Improving solid-supported catalyst productivity by using simplified packed-bed microreactors
Improving solid-supported catalyst productivity by using simplified packed-bed microreactors
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DOI：
10.1002/anie.200603854
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发表时间：
2007-01-01
影响因子：
16.6
通讯作者：
McQuade, D. Tyler
中科院分区：
文献类型：
--
作者：
Bogdan, Andrew R.;Mason, Brian P.;McQuade, D. Tyler
在聚合树脂上支持的催化剂很容易合成，并且有望通过过滤从反应混合物中回收和容易去除然而，这样的支撑通常会显著降低催化剂的活性虽然在间歇式反应器中，均相催化剂的负载只是通过添加更多的催化剂而增加，但额外的支撑催化剂会阻碍反应容器内的试剂混合。使用连续流系统可以避免这些问题。流动的使用是有利的，因为支撑不需要从反应混合物中移除，而且连续处理也是可能的我们对微反应器的兴趣促使我们提出这样一个问题：负载型催化剂如果被装入小通道中，是否还能起作用？微反应器是一种相对较新的技术，可以进行更安全、更高效、更有选择性的反应。[1a， 4]性能的提高是由于表面积体积比的增加导致更快的传热和混合。[4a]尽管关于微反应器的文献越来越多，但很少有报道讨论填充床微反应器在合成化学中的应用（图1）。有关这些通道内的合成的文献描述了使用需要再生的固体支撑试剂进行的反应。[5-7]用负载型催化剂填充微通道时遇到的一个主要问题是由于填充材料的膨胀或尺寸引起的通道压降。[8-10]普通的merrifield型树脂和凝胶状树脂不适合用于微通道填充，因为它们在被溶剂膨胀时会堵塞通道，导致不可复制的流动。[8,9]除了单片材料外，迄今为止所研究的材料都不允许在各种溶剂中通过填料床微反应器。在这里，我们证明了一种市售树脂在高通量填料床微反应器中作为催化剂载体的效果很好，并且在流动系统中支撑催化剂可以产生更高的生产率[Eq.(1)]。我们将此讨论限制在市售聚合物树脂上。生产效率¼摩尔产品反应器体积Â时间Â摩尔催化剂ð1ÞAlthough使用电渗透流允许流动通过更广泛的包装材料，[12]这些系统比压力驱动系统复杂得多，只能与极性溶剂一起工作。随后，我们通过将不同的溶剂通过一个10厘米的填充床，并定性地评估流动是自由的还是受限的，研究了一系列用于压力驱动系统的树脂（见支持信息）。通常，轻度交联树脂在某些溶剂中会膨胀，从而阻止流体通过微通道。另一方面，高交联或大网状树脂和二氧化硅几乎在所有溶剂条件下都可以流动，因为它们不会膨胀。文献中已经报道了许多固体负载催化剂，包括本文讨论的负载催化剂的类似物。[1a]然而，我们的流动实验表明，许多聚合树脂不允许在各种溶剂中流动。由于可以获得更高的流量和输出，需要一种不限制流量的填料材料。
Catalysts supported on polymeric resins are readily synthesized and offer the promise of recycling and easy removal from reaction mixtures through filtration.[1] Often, however, such a support significantly diminishes a catalyst s activity.[2] Although homogeneous catalyst loadings in a batch reactor are simply increased by the addition of more catalyst, additional supported catalyst can hinder reagent mixing within a reaction vessel. These issues are circumvented by using continuous-flow systems. The use of flow is advantageous as the support does not need to be removed from the reaction mixture and continuous processing is also possible.[3] Our interest in microreactors prompted us to ask if supported catalysts would work when well packed into small channels. Microreactors are a relatively new technology for performing safer, more-efficient, and more-selective reactions.[1a, 4] The improved performance is attributed to faster heat transfer and mixing as a result of the increased surfacearea-to-volume ratio.[4a] Despite the increasing body of literature on microreactors, few reports discuss the use of packed-bed microreactors applied to synthetic chemistry (Figure 1). What literature does exist concerning synthesis within these channels describes reactions performed by using solid-supported reagents that require regeneration.[5–7] A major issue encountered in packing microchannels with supported-catalysts is the pressure drop across the channel caused by either the swelling or size of the packing material.[8–10] Common Merrifield-type and gel-like resins are not appropriate for microchannel packing as they clog the channels when swollen with solvent, leading to irreproducible flow.[8, 9] Other than monolithic materials,[11] no material investigated so far permits facile flow through packed-bed microreactors in a wide range of solvents. Herein, we demonstrate that a commercially available resin works well as a catalyst support in a high throughput, packed-bed microreactor and that supported catalysts in flow systems yield greater productivity [Eq.(1)]. We limit this discussion to commercially available polymeric resins. productivity ¼ moles product reactor volume  time  moles catalyst ð1ÞAlthough the use of electroosmotic flow permits flow through a wider range of packing materials,[12] these systems are far more complex than pressure-driven systems and only work with polar solvents. We subsequently examined a wide range of resins to be used in a pressure-driven system by passing different solvents through a 10-cm packed bed and qualitatively assessing whether flow was free or constricted (see the Supporting Information). Typically, lightly crosslinked resins swell in certain solvents, which prohibits flow through the microchannels. Highly cross-linked or macroreticular resins and silicas, on the other hand, allow flow under nearly all solvent conditions as they do not swell. Numerous solid-supported catalysts have been reported in the literature, including analogues of the supported catalysts discussed herein.[1a] Nonetheless, our flow experiments showed that many polymeric resins do not permit flow in a wide array of solvents. A packing material that does not restrict flow is desired as higher flow rates and output can be attained.