Hongthong Sukanya, Leese Hannah S, Chuck Christopher J
Department of Chemical Engineering, University of Bath, Claverton Down, Bath BA2 7AY, U.K.
ACS Omega. 2020 Aug 7;5(32):20586-20598. doi: 10.1021/acsomega.0c02854. eCollection 2020 Aug 18.
Food waste is a promising resource for the production of fuels and chemicals. However, increasing plastic contamination has a large impact on the efficiency of conversion for the more established biological routes such as anaerobic digestion or fermentation. Here, we assessed a novel route through the hydrothermal liquefaction (HTL) of a model waste (pistachio hulls) and polypropylene (PP). Pure pistachio hulls gave a biocrude yield of 34% (w/w), though this reduced to 16% (w/w) on the addition of 50% PP in the mixture. The crude composition was a complex blend of phenolics, alkanes, carboxylic acids, and other oxygenates, which did not change substantially on the addition of PP. Pure PP does not breakdown at all under HTL conditions (350 °C, 15% solids loading), and even with biomass, there is only a small synergistic effect resulting in a conversion of 19% PP. This conversion was enhanced through using typical HTL catalysts including Fe, FeSO·7HO, MgSO·HO, ZnSO·7HO, ZSM-5, aluminosilicate, Y-zeolite, and NaCO; the conversion of PP reached a maximum of 38% with the aluminosilicate, for example. However, the PP almost exclusively broke down into a solid-phase product, with no enhancement of the biocrude fraction. The mechanism was explored, and with the addition of the radical scavenger butylated hydroxytoluene (BHT), the conversion of plastic reduced substantially, demonstrating that radical formation is necessary. As a result, the plastic conversion was enhanced to over 50% through the addition of the co-solvent and hydrogen donor, formic acid, and the radical donor, hydrogen peroxide. The addition of formic acid also changed the crude composition, including more carboxylic acids and oxygenated species than the conversion of the biomass alone; however, the majority of the carbon distributed to the volatile organic gas fraction producing an array of short-chain volatile hydrocarbons, which potentially could be repolymerized as a polyolefin or combined with the biocrude for further processing. Catalytic HTL was therefore shown to be a promising method for the valorization of polyolefins with biomass under typical HTL conditions.
食物垃圾是生产燃料和化学品的一种有前景的资源。然而，塑料污染的增加对厌氧消化或发酵等更成熟的生物途径的转化效率有很大影响。在此，我们评估了一条通过对模拟废弃物（开心果壳）和聚丙烯（PP）进行水热液化（HTL）的新途径。纯开心果壳的生物原油产率为34%（w/w），不过在混合物中添加50%的PP后，该产率降至16%（w/w）。原油成分是酚类、烷烃、羧酸和其他含氧化合物的复杂混合物，添加PP后其成分变化不大。纯PP在HTL条件（350℃，15%固含量）下根本不会分解，即使与生物质一起，也只有很小的协同效应，导致PP的转化率为19%。通过使用典型的HTL催化剂，包括铁、FeSO₄·7H₂O、MgSO₄·H₂O、ZnSO₄·7H₂O、ZSM - 5、硅铝酸盐、Y型沸石和Na₂CO₃，这种转化率得到了提高；例如，使用硅铝酸盐时，PP的转化率最高达到38%。然而，PP几乎完全分解为固相产物，生物原油部分没有增加。对其机理进行了探索，添加自由基清除剂丁基羟基甲苯（BHT）后，塑料的转化率大幅降低，这表明自由基的形成是必要的。因此，通过添加共溶剂和氢供体甲酸以及自由基供体过氧化氢，塑料转化率提高到了50%以上。甲酸的添加也改变了原油成分（相较于仅生物质的转化），包括更多的羧酸和含氧化合物；然而，大部分碳分布到挥发性有机气体部分，产生一系列短链挥发性烃，这些烃有可能重新聚合成聚烯烃或与生物原油结合进行进一步加工。因此，催化HTL被证明是在典型HTL条件下将聚烯烃与生物质进行增值利用的一种有前景的方法。
