CHAPTER 3 EXPERIMENTAL METHODS AND ANALYSIS

Transcription

1 37 CHAPTER 3 EXPERIMENTAL METHODS AND ANALYSIS 3.1 MATERIALS H-Mordenite (MOR) (Si /Al ratio= 19), - zeolite ( ) (Al /Si ratio= 25), silica gels with two different mesh sizes, (S 1 ) and (S 2 ) were obtained from Sud-Chemie India Ltd, Mumbai, India. Commercial non-edible grade neem oil (average molecular weight = 815) and pinnai oil (853) were obtained from local market. Phosphoric acid and 3-aminopropyltriethoxysilane, used for modifications were purchased from Ranchem Fine chemicals ltd., New Delhi, India. Phenolphthalein, potassium hydroxide (KOH) and ethanol used for the determination of acid value were purchased from Qualigens Fine Chemicals Ltd, India. Oleic acid, ethyl oleate and methanol, used for esterification and transesterification studies were purchased from SRL, Mumbai, India. All the chemicals used in the experimental studies were analytical grade and used as purchased. 3.2 PREPARATION OF PHOSPHORIC ACID MODIFIED ZEOLITES Preliminary trails were carried out to find the suitable concentration of phosphoric acid (wt%) for the modification of zeolites. About 2.25 g of MOR in 25 ml of double distilled water was mixed with 0.75 g of phosphoric acid. The mixture was kept under vigorous stirring at room temperature for 12 h then evaporated and dried in an air oven at 120 C. The obtained white

2 38 colored powder was abbreviated as PMOR. Similar treatment was given to -zeolite and the product was abbreviated as P. 3.3 PREPARATION OF SILANE MODIFIED SILICA The solid base catalyst used for transesterification was prepared by modifying the surface of silica gel with the help of a modifying agent 3-aminopropyltriethoxysilane. A solution containing 3 parts of the modifier was prepared in acetone solvent and is used to modify 100 parts by mass of SiO 2 gel (S 1 ). The volume of the modifier solution was adjusted so that a uniform wetting of the silica surface. The modification was performed in a magnetic stirrer. The modifier solution was added drop wise to the silica containing round bottom and stirred for 1 h at room temperature. The resultant silica solution was dried at 100 C. The product obtained is silane modified silica (SMS 1 ). Similar producer was followed for silica gel (S 2 ) and the product was abbreviated as (SMS 2 ). 3.4 CHARACTERIZATION For better understanding of the properties of modified and unmodified catalysts composition and important characteristics of non-edible oils and the obtained biodiesel, various analytical techniques were used Characterization of MOR,, PMOR and P X-ray diffraction analysis In powder diffraction characterization of materials, the diffraction pattern is the fingerprint of any crystalline phase and to identify the mixture of phases. The sample was packed on the surface of the sample holder. XRD patterns of the zeolites were recorded on an X-ray diffractometer (Rigaku D/Max Ultima III) operating less than 40 KV and 40 ma with the scan rate of

3 39 2 / min. Cu k X-ray was nickel filtered ( = A ). The amorphous nature of silica was examined using XRD. The samples were recorded in the range of 2 between Scanning Electron Microscope analysis SEM measurements were carried out using JEOL, JSM The images are taken with an emission current = 100µA by the Tungsten filament and an accelerator voltage =12 Kv. The samples were secured onto brass stub with carbon conductive tape, sputter coated with gold and viewed in JEOL, JSM-6360 microscope. The pre-treatment of the samples consisted of coating with an evaporated Au film in a polaron SC 500 sputter Coater metallizator to increase electric conductivity Fourier Transform Infra Red analysis Fourier Transform Infrared spectra of the zeolites and silica gels were recorded on a Nicolet (AVATAR 360) instrument using KBr pellet technique. About 10 g of the sample was ground with 200 mg of spectral grade KBr to form a mixture, which was then made as a pellet. This pellet was used to record infrared spectra in the range of cm NH 3 - Temperature Programmed Desorption studies The acidity of zeolites was analyzed by NH 3 Temperature Programmed Desorption method. Adsorption of ammonia was carried out on each sample in a quartz tube packed with 100 mg of the sample. The initial flushing was carried out with pure Helium (at 25cc/ min flow) for 1 h and cooled to 115 C. Ammonia adsorption was performed by passing the ammonia vapors over the catalyst bed. Later, helium was passed to remove the physisorbed ammonia.

