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The new plant, located near Montreal, Canada, is operated by PTT Poly Canada, a joint venture between Shell Chemicals Canada and SGF Chimie. It has a capacity of 95,000 tonnes per year, is the world's first large scale continuous plant to commercially produce PTT thermoplastic, and uses proprietary technology developed by Shell and Zimmer AG.

PTT, which is marketed under the Shell Chemicals trade name CORTERRA* Polymers, is a polymer derived from 1,3-propanediol (PDO) and terephthalic acid. It is part of the polyester family but has a different chemical and molecular structure to other polyesters such as PET.

Inherent resiliency

PTT can be processed into fibre or yarn, which are then converted into carpet or textile applications. The molecular structure of PTT gives it inherent resiliency and stain-resistant characteristics that are key to these end uses.

The Shell-licensed technology behind the new plant was developed at Shell Global Solution's Westhollow Technology Center in conjunction with Frankfurt-based Zimmer, a leader in the design and construction of polyester plants.

Stan Park, PDO/CORTERRA General Manager, says Zimmer had been an excellent partner in developing, engineering and constructing the plant. "Zimmer was chosen because of its leadership position in PET technology. Working together made the development of this world-class process possible.

"The first commercial plant employing the Shell-Zimmer PTT process has delivered the designed product quality."

Development of the PTT process was the result of extensive laboratory studies and pilot plant trials. "It took years of studying the chemistry, and its relationship to the polymer properties, to go from what was initially created as a small-scale batch process to the continuous, all-melt process required for a commercial plant," says Betty Scardino, PDO/CORTERRA Quality Assurance Manager. "It had never been done before so there was nothing to copy or follow. There were a lot of theoretical studies even before we tested the process on any hardware," she says.

One of the major considerations when designing a process that would produce consistent high quality PTT was that its reaction kinetics are significantly different from other polyesters. "You have to balance the reaction carefully, with the optimum levels of heat, vacuum and catalyst, to achieve a consistent molecular weight," she says.

Following initial tests in lab-scale equipment, the continuous process underwent extensive trials on a Zimmer pilot plant in Germany. These trials were used to finalise the design parameters of the full-scale plant, and highlighted some hurdles that had to be overcome in order to successfully adapt the process for commercial production.

Bob Blackbourn, a Research Chemist involved in the development programme, explains: "On the face of it the PTT process appears to be very similar to the PET (poly-ethylene terephthalate) process but there are a number of detailed technical differences, including reaction kinetics, that had to be taken into consideration.

"We had to develop modifications that have never been employed on a conventional PET plant. They effectively make it a more robust unit."

Major modifications

One of the major modifications involved the way the majority of the PDO feedstock is fed into the plant. "It's designed to purge unwanted solid deposits which could otherwise cause fouling of some critical plant components and result in unreliable operation," he says.

Advanced pollution and emissions control equipment has also been installed in the plant. The PTT is produced in an inert environment, avoiding contamination from oxygen, and all equipment and connections are impermeable to minimise emissions.

Water generated from the process is treated with a bio-oxidation process while vents from the plant are contained and purified using a catalytic treatment process. Now proven, the Shell-Zimmer PTT manufacturing technology can be licensed to other companies.

Current demand for PTT is estimated at around 30,000 tonnes per year, and the market is growing by 50% a year.

The principal markets are the carpet industry in the US, although carpet and textile production in Europe and Asia-Pacific is gathering pace. Global demand is expected to jump to over one million tonnes in ten years.

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Service status
The personal touch
Fuel for thought
Relax in the new look Lounge
Latin partners
Close relations
Filling to capacity
Vapour trail
Getting on with the neighbours