Vinu R

Thermal aging of natural ester oil shows drastic reduction in partial discharge inception voltage (PDIV) and a significant variation is observed only above a certain aging time, under AC, DC, high frequency AC voltages and with harmonic voltages with different total harmonic distortion. Weibull distribution studies on PDIV measurements indicate a reduction in scale parameter (α) with increase in thermal aging temperature. A characteristic reduction in breakdown voltage was observed with the thermally aged ester oil, under AC, DC and standard lightning impulse voltage. The breakdown voltage variation with aged ester oil follows normal distribution. Ultraviolet (UV) analysis of ester oil thermally aged at 160°C has revealed a regular shift of the derived absorbance parameter to longer wavelengths. The interfacial tension and turbidity exhibits an inverse relationship with the thermally aged ester oil. Gas chromatography/mass spectrometric analysis of the thermally aged ester oil predicted the formation of more carboxylic acids and ketones with aging duration. The steady-state fluorescence on thermally aged ester oil exhibits a shift in its emission profile, which is in tandem with the UV absorption spectroscopic analysis. Fluorescence analysis can be adopted as a real-time monitoring tool in transformers, to understand the condition of liquid insulation. The viscosity dependence on the wavelength of derivative absorption maxima follows a direct relationship with the thermally aged natural ester oil.

A fundamental understanding of reaction chemistry and pathways in fast pyrolysis of microalgae is hindered by the complex structure of proteins, lipids and carbohydrates that constitute them and the interactions among the intermediates at short timescales. In this study, bovine serum albumin (BSA), sunflower oil (SO) and potato starch (PS) were chosen as microalgae model compounds representing proteins, lipids, and carbohydrates, respectively. Fast pyrolysis of individual and binary mixtures of the model compounds was investigated at 500 °C using an analytical pyrolysis reactor interfaced with a gas chromatograph/mass spectrometer (GC/MS) and a Fourier transform infrared spectrometer (FTIR) to investigate the composition of pyrolysates and their time evolution. The composition of BSA, SO and PS was chosen to be 1 : 2, 1 : 1 and 2 : 1 (wt. basis) to emulate the microalgae composition. Fast pyrolysis of BSA : SO mixtures promoted esterification of carboxylic acids and alcohols, whereas BSA : PS and SO : PS mixtures promoted the formation of carboxylic acids via syn-elimination of esters, while inhibiting the decarboxylation pathway. The presence of SO and PS altered the pyrolysis mechanism of BSA by inhibiting the formation of aromatic hydrocarbons and nitrogen-containing compounds. The time evolution of C-H (aromatic and aliphatic), N-H, O-H, and CO stretching vibrations was monitored up to 60 s using in situ FTIR. The maximum vapor evolution time for fast pyrolysis of SO (50 s) was higher than that for BSA and PS (both 8-10 s). The addition of BSA and PS to SO increased the rate of evolution of volatiles, with the maximum vapor evolution occurring at shorter time periods. The first order apparent rate constants of fast pyrolysis followed the trend: 0.294 s -1 (PS) > 0.162 s -1 (BSA) > 0.107 s -1 (BSA : PS (2 : 1)) > 0.073 s -1 (BSA : SO (2 : 1)) > 0.048 s -1 (SO : PS (2 : 1)). Fast pyrolysis char was characterized by FTIR and GC/MS, and it contained polycyclic nitrogen compounds. The plausible reactions including the interactions among the various intermediates were unraveled, and a tentative mechanism was proposed.

The present study investigates the isotherm and kinetics of aqueous hexavalent chromium [Cr(VI)] removal using biochar (Ka-BC) and magnetic biochar (Ka-MBC) derived from seaweed biomass, Kappaphycus alvarezii. Characteristics of prepared Ka-BC and Ka-MBC were explored by FT-IR, XRD, SEM, EDAX, and surface area analysis. The effects of initial pH, contact time, and chromium concentration were investigated based on batch adsorption experiments. The maximum chromium adsorption was 64.8% and 82.5% using Ka-BC and Ka-MBC, respectively, corresponding to 500 mg/L loading at pH 3 with initial chromium concentration of 1 mg/L after 150 min of sorption reaction. The removal of chromium is mainly dependent on pH and follows a pseudo-second-order kinetic model. The adsorption experiments showed that Ka-MBC has better removal capacity than the Ka-BC due to multi-layer mechanism and surface roughness phenomenon in Ka-MBC. The chromium adsorption on Ka-MBC followed Langmuir isotherm. The current study demonstrates the utilization of seaweed-derived magnetic biochar composite as an efficient sorbent and low-cost alternative for the removal of Cr(VI) from the environment. Graphical abstract: [Figure not available: see fulltext.]

