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Removal of Particulate Matter by Filtration and Sedimentation
Published in Samuel D. Faust, Osman M. Aly, Chemistry of Water Treatment, 2018
Membrane materials are manufactured from a variety of materials, such as cellulose acetate (CA), cellulose diacetate (CDA), cellulose triacetate, polyamide (PA), other aromatic polyamides, polyetheramides, polyetheramines, and polyetherurea. In CA membrane chemistry, the higher the acetyl content, the higher is the scale rejection, and the lower is the water flux. Cellulosic membranes are usually inexpensive and can tolerate some chlorine (<1.0 mg/L). However, there are several disadvantages: CA membranes are subject to biological attack and to hydrolysis that reverts CA to cellulose and acetic acid. This reversion occurs very rapidly at very low or high pH values.81 PA and thin-film composite (TFC) membranes may be degraded by oxidants (i.e., Cl2), but they are not susceptible to biological attack, and resist hydrolysis.
Postcombustion Carbon Capture Using Polymeric Membrane
Published in I. M. Mujtaba, R. Srinivasan, N. O. Elbashir, The Water–Food–Energy Nexus, 2017
Another polymeric membrane is cellulose acetate (CA) that draws attention of researchers and scientists in reverse osmosis, ultrafiltration, and gas separation field because of unique properties. The product is highly hydrophobic, flexible, and also has very high flux. Having these properties made them very interesting for CO2 gas separation so that the main usage is in offshore plants where the capital and maintenance cost need to be minimized. Even, the capture plant with CA is as effective as amine absorption for the amount of CO2 over 20 mol% (Stern et al. 2000). CA is the product of a reaction between cellulose with acetic anhydride and acetic acid in the presence of sulfuric acid (Fischer et al. 2008). With respect to the degree of acetylation, this type of membrane is named CA, cellulose diacetate and cellulose triacetate (Chen et al. 2015). Figure 12.111 shows the chemical structure of CA. As discussed earlier, the mobility of polymer bone is proportional to the permeability and selectivity of species of a gas mixture. The substitution of hydroxyl with acetyl groups affects the chain packing and consequently improves the mobility (Kamide and Saito 1987).
Electrospinning and Electrospraying Technologies and Their Potential Applications in the Food Industry
Published in V Ravishankar Rai, Jamuna A. Bai, Nanotechnology Applications in the Food Industry, 2018
Alex López-Córdoba, Clara Duca, Jonathan Cimadoro, Silvia Goyanes
Cellulose is an abundant, renewable, and cheap biopolymer consisting of β-1,4-glycosidic linked d-glucopyranose units. It is attractive for use in electrospinning/electrospraying because it is biodegradable, biocompatible, and nontoxic. However, one of the most critical factors in this processing of cellulose is its limited solubility in common organic solvents and its inability to melt, due to strong inter- and intramolecular hydrogen bonds (Frey, 2008; Lee, Jeong, Kang, Lee, and Park, 2009). Therefore, several solvent systems that directly dissolve cellulose have been investigated and used for electrospinning, including N-methyl-morpholine-N-oxide/water (NMMO/water), lithium chloride/dimethylacetamide (LiCl/DMAc), and ionic liquids (Frey, 2008). However, some of these substances are not suitable for food applications because they have associated adverse effects on human health. As an alternative, cellulose derivatives have been extensively exploited due to their better solubility and electrospinnability. Several works that deal with the electrospinning of cellulose derivatives (e.g., cellulose acetate, cellulose diacetate nitrate, cellulose triacetate, and hydroxypropyl cellulose) have been reported (Lan, Shao, Wang, and Gu, 2015; Lan et al., 2014; Rodríguez, Sundberg, Gatenholm, and Renneckar, 2014). Of these, cellulose acetate is the most commonly used because it can be subsequently deacetylated to form cellulose nanofibers or functionalized with other side groups. For instance, Rodríguez, Sundberg, Gatenholm, and Renneckar (2014) electrospun cellulose acetate solutions at 17 wt.% in 2:1 ratio of acetone/dimethylacetamide. The cellulose acetate nanofibers were regenerated to cellulose by saponification reaction with 0.05 N NaOH solution in ethanol at room temperature for 24 h (Figure 21.2). This approach constitutes a useful strategy to create pure cellulose electrospun fibers using solvent systems more suitable for food applications.
Prospects on utilization of biopolymer materials for ion exchange membranes in fuel cells
Published in Green Chemistry Letters and Reviews, 2022
Angelo Jacob Samaniego, Richard Espiritu
Cellulose acetate (CA) is a derivative of cellulose wherein the three hydroxyl groups in each anhydroglucose unit can be replaced by acetyl groups (Figure 3(b)). The degree of substitution (DS) dictates whether the CA is classified as a monoacetate (DS < 2.2), diacetate (DS = 2.2-2.7), or triacetate (DS = 2.7-3.0) (31). Replacing hydroxyls with acetyls disrupts the crystallinity of cellulose and enables solubility in common organic solvents. Cellulose diacetate, for example, is soluble in acetone, while cellulose is not, which allows for reshaping through spinning and other forming processes (32). One of the most common ways to prepare CA is by reacting cellulose with acetic anhydride in an anhydrous acetic acid solution with sulfuric acid as a catalyst. The reaction is performed in excess to produce cellulose triacetate which is then hydrolyzed to partially remove acetyl groups and achieve the desired degree of substitution. Notably, the hydrophilicity of the cellulosic structure decreases as more hydroxyls are substituted with acetyls (75).