Biodiesel. As fossil fuels become increasingly expensive to extract and produce, bio-diesel is

Transcription

1 Aaron Paternoster CHEM D Prof. Laurie Grove January 30, 2015 Biodiesel Introduction As fossil fuels become increasingly expensive to extract and produce, bio-diesel is proving to be an economically and environmentally friendly alternative to traditional fuels. Because it is synthesized from waste vegetable oil, biodiesel is much cheaper to produce and leaves less of a carbon footprint during the refining process. Simple unrefined waste oil is full of impurities and is too viscous to be used directly in diesel engines and must therefore be cleaned and broken down into pure methyl ester. The fundamental process of refining biodiesel involves reacting used vegetable oil with methanol (MeOH) via a catalyst, potassium hydroxide (KOH) in the case of this experiment. MeOH breaks down the vegetable oil to form biodiesel and glycerol. Additionally, the catalyst also reacts with the free fatty acids contained in the oil that are a byproduct of the cooking process, therefore it is important for the reaction to contain an excess of KOH. The purpose of this lab was to discover through experimentation the most efficient way to refine waste vegetable oil into clean burning biodiesel. Several experiments were performed over four days to determine the ideal conditions for refining biodiesel. Day 1 involved multiple experiments altering specific variables during the refining process to determine which conditions resulted in the highest and most pure yields. Day 2 involved titrating a sample of the waste oil to determine the amount of free fatty acids present in the larger source. Day 3 was spent upscaling

2 the synthesis process to yield large amounts of biodiesel. On Day 4 the final product was tested to determine its purity and further refined to remove glycerol byproducts. Procedure Day 1 - Exploration Before beginning the experiment, several variables involved in synthesizing biodiesel were identified, such as the amounts of methanol, catalyst, and oil used, the reaction time allowed, and the reaction temperature. Different experiments were performed altering each variable. The following procedure was performed on both clean, unused vegetable oil and used dirty vegetable oil with the purpose of determining if using twice the recommended amount of methanol affected the synthesis of biodiesel. After massing a gram pellet of KOH and dissolving it in 1 ml of MeOH in a 50 ml test tube, the volume of oil required for synthesis was calculated as follows: volume of oil = grams KOH 1 Liter oil 4.9 grams KOH g KOH 1 L Oil = 13.3 ml oil 4.9 g KOH The remaining MeOH required could be calculated as follows: additional MeOH = (volume of oil 0.44) 1mL MeOH (13.3 ml oil 0.44) 1 ml MeOH = 4.85 ml additional MeOH Note that the control conditions called for the total MeOH required to be calculated at 22% of the volume of oil, rather than the 44% used in this experiment. For the dirty oil, g

3 of KOH were dissolved in 1.1 ml of MeOH ml of oil was required, as was an additional 4.06 ml MeOH. After the remaining methanol was added to the KOH, the solution was mixed with the clean and dirty oil, which had been heated to a temperature of 60 C. The mixtures were shaken vigorously for 15 minutes then allowed to separate. Once the mixtures settled, two tests were performed on both the clean and dirty processed oil to measure the success of the biodiesel conversion (see Data and Results for test results). The first test was a 3/27 test, which refers to the ratio of oil to MeOH used for the test. 1 ml of the processed oil was measured into a test tube and combined with 9 ml of MeOH. The solution was shaken and then allowed to settle again. Any oil separation indicated unreacted vegetable oil. The second test was an emulsion test. Equal amounts of processed oil and water were added to a test tube and the solution was shaken. Any foamy material that formed indicated the presence of soap. Day 2 Titration To determine the amount of free fatty acids (FFA) present in the used vegetable oil, a series of four titrations were performed by measuring the volume of KOH solution required to react with all of the FFA in a solution of 1 ml oil and 10 ml isopropyl (see Table 1 in Data and Analysis ). The titrating solution was a mixture of g KOH and 100 ml H2O. The KOH solution was added by burette to the oil and isopropyl mixture until the phenolphthalein indicator turned pink indicating that he FFA had been neutralized. The total volume of KOH used in each titration was recorded as the change in volume in the burette (see Table 1 for titration results).

4 Day 3 Synthesis g of KOH (see Data and Results for how the required mass was calculated) were massed and dissolved in 22 ml MeOH which was then added to 100 ml used vegetable oil. The mixture was heated to 60 C and stirred for 50 minutes. The processed oil was then set aside to settle for 1 week. Day 4 Purification and Testing Before the biodiesel was purified, a 10 ml sample was taken from the top layer of the processed oil and a 3/27 test, an emulsion test, and a cloud point test were performed on the crude biodiesel (see Data and Results for test results). After testing, the remaining processed oil was poured into a separation funnel. Once the glycerol settled to the bottom of the funnel, it was drained into a 50 ml flask and set aside. The crude biodiesel was then washed by adding an equal volume of water to the separation funnel. The funnel was then agitated slightly so as to gently mix the water with the crude oil. During this process, approximately 80% of the remaining glycerol and impurities were removed from the crude oil. After the oil was washed, the water was allowed to separate out again and was then drained off the bottom into a waste container. This process was repeated 4 more times with increasing vigor, with 50 ml of 1% acetic acid added after the 4 th and 5 th washes to speed up separation. Once purified, the biodiesel was then poured into a container and placed on a hot plate set to 120 C. This allowed any water left in the biodiesel to evaporate, leaving pure biodiesel. A 3/27 test and an emulsion test were then performed on the purified biodiesel (time did not allow for a cloud point test). Data and Results Day 1 - Exploration

