Optimization of Selective Acid Hydrolysis of Cellulose for Microcrystalline Cellulose using FeCl3

Abstract

In the process of acid hydrolysis of cellulose, hydrolyzing the amorphous regions while retaining the crystalline regions is the key technology for obtaining microcrystalline cellulose products. This paper investigated the influence of FeCl 3 on selective acid hydrolysis of crystalline regions and amorphous regions of cellulose. X-ray diffraction data indicated that FeCl 3 can enhance the selectivity of acid hydrolysis for amorphous regions of cellulose, thus improving the crystallinity of hydrocellulose. Meanwhile, the crystalline structure did not change. Response surface methodology (RSM) was employed to optimize the crystallinity of hydrocellulose with respect to FeCl 3 concentration, HCl concentration, reaction time, and temperature, and the relevant mathematical regression equation model was established. Under optimal conditions, the crystallinity of hydrocellulose was as high as 63.59% at 88.28 °C, 2.46 M HCl, 0.4 M FeCl 3 , and reaction duration of 64.02 min, which was in agreement with the predicted value.

A Response Surface Methodology Study: Effects of Trivalent Cr3+ Metal Ion-Catalyzed Hydrolysis on Nanocellulose Crystallinity and Yield

“…2a). Generally, this result agreed with a previous study in which increased reaction temperature and acid concentration increased the crystallinity index (Li et al 2014). Therefore, the reaction conditions must be controlled in order to prevent overdegradation of cellulose into undesirable products.…”

“…It was observed that the CV value for the models of crystallinity index and nanocellulose yield was 5.09 and 2.06, respectively, which implied that there was a high degree of precision and a good deal of reliability of the experimental values in the reaction models. Moreover, the small value of standard deviation (SD) for both responses (y1 and y2) at 3.94 and 1.73, respectively, indicated good precision, reproducibility, and reliability of the experimental models (Li et al 2014). The precision of the model reflects the signal-to-noise ratio, and a value larger than 4 is normally desirable .…”

Preparation of Nanostructured Cellulose via Cr(III)- and Mn(II)-Transition Metal Salt Catalyzed Acid Hydrolysis Approach

“…showed a similar acid hydrolysis mechanism as inorganic acid (H2SO4) during the depolymerization of cellulose. The metal ions (Cr 3+ and Mn 2+ ) were generated from transition metal salts capable of attaching to the high electronegativity of oxygen atoms in β-1,4-glycosidic bonds of the cellulose chain, which resulted in weakening of the bond strength between pyranose rings in the amorphous region and thus led to the easy rupture of the cellulose chain into smaller fiber fragments (Li et al 2014a). Compared with single-charge protons (+1) from typical mineral acids (e.g., HCl or H2SO4), transition metal ions with higher valence states (e.g., +2, +3) can efficiently hydrolytically cleave the extensive network in the cellulose fibers.…”

http://www.asianjournalofchemistry.co.in/user/ViewFreeArticle.aspx?ArticleID=30_5_23

“…Amorphous part of the glycosidic bond partially degraded to form an acid insoluble nature of the final product, while the crystalline leaves a residue and only a change slightly due to acid hydrolysis. A slight change in the structure of the crystalline portion cellulose microcrystalline and amorphous parts will result in removal an increase in the degree of crystallinity of the microcrystalline cellulose [23]. Karim et al [24] reported for the treated sample, the disordered amorphous region was decreased with the increase of the hydrogen bond crystalline region of the cellulosic matrix, which might be due to the partial breaking up of glycoside linkages inside the amorphous region, whereas the crystalline region was almost unaltered [8].…”