2014 Team One – Executive Summary The Diesel Crew Adam Alexander, Michael Lubben Angus Richeson, Thomas Voss Calvin College Engineering 4/11/2014 1 Introduction When selecting a project for this year, the team shared a desire to work with a tangible project, and to choose a project from the area of renewable energy. The team searched through the senior design archives and found a waste cooking oil (WCO) to biodiesel reactor built by Team Rinnova in 2008. After some preliminary research, the team learned that many different types of reactors and reactions are being implemented in the production of biodiesel from WCO. The team decided to investigate reaction systems, and design, build and test an experimental biodiesel reactor system. Much of the fall was spent in the library and on the computer researching the various components of the reactor system. The reactor system breaks down into the following components: pre-filter and water removal, reactor, separation train, methanol recovery, biodiesel polisher and a final filtration system. The team determined that the focal point of the system was the reactor. Both the type of reaction used and the type of reactor implemented would determine what was needed in the rest of the system. First, the team decided to implement a solid catalyst reaction to allow for a continuous process, and a microwave oven as the energy source. The team needed a method to determine the amount of conversion achieved to better determine the requirements for the separation train. The team determined two methods were possible for determining conversion, HPLC, and a methanol solubility test (biodiesel is soluble in methanol, while cooking oil is not). The team met with Professor Tatko of the Chemistry Department and were approved to borrow a HPLC unit for the year. Secondly, the team selected a pretreatment system similar to a design from the Utah Biodiesel Supply Company. Next the team was put into contact with a representative with the DOW Chemical company who donated a polishing resin, AMBERLITETM BD10DRYTM, for the use of our project. After the polishing column, the last step of the system is a final filter to remove any fine particulates from the fuel stream. The team decided to implement a normal petrodiesel filter. The remaining portions of the reaction system, the separation unit and methanol recovery system, became the largest obstacles the team faced. The decision to use a solid catalyst reaction added another requirement to the separation unit. The unit separates the biodiesel product from the glycerol byproduct, the excess methanol, and the solid catalyst. The team is yet determining the final design of this system, but is looking to implement a cascade system which will trap the catalyst for later removal. This unit will be followed by a heating system to boil off the excess methanol for recovery. The team received a large condensing unit from an old reactor system donated to Calvin College from Pfizer Inc. The team will use this as the method of recovery for the methanol. In addition to the design decisions, the project involves many additional choices that affect the success of the project. First, the team asked for permission from the Chemistry Department for use of the Advanced Organic Chemistry Lab. This space was used for all lab experiments for determining the proper conditions of the different units. Secondly, to better control a continuous process, the team decided to implement a control system. The Calvin Engineering Department donated LabVIEW Software and FieldPoint control modules for the project. The team had much to learn about implementing a control system and will provide control and sensor information for the majority of the system. 2 Project Scope The objective of Team One’s senior design project is to construct a reaction system for producing biodiesel from waste cooking oil (WCO), suitable for use by Calvin-sized institutions (approximately 4000 students / 8.6 gallons of WCO per day). Originally, we set out only to improve upon Rinnova’s 2008 design. As the team has progressed on the project, this goal has shifted slightly. Now, the primary objective is not to outcompete Team Rinnova’s design, but to show the feasibility of a continuous reactor system utilizing a solid metal catalyst for small scale biodiesel production. TABLE 2-1: PROJECT GOALS 1 2 3 4 5 6 7 Make the new system small enough to fit through a standard doorway and easily maneuverable Match or exceed Rinnova’s production rate of 40 gal in 16 hours (2.5 gal/hour) Improve feedstock filtration and dewatering Improve consistency of system operation and biodiesel product Have a capital cost lower than $6,000 for the reactor system Create a transparent system design, such that operation is possible by a non-professional with little training Require infrequent operator interaction, such that the operator could work on something else while in the same room as the system Make the new system easily serviceable, ensuring that all consumables are easily and inexpensively replaced Meet ASTM quality specifications for biodiesel, the industry standard Meet and exceed all safety