Transformation of tetramethyldisiloxane in used oil alkali treatment conditions: mechanism and kinetic modeling

Abstract

BACKGROUND The behavior of silicon species in the recycling processes of waste lube oils is of great interest because of the negative effect of silicon compounds on the performance of hydrotreating catalysts and the formation of undesired solid deposits at various locations in the re‐refining units. To operate alkali treatment of silicon‐containing used oils efficiently in the recycling industry prediction of silicon species behavior is required. To this end kinetic modeling of the base catalyzed transformation of a model siloxane compound was done. RESULTS A kinetic model was developed for tetramethyldisiloxane (TMDS) transformation reactions under industrially relevant alkali treatment conditions in dodecane with sodium hydroxide as alkali agent. A reaction scheme describing the main pathways of TMDS transformation was proposed considering experimental and literature data. The studied model compound underwent hydrolysis, condensation and disproportionation reactions with formation of different molecular weight linear siloxanes. The latter were transformed to cyclic siloxanes through sodium silanolates generation. The data obtained experimentally were validated with the advanced kinetic model. CONCLUSIONS The proposed model fitted experimental data adequately, indicating that it can be used in the design and control of the caustic treatment of used oil containing silicon species. © 2015 Society of Chemical Industry

Stable hydrophilic poly(dimethylsiloxane) via glycan surface functionalization

“…The first step consists in an activation pre-treatment of PDMS surfaces via exposure to a solution of bleach and base (BB), or via exposure to UV in air. BB solutions are known to be good oxidants [27][28][29][30][31][32][33] and their elevated hydroxide concentration can also chemically degrade PDMS via well known base-catalyzed depolymerization reactions [34][35][36][37]. To our knowledge, however, BB solutions have not been previously investigated as a means of activating PDMS for functionalization.…”

“…This result suggests that treatment with BB solutions does not yield increased concentrations of surface bound O-containing groups as in the case of the UV treatment. Hydroxide ions are known to catalyze the depolymerization of PDMS which results in chain cleavage, cyclicized products and formation of insoluble and soluble silanolates [34][35][36][37]. In particular, the loss of soluble disilanolates should lead to a reduction in surface oxygen content and is likely to explain the observed change in Si/O ratio; the modest reduction in the Si 2p peak width is also supportive of depolymerization via cyclization.…”