Sutha Shobana

A review of thermochemical conversion of microalgal biomass for biofuels: chemistry and processes

Renewable biomass sources are organic materials, in which solar energy is stored in bio-chemical bonds, and which commonly contain carbon, hydrogen, oxygen, and nitrogen constituents, along with traces of sulfur. Renewable biomass is now considered as a crucial energy resource, which is able to meet a range of energy requirements, including generating electricity and fueling vehicles. Among all the renewable energy sources, microalgal biomass is unique, since it profitably stores solar energy. It is one of the renewable sources of carbon that can be effectively converted into expedient solid, liquid, and gaseous biofuels through different conversion techniques. In this review, thermochemical conversion technologies involving microalgal biomass are highlighted, with emphasis on the background chemistry and chemical processes. Thermochemical conversion of microalgal biomass via pyrolysis, hydrothermal liquefaction, gasification, torrefaction, and direct combustion for bioenergy production from microalgal species is discussed, though there are limited literature sources available on these technologies. The unique features of hydrothermal gasification and supercritical gasification technologies are described, with the chemical reactions involved in these processes. The decomposition pathways of the main chemical components present in the microalgal biomass, such as carbohydrates and proteins, are well elucidated with the chemical pathways. The pros and cons of direct combustion are also spotlighted.

A review on the biosynthesis of metallic nanoparticles (gold and silver) using bio-components of microalgae: Formation mechanism and applications

The synthesis of nanoparticles (NP) using algae has been underexploited and even unexplored. In recent times, there are few reports on the synthesis of NP using algae, which are being used as a bio-factory for the synthesis. Moreover, the algae are a renewable source, so that it could be effectively explored in the green synthesis of NP. Hence, this review reports on the biosynthesis of NP especially gold and silver NP using algae. The most widely reported NP from algae are silver and gold than any other metallic NP, which might be due to their enormous biomedical field applications. The NP synthesized by this method is mainly in spherical shape; the reports are revealing the fact that the cell free extracts are highly exploited for the synthesis than the biomass, which is associated with the problem of recovering the particles. Besides, mechanism involving in the reduction and stabilization is well demonstrated to deepen the knowledge towards enhancement possibilities for the synthesis and applications.

Bio-hythane production from microalgae biomass: Key challenges and potential opportunities for algal bio-refineries

The interest in microalgae for wastewater treatment and liquid bio-fuels production (i.e. biodiesel and bioethanol) is steadily increasing due to the energy demand of the ultra-modern technological world. The associated biomass and by-product residues generated from these processes can be utilized as a feedstock in anaerobic fermentation for the production of gaseous bio-fuels. In this context, dark fermentation coupled with anaerobic digestion can be a potential technology for the production of hydrogen and methane from these residual algal biomasses. The mixture of these gaseous bio-fuels, known as hythane, has superior characteristics and is increasingly regarded as an alternative to fossil fuels. This review provides the current developments achieved in the conversion of algal biomass to bio-hythane (H2+CH4).

Coordination behavior and bio-potent aspects of Ni(II) with 2-aminobenzamide and some amino acid mixed ligands--Part II: Synthesis, spectral, morphological, pharmacological and DNA interaction studies.

A series of novel bioactive mixed ligand Ni(II) complexes (1a-1d) have been synthesised by using 2-aminobenzamide (2AB) and some bio-relevant amino acid ligands. The synthesised Ni(II) complexes were structurally characterized by various physico-chemical and spectral studies. Elemental analysis and molar conductance values suggest that 1:1:1 stoichiometry with non-electrolytic nature. Based on the spectral studies, both the ligands act as bidentate and they chelate with Ni(II) ion via amino-NH2 and amido-O and deprotonated carboxylato-O and amino-NH2 atoms respectively to form a stable six, five membered chelate rings with mononuclear octahedral geometry. Thermal studies show the presence of coordinated water and acetate molecules in the coordination. The powder X-ray diffractogram and SEM pictograph imply that all the complexes have fine crystalline peaks with homogeneous surface morphology. In vitro antimicrobial and antioxidant studies indicate the complexes are more active than free 2-aminobenzamide ligand. The Ni(II)-2AB-gly/phe complexes (1a and 1d) show significant oxidative cleavage and DNA binding activities. Moreover, the 3D molecular modeling, analysis of the complexes has also been studied.

