Ethanol from Sorghum
The stem juice of sweet sorghum is rich in fermentative sugar and is a desirable fermentation material for the production of ethanol. Primarily grown for silage, forage and sugar production, sorghum is often cited as a promising crop because it costs less to grow than corn and can thrive in conditions that are less than ideal for corn production. In North American, sweet sorghum has been traditionally grown for the syrup or “molasses” made from it. Ethanol production from sweet sorghum is largely still in trial stages in North America but is more widely done in China and India. One of the main challenges is that the sugar has to be fermented immediately. Special harvesting equipment has been designed to squeeze the sorghum stems on the field.
Conversion to Ethanol
This first section calculates raw cane juice into ethanol.
- 1 gallon of juice = 3.785 liters.
- 1 liter @ 18 brix = 180 g sugar.
- 80 g sugar -> 92 g EtOH + 88 g CO2 (theoretical yield).
- 92 g EtOH/720 g/l ethanol = .128 liters of ethanol per liter of juice.
- .128 l EtOH x 3.785 l/gal = .484 liters of EtOH per gallon of juice / 3.785.
- 1 gallon of sorghum juice produces .128 gallons of ethanol.
- 7.8125 gallons of sorghum juice produce 1 gallon of ethanol.
The next section calculates the necessary acreage planted in sweet sorghum (central Florida application) to provide feedstock for an ethanol plant.
- A gallon of sorghum juice weighs the same as a gallon of water 8.39 lbs + the weight of the sugar dissolved in the gallon -- ~10 pounds for a 18 brix solution.
- In two years of field trials, the lowest yields per acre, per harvest have been ~30 green (wet) tons per acre.
Lab analysis of the sweet sorghum reflects (conservatively) a moisture level of 70%.
Links
- Sweet Sorghum Ethanol Association
- economic calculations: Sorganol