Optimizing bio-crude oil production from Arthrospira: Effects of temperature and residence time in hydrothermal liquefaction

Abstract

Biomass, comprising renewable organic materials from animals and plants, stores chemical energy captured through photosynthesis. Hydrothermal liquefaction (HTL) is a promising thermochemical process that converts biomass into liquid fuels by treating it in hot, pressurized water, breaking down complex biopolymers into liquid bio-oil. This study investigates HTL of Arthrospira, utilizing Response Surface Methodology (RSM) to optimize yield and bio-crude quality, focusing on temperature and residence time. In this study, bio-crude quality is defined by HHV (MJ/kg), H/C atomic ratio, oxygen content (%wt), viscosity, and stability index, while process efficiency is quantified as bio-crude yield (% dry ash-free basis) and energy recovery (%). Results reveal both temperature and residence time significantly impact bio-crude yield and quality, with maximum yield at T > 260°C and retention time > 60 min. Conversely, yields are minimized below 230°C and 59 min. Sulfur content was also analyzed; ANOVA indicates the dominant effects of temperature and residence time, with the second-degree temperature term being highly significant, while the residence time term and their interaction show negligible influence on sulfur concentration. Scatter and contour plots demonstrate strong agreement between predicted and actual values, affirming model reliability. Increasing residence time enhances bio-crude density, with the highest density observed at > 69 min and T < 230°C. The flash point, an indicator of fuel safety, was positively affected by higher temperatures and longer residence times, peaking at > 70 min and > 270°C. Overall, the findings provide valuable insights into optimizing HTL conditions for high-quality bio-oil production from Arthrospira, with crucial parameters influencing yield, density, and safety properties.