SSP Processes

Titanium catalysts have long had a reputation for excellent melt phase reactivity coupled with poor solid state polymerisation (SSP) performance. Until now SSP rate reductions from 30-70% have been found, which is unacceptable to even the most forgiving polyester producer. Even if rate reduction is tolerated then the low thermal stability of the Ti-PET means that it cannot be successfully processed into an article of acceptable quality.

Following the launch of Catalytic Technologies Limited’s brand new and unique catalyst CTL Ti638 UP there is now a genuine alternative for polyester producers to manufacture high quality, high IV Ti-PET by conventional SSP processes. While some slight recipe modification may be required, the manufacturing process can be optimised to produce improved quality Ti-PET without a compromise on SSP rate.

To maximise SSP rates it is important to utilise the correct amount of CTL Ti638 UP with a phosphonic acid based stabiliser, e.g. triethylphosphonoacetate (TEPA, CAS# 867-13-0). To match the CP and SSP rates of 250 ppm Sb CTL recommends 10 ppm Ti (200 ppm Ti638 UP) with 19 ppm P (138 ppm from TEPA) in the final polymer. Care must be taken to consider any volatile TEPA in the glycol recycle loop and to ensure that alternative P sources such as phosphoric acid (PA) and triethylphosphate (TEP) are avoided.

TEPA is listed on the European Union Plastics Implementation Measure approved Union list for food contact and while cost is typically slightly higher than for PA and TEP, PET manufacturers can expect to enjoy cost savings in:

– Ethylene glycol efficiency

CTL Ti638 UP generates far less acetaldehyde during the production process than antimony catalysts (up to 7x less). This AA is formed directly from ethylene glycol and leads to expensive losses.

– Isophthalic acid acid reduction/elimination

Isophthalic acid (IPA) costs typically 1.5x that of terephthalic acid but is required in the PET production process to minimise the crystallinity of Sb-PET for lower energy PET resin processing. CTL Ti638 UP naturally produces much lower crystallinity Ti-PET (5% absolute value) than for corresponding Sb-PET under the same production conditions. PET producers can take advantage of this lower crystallinity by reducing or even eliminating the use of IPA entirely.

– Prolonged filter life times and longer campaigns between shut downs

CTL Ti638 UP is a highly stable catalyst added at very low metal addition levels. As the particulate level in both the process and polymer is so low the build-up over time reflects this and limits plant and filter fouling.

– Elimination of the need to dissolve solid antimony catalysts in glycol

As CTL Ti638 UP is a low viscosity, free flowing liquid that is completely miscible with ethylene glycol, the rapid and accurate dilution of the catalyst for process injection is both straight forward and low cost.

These cost savings are offered on top of the wide ranging polyester resin and article properties that highly stable Ti-PET produced with CTL Ti638 UP can offer. Full details of the key features of CTL Ti638 UP can be found here: Key features of Ti638UP PET