Hwei Voon Lee

Conversion of Lignocellulosic Biomass to Nanocellulose: Structure and Chemical Process

Lignocellulosic biomass is a complex biopolymer that is primary composed of cellulose, hemicellulose, and lignin. The presence of cellulose in biomass is able to depolymerise into nanodimension biomaterial, with exceptional mechanical properties for biocomposites, pharmaceutical carriers, and electronic substrates application. However, the entangled biomass ultrastructure consists of inherent properties, such as strong lignin layers, low cellulose accessibility to chemicals, and high cellulose crystallinity, which inhibit the digestibility of the biomass for cellulose extraction. This situation offers both challenges and promises for the biomass biorefinery development to utilize the cellulose from lignocellulosic biomass. Thus, multistep biorefinery processes are necessary to ensure the deconstruction of noncellulosic content in lignocellulosic biomass, while maintaining cellulose product for further hydrolysis into nanocellulose material. In this review, we discuss the molecular structure basis for biomass recalcitrance, reengineering process of lignocellulosic biomass into nanocellulose via chemical, and novel catalytic approaches. Furthermore, review on catalyst design to overcome key barriers regarding the natural resistance of biomass will be presented herein.

Production of new cellulose nanomaterial from red algae marine biomass Gelidium elegans

Nanocellulose was successfully isolated from Gelidium elegans red algae marine biomass. The red algae fiber was treated in three stages namely alkalization, bleaching treatment and acid hydrolysis treatment. Morphological analysis was performed by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). TEM results revealed that the isolated nanocellulose had the average diameter and length of 21.8±11.1nm and of 547.3±23.7nm, respectively. Fourier transform infrared (FTIR) spectroscopy proved that the non-cellulosic polysaccharides components were progressively removed during the chemically treatment, and the final derived materials composed of cellulose parent molecular structure. X-ray diffraction (XRD) study showed that the crystallinity of yielded product had been improved after each successive treatments subjected to the treated fiber. The prepared nano-dimensional cellulose demonstrated a network-like structure with higher crystallinity (73%) than that of untreated fiber (33%), and possessed of good thermal stability which is suitable for nanocomposite material.

Preparation and Characterization of Cellulose Crystallites via Fe(III)-, Co(II)- and Ni(II)-Assisted Dilute Sulfuric Acid Catalyzed Hydrolysis Process

Hydrolyzing the cellulose amorphous regions with high selectivity while protecting the crystallite phases unaltered during acid hydrolysis is still a great challenge in nanocellulose industry. Due to this reason, transition metal based catalysts such as Fe (NO3)3-, Co (NO3)2- and Ni (NO3)2metal salts were chosen as promoter to co-catalyze with H2SO4 in order to develop a facile hydrolysis technique for the preparation of cellulose crystallites inform nanodimension from native cellulose source. This study investigated the hydrolysis efficiency of three different transition metals (Fe3+, Co2+ and Ni2+) on cellulose crystallinity index, structure and morphology of the products.Results showed that the transition metal salts (Ni2+, Co2+ and Fe3+) were capable to selectively degraded cellulose amorphous structure with increase of crystallite sizes (8.12-27.8 nm) and improved of crystallinity index (65.5-70.3 %), as compared to native cellulose. Furthermore, surface morphology study indicated the cellulose fibers were successfully disintegrated into smaller fragments (diameter ranges of 18.5-31.5 nm) with spider-web-like nanostructured surfaces. Higher oxidation state of Fe (III)-cation with trivalent state rendered more effective hydrolysis effect in preparing the cellulose crystallites as compared to divalent state of Co (II)- and Ni (II)-cations.

Advancement in heterogeneous base catalyzed technology: An efficient production of biodiesel fuels

Price fluctuation of petroleum-based diesel, climate change, emerging mandate obligations, availability of new feedstock and the upgrading of conversion technologies are expected to drive biodiesel market to grow robustly in the next coming 10 years. However, the current bottleneck in biodiesel production is the lack of economical sustainable conversion technologies. Generally, industrial production of biodiesel is greatly relied on alkaline homogeneous transesterification reaction. Limitation of the technology, such as multistep process which incur extra pre-step for high acid oil treatment and post-step for biodiesel purification and alkali washing as diminished the economic feasibility and low environmental impact of the entire biodiesel process. Heterogeneous catalysis offers immense potential to develop simple transesterification process, including one step reaction, easy separation, reusability of catalyst, and green reaction. Thus, the aim of this paper is to review the biodiesel production technologies such as blending, micro-emulsion, pyrolysis, and transesterification. Furthermore, recent studies on heterogeneous catalyzed transesterification were presented by discussing the issues such as catalytic performance on different types of biodiesel feedstock, transesterification reaction conditions, limitations encountered by heterogeneous catalysts, and reusability of solid catalysts. The heterogeneous catalysts presented in this review is mainly focused on solid base catalysts, which include single metal oxides, supported metal oxide, binary metal oxide, hydrotalcite, and natural waste shell-based catalyst. Furthermore, current perspectives on application of heterogeneous catalyzed technology in biodiesel industry were discussed herein.