4 Thermogravimetric analysis Thermogravimetric Analysis is a technique for characterizing thermal stability of a material by measuring changes in its physicochemical properties expressed as weight change as a function of increasing temperature. Thermograms were recorded using a Thermo gravimetric analyzer (TGA Q 50 V 20.6 Build 31 instrument) Characterization of Non-edible oils The non-edible oils chosen for biodiesel production were neem (Azadirachta indica) and pinnai (Calophyllum inophyllum) and their properties were analyzed using the following techniques Gas Chromatographic analysis (GC) The fatty acid profile of the two non-edible oils was determined by gas chromatography. The fatty acid compositions of three non-edible vegetable oils have been analyzed by a CN Gas Chromatography with a flame-ionization detector. The used capillary has a length of 30 m with an internal diameter of 0.25 mm. Carrier gas is nitrogen at a flow rate of 1 ml/min. The injection port temperature is 150 C and ionization detector temperature is 170 C Physico chemical properties of oils. The physico-chemical properties of these two non- edibile oils were determined by ASTM methods. Iodine values were determined using Wiji s method based on ASTM D Acid values were determined using ASTM D974. Saponification value was calculated based on ASTM D5558. Specific gravity was measured using ASTM D5355.

5 Nuclear Magnetic resonance spectroscopy The spectra were recorded on a Bruker AVIII spectrometer operating at 500 MHz at room temperature. 1 H spectra were recorded with pulse duration of 45, a recycle delay of 2 s and 16 scans. The spectra were referenced to dimethyl sulfoxide (DMSO). 3.5 ANALYSIS AND FUEL PROPERTIES OF BIODIESEL Physical and chemical properties of fatty acid methyl esters were analyzed by ASTM standard procedures. The flash point and fire point were determined by a Pensky Martens closed-cup tester (ISL, Model FP93 5G2), using ASTM D 93. Cloud point and pour point determinations were made using ASTM D 2500 and ASTM D 97. The kinematic viscosities were determined at C, using a Viscometer (Anton Parr, Stabinger, Model SVM3000). The procedure of ASTM D 7042 was followed. The water contents were determined following ASTM D ATOMIC ABSORPTION SPECTROSCOPY (AAS) The esterified product was checked for the presence of P, Al and Si using AAS (Shimadzu AA-6300) to confirm there is no catalyst leaching into the product. The transesterified product was also checked for the presence of Si and N. 3.7 TWO-STEP BIODIESEL PRODUCTION Both the steps of biodiesel production were carried out in a three necked round bottom flask equipped with a reflux condenser to avoid alcohol evaporation. Stirring was performed with the help of a mechanical stirrer. The rate of stirring was maintained at 200 rpm. The temperature of the flask was maintained at different levels using silicon oil bath, which was in connection

6 42 with the dimmer stat. Thermometer inserted in the three necked flask was used to monitor the temperature maintained inside Acid catalyzed pre-treatment Non-edible oil was poured into the flask and solid acid catalyst was added followed by methanol. The progress of the reaction was monitored by measuring the acidity value. Acid value is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance. The acid number is a measure of the amount of carboxylic acid groups in a chemical compound such as a fatty acid. In a typical procedure, a known amount of sample dissolved in ethanol is titrated with a standard solution of KOH and phenolphthalein as a colour indicator. The acid value, A was calculated using the equation, 1000VMC A (3.1) W Where W - Weight of the sample, g. V - C - M - Volume of KOH consumed, ml Concentration of the solution, mol/l Molecular weight of the solution, g/gmol Acid value of oils was determined before commencing the reaction and the samples were withdrawn from the reaction mixture at regular intervals and the acid value was determined. From the results conversion efficiency was calculated. Conversion efficiency is the percentage of FFA converted into their corresponding methyl esters during the esterification reaction of nonedible oils. It is calculated from the residual acid value during or after the esterification reaction under a set of reaction conditions. The acid value of the

