Institut für Agrartechnik

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Acid-assisted extraction and hydrolysis of inulin from chicory roots to obtain fructose-enriched extracts
(2023) Stökle, Katrin; Jung, Dennis; Kruse, Andrea
Chicory (Cichorium intybus var. foliosum) roots are an agricultural residue and a low cost feedstock for the production of the platform chemical 5-Hxdroxymethylfurfural (HMF). In a first step, inulin and fructose have to be extracted from the roots. The resulting aqueous extract represents the starting material for the HMF production. In the reaction to HMF, inulin has to be hydrolyzed first to fructose. For this reason, two methods to increase the fructose content in these extracts before the reaction were investigated. This was conducted within the framework of integrating acid hydrolysis into a biorefinery process for HMF production. The first method (one-step process) was acid-assisted extraction to directly hydrolyze inulin in the course of the extraction process. Chicory roots were extracted at 60 and 80 °C at pH 2 and 4 using buffer solutions. The second approach (two-step process) was aqueous extraction at neutral pH followed by nitric acid hydrolysis of the extract at 60 and 80 °C under reduced pH. It was found that in the first approach, the pH of 2 led to a fivefold increase in the fructose content of the extract, resulting from inulin hydrolysis and corresponding to 56% of theoretical fructose yield. For the second approach, it was possible to achieve complete hydrolysis at pH below 2.5 and at 80 °C. Separating extraction and hydrolysis was found to be more suitable in terms of including this process step into a biorefinery concept for HMF production. It was possible to reduce the initial inulin content by 95%.
Extraction of common microalgae by liquefied dimethyl ether: Influence of species and pretreatment on oil yields and composition
(2020) Bauer, Manuel C.; Konnerth, Philipp; Kruse, Andrea
Liquefied dimethyl ether (DME) is regarded as a promising, green solvent for biomass lipid extractions. It is non-toxic, applicable to wet feedstocks, and allows easy product separation by pressure reduction. Yet, knowledge about its usability in combination with oleaginous microalgae is limited. In the current work, four common microalgae and cyanobacteria species were used to study DME extraction characteristics: Arthrospira platensis, Nannochloropsis gaditana, Phaeodactylum tricornutum, and Scenedesmus almeriensis. Dried samples were subjected to a batch DME extraction and compared to a standard chloroform/methanol procedure. To evaluate the influence of pretreatment, particle size distributions of two different milling sequences (knife- and cryo-milling) and the resulting effects on DME extraction and oil composition were addressed. Additionally, an algae washing procedure was tested. DME extractions resulted in oil yields of 0.5–2.7% of dry mass (equal to 5–19% of total lipids) without further pretreatment. Cryo-milling reduced median particle sizes by 25–87% and simultaneously increased lipid yields to 1.7–5.6% of dry mass (17–50% of total lipids). Phaeodactylum tricornutum showed the highest extraction efficiency with DME, combined with a favorable fatty acid profile. Although being most affected by the additional milling pretreatment, Arthrospira platensis performed worst in both scenarios. DME extracted oils were generally characterized by enhanced contents of C14:0, C16:0, and C16:1 fatty acids. However, relative abundances were strongly influenced by the properties of the tested algae species. The additional cryo-milling pretreatment affected fatty acid compositions by increasing the shares of potentially valuable polyunsaturated fatty acids.
Hydrothermal carbonization of fructose—effect of salts and reactor stirring on the growth and formation of carbon spheres
(2021) Jung, Dennis; Duman, Gözde; Zimmermann, Michael; Kruse, Andrea; Yanik, Jale
Hydrothermal carbonization (HTC) has become a promising technology for the production of hydrochar and carbon spheres. Several studies indicate a strong dependency of the reaction conditions on the sphere diameter. The usage of additives, such as salts, is one possibility to increase the size of the spheres. However, the growth mechanism which leads to larger particles is not fully understood. In this work, kinetic studies of HTC with fructose were performed with different salts as additives. The growth of the particles (the increase in size) has been compared to the formation rates (increase in yield) of hydrochar by using the reaction rate constants from the kinetic model. The results indicate that the acceleration of the growth rate is independent of the formation rate. It is therefore assumed that coagulation, as a growth mechanism, took place. With longer reaction times, the particles reached a stable particle size, independently from the added salts; therefore, it was assumed that the particles underwent some sort of solidification. The state of matter can therefore be described as an intermediate state between liquid and solid, similar to mesophase pitch. Experiments with a stirrer resulted in squashed particles, which supports the model, that the particles exhibit emulsion-like behavior.

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