There are significant economic and environmental benefits to the recycling of waste plastics, especially that of polystyrene. Currently, much of polystyrene waste is sent to landfills due to the difficulty in separation and cleaning processes, where it accumulates indefinitely. It contributes to plastic pollution and adversely affects wildlife, oceans and humans. Pyrolysis of waste polystyrene is explored in this paper as a chemical recycling method. This reaction yields useful liquid fuel products such as styrene, ethylbenzene, toluene, and methylstyrene, which can be sold to provide project revenues. Beginning with a polystyrene feed of 100 tons per day, the suggested design achieves a liquid styrene product purity of 99.9%. The plant includes a rotary- kiln reactor to carry out the pyrolysis reaction and a distillation train to isolate the liquid products. Pumps, blowers and storage equipment are also included in the design. Heat and energy are optimally integrated using heat exchangers to reduce the cost of purchased utilities. The suggested design requires a capital investment of $25.0 MM and yields a fifteen-year net present value of $5.1 MM. The internal rate of return it achieves is equal to 18.5%. The projected cash flows of this plant suggest that it will break even by 2030 on a cumulative discounted free cash flow basis. The design is recommended based on project specifications and current price projections, though investors should exercise caution with regards to the effect of realistic market prices of styrene and polystyrene on the project’s profitability measures.