High viscosity preparative chromatography for food applications

The strength of chromatography lies in the ability of fine-tuning recovery for specific target components or fractions of interest. A downside of industrial chromatography is the need to dilute streams, as it is often applied today. This article challenges the conventional low concentration of input streams and investigates size exclusion chromatography at concentrated streams of high viscosity. Chromatographic operation with concentrated streams leads to an increased pressure drop over the column and decreased mass transfer kinetics, but also lower volumes compared to diluted streams. The objective of this research was to investigate separation performance and system dimensions as a function of viscosity for food type streams, in scenarios where viscosity is not caused by target components. Disadvantages due to increased stream volume with decreasing concentration and benefits due to decreased viscosity were evaluated, aiming to find minimal column volume. Separation performance was evaluated for a range of target components in a preparative lab-scale system using a size exclusion resin and mobile phase viscosities in the range of 1.2–8.7 mPa⋅s. Mobile phases were viscosified through addition of sucrose, glycerol, or dextran. Change in mass transfer resistance, measured via van Deemter curves, was related to the change in diffusivity through viscosity. The analysis of different viscosifying agents emphasized the influence of viscosity inside the pores, rather than viscosity of the bulk phase. The viscosity inside the pores was calculated via the partition coefficient of each viscosifying agent. Based on the slopes of van Deemter curves, column dimensions were calculated for different scenarios, assuming a non-compressible stationary phase. Column volume remained constant with stream dilution from 8.7 mPa⋅s down to about 2.5 mPa⋅s. However, at the same time column geometry changed to thinner and longer columns with decreasing viscosity, in order to accommodate throughput and pressure drop. When diluting to even lower viscosities, column volume increased, since stream viscosity is less sensitive to stream concentration at the low viscosity range. These results are relevant to a wide range of industries utilizing weak interaction chromatography, especially those where the main driver of process development is cost reduction and where a trade-off between purity, yield, and costs has to be made.</p

Elevated viscosities in a simulated moving bed for γ-aminobutyric acid recovery

Process streams of agro-food industries are often large and viscous. In order to fractionate such a stream the viscosity can be reduced by either a high temperature or dilution, the former is not an option in case of temperature sensitive components. Such streams are diluted prior to chromatographic fractionation, resulting in even larger volumes and high energy costs for sub-sequential water removal. The influence of feed viscosity on the performance of simulated moving bed chromatography has been investigated in a case study of the recovery of a γ-aminobutyric acid rich fraction from tomato serum. This work addresses the chromatographic system design, evaluates results from a pilot scale operation, and uses these to calculate the productivity and water use at elevated feed concentration. At the two higher feed viscosities (2.5 and 4 mPa·s) water use is lower and productivity higher, compared to the lowest feed viscosity (1 mPa·s). The behavior of the sugars for different feed viscosities can be described well by the model using the ratio of feed to eluent as dilution factor. The behavior of γ-aminobutyric acid is highly concentration dependent and the recovery could not be accurately predicted.</p

Sr isotopes in arcs revisited: tracking slab dehydration using δ88/86Sr and 87Sr/86Sr systematics of arc lavas

Dehydration of the subducting slab is a crucial process in the generation of hydrous convergent margin magmas, yet the exact processes of how and where the slab dehydrates and how these fluids are transported to the mantle wedge remain obscure. Strontium is a “fluid-mobile” element and as such well suited to investigate the source of slab-derived fluids. We employ mass-dependent Sr isotope systematics (δ88/86Sr; the deviation in 88Sr/86Sr of a sample relative to NIST SRM 987) of primitive arc lavas, in tandem with conventional radiogenic 87Sr/86Sr measurements, as a novel tracer of slab dehydration. To characterise the δ88/86Sr composition of subduction zone inputs, we present new δ88/86Sr data for subducting sediments, altered oceanic crust and MORB. Calcareous sediments are isotopically lighter and carbonate-free sediments are isotopically heavier than mid-ocean ridge basalts (MORB). Samples of the altered oceanic crust display elevated 87Sr/86Sr but only the most intensely altered sample has significantly higher δ88/86Sr than pristine MORB. Mafic arc lavas from the Aegean and Mariana arc invariably have a mass-dependent Sr isotope composition that is indistinguishable from MORB and lower 87Sr/86Sr than upper altered oceanic crust. This δ88/86Sr-87Sr/86Sr signature of the arc lavas, in combination with their high but variable Sr/Nd, can only be explained if it is provided by a fluid that acquired its Sr isotope signature in the deeper, less altered part of the subducted oceanic crust. We propose a model where the breakdown of serpentinite in the slab mantle releases a pulse of fluid at sub-arc depths. These fluids travel through and equilibrate with the overlying oceanic crust and induce wet partial melting of the upper altered crust and sediments. This hydrous melt is then delivered to the mantle source of arc magmas as a single metasomatic component. From mass balance it follows that the slab-derived fluid contributes >70% of the Sr budget of both Mariana and Aegean arc lavas. Whereas this fluid-dominated character is unsurprising for the sediment-poor Mariana arc, the Aegean arc sees the subduction of 3–6 km of calcareous sediments that were found to exert very little control on the Sr budget of the arc magmas and are overwhelmed by the fluid contribution