Laboratory Testing: Methods and Approach
The goal in the lab was to identify and optimize a successful way to produce biodiesel given the project constraints. Using the nickel-oxide coated microreactors and having selected methanol and soy oil as the reactants, the group manipulated other variables based on research and software simulations to identify a successful process. Namely, those variables manipulated specifically in the lab were the temperature, the residence time, and the molar ratio of methanol to soy oil.
The lab set up in the first semester consisted of a syringe pump, heating tape, variac, multimeter, thermistor, micro-reactor, and test tube. A picture of this set-up is shown in Appendix B. The syringe pump was a good positive displacement pump with two syringes (one for each reactant) that could pump each fluid separately until they mixed in the microreactor. After leaving the microreactor, the product flowed into the test tube for collection and testing. The reaction was heated by placing the microreactor on a heating tape whose temperature was controlled by the variac and measured by the multimeter attached to a thermistor. In the second semester, the set-up stayed the same except all the components used for heating the microreactor were switched out for a hot water bath. The microreactors were submerged in heated water and the heat was both controlled and measured by the controls on the hot water bath. Using the hot water bath in the lab was crucial because it was a safer means of heating the reaction. This meant that the process could be left unsupervised, allowing many more tests to be run throughout the semester, despite the slow flow rates of the reactants. Appendix B also shows a picture of this set-up. In the picture, solar power is being used to power the pump and the hot water bath; this shows the success of the solar power goals of the project; however, for research purposes in the lab, no further investigation of the solar power was needed to continue to run experiments, and hence, solar energy will be discussed in more detail later in the paper.
The different variables in the laboratory experiments were controlled by the temperature control and the syringe pump. The residence time was an average time the fluid would be in the reactor given the dimensions of the reactor and the sum of the two flow rates being controlled by the pump. The molar ratio was controlled by the chemistry of the reaction, and could be adjusted if more methanol was desired to drive the reaction. As will be shown later, an excel spreadsheet was made that provides these calculations; by inputting the desired residence time and molar ratio to be tested, the respective flow rate for each reactant was given. Specifically, this spreadsheet analysis will be discussed in detail in the Theory for Design portion of the paper.
As different tests were run at varying speeds, temperatures, and ratios, the data from the software simulations was used to try to gain a better understanding of the nature of the flow and of the reaction within the reactor. By changing the variables in the simulation, different variable combinations were developed that seemed to provide better conditions for the reaction to occur, and then those values would be tested in the lab.
The plan was to then optimize the process and create a final design. This involved finding the optimal temperature for the reaction and finding the most energy efficient way to heat the microreactors. This also involved a balance of flow rate speed and the percentage of completion of the reaction. The faster the flow rate, the better, but it had to be slow enough to allow for the reaction to occur. Optimization also involved a study of what percent of biodiesel produced would be desired in order to make use of the faster initial reaction rates. The group was not actually able to get to the optimization step within the lab, however, because it was never successful in producing biodiesel. Therefore, for the design requirements of the project, the group was forced to move forward with an optimized design based only on theoretical computer simulations, which, unfortunately, have not yet been proven to be consistent with the real-life lab results.
Table 1 below shows the details of the fourteen experiments ran over the course of the year in sequential order. The group initially started out with shorter residence times and an abundance of methanol. Later, it was decided that the reaction was not being given enough time, so the residence times were then greatly lengthened which was possible by the usage of the hot water bath. Using the software, the group also honed in on what was simulated to be a better molar ratio to create flow properties that were best for the reaction. As tests continued to be unsuccessful, the next step, after doing an analysis of the increased internal pressure in the reactors, was to gradually increase the temperature. Originally the group wanted to stay below the boiling point of methanol at atmospheric pressure but gradually became more daring at risking boiling some methanol off in order to go to higher temperatures to try to initiate the reaction. For the final experiment performed, the group sent the results away for analysis by Nuclear Magnetic Resonance in order to be sure that the Thin Layer Chromatography (TLC) analysis being done in the lab was not missing some amount of biodiesel.