Novel carbon-based solid acid catalysts were synthesized through a sustainable route from lipid-extracted microalgal residue of , for biodiesel production. Two carbon-based solid acid catalysts were prepared by surface modification of bio-char with sulfuric acid (H₂SO₄) and sulfuryl chloride (SO₂Cl₂), respectively. The treated catalysts were characterized and their catalytic activities were evaluated by esterification of oleic acid. The esterification catalytic activity of the SO₂Cl₂-treated bio-char was higher (11.5 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) than that of commercial catalyst silica-supported Nafion SAC-13 (2.3 mmol Prod.∙h⁻¹∙g Cat. ⁻¹) and H₂SO₄-treated bio-char (5.7 mmol Prod.∙h⁻¹∙g Cat. ⁻¹). Reusability of the catalysts was examined. The catalytic activity of the SO₂Cl₂-modified catalyst was sustained from the second run after the initial activity dropped after the first run and kept the same activity until the fifth run. It was higher than that of first-used Nafion. These experimental results demonstrate that catalysts from lipid-extracted algae have great potential for the economic and environment-friendly production of biodiesel.
Sodium hydroxide solutions are often employed as sterilization agents in the pharmaceutical industry. Here, the chloride content is considered as a critical impurity. In this study, an electrochemical method was developed to remove chloride ions (Cl¯) through the oxidative deposition of AgCl on a Ag anode. The Cl¯ content in the commercially available 50% w/w NaOH solution employed was approximately 100 mg Cl¯/kg NaOH. As the OH¯ content is approximately 18,000 times higher than the Cl¯ content, the formation of AgCl may be expected to be thermodynamically less favorable than the formation of Ag 2 O. However, activation energies for AgCl and Ag 2 O formation have been reported to be approximately 3.8 and 31.2 kJ/mol, respectively, and indicate that AgCl formation is favored. AgCl can be selectively produced by controlling the anode potential. Here, the Cl¯ concentration was reduced to less than 50 mg Cl¯/kg NaOH when an anode potential of 0.18 or 0.19 V vs. Hg/HgO (reference electrode) was applied for one hour at 50°C. XRD analysis and visual monitoring of the Ag anode confirmed the oxidative deposition of AgCl on the anode surface as well as the electrochemical desalination of the concentrated NaOH solution.
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