Polyester (PET) fibers are the first major variety of synthetic fibers. The garment made of polyester fiber is comfortable, crisp, easy to wash and dry. Polyester is also widely used as a raw material for packaging, industrial yarns, and engineering plastics. As a result, polyester has developed rapidly in the world, with an average increase of 7% per year and a large output.
The production of polyester can be divided into a dimethyl terephthalate (DMT) route and a terephthalic acid (PTA) route from the process route, and can be divided into a batch process and a continuous process from the operation. Whichever production routes using polycondensation reactions are required as the catalyst metal compound. The polycondensation reaction is a key step in the polyester production process. The polycondensation time is the bottleneck for improving the yield. The improvement of the catalyst system is an important factor for improving the quality of the polyester and shortening the polycondensation time.
Domestic and foreign scholars generally believe that the polyester polycondensation reaction is a chain-increasing reaction, and the catalytic mechanism belongs to the chelate coordination. It requires the catalyst metal atom to provide an empty orbit to coordinate with the arc-electron of the carbonyl oxygen to achieve the catalytic purpose. . For the polycondensation reaction, the carbonyl oxygen electron cloud density in the hydroxyethyl ester group is low. Therefore, the electronegativity of the metal ion is relatively higher when the coordination is performed, so as to facilitate coordination and chain extension.
Among the polyester catalysts that can be used are: Li, Na, K, Be, Mg, Ca, Sr, B, A1, Ga, Ge, Sn, Pb, Sb, Bi, Ti, Nb, Cr, Mo, Mn, Fe. oxide Co, Ni, Pd, Pt, Cu, Ag, Zn, Cd, Hg and other metals, alcoholates, carboxylates, borates, halides, and amines, urea, guanidine, sulfur-containing organic compounds. However, at present, the catalysts for industrial production applications and research are mainly three series of compounds of Sb, Ge and Ti. A large number of studies have shown that although the Ge-based catalyst has few side reactions, the quality of PET is high, but the activity is not high, and the resources are small and expensive. The Ti-based catalyst has high activity and fast reaction speed, but its catalytic side reaction is obvious, resulting in products. Poor thermal stability, yellow color, generally only used for the synthesis of PBT, PTT, PCT, etc.; Sb catalyst is not only high activity. Moreover, the product quality is high due to the high activity of the Sb-based catalyst, less side reactions, and lower prices. Therefore, it has been widely used. Wherein, the most widely used Sb-based catalyst is antimony trioxide (Sb 2 O 3), antimony acetate (Sb (CH 3 COO) 3 ) and the like.
Looking at the history of the polyester industry, it can be found that more than 90% of the polyester plants in the world use lanthanide compounds as catalysts. By the year 2000, China has introduced a number of polyester units, all of which are lanthanide compounds, mainly Sb 2 O 3 and Sb (CH 3 COO) 3 . After the joint efforts of China's scientific research, universities and production departments, these two catalysts have all been localized.
Since 1999, Elf Chemical Company of France has introduced a catalyst of ethylene glycol hydrazine [Sb 2 (OCH 2 CH 2 CO) 3 ] as an upgraded product of traditional catalysts. The polyester chips produced by the company have high whiteness and can be The spinning property is good, which has caused the domestic catalyst research units, enterprises and polyester manufacturers to attach great importance.
Development and application of bismuth trioxide
The United States was one of the earliest countries to produce and use Sb 2 O 3 . In 1961, the consumption of Sb 2 O 3 in the United States reached 4,943 tons. In Japan in the 1970s, five companies produced Sb 2 O 3 . The total production capacity is 6,360 tons / year.
The main research unit of domestic Sb 2 O 3 is the Tin Mine Mining Bureau of Lengshui City, Hunan Province. The manufacturers include Hunan Yiyang City Tan Products Factory, Hunan Qijiang County Chemical Plant, and Shanghai Reagent Fourth Plant.
(1) Method for producing dicerium trichloride
Sb 2 O 3 is usually produced by using samarium ore as a raw material, first preparing metal ruthenium, and then using metal ruthenium as a raw material to prepare Sb 2 O 3 .
The Sb 2 O 3 produced from metal ruthenium mainly has a direct oxidation method and a nitrogen solution method.
