Current Organic Chemistry - Volume 17, Issue 15, 2013

There is a world- wide growing interest in using lignocellulosic raw material for the production of fuels and chemicals, particularly related to the pulp and paper industry, and this is no exception in Bangladesh. On the other hand, Bangladesh and other Southeast- Asian countries are densely populated, forest deficient, thus heavily dependent on agriculture residue for such a purpose. This study reviews the availability and suitability of nonwood raw materials for pulp production following the biorefinery concept in Bangladesh. The problems related to non-wood pulping are also discussed. Non-woods like bagasse, corn stalks, straw, Saccharum spontaneum etc. are composed of vascular bundle surrounded by parenchyma cell. So they are easy to delignify but create problems in pulp washing, screening, and paper machine runnability due to high drainage resistance (0SR). Pre-extraction prior to pulping of these raw materials improved the drainage resistance and also increased the value by extracting acetic acid, chemicals and energy from the preextracted liquor. The amount of non-wood available in Bangladesh is not sufficient to run an economically viable mill based on a single raw material. Research results showed that the organic acid-based fractionation is technically feasible using non-wood to produce pulp, together with lignin and sugars as by-products, which are starting raw materials for biomaterials, fuel and chemicals. Non-wood biomass can be used as the raw material following the integrated biorefinery concept if a suitable pulping process is correctly selected.

Acetic acid is one of the promising bio-products following the Value Prior to Pulping (VPP) concept, which is one of the options for Integrated Forest Biorefinery. In a typical chemi-thermo-mechanical pulping (CTMP) process, the chemical pre-treatment may be retrofitted into the pre-extraction stage. The potential of pre-extraction of acetic acid under the conditions similar to a CTMP process was evaluated in this study. The pre-extraction yield of acetic acid increased with the increase of cooking time and temperature. The maximum acetic acid yield was 31.25% at 150°C and 60 min after the cooking in an M/K digester. The pre-extraction yield increased to 42.05% after the cooked chips were broken down into pulp fibers, indicating that some of the released acetic acid was trapped inside the wood chips and a post-mechanical treatment could enhance the diffusion of acetic acid to the liquid phase.

The effective use of prehydrolysis liquor (PHL), from the kraft-based dissolving pulp production process, may fit into the concept of integrated forest biorefinery (IFBR). The dissolved organics in the PHL include hemicelluloses, lignin, acetic acid, furfural and extractives. Adsorption of hemicelluloses and lignin onto the neutral sulphite semichemical (NSSC) pulp fibres may be a potential method of utilizing the dissolved organics in the PHL. The principal goal of this work was to study the adsorption of lignocelluloses of PHL onto the NSSC pulp fibres. In addition to the typical process variables, the effect of using polymers, such as coagulant and flocculant, on increasing the adsorption, was investigated. The effects of time and temperature were examined. It was shown that adsorption reached its maximum almost in 1 h. Also, it was demonstrated that a higher temperature improved the adsorption. Furthermore, the use of cationic polymers, such as polydiallyl dimethyl ammonium chloride (PDADMAC), a coagulant (Nalkat 2020) and flocculant (Ultimer 1470), could enhance the adsorption of lignocelluloses from PHL onto NSSC pulp fibres. The maximum lignin and hemicelluloses adsorption was 160 mg/g and 320 mg/g onto pulp (58% and 22% removal from PHL), respectively. It is concluded that lignocelluloses of the PHL can be adsorbed onto NSSC pulp fibres so as to work as papermaking additives; and typical polymers, such as coagulant and flocculant, can be used to enhance the lignocelluloses adsorption.

The kraft-based dissolving pulp production process can be a model for the forest biorefinery concept. The objective of this study is to characterize the dissolved lignin present in the pre-hydrolysis liquor (PHL) to facilitate its subsequent use following the forest biorefinery concept. In this work, lignin was isolated from PHL by acidification using dilute H2SO4, followed by purification through dissolution in a dioxane solution (9:1) and re-precipitation with diethyl ether. The characteristics of PHL lignin were compared with those of the dioxane lignin, acetic acid (AA) lignin and ethanosolv (EL) lignin isolated from the same mixed hardwood (maple, poplar and birch wood chips, in a ratio of 7:2:1), which is the raw material used for dissolving pulp production. The obtained lignin samples were characterized by UV, FTIR, 1H-NMR spectroscopy, molecular weight determination, elemental and methoxyl analyses. The results showed that the absorptivity of dioxane lignin at 276 nm was 10.0 l g-1cm-1, while that of PHL lignin was 17.2 l g-1cm-1. The presence of condensed structures in the PHL lignin was also observed in the FTIR spectrum (strong bands at 870 and 890 cm-1), which was also present in the AA and EL lignins. The lignin isolated from PHL had a lower molecular weight and methoxyl group per C9 unit, in comparison with other lignin samples. 1H-NMR analysis indicated a significant increase in the phenolic hydroxyl content in the PHL lignin, caused by cleavage of aryl-ether bonds during the prehydrolysis.

