Elsevier

Chemical Engineering Journal

Volume 255, 1 November 2014, Pages 356-364
Chemical Engineering Journal

Increasing reaction rate and conversion in the spinning cloth disc reactor: Investigating the effect of using multiple enzyme immobilized cloths

https://doi.org/10.1016/j.cej.2014.06.049Get rights and content

Highlights

  • Multi-cloth operational mode developed for the spinning cloth disc reactor (SCDR).

  • Multi-cloth SCDR increases the enzyme loading per liquid pass in the SCDR.

  • Reaction rate and conversion increased with increasing number of cloths in the SCDR.

  • Well-mixed behavior increased with increasing numbers of cloths in the SCDR.

  • Dye penetration showed all three layers were wetted in the multi-cloth SCDR.

Abstract

The spinning cloth disc reactor (SCDR) is a novel mesh supported enzyme rotating reactor system for process intensification. In this study, to increase the enzyme loading in the SCDR, a new reactor operational mode was designed by increasing the number of cloths used in the SCDR to form a multi-cloth stack on the spinning disc. To test its effectiveness, the influence of the number of cloths in the SCDR on reaction conversion and rate was investigated. The flow within the multi-cloth stack was characterized by residence time distribution (RTD) analysis and an imaging of the flow and dye penetration in the SCDR.

For different tributyrin substrate concentrations (10–40 g L−1), the reaction rate and conversion increased when the number of cloths was increased from one to two, indicating that the enzyme loading in the SCDR can be easily tailored to the desired reaction system by simply changing the number of immobilized enzyme cloths. The mean residence time increased with an increase in the number of cloths at different spinning speeds and flow rates, due to flow existing inside the volume of the multi-cloth stack. The number of tanks-in-series (N) decreased as the increase of cloth number on the spinning disc, indicating that more cloths caused larger deviation from plug flow. The visual study showed that the multi-cloth stack would not essentially change the flow types in the SCDR, and the fluid could penetrate through the three layers of multi-cloth at both low (100 rpm) and high (400 rpm) spinning speeds.

Introduction

The spinning disc reactor (SDR) is a process intensification technology, which utilizes centrifugal forces to produce a thin and highly sheared film on the spinning disc surface, resulting in rapid mixing and short residence time. Research has shown that the heat and mass transfer in the SDR can be significantly enhanced due to the fluid dynamics within the films [1], [2], [3], [4]. The SDR has been applied in several chemical reactions such as polymerization [5], photocatalysis [6], [7], transesterification [8] and nanoparticle preparation [9], [10], [11], [12]. Recently, the SDR concept has been introduced to enzymatic reactions by using a novel mesh supported enzyme rotating reactor system: the spinning cloth disc reactor (SCDR) [13], [14], [15]. As shown in Fig. 1, similar to the SDR configuration, the SCDR is also driven by the centrifugal forces on the spinning disc, however, this disc has immobilized enzymes on a woolen cloth resting on it. Therefore, the thin film is expected to be produced both on top of and within the cloth, where mass transfer enhancement and rapid mixing can be achieved.

The SCDR, like the conventional SDR, is scaled up through the micro-reactor concept of “numbering-up” rather than traditional scale-up. This means that feasibility proven at the small scale in these reactors (such as in this work) can be almost directly translated into an industrially feasible system. The SCDR has been successfully applied to oil hydrolysis reactions, primarily to tributyrin emulsion hydrolysis. The SCDR has shown higher reaction rates and conversions in comparison to the equivalent reaction system in a conventional batch stirred tank reactor (BSTR), for example, under comparable conditions (i.e. the same reaction conditions and the same enzyme to substrate ratio), the conversion of tributyrin hydrolysis increased by 18.1% and 13.5% in 4 h for substrate concentration of 10 g L−1 and 40 g L−1 respectively, indicating process intensification has been achieved. The reasons for this reaction rate and conversion enhancement are as follows: enhanced mass transfer, increased interfacial surface area, the protection of the enzymes by woolen cloth from deactivation, and the increased residence time of the substrate on the disc due to the liquid flow within the cloth [13]. Besides, the immobilized enzyme in the SCDR had good reusability retaining 80% of its initial activity after 15 consecutive runs. The enzyme leakage from the cloth support was very slight when the SCDR was operated under surface shear of 9500 s−1: only accounting for 0.32% of total immobilized enzyme amount on the cloth [13]. The thermal stability of immobilized lipase was found to be significantly improved compared to its free form. The thermal deactivation rate of immobilized lipase followed the Arrhenius law with the thermal deactivation energy of 199 kJ mol−1 [14].