A review on the biomass pretreatment and inhibitor removal methods as key-steps towards efficient macroalgae-based biohydrogen production

(Red, green and brown) macroalgal biomass is a propitious candidate towards covenant alternative energy resources to be converted into biofuels i.e. hydrogen. The application of macroalgae for hydrogen fermentation (promising route in advancing the biohydrogen generation process) could be accomplished by the transformation of carbohydrates, which is a topic receiving broad attention in recent years. This article overviews the variety of marine algal biomass available in the coastal system, followed by the analyses of their pretreatment methods, inhibitor formation and possible detoxification, which are key-aspects to achieve subsequent H2 fermentation in a proper way.

Biomass based hydrogen production by dark fermentation — recent trends and opportunities for greener processes

The generation of biohydrogen as source of biofuel/bioenergy from the wide variety of biomass has gathered a substantial quantum of research efforts in several aspects. One of the major thrusts in this field has been the pursuit of technically sound and effective methods and/or approaches towards significant improvement in the bioconversion efficiency and enhanced biohydrogen yields. In this perspective, the present contribution showcases the views formulated based on the latest advances reported in dark fermentative biohydrogen production (DHFP), which is considered as the most feasible route for commercialization of biohydrogen. The potential prospects and future research avenues are also presented.

Studies on Ni(II), Cu(II) and Zn(II) complexes with 2-aminobenzamide and some bioactive imidazole enzyme constituents

A series of Ni(II), Cu(II), and Zn(II) complexes of 2-aminobenzamide(2AB : L) and some imidazole enzyme constituents(B) viz., imidazole(him), benzimidazole(bim), histamine(hist), and L-histidine(his) have been synthesized and characterized using analytical and various spectral studies. Vibrational spectral data of the synthesized complexes reveal that the ligands bind with metal(II) ions through nitrogen and oxygen. The calculated g-tensor values of Cu(II) complexes suggest that the unpaired electron is localized in the orbital. The results obtained from the spectral studies confirm the distorted octahedral environment around the metal(II) ions. Their powder XRD indicates microcrystalline nature and SEM pictographs identify their uniform surface morphology. Cu(II) and Ni(II) complexes show biological, antioxidant, and DNA activities when compared to free 2-aminobenzamide. Equilibrium studies have been carried out pH-metrically in 50% (v/v) water–ethanol mixture at 37 °C and I = 0.15 mol dm−3 NaClO4. Analysis reveals the presence of certain heteroligand species viz., MLBH/MLB/MLB2, in addition to various primary species. In MLB/MLB2 species, 2AB(L) binds with M(II) ions via N-amino and O-amido, whereas the ligands(B) him and bim are monodentate, hist and his are bi and tridentate, respectively. The stabilization parameters Δ log K, log X, log X′, and % RS clearly indicate all the heteroligand complexes have higher stabilities than their primary.

Valorization of spent coffee grounds recycling as a potential alternative fuel resource in Turkey: An experimental study

