Introduction:
The increase in the trend of renewable energy in recent times has provoked the engineers and scientists of various domains to research on these self-sustaining fuel resources. One of the most commonly known fuel resource among them is biodiesel, which was first developed by Rudolf Diesel in late 1800’s to power his diesel engine with aid of vegetable oil. Presently, 150 million gallons of biodiesel is being produced every month to meet the energy demand that has been increasing continuously because of population overgrowth. The demand for this ecofriendly biofuel is increasing because of its robustness and easy availability. Apart from these added advantages, it has proved to be a carbon neutral fuel1 with zero aromatic causing lower emissions rate with higher oxygen content. Biodiesel is the common name of any fatty acid alkyl ester produced by transesterifying fatty acids in triglyceride with alcohol in presence of either homogeneous or heterogeneous catalyst under the influence of temperature and continuous stirring. For better yield, various catalysts have been improvised depending upon the nature of the feedstock used. The evolution of catalyst for the transesterification reaction began with hydroxides of alkali metals followed by acids with recent development into heterogeneous catalysts. Most common catalysts used for transesterification reactions are NaOH, KOH, H2SO4, HCl and even nano particles like CaO-Al2O3 as heterogeneous catalysts. In recent times, enzyme and lipase based catalysts have been used as organic substitutes for nanoparticles based catalysts. Considering the economic grounds, the nano based heterogeneous catalysts have been widely accepted because of its simplicity and reusability. Nanoparticles have proved to be providing higher yield without being disposed-off during biodiesel washing. It has also gained popularity among the researchers to produces biodiesel using transesterification effectively. These catalysts not only involve effectively in reaction, but also reduce the overall production cost of the reaction as well as the product. γ-alumina-zirconia was proven to be effective heterogeneous catalyst for transesterifying various animal fats and vegetable oils2. Certain alkali earth metals in form of metal oxides exhibited better effectiveness for unsaturated fat transesterification3. Calcium oxide (CaO) produces environmental pollution when extracted from lime stones, which can be reduced by synthesizing it from calcium rich bones of animals4.Marine based mollusk shell, has also demonstrated as better source for the naturally occurring CaO from life forms5. Recent researches have been carried out for synthesizing nanoparticles from organic bacteria, actinomycetes, fungus6,7,8 and even from the extract of plants such as Nelumbo lucifera, Ocimum sanctum, Coriandrum, Camellia sinensis and other compatible extracts9,10,11. The biological syntheses of nanoparticles from these organic compounds are completely based upon the Redox reaction, in which the floral phytochemicals or microbial enzyme possessing antioxidant or reductant properties holds key role in the synthesis of metal and metal oxide. Any nanoparticle possessing intelligently identified solvency medium, suitable reducing agent and exhibits non toxicity through its process can be identified as a suitable nanoparticle in the grounds of green chemistry12, 13. This paper concentrates on the work related to production of biodiesel from mutton suet using Calcium Oxide infused titanium dioxide from animal bone and Nyctanthes Arbor-Tristis leaves extract’s.
Materials and methodology:
Collection of mutton waste fat and bones:
The waste mutton fats and mutton bones were collected from nearby meat processing units and slaughter houses. These wastes were preserved in refrigerator to avoid contamination and foul smelling odor.
Extraction of Suet:
The suet were extracted from the wastes by the means of wet rendering, where these wastes were heated at 120oC along with water, which forces the fats to diffuse from the proteins and non-fatty contents and get accumulated at the top . The density variance between fat and water makes it to stay afloat on the top, which on gradual cooling can be removed as condensed saturated mutton suet.
Refining of Suet:
The non-fatty residues carried along with the suet must be removed before being processed into biodiesel. The suet was heated slightly above its melting point and solid residues were removed by filtration. Filtered suet was degummed to remove excess phospholipids present in it by adding orthophosporic acid. For an effective degumming, 1% of orthophosporic acid was added to molten suet under the influence of heat at 60oC for 15-20 mins, which forces the phospholipids to get settled down at the bottom as lecithin.
Glycerolysis reaction:
The refined suet was pretreated by low temperature glycerolysis reaction which reduced the overall free fatty acid (FFA) content in it. The reaction was carried out for varying volumetric ratio between suet and glycerol for a range of 1 to 3 g/g, for various reaction temperatures between 70-150oC and reaction time lying between 30 to 120 minutes. The conversion efficiency was calculated based upon the change in FFA% with respect to initial FFA% using the equation 1
Free fatty acid % was calculated by titrating mixture of 1ml of suet with 10 ml of iso propyl alcohol against 0.1N of NaOH. The end point of the reaction was pale pink colour and was considered as the acid value of the suet. The FFA% was calculated using equation 2
Preparation of catalyst:
Preparation of Nyctanthes Arbor-Tristis Leaves extract14,15:
100ml of methanol was refluxed with 1 gram of dried Nyctanthes Arbor-Tristis leaves powder for 6 hours at 60oC. The methanolic reflux mixture was filtered using Whatmann filter paper to remove any residues that may affect the purity of nanoparticles and was subjected for reduction-oxidation reaction.
