) Investment is lower than continuous production.

2) It is easier to switch varieties than continuous production, and it is more suitable for producing multi-variety plasticizers.

3) partial continuous production, convenient operation, and the output of raw materials is basically the same as that of full continuous production.

4) Compared with mass production, the production mode is large and the labor productivity is high.

Disadvantages 1) Compared with continuous production, the labor intensity is high and the product quality is easy to fluctuate.

2) Intermittent esterification consumes more energy than continuous esterification.

3) The degree of automation is lower than that of continuous production.

Semi-continuous production is more suitable for the production of plasticizers with moderate scale and diverse varieties. Flexible production varieties is a major advantage of semi-continuous production.

5. Concluding remarks

Due to the large amount and variety of plasticizers, the production technology of plasticizers tends to develop in two aspects. On the one hand, it is the continuous mass production of main plasticizer; On the other hand, it is the batch production of special plasticizer with many varieties and small batches.

With the increase of PVC production and the development of petrochemical industry, plasticizer has developed into a large-scale production chemical industry based on petrochemical industry and mainly producing phthalate esters. Phthalates account for more than 80% of the total output of plasticizers, which provides conditions for large-scale continuous production. Because of the existence of many varieties and small batches of plasticizers, it is still necessary for the development and survival of "universal" production equipment, that is, batch production.

In order to reduce the color of products, improve the thermal stability of products and further simplify the technological process, non-acidic catalysts have been industrialized. The main advantages of using non-acidic catalyst are less side reactions, light product color, simple product refining, less waste water, good water quality, good product thermal stability and high yield.

harm

Not long ago, Guangzhou Food Safety Information Network released a message saying that a study by Tongji University confirmed that the plasticizer in plastic barrels of edible oil was harmful to human body. "With plastic barrels of cooking oil, the cooking oil will dissolve into a plasticizer that is harmful to the human body." According to the news, the research group of Professor Li Shuguang from Tongji University School of Basic Medicine collected plastic barrels of soybean salad oil, blended oil, peanut oil and bulk soybean oil sold in the market with different brands and different factory dates. It was found that almost all brands of plastic barreled edible oil contained plasticizer "dibutyl phthalate". It is inferred that the plasticizer detected in edible oil mainly comes from plastic containers. This plasticizer is toxic to human reproductive system, especially to men.