聚丙烯酸酯类柴油降凝剂的合成与降凝机理研究
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摘要
柴油降凝剂能有效地提高柴油的低温流动性，是改善柴油低温流动性最经济最方便的方法。通过添加降凝剂形成低凝柴油，可以增加原油中柴油馏分切割，节约原油能源，有很大的社会经济效益。柴油降凝剂的研究已有大量报道，但降凝剂的降凝效果强烈依赖于柴油的组成，且有关降凝机理还不甚清楚。为此，本文以长庆油田生产的柴油为原料，重点考察了不同组成和结构特点的聚丙烯酸酯对其降凝性能。同时依此为模型对其降凝机理进行了研究。
基于降凝剂性能与柴油本身的组成有很大关系，故本文首先对柴油中蜡含量和正构烷烃的碳数分布进行了分析。结果表明：本文所用柴油为一种含蜡量为21.6％的高蜡柴油，碳数为13、14和15的正构烷烃占总正构烷烃的质量百分数为30.9％，峰值碳数为15，平均碳数为15.4。
为了考察不同侧链碳数对其降凝行为的影响，通过酯化反应合成了不同侧链碳数的丙烯酸高碳醇酯，以此为单体进行聚合，得到不同侧链碳数的PA。通过降凝效果测试发现，以侧链碳数为14的降凝剂对柴油的降凝效果最好，验证了碳数匹配理论。因为聚合条件对降凝效果有影响，本文进一步对PA-14的聚合条件进行四因素三水平正交优化。优化聚合物分别能使柴油的凝点降低18℃，冷滤点降低6℃。此研究结果说明，同一类降凝剂对凝点降和冷滤点降存在一定差异。通过对降凝剂不同加入量对降凝行为的研究，发现凝点存在最佳值，而冷滤点随着降凝剂增多而下降，当降凝剂量达到一定值时冷滤点不再降低。
为了考察降凝剂对具有混合成分特点的柴油可能存在的协同作用，本研究特意制备了丙烯酸高碳醇酯混合共聚物和混合聚丙烯酸高碳酯，并测定了它们的降凝效果。结果说明，降凝剂侧链碳数与柴油中正构烷烃的匹配性对良好的降凝效果起决定性作用。为了考察短链分子是否具有降凝剂的作用，本文以丙烯酸十四酯作为降凝剂加入柴油中，结果发现短链的丙烯酸十四酯对柴油没有降凝作用。可见，聚合物的骨架碳链在降凝效果上起到很大的作用。同时，测定了PA-14与AEO-3、Span80和Span85复配降凝剂的降凝效果，发现这三种非离子表面活性剂对聚丙烯酸酯类降凝剂有协同性，这是降低降凝剂成本的重要途径之一。
通过内烯酸十四酯与马来酸酐、苯乙烯和丙烯酸丁酯等第二单体进行共聚来研究不同结构降凝剂对柴油的降凝效果。研究发现，第二单体的加入能有效提高凝点降，而对冷滤点降的改善不好。
为了研究聚丙烯酸高碳醇酯对柴油的降凝机理，本研究通过冷热台偏光显微镜对蜡晶形成过程进行了在线跟踪。显微观测显示降凝剂(PPD)能够有效地改变蜡晶的形貌，使蜡晶由大块片状变为均匀的圆球状。依据不同时间及不同条件下显微观察结果，提出了降凝剂的晶核分散机理。降凝剂用量较少时，将出现以蜡晶为晶核，降凝剂吸附在蜡晶周边形成边界层，从而使高分子具有分割蜡晶的作用。当降凝剂用量适量时，作为高分子的降凝剂首先形成晶核，较为分散和尺寸较小的高分子晶核使蜡晶结晶尺寸更小，从而能有效地发挥降凝剂的降凝性能。运用晶核分散机理能够解释大多数降凝剂对凝点具有较好的感受性，而对冷滤点感受性较差的现象。
另外，通过降凝效果测定和显微观测柴油储存时间对低温流动性的影响，结果发现，延长储存时间能提高柴油低温流动性，但也使降凝剂的作用效果降低。
最后，运用冷冻干燥处理蜡晶，可以有效分离柴油中的轻组分，同时保留蜡晶的形貌。通过上述处理可在显微镜下清楚地看到降凝剂分子在蜡晶中的分布。与此相关的观测结果进一步验证了本文提出的晶核分散机理。
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.