Titration with titanium tetraisopropoxide:
0.6M of titanium tetraisopropoxide was reacted with methanolic leaf extract under the influence of continuous stirring for 4 hours at 60oC, which resulted in the formation of nanoparticles of titanium di oxide. The mixture was centrifuged at 15000rpm for 10 minutes initially and re-centrifuged for 5 minutes for maximum efficiency.
Preparation of titanium dioxide:
The centrifuged residue was ethanol washed and centrifuged for last time at 6000rpm for 10 minutes with an intermittent break after 5 minutes for better settling. The settled titanium dioxide was dried in moisture free condition and was calcinated in muffle furnace at 600oC for 3-4 hours after grinding it.
Thermal decomposition of mutton bone:
100g of dried mutton bones were thermally decomposed in an electric furnace for 4 hours by varying the temperature between 400 – 1100oC. The bones that were combusted into animal ash were cooled to room temperature before being preserved in silica gel sealed desiccators.
Preparation of heterogeneous catalyst:
The titanium dioxide from the Nyctanthes Arbor-Tristis leaves extract and Calcium oxide based animal ash from mutton bones were mixed in 1:1 (mass ratio) and was heated in muffle furnace for 300oC for 4 hours for the purpose of catalyst activation. The prepared catalyst was studied using infrared (IR) spectroscopy, scanning electron microscope (SEM) and X Ray Diffraction (XRD) analysis.
Transesterification reaction:
The pretreated fat was transesterified using methanol and the prepared catalyst. The reaction was carried out by varying the molar ratio between suet and methanol in a ratio of 1:1 to 1:6, for various reaction temperatures between 50-75oC and time duration ranging from 30 to 120 minutes. The biodiesel yield was calculated based upon the amount of biodiesel produced to amount of suet taken using the equation 3
………………………… (Equation 3)
Refining of biodiesel:
The reaction mixture was separated using separating funnel, where the residual glycerol along with unreacted reactants settled down at the bottom whereas the biodiesel was found at the top. Post settling, the separated biodiesel was washed, refined and was given for FTIR and GC analysis. The FTIR is used to determine the functional group and GC was used to determine the fatty acids that were dominant in the transesterification reaction. Sample preparation for these analyses was carried out as per the standards.
Results and discussions:
The discarded wastes were mainly made up of adipose and subcutaneous fats and maximum amount of suet recovered from these was 85% by wet rendering technique. Free fatty acid content in extracted suet was found to be 11.4 % using chemical titration method.
The low temperature glycerolysis reaction was carried out with optimized parameters for better FFA% reduction. The Suet to glycerol ratio was maintained at 2:1 (glycerol to suet volumetric ratio) for a temperature of 110oC and reaction time of 1 hour. The reaction temperature of 110oC was fairly enough for the vaporization of water content formed as byproduct during reaction. The treatment of suet with glycerol reduced the overall FFA % content from 11.4 to 0.25%, which can be carried out for transesterification reaction. Figure 1 represents about the contour plot of the optimized glycerolysis reaction carried on Mutton Suet.
Figure 1:- Contour Plot of the optimized glycerolysis reaction carried on Mutton Suet
The transesterification reaction was carried out for a molar ratio of 1:3 between suet and methanol for a catalyst concentration of 2 wt% of suet at of 60oC for a reaction time of 120mins. The yield of biodiesel decreased with increase in molar ratio because of reduction in availability of methanol content. Increase in catalyst concentration greater than 2% gradually decreased the yield of biodiesel because of agglomeration of catalysts thereby causing reduction in catalyst activity. The optimum temperature ensured that both suet and methanol was in liquid phase throughout the reaction. Figure 2 represents the contour plot of the optimized transesterification reaction on Mutton Suet.
Figure 2:- Contour Plot of the optimized transesterification reaction on Mutton Suet
The green synthesis of titanium dioxide nanoparticles from the extract of Nyctanthes Arbor-Tristis leaves extract was achieved by following the redox reaction using titanium tetraisoproxide. Similarly, the calcium carbonates present in the bones of mutton has been reduced into calcium oxide by thermally decomposing it at 1120oC, resulting as bone ash. The heat treatment of Calcium Oxide and titanium dioxide at 300oC activated their microstructures which further improvises the catalytic activities during transesterification reaction.