The flow characteristics in the SCDR was also investigated by using residence time distribution (RTD) analysis and visual dye staining of the cloths with immobilized enzyme [15]. The results indicated that the flow pattern in the SCDR was essentially well-mixed – a vast contrast to the plug flow behavior found in the conventional SDRs. This indicates that the SCDR is a different class of rotating process intensification reactor from the traditional SDR – a new reactor class the authors have classified as the spinning mesh disc reactor (SMDR). The flow patterns and regimes in the SCDR were also classified at different spinning speeds and flow rates, with two flow regimes observed in the visual study within the spinning cloth: radial finger-like flow and concentric flow [15].

The previous research has also shown that the liquid in the SCDR can penetrate through the cloth and there is immobilized enzyme inside the cloth, thus allowing the enzyme catalyzed reaction to occur inside as well as on the outside of the woolen cloth [13], [16]. This allows the SCDR to utilize all the available surface area of the woolen cloth that has been occupied by the immobilized enzymes for reactions. Currently only one woolen cloth has been characterized in the SCDR, however this has also limited the enzyme loading in the SCDRs to the maximum amount that can be immobilized on one woolen cloth. In order to increase the enzyme loading in the SCDR, the simplest method would be to increase the number (or thickness) of cloths used in the reactor to form a multi-cloth stack on the spinning disc. This is desirable, since a higher catalyst loading brings more catalytic sites being available and therefore should result in faster reaction rates and a higher volumetric efficiency in the SCDR, as long as there are no negative consequences of additional cloth layers present in the SCDR (which could include: poor penetration of the liquid throughout the multi-cloth stack, poor mass transfer and mixing within the cloth stack). Therefore, to test this hypothesis, in this study the effect of the number of cloths in a stack in the SCDR on reaction conversion was investigated using tributyrin emulsion hydrolysis as a model reaction. The flow within the multi-cloth was characterized by conventional RTD analysis and image study [15].

Section snippets

Materials

Unbleached organic woolen cloth (color: natural cream, thickness: 1.5 mm) was purchased from Treliske (Otago, New Zealand). Amano lipase derived from Pseudomonas fluorescens, tritonX-100, tributyrin (98%), sodium bicarbonate, sodium carbonate and polyethyleneimine (PEI) were obtained from Sigma–Aldrich (New Zealand). Hydrogen peroxide 30% was obtained from Scharlau (Thermofisher, New Zealand). Glutaraldehyde (GA) 25%, disodium hydrogen phosphate, sodium dihydrogen phosphate, potassium chloride

Preparation of multiple lipase immobilized cloths with similar enzyme activity

Ten new cloths with immobilized lipase were prepared for the multi-cloth SCDR study. Each of the ten new cloths was placed in the SCDR using deionized water as feed and spun at 350 rpm for 2 h to wash off the free lipase. After that, the activity of each cloth was tested in the SCDR for 1 h with 10 g L−1 tributyrin emulsion as feed. The reaction time course is shown in Fig. 2. The conversion among the ten different new cloths is similar (conversion ranges from 48.4% to 51.6%) and the relative

Conclusions

In this study, a multi-cloth stacked SCDR (using one to four cloths) was investigated using tributyrin emulsion hydrolysis as a model reaction. The flow characteristics within the multi-cloth stack were characterized by RTD and visual/image analysis. Initial experiments showed that increasing the number of cloths in the SCDR could increase reaction rate and conversion: for different tributyrin concentrations (10, 20, 30 and 40 g L−1), the reaction rate and conversion increased when the number of

Acknowledgments

The authors thank the China Scholarship Council for the PhD scholarship. The authors also thank University of Auckland PRESS accounts and the Department of Chemical Engineering at the University of Auckland for funding consumables. The authors acknowledge Laura Liang, Peter Buchanan, Raymond Hoffmann, Cecilia Lourdes, Jessie Matthew, Frank Wu and Allan Clendinning for their technical help in this work.

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