(104a) Adventures in Autothermal Processing

Autothermal operation of a chemical reactor involves directly or indirectly coupling exothermic and endothermic chemical reactions for the purpose of thermal management without resorting to external energy sinks or sources. Often this is accomplished through regenerative or recuperative heat exchange between spatially or temporally separated exothermic and endothermic reactions. However, it is also possible to directly couple these reactions simultaneously within the same reactor volume, eliminating the heat transfer bottleneck that characterizes much of chemical manufacture. It is not widely recognized that directly coupled autothermal operation allows dramatic process intensification, increasing reactor throughput several fold. The most familiar examples of directly coupled autothermal processes involve partial oxidation of reactants (coal, biomass, or natural gas) to produce gaseous products near their equilibrium composition. More challenging are devising directly coupled autothermal processes involving reactions that proceed far from equilibrium, although there are several examples in the scientific literature.

In the last few years, our research group has been developing autothermal pyrolysis for the production of sugars, phenolic oil, and biochar. Contrary to conventional wisdom on fast pyrolysis, we have found that oxygen admitted at low equivalence ratios can achieve autothermal operation without significantly impacting oil yield. These studies have demonstrated the dramatic process intensification that occurs upon eliminating heat transfer from thermal management of the reactor, increasing throughput several fold compared to a conventional pyrolyzer.

We have recently begun to explore how principles of autothermal operation could be applied to other processes including treatment of wastewater and thermal depolymerization of plastics. The preliminary results from adding oxygen plastics pyrolysis are so distinctive that we refer to it as “thermal oxo-degradation” (TOD) of plastics. In this case, admitting oxygen not only makes possible autothermal operation of this otherwise endothermic process, the products of oxidation are fatty alcohols and fatty acids – feedstocks in the production of high-value oleochemicals.