Electroassisted Filtration of Microfibrillated Cellulose: Insights Gained from Experimental and Simulation Studies

Nabin Kumar Karna,Anna Lidén,Hans Theliander,Jakob Wohlert

doi:10.1021/acs.iecr.1c03749

Abstract

An electroassisted filtration technique has been employed to improve dewatering of a suspension of microfibrillated cellulose (MFC) produced via 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO)-mediated oxidation. In addition, all-atom molecular dynamic (MD) simulations were performed to deepen the understanding of the complicated dewatering mechanism on a molecular level. Both the experimental and the simulation results implied that the dewatering rate was not only improved when electroassisted filtration was used but also found to be proportional to the strength of the electric field. A channeled dewatered structure was observed for these experiments and may have contributed to enhanced dewatering by providing high overall permeability. The MD simulations revealed that the electric field had a significant impact on the fibril movement, whereas the impact of pressure was limited. The simulations also suggested that the increased filtrate flow upon the application of an electric field was not only due to electroosmotic flow but also due to electrophoretic movement of the fibrils toward the anode that led to the release of water that had been trapped between the fibrils, allowing it to be pressed out together with the rest of the bulk water. This study shows that electroassisted filtration has the potential to improve the dewatering of TEMPO-MFC, and the MD simulations provide further insights into the dewatering mechanism.

Highlights

Cellulose, a biopolymer built up of glucose monomers, is of great importance in today’s society
It is generally accepted that the water molecules confined in complex colloidal systems such as microfibrillated cellulose (MFC) suspensions can be categorized into four different groups: (a) free water or bulk water that is not attached to the particles or influenced by surface forces, (b) interstitial water that is trapped between the cellulose fibrils, (c) surface water that is held on the surface of the cellulose surfaces by adsorption and adhesion, and (d) intercellular and chemically bound water
Despite the extensive knowledge of the efficacy an external electric field has on the dewatering phenomenon, studies have been restricted mainly to sludge[19−25] and clay.[26,27]

Summary

Introduction

A biopolymer built up of glucose monomers, is of great importance in today’s society It is currently used in applications such as paper and board products, textiles, and specialty chemicals (e.g., carboxymethyl cellulose). The cellulose polymer is found in the wall of various cell structures as bundles of cellulose fibrils formed by stacks of cellulose polymers This hierarchical structure allows cellulose to be used in a variety of applications: from a cellulose fiber (micrometer scale) down to single cellulose chains (nanometer scale). The intermediate structures have not been used as extensively on a large industrial scale One of these intermediate structures is microfibrillated cellulose (MFC), which is liberated from bundles of cellulose fibers by mechanical means.[1] This type of structure has a number of interesting properties, including a high surface area with the potential for modifications and good mechanical properties. A great deal of research has focused on understanding the properties[2−5] and applications[6−8] of MFC since the pioneering work of Herrick et al.[9] and Turbak et al.[10] in the beginning of the 1980s

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