Biorefinery approach for production of biofuels from energycane and sweet sorghum

Daira Aragon, Attaway, Denise, Ensley, Carlen  |  3/7/2014 9:48:53 PM

Daira Aragon Mena

Figure 1a. Sugars Model for extraction plant. (Click on image to enlarge)

Figure 1b. Sugars Model for co-generation plant. (Click on image to enlarge)

The need for decreasing greenhouse gas emissions, the desire for energy independence and the exhaustion of fossil resources have encouraged worldwide interest in fuels and chemicals obtained from renewable sources. In the United States, for example, 36 billion gallons per year of renewable fuels are to be produced by 2022. Of this 36 billion gallons, 16 billion gallons must originate from cellulosic material.

Biomass is currently the only renewable source for production of liquid substitutes of petroleum-based fuels for transportation. However, first experiences with biomass conversion to liquid fuels have not resulted in cost-effective solutions. Alternative products, such as biobased chemicals and power generation, must be considered to make the integrated biorefinery concept more viable. Regional scenarios that take advantage of specific growth areas, types of feedstock and available infrastructure must be considered. Energycane (hybrid of commercial sugarcane, Saccharum officinarum, and wild sugar canes) and sweet sorghum (Sorghum bicolor L. Moench) are potential crops for conversion into fuels and chemicals because of their low agricultural input requirements, potentially high fiber content and processing similarities with established sugarcane crops.

A conceptual approach to a biorefinery producing fuels and chemicals from these crops is being developed. The front end of the facility processes 10,000 tons per day of feedstock to extract convertible sugars and concentrate them into storable syrups. The latter can be processed into gasoline, jet fuel and isoprene using proprietary technologies. The fiber remaining after extraction, called bagasse, is used in boilers of the front-end plant for steam and power generation and, possibly, to produce additional second-generation sugars by pretreatment and hydrolysis in the lignocellulosic conversion plant. The front-end plant and the lignocellulosic conversion plant were modeled using Sugars software (Figures 1a and 1b).

Seven energycane varieties (Ho 01-007, Ho 02-147, Ho 02-113, Ho 02-144, HoCP 72-114, Ho 06-9001 and Ho 06-9002) were evaluated for the generation of biofuels, chemicals and power. Compositional data obtained at the Audubon Sugar Institute was used in the model to determine the potential amount of electricity for export and the amount of sugars that can be produced from each variety. The energycane varieties Ho 01-007 and Ho 02-113 are most promising for sugar production, with 157 kg and 155 kg of fermentable sugars per ton of cane, corresponding to 91 and 90 liters of ethanol per ton of cane. Varieties Ho 06-9001 and Ho 06-9002 are most promising for power generation, producing 286 and 278 kilowatt-hours per ton of cane.

Sweet sorghum (Durasweet, 120-day hybrid) can produce up to 133 kg of total fermentable sugar per ton. Power generation up to 208 kilowatt-hours per ton is possible.

These results show that sweet sorghum and energycane may complement Louisiana sugar mills so they could supply biorefineries with sugar syrups, biomass and/or power for an extended season.

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