23 May 2018
Cement Waste for Biodiesel Production
Biodiesel, as an alternative to petroleum fuels, is still limited by the amounts produced. To increase biodiesel production, there is a need to optimise processes. This means three things: simplified operations with high yields, easy access to low cost raw materials and reduction in waste output.
Researchers from the Centre for Environmental Sciences, Central University of Jharkhand, took the middle path, looking for low cost raw materials. And they came up with an unlikely candidate as catalyst: cement waste!
High specific surface area, strong base strength and high concentration of base sites are characteristics of an active transesterification catalyst. The research team found that cement fits the bill for the transesterification of karanja and sunflower oil to biodiesel. But then, cement is costly. So they compared the catalytic activity of pure and commercial grade cement with that of cement wastes.
The team washed locally collected concrete and mortar. They dried, ground, sieved and calcined the samples at 850 °C for 3 hours. Calcination increases the basic strength due to the decomposition of hydroxides and carbonates to the more basic oxide phase.
The researchers analysed the effect of the catalysts on the conversion of oil to biodiesel by altering catalyst concentration. They found maximum conversions for cement. But, mortar and concrete also yielded good results.
Temperature plays a crucial role in transesterification. Increasing the temperature from 55 to 60˚C had a notable effect on the conversion of oil. But, increasing the temperature further did not seem to have any signiﬁcant impact. For all the tests, the team observed maximum conversion at 60˚C.
The combined concentration of calcium and magnesium in the reﬁned biodiesel was well below the permissible level say, the researchers.
What is more interesting is that the solid catalyst from cement waste is recyclable. “There is no signiﬁcant leaching of catalytically active sites from the solid catalyst matrix to the liquid”, says Bhaskar Singh,
The team did an economic analysis of a 50 kt biodiesel production facility. “The manufacturing cost of biodiesel using the method comes to about 82 rupees per kilo” says Dipesh Kumar.
“Owing to growth in construction, it is expected that construction and demolition waste generation in India will increase. This threat to the environment can be converted into an opportunity”, adds Ayan Banerjee.
“The use of cement waste to produce catalysts for biodiesel production reduces costs on the one hand and is environmentally more sustainable”, says Sandeep Chatterjee.
The research was funded by the UGC. The team hopes that the technology can be further investigated to scale-up for industrial application.
J. Cleaner Production, 183: 26-34
Mahadeva swamy H
27 May 2018
Nebuliser Spray for Solar Cells
Nanoscales to reduce the cost of energy capture
Presently, counter electrodes in dye-sensitised solar cells use platinum – a high cost metal, with limited availability and low corrosion resistance. Scientists from Tamil Nadu along with collaborators from the United Kingdom have advanced a copper-indium-aluminium sulphide as low-cost alternative. They propose a simple, inexpensive nebuliser spray method to make dye sensitised solar cells.
When droplet size is precisely controlled, the spray produces pinhole-free nanostructured films with good adherence, says Ravi Dhas, Bishop Heber College, Tiruchirappalli.
The team used copper sulphide as semiconductor with indium and aluminium as acceptors for photo-induction. They sprayed copper-indium-aluminium sulphide solution with constant pressure at different temperatures on a clean fluorine-doped tin oxide glass to prepare the photo-anodes.
Using energy dispersive X-ray analysis, they confirmed the purity of the deposited films. The scientists also examined the X-ray photoelectron spectrum which showed copper in the more reactive cuprous form. This facilitates better charge transfer, says Subhendu Panda from CSIR -CECRI, Karaikkudi.
The Raman spectrum and X-ray diffraction patterns showed that the films had dense grains of tetragonal crystalline structure till 300°C. However, at 300 °C, the films deposited had uniform nanoflake-like morphology under scanning electron and atomic force microscopes.
Visible absorbance spectroscopic studies for the film deposited at 300°C showed optimum band gap energy over a broad spectral range of visible light. Higher temperatures induced defects in crystallite size and lattice structure leading to decrease in the charge transfer efficiency, say the scientists.
The scientists used cyclic voltammetry and confirmed rapid charge transfer at the electrolyte interface. “This could be due to the high surface area of the nanoflake structures”, says Moses Ezhil Raj from Scott Christian College, Nagercoil.
The scientists studied the carrier mobility and density of this semiconductor film by evaluating Hall measurements. This confirmed the p-type semi-conductivity of the film: holes were predominant charge carriers.
When the team conducted electrochemical impedance spectroscopic analysis, they found low series resistance and low charge transfer resistance values, indicating highly efficient electron transfer.
“Tafel polarisation values indicated that the voltage efficiency of this film was as good as that of platinum counter electrodes”, says A. Jennifer Christy, Bishop Heber College. Temperature dependent conductivity measurements confirmed that the film deposited at 300 °C is non-degenerate, stable and robust even after 40 cycles.
“Replacing platinum with copper-indium-aluminum sulphide counter electrodes will help reduce the costs of solar cells,” says Esther Santhoshi Monica, Bishop Heber College.
“The nebuliser spray method is a scalable technique. So it is a good technique for fabricating dye sensitised solar cells at commercial scale,” says R. Venkatesh, Bishop Heber College.
The study was funded by the UGC and DST.
