Sulzer Chemtech's Alex Battù: "PLA perfectly complements the polymers that are already available on the market"

PLA has been a focus at Sulzer Chemtech for many years – even before the current surge of interest in ‘green’ solutions. Sustainable Plastics talked with Alex Battù, sales manager of the PLA team at the company, about the challenges involved in building systems to produce this bioplastic, compared to conventional materials.

So, starting with the obvious question - when and why did the company decide to become involved in PLA?

In recent years, PLA has gained significant market attention, with several large brand owners announcing evaluation of this material or even launching new solutions based on PLA as a sustainable alternative to existing fossil-based plastics in packaging, compounding and thermoplastic applications.

Sulzer has developed, firstly thanks to its work in the lab and then in the pilot plants, a flexible and robust technology to enable PLA producers to enter into the biopolymer market at customizable scale with various PLA grades, from low to high molecular weights, and various L/D contents.

We have been involved in developing the technology for over 25 years. Our process has been scaled-up from lab scale bench tests and extensive pilot testing, to large production capacities and it is nowadays state-of-the-art in PLA technology, ensuring stable operation, fast control and short residence time.

Thanks to our engineering and assembly capabilities, we develop and execute entire projects, from the first concept to an industrial scale plant using in house engineering, equipment, assembly, commissioning & start-up capabilities. The test centre makes it possible to carry out laboratory and pilot scale trials in order to validate the process for specific client requests.

Our company has also developed innovative key equipment as part of its PLA production offering, such as falling film crystallizers, loop and plug-flow reactors (SMXTM), Sulzer Mixer Reactors (SMRTM) distillation and degassing technologies, all of which are already well-established members of its technology portfolio.

We also design and implement equipment and integrated modular solutions for individual steps of the polymerization process. We offer several additional services to ensure that customers in the agricultural, chemical and fibre sectors can continuously benefit from their integrated PLA technology.

You said that PLA is generating an increasing amount of attention in the market. But what is PLA, exactly? What kind of feedstock is used today, and what will this be in the future? Can you give examples of some applications?

PLA is a versatile, bio-based and biodegradable polymer that can replace petroleum-based plastics in a wide range of applications. The technology we developed is feedstock agnostic. This means that process industries around the globe can use the local plant-based resources available  to produce the necessary sugars. This possibility allows users to maximize the process’s cost-effectiveness, and the reliability of the supply chain, while minimizing the carbon footprint for raw material transportation. For example, sugar cane and its bagasse can be chosen as the raw material for PLA production in equatorial regions, while straw, corn or wood chips can be the most suitable options in moderate temperature zones.

Although I should point out: our technology starts from sugar. The development of second generation feedstock - extracting sugar from lignocellulosic feedstocks - is not our core business, but is an upstream activity.  Give us the sugar and we can make PLA.

PLA can be used in many applications: thermoformed products, fibres and non-woven materials, films or moulding. It performs like traditional polymers — such as PET and nylon 6 — and it can be processed in casts made by blown film machines. It can be spun into fibre on conventional extruders. All these exceptional properties make PLA not only suitable for packaging, medical devices and implants, as well as electronic devices, but also for textiles, 3D printing processes and components for the automotive sector. And the possibility to produce PLA composites, such as foamed PLA, further expands the range of applications for this bioplastic.

You explained how long Sulzer has been working on the development of the technology  - but was some kind of PLA production technology already available or did you start from scratch? And how efficient is your technology? Do you have competitors?

As mentioned, since the early 2000s, Sulzer has been involved in the PLA activities. We developed our PLA polymerisation technology in testing facilities where we tested mixing effects, heat transfer, polymerisation reactions and devolatilisation in order to secure reliable equipment design and the desired process performance.

Individual key equipment and pilot plant subsystems make it possible to tailor pilot configurations to very specific requirements. We built the first lab scale PLA pilot in test facilities to control and refine the most important parameters, such as the effect of polymer viscosity on mixing, hydraulic behaviour of the various chemicals, reaction kinetics and related residence time, etc.

