Terephthalic acid alternative production routes

An alternative route to PET is by the direct reaction of terephthalic acid and ethylene oxide. The product bis(2-hydroxyethyl)terephthalate reacts in a second step with TPA to form a dimer and ethylene glycol, which is released under reduced pressure at approximately 300°C. 

Toluene also provides an alternative source for the manufacture of the xylene isomers, especially /uxylene. The last two products provide routes respectively to terephthalic acid and /uxylene without the need for an isomer separation, a very appealing use for toluene that is often in excess supply, unlike the xylene isomers. 

Initially, the development of fibers based on terephthalic acid met with extraordinary difficulties. Terephthalic add is a white powder, which is virtually insoluble in almost all solvents, does not melt and cannot be distilled. These properties render refining of crude terephthalic acid very intricate. Since high purity of the monomer feedstock material is an absolute necessity for the production of synthetic fibers, an alternative purification route via the dimethyl ester was developed. Dimethyl terephthalate (DMT) is a crystallizable substance which can also be distilled it is therefore relatively easy to produce in pure form. 

The alkylation of toluene with methanol has been investigated for many years as a potential alternative route to / - Qflene, ethylbenzene, and styrene. Conventional / -xylene production from petroleum reformate requires costly purification and separation from jQ lene isomers and other aromatics. A process that selectively produces /)-xylene could have a significant commercial impact by eliminating the need for p-xylene separation. Furthermore, styrene or ethylbenzene production from methanol and toluene is desired as part of the development of processes based on Cl feedstocks rather than ethylene or propylene feedstocks [48], Para- xyl ae is used primarily in terephthalic acid production, a major component of polyester manufacture. 

---