(731b) Probabilistic Analysis of Converting Marine-Borne Plastics into Usable Fuels

Oceanic plastics represent a major global environmental pollution problem. Every year between 4.8 and 12.7 million tons of plastic enter the ocean and as a result a potentially dangerously high amount of plastic has already accumulated in the oceans. This plastic is highly concentrated in the naturally occurring gyre’s in the ocean which could aide in any clean-up efforts, but the question remains what should be done with the plastic once it is collected? We have proposed a process that would involve a ship collecting plastic in the ocean and converting it into fuel in an onboard hydrothermal liquefaction reactor to fuel itself. Before starting experimental work, we wanted to determine whether the afore mentioned process could in fact make more energy than it consumes. To do this in the presence of uncertainty a probabilistic exergy analysis was carried out on a theoretical system for three different and common plastics, polystyrene, polyethylene and polypropylene, as well as for a mixed plastic stream. The theoretical process consisted of a plastic shredder, reverse osmosis system, reactor, separator and an ultraviolet & hydrogen peroxide oxidation system. The exergy model accounted for the energy requirements of the equipment, heating up the reactants to the reaction temperature and the chemical exergy of the streams before and after reaction. This analysis allowed us to determine the break even point (when the net exergy was equal to zero) as well as the point at which there was a 50% chance of having net exergy production and create probability curves as seen in Figure 1. The analysis showed that with less than 10% by volume plastic in the feed (ocean) enough energy could be created to run the equipment and fuel a boat large enough to hold it. The work also allowed for the creation of a decision-making tool that allows one to assess the risk associated with a project.