Progress 07/01/19 to 12/31/20
Outputs
Target Audience:This membrane system would be a part of a controlled atmosphere (CA) system. This would include a room, cargo container, truck, or other system, that requires the removal of ethylene being generated by postharvest fruits and vegetables. Any organization that is concerned with fruit or vegetable spoilage andshelf life would benefit from this technology and the successful commercialization of the results of this project. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?We hire summer interns from University of Delaware, Drexel, and other nearby schools who have worked part-time on this project. We have hired 4 interns this summer (2021). How have the results been disseminated to communities of interest?We have reviewed this product concept with both Air Products (AP) and Prof. Jeff Brecht (Prof. Brecht is post-harvest expert and will be consultant on program. AP, which presently sells CA membranes, has indicatedsupport). Collectively, we have designed the system to place the CMS ethylene selective membrane downstream of the existing O2 selective membranes. This will allow us to operate the CMS ethylene selective membrane at optimal pressure. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
Task 1 - CAF development: Customized Amorphous fluoropolymers (CAF) with sufficient hydrophilic character have been synthesized. These polymers can directly have the needed water permeability or they can be intermediate structures which allow for downstream side chain reactions. These reactions include crosslinking in order to maintain membrane integrity in the water environment. Special interest will be given to polymers with side chains which have terminal functionality such as -CF2SO2F and -CF2COOCH3 which are readily available by copolymerization of PDD with commercially available perfluorovinyl ethers. Hydrolysis of these groups to the corresponding acids or metal salts -CF2SO3Ag and CF2COOAg provided the hydrophilic character for enhanced water flux and required olefin permeabiltiy. The initial sulfonyl fluoride or ester groups can also be reacted with hydrophilic reagents, such as amine-terminated poly(alkylene oxides) which introduces the highly hydrophilic polyether groups as side chains. The functionality in the initial polymers also allows for crosslinking by reaction with, for example, diamines to form sulfonamides or amides, respectively. It is noted the sulfonamide and amide groups introduced by this crosslinking process are stable and highly hydrophilic. Task 2 - Fabricate Target Composite Membranes:Using the polymers from Task 1 we fabricated composite membranes on appropriate porous supports. From our commercial products we have many porous supports to choose from including PVDF, polysulfone, and PAN to name three. We are focusing on PVDF because of its chemical resistance and PAN (polyacrylonitrile) because of ease to fabricate thin film composites. These thin film composites were first evaluated for flux and separation. Only the membranes with high He/N2 selectivity (means no significant defects) can be used for the tests in the next step. Our membrane is a facilitated transport membrane and water is needed to help the silver ion to interact with olefin. A 60+% relative humidity is required to optimize the performance of the membrane.We found CMS72/PVDF membrane has very low gas permeance under dry conditions (<10% humidity). Under humidified condition (>90%), we observed increased gas permeance for all gases. We believe the good solubility of CO2 in water makes CO2 permeance through the CMS72-Ag membrane increases much more than those of other gases under humidified conditions. Task 3 - Initial Testing with Ethylene and Aroma Compounds:CMS developed an analytical method to measure the low concentration (ppm level) ethylene membrane permeation, the test set-up is a1 gallon bottle fitted with 3 inch diameter membrane on top. The test procedure: We first inject a certain amount of ethylene into the bottle (100-1000 ppm) and a few microliters of pentane was also added as a reference chemical. With a humidified sweep air over the top of membrane, we monitored the ethylene and pentane concentration change over the time by GC.Compared with the N2 (9 GPU under humidified condition) and O2 (30 GPU), we can say the CMS membrane has a good ethylene selectivity over air and it can selectively remove ethylene from fruit storage.With a 10% humidity of the surrounding air. The membrane only had a ethylene permeance of 14.4 GPU and pentane permeance of 4.5 GPU. After adding a few drops of water to the bottle, the humidity in the bottle increased from 10% to 60-70%. The ethylene permeance jumped to 271 GPU while pentane permeance (6.9 GPU) did not change much. Task 4- Long Term Testing and Pressure Testing:The CMS72-Ag membrane was evaluated for extensive long-term testing to determine if the promising initial performance was maintained over extended periods of time consistent with a Phase I program. We have seen stable performance of the membrane and no significant permeance or selectivity change after 1-2 months of membrane operations. In those aging tests, we used 180 psig of 50% ethylene