Grantee Research Project Results
Final Report: Synthesis and Characterization of a Novel Solid Acid Catalyst for Improved Use of Waste Oil Feedstock for Biodiesel Production
EPA Grant Number: SU833513Title: Synthesis and Characterization of a Novel Solid Acid Catalyst for Improved Use of Waste Oil Feedstock for Biodiesel Production
Investigators: Webster, H. Francis , Bean, Bryan B. , Fuhrer, Timothy J. , Estes, Christopher
Institution: Radford University
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 1, 2008 through July 31, 2010
Project Amount: $9,996
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2007) RFA Text | Recipients Lists
Research Category: Pollution Prevention/Sustainable Development , P3 Challenge Area - Chemical Safety , P3 Awards , Sustainable and Healthy Communities
Objective:
The Environmental Protection Agency and the American Chemical Society share a common vision of promoting and implementing chemical and engineering practices that are safe for the environment. The concept of green chemistry began in the early 1990s with the passing of the Pollution Prevention Act as an attempt to reduce hazardous chemical processes. The green chemistry movement was made famous in 1998 when Paul Anastas and John Warner published Green Chemistry: Theory and Practice outlining 12 principles every chemist, engineer, and company should consider whether at the lab bench or on the industry floor. The general them of these principles, though detailed and unique, is that prevention is better than treatment. Specifically relevant to our P3 project is the fifth principle which encourages the use chemical catalysts that minimize waste by their use in small amounts and their ability to carry out a single reaction many times2.
Concurrent with the green chemistry movement is the growing concern for America’s ability to meet its energy needs. This has prompted scientists to research and develop alternative fuels, and biodiesel, a non-toxic and carbon neutral fuel, represents one of these alternative fuels. Biodiesel is produced by transesterification, a reaction in which triglycerides (animal fat or vegetable oil) are combined with alcohols in the presence of a catalyst. Commonly, biodiesel is made from new vegetable oil typically from soybean or rapeseed sources, but the use of virgin quality oils presents a challenge to sustainability as we divert these food resources for energy use. This ethical dilemma can be avoided by the more efficient use of waste oil as a feedstock and can provide one component in the varied alternative fuel portfolio needed to address our future energy needs.
One hurdle of using waste oil for biodiesel production is the high free fatty acid (FFA) content often found in waste oil. This can lead to the formation of soap during the typical base-catalyzed reactions. Therefore, FFA’s must be removed from waste oil before processing, leading to a number of additional processing step to efficiently use this waste material. The most commonly used removal method utilizes sulfuric acid as a catalyst to remove these acids by esterification, but this corrosive homogeneous (non-solid) catalyst must then be removed by neutralization generating a number of processing steps and waste streams. A better method would be to develop a heterogeneous, or solid, catalyst for biodiesel production that could be removed from the reaction mixture and re-used.
The importance of the development of new heterogeneous catalysts was emphasized in a recent workshop sponsored by the National Science Foundation3. Experts in the field of catalysis were brought together to discuss the state of catalysis technology related to bio-renewable use. To meet the desired goal of using bio-based feedstock as raw materials for chemical production, one clear challenge is the need for an increased research effort in the area of solid catalyst development. For biodiesel, the development of heterogeneous catalysts for biodiesel production was specifically singled out to ensure the economic viability for production of this fuel.
As outlined in the P3 Phase I proposal, our objective was to develop a solid acid catalyst to improve the utilization of waste oil as a feedstock for biodiesel production through the removal of free fatty acids by esterification. While several commercially produced solid acid catalysts are readily available for use in esterification reactions (i.e. Amberlyst and Nafion), they are very expensive synthetic petroleum based products. Our catalyst is developed from a renewable sugar source, is inexpensive, simple to produce, and is expected to find use in the synthesis of a number of industrially important reactions including esterification, hydrolysis, and etherification. These advantages may allow the adoption of the technology by not only interested businesses but also individuals in the growing biodiesel community in both the developed and developing world.
Summary/Accomplishments (Outputs/Outcomes):
Carbon Catalyst Synthesis - Sucrose was treated directly with excess sulfuric acid sulfuric acid (9:1 mol/mol, 25°C). A carbon foam (nearly 20 fold increase in bulk volume) was immediately formed. The foam was then washed until no sulfate was detected, dried, and sieved to varying particle sizes. Carbon made at room temperature is designated SCRT. Thermal treatment of the carbon was conducted for some samples under nitrogen at 155°C, 205°C, and 255°C and are designated as SC155, SC205, and SC255.
Figure 1. Granular carbon solid acid catalyst.
