UC Santa Barbara

The escalating accumulation of plastic waste in landfills as well as the environment has raised many concerns regarding pollution, toxicity and resource depletion. Polyolefins, comprising of polyethylene (PE) and polypropylene (PP), contribute to about half of plastic waste production. Despite their inherent chemical inertness that makes recycling especially challenging, waste polyolefins are also a potential resource for the production of chemicals and new materials. The work presented demonstrates the transformation of polyethylene into value-added alkylaromatics via tandem hydrocracking/aromatization using bifunctional catalysts. By replacing a more acidic Pt/F-Al2O3 over a previously reported Pt/Al2O3 catalyst, 70 wt% PE was converted to liquid products containing surfactant-range alkylaromatics at 280 °C in 8 h. Moreover, a 5-fold enhancement in the carbon-carbon bond scission rate and doubling in the molar yields of alkylaromatics were achieved. Mechanistic studies revealed that the Pt site(s), responsible for hydrogenation/dehydrogenation, work synergistically with Brønsted acid sites, which facilitate C-C bond scission, isomerization, and aromatization.While alkylbenzenes are used for manufacturing anionic surfactants, they are present in a complex mixture of liquid hydrocarbons in the described reactions. A two-step/one-pot reactive separation process was envisaged and demonstrated using silica sulfuric acid to sulfonate long-chain alkylaromatics, followed by neutralization with sodium hydroxide. This simple process effectively turns the complex liquid hydrocarbons mixture into two valuable and easily separable products, sodium alkylbenzene sulfonates and lubricant-range saturated hydrocarbons. Overall, a PE-derived surfactant was synthesized using polymer waste as a feedstock, providing a potential route to displacing alkylbenzene production from petroleum resources.