ABSTRACT In this study, recycling of spent coffee grounds (SCG) as a potential feedstock for alternative fuel production and compounds of added value in Turkey was assessed. The average oil content was found (≈ 13% w/w). All samples (before and after extraction) were tested for scanning electron microscopy (SEM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), X-ray diffraction (XRD), calorific value, surface analysis and porosity, Fourier transform infrared (FT-IR), and elemental analysis to assess their potential towards fuel properties. Elemental analysis indicated that carbon represents the highest percentages (49.59% and 46.42%, respectively), followed by nitrogen (16.7% and 15.5%), hydrogen (6.74% and 6.04%), and sulfur (0.851% and 0.561%). These results indicate that SCG can be utilized as compost, as it is rich in nitrogen. Properties of the extracted oil were examined, followed by biodiesel production. The quality of biodiesel was compared with American Society for Testing and Materials (ASTM) D6751 standards, and all the properties complied with standard specifications. The fatty acid compositions were analyzed by gas chromatography. It was observed that coffee waste methyl ester (CWME) is mainly composed of palmitic (35.8%) and arachidic (44.6%) acids, which are saturated fatty acids. The low degree of unsaturation provides an excellent oxidation stability (10.4 hr). CWME has also excellent cetane number, higher heating value, and iodine value with poor cold flow properties. The studies also investigated blending of biodiesel with Euro diesel and butanol. Following this, a remarkable improvement in cloud and pour points of biodiesel was obtained. Spent coffee grounds after oil extraction is an ideal material for garden fertilizer, feedstock for ethanol, biogas production, and as fuel pellets. The outcome of such research work produces valuable insights on the recycling importance of SCG in Turkey. Implications: Coffee is a huge industry, and coffee has been widely used due to its refreshing properties. This industry generates large quantities of waste. Therefore, recycling of spent coffee grounds for producing alternative fuels and compounds of added value is crucial. Elemental analysis indicated that coffee waste can be utilized as compost, as it is rich in nitrogen. Coffee waste after oil extraction is an ideal feedstock for ethanol and biogas production, garden fertilizer, and as fuel pellets. The low degree of unsaturation provides excellent oxidation stability. Its biodiesel has also excellent cetane number, higher heating value, and lower iodine value.

A review on lignin structure, pretreatments, fermentation reactions and biorefinery potential

In recent years, lignin valorization is commercially an important and advanced sustainable process for lignocellulosic biomass-based industries, primarily through the depolymerization path. The conversion of the lignin moieties into biofuels and other high value-added products are still challenging to the researchers due to the heterogeneity and complex structure of lignin-containing biomass. Besides, the involvement of different microorganisms that carries varying metabolic and enzymatic complex systems towards degradation and conversion of the lignin moieties also discussed. These microorganisms are frequently short of the traits which are obligatory for the industrial application to achieve maximum yields and productivity. This review mainly focuses on the current progress and developments in the pretreatment routes for enhancing lignin degradation and also assesses the liquid and gaseous biofuel production by fermentation, gasification and hybrid technologies along with the biorefinery schemes which involves the synthesis of high value-added chemicals, biochar and other valuable products.

Stability and Structural Studies on Ni(II)–5-Fluorouracil Mixed Ligand Complex Systems

Binary and mixed ligand species formation and their distribution in the 5-fluorouracil (5-FU; A) and Ni(II) system in the presence of amino acids (B), namely glycine (gly), l-alanine (ala), l-valine (val) and l-phenylalanine (phe), were studied potentiometrically at different temperatures and pHs. The computer assisted analysis illustrates the existence of MAB and MAB2 species, where 5-fluorouracil and amino acids act as bidentates to form stable metal chelates. The distribution of different chemical species with temperature and pH was also studied. In addition, the coordination environments in the MAB system were determined by spectrophotometric measurements. The binding nature of both 5-FU (A) and amino acids (B) in MAB species of the Ni(II)–5-FU–amino acid systems reveal tetra coordination to the central Ni(II) ion. The fifth and sixth positions in MAB complexes are occupied by solvent water molecules/perchlorate ions and thus form a stable hexa coordinated environment. The calculated stabilization parameters indicate that the formed mixed ligand species have higher stabilities than their corresponding binary systems. Thermodynamic parameters were determined from the temperature dependent stability constant values. The mixed ligand complex systems show remarkable in vitro antimicrobial, antioxidant and nuclease activities.