Chemisorbent Materials for Olefin/Paraffin Separation

丙烯和乙烯通常用于食品包装和化学品等。1 -4为了满足对丙烯和乙烯产品的更大需求，轻质烯烃的生产也必须增加。3目前，最可行的路线是通过原油精炼制备。5石化工业从原油中生产烯烃（乙烯和丙烯）。7原油加工后，有烯烃和低级链烷烃的混合物。因此，需要分离工艺来分离烯烃和链烷烃。混合物对工业没有用处。就丙烯而言，有三种不同的等级：聚合物级纯度最低为99.5%，化学级纯度最低为93-94%，以及精炼级纯度最低为60%。用于分离烯烃和链烷烃的标准方法是低温蒸馏。6例如，丙烯和丙烷的分离是困难的，因为两种气体具有非常相似的沸点，（丙烯为-47.6摄氏度，丙烷为-42.1摄氏度），10因此，需要能够保持在低温和高压下的蒸馏塔。然而，低温蒸馏是能量密集型过程。一般来说，低温蒸馏塔在-40摄氏度至-90摄氏度的温度下使用150-200个塔板，压力范围为16至20 bar。13为了了解能源的数量，2016年生产的每公吨乙烯需要20千兆焦的能源。平均而言，这是2016年一个人在英国生活一年所需的相同能量值。14即使有如此大的能量需求，自20世纪60年代引入以来，低温蒸馏仍然是首选的分离方法。文献中已经报道了基于质量转移系统而不是能量转移方法的替代分离方法，然而，围绕这些系统的实施仍然存在问题，导致公司不愿意将其应用于其工艺中。替代品包括银盐和铜盐、膜、金属有机框架、沸石咪唑盐框架。15 -19本项目的重点将集中在离子液体替代品上。离子液体在气体分离和捕获领域一直是人们极大兴趣的焦点。20这是由于它们可以带来独特的性质，例如可忽略的蒸气压、高热稳定性、22 -24此外，它们可以被改性，并且离子液体的物理化学性质可以被精细地调节，因此它们被命名为“设计者溶剂”。然而，一些离子液体的限制因素包括它们的低气体溶解度、分离选择性和高粘度。25该项目旨在开发和测试新的化学吸附剂（形成溶质和离子液体之间的强相互作用）。这些相互作用通常不可逆地结合到用于分离轻质烯烃和链烷烃的表面材料。此外，该项目将专注于气体钻机的设计，开发和基准测试，以测试这些材料在模拟工业条件下分离烯烃和石蜡气体的能力。该设备允许气体混合物与离子液体接触，并且通过顶空气相色谱法监测气体组成随时间的变化，直到达到平衡（并且确定平衡时间）。实验将使用纯（单一）气体、烯烃和石蜡的二元混合物以及随后存在的污染物进行，以模拟蒸汽裂解后获得的气流。

Propylene and ethylene are commonly employed for food packaging, and chemicals amongst others.1-4 To keep pace with a greater demand for propylene and ethylene products, the production of light olefins must also therefore increase.3 Currently, the most feasible route is preparation via the refinement of crude oil. 5The petrochemical industry produces olefins (ethylene and propylene) from crude oil.7 After the processing of the crude oil, there is a mixture of olefins and lower chained paraffins. Therefore, a separation process is required to separate the olefins and paraffins. A mixture is not useful to industry. In terms of propylene there are three different grades: polymer grade is a minimum of 99.5% purity, chemical grade a minimum of 93-94% purity, and a refinery grade with a minimum of 60% purity. The standard method used for the separation of olefin and paraffins is cryogenic distillation.6 For example, propylene and propane separation is difficultas both gases have very similar boiling points, (-47.6 degree centrigrade for propylene and -42.1 degree centrigrade for propane),10 thus, distillation columns that can be maintained at low temperatures and high pressures are required. However, cryogenic distillation is an energy intensive process. Generally, cryogenic distillation columns operate with 150-200 trays at temperatures between-40 degree centrigrade and -90 degree centrigrade with pressures ranging from 16 to 20 bar.13 To understand the quantity of energy, every metric ton of ethylene produced in 2016, 20 Gigajoules of energy was required. That, on average is the same value of energy required for an individual to live in the UK for one year in 2016.14Even with this large energy requirement, cryogenic distillation is still the preferred method of separation since its introduction in the 1960s. Alternative separation methods have been reported in the literature, based on mass transfer systems instead of the energy transfer methods, however, there are still issues surrounding the implementation of these systems, resulting in the reluctance of companies to adopt them into their processes. Alternatives have included silver and copper salts, membranes, metal organic frameworks, zeolite imidazolate frameworks.15-19 The focus of this project will focus upon the ionic liquid alternative.Ionic liquids have been the focus of great interest in the field of gas separation and capture.20 This is due to the unique properties they can bring such as negligible vapor pressure, high thermal stability, and large liquidus range.22-24 Furthermore, they can be modified and the physical-chemical properties of ionic liquids can be finely tuned, and so they have been named as "designer solvents". However, the limiting factor for some ionic liquids include their low gas solubilities, separation selectivities, and high viscosities.25This project aims to develop and test new chemisorbent (forming strong interactions between the solute and the ionic liquid. These interactions are usually irreversibly bound to the surface) materials for the separation of light olefins and paraffins. Furthermore, this project will focus on the design, development, and benchmark of a gas rig to test the ability of these materials to separate olefin and paraffin gases, whilst mimicking industrial conditions. The equipment allows the gas mixture to come into contact with the ionic liquid, and the gas composition change over time being monitored by headspace gas chromatography, until equilibrium is reached (and equilibrium time determined). Experiments will be carried out with pure (single) gas, binary mixtures of olefin and paraffin, and subsequently with contaminates present, to mimic gas streams obtained after steam cracking.References available.