Catalyst Characterization
Scanning Electron Microscopy (SEM) - Samples were analyzed by SEM to characterize the surface topology. Figure 2 shows a SEM micrograph of the carbon surface at a low magnification illustrating a relatively smooth surface structure. The image insert is at a much higher magnification and clearly shows the presence of a sponge-like surface structure. Since transport of reactants and products in and out of the catalyst is key to its activity, fine tuning the pore structure is of utmost importance. Surface area analysis was performed and shows a very low surface area of less than 1 m2 /gram.
Figure 2. SEM micrograph of carbon at low
(5000x) and high (insert; 500,000x) magnification.
Determination of Strong and Weak Acid Sites – For a solid to be a promising candidate to replace sulfuric acid for the esterification of free fatty acids, it must have a significant number of strong acid catalytic sites (sulfonic acid groups). Also of interest is the number of weak acids that may alter the chemical environment near the active surface sites, which could possibly improve the catalytic activity in the presence of water. The number of strong acid sites in our carbon catalyst was evaluated through the determination of ion-exchange capacity (IEC) by measuring the amount of H+ exchanged with Na+. Carbon samples were equilibrated with 2.0 M NaCl overnight and then titrated with 0.01 M NaOH. To determine the presence of both strong and weak acid sites, samples were treated with a strong base solution to react with all sites, and then back titrated with a standard 0.1 M HCl solution. A large number of weak acid sites were found ranging from 6-7 mmol/g. The number of strong acid sites was found to range from 0.8-1.2 mmol/g which compares favorably to commercial solid acid catalysts.
X-Ray Photoelectron Spectroscopy - To determine the chemical structure of the strong and weak surface acid sites, samples were analyzed using x-ray Photoelectron Spectroscopy (XPS). XPS is a high vacuum technique in which a surface is bombarded with x-rays causing electrons at the surface to be ejected (Figure 3). Electron energy is then analyzed and related to the surface atomic composition.
Figure 3. X-ray photoelectron spectroscopy
Results indicated that sulfonic acid groups were present as indicated by the sulfur photopeak at 168 eV (Figure 4). Other surface functional groups, including carboxylic acid groups, were also detected by examination of the carbon photopeak. The analysis revealed high surface concentrations of carboxylic acid groups (weak acids) and very low concentrations of sulfonic acid groups (strong acids) which is in agreement with IEC analysis.
Figure 4. Typical XPS analysis showing carbon and sulfur
surface functional groups.
Figure 5. Typical TGA results showing percent mass loss
versus temperature (left axis) and the rate of mass loss
(right axis).
Thermal Stability – For maximum effectiveness, catalysts should have the capacity to operate under a wide range of temperature conditions. Amberlyst, a commercially used solid acid catalyst, and other polymer based catalyst generally cannot be used at elevated temperatures (>120°C) due to degradation. Thermogravimetric analysis (TGA) was therefore used to evaluate the thermal stability of our carbon catalyst. As can be seen in Figure 5, the onset of degradation occurred at temperatures in excess of 250°C showing the potential of our catalyst to operate at much higher temperatures than found for many other polymer based catalysts. IEC, XPS, and TGA results for all carbon samples are summarized in Table 1 below:
1Results reported as meq/g 2Mbaraka et al. J. Catal. (219) 2003 329
Computational Chemistry - Currently, finding the best performance for a catalytic material involves the time consuming practice of screening large numbers of candidate materials. With the computational tools now available to chemists, predicting catalytic activity by modeling the catalytic reaction could reduce wasted time and material and is a key component in the drive to sustainable chemistry. In an attempt to better understand catalyst structure and function, the theoretical sub-group of our P3 team began work on modeling the structure for our carbon catalyst. This was done by optimizing a hypothetical geometry using a Gaussian 03 and GaussView03 software packages. The carbon structure was modeled on a geometry for carbon found in the literature with added SO3H groups that serve as the catalytically functional group.4, 5 Carboxylic acid functionality was also included as suggested by analysis of the XPS results. While still in the preliminary stages of development, the theoretical infrared spectra generated did allow us to better understand the absorption frequencies expected for this material.
Figure 6. Suggested carbon catalyst
structure
Catalyst Evaluation for Chemical Activity - Catalyst activity was evaluated using the esterification of oleic acid with methanol. The reaction scheme is shown in Figure 7.
Figure 7. Esterification reaction of oleic acid with methanol in the presence of a catalyst to
produce the methyl ester (biodiesel) and water.
