VALORIZATION OF SOLID DIGESTATE THROUGH AUTOTHERMAL HYDROTHERMAL LIQUEFACTION

该项目探讨了解决日益严重的湿废物问题的新方法，从农场产生的动物粪便到食品工业中加工水果和蔬菜的废水。湿废物通常比固体废物含有更多的水，妨碍了正常的运输和在垃圾填埋场储存或通过燃烧处理。相反，通常采用生物方法处理湿废物，但这些方法很慢，往往会留下大量固体残留物，需要特殊处理。该项目探索了水热液化（HTL）过程，这是一种高温高压过程，将氧气溶解到湿废物中，将这些废物转化为液体燃料，而无需外部能源来驱动该过程。通过将废物转化为液体燃料，该过程既消除了废物，又产生了有价值的产品。如果成功，该项目将提供扩大HTL工艺的新方法，使其可用于更普遍的用途，从而加强国家的能源安全，同时减少农业和其他食品工业的废物量。该项目还将培训博士后研究人员和研究生，以便在未来的工程工作中通过使用由首席研究员指导的分层指导方法有效地指导他们自己的学生。该项目的目标是通过直接耦合的自热操作强化水热液化（HTL）。这种操作将克服为该过程提供能量的传热瓶颈，并允许扩大到商业用途。爱荷华州州立大学之前的研究通过向反应器引入少量空气来演示了快速热解器的自热操作。与传统的（非氧化）热解相比，这种氧气的增加实现了产量的三倍增加，同时生物油生产的损失最小。本研究提出了一个类似的HTL反应器的自热操作，通过部分氧化的液化的一些低价值的水相产品的过程中提供的焓。据推测，氧将优先溶解在HTL产物的水性部分中，在那里它将容易与溶解的有机物反应。相比之下，更有价值的生物原油，即悬浮在水性部分中的乳液，其暴露于溶解氧的程度要低得多，基本上不会氧化。该项目的方法是开发一种量热HTL反应器，该反应器将允许在动物粪便厌氧消化的固体厌氧状态的HTL过程中确定能量流以及产物组成。在惰性和氧化环境下的实验将确定液化焓可由价值较低的液化产物的部分氧化提供的程度。除了大气条件下溶解固体的湿式氧化外，对高温高压水环境中有机化合物的氧化研究很少。如果成功，这项研究将有助于修复美国每年产生的约565太克湿废物。此外，在这项工作中实施的科学和工程原理将作为基础研究所需的过程强化HTL的湿废物，包括农业残留物，食品废物，城市固体废物，污水污泥和动物粪便的范围。一个正式的博士后研究员和研究生指导结构，结合有效的推广到幼儿园到12年级的学生，将有助于激励新的和培训未来的研究人员在这些工程实践。这个奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。

This project explores new ways to address the growing problem of wet wastes ranging from animal manure produced on farms, to wastewater from processing fruits and vegetables in the food industry. Wet wastes usually contain more water than solid material wastes, preventing the normal transport and storage at landfills or treatment by burning. Instead, biological processes are often employed to treat wet wastes, but these processes are slow and often leave a significant solid residue requiring special disposal. This project explores the hydrothermal liquefaction (HTL) process, a high-temperate, high-pressure process that dissolves oxygen into the wet wastes, to convert this waste into liquid fuel without requiring external energy sources to drive the process. By turning waste into liquid fuel, the process both eliminates the waste and generates a valuable product. If successful, this project will provide new ways to scale up HTL processes to make them available for more common use, thereby strengthening the Nation’s energy security while reducing the amount of waste from agriculture and other food industries. This project will also train postdoctoral researchers graduate students to effectively mentor their own students in future engineering efforts through the use of a tiered mentoring approach guided by the lead investigator.This goal of this project is to intensify hydrothermal liquefaction (HTL) through directly coupled autothermal operation. This operation will overcome the heat transfer bottleneck of providing energy to the process and allow for scale-up to commercial use. Previous research at Iowa State University demonstrated autothermal operation of a fast pyrolyzer by admitting a small amount of air to the reactor. This increase in oxygen achieved a three-fold increase in throughput compared to conventional (non-oxidative) pyrolysis with minimal loss in bio-oil production. This study proposes a similar autothermal operation of an HTL reactor, providing the enthalpy for the process through partial oxidation of some of the low value aqueous phase products of liquefaction. It is hypothesized that oxygen will preferentially dissolve in the aqueous fraction of HTL products where it will readily react with dissolved organics. In contrast, the more valuable biocrude, an emulsion suspended in the aqueous fraction with far less exposure to the dissolved oxygen, will not substantially oxidize. The approach to this project is to develop a calorimetric HTL reactor that will allow energy flows as well as product composition to be determined during HTL of solid digestate from anaerobic digestion of animal manure. Experiments under both inert and oxidative environments will determine the extent that the enthalpy for liquefaction can be provided by partial oxidation of the less valuable products of liquefaction. The oxidation of organic compounds in high temperature, high pressure aqueous environments has been little studied outside wet oxidation of dissolved solids at atmospheric conditions. If successful, this research will help remediate the approximately 565 teragrams of wet waste generated annually in the United States. Additionally, the scientific and engineering principles implemented in this work will serve as foundational research required for the process intensification of HTL for a range of wet wastes including agricultural residue, food wastes, municipality solid wastes, sewage sludge, and animal manure. A formal postdoctoral researcher and graduate student mentoring structure, combined with effective outreach to kindergarten through twelfth grade students, will help inspire new and train future researchers in these engineering practices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.