Efficient n-caprylic acid production from syngas fermentation: Chain elongation and recovery with magnetic nanomaterials and supported liquid membrane contactor

Syngas fermentation using anaerobic bacteria represents an innovative chain elongation technique for converting CO and CO₂-rich waste gases into high-value bioproducts, including medium-chain fatty acids (MCFAs) and biofuels. While this process offers significant potential for greenhouse gas reduction and sustainable biochemical production, its industrial application has been limited by inefficient cell disruption methods and low MCFA recovery rates. This study addresses these challenges through a novel integrated approach combining functionalized magnetic nanoparticles for enhanced cell disruption with supported liquid membrane contactors for selective MCFA recovery. Fe₃O₄@MIL-100(Fe)@TEOS@CTAB (FMT@CTAB) nanoparticles, engineered with cationic surfactant modifications, achieved a remarkable harvesting efficiency of 98.8 %, substantially higher than conventional mechanical and chemical disruption methods (typically 60–85 %), attributed to their superparamagnetic properties and amphiphilic surface functionalization. At a concentration of 25 g/L, FMT@CTAB enabled high product yields, including acetic acid (4.15 g/L), butyric acid (5.35 g/L), caproic acid (4.39 g/L), caprylic acid (4.09 g/L), ethanol (3.27 g/L), and butanol (3.46 g/L). Furthermore, this study pioneered the application of supported liquid membrane contactors (SLMCs) as an eco-friendly and cost-effective alternative to traditional energy-intensive separation methods for MCFA recovery efficiency of 69.2 % and a mass flux of 23.11 ± 0.75 g/(m²·h). The PVDF-TDDA membrane significantly outperformed virgin PVDF membranes, demonstrating its potential for enhanced MCFA separation and recovery. These findings contribute to the optimization of bioproduct recovery from waste gases, advancing sustainable and economically viable biotechnological solutions that align with global climate targets and support the circular bioeconomy.