Sustainable aviation fuel from waste biomass

Bashir, Muhammad Asif (2022). Sustainable aviation fuel from waste biomass. University of Birmingham. Ph.D.

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Abstract

The aim of this work was to produce jet fuel via TCR® route. Several biomass wastes such as food and market waste, digestate, humus, and sewage sludge were tested through TCR® system to find a suitable oil for upgrading. Sewage sludge TCR® oil was chosen due to its lower oxygen content, greater calorific value, lower acidity, lower viscosity, and lower water content in comparison to the rest of the TCR® oils. Sewage sludge oil was processed through the TCR®-2 system and converted into TCR® oil, gas, and char. The TCR® oil was hydroprocessed in an autoclave under the process parameters carefully selected from in-depth literature review. A two-step hydroprocessing (hydrodeoxygenation and hydrocracking) was applied with H\(_2\) pressure as a variable between 30–60 bar. For the hydrodeoxygenation reaction, sulfided NiMo catalyst supported on alumina, while sulfided NiW supported on silica-alumina catalyst was used for the hydrocracking. In the hydrodeoxygenation step, phenols, ketones, and fatty acids methyl esters were converted into hydrocarbons. whilst the monocyclic aromatic hydrocarbon (benzene and its derivatives), bicyclic aromatic hydrocarbons (naphthalene and its derivatives) and N-heterocyclic compounds (nitriles, amines etc.) were converted into hydrogenated derivatives. The hydrodeoxygenation step was followed by hydrocracking to crack and isomerise the longer n-paraffins into jet fuel range (C\(_8\)–C\(_{16}\)) paraffins and heavier aromatics into lighter aromatics. Jet fuel range hydrocarbons including a wide range of paraffins (normal, cyclo and branched) and aromatics were produced at 60 bar H\(_2\). The jet fuel fraction was separated from the hydroprocessed sewage sludge oil at 60 bar H\(_2\) via atmospheric distillation. The jet fuel range fraction was characterised and compared with the ASTM D7566 standard for some essential jet fuel characteristics. The jet fuel fraction met majority of the ASTM D7566 fuel specification for calorific value, viscosity, density, and freeze point. Some parameters such as smoke, flash point and TAN slightly fell out of specification. In addition, naphtha and diesel fractions were recovered and analysed as by-products. The process was also tested for catalyst reusability and regeneration potential under the same process parameters with positive outcome.
Further to standalone upgrading of the sewage sludge oil to jet fuel range hydrocarbons; biodiesel and sewage sludge crude oil were co-hydroprocessed in order to produce jet fuel range hydrocarbons. A two-step co-hydroprocessing was carried out by blending biodiesel with 5%, 10% and 20% TCR® oil (volume basis) under the same process conditions and catalysts as the neat sewage sludge oil. The conversion of neat biodiesel to jet fuel range hydrocarbons was encouraging. However, blending sewage sludge oil did not produce the desired results as the catalyst appeared to have lost their catalytic activity, possibly deactivation of catalysts. Consequently, the yield of jet fuel range hydrocarbons suppressed, and it was assumed that co-hydroprocessing sewage sludge oil and biodiesel created a H\(_2\) deficit leading to coking. It was concluded that co-hydroprocessing of both feedstocks will require a higher H\(_2\) pressure in comparison to their standalone processing. In addition to jet fuel investigation, bio-oil deoxygenation potential of de-inking sludge and reforming effect of TCR® system were explored. De-inking sludge showed a remarkable catalytic effect through cracking and reforming of oxygenated compounds produced during its neat conversion and co-processing with wood. Increasing the amount of de-inking sludge enhanced the oil quality due to deoxygenation and aromatisation reactions. It was concluded that catalytic effect of de-inking is associated with its inherently high concentration of Ca, most of which is retained by the de-inking sludge char. Besides, the reforming effect of the TCR® system was investigated. Under the effect of reforming, the physicochemical characteristics of the oil improved through tar cracking and reforming. This also accelerated the water gas shift and methanation reactions in the gas. It was assumed that TCR® char is catalytically active and plays a key role in the reforming process.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):