Variable Volume Diafiltration Research Articles

Effect of different diafiltration process on the protein fractionation of skim milk by cross flow microfiltration

Diafiltration had been widely used in milk protein fractionation for almost thirty years to produce casein-enriched retentate. Among them, intermittent feed diafiltration was the only way ever used. But we noted some other diafiltration types had been used in other fields such as chemical engineering. In this study. The separation performance, chemical properties, component resistance and mass balance analysis were compared under different diafiltration types, aiming to find suitable diafiltration processes for milk protein fractionation. Research suggested that different diafiltration process may have different advantages. From the separation performance point of view, the highest removal rate of native whey proteins was observed under variable volume diafiltration (VVD) mode. But in terms of average flux, constant volume diafiltration (CVD) mode was utmost time and energy saving with an average flux of 81.25 kg m−2h−1. In addition, the percentage loss of protein under CVD and constant volume concentration ratio diafiltration (CVCRD) mode were significantly lower than that of other diafiltration modes (P < 0.05), indicating fewer protein were absorbed or compacted by the membrane. Therefore, diafiltration type should be selected according to the purpose of production.

An alternate diafiltration strategy to mitigate protein precipitation for low solubility proteins

Application of the minimum diafiltration (DF) time solution for a monoclonal antibody resulted in a 20-h process time rather than the expected 12 h. Further investigation indicated high turbidity associated with a product solubility issue that caused a flux decline. As a result, the gel flux model and the associated minimum DF time were not predictive. Multiwell plate solubility screening confirmed that the protein passed through a region of low solubility during the ultrafiltration step. Multiple approaches to address this issue were considered and a new strategy involving variable volume diafiltration (VVDF) was developed. Process modeling and simulation were used to predict performance and to select a value of the DF ratio control parameter (buffer flow/permeate flow = 0.65). Feasibility testing at the bench and pilot scales confirmed that the new strategy reduced solubility issues, fit within existing manufacturing tank volume and system area constraints, matched model predictions, and did not present significant implementation issues. Recommendations are made regarding the general value of this strategy, when it should be used, and how to implement it.

Quality by Design for peptide nanofiltration: Fundamental understanding and process selection

Recently, nanofiltration techniques have been introduced by pharmaceutical industries in the downstream processes for peptides, to perform concentration, purification and salt/solvent exchange, and have been demonstrated as being suitable for integration with conventional chromatographic purification techniques, providing savings in terms of time and costs. Design of Experiments (DoE) methods have been extensively applied in the process design of the conventional techniques, under the so-called Quality by Design (QbD) concept, but applications of DoE methods to nanofiltration are still few. In this study, the nanofiltration of a model peptide, conventionally named PEP1, in trifluoroacetic acid/acetonitrile/water mixtures is studied by DoE. Statistical models for solvent flux, peptide and trifluoroacetic acid rejections are obtained by statistical Analysis of Variance and the best operating conditions for concentration are found by numerical optimization of the statistical models. The statistical models from DoE are included in the mathematical framework of the diafiltration process, to calculate the evolution of peptide, counter-ion and solvent concentrations over time, compare constant volume vs. variable volume diafiltration modes, and select the best process in terms of operating time and solvent consumption. This work demonstrates that empirical DoE models can provide phenomenological understanding of the transport mechanism through nanofiltration membranes for a specific solute of interest and successfully support the process modelling for concentration and diafiltration, providing a methodology to select the most appropriate filtration technique for a given separation problem.

Evaluation of variable volume diafiltration processes using the Logarithmic Integral

The minimum process times for ultrafiltration with constant volume diafiltration (UFCVD) and ultrafiltration with variable volume diafiltration (UFVVD) are compared for limiting flux conditions. Using the series definition of the Logarithmic Integral, the optimum concentration to begin VVD is found by numerical solution of a non-linear algebraic equation. This equation is used to establish a criterion for UFVVD to be faster than UFCVD. Calculations indicate that this criterion is never satisfied and thus UFVVD can never be done more rapidly than UFCVD.

Process Duration and Water Consumption in a Variable Volume Diafiltration for Partial Demineralization and Concentration of Acid Whey

Process duration and fresh water consumption were determined (experimentally and statistically) for variable volume diafiltration (VVD) of cottage cheese through a flat sheet membrane (0.046 m2). The VVD process was performed at two volume decreasing ratios (α = 0.75 and α = 0.5). The VVD-0.75 process lasts much longer than the VVD-0.5 process if the same concentration degree is required. The VVD-0.5 process lasts longer than the VVD-0.75 process if it is aimed to achieve the same purification degree. At low purification degrees, both processes require similar quantities of fresh water, but better demineralization is possible after higher dilution, which is typical of the VVD-0.75 process. The mathematical model applied in estimating the duration of the process proved very accurate, which cannot be said about the fresh water consumption model.

Diafiltration and water recovery of Reactive Brilliant Blue KN-R solution by two-stage membrane separation process

The conventional process of Reactive Brilliant Blue KN-R production is low purity, labor intensive, inconsistent in the production quality and also causes pollution. The improved process based on membrane technology still generates large volume of effluent though with low pollutants. In this paper, a two-stage membrane separation process is introduced to resolve these shortcomings, in which the first stage is used for diafiltration and concentration of dye solution, and the second is to recover the dye and salt water from the produced permeate. Comparing results from one ultrafiltration (UF) membrane (GH) and four nanofiltration (NF) membranes (AFC40, DL, CA865 and MPT-31), UF membrane ES404 showed the same dye rejection, higher permeate flux and lower sodium sulfate rejection. In the diafiltration and concentration stage, pre-concentration and constant volume diafiltration had the best salt permeability as compared to constant volume diafiltration and post-concentration in addition to variable volume diafiltration. In the dye and salt water recovery, membrane ES404 had the same dye rejection, but higher permeate flux and lower sodium sulfate rejection as compared to membrane GH. The proposed two-stage membrane separation process offers the advantages of high-purity, less labor intensive, consistent in production quality and less pollution.

