Artificial Photosynthesis (Riley Hutson)
Artificial photosynthesis is a chemical process, similar to the natural photosynthesis process performed in nature, with the goal of creating “solar fuels” or chemical fuels produced either directly or indirectly from solar energy. Currently, this process is done through the usage of water and carbon dioxide as the reactants with solar energy input to form glucose and oxygen for products. From there, the glucose is fermented over a multi-step process to form ethanol. First, any cellulose with the sugar must be broken down. Then the fermented product has to be distilled, resulting in an ethanol-water mixture that is about 4% water. Lastly the water from the mixture is absorbed with molecular sieves; allowing for pure ethanol to be extracted and used in a variety of ways for fuel.
While ethanol can certainly be used as fuel for an internal combustion engine, ethanol is primarily used in combination with gasoline for ethanol grade vehicle fuel. Most standard gasoline engine vehicles can use E10 or 10% ethanol gas with no issues. However if one wants to use higher grade E85 gas one would have to either buy a flex fuel vehicle or modify their existing engine. Before using such fuel, it is important to look at the difference in energy content between ethanol and gasoline when analyzing fuel cost, consumption, and driving distance.
For instance, the energy content of ethanol is 23.5 MJ/L whereas the energy content of gasoline is 34.8 MJ/L. One can use these values to quantitatively compare the tank sizes of ethanol and gasoline that have the same energy content. By taking the gas tank volume and multiplying it by the energy content of gas you can find the gas tank size. From there you can divide the tank size by the energy content of ethanol to find the tank size of ethanol equivalent to the total energy of the gas tank. If needed, you can then multiply the ethanol volume by its density to find the mass of ethanol in the tank as well. This process would obviously be usable when comparing any other similar solar fuel to gasoline as well.
On top of the difference in energy content between the gasoline and ethanol, there are many other setbacks for artificial photosynthesis. One of the larger setbacks of photosynthesis is that the process of converting CO2 to complete photosynthesis is a time-consuming process with six separate chemical steps with no catalyst available right now that can convert the CO2 efficiently. Pairing with this fact, currently there is not a way to capture and use CO2 directly from the atmosphere in order to make the process carbon neutral. Future technologies will have to be developed in order for such capture to be possible. However those technologies also look far off as the Joint Center for Artificial Photosynthesis, the primary research group in the field, recently had its funding cut and its focus shifted towards other goals thus decreasing its research in the area.
So while there is a lot of potential for solar fuels and artificial photosynthesis, current technology limitations prevent the efficiency and resourcefulness of the process as a whole and make it less practical than other renewable energy sources in the current time.
References
"Artificial Photosynthesis: Creating Fuel from Sunlight."Artificial Photosynthesis: Creating Fuel from Sunlight. Monash University, 10 Nov. 2014. Web. 16 Oct. 2016.
Bullis, Kevin. "Artificial Photosynthesis Effort Takes Root."MIT Technology Review. MIT, 22 Oct. 2012. Web. 16 Oct. 2016.
Bullis, Kevin. "Artificial Photosynthesis Takes a Step Forward."MIT Technology Review. MIT, 09 Mar. 2015. Web. 16 Oct. 2016.
Dunlap, Richard. "Biomass Energy."Sustainable Energy. 395-403. Print.
Martin, Richard. "The Road to Solar Fuels Hits a Speed Bump."MIT Technology Review. MIT, 16 June 2016. Web. 16 Oct. 2016.