Thermaquatica has developed and patented a simple and inherently environmentally friendly technology called Oxidative Hydrothermal Dissolution (OHD) for the conversion of low value complex macromolecular feedstocks into high value low molecular weight products.
What is OHD?
OHD works by taking advantage of the unique properties of water at elevated temperatures and pressures and the propensity of many natural and synthetic organic materials to spontaneously oxidize when exposed to oxygen and water. The solid feed (for example: coal, biomass, or virtually any other solid organic material) is crushed and mixed with water to form a slurry which is them pressurized and heated. Small amounts of dissolved oxygen are introduced and allowed to react with the solid. No exotic catalysts or other solvents are required. The entire process requires only water, oxygen, and the right set of conditions (Figure 1). The process uses an oxidative, rather than a reductive step. This means carbon is not rejected, as with other similar processes, and a hydrogen/methane supply isn’t required. By using small amounts of oxygen in water, we can readily achieve 100% conversion of the organic feed, most of which is recoverable as low molecular weight, water soluble products. At a molecular level, the oxygen attacks the most reactive structures first, effectively and selectively breaking apart the structure and directly producing low molecular weight products. By controlling the amount of oxygen, the contact time, and other variables, the extent of reaction can be controlled. For most feeds, essentially complete conversion of the initial feed with recovery of high yields of low molecular weight products can be readily achieved with relatively short contact times (for most materials, reaction times are of the order of a few 10s of seconds).
The nature and complexity of the products obtained depends primarily on the nature of the initial feed (biomass gives a different suite of products than coal, for example) and to some extent can be tailored by optimization of key process parameters. OHD produces very little CO₂, and no gaseous nitrogen or sulfur oxides. The initial raw product, known as “liquor”, is an aqueous solution of the low molecular weight products produced by OHD. Depending on the nature of the products, and the goals of the operator, individual high value products can be isolated from the liquor, or the solubilized organics can be handled as a mixture that can be further processed into fuels or other materials.
Figure 1. Schematic diagram of the OHD process.
You can read more about Thermaquatica’s facilities and the OHD downstream Process Flow Diagram (PFD) in the sub-tab of the Technology menu selection above.
Thermaquatica has successfully demonstrated OHD, for a wide variety of feeds, at both the laboratory scale and small engineering scale (up to 5 kg/h feed) via our Process Development Unit (PDU) as a scale-up step. The PDU has already been successfully operated with excellent results for a small number of feeds and testing of additional feedstocks is planned for the near future. Thermaquatica has also signed an agreement with Australian energy producer Greenpower, to complete development work necessary for the design of a 20 tonne per day demonstration facility using Victorian Brown Coal (VBC) as feedstock in Australia. The proposed plant will operate continuously, using commercial-scale equipment and industrially-sourced VBC.
As part of this process, Impact Technology Development, a chemical engineering consulting firm located in Devens, MA, conducted a technology assessment including mass/energy balances, a techno-economic analysis, and technology GAP analysis for both a 20 tonne per day, as well as a 1,000 tonne per day commercial OHD demonstration facility, using Victorian Brown Coal (VBC) as feed.