Grantee Research Project Results
Final Report: Production of Biobutanol from Biomass using Novel Membrane Reactor
EPA Grant Number: SU833927Title: Production of Biobutanol from Biomass using Novel Membrane Reactor
Investigators: Hestekin, Jamie , Clausen, Edgar , Draehn, Ellen , Thoma, Greg , Thomas, Nicole , Beitle, Robert
Institution: University of Arkansas
EPA Project Officer: Page, Angela
Phase: I
Project Period: August 15, 2008 through August 14, 2009
Project Amount: $10,000
RFA: P3 Awards: A National Student Design Competition for Sustainability Focusing on People, Prosperity and the Planet (2008) RFA Text | Recipients Lists
Research Category: P3 Challenge Area - Air Quality , Pollution Prevention/Sustainable Development , P3 Awards , Sustainable and Healthy Communities
Objective:
Developing renewable energy resources is one of the main challenges facing the world today. Our energy sources must become more renewable, more efficient, and safer for the environment. With the use of automobiles, the world has been able to make long distances seem shorter, but those automobiles have recently come under scrutiny due to sustainability and emission issues. The predominant current fuel source, gasoline, is from a limited resource – fossil fuels – which is in high demand. Most of the world’s supply is purchased from a limited number of sources. The high demand has caused depletion of oil wells and mass outflow of capital which threaten the continued operation of automobiles. Currently, the United States imports 5 billion barrels of oil per year, creating a pressing need to find a viable, sustainable alternative.
Past research efforts have made significant progress on electric and ethanol-based solutions; however, butanol is another sustainable alternative. First generation biofuel research has focused mainly on ethanol. Recently, biobutanol has become an attractive alternative to ethanol as a fuel oxygenate due to its low vapor pressure, high energy density, and ability to be blended with gasoline at the refinery which saves the trouble of transporting ethanol and gasoline separately to the fueling stations. Butanol’s higher energy density increases a vehicle’s fuel efficiency in comparison to ethanol. The high miscibility of butanol and gasoline gives greater flexibility in mixture composition. In addition, modern gasoline automobile engines can use butanol without any engine modifications. Biobutanol does not require automakers to compromise on performance to meet environmental regulations. Older automobiles also benefit from butanol being less corrosive than ethanol since it will not corrode rubber seals.
The purpose of Phase I was to investigate a method for producing biobutanol on a large scale from a waste feed stock using a novel fermentation and membrane separation method. The accepted method for biobutanol production is based on a fermentation process that produces acetone, butanol, and ethanol utilizing Clostridium beijerinckii in a bioreactor. The product solvents are also accompanied by water in the process and require several separations to produce a pure butanol product.
Producing biobutanol from a waste product on a large scale is a novel idea. Because of this, there is very little research available in this area. Previous fermentation research has primarily focused on the production of ethanol or biobutanol using cellulosic or agricultural feed stocks.
The Phase I research team, Team Razorbacks Engineering FUel Solutions for Everyone (Team REFUSE), sought to design a fermentation process that would produce butanol from food waste. Team REFUSE cultivated a partnership with Chartwells, the campus food service provider for the University of Arkansas, for the acquisition of food waste. They used the samples provided to conduct tests on food waste composition and determine the viability of using the food waste in an ABE fermentation process.
Proposed Phase II Objectives and Strategies
Research on a larger scale is necessary to the development of a full-scale design of a continuous, economically viable butanol fermentation process from food waste. To achieve this goal a pilotscale model has been designed that incorporates and builds upon the methods proven successful in Phase I.
In Phase II, senior chemical engineering design students will build and operate a pilot scale model that will process 150 pounds per day of food waste from one of the cafeterias at the University of Arkansas to approximately 190 mL per day of biobutanol. This is made possible due to the teams’ strong relationship with Chartwells, the on campus food supplier at the University of Arkansas. Building and operating this unit will allow the Phase II team to experiment with several operating variables that affect yield and process efficiency. One of the questions raised by the experimental results in Phase I was the potential benefit of the conversion of starches to butanol. In Phase II, a student team will determine the relationship between residence time and starch conversion. Although a longer residence time will allow more of the starches to be converted to butanol, at a certain point the bacteria will actually begin to decrease butanol production due to a lack of sugars. Experimentation in Phase II will determine the optimal balance between residence time and starch conversion.
Experimentation is also needed to increase the effectiveness of the pervaporation system. Altering the vacuum pressure and feed temperature of the pervaporator unit will affect the flux through the membrane. Increasing vacuum on the membrane or increasing the temperature of the liquid through the membrane will increase the flux. When using a hydrophobic membrane, increasing the component flux will increase the butanol concentration in the permeate stream.
The experimentation period will last for one month and the results of the process optimization will assist the team in designing a full-scale facility that could be implemented on a university campus. Approximately 365 million pounds of food waste are disposed of each year by American universities which could potentially be turned into 8 million gallons of butanol per year. Processing all of a university’s food waste will make the institution more sustainable and will offset a portion of the fuel costs for the university vehicles. Successful university partnerships could also lead to the conversion of food waste from restaurants, groceries stores, etc., which would a significant feedstock for fuel production.
