(285e) Harnessing Pressure-Tunable Properties of Liquid Propane for Extraction of Corn Kernel Oil. | AIChE

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(285e) Harnessing Pressure-Tunable Properties of Liquid Propane for Extraction of Corn Kernel Oil.

Authors 

Kothinti, P. - Presenter
Allgeier, A., University of Kansas
Binder, T., University of Kansas
Camarda, K., University of Kansas
Subramaniam, B., University of Kansas
Compared to conventional organic solvents such as hexane and ethanol, condensed propane offers pressure-tunable density and transport properties for enhancing extraction. For example, liquid-like density and transport properties in between that of a liquid and a gas can be realized in liquid propane. These facilitate selective extraction of ingredients from porous matrices such as oils from plant matter at relatively mild processing pressures (few tens of bars) and temperatures (<90°C). Further, the extracted oil can be separated from the oils-laden propane by simple depressurization to isolate virtually solvent-free oils. The released propane can be recycled. This study compares propane extraction of corn kernel oil to extractions by either ethanol or hexane.

Ethanol production from corn has evolved over decades to improve efficiency and generation of valuable coproducts. Corn oil for human consumption is not currently generated from ethanol manufacturing processes (dry mills). Instead, lower quality corn oil is extracted for either animal nutrition as a component of the distiller’s dried grain and soluble (DDGS) or conversion to biodiesel. Efficiently extracting corn oil before saccharification and fermentation as shown in Figure 1 will offer enhanced value if the oil can be sold for human consumption.

Corn kernel is known to contain around 5% of corn oil. Oil yields from ground corn using either ethanol or hexane as a solvent in a glass round bottom vessel (55°C) were estimated to be 4.8 ± 0.3 g of oil per 100 g corn and 3.12 ± 0.2 g oil / 100 g corn, respectively. The hexane yield is limited by mass transport and yields as high as 5 wt.% relative to corn mass are possible. Using a 150 mL pressure reactor (Parr reactor), the propane extraction process (~20 bar, 55°C) yielded 2.76 wt.% oil relative to corn mass. This is a promising outcome given propane’s lower density (0.493 g/cc at 55C and 23 bar) compared to ethanol (0.789 g/cc). It should be possible to further increase the oil yield from the propane-based extraction by tuning the pressure and temperature.

Using the initial experimental data, we conducted techno-economic analysis of corn kernel oil extraction for a 100-million-gallon-per-year ethanol plant, comparing propane extraction to conventional solvent extraction. Interestingly, the total capital costs (~$2.2MM USD) did not differ by more than 5% among the options, but the operating expenses for propane ($235.6MM/year) were 11% lower than for ethanol and 33% lower compared to hexane. Raw material costs, heavily influenced by corn prices and solvent consumption, dominate operating expenses. A sensitivity analysis indicates that solvent recycling efficiency has a significant impact on overall revenue and profit, with propane reaching breakeven at 97% recycling efficiency. The utilities were estimated to be only 0.4-1% of the total operating expenses. Cooling water and steam costs dominated the total utility costs by 93-95%, whereas electricity accounted for only 5-7% of the total utility costs. The study suggests opportunities for further development, including improving volumetric productivity and yield, accessing cost-effective feedstocks, and demonstrating product acceptance. From a fundamental perspective, determination of internal mass transfer coefficients as a function of propane pressure is targeted, along with the influence of residual water content upon these mass transfer coefficients.

Topics 

Extraction
Process Design & Development
Food (Sustainability & Environment)

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