低碳烷烃选择氧化反应循环尾气中CO选择性氧化脱除研究

Partial oxidation of hydrocarbons played a key role in the chemical industry. In the past, the majority of studies have dealt with oxidation of olefins or aromatic hydrocarbon. However, it is of great importance to study the selective oxidation of light alkanes from a fundamental and industrial point of view due to their higher abundance and lower price compared to the corresponding olefins.. The oxidation of light alkanes is still a challenging task due to the low intrinsic chemical reactivity of the alkanes. Although selectivity and conversion are the two most critical parameters that impact the overall economics of oxidation of light alkanes, efficient heat removal is also major concern for extremely exothermic oxidation of alkanes. Under the premise of ensuring high selectivity, conversion of alkanes would necessarily has to be reduced to accommodate the larger heat generated by alkane oxidation for industrial purpose. In order to minimize losses of alkane feedstock and maximize the process economics, recirculation of unconverted alkanes after strippping the condensables becomes a compulsory choice. However, one drawback of recycling technique is that concentration of CO in the off-gas stream would build-up and this will create a highly dangerous mixture due to a high risk of explosion for CO (explosion limit of 12.5~74.2%). Therefore, removal of CO from the off-gas stream before returning it to feed steam is a critical issue for ensuring the reactant mixture in a recycle loop outside the flammability region. A promising catalyst for producing an essentially CO-free recycle off-gas stream must be highly selective towards oxidation of CO without measurable consumption of hydrocarbons for the economic efficiency for alkane oxidation.. Catalytic oxidation of CO is of great importance in a variety of practical application. However, in many of the studies reported so far, the CO oxidation reactor feed did not simultaneously include CO2, olefins, alkanes and H2O, all of which occur in significant concentrations in effluents for real-life chemical process, and obviously their co-presence can lead to results not anticipated from studies with only a mixture of CO and O2. Although noble metal catalysts have exhibited the unique low-temperature activity for CO oxidation, their CO catalytic oxidation performance would be strongly inhibited upon introduction of hydrocarbons or CO2 due to competition adsorption on active sites. This critical weakness, as well as high cost and availability of noble metal have limited their practical application in CO oxidation removal of real-life chemical process with many components. Obviously, the separation of active sites for the CO and other components is indispensable for a high effective catalyst for CO oxidation. Mixed metal oxides are a group of materials with highly diversified properties by tailoring the compositions and structures. It is possible to develop a mixed metal oxide containing the desired multi-functional active sites to eliminate inhibition effect of other components on CO oxidation. . Accordingly, it is prospected that mixed metal oxides with multi-functionality can be responsible for optimizing catalytic efficiency of CO removal by facilitating compositions and structures. The present task will focus on oxidative removal of CO in an off-gas from propane oxidation to acrylic acid. Much effort will be devoted to building a catalyst with multi-functional active sites by tailoring component and structure and further advancing our understanding of relationship between structure and performance. Another important objective is to reveal the nature of synergetic effect of multi-functional active sites, which will exhibit high resistance to hydrocarbon or CO2 inhibition and excellent removal performance of CO oxidation. We expected that the results enable us to throw a universal light on the CO removal performance for an actual effluent from a practical chemical processes.

低碳烷烃选择活化和氧化转化是21世纪化学化工和催化发展的优先研究方向。本项目针对低碳烷烃选择氧化过程强放热所采用的尾气循环工艺中CO逐渐累积所造成的潜在安全隐患,提出了在组成复杂多样的丙烷选择氧化制丙烯酸循环尾气体系下，选择性氧化脱除CO并完全保留尾气中需循环利用的烷烃及其它副产的碳氢化合物的新方法；特别是针对催化剂上由于竞争吸附所导致的尾气中其它组分对CO氧化的抑制作用，创新性提出通过结构、组成、功能设计或可控合成等手段在复合金属氧化物催化剂表面设计和构筑多功能活性中心来消除竞争吸附以及尾气中其它组分对CO氧化脱除的抑制作用；系统研究催化剂表面不同功能活性位与尾气中各组分氧化性能间的构效关系；揭示多功能活性中心间协同作用对CO选择氧化脱除反应抑制作用或促进作用的本质及机理；开发具有普适性的多元复合金属氧化物催化剂，实现低碳烷烃选择氧化反应循环尾气体系中CO的高活性和高选择性定向氧化脱除。

低碳烷烃的选择活化和氧化转化已被一些发达国家列为21世纪化学化工和催化发展的优先研究方向之一。与烯烃和芳烃等不饱和烃相比，烷烃选择活化和氧化转化技术仍面临巨大挑战，在高效催化剂开发、工艺过程设计以及化学工程等方面均存在许多困难。由于低碳烷烃选择氧化为强放热过程，尽管转化率和产物选择性是衡量所设计开发的烷烃选择氧化反应催化剂性能的二个重要指标，但在实际工业生产中，从工艺过程设计的角度考虑，为了控制并有效移去烷烃选择氧化反应过程中释放的大量热量，通常在保持高的产物选择性的前提下，适当降低原料的转化率以保证反应过程中热量的及时移出。由于烷烃的转化率被控制在较低的范围（<50%），为了降低原料成本和节能环保，尾气循环工艺在烷烃选择氧化反应中通常是优先选择的工艺过程。但该工艺过程中循环尾气中含量相对较高且具有较宽爆炸极限(12.5%-74.2%）的CO在循环过程中的逐渐累积将对工业装置的安全运行构成潜在威胁。因此，针对组成复杂多样的低碳烷烃选择氧化反应尾气体系，如何高选择性地氧化脱除CO，而完全保留需循环利用的烷烃原料以及副产的其它碳氢化合物是尾气循环工艺亟需解决的关键问题，也是低碳烷烃催化转化和利用能否实现工业应用的关键工艺过程之一。.本项目针对低碳烷烃选择氧化过程强放热所采用的尾气循环工艺中CO逐渐累积所造成的潜在安全隐患,提出了在组成复杂多样的丙烷选择氧化制丙烯酸循环尾气体系下，选择性氧化脱除CO并完全保留尾气中需循环利用的烷烃及其它副产的碳氢化合物的新方法；通过结构、组成、功能设计或可控合成等手段在复合金属氧化物催化剂表面设计和构筑多功能活性中心来选择性脱除循环尾气中的CO；开发出具有普适性的多元复合金属氧化物催化剂，实现低碳烷烃选择氧化反应循环尾气体系中CO的高活性和高选择性定向氧化脱除。