Reaction & Synthesis

Supercritical Process Reaches Critical Stage

The technology converts low-value feedstocks that would otherwise be landfilled into valuable fuels and chemicals.

By Chemical Processing Staff

Construction soon will start on the first commercial plant to use catalytic hydrothermal reactor (Cat-HTR) technology from Licella, North Sydney, Australia. The Wilton, U.K., facility will take advantage of ten years and Aus$75 million (U.S. $54 million) in development work on the process.

The technology, which relies on water at or near supercritical temperatures and pressures for its action, converts low-value feedstocks such as biomass residues and end-of-life plastics that would otherwise be landfilled or incinerated into valuable fuels and chemicals (Figure 1). It exemplifies the increasing interest in using supercritical water to improve sustainability (see “Is Supercritical Water the Green Future of Chemical Processing?”).

Licella is collaborating with ReNew ELP, Redcar, U.K., on construction of the plant and with Armstrong Energy, London, on financing. Neste, Helsinki, Finland, recently joined as an advisor on technology and regulatory issues.

The process begins with converting feedstock into a powder and then mixing that with water to create a slurry. This then goes to a high-pressure reactor (typically above 22 MPa, according to the literature), where it is heated to around 400°C; water hydrolyzes the biomass while oxygen is removed as carbon dioxide. The final product incorporates some of the hydrogen released by the water — an important point because this avoids the cost and complexity of an external hydrogen supply.

The process lasts 20 minutes. Then, products are released, byproducts separated out and waste heat recycled.

“The advantages of Cat-HTR over other processes that try to do a similar thing, for example pyrolysis, are that the product is stable, i.e., shippable, non-acidic, and compatible immediately with fossil fuel refineries. That’s the breakthrough,” says Licella CEO and technology co-inventor Len Humphreys.

Other advantages he points to include easy scaleup of the modular process design and no need for dry raw materials.

The Wilton plant has planning consent for four process lines, each capable of handling 20,000 metric tons/yr of waste plastic, according to ReNew ELP business development manager Andrew Buchanan.

“Initially, ReNew ELP is focusing all design efforts on one line. Construction of this is due to commence in 2019 and the site will be operational in early 2020,” he adds.

The ten-year development process has progressed from laboratory scale through three further iterations to large pilot-plant scale, which is the size planned for the first line at Wilton “The process has been proven at each scale and therefore could be reproduced at smaller scale if necessary. This would likely be for the trialling of alternative feedstocks,” Buchanan explains.