Polymerization in Presence of Hydrogen
Publication Date: 2011-Aug-16
The IP.com Prior Art Database
Polytetramethylene ether glycol (PTMEG, PTME, PolyTHF, PTG) is an important intermediate for the production of spandex fibres and can be produced via polymerisation of THF in presence of oleum or fluorosulfuric acid (e.g. US 3,358,042, US 4569990)but work-up of the resulting PTMEG is difficult and gives significant amount of waste.
In more environmentally friendly process, tetrahydrofuran (THF) is polymerized in presence of heteropolyacids yielding directly the desired diol. However, the high cost of heteropolyacids and the need of its complete removal from the polymer are disadvantageous.
Yet another process includes polymerisation of THF in presence of solid acidic catalysts like acid-activated clays (e.g. US 5218141, EP 104609, US 5262562, EP 2006069095, US 6274700, US 6362312, or WO 2004/030811), metal oxides on carriers (e.g. JP 11269261, JP 2003135958 and JP 2000327770), or strong acidic ion exchange resins (e.g. WO97/21755). Acetic acid anhydride is normally used as a molecular weight control agent for the process in order to adjust the molecular weight of the polymer. The resulted diacetate (PTMEA) is than subjected to a base-catalyzed transesterefication to yield pure polytetramethylene glycol.
The latter process has normally a drawback that the PTMEA has to be subjected to hydrogenation in a separate step in order to decrease the colour number of the PTMEG (e.g. DE 10040091, US 4480124).
Another drawback of the process could be the limited life time of the polymerisation catalyst because it could be deactivated by unsaturated impurities in starting THF monomer. A possible solution of this problem is use of hydrogenated THF as described, e.g. in WO 2003099905 . However, this leads to introduction of expensive additional hydrogenation step and may still require further hydrogenation of the polymer obtained.
Several pathways to lower the colour number of the PTMEG have been described.
For example, US 4480124 describes decolouring hydrogenation process for PTMEG over Ni, Co, Cu, Fe, Ru, Pd, Pt catalysts in e.g. fixed bed
US 5112943 describes improved decolouring hydrogenation process for polymers and copolymers of THF, in which hydrogen with a bubble diameter of less than 50 microns (10 microns) is passed into hydrogenation system
US6069226 claims polymerisation of THF using activated synthetic kaolin, zeolites or amorphous aluminium silicates in the presence of from 1 to 10% by weight of a hydrogenation catalyst under hydrogen atmosphere for improving the quality of PTMEG. The hydrogenation catalyst was added to the pre-shaped polymerisation catalyst to afford after polymerisation a polymer solution containing 53% of PTMEA. The benefit of the catalysts described in US6069226 is absence of the need to subject the THF to pre-treatment with highly acidic substances, as was unavoidable, according to authors, when bleaching earth is used as a catalyst. Another benefit, according to authors, was a v...