engleski

From waste edible oil to biofuel: Development of integrated microsystem for enzymatic production of biodiesel

Biodiesel has been identified as one of the most prominent options for partially reducing the use of conventional fossil fuels, a major cause of climate change. Biodiesel, a mixture of monoalkyl esters of long-chain fatty acids methyl esters (FAME), provides valuable improvements over petroleum diesel in terms of biodegradability and renewability, better quality of exhaust gas emission and reduced environmental impact. Conventional biodiesel production processes cannot meet the demand for biodiesel, so new intensified processes are being rapidly developed. The use of microreactors is one way to intensify conventional processes in terms of mixing, mass transfer, and reduction of reaction time. To maximize the potential of biodiesel production, several experimental set-ups for biodiesel production by transesterification of edible oils were proposed and developed. Different combinations of inlets were investigated to maximize biodiesel yield while lipase was used as a catalyst in both, free and immobilized form, respectively. Different mass ratios of inlet streams, namely oil, methanol and lipase were also investigated. The production of biodiesel is only a first step towards gaining a product that meets the quality standards according to EN 14214. After transesterification, separation of biodiesel and byproducts, primarily glycerol, is usually carried out by a phase separation process based on the difference in density. Common purification methods include washing the biodiesel with water (also known as wet washing). However, rinsing with water generates large amounts of wastewater that must be properly disposed of, which is a major economic and environmental problem. Therefore, alternative solutions for biodiesel purification have been developed, of which the use of deep eutectic solvents (DESs) is of particular interest. It has been shown that DESs prepared from choline chloride and glycerol as hydrogen bond donor can efficiently and completely remove free glycerol from biodiesel. To further investigate biodiesel purification, a membrane separator was used. Several membranes can be used for glycerol removal, and the polyacrylonitrile membrane (PAN) showed the best performance, resulting in the lowest glycerol content in the permeate (0.006% (w/w)). Finally, an integrated biodiesel production process was developed. It consisted of lipase- catalyzed transesterification of sunflower oil and product purification carried out in sequentially connected microreactor and microseparator units. Glycerol, the by-product of the transesterification process, was removed from the reaction mixture by two different separation methods, namely DES based extraction and membrane separation. Different integrated setups were developed and evaluated in terms of FAME yield and glycerol concentration. The most promising integrated process was found to be the combination of 2-inlets feeding strategy for biodiesel production in a microreactor with a microextractor connected in series, in which a choline chloride-glycerol DES was used. In this integrated system, a FAME yield of 94% and a glycerol content below 0.02% (w/w) were achieved for the residence time of 20 min.

microsystems ; biodiesel production ; biodiesel separation ; integrated system

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