1. Direct oxidation method
The metal ruthenium reacts with oxygen to form Sb 2 O 3 under heating, and the reaction process is as follows:
4Sb+3O 2 ==2Sb 2 O 3
2. Ammonia solution
The metal ruthenium reacts with chlorine gas to synthesize ruthenium trichloride. After distillation, hydrolysis, aminolysis, washing and drying, the Sb 2 O 3 product is obtained. The basic equation of the reaction is:
2Sb+3Cl 2 ==2SbCl 3
SbCl 3 +H 2 O==SbOCl+2HCl
4SbOCl+H 2 O==Sb 2 O 3 •2SbOCl+2HCl
Sb 2 O 3 •2SbOCl+OH==2Sb 2 O 3 +2NH 4 Cl+H 2 O
(2) Use of dichlorochloride
The main use of antimony trioxide is as a catalyst for polymerase and a flame retardant for synthetic materials.
In the polyester industry, Sb 2 O 3 was first used as a catalyst. Sb 2 O 3 is mainly used as a polycondensation catalyst for the DMT route and the early PTA route, and is generally used in combination with H 3 PO 4 or its enzyme.
(3) Problems with diclosan trichloride
Sb 2 O 3 is less soluble in ethylene glycol, 150. The solubility at C is only 4.04%. Therefore, when the catalyst is prepared by using ethylene glycol, the dispersibility of Sb 2 O 3 is inferior, and it tends to cause excessive local catalyst in the polymerization system to form a cyclic trimer having a high melting point, which is difficult to spin the ribbon. In order to increase the solubility and dispersibility of Sb 2 O 3 in ethylene glycol, an excess of ethylene glycol or an increase in the dissolution temperature to 150 ° C or higher is generally employed. However, above 120 ° C, Sb 2 O 3 and ethylene glycol have a long-term effect, which may cause precipitation of ethylene glycol, and in the polycondensation reaction, Sb 2 O 3 may be reduced to metal ruthenium, which can make poly "Fog" appears in the ester chips and affects product quality.
Second, the development and application of barium acetate
(1) Preparation method of cerium acetate
The earliest use of antimony trioxide and acetic acid to produce yttrium acetate, while using acetic anhydride as a water removal agent to absorb the water formed by the reaction, the quality of the finished product is not high, antimony trioxide dissolved in acetic acid The reaction takes more than 30 hours. Later, the use of metal ruthenium, ruthenium trichloride or antimony trioxide to react with acetic anhydride to prepare yttrium acetate, without the use of water removal agent
1, antimony trichloride method
In 1947, the former West German H. Schmidt et al. reacted SbCl 3 with acetic anhydride to produce Sb(CH 3 COO) 3 with the following reaction formula:
SbCl 3 +3(CH 3 CO) 2 O==Sb(CH 3 COO) 3 +3CH 3 COCl
2, metal 锑 method
In 1954, the former Soviet Union TAPaybea produced Sb(CH 3 COO) 3 by reacting metal ruthenium and peroxyacetyl in a solution of benzene. The reaction formula is:
Sb+(CH 3 COO) 2 ==Sb(CH 3 COO) 3
3, antimony trioxide method
In 1957, the former West Germany F. Nerdel used Sb 2 O 3 to react with acetic anhydride to prepare Sb(CH 3 COO) 3 .
Sb 2 O 3 +3(CH 3 CO) 2 O==2Sb(CH 3 COO) 3
The disadvantage of this method is that the crystals tend to aggregate into large pieces. Firmly adhered to the inner wall of the reactor, the product quality and color are relatively poor.
4, antimony trioxide solvent method
In order to overcome the disadvantages of the above methods, a neutral solvent is usually added during the reaction of Sb 2 O 3 and acetic anhydride, and the specific preparation methods are as follows:
(1) In 1968, R.Thoms of the American Lushan Chemical Company published a patent on the preparation of lanthanum acetate. This patent uses xylene (o-, m-, para-xylene or a mixture thereof) as a neutral solvent to obtain fine-grained crystals of cerium acetate.
(2) In 1973, the Czech Republic invented a production method for preparing fine cerium acetate using toluene as a solvent.
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