Abstract This review presents and discusses the progress in combining fast pyrolysis and catalytic hydrodeoxygenation (HDO) to produce liquid fuel from solid, lignocellulosic biomass. Fast pyrolysis of biomass is a well-developed technology for bio-oil production at mass yields up to ∼75%, but a high oxygen content of 35–50 wt% strongly limits its potential as transportation fuel. Catalytic HDO can be used to upgrade fast pyrolysis bio-oil, as oxygenates react with hydrogen to produce a stable hydrocarbon fuel and water, which is removed by separation. Research on HDO has been carried out for more than 30 years with increasing intensity over the past decades. Several catalytic systems have been tested, and we conclude that single stage HDO of condensed bio-oil is unsuited for commercial scale bio-oil upgrading, as the coking and polymerization, which occurs upon re-heating of the bio-oil, rapidly deactivates the catalyst and plugs the reactor. Dual or multiple stage HDO has shown more promising results, as the most reactive oxygenates can be stabilized at low temperature prior to deep HDO for full deoxygenation. Catalytic fast hydropyrolysis, which combines fast pyrolysis with catalytic HDO in a single reactor, eliminates the need for reheating condensed bio-oil, lowers side reactions, and produces a stable oil with oxygen content, H/C ratio, and heating value comparable to fossil fuels. We address several challenges, which must be overcome for continuous catalytic fast hydropyrolysis to become commercially viable, with the most urgent issues being: (i) optimization of operating conditions (temperature, H2 pressure, and residence time) and catalyst formulation to maximize oil yield and minimize cracking, coke formation, and catalyst deactivation, (ii) development of an improved process design and reactor configuration to allow for continuous operation including pressurized biomass feeding, fast entrainment and collection of char, which is catalytically active for side reactions, efficient condensation of the produced oil, and utilization and/or integration of by-products (non-condensable gasses and char), and (iii) long-term tests with respect to catalyst stability and possible pathways for regeneration. By reviewing past and current research from fast pyrolysis and catalytic HDO, we target a discussion of the combined processes, including direct catalytic fast hydropyrolysis. By critically evaluating their potential and challenges, we finally conclude, which future steps are necessary for these processes to become industrially feasible.

中文翻译：

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来自生物质快速热解、催化加氢脱氧和催化快速加氢热解的运输燃料

摘要 本综述介绍并讨论了结合快速热解和催化加氢脱氧 (HDO) 以从固体木质纤维素生物质生产液体燃料的进展。生物质的快速热解是一种成熟的生物油生产技术，产量高达 75%，但 35-50% 的高氧含量严重限制了其作为运输燃料的潜力。催化 HDO 可用于升级快速热解生物油，因为含氧化合物与氢反应生成稳定的碳氢燃料和水，通过分离将其去除。对 HDO 的研究已经进行了 30 多年，而且在过去的几十年中强度越来越大。已经测试了几种催化系统，我们得出结论，冷凝生物油的单级 HDO 不适合商业规模的生物油升级，因为焦化和聚合，这发生在重新加热生物油时，迅速使催化剂失活并堵塞反应器。双级或多级 HDO 已显示出更有希望的结果，因为在深度 HDO 进行完全脱氧之前，活性最强的含氧化合物可以在低温下稳定。催化快速加氢热解，将快速热解与催化HDO结合在一个反应​​器中，无需再加热冷凝的生物油，减少副反应，生产出含氧量、H/C比和热值与化石燃料相当的稳定油燃料。我们解决了几个挑战，必须克服这些挑战才能使连续催化快速加氢热解在商业上可行，最紧迫的问题是：（i）优化操作条件（温度、氢气压力、和停留时间）和催化剂配方，以最大限度地提高油产量并最大限度地减少裂化、焦炭形成和催化剂失活，(ii) 开发改进的工艺设计和反应器配置，以允许连续操作，包括加压生物质进料、快速夹带和收集焦炭，其对副反应、所产油的有效冷凝以及副产品（不可冷凝气体和炭）的利用和/或整合具有催化活性，以及​​ (iii) 关于催化剂稳定性和可能的​​长期测试再生途径。通过回顾快速热解和催化 HDO 的过去和当前研究，我们针对组合过程进行了讨论，包括直接催化快速加氢热解。通过批判性地评估他们的潜力和挑战，我们最终得出结论，