Grantee Research Project Results
Final Report: Small Scale Ethanol Drying
EPA Contract Number: EPD08052Title: Small Scale Ethanol Drying
Investigators: Majumdar, Sudipto
Small Business: Compact Membrane Systems Inc.
EPA Contact: Richards, April
Phase: II
Project Period: May 1, 2008 through April 30, 2011
Project Amount: $225,000
RFA: Small Business Innovation Research (SBIR) - Phase II (2008) Recipients Lists
Research Category: SBIR - Agriculture and Rural Community Improvement , Small Business Innovation Research (SBIR)
Description:
Membrane processes are ideal for small applications because the key components in membrane processes are the membranes themselves, and the associated hardware scales down linearly. Although many existing biomass-to-ethanol plants are at 40 million gallons per year or greater and very few are at 10 million gallons per year, a membrane process will lend itself to focus on small-scale fuel grade ethanol production. In addition to being ideal for small-scale operations, membrane processes are ideal for removing the minor component. Specifically, fuel-grade ethanol at the fermentation level has upwards of 5-8 percent ethanol in water, which can be achieved with silicone rubber membranes. For highly concentrated streams, such as 90 percent ethanol, a different membrane, as proposed by Compact Membrane Systems Inc. (CMS), which preferentially removes water would be ideal for the final drying to 99.5 percent ethanol.
The proposed concept is to operate primarily membrane and related processes to convert low volumes of biomass to fuel-grade ethanol. The process consists of three components. These components are: a small fermenter that will convert biomass to ethanol containing approximately 5 percent ethanol; a pervaporation membrane that preferentially permeates 20-25 percent ethanol; a simple unit operation that takes the 20-25 percent ethanol up to 90-95 percent ethanol; and a second membrane device. In this case, because water is the minor component at 5-20 percent, this membrane will be water permeable. The net result from the process is the conversion of 5 percent ethanol to 99.5 percent fuel-grade ethanol in one small-scale process.
Summary/Accomplishments (Outputs/Outcomes):
CMS has found that an innovative water-permeating membrane module design with a commercially available microporous hollow fiber support with bundle-end seals using an appropriate epoxy formulation is highly ethanol/water resistant. These membrane modules have tolerated 120oC temperature and 60 psia pressure conditions with no apparent degradation. The company determined early in the program that PDVF microporous hollow fiber supports were not ethanol resistant enough to be used in effectively drying the ethanol to fuel-grade quality (99.5% wt.). CMS also confirmed that polysulfone (PS) and polyethersulfone (PES) microporous hollow fiber supports were not ethanol/water resistant under the conditions for effective ethanol-water separation.
A number of fiber-bundle seal epoxies were evaluated and the best epoxy for this application was determined. The selected fiber-bundle seal epoxy proved stable under vapor permeation tests at 120oC and 60 psia conditions.
Vapor separation is preferred to pervaporation because of the higher water permeation and greater water-ethanol selectivity.
CMS completed the fuel-grade ethanol drying test rig for the experiments outlined for this program. Experimental results have been completed for: pressure drop as a function of flow rate tests shell and lumen; optimal feed port strategy; boiling ethanol exposure test; water permeance averages about 650 GPU and ranges from about 500 to 800 GPU; water/ethanol selectivity averages about 8.5 and ranges from about 7 to 10 during vapor permeation tests at 120oC and 60 psia conditions.
A 200 cm2 membrane module was made and tested with a feed of 90 percent ethanol at 120oC and about 55 psia. The module was tested daily for about 8 hours during 25 days with daily startups and shutdowns. With daily abrupt startups and shutdowns for 25 days, this testing shows that there is no excessive module performance decline, and the module was highly stable within 4 days.
The membrane performance is not affected by the presence of the normal contaminants in the effluent from an actual bioethanol plant (from ICM).
The membrane cost is a significant component of the total capital cost. In the optimum system: (a) at $15/ft2, the membrane accounts for about 32 percent of the total capital cost; (b) at $100/ft2, the membrane accounts for about 75 percent of the capital cost.
During a 5-year period, the total operating cost is the biggest component of the total plant cost even at high membrane cost. For instance, at $15/ft2 of membrane, the operating cost is about 92 percent of the total system cost. Even at $100/ft2 of membrane, the operating cost is still about 80 percent of the total system cost.
