Liquefaction of polyolefins: exploring the role of sulphur promotion

Pedro Guilherme Rodrigues Bizarro

Key information

Authors:

Pedro Guilherme Rodrigues Bizarro (Pedro Guilherme Rodrigues Bizarro)

Supervisors:

Ana Teresa Fialho Baptista; Pedro Simão Freitas Mendes (Pedro Simão Freitas Mendes)

Published in

November 16, 2022

Abstract

The development and implementation of recycling technologies is needed to deal with the global plastic issue: polyolefins are promising for processes seeking conversion to fuels. This work is focused on liquefaction and its main goal was the investigation of possible benefits of sulphur. Batch tests were performed on polypropylene under high temperate and hydrogen pressure, with pre-sulphided catalysts containing (de-)hydrogenating and acid functions. It was observed that increasing the amount of sulphur loaded into the reactor notably increased the conversion of polypropylene into liquid or gas, while having a minimal effect on the boiling point curves of the filtrates. A secondary goal for this work was the comparison of distinct catalysts. Three catalysts with different formulations were tested, resulting in characteristic product distributions: two of them yielded high fractions of gasoline, kerosene and diesel range hydrocarbons, while the third displayed poorer results, yielding higher fractions of both gas and heavier liquids. Strong effects of site accessibility and size exclusion are present in polypropylene hydrocracking, evidenced by the preferential cracking of hydrocarbons with boiling point between 540-740°C than those with boiling point higher than 740°C. Sulphur promotion and catalyst impact can be rationalized under a sequential mechanism where the polymer chains are initially cleaved via thermal reactions, followed by the hydrocracking of smaller fragments on catalytic sites. From an industrial perspective, the liquefaction of plastic waste might be a valuable technology and sulphur promotion could allow degradation at lower temperatures while catalyst engineering might increase the yields of valuable products.