Performance Evaluation of Tight Ultrafiltration Membrane Systems at Pilot Scale for Agave Fructans Fractionation and Purification

Abstract

Ceramic and polymeric membrane systems were compared at the pilot scale for separating agave fructans into different molecular weight fractions that help to diversify them into more specific industrial applications. The effect of the transmembrane pressure of ultrafiltration performance was evaluated through hydraulic permeability, permeate flux and rejection coefficients, using the same operating conditions such as temperature, feed concentration and the molecular weight cut-off (MWCO) of membranes. The fouling phenomenon and the global yield of the process were evaluated in concentration mode. A size distribution analysis of agave fructans is presented and grouped by molecular weight in different fractions. Great differences were found between both systems, since rejection coefficients of 68.6% and 100% for fructans with degrees of polymerization (DP) > 10, 36.3% and 99.3% for fructooligosaccharides (FOS) and 21.4% and 34.2% for mono-disaccharides were obtained for ceramic and polymeric membrane systems, respectively. Thus, ceramic membranes are better for use in the fractionation process since they reached a purity of 42.2% of FOS with a yield of 40.1% in the permeate and 78.23% for fructans with DP > 10 and a yield of 70% in the retentate. Polymeric membranes make for an efficient fructan purification process, eliminating only mono-disaccharides, and reaching a 97.7% purity (considering both fructan fractions) with a yield of 64.3% in the retentate.

Effect of Operating Conditions and Fructans Size Distribution on Tight Ultrafiltration Process for Agave Fructans Fractionation: Optimization and Modeling

“…The response surface was plotted by varying two operating factors, and the third factor was kept constant at center point conditions (Level 0 in Table 1) using Equation (13). It was observed that mean values of TMP and temperature, colored red on the graph, favored the SF (Figure 2A,B), which agrees with results previously reported by Luiz et al [38], where an increase in the apparent rejection coefficient for the Fc and FOS at 3 bar was observed. However, by increasing the TMP to 5 bar, the SF decreases.…”

“…With multiple responses, an SF of 2.57 and Ji of 1.82 kg•h −1 •m −2 of fructans were obtained with the desirability of 0.72, which, according to Svetlana et al [56], is considered an acceptable value. The optimal values obtained for the fractionation of agave fructans are higher than those reported by Luiz et al [38], who only used different values of TMP at 45 • C; however, similar trends were obtained. Table 5.…”

“…Regarding the TMP used, it has been reported that low pressures favor fractionation. The previous study reported by Luiz et al [38] showed that in the range of 1 to 5 bar of TMP, better separation is obtained, for which these values were considered in this studio. Thus, the range of operating conditions was temperature (30-60 • C), TMP (1-5 bar) and feed concentration (50-150 kg•m −3 ).…”

“…The above deviations in some experimental data could be attributed to membrane fouling, which is not considered in the model and has been reported to reach values of around 14% of the global resistance generated in the UF process of agave fructans using ceramic systems [38]. Another hypothesis is that depending on the proportion of FOS:Fc in the initial sample, the composition also changes in the limiting layer of the membrane; therefore, different osmotic pressure values could be generated, as occurs in solutions of dextran and polyethylene glycol, which has been reported to be greater than 10-15 psi (0.68-1.03 bar) [59].…”

“…For agave plants, NF studies at the laboratory level have been reported to enhance the purity of fructans by removing the low molecular weight sugars [34,35]; Flores Montaño et al [36] and Pérez Martínez et al [37] proposed the fractionation process by UF. In a previous study, Luiz et al [38] showed the feasibility of obtaining fractionated fructans by Tight UF systems using a ceramic membrane on a pilot scale. However, as the processes are scaled, it is vitally important to optimize the operating conditions that allow for more efficient operations and lower costs.…”