and 50% ethane, which is a much harsher condition than fruit ripening test (ppm level ethylene).The aging test data gave us a high confidence that our membrane will have a very stable performance in the fruit storage operations. Task 5. Engineering and Economic Evaluation of Ethylene Removal from Fruit Shipping Containers: The results of the economic analysis showthe cost of the ethylene removal system per unit mass of apples transported is very low, ranging from a high of 1.33 cents/lb to a low of 0.38 cents/lb, depending on ethylene concentration and membrane performance. (These costs are calculated from the total annual cost, which includes the amortized capital cost of the system.) Maintaining the ethylene concentration in the container at 1 ppm costs about twice as much as maintaining it at 3 ppm. At the expected ethylene permeance of the membrane, 590 GPU, the costs per unit mass of apples shipped is 0.93 cents/lb and 0.44 cents/lb at 1 ppm and 3 ppm ethylene maintenance concentrations, respectively. If the ethylene permeance is greater than anticipated, 1000 GPU, the cost per unit mass of apples is reduced by about 19% at 1 ppm ethylene and 14% at 3 ppm ethylene to 0.75 cents/lb and 0.38 cents/lb, respectively. If the ethylene permeance is lower than anticipated, 300 GPU, the costs per unit mass of apples shipped is 1.33 cents/lb and 0.58 cents/lb at 1 ppm and 3 ppm ethylene maintenance concentrations, respectively. Apples typically sell for about $1.50 per pound. In the worst case, the ethylene removal system costs less than 1% of the selling price. At the expected membrane performance, the cost is 0.3% to 0.6% of the selling price of apples, depending on the ethylene maintenance concentration chosen. Note: membrane costs can be less than $1000-$2000 and annual operating costs can be less than $1,000 for the system. Based on reviewers comments we discussed this analysis in detail with Prof. Brecht and AP. Prof. Brecht indicated different apple varieties had ethylene production rates that varied quite a bit from 0.05-0.5 µL/Kg hr (i.e., 10-fold higher than my calculations) and could rise to 100 µL/Kg hr in storage. This leads to the question, can FTM remove enough ethylene to prevent rise in ethylene concentration? This will be resolved in Phase II. Based on discussions with AP, we have the option of operating the CMS FTM at either high pressure (e.g., 60 psig) or low pressure (e.g., 5 psig). High pressure will have significantly higher ethylene removal rates, but also higher loss of CA (i.e., N2). By contrast, operating at low pressure will have both lower ethylene removal and lower loss of CA.
Publications
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Progress 07/01/19 to 06/30/20
Outputs
Target Audience: The enhanced value that we seek will help to ensure that nutritious fruits and vegetables are delivered to remote geographic regions with a reduced loss in food quality. The technology has potential application for cargo holds used to ship produce long distances. Removal of ethylene extends produce storage life by reducing the rate of quality deterioration.The US military has found that ethylene control improves the quality of mixed loads of fruits and vegetables shipped overseas in marine containers.? Therefore, removing ethylene can result in higher product quality under any postharvest storage or transport scenario. Also, a cost-effective strategy for ethylene control would be of great value. Market focus would be for postharvest produce handling. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?
Nothing Reported
How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals??Task 4- Long Term Testing and Pressure Testing The membrane composites from Task 3 that provide the most promising performance is being evaluated for extensive long term testing to determine if the promising initial performance is maintained over extended periods of time consistent with a Phase I program. So far we have seen relatively stable performance of the membrane and no significant permeance or selectivity change after a few weeks of membrane operations. Professor Jeff Brecht from University of Florida is working with us and helping to evaluate the long term performance of the membrane and the fruit flavor membrane sorption test. Task 5. Engineering and Economic Evaluation T The basic data from the above tasks, we will conduct an engineering and economic evaluation of the Phase I results. Our goal is to show the CMS membrane system will be not only efficient in selective ethylene removal but also cost effective for the fruit storage. Task 6, Contingency In this contingency task, we will focus on significantly enhancing membrane flux while minimizing the loss in robustness. The greater flux will reduce the membrane area required and therefore reduce the system size and costs. We will introduce known fabrication techniques to make thinner / higher flux membranes. Techniques could include, (1) blocking pores with water during composite fabrication, (2) Using gutter layers, or (3) Casting from diluter solutions, to name a few. Also if membrane life is projected to be less than 2-3 yrs we will evaluate possible regeneration techniques.
