CONCEPTUAL PROCESS DESIGN OF SILVER-BASED EXTRACTION PROCESS

The FO ethyl ester is the major feedstock during the concentration of co-3 PUFA that is made of a blend of fatty acids containing the varying unsaturation degree. However, the separation of interesting fatty acids is quite difficult to produce highly concentrated components. Several processes for the concentration and separation of co-3 PUFA are being researched in an effort to improve extraction efficiency; however, the large-scale production is possible only by few methods such as molecular distillation, adsorption chromatography, enzymatic splitting, low-temperature crystallization, urea complexation and supercritical fluid extraction (SFE) which has its own limitations and strength. Typically, the carbamate formation which is highly carcinogenic compounds in Urea Precipitation of co-3 PUFA is a potential disadvantage. The use of organic solvents in Low-temperature crystallization of oils is a considerable limitation. The operation cost of super-critical extraction and molecular distillation is very expensive even though the yield of co-3 PUFA is quite good. The FO ethyl esters derived co-3 PUFA via LLE used an aqueous concentrated solution of silver nitrate and was previously evaluated as an alternative extraction technology to conventional concentration and extraction processes of co-3 PUFA (i.e., Urea Precipitation and molecular distillation). In this work, the conceptual process designs for extraction of co-3 PUFA from FO using a batch-wise stirred tank reactor is compared to a mini-fluidic contractor in continuous operation. Laboratoiy investigation showed that the yield of co-3 PUFA in silver LLE is 80-90% when compared with conventional processes and the data from the laboratory investigation is used for developing for the conceptual process design for silver-based solvent extraction. Furthermore, the process design for recovery silver from the waste is developed and discussed within the context of economic feasibility given the high cost of this solvent type.

Based on the economic analysis, the silver-based solvent extraction in the mini-fluidic contacting system is only feasible when nearly complete recovery of silver nitrate from the waste is completely possible, with minifluidics only providing moderate advantages if the oxidation of silver ions is independent of the number of heat/cool cycles.

Solvent extraction is a common process for separating numerous biological compounds from natural material. In this solvent extraction, the concentrate aqueous silver nitrate salt solution is used as a solvent for extraction of co-3 PUFA from FOs because of the double bond of unsaturated fatty acid fonn the complexes with Ag⁺ ions in a reversible reaction on the basis of which PUFA-Ets can be purified. A novel laboratory-scale method of solvent extraction based on silver was reported by Yazawa et al. (1991) which has been investigated by other authors on the basis of idealized extraction methods and lab-scale analysis (Li et al., 2008). Since the separation is based exclusively on a fast reversible chemical reaction, the simple method would have huge potential to purify the PUFAs.

LIQUID-LIQUID EXTRACTION (LLE) OF Ω-3 PUFA BASED ON AGNО3 SOLUTIONS

The laboratory-scale solvent extraction of co-3 PUFA in mini-channel was reported a potential application for scalable, consisting of five key steps:

• 1. Contacting FO ethyl ester and concentrated Ag salt solution so that an aqueous and organic phase-FO ethyl ester can be produced wherein a complex was formed between the aqueous Ag salt solution and co-3 PUFA that is as extracted from the FO ethyl esters;
• 2. Separation of aqueous phase (AgN0₃ + co-3 PUFA Complex) from FO ethyl esters and emulsion phase by gravity settling and alkane solvent addition;
• 3. De-complexing of the aqueous phase with hexane and/or deionized water, resulting in the formation of an organic phase that contains formation of concentrated co-3 PUFA in hexane fraction;
• 4. Separation of the organic phase containing the concentrated co-3 PUFA from the aqueous Ag salt phase. The organic phase is then distilled to recover the hexane solvent, yielding a purified co-3 PUFA product stream; and

5. Recovery of silver nitrate from diluted the aqueous phase by various recycling methods. The above process is detailed in step by step in Figure 6.9 and was the basis for this comparison.

FIGURE 6.9 A brief overview of extractions of co-3 PUFA from fish oil EE based on the silver salt solution.