Hydroxyapatite Formation during Hydrothermal Liquefaction of Algae: Synthesis and Catalytic Implications

摘要标题：长期以来，人们一直在研究磷酸钙在废水供养藻类热化学转化为生物粗藻过程中改善石油性质的作用，以此作为可再生、负担得起和减少碳足迹的燃料的潜在原料。热液液化(HTL)是将湿藻类转化为富碳生物体的过程。对城市污水中生长的藻类进行HTL处理已被证明可以产生一种具有与传统石油原油相似性质的生物原油。此外，废水喂养的藻类的HTL会产生一种固体生物炭产品，到目前为止，这种产品一直被认为是一种废物。然而，有证据表明，废水生物炭中含有一种形式的磷酸钙，它可以作为催化剂来改善生物原料的组成和稳定性。堪萨斯大学的Susan Stagg-Williams教授和Belinda Sturm教授被授予一个奖项，以了解生长条件、HTL反应中生物炭的形成、磷酸钙晶体的形成以及最终对生物粗品产量和性能的影响之间的基本关系。这一知识对于藻类可再生燃料和化学品技术的最终商业化是必要的。调查人员计划了各种教育方案，以提高公众对可持续能源生产的认识和参与。水热液化是一种很有前途的全细胞转化技术，利用亚临界水将藻类生物质转化为富碳的生物原料。堪萨斯大学的初步工作表明，废水培养藻类的HTL可以导致高生物粗品产量、低生物粗品O/C比、低水平的高沸点化合物和高生物炭产量。表征研究表明，产生的生物炭是一种缺钙的取代羟基磷灰石(HAP)形式的磷酸钙。HAP具有酸碱性质，对脱水和脱氢反应具有催化活性。本研究将对藻类和模型化合物的液化进行研究，以确定：1)藻类生长条件(钙、氮、磷)对HAP在HTL反应器中结晶的影响及其对生物体组成的影响；2)HAP微晶形成对液化反应中形成的大分子单体的影响；3)液化过程中合成的HAP通过脱水和脱氢反应催化改变生物体组成的能力。将可控羟基磷灰石晶体生长与生物粗品生产相结合是一种新颖的方法。了解生长条件、HAP的形成以及最终对生物粗品产量和性质的影响之间的关系，对于藻类HTL技术的最终商业化具有重要意义。该项目支持获奖建议的另一个方面是环境重点。增加关于应用藻类处理系统去除和回收城市和农业废水中的磷的基本知识，应会产生积极的环境和经济影响。利用藻类处理系统作为去除营养物质的低成本替代方案，同时生产生物粗品和高价值催化剂和生物材料，有可能将历史上受监管的业务(废水处理)转变为创收业务。

Abstract Title: Understanding the role of calcium phosphate in improving oil properties during thermochemical conversion of wastewater-fed algae to biocrude Algae have long been investigated as a potential feedstock for renewable, affordable, and reduced carbon-footprint fuels. Hydrothermal liquefaction (HTL) is a process to convert wet algae to a carbon-rich biocrude. HTL processing of algae grown in municipal wastewater has been shown to produce a biocrude with properties similar to conventional petroleum crude. Furthermore, the HTL of wastewater-fed algae results in the production of a solid biochar product, which has hitherto been considered a waste product. However, evidence shows that wastewater-derived biochar contains a form of calcium phosphate, which may act as a catalyst to improve biocrude composition and stability. An award is made to Professors Susan Stagg-Williams and Belinda Sturm of the University of Kansas to understand the fundamental relationships between growth conditions, the formation of biochar during the HTL reaction, the formation of calcium phosphate crystals, and the ultimate impact on biocrude yield and properties. This knowledge is necessary for the ultimate commercialization of algal technology for renewable fuels and chemicals. Various educational programs are planned by the investigators which will increase public awareness and engagement with sustainable energy production. Hydrothermal liquefaction has emerged as a promising whole cell conversion technology utilizing subcritical water to convert algal biomass to a carbon-rich biocrude. Preliminary work at the University of Kansas has demonstrated that HTL of wastewater-cultivated algae leads to high biocrude yields, low biocrude O/C ratios, low levels of high boiling point compounds in the biocrude, and high production of biochar. Characterization studies have shown that the biochar produced is a calcium-deficient substituted hydroxyapatite (HAp) form of calcium phosphate. HAp has been shown to have acid-base properties and be catalytically active for the dehydration and dehydrogenation reactions. In this study, the liquefaction of algae and model compounds will be investigated to determine: 1) the impact of algal growth conditions (Ca, N, P) on the crystallization of HAp in the HTL reactor and the resultant impact on biocrude composition, 2) the impact of the HAp crystallite formation on the macromolecule monomers formed during the liquefaction reaction, and 3) the ability of HAp synthesized during liquefaction to catalytically alter the biocrude composition through dehydration and dehydrogenation reactions. Coupling controlled HAp crystal growth with the production of biocrude is novel. Generating an understanding of the relationship between growth conditions, the formation of HAp, and the ultimate impact on biocrude yield and properties has significant merit for the ultimate commercialization of algal HTL technology. Another aspect of this project supporting the recommendation for award is the environmental focus. Increasing the fundamental knowledge about the application of algal treatment systems for phosphorus removal and recovery from municipal and agricultural wastewater should yield positive environmental and economic impacts. Utilizing algal treatment systems as a low-cost alternative to nutrient removal, while generating biocrude and high-value catalysts and biomaterials, has the potential to turn a historically regulatory operation (wastewater treatment) into a revenue-generating operation.