Facile production of nanostructured cellulose from Elaeis guineensis empty fruit bunch via one pot oxidative-hydrolysis isolation approach

Cellulose in nanostructures was successfully isolated from empty fruit bunch biomass via a novel one-pot oxidative-hydrolysis technique. The physicochemical properties of nanocellulose prepared via one-pot process have shown comparable characteristics as products isolated via conventional multistep purification approach (namely dewaxing, chlorite bleaching process, alkalization, and acid hydrolysis). The chemical composition study indicated that the one-pot oxidative-hydrolysis process successfully extracted cellulose (91.0%), with the remaining minority being hemicellulose and lignin (∼6%) in the final product. Crystallinity profile of one-pot treated product (80.3%) was higher than that of multistep isolated nanocellulose (75.4%), which indicated that the disorder region (amorphous) in cellulose fibers was successfully removed. In additional to that, the morphology study demonstrated that nanocellulose prepared by one-pot process rendered spider-web-like network nanostructure, with an average diameter of fibers at a range of 51.6±15.4nm. The nanocellulose product showed high thermal stability (320°C), which was ready for nanocomposite application. One-pot oxidative-hydrolysis technique is a simple and versatile route for the preparation of nanocellulose from complex biomass within 90°C and 6h period, with minimum wastewater as compared to the multistep process.

Recent advances of titanium dioxide (TiO2) for green organic synthesis

Titanium dioxide (TiO2) has become increasingly popular as a catalyst. Although many applications of TiO2 involve photocatalysis and photoelectrochemical reactions, there are numerous interesting discoveries of TiO2 for other reactions. This review focuses on the recent development of TiO2 as a catalyst in green organic synthesis including in hydrodeoxygenation, hydrogenation, esterification/transesterification, the water–gas shift reaction, and visible light-induced organic transformation owing to its strong metal-support interaction (SMSI), high chemical stability, acidity, and high redox reaction at low temperature. The relationship between the catalytic performance and different metal or metal oxide dopants, and different polymorphs of TiO2 are discussed in detail. It is interesting to note that the reduction temperature and addition of promoters have a significant effect on the catalytic performance of TiO2.

Catalytic role of solid acid catalysts in glycerol acetylation for the production of bio-additives: a review

Bio-additives obtained from the acetylation of biodiesel-derived glycerol have been extensively synthesized because of their nature as value-added products and their contribution to environmental sustainability. Glycerol acetylation with acetic acid produces commercially important fuel additives. Considering that the recovery of individual monoacetin, diacetin (DA), and triacetin (TA) is complicated, many endeavours have enhanced the selectivity and total conversion of glycerol using acetic acid during catalytic acetylation. In this work, we extensively review the catalytic activity of different heterogeneous acid catalysts and their important roles in glycerol acetylation and product selectivity. In addition, the most influential operating conditions to attain high yields of combined DA and TA are achieved by closely examining the process. This review also highlights the prospective market, research gaps, and future direction of catalytic glycerol acetylation.

Transesterification of Jatropha Curcas Oil to Biodiesel by Using Short Necked Clam (Orbicularia Orbiculata) Shell Derived Catalyst

Investigation has been conducted to develop an environmental friendly and economically feasible process for biodiesel production. Natural short necked clam shell was utilized as calcium oxide (CaO) source for transesterification of non-edible Jatropha curcas oil to biodiesel. The powdered clam shell was calcined at 900°C for 3 h to transform calcium carbonate (CaCO3) in shell to active CaO catalyst. The effect of catalyst loading, methanol to oil molar ratio and reaction time on fatty acid methyl ester (FAME) yield was investigated. Under optimal condition, biodiesel yield achieved 93% within 6 h at 65°C. As a result, the catalytic activity of waste clam shell-derived catalyst is comparable to commercial CaO catalyzed reaction. Hence, it can be used as another renewable yet cost-effective catalyst source for biodiesel production.

Higher Grade Biodiesel Production by Using Solid Heterogeneous Catalysts

To date with the day of less dependence with fossil-based energy, there has been extensive research into the area of generation for alternative fuel—biodiesel for utilization in diesel engine. Development of effective catalyst is important for continuous biodiesel production. Select a right catalyst together with suitable feedstock is necessary to create an economically viable and sustainable energy source. Although homogeneous catalyzed reaction showed superior transesterification activity than heterogeneous system, but the focus on the development of solid green catalyst becomes more attractive due to the point of easy process and economics concern. Furthermore, the catalytic activity of solid catalyst was comparable to that of the existing liquid catalyst. This chapter reviews various types of homogeneous and heterogeneous catalysts used for transesterification of high free fatty acid oil (Jatropha oil). The process involves single-step or two-step reactions which rely on the physicochemical properties and flexibility of catalyst.

Revalorization of selected municipal solid wastes as new precursors of “green” nanocellulose via a novel one-pot isolation system: A source perspective

In the present work, four types of newly chosen municipal solid wastes (Panax ginseng, spent tea residue, waste cotton cloth, and old corrugated cardboard) were studied as the promising sources for nanocellulose, which has efficiently re-engineered the structure of waste products into highly valuable nanocellulose materials. The nanocellulose was produced directly via a facile one-pot oxidative hydrolysis process by using H2O2/Cr(NO3)3 solution as the bleaching agent and hydrolysis medium under acidic condition. The isolated nanocellulose products were well-characterized in terms of chemical composition, product yield, morphological structure and thermal properties. The study has found that the crystallinity index of the obtained nanocellulose products were significantly higher (62.2-83.6%) than that of its starting material due to the successive elimination of lignin, hemicellulose and amorphous regions of cellulose, which were in good agreement with the FTIR analysis. The evidence of the successful production of nanocellulose was given by TEM observation which has revealed the fibril widths were ranging from 15.6 to 46.2nm, with high cellulose content (>90%), depending on the cellulosic origin. The physicochemical properties of processed samples have confirmed that the isolation of high purity nanocellulose materials from different daily spent products is possible. The comparative study can help to provide a deep insight on the possibility of revalorizing the municipal solid wastes into nanocellulose via the simple and versatile one-pot isolation system, which has high potential to be used in commercial applications for sustainable development.