The confirmation of Calcium oxide infused titanium dioxide nanoparticles were done using the Fourier Transform Infrared spectrum which revealed the bending & stretching of TiO2 and CaO molecules. Titanium dioxide exhibited its bending at a wavelength of 990cm-1, where CaO exhibited its stretching for a wavelength of 1020cm-1.16,17. Figure 3 represents the FTIR spectrum of the Calcium oxide infused titanium dioxide nanoparticles. The vibrational activities which virtualize the catalytic activity of the nanoparticles were studied by analyzing the nanoparticles in Raman spectroscopy, whose activity spectrum revealed the vibrational intensity was found to be more in titanium dioxide than in the calcium oxide because of its twin double bond. The spectrum identified the dominant characteristic of titanium dioxide as catalyst whereas the Calcium Oxide exposed its recessive characteristics in reaction but deployed a major role in activation of Titanium dioxide. Figure 4 explains the Raman activity spectrum of the Calcium oxide infused titanium dioxide nanoparticles. Also, figure 5 (a) & (b) explains the U- depolarization and P- depolarization spectrum of the Calcium oxide infused titanium dioxide nanoparticles.
Figure 3:- FTIR spectrum of the Calcium oxide infused titanium dioxide nanoparticles
Figure 4 explains the Raman activity spectrum of the Calcium oxide infused titanium dioxide nanoparticles
Figure 5(a):- U- depolarization spectrum of the Calcium oxide infused titanium dioxide nanoparticles.
Figure 5(b):- P- depolarization spectrum of the Calcium oxide infused titanium dioxide nanoparticles.
The microscopic images of the CaO and TiO2 nanoparticles were obtained by examining them under the scanning electron microscope (SEM) which displays their porosity behavior. The images of the nanoparticles were recorded at a magnification level of 100-150nm which clearly displayed the surfaces the titanium dioxide and calcium oxide. Figure 6(a)&(b) show the SEM images of the titanium dioxide and calcium oxide respectively. Figure 6(c) shows the SEM image of the heterogeneous catalyst.
Figure 6(a) & (b):- SEM images of the titanium dioxide and calcium oxide
Figure 6(c):- SEM images of the heterogeneous catalyst
The XRD spectrum explains clearly about the initiation of the stable thermal decomposition of CaCO3 into CaO. It can be observed that the spectrum produces a sharp peak beyond 800oC below which the chance of peak formation responsible for CaO was very slim. The peak intensity was at its threshold limit for temperature 1100oC18 and above, making it the optimum temperature for thermal decomposition of animal bones. This high temperature makes the CaO anhydrous and less reactive to moisture content18. Figure 8 depicts the XRD spectrum of CaO formation19.
Figure 8:- XRD spectrum of CaO at various temperatures
Maximum recorded biodiesel yield was found to be 93%, which was 3% superior to the conversion yield recorded for other heterogeneous catalysts20 when employed for same mutton suet and 1% superior in case of homogeneous catalyst. The refined biodiesel sample was analyzed using Fourier Transform Infrared spectroscopy and Gas chromatography for confirmation of ester group and also identification of various esters in the sample. The peak in FTIR spectrum for the wavelength of 1744.3 cm-1 with an intensity of 70.7406%, confirmed the presence of ester group representing FAME in the sample. The GC spectrum revealed that Palmitic acid, stearic acid, Lauric acid and oleic acid were the most dominant fatty acids present in the mutton suet sample, which has been converted into their respective methyl esters. Figure 9 depicts the FTIR and GC spectra of the mutton suet biodiesel.
Figure 9:- FTIR (a) and GC (b) spectrum of the mutton suet biodiesel
Conclusions:
The biodiesel from the mutton suet has been successfully produced by using calcium oxide infused titanium dioxide synthesized from animal bone and Nyctanthes Arbor-Tristis leaves extract, which has proved to be a very effective heterogeneous organic nano catalyst in production process of biodiesel at the stage of transesterification reaction, which produced a biodiesel yield of 93% efficiency. This work also paved a path for the utilizing organic wastes possessing serious environmental threats, into useful resources in terms of “waste to Energy” concept. In addition, the green synthesis of nanoparticles from the leaves extracts, which are employed in the production of a self-sustaining fuel, makes the conception of self-sustaining energy a true concept which has been creating a wider scope of research for many engineers.
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