Progress 05/15/04 to 12/31/04
Outputs
Over the course of this study, we designed, built, and tested a flow cell for demonstration of the electrochemical ethylene detection approach. This electrochemical approach relies on catalytic reaction of the ethylene present in air, which reacts with our catalytic, nano-porous, gold/nafion surface to release electrical energy, which is then measured in the form of current. This reaction takes place at a specific voltage potential that must be maintained constant during current measurements. The level of current generated by the reaction is proportional to the concentration of ethylene present in the air. Our efforts during this project were focused on demonstrating ppb-level detection, as well as characterizing the requirements of the flow cell and the catalyst. In the process of catalyst preparation, the chemistry of the preparation process was characterized and explored in order to be able to put together a list of important factors, and relationships between these
factors and the catalyst sensitivity to ethylene. Although each of these factors was not fully explored during this project, we gained crucial insight into how to assess them more effectively in the future. Even without the optimization of the catalyst our detection was more than adequate. Our detection level went down to 100 ppb with high confidence and down to 25 ppb with somewhat lower confidence. This lower confidence can be attributed to flow measurement uncertainty rather than electrochemical measurement uncertainty and we believe that with the proper test apparatus modifications higher confidence will be attained for 25 ppb and even lower concentrations. We discovered flow effects on current at low flow velocities which become insignificant at a threshold flow velocity. We also discovered that at sufficient flow velocities a very linear relationship can be found between ethylene concentration and current, again down to 100 ppb with high confidence and 25 ppb with lower
confidence. Modeling of the electrochemical cell was also performed which included flow properties, mass transport properties, and limited catalyst properties. The modeling results went well with the experimentally obtained results and provide great insight into the most efficient configuration for hand held ethylene sensors with minimal cost, while maintaining excellent sensitivity. Market research was also carried out in order to assess the needs of our target markets which suggested that additional features, such as humidity sensing, temperature sensing, and data logging be added to our hand held package. Such features were investigated and found to be easy to incorporate into a hand held device with minimal cost impact considering the increased functionality. Overall, we found our initial ethylene sensor to be a success and learned enough about the important parameters of the cell design, both from theoretical and experimental results, to be able to design a prototype hand held
device that is inexpensive and has high sensitivity as well as additional features.
Impacts
Year round availability of high quality fresh fruits, vegetables and flowers depends on a vast infrastructure of refrigerated transportation and storage facilities. The natural process of ripening and spoilage of fruits, vegetables and flowers releases ethylene gas. As a ripening hormone, ethylene further accelerates the ripening and spoilage process at concentrations greater than 0.1 ppm. Therefore, the measurement and control of ethylene in storage and processing is a prerequisite to providing ultimate quality to the consumer and in achieving desirable economic benefits to the producer, distributor and retailer. Commercially available devices for monitoring airborne ethylene concentrations below 1 ppm are very costly and oversized, limiting their commercial usefulness. A miniature and inexpensive device would promote a wider use of ethylene detection for local monitoring and control, minimizing waste and cost of that waste due to spoilage and premature ripening. Not
only can our ethylene detection device have great impact on the prevention of spoilage, but it can also have significant impact on the controlled ripening of many fruits by allowing for well controlled ethylene levels in ripening rooms. Due to its low cost, high sensitivity, and functionality, our sensor has the potential to create a major influence for many areas of agriculture, will make ethylene detection technology readily available to both small and large companies, and greatly decrease the waste of spoiled fruits, vegetables and flowers in the growing, storage and shipping processes.
Publications
- No publications reported this period
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