Once we validated the main parameters, Sulzer built a 1,000 t/y PLA demo plant in Switzerland to confirm what had been studied and developed in the small-scale lab plant. The demo plant allowed us to fine-tune the technology and increase the yield up to 95% - 98%, which is what it is currently offered industrially.

Competitors? Not very many, mainly because both the product and the process are relatively new. and the Sulzer process is a new highly efficient and patent protected way of polymerisation. Initially, we faced some competition from China, but that disappeared quite quickly. There is a German company with whom we are in a kind of technological competition: they have developed PLA technology but are not yet on the market at the industrial level. Competition, though, is not a bad thing!

Do the different kinds of PLA  require different technologies?

One of the main benefits of the Sulzer technology is that with the same plant hardware, the properties of the polymer can be adapted easily, with no need for different process lines. With the Sulzer technology, the monomer ratio and the molecular weight of the PLA can be set precisely according to the requirements of the market applications.

This flexibility of the process lines is important because the specific setting influences the speed of biodegradability of PLA-based products. The biodegradability is controlled by adjusting the relative amounts of D- and L-lactides. In fact, PLA polymers with high amounts of D-isomer are easily bio compostable, so suitable for disposable applications; PLA polymers with high amounts of L-lactides are less biodegradable, so suitable for durables such as electronic components or car parts. Thanks to Sulzer’s smart process and its precise control, the amount of L- and D-lactides in the PLA pellets can be easily adjusted.

What are the challenges in PLA production?

The most important factor for good polymerisation is that the process temperature is maintained at a controlled level and that the feed material is thoroughly mixed. This is more difficult in conventional polymerisation, where the dimerization process and polymer reaction take place in a continuously stirred tank.

Sulzer’s mixer reactors combine these two processes: mixing and heating or cooling. These reactors have a smaller diameter than the tank and provide uniform temperature distribution. The tubes inside the mixer heat exchanger are filled with a transfer media, depending on the application, and allow a regular temperature transfer. The transfer tubes have a special shape which ensures the material passing through the reactor is well mixed and homogenized. Because the mixer reactors are properly arranged, continuous material flow is possible, and uniform polymerization can be achieved. The process control system monitors the main process parameters to guarantee the polymer final specifications.

Another important parameter to be controlled is the residual monomer content of the final PLA product. Our devolatilisation technology is used to strip the monomer from the PLA melt to achieve a high quality material. Degassing occurs quickly; the material does not stay in the vessel for a long time. This is important because a long dwell time increases the yellowness of the material or degradation of the polymers.

What are the capacities of the plants you build?

Our PLA technology was developed in Switzerland, at our R&D centre, and most of the activities have been focused on the plant optimisations and production in order to better convert the lactides into PLA. But we also can prepare the scale up activities for industrial plants - the results of the pilot plant constitute the basis for the design of the big-scale facilities up to 100,000 t/y PLA throughput.

Specialized and highly qualified teams perform extensive laboratory and pilot testing and propose a customized design that meets the plant and manufacturing requirements. In this way, one of the world’s top two PLA manufacturers has built a large plant in Thailand to produce 75,000 tons per year of PLA plastics including heat-resistant PLA composites, for a wide range of applications using Sulzer’s technology. Other than that, other plants have been built in The Netherlands – 5,000 t/y PLA and in China with capacities of 10,000 t/y and 30,000 t/y respectively.

Has the technology evolved over the years?

The process of converting sugar into PLA plastic involves several steps. First, sugar is fermented with robust and efficient non-genetically modified microbial strains to generate lactic acid (LA). The monomer lactide is obtained from this and then polymerized.

The reactors, thanks to their flexible operating conditions, help to remove by-products and maximize the yield. The lactide is then purified with Sulzer distillation and crystallization equipment before being polymerized. After being fed to a series of loop and plug-flow reactors, the lactide is converted to PLA. Thanks to the proprietary devolatilisation equipment of Sulzer, the remaining volatile components are separated by degassing the PLA melt. Depending on the final product application, the final mixer is used to add colour or additives / masterbatches to the melt. As the last step, PLA is converted into solid pellets in order to be transported or stored.

All the partners at the respective R&D centres are continuously, working to evolve this technology, with more efficient solutions and stream integrations, to improve the overall yield of the plant and provide best in class, up-to-date technology to clients.