Impacts
What was accomplished under these goals?
Progress towards Original Work Plan Phase I focus is to demonstrate feasibility. Therefore, focus will be to demonstrate needed ethylene permeance, very low aromatic compounds permeance, high selectivity and good projected economics. Phase II will build prototypes plus resolve any remaining Phase I scale up and commercialization issues. Work Plan Task 1 - CAF development -- 100% Complete Customized Amorphous Fluoropolymers (CAF) with sufficient hydrophilic character have been synthesized. These polymers can directly have the needed water permeability or they can be intermediate structures which allow for downstream side chain reactions. These reactions include crosslinking in order to maintain membrane integrity in the water environment. Special interest will be given to polymers with side chains which have terminal functionality which are readily available by copolymerization of PDD with commercially available perfluorovinyl ethers. The functionality in the initial polymers also allows for crosslinking by reaction with, for example, diamines to form sulfonamides or amides, respectively. It is noted the sulfonamide and amide groups introduced by this crosslinking process are stable and highly hydrophilic. In this task, we prepared 2 to 3 copolymers discussed in the above paragraph with polar comonomer content ranging from about 30 to 40 mole percent for treatment as described above. Task 2 - Fabricate Target Composite Membranes - 100% Complete Using the polymers from Task 1 we fabricated composite membranes on appropriate porous supports. From our commercial products we have many porous supports to choose from including PVDF, polysulfone, and PAN to name three. We are focusing on PVDF because of its chemical resistance and PAN (polyacrylonitrile) because of ease to fabricate thin film composites. These thin film composites were first evaluated for flux and separation. Only the membranes with high He/N2 selectivity (means no significant defects) can be used for the tests in the next step. Our membrane is a facilitated transport membrane and water is needed to help the silver ion to interact with olefin. A 60+% relative humidity is required to optimize the performance of the membrane. Task 3 - Initial Testing with Ethylene and Aroma Compounds - 100 % Complete We developed an analytical method to measure the low concentration (ppm level) ethylene membrane permeation, the test set-up: (1 gallon bottle fitted with membrane on top. white top: CMS membrane, pink top: thick plastic film). The test procedure: First we inject some ethylene into the bottle (100-1000ppm) and a few microliters of pentane was also added as a surrogate chemical for aroma compounds. Then with a humidified sweep air over the top of membrane, we monitored the ethylene and pentane concentration change over the time. The reason that pentane is chosen because most of aroma compounds have similar or higher molecular weight than pentane and do not have double bonds, so most of aroma compounds will have same or lower permeance than pentane. We did the test in January and the relative humidity in house is very low (10-20%). We had to use humidified air to sweep the membrane so the humidity of the air above the membrane has more than 80%. The concentration of ethylene and pentane was monitored by GC and we obtained the concentration/time change. Our calculation gave ethylene permeance 497 GPU and pentane permeance 12 GPU. Selectivity of ethylene/pentane >40. The initial data showed the CMS membrane can remove ethylene highly selectively over other aroma compounds. Task 4- Long Term Testing and Pressure Testing - 30 % Complete The membrane composites from Task 3 that provide the most promising performance is being evaluated for extensive long term testing to determine if the promising initial performance is maintained over extended periods of time consistent with a Phase I program. So far, we have seen relatively stable performance of the membrane and no significant permeance or selectivity change after a few weeks of membrane operations. Professor Jeff Brecht from University of Florida is working with us and helping to evaluate the long term performance of the membrane and the fruit flavor membrane sorption test. Task 5. Engineering and Economic Evaluation 0% complete Using the basic data from the above tasks, we will conduct an engineering and economic evaluation of the Phase I results. Our goal is to show the CMS membrane system will be not only efficient in selective ethylene removal but also cost effective for the fruit storage. Task 6, Contingency 0% complete In this contingency task, we will focus on significantly enhancing membrane flux while minimizing the loss in robustness. The greater flux will reduce the membrane area required and therefore reduce the system size and costs. We will introduce known fabrication techniques to make thinner / higher flux membranes. Techniques could include, (1) blocking pores with water during composite fabrication, (2) Using gutter layers, or (3) Casting from diluter solutions, to name a few. Also, if membrane life is projected to be less than 2-3 yrs we will evaluate possible regeneration techniques.
Publications
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