Evaluation of Sweet Sorghum and Sorghum × Sudangrass Hybrids as Feedstocks for Ethanol Production

Abstract

Field studies were conducted at the USDA-ARS Sugarcane Research Laboratory in southeast Louisiana to evaluate the ethanol yield potential of five sweet sorghums (Dale, M81-E, Rio, Theis, and Topper) and two nonflowering sorghum × sudangrass forage hybrids (MMR 333/27 and MMR 333/47). The sorghums were planted in the spring and harvested at 85, 101, 119, and 138 days after planting (DAP). Theoretical sugar-based ethanol yield increased for the sweet sorghums (except Rio) from 85 through 119 days, but did not significantly increase further at 138 days. The forage sorghums did not show a similar increase, though the theoretical sugar-based ethanol yield of MMR 333/47 at 138 DAP was greater than at 85 DAP. Conversely, theoretical fiber-based ethanol yields increased two-fold in the two forage sorghums from 85 to 138 DAP; a significant increase in fiber-based ethanol yield was not observed in any of the sweet sorghums over the same period. At 138 DAP, sugar-based ethanol yield of Theis (6,060 L ha −1 ), was greater than that of Rio or either of the two forage hybrids. Fiber-based ethanol yield of MMR 333/ 47 (8,860 L ha −1 ) was greater than that of any other variety in the test. Theoretical ethanol yield from hexose sugar and fiber components averaged across varieties was 6,500, 7,720, 9,100, and 10,810 L ha −1 at 85, 101, 119 and 138 DAP, respectively. As a complementary crop for Louisiana's sugarcane growers, sorghum would need to be harvested not later than 120 DAP so as to not interfere with the planting of sugarcane in these fields. Both Theis and MMR 333/47 produced greater than 11,000 L ha −1 combined theoretical ethanol at 119 DAP, Theis, equally from sugar and fiber, MMR 333/47 about two-thirds from fiber. Choice of sorghum type would depend on the conversion process(s) being used at the biorefinery.

Evaluation of Public Sweet Sorghum A-Lines for Use in Hybrid Production

“…Estimated ethanol yields for each fraction (grain, juice, and fiber) were calculated by multiplying grain, soluble solids in the juice, and bagasse by conversion factors: ethanol yield from grain 0 grain yield/2.40 [26], ethanol yield from juice 0 soluble solids (assumed to be hexose sugars)/ 1.70 [5], ethanol yield from fiber 0 fiber yield/2.65 [5]. All estimated ethanol yields were based on the theoretical conversion to ethanol, including an 80 % estimated conversion efficiency [27].…”

“…To date, most research supporting the potential commercialization of sweet sorghum has utilized open-pollinated varieties such as 'Dale,' 'Della,' 'M81-E,' 'Rio,' 'Theis,' and 'Topper' [4,5]. Obtaining adequate seed to support relatively small-scale research efforts has at times proven difficult because these tall varieties are prone to lodging and not amenable to mechanical harvest.…”

Review of Sorghum Production Practices: Applications for Bioenergy

“…While sweet sorghum can give sugar yields comparable to sugar cane, it is not used for refined sugar production because its high sugar content interferes with sucrose crystallization and hastens the inversion of sucrose to glucose and fructose (Tew et al, 2008).…”

“…[In other parts of the world, replanting may occur less frequently, every 7+ years.] In the continental United States, sugar cane fields are replanted in Louisiana from August through October, usually in September (Tew et al, 2008) and in Florida from late August through January (Baucum et al, 2006). Part of existing sugar cane production fields are used to take vegetative material and replant fields.…”

High-Throughput Profiling of the Fiber and Sugar Composition of Sugarcane Biomass

“…Combination of the juice characterization, provided by HPLC, and fiber characterization, provided by NIR spectroscopy, gives a comprehensive profile of all phenotypic factors contributing to the total biomass for genetic studies. A complete data of sugar and fiber content in the biomass across a given population would allow to estimate the theoretical ethanol yield, and hence, the potential for biofuel production, as illustrated in [25].…”