Ekstrakcija hmelja (Humulus lupulus L.) s sub- in superkritičnimi fluidi : doktorska disertacija

slovenian

doktorska dela

2023

carbon dioxide   dimethyl ether   financial analysis   hops (Humulus lupulus L.)   hops essential oil   propane   sub- and supercritical extraction   sulphur hexafluoride

Univerza v Mariboru, Fakulteta za kemijo in kemijsko tehnologijo

The main objective of the PhD research was to conduct preliminary studies on extractions with different solvents and to obtain data for the design of an industrial scale-up for supercritical extraction of hops. The work consists of three parts. The first part focuses on the study of hop varieties in Slovenia and on the characteristics of the world market.The second part of the work investigates the extraction efficiency of hops with different solvents under sub- and supercritical operating conditions. The solvents were selected according to their different polarity. CO2, propane and SF6 were used as non-polar solvents and DME as polar solvent. We were particularly interested in DME and SF6 because no previous study has investigated the extraction process of hops using these two solvents. Under the same operating conditions, the solvents were in different states. The extractions were carried out in a temperature range of 20 °C to 80 °C and a pressure range of 50 bar to 150 bar for all solvents. A semi-continuous operating mode was used for the extraction process, and the influence of the process parameters on the total extraction yield and the content of bitter acids in the extract was studied. The mathematical model based on Fick's second law described well the experimental extraction results. In addition, high-performance liquid chromatography (HPLC) was used to determine the content of ?- and ß-acids in all 27 extract samples. The yield of bitter compounds in the hop extracts was highly influenced by the type of solvent, temperature, and pressure applied during extraction. The results show that CO2 and propane were approximately equivalent to DME in terms of solvating power, while SF6 was a poor solvent under the same conditions.The essential oil and the content of the prenylated flavonoid xanthohumol (XN) in the hop extracts were also evaluated. The content of XN in the extracts was determined by high-performance liquid chromatography. The highest concentration of XN was obtained in the extracts derived by DME.For the analysis of the essential oil components in the extracts associated with a distinct odour, steam distillation of the extracts was carried out and GC analysis was performed. Hop oil obtained from CO2 extracts under certain conditions had the highest relative concentrations of linalool, ß-caryophyllene, and ?-humulene, and oil obtained from propane extracts had the highest content of all other five selected components (myrcene, geraniol, farnesene, ?-selinene, and ?-cadinene).The influence of oxidation and temperature on the shelf life of the extracts was studied with an accelerated ageing test, and the difference in the content of ?- and ß-acids, XN, and EO was determined at specific extraction conditions.The last part of the thesis proposes the design of a CO2 extraction process and an economic analysis of the investment. For this purpose, a "scale-up" process design and optimization of the CO2 extraction process were performed. For the separation processes, we developed a model for mass transfer between solid and liquid phases, enriched with knowledge of thermodynamics, transport phenomena and mass balance. The characteristics of each process unit were determined and the investment values were estimated. We evaluated the operating costs and determined the costs of propellants, which includes the time portion of operation, electricity costs, steam costs, and cooling water costs. In the light of the situation in hop growing sector, the cost of hops was also determined. The market is the place where information about supply and demand is available and where the price of hops is formed - within the framework of a market flow. With regard to the extraction process itself, we also determined the cost of labour and evaluated the income from the sale of the extract. A financial analysis was carried out with criteria for deciding whether the investment is acceptable.

07.08.2023