Separation of secondary dispersed diesel-water emulsions by electrospun membranes identified by inverse-quantitative structure-activity relationship
Translated title
Separation af sekundære diesel-vand emulsioner med electrospundet membraner identificeret ved brug af inverse-quantitative structure-activity relationship
Author
Knudsen, Kristian Bastholm
Term
4. term
Education
Publication year
2012
Submitted on
2012-05-31
Pages
75
Abstract
Dette projekt udvikler nye membraner til at adskille sekundære dispersioner af vand‑i‑diesel, dvs. meget små vanddråber blandet i diesel. Behovet er blevet større med biodiesel, som indeholder overfladeaktive stoffer (surfaktanter), der gør dråberne mindre og øger den samlede vandmængde. Det forringer forbrændingseffektiviteten og kan forkorte motorers levetid. Tidligere er det vist, at adskillelsen afhænger af membranens hydrofobicitet (hvor meget overfladen frastøder vand), som bestemmes af både overfladeenergi og overflademorfologi. For at finde et nyt membranmateriale blev der udviklet en omvendt kvantitativ struktur‑aktivitets‑relation (inverse‑QSAR) baseret på polymerers kritiske overfladespænding, et mål for hvor let væsker væder en overflade. Modellen pegede på polymerer med lav kritisk overfladespænding, dvs. hydrofobe materialer. Kandidaterne blev derefter vurderet, og poly(styren‑co‑a‑methylstyren) (PSMS) blev valgt. PSMS‑overfladen blev karakteriseret ved vandkontaktvinkelmåling og viste 94.10±3.73°, hvilket bekræfter hydrofobicitet. For at øge vandafvisningen yderligere blev PSMS elektrospundet, en proces der bruger elektrostatiske kræfter til at danne tynde polymerfibre med porer og hulrum, som øger hydrofobiciteten. De elektrospundne PSMS‑overflader havde en vandkontaktvinkel på 165.85±0.51°, dvs. de var superhydrofobe. På den baggrund blev der fremstillet membraner ved at elektrospinde PSMS på et bæremateriale. Membraner fremstillet fra en 60% (w/w) PSMS/DMF‑opløsning og med en afsat masse på 30 g PSMS/m² gav den højeste separationseffektivitet på 93.85±2.65% med et trykfald på 0.64±0.17 kPa.
This project develops new membranes to separate secondary dispersions of water‑in‑diesel, that is, very small water droplets mixed into diesel fuel. The need has grown with biodiesel, which contains surfactants that make the droplets smaller and increase the total water content, reducing combustion efficiency and shortening engine lifetime. Separation of such dispersions is known to depend on the membrane’s hydrophobicity (how strongly the surface repels water), which is influenced by both surface energy and surface morphology. To identify a new membrane material, an inverse quantitative structure–activity relationship (inverse‑QSAR) was built using polymers’ critical surface tension, a measure of how easily liquids wet a surface. The model predicted polymers with low critical surface tension, i.e., hydrophobic materials. The predicted candidates were then evaluated, and poly(styrene‑co‑a‑methylstyrene) (PSMS) was selected. The PSMS surface was characterized by measuring the water contact angle, which was 94.10±3.73°, confirming hydrophobicity. To further increase water repellency, PSMS was electrospun—a process that uses electrostatic forces to form thin polymer fibers with pores and hollows, increasing hydrophobicity. Electrospun PSMS surfaces showed a water contact angle of 165.85±0.51°, i.e., they were superhydrophobic. Based on these results, membranes were fabricated by electrospinning PSMS onto a support layer. Membranes produced from a 60% (w/w) PSMS/DMF solution with a deposited mass of 30 g PSMS/m² achieved the highest separation efficiency of 93.85±2.65% with a pressure drop of 0.64±0.17 kPa.
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