Liquefaction of lignocellulosic biomass is a promising process to produce liquid biofuels and valuable chemicals. The main purpose of this work is to efficiently liquefy biomass into energy-dense bio-oils through direct liquefaction. Pinewood sawdust was liquefied in supercritical carbon dioxide (SCCO2) at various temperatures (225-375°C) and residence time (0-4 hours) with alkaline catalyst (K2CO3). The results showed that the yield of bio-oils varied from 12 wt% to 29 wt% under various conditions. The optimal parameters for SCCO2 liquefaction were 300°C and 2 hours in this study, which generated the maximum bio-oil yield 29 wt%. The effects of temperature and residence time on SCCO2 liquefaction process were discussed. Multiple analytical methods such as GC-MS, FT-IR and elemental analyzer were applied to study the compositions and properties of liquid bio-oils.

In this study, mountain pine beetle (MPB, Dendroctonus ponderosae Hopkins) infested lodgepole pine (Pinus contorta Dougl.) barks were liquefied in phenol using sulfuric acid as the catalyst. Results showed that liquefaction conditions, such as reaction time, reaction temperature, phenol/bark ratio, and catalyst loading had significant effects on the liquefaction yield, free phenol content of the liquefied bark fraction and the properties of the unliquefied bark residues. Higher reaction temperature and prolonged reaction time not only promoted the degradation of the bark components during the liquefaction but also induced recondensation reactions among the degraded bark components. Higher phenol/bark ratio increased the bark liquefaction yield by retarding the recondensation reactions among the degraded bark components. The liquefaction yield, free phenol content in the liquefied bark fraction and residues properties were found to be mostly affected by the catalyst loading, followed by the reaction temperature, reaction time and phenol/bark ratio.

Hydrolyzing the amorphous region of cellulose with high selectivity while protecting the crystalline region during acid hydrolysis of cellulose still remains a key technical barrier in cellulose hydrolysis and Microcrystalline Cellulose (MCC) production. This study investigated the effects of two transition metals (Fe3+ and Cu2+) on cellulose yield after acid hydrolysis, α-cellulose content and crystallinity of the Eucalyptus pulp cellulose. The correlations of metal ion catalysis and hydrolysis selectivity were studied and optimized using Orthogonal Experimental Design. The results showed that metal ion catalysts enhanced the selectivity of acid hydrolysis of amorphous cellulose region over crystalline region with enhanced hydrolysis conditions. Thus, high degree crystalline MCC was obtained. However, the selectivity did not show clear improvement with mild acid hydrolysis conditions. Overall, Fe3+ catalyst had better acid hydrolysis selectivity than Cu2+ catalyst. The factors that affect cellulose crystallinity follow the order: metal ion concentration > HCl concentration > hydrolysis temperature > hydrolysis time. The optimal conditions to get the highest crystallinity of cellulose were 0.4 mol/l Fe3+, 2.5 mol/l HCl, 80°C, 55 min at solid-liquid ratio of 1:15.

This study focuses on the conversion of cellulose and hemicelluloses present in kenaf stalks into fermentable sugars using sulfuric acid pretreatment followed by enzymatic hydrolysis. The first step prior to pretreatment was to determine the compositions of hexose, pentose sugars and lignin in pulverized kenaf stalks. Pretreatment on kenaf was performed by varying three independent parameters: 1) reaction temperatures (150 -160 °C); 2) reaction time (10 - 30 min) and 3) diluted sulfuric acid concentration (0.5 – 2.0 %). Regression analysis was employed to examine the effects of these parameters on two responses: 1) the solubility of hemicelluloses in liquid fraction (Y1); and 2) the yield of cellulose digestibility (Y2). The observed R2 values were 0.99 and 0.97 implying the statistical significance of the model equations. The optimum conditions of the factors were 153 °C for 20 min at 1.55% acid concentration. The maximum experimental cellulose digestibility (87%) was observed at 160 °C for 20 min at a 2% acid concentration. The model predicted maximum digestibility was 89% at the same reaction conditions. The results showed that kenaf biomass pretreatment at a low acid concentration (0.5% sulfuric acid) led to limited hemicellulose solubility and therefore resulted in limited cellulose digestibility. The maximum concentrations of fermentable inhibitors were 4.21 g L-1 for acetic acid at 2.29 combined severity factor, 2.29 g L-1 furfural, and 0.71g L-1 Hydroxymethylfurfural (HMF) at 1.75 combined severity factor (CSF).

In this work, bio-based products from starch biopolymer and rape biomass were produced. The physicochemical properties at interface of the biodegradable composites were analyzed and the intrinsic tensile strength of the rape fibers was determined from biocomposites containing up to 40 wt% of starch substitution. Rape thermomechanical fibers showed potential to undergo efficient fiber/fiber joints, and this was evidenced by their aptitude to paper production and to reinforce biopolymers such as thermoplastic starch. The high yield thermomechanical process brought rape fibers rich in lignin at the fiber surface, and this helped to fiber individualization and dispersion into the matrix. The surface characteristics of rape fibers allowed anchoring to the starch matrix, by means of Van der Waals interactions and hydrogen bonding. The quality of the rape/starch interface was analyzed in this study, and values for the interfacial shear strength (τ) and the intrinsic strength of rape fibers (σtF) were evaluated.