5 For 13.3 ml of clean vegetable oil, 5.85 ml of MeOH, and g of KOH, no biodiesel was synthesized (see Discussion for a hypothesis as to why this happened). During the 3/27 test the methanol immediately separated on top of the vegetable oil confirming the lack of synthesis. An emulsion test resulted in significate formation of soap ml of dirty oil, 5.16 ml of MeOH, and g of KOH also resulted in no synthesis of biodiesel with similar results for the 3/27 and emulsion tests. Day 2 - Titration After analyzing the titration data from Day 2, it was determined that the amount of excess KOH required to react with the FFA in 1 L of used vegetable oil could be calculated as follows: 8.45 ml titration solution 1 ml oil g KOH 1000 ml g KOH = 100 ml MeOH 1 L oil 1 L oil Table 1 Titration results Titration Total ml KOH solution g KOH used per 1 L oil Average Day 3 Synthesis The total amount of KOH required for synthesis of 100 ml of oil was calculated as: g excess KOH g KOH 1 L oil = g KOH 100 ml oil

6 The resulting solution separated into a thin brown layer of glycerol approximately 20% by volume on the bottom and a light yellow layer of biodiesel approximately 80% by volume on top. Day 4 Purification and Testing The 3/27 test on the crude oil resulted in no separation, confirming complete synthesis of biodiesel. The emulsion test resulted in no soap formation, indicating that the FFA had been neutralized. The biodiesel began to get cloudy at approximately -3.6 C, however it was difficult to determine if the fuel was indeed freezing or if condensation was simply forming on the test tube. Once processed, the refined biodiesel returned similar results for the emulsion test. Unlike with the crude oil, the 3/27 test resulted in less than 0.2 ml of separation in the refined oil (see Discussion for implications). Unfortunately time did not allow for a cloud point test of the refined biodiesel. Discussion The fact that similar simultaneous experiments performed using twice the recommended amount of MeOH were successful in synthesizing biodiesel during the Exploration process indicated that there was potentially a flaw in the methodology of this particular group s experiment. The likely culprit was a failure to maintain the oil at a constant temperature of 60 C. Once the oil was removed from the sample jugs, due to the small sample sizes (10 ml) the heat loss was rapid. Because heat acts as a catalyst for the formation of biodiesel, if the solution was allowed to cool, 15 minutes of shaking was not nearly long enough to facilitate a reaction. This explains the 3/27 tests resulting in the MeOH separating completely from the vegetable oil.

7 The emulsion test on the clean oil resulting in soap formation could have been due to the clean oil being exposed to the moisture in the air while it was preheating resulting in the formation of FFA. Much more care was taken to maintain the oil at a constant temperature during the experiment on Day 3 which resulted in successful synthesis. Because the stoichiometric ratio of free fatty acids to KOH in this process is 1:1, the amount of FFA present in the waste vegetable oil was calculated using the titration results from Day 2: g KOH 1 L oil 1 mole KOH g KOH 1 L 1000 ml = moles FFA 1 ml oil The moles of oil in a 1 ml sample were calculated as follows: 0.88 g oil 1 ml 1 mol 800 g oil = mol oil This indicated a 13.4% ratio of FFA to oil in the used vegetable oil. This exceeded the generally accepted amount of 8% for waste oil to be considered usable. Because of the high percentage of FFA present, there was the potential for significant amounts of soap to form during synthesis. Due to the excess amounts of KOH used in the experiment, this had the potential to spoil the biodiesel turning it into a soapy mess. While the fact that the 3/27 result on the refined biodiesel indicated the presence of unprocessed vegetable oil seemed to conflict with the negative results from the crude oil, this was most likely due to the fact that the sample of crude oil was taken from the top of the processed biodiesel. Because the processed oil sat for a week, any small amount of unprocessed vegetable oil was allowed to settle towards the bottom due to its greater density, thus it was not

8 present in the initial tested sample. The refined oil, however, had been vigorously mixed during the washing process allowing any unprocessed oil to be suspended within the fuel. The fact that the biodiesel began to solidify at -3.6 C during the cloud point test indicated that it would not be a viable in the cold New England climate where winter temperatures can often dip below -6 C. While the biodiesel would work fine in the spring and summer months, some sort of anti-freezing agent would have to be added during the late fall and winter. Because the synthesis reaction in this experiment was an equilibrium reaction, an excess of methanol was used to favor the formation of the product, biodiesel. The stoichiometric formula for synthesis is as follows: 1 vegetable oil + 3 MeOH 3 biodiesel + 1 glycerol closer to 1:5: This implies a molar ratio of oil to MeOH of 1:3. This experiment however used a ratio 100 ml oil = 0.11 mol oil 0.79 g MeOH 1 ml 1 mol MeOH g 100 ml oil = 0.54 mol MeOH 22 ml MeOH Conclusion This experiment reinforced several fundamental concepts of chemistry. The failure to synthesize any biodiesel during the exploration process served as a lesson in methodology. Further experimentation was performed with much more care as to closely follow the recommended procedures. This lab also involved some rather complex stoichiometric calculations in order to derive the required amounts of reactants. The fact that the synthesis of

9 biodiesel was an equilibrium reaction also helped to further understanding of how to control different factors of a reaction in order to facilitate desired results. In general this was an engaging and thought provoking lab, however, burning the fuel in a working diesel engine would have been truly rewarding.