新型金属负载生物炭催化微藻与富氢废弃物共热解蒸汽制备烃类的机制研究

Microalgae as the third generation biofuel have the potential to substitute fossil fuels, but still possess disadvantages such as high oxygenate and low hydrogen content. On the other hand, the traditional catalysts exhibit high production cost, single catalytic function, and are easy to be deactivated by coke. Based on the above two points, hydrogen-rich wastes are selected as the hydrogen donator for co-pyrolysis with microalgae; Meanwhile, in order to improve the hydrogen utilization ratio, we proposed to prepare the biochar-zero valent metal catalysts with high surface area and low coking rate through one-step microwave-assisted pyrolysis. The catalysts provide dual catalytic properties of deoxycracking and hydrogen transferring for the reforming the co-pyrolysis steam to produce hydrocarbon-rich oil. In the project, the properties and structure of the prepared catalysts are analyzed to understand the catalyst formation mechanism; The effective hydrogen donating groups are confirmed through the study of the linear relationship between effective hydrogen index and hydrocarbon products as well as the analysis of the elemental composition and structure characteristics of hydrogen-rich wastes. Furthermore, the catalytic active sites of “catalytic cracking” and “catalytic transfer hydrogenation” and the corresponding key affecting factors are analyzed. We also focus on building the kinetic models of catalyst deactivation, catalytic cracking, and catalytic transfer hydrogenation for the in-depth study of hydrocarbons formation mechanism. Moreover, the catalytic co-pyrolysis of biomass-derived model compounds and 2H marked isopropanol is studied to verify and supplement the conversion mechanism through isotopic tracing.

微藻作为第三代生物能源有完全取代化石能源的潜力，但是存在多氧少氢的缺点；另一方面，传统催化剂生产成本高，催化功能单一，且易结焦失活。基于上述两点，本项目拟采用富氢废弃物作为供氢体，与微藻进行共热解；同时为了提升转化过程中氢利用率，提出采用微波热解一步法制备一类表面积大、结焦率低的新型生物炭-零价金属催化剂，提供脱氧裂化及氢转移双重催化功能，用于共热解蒸汽的催化重整获得烃类燃油。通过分析催化剂性质及结构，解析催化剂形成机制；通过探究有效氢系数与烃类产物形成的线性规律，结合富氢废弃物的元素组成及结构特征分析，明晰有效供氢基团；此外，确立催化剂“催化裂化”及“催化转移氢化”活性位点，解析关键影响因素；建立催化剂失活、催化裂化以及催化转移氢化等反应动力学模型，深化揭示烃类化合物的形成机制，并通过研究氘代异丙醇与生物质模型化合物的催化共热解，根据同位素示踪结果验证并补充催化机制。

微藻作为第三代生物能源有取代化石能源的潜力，但是存在多氧少氢的缺点；另一方面，塑料等富氢废弃物难以自然降解、环境影响大。本项目提出采用富氢废弃物为供氢体，与微藻进行共热解；同时为了提升转化过程中氢利用率，提出采用表面积大、结焦率低的新型生物炭-零价金属催化剂，提供脱氧裂化及氢转移双重催化功能，用于共热解蒸汽的催化重整获得烃类燃油。本项目搭建了连续搅拌式微波快速热解耦合异位催化系统，以聚乙烯类塑料废弃物为原料，对该反应系统表现进行评估，结果表明连续搅拌体系的产物的碳数分布主要为短链烃和单环芳烃，汽油烃类的选择性最高可至98.0%，连续式体系达到的净能量收益高达34.16 MJ/kg，而相同条件下，间歇式热解系统净能量收益为负值（-38.86 MJ/kg）。本项目对微藻热解特性及其组分间相互作用进行了研究，微藻微波热解后生物油组成主要包括含氧化合物、含氮化合物以及脂肪烃化合物，蛋白质、碳水化合物以及脂质各组分间相互作用机制表现为碳水化合物和脂质间的相互作用会持续促进醇类和酯类物质的产生，脂质和蛋白质间的相互作用会促进腈类、胺和酰胺类物质的生成，蛋白质和葡萄糖间的相互作用主要对芳香烃类、酯类和酰胺类物质由促进作用。采用金属负载生物炭分别对塑料和微藻进行催化共热解研究，以LDPE、聚丙烯 (PP) 和聚苯乙烯 (PS) 模拟塑料废弃物，结果表明，Ni负载生物炭对C4-C12烃类化合物的选择性最高可达 87.9%，对苯、甲苯和二甲苯 (BTX) 的产率可达 78.1 mg/g；对微藻的催化热解结果表明BTX的选择性高达75.62%，其中苯的定量收率为58.01 mg/g；研究提出了聚乙烯、聚丙烯和聚苯乙烯长链自由基的裂解及脂肪族芳构化以及微藻/微藻模型化合物催化转化为芳烃的机制。将微藻与富氢废弃物经生物炭催化剂催化共热解，分析了两者的协同效应，表明烃类自由基会促进含氧氮基团的去除，而氧氮类中间产物则利于长链烃类分子的断键。