| Pour point depressant (PPD) to improve the fluidity of diesel fuel atlow temperature is not only effective but also economical and convenient. By this way,PPD can enlarge the distillate line of crude oil for diesel fuel. So, it is very profitable foreconomy and society due to saving energy sources of crude oil.Firstly, the content of wax and n-paraffin distribution for a given diesel fuel wereanalyzed. The results show the diesel fuel is high-wax oil with 21.6% of wax content.The n-paraffin with carbon number (CN) 13, 14 and 15 has 30.9% in total n-paraffin.The dominant CN of n-paraffin is 15, and the average CN is 15.4.The higher alcohol acrylates as polymerisable monomer are synthesized byesterifying acrylic acid with higher alcohols. Then, the higher alcohol acrylate polymerswith different alkyl branch-chain are prepared. By means of examining the cold flowperformance, the poly (tetradecyl acrylate) (PA-14) shows the best performance, whichis attributed to the fact that carbon number of side chain matches with that of the dieselfuel. Then the polymerization conditions of PA-14 were optimized by orthogonalmethod. The polymers with the best solidifying point depression (ΔSP) and cold filterplugging point depression (ΔCFPP) were prepared, and volume ofΔSP andΔCFPPwere 18℃and 6℃, respectively.Copolymers with different higher alcohol acrylates and mixtures of the poly(higher alcohol acrylates) with different branch-chain carbon number were prepared andtheir cold flow performances were determined. The copolymers have a better cold flowperformance than the mixture of the polymers, in which copolymers with more 14 ofbranch-chain CN segments is very better in cold flow performance. Based theexperiments of PPD of the mixtures of PA-14 with AEO-3, Span-80 or Span-85, theresults indicate that three kinds of non-ionic surfactants have synergism with poly(higher alcohol acrylates). Otherwise, the addition of surfactants can reduce the cost ofPPD.To study the cold flow performance of PPD with different structures, tetradecylacrylate is copolymerized respectively with maleid anhydride, styrene and butyl acrylate.It is found that copolymers can enhance theΔSP, but have no effect withΔCFPP. The effect of amount of PPD on the cold flow performance was investigated. Theresults illustrated that a given PPD in certain content has the best performance in△SP, however, the PPD in this case has not a performance in△CFPP. This experiment impliesthat the interaction between PPD and diesel fuel in molecular scale makes the effect on△SP and△CFPP in defferent way.The formation of wax crystal was observed by in-situ polarizing microscope.Comparing the wax crystal morphology in presence of PPD with absence of PPD, theobservations indicate that PPD could efficiently reform the morphology of wax crystalthrough changing the wax crystal from slice agglomeration to even spherulites.Consequently, this effect makes the wax crystal hardly form in big size. Based on theobservations, it makes a conclusion that the mechanism for effect of PPD on△SP and△CFPP is attributed to dispersion-nucleation. When the content of PPD is lower, thewax directly forms crystal nucleus, and PPD wraps the wax crystal. When the content isproper, PPD as crystal nucleus firstly appears, and the wax crystal is incorporated intoPPD crystal. Owing to PPD nucleus being small and dispersed, the small co-crystalcould be observed. According to the mechanism proposed in this research, thedifference of performance in△SP and in△CFPP could be explained.It was examined and observed with microscope that the aged diesel fuel influencesthe cold flow performance. Aged diesel fuel can improve the cold flow performance, butthe effect of PPD on cold flow of diesel fuel is reduced.At last, freeze drying treatment of wax crystal was observed by microscope. Bymeans of this method, the effect of PPD on the wax crystallization can be seen clearly.The result further proves the proposed mechanism.
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