A multi-channel micro-reactor was built using a custom-made heating block mounted to a horizontal orbital shaker. Vials were filled with methanol and oleic acid (10:1 molar ratio, 4 mL total volume) and allowed to equilibrate at 65°C before the reaction was initiated by adding 0.1g of the carbon catalyst. Samples (25 μL) were removed from the vials at varying times for 24 hours. The samples were then purged with nitrogen (65°C) to remove residual methanol from the sample. Samples (5μL) were tested for oleic acid and methyl ester content using attenuated total reflectance infrared spectroscopy (ATR). This novel technique requires very little sample for analysis and cleanup between samples is minimal. The analysis time is approximately one minute and much faster than traditional gas chromatography methods.
Figure 8. Nine channel micro-reactor
Two absorbance bands (1710 cm-1 and 1742 cm-1) were used to monitor the progress of the esterification reaction and typical ATR results are shown in Figure 9. The peak at 1710 cm-1 represents the carbonyl stretching frequency for oleic acid, and the peak at 1742 cm-1 is due to the stretching frequency for the fatty acid methyl ester. Fig. 9 shows ATR results for early, middle, and late reaction times and shows the shift from acid to methyl ester. Results showed that the technique was very effective for monitoring the reaction kinetics.
Figure 9. ATR results showing the conversion of fatty acid to
fatty acid methyl ester.
Carbon catalysts were evaluated and compared to commercial polymer based catalysts (Amberlyst and Nafion), and the results are shown in Figure 10. The carbon post-treated at 155°C performed better than all other treatments and clearly outperformed Amberlyst and Nafion. The 255°C carbon was found to have significantly lower catalytic activity than other carbon samples tested, possibly due to degradation which is in agreement with the TGA results at these temperatures.
Figure 10. Percent conversion versus time for the kinetic studies of
the carbon catalysts and commercial solid acid catalysts.
The data was fit to a pseudo-homogeneous kinetic model which is often used for esterification reactions catalyzed by polymer based catalysts. The initial rate of the reaction was determined and is shown in Fig. 10.
Removal of Fatty Acids Using a Model Waste Oil System - The primary goal of the Phase I project was to investigate the use of our solid acid carbon catalyst for efficiency in esterification reactions and particularly for the removal of free-fatty acids (FFA) from waste vegetable oil. A simulated waste oil system was designed using soy based vegetable oil (ADM) and oleic acid (at 15 wt. %). Tests were conducted using excess methanol at 65°C with a carbon loading of 12% (155-SC) and the total reaction volume was 2 - 4 milliliters. For analysis, samples were purged with nitrogen to remove methanol and titrated using standard methods to determine the fatty acid content. The experiment was repeated using Amberlyst and Nafion. Figure 11 shows a plot of free fatty acid content as a function of time for both the carbon and commercial catalysts. Results show that the carbon catalyst is very efficient in removing free fatty acids through esterification and this removal can occur at moderate temperatures and ambient pressure. Results also show that the carbon performs more effectively than the common petroleum-based commercial catalysts investigated (Amberlyst and Nafion). This is quite impressive considering the lower cost and more sustainable method of producing a catalyst made from a completely renewable resource.
Figure 11. Percent fatty acid removed comparing the carbon
catalyst with commercial polymer based catalysts.
Integration of P3 Concepts as an Educational Tool
Dissemination - A key component of our team’s efforts has been the dissemination of our findings on sustainable catalyst development to the broader scientific community. With a matching internal grant from Radford University (RU), students were able to begin the P3 research in the spring of 2007. The early success of the project resulted in four presentations being given at national meetings related to this work:
S.R. Hash, C.S. Estes and H. F. Webster “Synthesis and Characterization of a Novel Solid Acid Catalyst for Improved Use of Waste Oil Feedstock for Biodiesel Production”, 11th Green Chemistry & Engineering Conference, Washington D.C., June 2007 (poster)
S.R. Hash, C.S. Estes and H. F. Webster “Synthesis and Characterization of a Novel Solid Acid Catalyst for Biodiesel Production”, 11th Green Chemistry & Engineering Conference, Washington D.C., June 2007 (poster; winner of a $1500 travel grant for best poster)
S.R. Hash, C.S. Estes and H. F. Webster “Esterification of Fatty Acids using a Novel Solid Acid Carbon Catalyst”, 11th Green Chemistry & Engineering Conference, Washington D.C., June 2007 (oral)
S.R. Hash, C.S. Estes and H. F. Webster “Synthesis and characterization of a novel solid acid catalyst for improved biodiesel production”, 234th National ACS Meeting, Boston, August, 2007 (oral)
In addition to dissemination of our research to the scientific community, we have advocated the principles of green chemistry and sustainability in both the local community and in the classroom. This research, in conjunction with the Center for Environmental Studies at RU was presented at the Clean Valley Summit in Roanoke, Virginia on November 2, 2007. A short presentation was delivered to high school students on the importance of utilizing an environmentally responsible scientific approach to today’s energy needs. Also in the Fall of 2007, a group of children (ages 10-13) were invited to RU for a biofuel workshop to learn about the importance of alternative fuels and were given a brief overview of what biodiesel is and how it is made. They then made biodiesel in the laboratory with the help of the P3 team. When finished, they poured their product right into the tank of a diesel car.
