Jessica Hoffmann

Hydrothermal liquefaction of Spirulina and Nannochloropsis salina under subcritical and supercritical water conditions

Six hydrothermal liquefaction experiments on Nannochloropsis salina and Spirulina platensis at subcritical and supercritical water conditions (220–375 °C, 20–255 bar) were carried out to explore the feasibility of extracting lipids from wet algae, preserving nutrients in lipid-extracted algae solid residue, and recycling process water for algae cultivation. GC–MS, elemental analyzer, FT-IR, calorimeter and nutrient analysis were used to analyze bio-crude, lipid-extracted algae and water samples produced in the hydrothermal liquefaction process. The highest bio-crude yield of 46% was obtained on N. salina at 350 °C and 175 bar. For S. platensis algae sample, the optimal hydrothermal liquefaction condition appears to be at 310 °C and 115 bar, while the optimal condition for N. salina is at 350 °C and 175 bar. Preliminary data also indicate that a lipid-extracted algae solid residue sample obtained in the hydrothermal liquefaction process contains a high level of proteins.

Conceptual design of an integrated hydrothermal liquefaction and biogas plant for sustainable bioenergy production.

Initial process studies carried out in Aspen Plus on an integrated thermochemical conversion process are presented herein. In the simulations, a hydrothermal liquefaction (HTL) plant is combined with a biogas plant (BP), such that the digestate from the BP is converted to a biocrude in the HTL process. This biorefinery concept offers a sophisticated and sustainable way of converting organic residuals into a range of high-value biofuel streams in addition to combined heat and power (CHP) production. The primary goal of this study is to provide an initial estimate of the feasibility of such a process. By adding a diesel-quality-fuel output to the process, the product value is increased significantly compared to a conventional BP. An input of 1000 kg h(-1) manure delivers approximately 30-38 kg h(-1) fuel and 38-61 kg h(-1) biogas. The biogas can be used to upgrade the biocrude, to supply the gas grid or for CHP. An estimated 62-84% of the biomass energy can be recovered in the biofuels.

Hydrothermal liquefaction of biomass

Biomass is one of the most abundant sources of renewable energy, and will be an important part of a more sustainable future energy system. In addition to direct combustion, there is growing attention on conversion of biomass into liquid energy carriers. These conversion methods are divided into biochemical/biotechnical methods and thermochemical methods, such as direct combustion, pyrolysis, gasification, liquefaction, etc. This chapter focuses on hydrothermal liquefaction, where high pressures and intermediate temperatures together with the presence of water are used to convert biomass into liquid biofuels, with the aim of describing the current status and development challenges of the technology. During the hydrothermal liquefaction process, the biomass macromolecules are first hydrolyzed and/or degraded into smaller molecules. Many of the produced molecules are unstable and reactive and can recombine into larger ones. During this process, a substantial part of the oxygen in the biomass is removed by dehydration or decarboxylation. The chemical properties of the product are mostly dependent of the biomass substrate composition. Biomass consists of various components such as carbohydrates, lignin, protein, and fat, and each of them produce distinct groups of compounds when processed individually. When processed together in different ratios, they will most likely cross-influence each other and thus the composition of the product. Processing conditions including temperature, pressure, residence time, catalyst, and type of solvent are important for the bio-oil yield and product quality.

Hydrothermal Conversion in Near-Critical Water – A Sustainable Way of Producing Renewable Fuels

Liquid fuels from biomass will form an essential part of meeting the grand challenges within energy. The need for renewable and sustainable energy sources is triggered by a number of factors; like increase in global energy demand, depletion of conventional resources, climate issues and the desire for national/regional energy independence. Especially in marine, aviation and heavy land transport suitable carbon neutral drop-in fuels from biomass are needed, since electrification of those is rather unlikely. Hydrothermal conversion (HTC) of biomass offers a solution and is a sustainable way of converting biomass feedstocks to valuable bio-crude. HTC is a high pressure and medium temperature thermochemical biomass conversion process and converts aqueous biomasses under sub- or super-critical conditions to a bio-crude similar to fossil crude oil.

Lignocellulosic Biomass—Thermal Pre-treatment with Steam

With the ever rising demand for more energy and the limited availability of depleted world resources, many are beginning to look for alternatives to fossil fuels. Liquid biofuel, in particular, is of key interest to decrease our dependency on fuels produced from imported petroleum. Biomass pre-treatment remains one of the most pressing challenges in terms of cost-effective production of biofuels. The digestibility of lignocellulosic biomass is limited by different factors such as the lignin content, the crystallinity of cellulose and the available cellulose accessibility to hydrolytic enzymes. A number of different pre-treatment methods are known to enhance the digestibility of lignocellulosic biomass by affecting these limiting factors. Some of them are: milling, thermal pre-treatment with steam or hot water, acid pre-treatment, and alkaline pre-treatment. This chapter will focus on one of the more promising technologies; thermal pre-treatment with steam.