Abstract
One production challenge of biodiesel is to lower the water concentration after the washing process applied to remove the excess of glycerin and catalyst. To address this issue, industry usually adopts vacuum distillation which requires high capital expenditure and costly operational expenditure to achieve legal water specification. Alternatively, water content specifications can be met by using hydrogels as adsorbents. Recent works applied polyacrylamide (pAAm) hydrogel and polyisopropylacrylamide microgel to remove water from biodiesel; however, one open question is if polyacrylic acid (pAA) or sodium polyacrylate (SpA) might adsorb water from the biodiesel. Our rationale was that SpA may adsorb more water than the previous studied hydrogels since the electrostatic interaction between water and acrylate group is stronger than the hydrogen bonding between water and amide or acrylic groups. To test this hypothesis, in this work we made the homopolymeric polyacrylamide, polyacrylic acid and sodium polyacrylate hydrogels by free radical polymerization. So, to determine if these materials can remove water from biodiesel, we compared the hydrogel-treated biodiesel with a control sample without adsorbent addition. The initial water concentration was 6977 mg/kg, and our findings showed that the final water concentration in hydrogel-treated biodiesel was lower than the control sample, and the water content after 24h of contact was lower than 1100 mg/kg for the best case. Moreover, SpA presented similar performance as pAAm; however, no clear difference between pAAm and SpA was observed in this screening experiment. The results from our study point towards the idea that SpA could be used in process and product development for new green technologies as alternative to costly and unfriendly environmental vacuum distillation.