7 43 non-edible oil before the start of the reaction and at any instant of time is found by titrimetric method. X FFA ai a t a i 100 where X FFA - percentage conversion (3.2) a i - initial FFA content of oil a t - FFA content at time, t The final reaction mixture was centrifuged at 8000 rpm and the supernatant methanol was removed. From the remaining residue, solid acid catalyst was separated and the pre-treated oil was processed by base catalyzed reaction Esterification of neem and pinnai oil with MOR and PMOR The objective of esterification is to reduce the FFA content in the neem and pinnai oil. FFA present in neem and pinnai oil was esterified with methanol in presence of both MOR and PMOR and the results were studied. The reaction regulatory parameters which can affect the efficiency of FFA reduction were studied. To obtain high FFA reduction, it is important to understand the relationship between these parameters and to optimize the suitable conditions accordingly. The reduction of FFA is influenced by factors such as reaction temperature, catalyst amount and methanol to oil ratio. Temperature clearly influenced the reaction rate and yield (Ma et al 1999). The methanol to oil molar ratio was studied because it is one of the most important factors affecting the ester yield. Catalyst concentration decides the esterification reaction and plays a major role in reduction of FFA.

8 44 In this work, the esterification of neem and pinnai oil in presence of MOR and PMOR were studied. The reactions were carried out in a round bottom flask, neem and pinnai oil was taken separately and to which calculated amount of methanol was added followed by the addition of MOR as catalyst and the reaction was carried out for a period of 70 min. The experimental factors for the present study are catalyst concentration (0.5-2 wt%), methanol to oil molar ratio (3:1 12:1) and temperature in the range of C. The same experiments were carried out with neem and pinnai oil in the presence of catalyst PMOR. Kinetic studies for the esterification of neem and pinnai oil with MOR and PMOR were done. During the esterification reaction of FFA in neem and pinnai oil with varying methanol to oil ratios and with different catalyst loading at 60 C, the samples were withdrawn at an interval of 10 min and analyzed for their acid values. To scrutinize the effect of phosphoric acid modification on MOR, esterification reactions were carried out with neem and pinnai oil in presence of both MOR and PMOR under a set of optimized conditions. Influence of catalyst activity on the conversion of FFA was evaluated and a comparison was made. For better comparison esterification of oleic acid was also carried out with both MOR and PMOR under optimum conditions Esterification of neem and pinnai oil with and P The esterification of neem oil and pinnai oil in presence of both and P were studied. The reactions were carried out in a round bottom flask, neem and pinnai oil was taken separately and to which calculated amount of methanol was added followed by the addition of as catalyst and the reaction was carried out for a period of 70 min. The experimental factors for the present study are catalyst concentration (0.5-2 wt%), methanol to oil molar ratio (3:1 12:1) and temperature; C. The same experiments were carried out with both the oils in the presence of catalyst P. Kinetic studies

9 45 were conducted for the esterification of neem and pinnai oil in the presence of both and P catalysts. During the esterification reaction catalyzed by and with varying methanol to oil ratios and different catalyst loading at 60 C, the samples were taken at an interval of 10 min and analyzed for their acid values. Esterification of FFA present in neem and pinnai oil was carried under optimum conditions in presence of and P catalysts separately to study the effect of phosphoric acid modification of zeolites and a comparison was also made. For better comparison esterification of oleic acid was also carried out with both and P under optimum conditions Base catalyzed transesterification After esterification of free fatty acids present in neem and pinnai oil, the acid value was reduced below 2 mgkoh/g of oil. These pre-treated oils were subjected to base catalyst transesterification. SMS 1 and SMS 2 were used as solid base catalyst for transesterification. In a typical reaction the pre-treated oil was added in a thin stream on to the mixture of solid base catalyst and methanol. The contents were refluxed under mechanical stirring. Several reaction parameters were studied to find out the optimum reaction conditions. After completion, the reaction was stopped and the contents were poured into a separating funnel. The lower layer, containing glycerol and other impurities were drained off. The upper layer biodiesel was washed with hot distilled water thrice, lower layer was discarded and the upper layer after the third wash is the final FAME product. The final reaction mixture was centrifuged at 8000 rpm for 10 min and the supernatant, excess methanol was removed. The progress of the reaction was monitored by 1 H NMR. The protons of the methylene group adjacent to the ester moiety in triglycerides and the protons in the alcohol moiety of the product methyl esters were used to monitor the yield. The conversion can be calculated using the following formula,