requirements 8 9 10 Once the team chose to use a solid catalyst rather than liquid sodium hydroxide or potassium hydroxide, the team decided the following are not considered within the scope of The Diesel Crew’s project: Catalyst cleansing and recycle Purification of glycerol byproduct Ensure all ASTM standards of quality are met (this requires very expensive analytical equipment not available at Calvin College) 3 Design Decisions 3.1 Process Flow Diagram Figure 3-1 Process Flow Diagram 3.2 LabVIEW Control System One of the original design goals for the biodiesel reactor was transparency of design and ease of use. We have chosen to implement the LabVIEW graphical programming platform to provide a simple and intuitive user interface for the reactor system. Calvin has supplied The Diesel Crew with several FieldPoint control modules that establish a connection between the LabVIEW software and the various components of the system. These FieldPoint modules will allow control of the metering pumps, microwave power output, heating coil power output, solenoid valves, and other electrical components. The modules will also enable monitoring of the system by way of thermocouples, pressure transducers (used to monitor fluid level in each of the containers), and flow meters. Figure 3-2 below provides an example of what the interface will look like. A touchscreen monitor will be used for easy user interaction. System safety is also improved by implementing thermal shut offs and overflow protection through LabVIEW. PID feedback controllers will be designed in LabVIEW for nearly all system variables resulting in a reactor that will run itself requiring little to no user input. Figure 3-2: Tank Level Measurement in LabVIEW 3.3 Dewatering System The purpose of the dewatering system is to remove large particulates and water from the WCO. Water is detrimental to the reaction. First, water will poison the catalyst, forming calcium hydroxide and severely limiting the conversion. Second, the presence of water in the reaction will push side reactions that form soap and will result in an emulsion. Finally, water present in the reaction solution can result in the hydration of the triglycerides to FFA instead of methylating the triglycerides. The limit of FFA in the final diesel product is very low, and thus this side reaction must be limited. Figure 3-3: Waste Cooking Oil Dewatering System The unit design, as seen in Figure 3-3 above, works as a small batch process before the reaction system. Oil will be pored through a fine filter mesh, 177 micron hole width, into a 15 gallon drum. The oil will be pumped out of the bottom of the drum past a heating coil and sprayed back into the top of the drum. The circulatory system allows for good mixing of the oil, as well as rapid heating of the solution. In an effort to save money, the team was able to 3-D print the spray valve from acrylic plastic. The team tested the plastic for heat and chemical degradation in an oil bath at 110 °C. The test revealed no signs of thermal or chemical degradation. Finally, the team chose a heating element that worked on 120 volt power, but would heat up the oil quickly. The team decided against a higher voltage for easier use of our reactor system at any location. The team purchased a 2000 W heating element capable of heating 10 gallons of oil to 100 °C in 45 minutes. To ensure the safety of the system, the team chose to contain the heating element within 1 inch galvanized steel pipe. 3.4 Catalyst SelectionThe reaction to produce biodiesel from WCO and methanol is both endothermic and reversible. A catalyst is necessary to promote the forward reaction towards biodiesel and to reduce the reaction time required to reach sufficient conversion. Many different catalysts can be used in this process, each with its own advantages and disadvantages. Rinnova used a solution of potassium hydroxide (KOH) dissolved in water, which worked well, but, as a liquid, it is difficult to separate out after the reaction, requires a water wash. This wash takes several hours, can potentially introduce water or soaps to the fuel, and prevents catalyst recycling. In addition to a desire for further exposure to the extracurricular topic of solids handling, The Diesel Crew chose to use a solid catalyst to eliminate the wash step and permit catalyst recycling. In the past five years there have been many papers published on a multitude of solid substances used as biodiesel catalysts. Among them, several contenders rose to Team One’s attention: zirconium oxide (ZrO2), calcium oxide (CaO), also known as quicklime, magnesium oxide (MgO), and strontium oxide (SrO). In many ways, ZrO2 is an excellent catalyst choice. It is reportedly quite effective at the transesterification reaction that turn oil to biodiesel, as well as a respectable catalyst of free fatty acid (FFA) esterification, which prevents these fatty acids from impairing the transesterification in a number of ways. ZrO2 is moderately resistant to poisoning by water in the WCO feed, can be heat-treated to restore its catalytic activity, and has negligible solubility in the reaction mixture. Its disadvantages are