What is the PLAnet venture? How did this venture happen – how did you pick your partners?

Basically, PLAnet offers the possibility of a “one-stop shop” for customers interested in PLA production by providing a single point of contact and responsibility. PLAnet is a partnership between 3 best-in-class companies who joined together in response to the lack of industrial seamless and integrated solutions for the production of PLA from sugars. Futerro is a well-established technology provider for lactic acid and lactide production, and TechnipFMC is a leading global EPC contractor with experience in technology development and licensing with fast growing activities in bioplastics and green chemicals.

Together, Sulzer Chemtech AG, Futerro SA and TechnipFMC license and supply the “PLAnet” sugar to PLA integrated technology package with licensing, sales and business development structures on bio-based chemistry and its related polymers. Futerro’s proprietary technology focuses on the production of lactic acid and raw lactide from sugar or, directly, from biomass; Sulzer contributes the process for the purification of lactide and its proprietary polymerization process to obtain PLA, while TechnipFMC acts as technology engineering integrator to deliver seamless and optimized Front-End Engineering Design (FEED) packages.

The set-up of PLAnet enables the production of all the different commercial grades of PLA, starting from sugars with process technology, design and equipment know-how fully developed and with firm industrial partners. The agreement between the three parties offers to agricultural, chemical and fibre industries, a fully integrated package addressing the whole PLA value chain. In this way, customers can benefit from direct access to state-of-the-art, customizable solutions for all the aspects and stages of PLA production.

Next to PLA, have you developed other technologies for renewably-sourced materials?

Sulzer has been very active in the field of bio-based products for more than 40 years. For the oleochemical market, we have a large installed base of efficient fractional distillation plants for fatty acids, alcohol and esters. We sell technologies to upgrade crude glycerin from bio-diesel or fatty acid plant to pharmaceutical grade and to propylene glycol. We introduced also our newly hydrogenated vegetable oil (HVO) to green diesel technology, named Bioflux, a month ago. On the bio-ethanol market, we are active in the concentration and dehydration of 1G and 2G ethanol from various feedstocks. Last but not least, we will be bringing novel bio-polymers and polymer recycling solutions on the market in the next years.

What do you consider the best end-of-life solution for PLA?

Unlike most petroleum-based plastics, PLA offers a true ‘cradle-to-cradle’ loop as PLA can be completely converted back into its fundamental building block, lactic acid. Once collected, PLA can be treated and be recycled back to its monomer form without losing the recycled PLA final properties. This recycling loop is one of the key benefits in the production of PLA.

Mechanical recycling is also possible. However, the amount of PLA in the market was, and is, small compared to, for example, PET. Yet, as these amounts rise, new sorting technologies are being explored that I am convinced will make mechanical recycling of PLA more feasible.

How has the Green Deal affected demand for PLA? Will demand continue to grow in the future?

Thanks to the growing awareness about waste, recyclability and sustainability, the plastics industry is looking for improved recycling processes and alternative materials to petroleum-based plastics. The Green Deal has a fundamental and important role in helping to increase such awareness.

As a biopolymer, PLA has a renewable origin, many end-of-life management possibilities and special properties. It perfectly complements the polymers that are already available on the market. Its recyclability, environmental benefits and cost of production competitiveness make PLA one of the fastest growing polymers, with a growth rate between 5% and 20% per year, depending on the region in the world.

What about the pandemic – has Sulzer been impacted?

Of course, we have also felt the effects of the corononavirus outbreak. While many projects have been put on hold or postponed, the majority have been delayed, not cancelled. We still have a lot of good projects in the pipeline.

Plus, the virus has, in a way, been good for PLA. It can be used, for example, to make face masks, which are of course, in huge demand. And I believe this new use of PLA for textile purposes, instead of just in packaging or for food trays, will open the door to more of these applications, significantly boosting PLA demand.

I think PLA will play an important role in the future, even maybe replacing PET or other polyesters in blends with other materials. Good blends are PLA and cotton, or PLA and wool, because they have similar properties. I really see textile as a promising future market for PLA.