Prospects of Biocrude Production Potential from Local Diatom

Abstract

A marine diatom Nitzchia reversa was grown in 5 sq. m open raceway pond (10 cm culture depth, 500 L culture volume) in the Qatari desert environment. After 7 days of growth, the final biomass density reached 0.52 g/L, and average biomass productivity was 6.7 g/m2/d. Next, Nitzchia reversa was harvested using a 25 m2 crossflow filtration membrane module. Crossflow harvested biomass slurry was centrifuged at 5000 RPM for 10 minutes to obtain a wet biomass paste containing 25 - 30% solid content. Centrifuged biomass was freeze-dried, and lipid, protein, carbohydrate, and ash were quantified as 12.3, 15.3, 44.3, and 27.8% respectively. Hydrothermal liquefaction (HTL) was conducted to convert Nitzchia reversa biomass to biocrude oil using 10-mL Swagelok union type reactors. Biocrude, biochar, aqueous and gas phase were quantified on an ash-free dry weight basis. Hydrothermal liquefaction was conducted at temperatures ranging from (300, 325, 350, 375, and 400 °C) at 30-minute reaction holding time, maximum biocrude yield of 57.26% was obtained at 375 °C. Carbon content within the biocrude decreased with increasing HTL reaction temperature, whereas, oxygen content increased with increasing HTL reaction temperature. The maximum higher heating value for biocrude oil was 35.1 MJ/kg at 300 °C. Hydrocarbons in biocrude were identified as alkanes, alkenes aromatics, and heterofunctional groups by GC-MS. However, high biocrude yields could be obtained from Nitzchia reversa with increasing HTL reaction temperatures with maximum energy recovery (ER) of 53.01% at 375 °C.