AAU Update

PhD defence by Tahir Hussain Seehar


18.05.2021 kl. 13.00 - 16.00


Tahir Hussain Seehar, Department of Energy Technology, will defend the thesis "Hydrothermal Liquefaction of Waste Lignocellulosic Feedstock from Agricultural, Urban, and Forest Waste Streams for The Production of Biofuels"


Hydrothermal Liquefaction of Waste Lignocellulosic Feedstock from Agricultural, Urban, and Forest Waste Streams for The Production of Biofuels


Tahir Hussain Seehar


Associate Professor Saqib Sohail Toor


Associate Professor Chungen Yin


Associate Professor Jens Muff, Department of Chemistry and Bioscience, Aalborg University (Chairman)
Dr. Klaus Raffelt, Karlsruhe Institute of Technology (KIT University), Germany.
Associate Professor, Souman Rudra, University of Agder, Norway.


The rapid growth of energy demand, depletion of fossil fuel reservoirs, global warming and the climate change concerns are the major issues nowadays. To meet the energy demands accompanied with GHG reduction in the transportation sector, renewable energy resources are highly required as an alternate of fossil fuels. In this context, hydrothermal liquefaction (HTL) process is increasingly gaining attention as a promising and efficient technology to produce biofuels. The feedstock flexibility, free from pre-drying requirement and the delivery of high yields- high quality biocrudes from variety of waste streams makes the HTL more sustainable and attractive route. The aim of the present work is to valorize the lignocellulosic feedstocks from three different waste streams to produce biocrude and valuable energy dense products through the HTL process and the investigation of effects of the process conditions on process performance.

In the first study, highly potential feedstock from agriculture waste stream i.e., wheat straw (WS) was processed through HTL process to produce biocrude and additive products. The effects of process temperature (sub-supercritical) and alkali catalyst (K2CO3) were investigated in detail. The experimental results revealed that, at 350 ̊C- catalyst condition, HTL has high performance from biocrude yield and energy recovery perspectives. The highest biocrude yield (32.34 wt. %) with lowest solid yield (4.34 wt. %) was achieved by the addition of alkali catalyst at subcritical condition. There was no significant variation was observed for the higher heating value (HHV) of biocrudes at all four conditions that was around 35 MJ/kg. Based on the outcomes of inorganic contents, it was noticed that the majority of micronutrients (Fe, Zn) and macronutrients (P, Ca, Mg) were recovered in the solid phase product that can be proposed to utilize as a soil conditioner etc. Furthermore, to keep consider the advancement of HTL process as a continuous process at commercial scale, the effect of aqueous phase recirculation was also explored. In results, the fruitful consequences were achieved by means of increasing biocrude yield.

In the second study, the construction wood waste (untreated wood, non-hazardous wood, hazardous wood, and mixed wood) from urban waste stream were processed through supercritical hydrothermal liquefaction process. The overall aim was to investigate the effect of impregnation on the performance of the HTL process. Additionally, the objective was to elucidate the fate of heavy metals (Cr, Cu, Ni, and Zn) involved in the liquefaction process and their migration to the different HTL product phases. By the HTL of different waste wood at 400 ̊C, maximum biocrude yield was achieved by processing of untreated wood followed by non-hazardous, hazardous and mixed wood samples. The overall biocrude yield was obtained in range between 24.86 and 36.35 wt.%. By the investigation of fate of heavy metals, it was concluded that the majority (80-95%) of detected heavy metals were migrated to the solid phase product in case of impregnated wood. However, very few amount of targeted heavy metals were also shifted to the biocrude and aqueous phase that needs proper attention before HTL upgrading process. Through this way, HTL is suggested as a sustainable and promising pathway for the disposal of contaminated wood waste materials by converting into renewable biofuel.

In the third study, eucalyptus biomass from forest waste stream was converted into biocrude through HTL process. The influence of different process parameters (temperature, catalyst) was initially investigated. The effect of process retention time (5, 10, 15, 20, and 25 min) on the biocrude yield and the energy recovery was examined. The major portion (about 65-71%) of obtained biocrude were identified as the fractions containing the nature of gasoline, diesel, jet fuel and maritime fuel range. In case of the chemical composition of biocrudes, the oxygen aromatics and ketones were common compounds in biocrude at all retention times. Additionally, around 21-97% of inorganics were shifted to the solid phase. In overall, it was concluded that the catalytic-subcritical liquefaction at 15 min process retention time is an optimum condition for biofuel production and nutrients recovery.

From the outcomes of above-mentioned studies of the PhD work, it was concluded that the HTL is an efficient and sustainable process to handle the different feedstocks from different waste streams. The energy dense biocrude, the nutrient rich solids, and the organic rich aqueous phase can be utilized as renewable resources for different purposes in different sectors. However, the biocrude from HTL process required upgrading to meet the drop-in fuel quality. The integration of HTL technology with agriculture, urban, and forest waste streams can play the fruitful role to reduce the energy and environmental concerns as well as improve the circular economy.



THE DEFENCE IN ENGLISH - all are welcome.

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Department of Energy Technology

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