Catalytic hydrothermal carbonization of microalgae biomass for low-carbon emission power generation: the environmental impacts of hydrochar co-firing

[Display omitted] •Microalgae biomass-based catalytic hydrochar for co-firing applications.•Catalytic hydrothermal carbonization to produce high-quality biofuel blends.•Increased greenhouse gas emission reduction potentials.•Enhanced decarbonization can be reached by using 43.9% co-firing ratio.•Fossil fuel partial substitution and efficiency improvement for low-carbon energy. This work aims to improve the synthesis of renewable hydrochar (HC) co-fired with coal to reduce grenhouse gas (GHG) emission. Acetic acid catalyzed hydrothermal carbonization (cHTC) of Chlorella vulgaris microalgae biomass was investigated based on a 33−1 fractional statistical design of the experiment to examine the effects of hydrothermal reaction temperature (T = 180–220 °C), biomass-to-suspension- (BSR = 5–25 wt.%), and catalyst-to-suspension (CSR = 0–10 wt.%) ratios on process performance indicators. Analysis of variance was used to assess the experimental data. The results show that the application of homogeneous catalyst improves the fuel ratio and energy recovery efficiency up to 0.38 and 36.3%. Ex-ante cradle-to-gate life cycle assessment was performed to evaluate the impacts of co-firing ratio (CFR) and hydrochar quality on multi-perspective mid-, and endpoint environmental indicators. The highest decarbonization potential (−1.54 kg CO2,eq kWh−1) is achieved using catalytic hydrochar biofuel produced at 195 °C, 25 wt.% BSR, and 8 wt.% CSR levels. The application of catalytic and autocatalytic hydrochar blends improves the overall environmental impacts and greenhouse gas footprint of solid fuel firing facilitating the transition toward low-carbon emission power generation.