A better technology solution: Waste carbon dioxide as a feedstock for performance polyurethanes

Adding renewable content and decreasing carbon footprint, while maintaining high performance, are two factors driving innovation in polyurethane suppliers, observes Dr Scott Allen

Dr Scott Allen is R&D director at Aramco Performance Materials in Houston.
2017 Michael Hart All Rights Reserved
Dr Scott Allen is R&D director at Aramco Performance Materials in Houston.

Chemicals have an impact that is measured in human terms. As energy demand rises with the looming nine-billion population milestone, and as more people aspire to and achieve middle-class status than at any other point in history, consumers seek the products that support a better living standard – but not at the expense of the environment.

More specifically, the market is increasingly demanding products that offer performance yet are more sustainable and renewable. The polyurethane industry is looking for opportunities to achieve this goal: reduce carbon footprint while improving performance, but without impacting production costs.

Wide variety of physical and mechanical properties of polyurethanes
Polyurethanes are a class of polymers that find use in a diverse range of applications due to their versatility and high performance. They are produced through the chain extension polymerisation between a polyol and an isocyanate. Polyols are low-molecular-weight polymers with hydroxyl functionality with typical values ranging from two to six hydroxyl groups per polyol.

Research and development building at Saudi Aramco.

Isocyanates are a class of compounds that react rapidly with polyols and do not generate by-products in that reaction. The polyol component of the polyurethane can be selected from many different polymer classes, including polyethers, polyesters, polycarbonates, polyolefins, and acrylics.

Because of the many types of polyols and isocyanates available, polyurethane manufacturers can formulate products that achieve a wide variety of physical and mechanical properties ranging from soft and flexible to tough and rigid.

Substituting the polyol component of the polyurethane with a polyol containing renewable, or recycled content is one area that has received a great deal of attention. In fact, new and beneficial applications for waste carbon dioxide are among the most exciting solutions to the climate-change challenge.

However, in many cases, substituting a traditional polyol with one containing renewable, or recycled content fails to provide adequate performance relative to the benchmarks. This drawback, in turn, limits the use of these polyols.

Converge polyol technology
Saudi Aramco is addressing this market incentive with a major complement to its growing chemicals portfolio: the ‘Converge’ polyol technology line using CO2 as a feedstock for next-generation polyurethane.

We are commercialising this innovative and transformative technology that combines waste carbon dioxide (CO2) with a hydrocarbon feedstock to create high-performance polyols. These polyols, under the tradename Converge, are initially finding use in many everyday applications such as Coatings, Adhesives, Sealants and Elastomers, a specialty polyurethane market segment with the acronym ‘CASE’.

Converge vs. specialty polyester.

The key is a proprietary catalyst that copolymerises CO2 with epoxides to generate polycarbonate polyols. The catalyst promotes the alternating copolymerisation between epoxides and CO2 to provide polyols with a substantial weight fraction of waste CO2 locked into the polyol structure, permanently trapping the greenhouse gas in the polyol backbone.

When propylene oxide is used in the polymerisation, polypropylene carbonate (PPC) is the product, which contains up to 42 wt% CO2. Another performance advantage of the Saudi Aramco catalyst is its high selectivity for alternating copolymerisation, providing polyols with a perfectly repeating unit that is 100% polycarbonate.

Polycarbonate polyols are known to have superior performance in many CASE products, particularly when polyurethanes with high abrasion resistance, high chemical resistance, and outdoor durability are required. The Converge epoxide/CO2 polycarbonate polyols are no exception, and performance advantages are observed in many CASE applications.

Coating formulations using Converge polyols show improved abrasion and environmental resistance. In adhesives, Converge polyols offer improved bond strength with a variety of substrates as well as improved green strength. In elastomers, the incorporation of Converge polyols provides improved tensile and tear properties as well as improved hydrolytic resistance.

In the specialties segment, Converge polyols offer a number of benefits. In electronic and ceramic applications, the polyols offer extremely clean burn-off at a low, tunable temperature with non-toxic by-products. In composites, Converge polyols improve both durability and compressive strength.

Excellent tool for formulators
Converge polyols are also an excellent tool for formulators in that they are compatible with conventional polyether and polyester polyols, allowing for a greater degree of flexibility for polyurethane manufacturers looking to enhance product properties.

Converge polyols combine greenhouse-gas CO2 with hydrocarbon feedstocks to create sustainable, high-value end-products with major improvements in performance, cost, and carbon footprint. Converge is a registered trademark of Aramco Performance Materials.

Polyether formulations incorporating Converge polyols exhibit improved tensile strength, toughness, and abrasion resistance in a number of CASE applications. When combined with polyesters, Converge polyols can bolster hydrolytic resistance.

In addition to the performance advantages, Converge polycarbonate polyols provide a lower CO2 footprint compared with other resins and polyols. The benefit of using CO2 as a feedstock is two-fold: first, incorporating CO2 directly into the polyol molecule uses a waste product as a key raw material; and secondly, the CO2 incorporated into the polyol displaces a petroleum feedstock.

In order to produce one kilogram of polyether polyol, one kilogram of epoxide (a petrochemical feedstock) is required. However, the same kilogram of epoxide can produce as much as 1.75kg of Converge polyol – nearly double the amount – greatly reducing the consumption of petroleum resources.

There is a general perception in the polyurethane industry that in order to incorporate polyols with renewable content, a compromise on performance is expected. The incorporation of Converge polyols into various applications has shown that this compromise is no longer necessary and that competitive, or superior properties can be achieved at attractive economics.

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