Separation of alkane / alkene gaseous mixtures by adsorption unto microporous carbons

气体被表面强烈吸引，尽管方式不尽相同。气体及其吸附表面化学成分的差异将决定气体对表面吸附的实际亲和力。碳，无论是天然的还是人造的，都可以经过适当的修饰（通过活化），以微观孔隙的形式具有相对较大的可用表面。这些孔隙的形状和大小分布以及活化后表面的最终性质将最终决定孔隙中给定气体的吸附特性。对于混合物，问题变得更加复杂，因为现在有其他因素起作用，如气体之间的相互作用和它们在表面的优先吸附。这项工作的目的是研究一种由小碳氢化合物（烷烃）和它们的不饱和对应物（烯烃）组成的特殊类型的混合物。烯烃作为聚合反应的起始点特别有用，聚合反应最终导致塑料和石化产品的生产。然而，在许多情况下，有必要在这些反应发生之前以纯形式获得它们。传统的分离技术是蒸馏。虽然可行，但蒸馏对这些类型的混合物需要大量的能量和技术努力。其他技术，如使用膜实现低选择性（分离差）和/或存在其他技术问题。这项工作的重点是碳吸附可能是一种可行的、经济的和绿色的替代方案。然而，选择合适的吸附剂是成功分离的关键。从实验中只能获得有限的信息，因为活性炭很难表征，实验不能一次集中在单个变量上（例如，结果很难解释）。理论发展仍处于起步阶段，除了描述更简单的系统之外，还不能做更多的工作。我们建议从分子的角度并使用适当的统计和计算工具，通过模拟乙烯/乙烷和丙烯/丙烷混合物在明确定义的碳狭缝孔中的吸附来研究这个问题。由于我们是在计算机上进行分子模拟，我们可以随意改变孔隙大小、压力、组成和温度，以获得最大分离的条件。这些信息可以作为合成和设计新型高性能吸附剂的起点。

Gases are strongly attracted to surfaces although not all in the same way. The difference in chemical composition of both the gases and the surfaces upon which they adsorb will determine the actual affinity for the adsorption of a gas unto a surface. Carbons, both natural, and man-made, may be appropriately modified (by activation) to have a relatively large available surface in the form of microscopic pores. The shape and size distribution of these pores along with the final nature of the surfaces after activation will ultimately determine the adsorption characteristics of a given gas in a pore. With mixtures, the problem becomes more complicated, since now other factors come into play such as the interactions amongst the gases and their preferential adsorption on the surface. This work porposes to study a particular type of mixture made up of small hydrocarbons (alkanes) and their unsaturated counterparts (alkenes). The alkenes are particularly useful as starting points for polymerization reactions which ultimately lead to the production of plastics and petrochemicals. However, in may scenarios, it is necessary to obtain them in pure form before such reactions take place. The conventional separation technique is distillation. While feasable, distillation involves an large energetic and technological effort for these type of mixtures. Other technologies, such as the use of membranes achieve low selectivies (poor separation) and/or present other technical problems This work focuses on the proposal that adsorption on carbons may be a feasable, economical and green alternative. The choice of the appropriate adsorbent is, however, the key to a sucessful separation. Only limited information can be obtained from experiments, since activated carbons are dificult to characterize and the experiments can not focus on a single variable at a time (e.g. the results are hard to interpret). Theoretical developments are still incipient and do not allow much more than the description of simpler systems. We propose to study this problem by modelling, from a molecular point of view and using the appropriate statistical and computational tools, the adsorption of ethylene/ethane and propylene/propane mixtures unto well-defined carbon slit pores. Since we are performing molecular modelling on a computer, we may vary at will the pore size, pressure, composition and temperatures to obtain the conditions at which the separation is maximized. This information can be used as a starting point for the synthesis and design of new and high-performance adsorbents.