Corona activity on the surface of silicone rubber has high impact on variation in hydrophobicity of the material, and on corona inception voltage (CIV) of water droplet sitting on the corona degraded surface. The CIV is high under negative DC as compared to positive DC/AC voltages. Increase in conductivity of water droplet reduces CIV. Surface charge accumulation studies indicate that the charge retention capability of the insulating material gets reduced drastically with silicone rubber damaged due to corona causing degradation of surface. Irrespective of the number of cycles of corona discharge activities carried out, the time constant of charge decay, after the removal of charge injection, remains the same. The water droplet initiated discharges under AC and DC voltages radiate UHF signal in the bandwidth 0.3-1.2 GHz. With single droplet sitting on top of the corona damaged silicone rubber, the amount of charge retained by the water droplet is low when the droplet is placed and charged immediately after corona discharge activity to surface of the insulating material. When the water droplet is placed after a certain time period, the charge accumulation characteristics of silicone rubber are regained. Leakage current measured during water droplet discharge studies through recurrent plot (RP) analysis reveals that, under AC voltage, it is possible to classify corona inception, arcing and bridging of water droplet between high voltage and ground electrode. The RP obtained for the current signals generated due to water droplet discharges under positive and negative DC voltages are different. The amount of damage caused to silicone rubber due to water droplet is high under negative DC voltage as compared to positive/AC voltages. While correlating the level of damage to the insulating material due to water droplet and the RQA parameters of RP, it is observed that higher the recurrence rate along with high determinism can cause severe damage to the insulating material. Structural analysis using ATR-FTIR and pyrolysis-GC/MS studies reveal significant functional group variation on surface of silicone rubber, especially when the number of cycles of corona ageing is more.

Microalgae is projected as a promising third generation biomass feedstock for the production of biofuel and fine chemical intermediates. This study is focused on the selective production of chemicals from Nannochloropsis oculata microalga via catalytic fast pyrolysis technique using Co-Mo/γ-Al2O3 catalyst. Non-catalytic and catalytic fast pyrolysis (CFP) experiments were conducted in an analytical micropyrolyzer coupled with gas chromatograph/mass spectrometer to study the effects of temperature, catalyst-to-algae ratio, and metal loading on support on pyrolysate composition. The catalyst, Co-Mo/γ-Al2O3, was prepared using wetness incipient impregnation method, and characterized for its structure and pore size distribution. Catalyst-to-algae mass ratios used to study the pyrolysate composition and quality were 1:3, 1:1 and 2:1. The major organic compounds from both non-catalytic fast pyrolysis and CFP of the microalga were long chain nitriles, long chain alkanes and alkenes, polyaromatic and monoaromatic hydrocarbons. The optimum fast pyrolysis temperature under non-catalytic conditions that promoted the selectivity of aliphatic and aromatic hydrocarbons was 500 °C. The incorporation of Co-Mo/γ-Al2O3 catalyst promoted the formation of specific organic compounds like 1‑isocyanobutane and dimethylketene to the tune of 35% selectivity. The formation pathways for these compounds are proposed to involve dehydration, isomerization, ketonization and CH addition reactions of the amide and carboxylic acid moieties generated from the protein and lipid fractions of the alga. Owing to the low oxygen content in the pyrolysates from CFP, the estimated calorific value of organics in the pyrolysates was higher (33–39 MJ kg−1) than that of the microalga (18 MJ kg−1).

This study focuses on characterization of silicon carbide (SiC)-epoxy nanocomposites with different mass loading of SiC using different techniques to evaluate the physicochemical, thermo-physical and surface discharge activity of the insulating materials. A marginal increase in surface discharge inception voltage (SDIV) was observed with increase in wt% loading of SiC in the epoxy but not much variation is observed with increase in supply frequency. Surface discharge process radiates electromagnetic waves in the UHF signal frequency range of 0.5–1.5 GHz. The dielectric properties of the material get altered with the percentage of SiC material in epoxy resin. TEM analysis indicates uniformity of dispersion of nano particle in epoxy resin. Charge retention capability of the material is high when the deposited charges are unipolar. Optical emission studies indicate the presence of silicon peaks with SiC-epoxy nanocomposites in wavelength range of 350-400 nm. Oxygen peaks were observed for all samples. Using the spectral peak positions and intensities of the peaks obtained, the plasma temperature for SiC-epoxy nanocomposites was estimated to be c.a. 2240 K low when compared to that for pure epoxy. LIBS spectra clearly indicate an increase in carbon intensity with corona damaged specimen. Also for the same level of fluency, the amount of damage is less with higher percentage of SiC included epoxy nanocomposites. Pyrolysis GC/MS study indicates that the presence of SiC in the epoxy matrix enhances the timescale of primary pyrolysis vapors such as bisphenol components to form more monomeric phenols via secondary cracking reactions. POLYM. COMPOS., 39:3268–3279, 2018. © 2017 Society of Plastics Engineers.

