Instability of Coalgae® pyrolysis oils and its stabilization

Title : Instability of Coalgae® pyrolysis oils and its stabilization

Abstract:

Obtaining diesel range oil from coal pyrolysis is not a new concept and South Africa relies on 95% crude oil product imports. This is due to immature development of the coal synthetic oils technologies. On the other hand, South Africa is suffering with accumulation of waste(unusable) low value coal fines/tailings which are by-products of its heavy reliance on coalmining. Full development of the (i) the Coalgae® technology (using algae and coal fines to make large briquets of a coal/algae composite), (ii) pyrolysis of Coalgae®, (iii) processing of the pyrolysis oil, and ensuring capture and utilisation of the pyrolysis by-products such as gases and ash, will ensure beneficiation of waste coal fines while reducing South Africa’s reliance on crude oil imports, and also providing room for use of material as sustainable feedstocks for pyrolysis. Use of algae presents a green sustainable solution since algae grows fast even in waste water while capturing large volumes CO₂.This study was meant to optimize production and processing of Coalgae® pyrolysis oil and focus was mainly placed on the biggest bottleneck; stability of the oil. Investigations were carried out to understand causes of the instability, map the rate and extent of the instability over time, and methods for stabilizing the oil. The instability of pyrolysis oil was monitored over time using Gc-MS, FT-IR, Gc x Gc viscosity, and simulated distillation. The studies revealed that there are further reactions occurring after pyrolysis which needs to be prevented to stabilize the oil for hydroprocessing. It was discovered that phenolic compounds are mostly responsible for the instability and react over time. A stable oil sample suitable for further processing was obtained, and it was further refined using conventional and improved hydroprocessing catalysts. This work serves as a bridge in transitioning from fossil fuels to 100% greener alternatives as the stabilization techniques implemented could also be effective in stabilizing biomass derived fuels.

Biography:

Olwethu Poswayo is a PhD candidate at Chemistry Department in Nelson Mandela University, South Africa. She holds a MSc degree in Nanosicence (Nanochemistry) but for PhD studies branched because of her passion to focus on energy, fuels and refinery project. In her PhD work, she was awarded the GCUA 2030 1^st prize Laurette in 2023 and did a seminar in Sweden early 2024. She has also presented her PhD work at 4 local conferences.