The antimony catalyst refers to an elemental antimony or antimony compound which has a catalytic function. Antimony belongs to the main group V element. Because it is at the boundary between the metal and the non-metal of the periodic table, the lanthanum element is metallic and non-metallic at the same time. Antimony often exists in the form of zero valence, positive trivalent, and positive valence, and most of the most common and stable ruthenium catalysts are positive trivalent. For example, ruthenium oxides such as antimony trioxide, antimony acetate and ethylene glycol antimony are all trivalent. Compared with the main group metal elements, the coordination ability of the antimony element is stronger. Based on the above properties, an antimony catalyst with novel structure and special properties can be selectively constructed and used for the synthesis of polyester.
Figure 1. Antimony catalyst
The use of antimony catalysts in organic synthesis reactions is relatively rare and has only been reported in the synthesis of polyesters. The production of polyester can be divided into dimethyl terephthalate (DMT) route and terephthalic acid (PTA) route from the process route. In the polyester industry, Sb-based catalysts have been widely used due to their high activity, low side reactions, low price, and high quality of the products obtained. Among them, the most commonly used catalysts are antimony trioxide (Sb2O3), antimony acetate (Sb (CH3COO)3) and antimony glycol oxime (Sb2(OCH2CH2CO)3). Antimony trioxide is the earliest used antimony catalyst. Antimony trioxide is mainly used as a polycondensation catalyst for DMT route and early PTA route in polyester synthesis, and is generally used in combination with H3PO4. Antimony acetate has the characteristics of high catalytic activity, less degradation reaction, good heat resistance and processing stability, and good dissolving and dispersing in ethylene glycol. At the same time, Antimony acetate is used as a single polycondensation catalyst for the PTA route without cocatalyst and a stabilizer. Antimony glycol oxime is a new ruthenium catalyst and is mainly used in the PTA route.