its high cost (>$1/gram), and that it requires a very small particle diameter to be effective, making it difficult to reclaim from the reactor effluent. Since the members of The Diesel Crew are inexperienced with solids handling, use of ZrO2 would likely inadvertently send a substantial portion of the allocated budget literally down the drain. Calcium oxide, on the other hand, is easily obtainable at very low costs, and can be regenerated by roasting if needed. However, it quickly becomes poisoned by water (even water in the air) or FFA, and at high FFA levels, soap formation can become a problem. Still, at 60°C and 1 atm, it can achieve WCO conversion as high as 97%. MgO was rejected due to poor conversion of WCO at the desired temperature and pressure (~60C, just under the boiling point of methanol at 1 atm), and because of its high solubility in methanol. SrO is much more active than CaO, but is moderately soluble in methanol, and fairly expensive. As a result, it too was rejected, resulting in calcium oxide being selected for use as the catalyst. 3.5 Dual reactor design- CSTR into Microwave PFR Research conducted towards the end of last semester indicated that the required level of conversion to biodiesel, greater than 90%, would not be achieved in the desired amount of time using our choice of CaO catalyst and a simple plug-flow or continuous-stirred tank reactor. To overcome this short coming, many alternative reactor designs were explored and a decision matrix was used to determine the best choice. Table 3-2 below shows the types of reactors explored, and Table 3-1 provides definitions for the abbreviations used in the decision matrix. Table 3-1: Summary of Abbreviations for Decision Matix in Table 3-2 Criteria Cost Construction Difficulty Operation costs Operation Difficulty Typical Fame Conversion Reaction Time Operating Temp Pressure Pretreatment of WCO Treatment of Pdts. Requires Catalyst Solid Metal Catalyst Flow Rate Heat Transfer Abbr. C CD OC OD conv t T P PT TP Cat SMC FR HT Reactor Type Microreactor Acoustical Cavitation Hydrodynamic Cavitation Microwave Batch Microwave Continuous Oscillatory Baffled Motionless Inline Abbr. Micro AC HC MB MC OB MI Table 3-2: Decision Matrix for Reactor Type Matrix Decisions Criteria C CD OC OD conv t T P PT TP Cat Decision Weight 10 7 5 9 8 5 9 9 4 4 15 Reactor Type Micro 2 8 8 8 10 10 7 10 2 2 5 AC 2 8 3 9 6 9 7 10 2 2 5 HC 4 8 5 9 8 7 7 10 2 2 5 MB 10 7 2 5 10 2 7 10 2 7 5 MC 8 6 2 9 8 7 7 10 2 7 5 OB 5 8 4 8 9 3 7 10 2 7 5 MI 8 6 7 10 9 2 7 10 2 7 5 SMC FR HT Weighted Total Normalized Score 15 5 5 110 (Higher=More Favorable) 0 1 7 3 10 5 3 8 5 7 2 10 7 8 10 7 5 5 2 8 5 602 5.5 629 5.7 655 6.0 723 6.6 771 7.0 704 6.4 688 6.3 From the above decision matrix, we determined that a microwave reactor was most suitable for our design. The use of microwave reactors for intensified biodiesel production is an emerging technology. The majority of journal articles found on this leading-edge technology have been published in the last two years. In order to test the value of the microwave, the team performed two batch reactions for one hour with a 6:1 volume ratio of MeOH:WCO and 2wt% CaO, one heated with a mantle, one heated in a microwave. The microwave reaction showed 38% conversion, and the conventionally heated reaction showed only 7.7% conversion, indicating the value of using a microwave. Microwave irradiation has two major benefits, no external heating is required and the catalyst efficiency is significantly improved. Microwave irradiation is a highly efficient way to heat the reactor contents, eliminating the need for another heat source. Microwave irradiation also encourages mixing on the molecular level. Small pockets of intense heat and pressure. This promotes transesterification of triglycerides with methanol, reaching near complete conversion depending on which catalyst is used. After significant design calculations and considerations, the team decided that a dual reactor scheme would be needed to achieve the high level of conversion in the given amount of time. First a large continuously stirred tank reactor (CSTR) at 60°C with a catalyst slurry is used to achieve reasonable conversion with a large space time. Then the reaction mixture moves to a plug flow reactor (PFR), which is passed through the microwave to achieve the rest of the conversion. It is typically difficult to have a catalyst slurry in a PFR, but the team overcame this challenge by finding static mixers, which cause the slurry to be mixed as it moves through the PFR. The team used batch testing to find the conditions for the reactor. A temperature of 60°C was chosen, as this is near the maximum achievable temperature without MeOH boiling at atmospheric pressure, which would cause safety and design concerns. The reaction is run with an excess of MeOH to ensure high conversion. The optimal volume ratio of MeOH:WCO and optimal ratio of catalyst to WCO were investigated in the lab. Results showed that using more catalyst resulted in higher conversion (Figure 3-4). Figure 3-4 Catalyst Ratio Determination The results showed that a catalyst ratio of 283g CaO per L of WCO would be the best. A higher amount of catalyst would have smaller effect on conversion and cause more difficulty in the separation processes. The team then tested different volume ratios at this catalyst ratio (Figure 3-5). Figure 3-5 Volume Ratio Determination Because using the same catalyst ratio with a lower volume ratio results in a larger catalyst concentration, lower volume ratios yielded higher conversions. The team chose a 3:1 volume ratio, as this ratio will give high conversion without putting unnecessary strain on the separation system. 