COMPARATIVE ANALYSIS OF CONTINUOUS AND DISCONTINUOUS DILUTION MODES IN THE DIAFILTRATION PURIFICATION OF SUCROSE-CONTAINING BEET EXTRACT

Abstract

The relevance of this study stems from the need to improve the resource efficiency of beet extract purification and reduce sucrose losses during membrane processing. Ultrafiltration enables the removal of highmolecular- weight non-sugars at moderate temperatures; however, a portion of the target component remains in the retentate and is consequently lost with it. The application of diafiltration creates opportunities for additional sucrose recovery, although process efficiency depends substantially on the mode of water addition, the fraction of permeate withdrawn, and the number of dilution stages. Therefore, comparing continuous and discontinuous diafiltration modes and determining rational operating parameters constitute a relevant scientific and practical objective in the development of energy– and resource-efficient sugar-production technologies. The study used experimental data obtained from the ultrafiltration of inverted beet extract through membranes with molecular weight cut-offs (MWCOs) of 10 and 50 kDa in a laboratory-scale dead-end filtration unit. The effective membrane areas were 1.38 × 10⁻³ and 3.42 × 10⁻³ m², respectively. Before use, the new membranes were compacted by filtering distilled water for 2 h at a pressure of 0.8 MPa. Diafiltration performance was evaluated using mass balances of the target component under constant-volume and stepwise concentration conditions. The membrane transmission coefficient for sucrose was determined using a combined experimental and calculationbased method; for the 10 kDa membrane, its value was 0.55. It was established that, during the first stage, the fraction of permeate withdrawn should not exceed 0.50 of the initial feed volume because of the accumulation of total solids in the retentate. After each subsequent dilution, the permissible permeate withdrawal may be increased to 0.80, and up to 0.90 during the final stage. At an overall permeate-to-initial-feed volume ratio of (V_p/V_0 = 3.0), the calculated sucrose losses with the retentate were 1.9% for the four-stage discontinuous diafiltration mode and 19.2% for the continuous mode. Continuous dilution can potentially provide higher specific productivity owing to the lower concentration of dissolved solids; however, it produces a more dilute permeate and requires greater energy input for subsequent concentration. Four-stage discontinuous dilution was found to be a rational operating mode for recovering sucrose from the retentate using a membrane with an MWCO of 10 kDa. The scientific novelty of the study lies in establishing a quantitative relationship between residual sucrose losses, the mode of diafiltration-water addition, and the extent of permeate withdrawal. The proposed operating mode can be applied in the design of a resource-efficient technology for beet extract purification.