10 46 C 100 (2A / 3A ) (3.3) ME CH 2 where C is the conversion of triglycerides to corresponding methyl ester, A ME is the integration value of the protons of the methyl ester and A -CH2 is the integration value of methylene protons. The factors 2 and 3 derived from the fact that the methylene carbon possesses two protons and the alcohol (methanol-derived) carbon has three attached protons Transesterification of pre-treated neem and pinnai oil with S 1 and SMS 1 The objective of transesterification is to convert the triglycerides into fatty acids methyl esters in the neem and pinnai oil. Pre-treated neem and pinnai oil were transesterified with methanol in presence of both S 1 and SMS 1 and the results were studied. To attain the high triglyceride conversion, it is important to understand the relationship between these parameters and to optimize the suitable conditions accordingly. The conversion of triglycerides is influenced by factors such as reaction temperature, catalyst amount and methanol to ratio. In the present work, the transesterification of pre-treated neem and pinnai oil in presence of both S 1 and SMS 1 were studied. Pre-treated neem and pinnai oil were taken in a round bottom flask and to which calculated amount of methanol was added followed by the addition of S 1 as solid base catalyst and the reactions were carried out for a period of 135 min. The experimental factors for the present study are catalyst concentration (1-5 wt%), methanol to oil molar ratio (3:1 12:1) and temperature in the range of C. The same experiments were carried out with both the oils in the presence of catalyst SMS 1. Kinetic studies for the transesterification of neem and pinnai oil with S 1 and SMS 1 were done. During the transesterification process, pre-treated neem and pinnai oil with varying methanol to oil ratios and with different

11 47 catalyst loading at 60 C, the samples were withdrawn at an interval of 15 min and analyzed for methyl ester content. To evaluate the effect of silane modification on silica gel, transesterification reactions were carried out both S 1 and SMS 1 under a set of optimized conditions by taking Pre-treated neem and pinnai oil and a comparison was made. For better comparison transesterification of ethyl oleate was also carried out with both S 1 and SMS 1 at optimum conditions Transesterification of pre-treated neem and pinnai oil with S 2 and SMS 2 The transesterification of neem oil and pinnai oil in presence of both S 2 and SMS 2 were studied. The transesterification reactions of neem and pinnai were carried out in a round bottom flask. Neem and pinnai oil were taken separately to which calculated amount of methanol was added. S 2 was added as catalyst to the reaction mixture and the reaction was carried out for a period of 135 min. The experimental factors for the present study are catalyst concentration (1-5 wt%), methanol to oil molar ratio (3:1 12:1) and temperature; C. The same experiments were carried out with both the oils in the presence of catalyst SMS 2. Kinetic studies were performed for all the runs with different methanol to oil ratios and different catalyst loading for pre-treated neem and pinnai oil in the presence of both S 2 and SMS 2 catalysts. Production of methyl ester was monitored by subjecting samples to NMR analysis. The influence of modified silica gel over transesterification of pre-treated neem and pinnai oil were also studied by carrying out the reaction with SMS 2 and a comparison was made with that of reaction of S 2. A comparison of the activity of the catalysts under optimum conditions was done by carrying out the esterification reaction of ethyl oleate with S 2 and SMS 2.

12 Catalyst recovery and reuse The catalysts separated from the reaction mixture by centrifugation were initially washed with hexane in order to remove the polar compounds like methyl esters followed by washing with methanol to remove the polar compounds such as glycerol. The obtained catalysts were finally dried at 100 C overnight. The recovered solid acid and base catalysts were reused for esterification and transesterification studies repeatedly.