Summary/Accomplishments (Outputs/Outcomes):
Food Waste Composition
Team REFUSE first performed sugar and starch assays on food waste from an on-campus cafeteria to determine its composition. The testing of the Chartwells food waste indicated the waste contained approximately 10% sugar and 25-30% starch content, which is sufficient for use in fermentation.
Fermentation
The fermentor used in the laboratory-scale was a two-liter Bioflow II reactor from New Brunswick Scientific. Bacterial cultures are difficult to maintain and do not initially adjust well to change. To minimize cell loss, inoculation of the reactor was accomplished in three steps. First the fermentor was run on a batch basis with media as a feed stock. When the cells were actively growing and producing product, the reactor was switched from a batch to continuous process. When the bacteria growth was stabilized in the continuous process, the growth medium was exchanged for food waste.
The team chose to use Clostridium beijerinckii, a bacterium that produces butanol, as the best bacterium to process food waste. Due to the difficulty in growing the C. beijerinckii culture, experimentation was performed with C. tyrobutyricum because it was readily available. C. tyrobutyricum is a close relative of C. beijerinckii that produces butyric acid instead of butanol and is often used in a two-step fermentation process to produce butanol. This culture successfully produced butyric acid from food waste, and from these results it is reasonable to postulate that experimentation with C. beijerinckii will also process food waste. At the time of this report’s submission, a healthy C. beijerinckii culture had been obtained and experimentation is ongoing. Team REFUSE will present the findings of these experiments at the expo in April.
Pervaporation
Pervaporation combines permeation and evaporation with good energy efficiency. This technology is based on the different diffusion rates of specific components through the membrane. The feed flows across the inlet side of a hydrophobic membrane, and a portion of this stream is pulled through the membrane in vapor form. A vacuum is applied on the opposite side of the membrane to increase mass transfer. The permeate vapor is then condensed and collected. The portion of the feed that does not diffuse through the membrane, the retentate, consists mostly of water and is recycled and disposed.
To obtain a purified butanol product, Team REFUSE built a custom pervaporation system with a PDMS (polydimethylsiloxane) membrane to evaluate the separation of butanol from water. Several condenser solutions were tested including chilled brine, liquid nitrogen, and dry ice in ethylene glycol. The best results were obtained from the dry ice in ethylene glycol at -15oC. The chilled brine solution failed to condense most of the permeate while the liquid nitrogen froze the condensate, plugging the vacuum. The permeate and feed concentrations were obtained using gas chromatography. Based on these test results, membrane separation has potential for largerscale implementation.
Life Cycle Assessment
In Phase I of this project Team REFUSE illustrated through a life cycle assessment (LCA) the environmental advantages of producing butanol. In America, transportation fuels account for 34% of greenhouse gas emissions; therefore, it was assumed for this assessment that the function of fuel is to move a vehicle. The basis for the assessment was the energy content of 1 kg of butanol, 33.3 MJ/kg.
The LCA compared butanol to gasoline and ethanol using the SimaPro software program and Recipe Endpoint (H). Gasoline emits 2.17 kg of CO2 more than biobutanol produced from food waste. When compared to corn ethanol, the process for producing biobutanol produces less CO2 by a margin of 1.05 kg of CO2 per kg butanol. The LCA confirms that biobutanol is more sustainable and better for the environment than both gasoline and ethanol.
Conclusions:
Phase I proved the feasibility of using a fermentation reaction as the primary step in production of biobutanol from food waste. Currently, carbohydrates, including sugars, starches, and even cellulose, can be used as the raw feed to produce alcohol-based fuels via microbial fermentations. Food waste contains an adequate amount (approximately 40%) of these raw materials in a form easily utilized by the bacteria, as proven by the team’s food waste analysis.
Phase I made substantial progress towards demonstrating the production of biobutanol from food waste. First, the team was successful in producing butyric acid from food waste using the bacteria culture C. tyrobutyricum, which is closely related to C. beijerinckii. Experimentation with C. beijerinckii is ongoing. Pervaporation experiments were also successful.
Based on Phase I research, biobutanol production via food waste is has potential to be a sustainable alternative fuel technology. Experimentation on the fermentor residence time and pervaporator operating conditions could increase the yield and profitability of the process. Based on the life cycle analysis performed in Phase I, it is clear that the separation of butanol from the fermentor effluent is a critical step in improving the sustainability of the production process. Therefore more research is required to improve this technology. Phase II proposes to do this by building a pilot-scale plant and gathering experimental data.
Supplemental Keywords:
Biobutanol, pervaporation, Clostridium beijerinckii, fermentation, ABE fermentation, food waste, alternative fuel source, alternative fuel, sustainability;, RFA, Scientific Discipline, Sustainable Industry/Business, POLLUTION PREVENTION, Sustainable Environment, Energy, Environmental Chemistry, Technology for Sustainable Environment, Environmental Engineering, sustainable development, environmental sustainability, alternative materials, biomass, alternative fuel, biodiesel fuel, energy efficiency, energy technology, alternative energy sourceThe 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.