Cellulosic pressboard is a key insulation material in oil filled transformers. Surface discharge or partial discharge degrades the insulation material and reduces the life time of the transformer. This study is aimed at understanding the effect of thermal aging of pressboard on the variation of its surface discharge and chemical characteristics. Thermal degradation of pressboard was carried out at 180 °C for 500 h in presence of ester oil under simulated aging conditions. The variation of salient electrical characteristics like surface discharge inception voltage (SDIV), charge measurement and optical emission spectra of the discharges were assessed at different aging periods. A significant reduction in SDIV was observed due to thermal aging. The charge measurement indicated that total charge deposition on pressboard increased with aging duration. Optical emission spectroscopy yielded valuable information regarding the elements evolved during discharge activity. Chemical characterization of the virgin and aged pressboard samples was carried out using analytical pyrolysis coupled with gas chromatograph-mass spectrometric technique (Py-GC/MS). The production of anhydrosugars, furan derivatives and oxygenates from the pressboard increased with aging time, while the esters in the oil were degraded to carboxylic acids with aging. Owing to the weakening of the hydrogen bonding network in oil impregnated pressboard with thermal ageing, high yield of end-chain depropagation products like anhydrosugars was observed during pyrolysis. The weak sites in cellulosic pressboard are expected to act as charge deposition sites.

Pyrolysis of algae is a promising route to produce high quality bio-oil and renewable chemicals. Owing to its complex structural composition, multiple pseudo-components are required to describe its thermal decomposition in a wide temperature range and evaluate the reaction kinetics. In this study, the pyrolysis behavior of the microalga, Nannochloropsis oculata (N. oculata), was studied by means of a thermogravimetric analyzer at various heating rates. A four-parallel-reaction scheme characterizing the pyrolysis of carbohydrate, protein, lipid and the secondary decomposition of char was employed to model thermal degradation using distributed activation energy model (DAEM). The average and standard deviation of activation energy, pre-exponential factor, and composition of the model components for pyrolysis of N. oculata were estimated. The model mass loss and differential mass loss profiles matched well with the experimental data at different heating rates. Based on the model predictions, the decomposition of proteins, carbohydrates, lipids and char occurred in the temperature regimes of 200–450 °C, 200–300 °C, 400–500 °C, and 750–900 °C, respectively. To gain valuable insights on the pyrolysate composition at various temperature regimes, analytical pyrolysis-gas chromatography/mass spectrometry experiments were performed. Indole and phenol, aliphatic and aromatic hydrocarbons, and long chain oxygenates were observed as the major pyrolysates in the temperature regimes of 30–350 °C, 350–600 °C and 600–1000 °C, respectively.

In this study, fast pyrolysis of lipid-rich microalga, Schizochytrium limacinum, is carried out to evaluate the potential of deriving valuable chemicals and fuel molecules from this algae variety. The alga was characterized for its proximate and elemental composition, and heating value. The pyrolytic mass loss profiles of the alga were obtained from thermogravimetric analyzer, and the apparent kinetic parameters of degradation were evaluated using advanced isoconversional method of Vyazovkin. Fast pyrolysis experiments were performed in analytical pyrolyzer coupled with gas chromatograph/mass spectrometer. Long chain carboxylic acids, primarily tetradecanoic and hexadecanoic acids, were observed as the major pyrolysates in the temperature range of 350–650 °C in the absence of catalyst. A clear increase in production of aromatics and cyclic hydrocarbons was observed at high temperatures owing to the cracking of long chain hydrocarbon portion of the carboxylic acids. Catalytic fast pyrolysis was performed at 400 °C using zeolite Y-hydrogen (ZYH), zeolite Y-sodium (ZYNa), and oxides like MgO, ZrO2 and TiO2. The production of polyaromatic hydrocarbons and nitriles increased, while that of long chain carboxylic acids decreased with increasing acidity of ZYH. Increasing the loading of ZYNa resulted in the formation of long chain ketones. The formation of ketones was more pronounced with MgO and ZrO2 catalysts. The major ketones obtained include 16-hentriacontanone and 14-heptacosanone, which were formed via ketonization reactions of palmitic and myristic acids present in the algae. This study demonstrates that selective production of valuable chemical intermediates can be achieved from complex feedstocks like microalgae via catalytic fast pyrolysis using zeolites and metal oxides.

Tree-like-trees are observed with electron beam irradiated XLPE cable insulation under AC voltages. Charge accumulation studies indicate that the level of charge deposited by +/- DC corona charging is almost same. However, the amount of accumulated charge increases with increase in level of irradiation of electron beam. The decay time constants are marginally high with positive charge deposition. Moreover, the decay time constant of accumulated charges increases with increase in level of irradiation of the material. The rise time of injected current signal formed during tree growth in positive and negative half cycle is about 900 and 700 ps, respectively. The UHF signal generated during tree growth in virgin and with irradiated specimen has its frequency content in the range 0.5-1.5 GHz. Weibull distribution studies indicate that the life time of electron beam irradiated specimen drastically gets reduced due to treeing. Sequential measurement of UHF signal indicates that tree growth involves high and low intensity discharges. Phase resolved partial discharge studies using spectrum analyzer indicates that discharges occur at the raising portion or near zero crossing of the applied AC voltage. FTIR spectroscopy and analytical pyrolysis-GC/MS analyses of the electron beam irradiated samples reveal the formation of alkoxy and alkyl peroxy radicals, and carbonyl and hydroxyl groups via scission of the crosslinks. The weak crosslinking sites are proposed to act as nodal points from where tree growth occurs.