3.6 Methanol Recovery A large volume of methanol must be recovered from the reactor stream on a continuous basis. A desired biodiesel production rate of 2.5 gal/hour and a methanol to WCO ratio of 3:1 means that roughly 0.125 gal/min (473mL/min) of methanol must be removed. Currently, we plan to use vacuum distillation and possibly a heating coil to evaporate the volatile methanol off of the reactor effluent. A water-cooled heat exchanger will then be used to condense the methanol into a collection vessel. The effluent leaving the reactor will be just below the boiling point of methanol; therefore, only a low vacuum, less than -5 psig, will be required for removal. The team plans to implement a large glass condenser acquired from a Pfizer donated reactor system (Figure 3-6). Figure 3-6 Glass condenser Available to Use for Methanol Recovery 3.7 Glycerol and Catalyst Removal Once most of the MeOH is removed, the glycerol and biodiesel product form a two-phase liquidliquid equilibrium (LLE), making it easy to separate out the glycerol in a vertical column. This vertical column would feature a feed at the middle, a valve to set the drip rate of glycerol at the bottom, and a stream off the top for the biodiesel product. This design will easily be constructed and implemented, but the glycerol may be removed elsewhere with the catalyst. The catalyst recovery has proved to be one of the most difficult design portions of the system. The small particle size of the CaO, which is necessary to achieve good performance, requires a very fine mesh/filter paper for filtration, resulting in a large pressure drop. There is also a very large amount of the catalyst, so a filter can get clogged very quickly, which is troubling in a continuous system. The CaO could be allowed to settle out, but the CaO volume is about the same as the volume of the biodiesel product phase, so a significant amount of biodiesel is lost if the CaO is allowed to settle out from the liquid mixture. In a settling design, the biodiesel could be re-claimed later in a batch process or recycled continuously. A settling design could also have the glycerol settle out with the CaO, eliminating the need for the LLE column described earlier. Whether a settling design or filter design is used, this part of the system is a batch process which accumulates CaO and is only implementable in a continuous design because it takes a long time before it needs to be cleaned out. The team has several designs for this part of the system: a large canister filter, a large flat filter mesh, a slanted filter drum (lower pressure drop because liquid hold-up does not have to pass through cake), and a cascade settling system before or after the MeOH recovery. The team has catalyst that is being delivered, so testing can begin on this part of the system. If none of these designs works semicontinuously, the team may have to convert to more of a batch system. 3.8 Amberlite™ BD10DRY™ absorbent polishing column The final step of the reactor process is the polishing column. The polishing column, otherwise known as a purification column, consists of a large cylindrical tube filled with ion-exchange polymer beads that prohibit the passage of various contaminates while allowing the biodiesel to pass through. Possible contaminants include small amounts of glycerol, CaO catalyst, remaining mono-, di- and triglycerides, and any remaining free fatty acids. This is a crucial step in producing a quality biodiesel product that meets all ASTM standards. Polishing column technology is well established and has not changed much since Rinnova’s design. The team has chosen a very similar design to Rinnova’s polishing column based on its effectiveness at removing most all contaminants, the ability of the column to work in a continuous fashion, and the affordable nature of the column. There are five ion-exchange resins commonly used for biodiesel purification, each with its pro and cons. The major design decision then becomes which ion-exchange polymer is most suited for our specific reactor. Due to limitations of time and money, the team has been unable to test these five polymers for their effectiveness at removing the CaO and other contaminants. However, Professor Sykes provided The Diesel Crew with a contact at the DOW Chemical Company who was able to supply the team with five pounds of Amberlite™ BD10Dry™ to perform testing. This is the same ion-resin used by Team Rinnova so we expect it to work well with our system. Bench scale testing of the ion-resin is expected to take place shortly, and final column construction shortly thereafter.