基于降凝剂性能与柴油本身的组成有很大关系，故本文首先对柴油中蜡含量和正构烷烃的碳数分布进行了分析。结果表明：本文所用柴油为一种含蜡量为21.6％的高蜡柴油，碳数为13、14和15的正构烷烃占总正构烷烃的质量百分数为30.9％，峰值碳数为15，平均碳数为15.4。
为了考察不同侧链碳数对其降凝行为的影响，通过酯化反应合成了不同侧链碳数的丙烯酸高碳醇酯，以此为单体进行聚合，得到不同侧链碳数的PA。通过降凝效果测试发现，以侧链碳数为14的降凝剂对柴油的降凝效果最好，验证了碳数匹配理论。因为聚合条件对降凝效果有影响，本文进一步对PA-14的聚合条件进行四因素三水平正交优化。优化聚合物分别能使柴油的凝点降低18℃，冷滤点降低6℃。此研究结果说明，同一类降凝剂对凝点降和冷滤点降存在一定差异。通过对降凝剂不同加入量对降凝行为的研究，发现凝点存在最佳值，而冷滤点随着降凝剂增多而下降，当降凝剂量达到一定值时冷滤点不再降低。
为了考察降凝剂对具有混合成分特点的柴油可能存在的协同作用，本研究特意制备了丙烯酸高碳醇酯混合共聚物和混合聚丙烯酸高碳酯，并测定了它们的降凝效果。结果说明，降凝剂侧链碳数与柴油中正构烷烃的匹配性对良好的降凝效果起决定性作用。为了考察短链分子是否具有降凝剂的作用，本文以丙烯酸十四酯作为降凝剂加入柴油中，结果发现短链的丙烯酸十四酯对柴油没有降凝作用。可见，聚合物的骨架碳链在降凝效果上起到很大的作用。同时，测定了PA-14与AEO-3、Span80和Span85复配降凝剂的降凝效果，发现这三种非离子表面活性剂对聚丙烯酸酯类降凝剂有协同性，这是降低降凝剂成本的重要途径之一。
通过内烯酸十四酯与马来酸酐、苯乙烯和丙烯酸丁酯等第二单体进行共聚来研究不同结构降凝剂对柴油的降凝效果。研究发现，第二单体的加入能有效提高凝点降，而对冷滤点降的改善不好。
为了研究聚丙烯酸高碳醇酯对柴油的降凝机理，本研究通过冷热台偏光显微镜对蜡晶形成过程进行了在线跟踪。显微观测显示降凝剂(PPD)能够有效地改变蜡晶的形貌，使蜡晶由大块片状变为均匀的圆球状。依据不同时间及不同条件下显微观察结果，提出了降凝剂的晶核分散机理。降凝剂用量较少时，将出现以蜡晶为晶核，降凝剂吸附在蜡晶周边形成边界层，从而使高分子具有分割蜡晶的作用。当降凝剂用量适量时，作为高分子的降凝剂首先形成晶核，较为分散和尺寸较小的高分子晶核使蜡晶结晶尺寸更小，从而能有效地发挥降凝剂的降凝性能。运用晶核分散机理能够解释大多数降凝剂对凝点具有较好的感受性，而对冷滤点感受性较差的现象。
另外，通过降凝效果测定和显微观测柴油储存时间对低温流动性的影响，结果发现，延长储存时间能提高柴油低温流动性，但也使降凝剂的作用效果降低。
最后，运用冷冻干燥处理蜡晶，可以有效分离柴油中的轻组分，同时保留蜡晶的形貌。通过上述处理可在显微镜下清楚地看到降凝剂分子在蜡晶中的分布。与此相关的观测结果进一步验证了本文提出的晶核分散机理。
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.
引文
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