Optimized continuous flow water removal from biodiesel and diesel (B15) using Raschig ring-shaped polyacrylamide/cellulose microfibrils hydrogels in fixed-bed columns

• Hydrolyzed composite hydrogel successfully molded into efficient Raschig rings. • Hydrogel bed lowers biodiesel water content to comply with EN specification. • Hydrolyzed PAM/MFC performs for 7 cycles, including 4 with regenerated material. • PAM/MFC bed effectively reduces diesel water content to meet quality standards. • Hydrolyzed polyacrylamide: cost-effective alternative to sodium acrylate copolymers. The rising biodiesel content in diesel, driven by global policies, intensifies the challenge of maintaining fuel quality, particularly regarding water content. Elevated water levels in fuels can cause mechanical failures, corrosion, microbial growth, and reduced fuel performance, leading to increased maintenance costs and environmental concerns. Composite hydrogel packings offer significant potential for fuel dehydration, particularly in continuous processes, where essential characteristics include robust mechanical strength, high hydrophilicity, rapid kinetics, and geometry that facilitates fluid flow without causing pressure drops. This study addresses these challenges by employing hydrolyzed and non-hydrolyzed PAM/MFC (polyacrylamide/cellulose microfibrils) hydrogels, shaped into Raschig rings, as packing materials in fixed-bed columns for continuous water removal from biodiesel and B15 diesel (diesel fuel containing 15 % (v/v) of biodiesel). For biodiesel, hydrolyzed PAM/MFC reduced water content from 952.8 ppm to 463.6 ppm (51 % removal) after a 2.3-hour residence time, meeting EN 14214 standards. When connected in series with a column containing hydrolyzed and lyophilized PAM/MFC hydrogels, water content was further reduced to approximately 350 ppm. Hydrolyzed PAM/MFC maintained performance over seven cycles, including four with regenerated material, demonstrating its reusability and durability. Conversely, non-hydrolyzed PAM/MFC hydrogels removed 40 % of water during a 2.3-hour residence time, highlighting the need for anionic hydrogels to achieve faster water removal kinetics from biodiesel. For B15 diesel, the same non-hydrolyzed material achieved a 36 % reduction in 17 min of residence time, lowering water content to below 200 ppm, in compliance with EN 590 standards. This study also optimized the production of Raschig ring-shaped hydrolyzed PAM/MFC hydrogels, demonstrating the feasibility of reusing the twice, reducing specific sodium hydroxide consumption by approximately 44 %. Additionally, washing hydrolyzed hydrogels in a cascade system significantly improved washing efficiency. An economic evaluation revealed that hydrolyzed PAM/MFC hydrogels provided a cost advantage over other anionic hydrogels with similar performance in removing water from biodiesel, being 17 % and 50 % less expensive than acrylamide-sodium acrylate copolymers and sodium polyacrylate hydrogels, respectively. Overall, this study presents a scalable and technically viable solution for industrial fuel dehydration, offering an integrated approach that combines operational efficiency in packing production and compliance with global fuel quality standards.