Rape biomass was the raw material for the preparation of thermomechanical fibers, and it was used to reinforce starch-based biopolymer. In this study, the mechanical properties of the produced biocomposites, including flexural strength, Young’ s and flexural moduli and impact strength, were characterized. Afterwards, the material properties were simulated to evaluate its suitability for substituting for oil-based raw materials. The results showed that the intrinsic flexural strength of rape fibers was 2.25 times of that of rape fibers. The impact strength of rape/starch biocomposites decreased with the increment in the reinforcement, even though the work to crack initiation slightly augmented with the fiber proportion increase. After the mechanical property analysis, the prepared biocomposites were tested as replacing materials for the development of real oil-based products. The engineering development stands out the feasibility of using these materials to develop new products truly based on bio-resources.

Paper industry uses various wet-end chemicals mainly for process control and the production of paper products. Although this industry currently uses various oil-derived chemicals, such as cationic polyacrylamide and poly (aminoamide)-epichlorohydrin, the use of bio-based chemicals derived from lignocelluosic resources has attracted attention since they are renewable and environmentally-friendly. In this review paper, the current status of chemicals used as refining, strength, retention, drainage, formation and sizing additives as well as filler materials in papermaking is discussed. Also, the current application and progress in producing lignocelluloses-derived wet-end chemicals for papermaking is demonstrated. Generally, the main challenge in producing bio-based wet-end chemicals is that naturally occurring lignocelluloses have insufficient properties to be used as wet-end chemicals. Therefore, they should be chemically and/or enzymatically modified so that they could have desired performance.

The paper discusses the misuse of two familiar chemical words in the chemical literature, namely hydrolysis and catalysis. The splitting of the acetate ester linkage in acetylsalicylic acid or aspirin, which has different mechanisms according to the pH of the solution is used as an example.

Molecular imprinting is a powerful technique to form a synthetic polymer receptor with tailor-made binding sites. This article gives a short overview of the application of the principle of molecularly imprinted polymers (MIPs) in capillary electrochromatography (CEC). Some new developments of monolithic column and coating based on MIPs in CEC mode are presented. Lastly, the review also discusses their applications for separation of organic compounds and future perspectives in this field.

Oxide nanocubes have received great research attention because of their unique chemical, optical, magnetic, and electrontransport properties, which are caused by the strong face-to-face interactions among the nanocubes. One of the main challenges in this field is how to realize larg-scale assembly oxide nanocubes in large scale. This review summarizes the recent progress in the organic solution- based routes for fabrication and self-assembly of oxide nanocubes, as well as related physical and chemical properties. Solvent and surfactants those may determine the growth and self-assembly behavior of the nanocubes are emphasized in this paper. This review aims to present a relatively general understanding of the correlation between the surface interactions and self-assembly behaviors of nanomaterials under organic solution based conditions and potential applications of self-assembled oxide nanocubes.

Graphene possesses outstanding electronic and structural properties and the possibility to functionalize it with different functional moieties has greatly broadened the scope of its applications. The copper (I) catalyzed azide-alkyne cycloaddition (CuAAC) reaction has been recently adopted as a universal coupling process with applications that extend far beyond organic synthesis to further challenging goals in chemistry, polymer science, and biology. In this article we critically examine the progress in the use of the CuAAC reaction with different carbon nanostructures and show how this research is merging now in the development of novel graphene-based functional materials. We believe that the selective functionalization of graphene using the CuAAC click reaction may play an important role in improving the integration of graphene in multicomponent systems, and consequently their applications.

Sodium nitrite and hydrogen peroxide are ubiquitous in bioorganic and environmental chemistry, and their role has been exceptionally important and under continuous investigation. Sodium nitrite is a potential source of cytotoxic peroxynitrite in biological systems, while in a tandem with hydrogen peroxide it may serve as a precursor of mutagenic aromatic nitro compounds in the environment. A biomimetic couple of sodium nitrite and an aqueous solution of hydrogen peroxide was utilized for the transformation of phenols in an acidic medium. Phenols were regioselectively converted into the corresponding nitro derivatives; the sterically hindered phenols of vitamin E type were oxidized into the quinone derivatives. This is an indication that vitamin E and its derivatives can be good nitrite scavengers. Cresols were transformed to the mixture of mono- and dinitro derivatives; the o-substitution was substantial. Regioselectivity of nitration of 3,4-dialkyl substituted phenols was in accordance with the Mills-Nixon effect; estrone was converted into a mixture of its 2- and 4-nitro analogues. Nitration of phenols obviously encountered a single electron transfer, because the transformation was completely suppressed in the presence of a free radical TEMPO. The most likely nitrating agent was nitronium ion derived from nitrogen dioxide. The NaNO2/H2O2/H2SO4 system differs from the ‘classic’ HNO3/H2SO4 system, since a considerably different selectivity was established.