PLA-production process – Commercial debut for a new PLA-production process - Archive

To reduce dependency on petroleum-based plastics, thyssenkrupp Industrial Solutions AG (Essen, Germany; www.thyssenkrupp-industrial-solutions.com) has developed a new manufacturing process for producing the biopolymer polylactide (PLA).

The company is now building the first commercial plant based on its patented PLA neo technology in Changchun, China, for COFCO Corp. (Beijing, China; www.cofcoagri.com).

The new plant will produce around 10,000 metric tons per year (m.t./yr) of PLA, and is scheduled for commissioning in the first quarter of 2018.

In the PLA neo process (flowsheet), lactic acid (LA) is first concentrated to remove residual water. PLA-production process

The monomer lactide is then purified by a patented distillation technology, using dividing-wall columns. PLA-production process

The subsequent ring-opening polymerization takes place using a combination of a continuous stirred-tank reactor (CSTR) and an efficient plug-flow reactor.

Before pelletizing, the polymer melt is stabilized and the remaining lactide removed.

A very low residual monomer content is achieved due to Uhde Inventa-Fischer’s (UIF; a subsidiary of thyssenkrupp; Berlin) proprietary PLA stabilization technology, combined with UIF’S unique one-step demonomerization technology.

Because feedstock costs have a large impact on production costs, the efficient conversion is an important factor, explains Udo Mühlbauer, product manager PLA at UIF.

With PLA neo, the conversion of LA to PLA is close to the theoretical maximum, thanks to the purification and polymerization techniques for handling the side product meso-lactide, says Mühlbauer.

Normally meso-lactide has to be separated and hydrolyzed back to LA, thus reducing the overall efficiency and increasing the feedstock-conversion costs.

In the PLA neo process, meso-lactide is polymerized and blended with standard, crystalline PLA, without affecting the properties of the PLA product, he says.

UIF first developed the PLA neo process in a miniplant in Berlin in 2005, and in 2011 subsequently started up a 500-m.t./yr pilot plant in Guben, Germany.

Data gathered from the pilot plant enables UIF to license its PLA process for industrial plants with capacities up to 100,000 m.t./yr.

Because the first commercial plant in China will use lactide (the cyclic dimer of LA) as raw material, only the ring-opening part of PLA neo— with the CSTR, plug-flow reactor and demonomerization unit — will be built, says Mühlbauer.

However, PLA neo can also be fully integrated with the LA process developed by thyssenkrupp Industrial Solutions ( Chem. Eng., July 2009, p. 13; www.chemengonline.com/a-gypsum-free-energy-saving-route-to-lactic-acid), whereby LA is produced by the fermentation of glucose or sucrose.