Fabrication and Characterization of Pulp/Chitosan Composite Membranes Crosslinked with 3-Methylglutaric Anhydride for Pervaporation of Ethanol/Water Mixture

Truong Thi Cam Trang, Nguyen Thi Nhung, Takaomi Kobayashi

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DOI: 10.4236/eng.2011.32014                

Abstract

Chitosan/Cellulose (CTS/CL) composite membranes were prepared by cross-linking reaction with 3-methy- lglutaric anhydride (3MGA). The cross-linked membranes with CTS/CL were obtained at different CTS con- tents in variations from 50 to 100 wt%, and these membranes were applied in the dehydration of ethanol/wa- ter mixtures. Especially, it was observed that in the case of a composite membrane containing chitosan 80% (CTS/CL-80/20) showed a performance with a separation factor of α = 17.1 and a total permeation flux of J = 326 g/(m2h). It was observed that the total permeation flux decreased when the cross-linking increased and the increase in the ethanol content in the feed solution showed an increase in the separation factor. The CTS/ CL-80/20 showed excellent performance with good mechanical strength and dehydration performance in the ethanol/water mixture separation.

Keywords

Pervaporation, Chitosan, Cellulose, Contact Angle, Ethanol, Composite Membrane

1. Introduction

It is known that pervaporation (PV) is a potential method for separation of liquid mixtures in membrane processes. It is used for dehydration process of mixtures with organic components which have close boiling points. PV has been proven as a highly efficient separation process [1-4]. In recent years, a major advantage of this process is the ability to separate azeotropic mixtures as an economical and simple alternative to conventional energy-intensive technologies, especially water-ethanol systems [5]. As an important application in industrial dehydration processes, several PV studies have been reported for the separation of aqueous/organic mixtures [6-11] using hydrophilic dense membranes. Among them, blended polymer membranes have been extensively studied resulting in increased flux and selectivity values. For example, the blended membranes of two oppositely charged polymers formed high density membrane structure and could result in high selectivity in the membranes [12]. In blended polyelectrolyte membranes for PV dehydration of alcohols, blended chitosan and polyacrylic acid membranes have been used [12,13], as well as blended chitosan and sodium alginate membranes [14]. It was furthermore studied that synthetic polymer membranes were also widely applied in PV separation [15-19]. We noted that, by the application of such blending techniques, the properties of the resultant polymer membranes could demonstrated superior changes in the intrinsic chemical, physical, mechanical, and morphological properties, as compared to non blended membranes. In addition, as biopolymers are being used, CTS is a material that can be found in crustacean shells, which is usually wasted from seafood industries. Therefore, as a suitable biopolymer, their applications for blended and composite membranes have been reported [12-14]. It is known that CTS is a cyclo-aliphatic polymer that contains both active amino groups and hydroxyl groups (Figure 1). By using CTS cross-linked membranes by several chemicals such glutaraldehyde [17,20-22], formaldehyde [16,19,23,24], sulfuric acid [19,23,25]. Therefore, the CTS membranes PV performance in blended chitosan and polyvinyl alcohol membranes for dehydration of isopropanol was investigated [26].

On the other hand, cellulose (CL) which usually has high molecular weights due to long chains of d-glucose

(a)(b)(c)

Figure 1. Schematic procedure of preparation of CTS/CL membrane.

units joined together by β-1,4-glucosidic bonds (Figure 1) is the most widely available organic biopolymer. It is nontoxic, renewable, biodegradable and modifiable to have great potential as an excellent industrial material [27,28]. More recently in PV processes, we have reported that vulcanized cellulose membranes showed very good dehydration performance in alcohol/water mixtures [Truong T. Cam Trang, Kobayashi Takaomi: Journal of Applied Polymer Science, DOI #33258]. Due to such excellent properties of CL membrane, the present work addersses the continuing efforts to develop new biopolymer membranes for PV separation of aqueous-organic mixtures by combining both CTS and CL in order to improve the membrane performance. In the present investigation, attempts to examine the applicability of CTS/CL composite by using the cross-linker 3-metylglutaric anhydride were made for the purpose of dehydrating ethanol/water mixtures. The present work also explores the effect of polymer swelling and sorption selectivity in addition to the PV performance by varying ethanol/water contents from 10 to 90 wt%.

2. Experimental

2.1. Materials

Chitosan, having a degree of deacetylation of 80%, was purchased from Wako (Osaka, Japan) and 3-methylglutaric anhydride was purchased from TCI, Tokyo, Japan. Cellulose was received from Hokuetsu Paper Mills (Tokyo, Japan). Ethanol was purchased from Nacalai Tesque. Inc. Water was deionized and distilled before use.

2.2. Membrane Preparation

Figure 2 shows the schematic procedure for the preparation of the CTS/CL membranes. The membranes were obtained as follows: CTS was dissolved in de-ionized water with 2 wt% acetic acid to be 1 wt% in concentration. The CTS solution was filtered in order to remove un-dissolved parts and impurities before preparation of the CTS/CL membranes. In the raw CL (15 g), 120ml of water were mixed and the mixture was crushed using a mixer stirring at 250 rpm. After the process was finished, the CL water mixture were mixed with the CTS solution under stirring at 250 rpm and kept for 36h in order to be sure it was completely homogeneous. For the cross-linking process, 5 ml of 5 wt% 3MGA in de-ionized water was added and mixed. The CTS/CL solution was poured into a flat glass plate and the CTS/CL membranes were formed after dried at 40℃ for 36 h to then be removed from the glass plate. The membranes were washed and rinsed repeatedly with de-ionized water and then dried at room temperature for 24 h. Six different membranes for the CTS/CL mixtures were prepared as weight ratio of 100/0, 85/15, 80/20, 75/25, 60/40 and 50/50 and were denominated as CTS/CL-100/0, CTS/CL-85/15, CTS/CL- 80/20, CTS/CL-75/25, CTS/CL-60/40 and CTS/CL-50/50, respectively. The thickness of each membrane was measured using a micrometer screw gauge and found to be of about 100-150 μm.

Conflicts of Interest

The authors declare no conflicts of interest.

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