Thermaquatica has designed and constructed three OHD reactor systems, and regularly uses these in research activities in Carbondale, IL. Two laboratory-scale microreactors are used for determining feed behavior and establishing basic OHD parameters such as temperature and oxidant loading. The semi-continuous system, which typically uses a 40mg sample size, allows oxidant flow to be delivered either continuously or as timed pulses, while a micro-scale continuous system allows for gram scale samples to be subjected to OHD where feed and oxidant are continuously delivered as two separate, continuous feed streams. A larger, small engineering scale fully instrumented Process Development Unit (PDU), with a slurry feed stream of up to 5 kg/h, was designed and constructed to maintain steady-state control over all important variables, including pressure, temperature, mass flow rates, residence time, and mixing. The PDU, shown in Figure 1, is used for process refinement studies, larger volume product generation, and the investigation of overall process economics.
Figure 1. Small engineering scale, fully instrumented Process Development Unit (PDU, up to 5 kg/h feed) in Thermaquatica’s laboratory in Carbondale, Illinois.
Because the OHD process produces a mixture of water-soluble products, the company has developed a novel downstream process to recover the bio-based chemicals as saleable products. A simplified Process Flow Diagram (PFD) is shown in Figure 1, which includes both unique (and proprietary) technology, as well as applications of commercially existing technology, for which extensive operational experience and data are readily available.
Figure 2. Simplified Downstream Process Flow Diagram (PFD).
Five unit operations (Unit Ops) can be identified in the PFD:
- Feed Preparation,
- OHD Reactor,
- Primary Dewatering,
- Solvent Exchange, and
- Chemicals Recovery.
The PDU in Thermaquatica’s laboratory integrates Unit Ops 1 and 2. A proprietary technology has been developed by Thermaquatica (patent in progress) for Unit Op 4, in which the residual water is replaced with an alcohol (usually methanol), and requires neither evaporative removal of the water, nor extraction of the organic products into an immiscible solvent. The recovered water is recycled internally in the OHD process. This proprietary Thermaquatica innovation is cost-effective, and allows for highly efficient use of the alcohol. The effluent from the exchanger consists of essentially 100% of the organic product from the concentrated aqueous liquor, now dissolved in >98% alcohol, sufficient for esterification in Unit Op 5 without further processing. The alcohol not consumed in the esterification is recovered and recycled in the process.
Each Unit Op has already been constructed of sufficient scale to be integrated with the PDU, and is the subject of an ongoing testing program. The basic PFD is versatile and can be used for any macromolecular feed. Only minor changes are needed to compensate for feed inorganics or removal of flocculants, both which can be achieved by the addition of a centrifuge and or clarifier, if needed.