Figure 12. Workshop students making
biodiesel
Integrated Laboratory – As part of the curriculum for chemistry majors, our Department requires students to complete an integrated lab course (CHEM403:404) that combines aspects of the traditional chemistry disciplines (organic, analytical, physical, and inorganic) in a research-like environment. In the Fall of 2007, two projects incorporating the principles of green chemistry and specifically the P3 project results were included in the course. In the first project, students investigated the possibility of using the carbon catalyst synthesized in this study to remove copper from solution. In a second project, students investigated the use of heterogeneous catalysts including our carbon for the transesterification of methyl acetate with butanol to produce butyl acetate, an important industrial solvent. While investigating real research problems is an important part of this course, students were also introduced to the concepts of heterogeneous versus homogeneous catalysis, green chemistry, and the role of chemistry in solving many of the barriers to sustainability.
Conclusions:
The objective of balancing the elements of people, prosperity and the planet was paramount for the duration of the Phase I research. An inexpensive carbon catalyst for the esterification of fatty acids was easily prepared from a bio-renewable material and was demonstrated to be more effective for fatty acid removal from waste oil than synthetic petroleum based catalysts. While sulfuric acid, which is often used as a homogeneous catalyst, was initially needed to prepare the catalyst, the potential for reusing the solid catalyst ultimately reduces the amount of this corrosive material used. This is significant in that it enables the biodiesel process to be streamlined, while still reducing costs and the number of waste streams. Production costs are also low as the starting material (sugar) is easily available and very inexpensive. The production of a catalyst from a renewable feedstock is in line with the drive toward sustainability as we move away from the petroleum based polymeric catalysts used in industry today.
While the project was successful and the team clearly showed the potential of the carbon catalyst, the need for further research and development is essential to fully evaluate carbon as a potential replacement for current technology. Several key areas of research were identified as needed and are outlined below:
- Extensive testing on the re-usability of the catalyst needs to be completed.
- A more sophisticated reactor is needed to study the optimum performance conditions and investigate the possibility of using this catalyst for the direct production of biodiesel by a combination of esterification and transesterification.
- Promising catalyst candidates need to be evaluated using a larger scale reactor, and run under real world conditions containing small amounts of water.
- Further computational work is needed to understand the catalyst chemical structure and reaction dynamics.
- Testing of the catalytic potential of our carbon for use in other commercially important reactions is needed.
- The potential for extending the life cycle of the carbon catalyst by using “spent” carbon as an adsorbent similar to activated carbon needs to be explored.
While the project primarily focused on bench chemistry, the involvement of the Green Team at RU kept the group focused on the role chemistry must play in achieving sustainability. Topics of “green” chemistry and sustainability were also incorporated into RU chemistry courses for the first time and workshops were held to involve the community in the discussion of biofuels and alternative energy.
Our P3 project success was ensured by a commitment of matching money for the project from RU through an internally funded research proposal. This allowed the team to begin work in spring semester of 2007 before P3 phase I funding arrived. While no external partners have been identified at this early stage in the development, the improved performance of our catalyst versus current commercial technology and low manufacturing cost based on renewable bio-materials should prove to be an attractive alternative to petroleum based products.
References
1. http://www.biofuelsjournal.com/articles/Axens_Selected_for_100_000_Tons_Per_Year_Biodiesel_Plant_in_Malaysia-48479.html Exit
2. https://www.epa.gov/green-chemistry
3. http://www.chem.uiowa.edu/research/sustainability/report.html Exit
Supplemental Keywords:
RFA, Scientific Discipline, Sustainable Industry/Business, POLLUTION PREVENTION, Environmental Chemistry, Sustainable Environment, Energy, Technology for Sustainable Environment, Environmental Engineering, sustainable development, environmental sustainability, alternative materials, biomass, alternative fuel, biodiesel fuel, energy efficiency, energy technology, alternative energy sourceProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.