Mathematical model of variable volume diafiltration with time dependent water adding

PurposeThe purpose of this paper is to introduce a mathematical model, an algorithm and numerical procedure for determining the duration of a diafiltration process with variable volume. This model should decrease diafiltration time and water usage.Design/methodology/approachA mathematical model of a diafiltration process, with constant water adding is considered, as well as the relationships between macro‐ and micro‐solute and the equation for process duration. By introducing α (t)=QD/QF, i.e. time dependent ratio of diafiltration water flow and filtrate flow rate, a mathematical model of diafiltration process with time dependent water adding is proposed. In order to solve this model, an algorithm is suggested, based on the simulation of single time dependent water adding process with a sequence of constant water adding processes. The algorithm is applied for developing both a numerical procedure and simple QBASIC‐program that are tested on one illustrative example.FindingsThe results obtained by the algorithm improve the diafiltration process time around 10 percent and are a step towards finding an optimal dependence function α (t).Research limitations/implicationsFurther on, the analysis of water usage in variable volume diafiltration needs to be done. Also, the problem of finding the optimal α (t) is still open.Practical implicationsThe suggested algorithm is applicable to various membrane filtration processes and can be applied with little modification of the existing filtration equitment.Originality/valueThis paper is the first to view ALFA as a continuous function of time. Previous authors have considered step functions but never used this general approach.

Partial demineralization and concentration of acid whey by nanofiltration combined with diafiltration

In this paper, nanofiltration (NF) combined with continuous variable volume diafiltration (CVVD) of cottage cheese whey (also known as acid whey) was investigated to simultaneously concentrate and partially demineralize it. The experiments were carried out in a laboratory NF equipment using a flat sheet membrane with the effective area of 0.046 m 2 and 96% sucrose rejection. Fat, protein, lactose and total solid content of the samples were analyzed by Infrared Milk Analyzer Bently 150. Ion composition of the samples was determined by ICP-MS instrument. The concentrations were carried out at different values of the ratio of the volume of dialyzation water and the volume of permeate ( α). The degree of demineralization of monovalent ions reached 70% and 90% at 2.5 volume concentration ratio, and at diafiltration and permeate volume ratios of 0.5 and 0.75, respectively. The amount of multivalent ions increased continuously during the NF combined with CVVD of acid whey. The rejection of the valuable compounds of whey such as protein and lactose was over 90%.

Water usage in variable volume diafiltration: comparison with ultrafiltration and constant volume diafiltration

Variable volume diafiltration (VVD), also known as volume-decreasing diafiltration, is a process in which fresh water is added continuously to the retentate in a batch ultrafiltration process at a rate that is less than the permeate flowrate, thus providing for simultaneous ultrafiltration (UF) and diafiltration. This process has been analysed recently and it is claimed that VVD uses less water than constant volume diafiltration (CVD) [1]. In this paper, we examine both VVD and UF–CVD and compare the water usage in each process. For a solution containing two solutes, A and B, with rejection coefficients σ A = 1 and σ B = 0, we show that VVD uses more water than CVD when CVD is performed at the final volume of a UF–CVD process. VVD uses less water than CVD only if the latter is performed at the initial volume of a UF–CVD process. When CVD is performed at the intermediate macrosolute concentration that minimises the process time, namely C g/ e where C g is the gel concentration and e is the base of the natural logarithm, it will generally use less water than VVD.

Ultrafiltration with variable volume diafiltration: a novel approach to water saving in diafiltration processes

Batch ultrafiltration (UF) and constant volume diafiltration (CVD) can be used to concentrate macrosolutes and remove microsolutes. In contrast to CVD, variable volume diafiltration (VVD) involves the addition of diluant at a rate that is less than the permeate flowrate. This causes a simultaneous concentration of macrosolute and diafiltration of microsolute. VVD has been analysed in some detail [1,2] but has not been compared with UF-CVD. Here, we generalise VVD and propose a new process, ultrafiltration with variable volume diafiltration (UF-VVD). We show that it uses less water than UF-CVD without incurring large time penalties.

Study on nanofiltration for purifying fructo-oligosaccharides: I. Operation modes

Purification of fructo-oligosaccharides (FOS) by nanofiltration (NF) technology under different operation modes was studied theoretically and experimentally. The characteristic function of variable volume diafiltration (VVD) was proposed. For concentration, constant volume diafiltration (CVD) and VVD, the relationships between (i) FOS purity and dilution water usage and (ii) FOS purity and yield were obtained. The relationship between purity and yield was found to be independent of operation mode, when the membrane rejection properties were the same. While for a given purity, the dilution water consumption under VVD was found to be less than that under CVD. These findings were confirmed by the experimental results of FOS purification, performed with two spiral wound NF membranes.

Mathematical Model of Variable Volume Diafiltration

The use of ultrafiltration as a separation technique is frequently accompanied by a diafiltration step to remove microsolutes. There are different ways to combine ultrafiltration and diafiltration to obtain the desired final concentration of components. Variable volume diafiltration is a continuous process in which water is continuously added at a rate less than the permeate flow rate so that the concentration of macrosolute continuously increases, and the final concentrations of macrosolute and microsolute can be reached simultaneously. In this paper a mathematical model of variable volume diafiltration is proposed. The model includes both initial volume and concentration, rejection coefficients, processing time as well as water volume added during diafiltration. The developed model could be served for design and optimization purposes.