Effect of Macro- and Microstructures on Catalytic Hydrogenolysis of Polyolefins
Effect of Macro- and Microstructures on Catalytic Hydrogenolysis of Polyolefins
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DOI：
10.1021/acs.macromol.2c00805
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发表时间：
2022-07-22
期刊：
影响因子：
5.5
通讯作者：
Delferro, Massimiliano
中科院分区：
文献类型：
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作者：
Hackler, Ryan A.;Lamb, Jessica V.;Delferro, Massimiliano
不同相对分子质量和支链密度的聚乙烯以及不同相对分子质量和规整度的聚丙烯被催化转化为低相对分子质量的液体产品，以展示混合废塑料流中这些不同性质如何影响最终产品。以钛酸锶纳米立方体(Pt/STO)为催化剂，在300℃、170psi的氢气存在下，在无溶剂条件下进行氢解反应。聚乙烯的初始相对分子质量对最终产物的产率有一定的影响(从类似7600 Da的M-n的55wt%到类似于50,950 Da的M-n的67wt%)。高相对分子质量聚合物的微观结构(定义为聚合物中支链的长度和密度)是决定产率的主要因素(含C-2支链的线性低密度聚乙烯(LLDPE)从67wt%到97wt%，而含C-6支链的线性低密度聚乙烯(LLDPE)的产率从38850Da到38850Da不等)。在不同相对分子质量的PE转化过程中，得到了相同的产物(M-n=C-29-C-46，D=1.1-1.6)和不需要的轻气分布(C-1-C-4约为90摩尔%，C-5-C-8约为10摩尔%)。在一定相对分子质量下，聚丙烯的规整度对最终产物的相对分子质量有显著影响，但对转化率影响不大。等规聚丙烯(IPP)的氢解产物与无规(APP)和间规聚丙烯(SPP)的产物C-54(D类似于1.0)相比，具有更宽的多分散度(D约为1.4)，而C-(D约为1.0)的多分散度更宽。甲基的立体化学决定了熔体中聚合物的形状和结构，这反过来又影响碳氢链与催化剂表面的相互作用，从而影响C-C裂解的数量。这些结果显示了各种特性，如废塑料的相对分子质量和结构如何影响最终产品。
Polyethylenes of varying molecular weight and branch density, as well as polypropylenes of varying molecular weight and tacticity, were catalytically converted to lowermolecular-weight liquid products to showcase how these various properties in a mixed waste plastic stream could affect the final product. A Pt nanoparticle on a strontium titanate nanocuboid (Pt/STO) catalyst was used under solvent-free conditions in the presence of 170 psi of H-2 at 300 degrees C for hydrogenolysis. The initial molecular weight of polyethylene was found to have a moderate effect on the yield to the final product (ranging from 55 wt% for M-n similar to 7600 Da to 67 wt% for M-n similar to 50,950 Da). The microstructure, defined as the length and density of branches in a polymer, of higher-molecular-weight polymers was the dominant factor in determining the yield (ranging from 67 wt% for M-n 50,950 Da for linear low-density polyethylene (LLDPE) with C-2 branches to 97 wt% for M-n similar to 38,850 Da for LLDPE with C-6 branches). The same products (M-n = C-29-C-46, D = 1.1-1.6) and distribution of undesired light gases (C-1-C-4 approximate to 90 mol%, C-5-C-8 approximate to 10 mol%) are obtained from conversions of PE of varying molecular weight. The tacticity of polypropylene at a given molecular weight had a significant effect on the molecular weight of the final product, while not strongly affecting conversion. Hydrogenolysis of isotactic polypropylene (iPP) produced approximate to C-18 with a wider polydispersity (D similar to 1.4) compared to the narrow approximate to C-64 (D similar to 1.0) and approximate to C-54 (D similar to 1.0) products from atactic (aPP) and syndiotactic (sPP) polypropylene, respectively. The stereochemistry of the methyl groups dictates the shape and structure of the polymer in the melt, which in turn affects how the hydrocarbon chain interacts with the catalyst surface, thereby impacting the number of C-C scissions. These results show how various characteristics such as the molecular weight and structure of a waste plastic stream could affect the final product.