Physica B: Condens. Matter, 537: 23-32
28 April 2018
Alternative Fuel for Diesel Engines
Biodiesel and alcohols are alternative fuel energy sources for diesel engines. Biodiesel is renewable, biodegradable and eco-friendly. Many studies explore the production of biodiesel from vegetable oil and animal fat. However, pure biodiesel generates low power output and torque to the engine due to its lower calorific value. This can be overcome, to some extent, by blending with other fuel sources, such as higher alcohols.
Recently, Nanthagopal and team from the VIT University, Tamil Nadu collaborated with the Indian Institute of Technology, Hyderabad to explore the possibility by studying the effect of blending Calophyllum inophyllum biodiesel with higher alcohols.
They used n-pentanol and n-octanol alcohols with methyl ester of Calophyllum inophyllum oil in different ratios. The researchers experimented with the samples in a single cylinder, with a constant speed engine at different loads.
The team found that adding higher alcohols to the methyl ester of Calophyllum inophyllum optimises engine performance and combustion. They noted that brake thermal efficiency and brake specific fuel combustion value improved with blending. This reduces biofuel consumption.
They also found that there are less oxides of nitrogen in an n-octanol blend with biodiesel. This, scientists say, may be due to the high latent heat of vaporisation of higher alcohols which produces a cooling effect in the combustion chamber.
However, biodiesel blended with higher alcohol produces more hydrocarbons, and carbon monoxide, and emits more smoke. So, blending the biodiesel with a small percentage of higher alcohol may help keep these emissions in check.
The team suggests that biodiesel blended with higher alcohols would be a suitable substitute for diesel engines. The combination can be used as a power source in the automotive, agricultural and construction sectors, for short-term application. However, technologies to reduce the environmental impact need to be implemented before deploying such engines on Indian roads.
J. Cleaner Production, 180: 50-63 (2018)
Perovskites Doped with Iron
No longer fussy
Solar cells are picky eaters. They absorb sunlight only within a certain wavelength. The rest goes waste. Even though sunlight is abundant, solar cells only use a tiny fraction of it. This limits the performance of the photovoltaic cells. Scientists are trying different methods to increase the efficiency of the solar cells. Maybe they need to add a new masala.
Rajamanickam and colleagues from the Gandhigram Rural University, Gandhigram and the Madurai Kamaraj University, Madurai want to work with barium stannate perovskite, an abundant mineral with a near perfect crystal structure. Perovskites have a broad ‘bandgap’ – they can absorb sunlight in a wider wavelength range. The crystalline shape allows the perovskite to conduct charges over a long distance. Thus, they are the ‘rock stars’ of photovoltaics.
The research team wanted to move the digits of efficiency. So, they doped the perovskite with iron particles. This leads to a reduced recombination of the excited charges. Which, in turn, improves the efficiency of the solar cell.
Adding iron impurities to barium stannate perovskite alters its Fermi level, a thermodynamic quantity in solid-state physics that relates to the flow of charge in a circuit. Thus, the conduction band gap of solar cells can be tuned by regulating the Fermi level. Now, the excited charge can move faster.
Moreover, the Fermi level changes the surface morphology of the perovskites. It allows the growth of nanorods structures. Which gives a uniform surface and thickness to the solar cells.
The solar cells that you see on roof tops today are made up of sheets of crystalline silicon, that can only collect lower energy, red and infrared, photons. Perovskite can snag higher energy blue and green photons. Even though perovskites are promising, silicon solar cells can’t go obsolete. Thus, piggy back riding perovskites over silicon crystals may combine their picky habits. Perhaps they need to be in tandem with each other.
Solar Energy Materials & Solar Cells, 166: 69–77 (2017)
Manish Kumar Tekam
Maximizing Wind Energy
Biogeography based farm layout
The major constraint in using wind energy is the production cost. The puzzle is to figure out the optimum set of locations for wind turbines in a wind farm to maximize total energy output. This depends on the pattern of windmills relating to the position of the turbines, rotor radius and farm radius.
Recently, Bansal and Farswan from the South Asian University, New Delhi, found a method to optimise some of the most important factors. They adapted Biogeography Based Optimization, an algorithm used to understand the evolution of the distribution of biological species in an area to optimise the wind farm layout.
They adjusted the mathematical models to maximize energy production in a wind farm with a large number of turbines. The space behind a wind turbine is marked by decreased wind power capacity since a part of the energy is used up in turning the blades. The wind behind the turbine is less effective at generating energy for some distance in the downwind direction, due to loss of energy in the turbulence created by the windmill. The effects of the wake spread out downwind and decay with distance. The model aimed to the reduce this wake effect by finding out appropriate placing and spacing of the windmills..
Their model is able to determine the maximum number of wind turbines which can be placed in a wind farm without any wake loss. The researchers considered different circular wind farms with radii 500 m, 750 m and 1000 m to test their model. While the earlier methodologies can ﬁt a maximum of three turbines in a farm of radius 500 m, this new model can ﬁt seven turbines in the same farm without any wake loss. This model outperforms for other sizes of wind farms. With this model, now we can optimise energy extraction from the winds efficiently at lower costs.
We should expect that similar mathematical models from ecology and evolution will throw light on other technology domains in the coming years.
Renewable Energy, 107: 386-402 (2017)