Cooking Oil --> Biodiesel + Soap

As a class, we synthesized biofuel from our school’s cooking oil. Although biofuel is a renewable resource, waste products are still formed. To purify our biofuel, we separated the desired product from the waste product, glycerin. As a way to be completely resourceful in our biodiesel synthesis, we made soap out of the glycerin. We performed this procedure by first heating the glycerin at 70 °C for about an hour in order to drive off the methanol used in the synthesis of our biofuel. We then allowed it to cool to 60 °C, at which point the original brown liquid began to congeal. We expected this to happen, as we were making solid soap. While making the catalyst solution, which consisted of water, potassium hydroxide, and citric acid, we brought the glycerin temperature back up to 70 °C, mixing throughout the heating process. At 70 °C, we added the catalyst solution and allowed it to stir for 10 minutes. While it was stirring we added green food coloring in order to make the soap more appealing than its’ original brown color. We also added hops and jasmine for texture and aroma. Each group added their own scent and color, but all other steps were followed as a class. During these 10 minutes, we also tested the pH of the soap to ensure that it was not acidic and therefore would be safe for human use. This ten-minute heating and stirring period was followed by 10 minutes of just stirring without heat, and then poured into a round mold to allow to solidify overnight. Each group’s soap seemed to have a different consistency before we allowed them to solidify, as the pictures below show. This was strange because we all used the same procedure and adding food coloring or scent should not produce such disparity in consistency. When we returned to our soap, none of the soaps seemed to have solidified; they all had a gummy consistency. The consistency was a mix between solid and liquid soap, but the goal was to synthesize solid soap. We are unsure why this occurred, but it may have to do with how much fat was in the original biomass. We used vegetable based biomass, which is mostly unsaturated fats, whereas animal fat is saturated and therefore congeals more easily. This is solely a hypothetical possibility and needs to be experimentally tested to prove. Another odd observation of the soap products was that some of them produced suds, while others did not. I am unsure why this happened but it could possibly be because the starting glycerin had too much water in it or not all the methanol was driven off.