The cost of heating is the biggest component of the total operating cost, accounting for about 98 percent of the total operating cost. Therefore, the energy cost is by far the biggest component of the total system cost.
The optimum ethanol concentration feed to the membrane is 90-92 percent. This produces the minimum total system cost.
In a parametric study, increasing the water-ethanol selectivity decreases the system total cost. For instance, (a) increasing the selectivity from 12 to 25 decreases the cost by 23 percent; (b) doubling the selectivity from 25 to 50 decreases the cost by 9 percent; and (c) doubling the selectivity from 50 to 100 decreases the cost by 4 percent. So there are diminishing returns in cost savings of increasing selectivity.
The water permeance has a very small effect on the total system cost. At $15/ft2 of membrane, increasing the water permeance has a negligible effect on the total system cost. At $100/ft2 of membrane, increasing the water permeance from 800 to 2,000 GPU decreases the total system cost by about 8 percent.
Conclusions:
A membrane module with a commercially available microporous hollow fiber support with bundle-end seals using an appropriate epoxy formulation has been developed that is ethanol/water resistant. These membrane modules have tolerated 120oC temperature and 60 psia pressure conditions with no apparent degradation. Experimental work with these membrane modules has determined optimal operating conditions. Long-term stability has been demonstrated.
The ethanol drying system using CMS membranes either in pervaporation mode or vapor permeation mode is the lowest cost technology for relatively small-scale ethanol plants. The proposed technology provides a cost savings of 7-14 percent compared to the conventional drying technology using pressure swing adsorption, depending on plant capacity and system design.
The technology using CMS membranes in the final drying step offers a cost savings of 11-21 percent over a system using PVA membranes, depending on plant capacity and system design.
A 7.6 MMgpy or larger plant using the proposed ethanol drying technology and waste material feedstocks is competitive with a 70 MMgpy plant using the conventional ethanol drying technology and switchgrass feedstock.
This small-scale fuel-grade ethanol drying technology makes possible an optimum distribution of locations and sizes for ethanol plants arranged to minimize feedstock expenses, including transportation costs.
The core market for this technology is the final drying step for shipping and drying fuel-grade ethanol in small plants (10 million gallons). With the expectations of upwards of 35 billion additional gallons per year of ethanol coming on the market based on Presidential and Congressional initiatives and Department of Energy (DOE) estimates in the next 10 years, this is a very large opportunity. The energy savings associated with 35 billion gallons/year is 2.4 Quads, which is a great deal of energy. The CMS membranes also can be used to dry ethanol at most manufacturing sites. This is a huge market in its own right and one that is becoming available with timing consistent with CMS' ability to get product to market.
CMS believes it has a number of competitive advantages, including intellectual property. The company has a number of core patents in place on using the CMS membranes for separations. In addition to these patents in place, CMS is filing numerous patents on its membranes for use in fuel-grade ethanol. These will represent sustainable competitive advantages.
Manufacturing infrastructure is a major advantage of CMS. Because manufacturing infrastructure with other key manufacturers is firmly established, the company can supply this market rapidly and in a relatively straightforward manner. Because CMS can supply it in a timely manner, the company believes it can have the product to customers within 2 years. Also, because the manufacturing structure is established, CMS will not be burdened by risk-oriented capital investments on the front end as it builds the business.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this projectSupplemental Keywords:
Fuel-Grade Ethanol, Membrane Permeation Vapor, Separation, Dehydration Large Core Market, Established Infrastructure, Minimal Investment, Optimal Plant/Feedstock Distribution, Sustainable Industry/Business, Scientific Discipline, RFA, Technology for Sustainable Environment, Sustainable Environment, Environmental Engineering, cellulose biomass, biofuel, alternative energy source, alternative fuel, ethanol
, RFA, Scientific Discipline, Sustainable Industry/Business, Sustainable Environment, Technology for Sustainable Environment, Environmental Engineering, alternative fuel, ethanol, alternative energy source, biofuel, cellulose biomass
SBIR Phase I:
Small-Scale Ethanol Drying | Final ReportThe 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.