(580f) Technoeconomic Study of AB Synthesis for Biobutanol Production

Over the last 15 years there has been an important effort towards climate change mitigation. Among the different actions, one of the more challenging is reducing emissions in the transport sector. Ethanol and biodiesel, from different biomass sources, represent the typical alternatives to substitute crude based gasoline and diesel nowadays. However, there are other options such as FT fuels (Martín & Grossmann, 2011), glycerol ethers (Martín & Grossmann, 2014) or biobutanol. Biobutanol is considered an advanced fuel. It has similar properties to gasoline, it can be directly used in gasoline engines without modification, and it has higher energy density and boiling point than ethanol reducing evaporation losses. Moreover, it is less hydroscopic than ethanol (Durre, 2007).

The ethical issues involving first generation biofuels have led to focus on obtaining biofuels from agricultural residues. Corn being the major crop in the world, results in the fact that corn stover is widely available. However, in the case of biobutanol, the yield has been low due to the fact that together with biobutanol, ethanol and acetone are typically obtained. Thus, this work is divided in two parts: the first part is devoted to the experimental evaluation of the lignocellulosic biomass degradation. In the second one, a technoeconomic study of a new production process is described. The novelty of this work relies on the scale up of AB fermentations, that does not produce ethanol, (Qureshi et al., 1999). In addition, in-situ recovery techniques such as evaporation are also included at the process to make it economically competitive with conventional fuels and bioethanol.

In the first stage of the work, comprehensive evaluation of the experimental conditions to break down switchgrass and corn stover from Castille and Leon region (Spain) has been performed. The study considers both pretreatment and hydrolysis. With regards to pretreatment, several physio-chemical techniques such as acid (H2SO4), alkali (using KOH or NH4OH), ultrasounds processing, surfactants or organic solvents are tested. With regard to hydrolysis, various enzyme cocktails were used. It turns out that corn stover reaches the highest yield, 677.00 mg of sugars by gram of biomass, when it is pretreated using a diluted sulfuric acid solution 0.5% v/v, autoclaving the mixture during 90 min at 121 ºC with no sonication stage. The hydrolysis method is set up at 50 ºC and 150 rpm with a solid loading of 2.5 % w/v and a ratio of enzymes/biomass of 400 and 440 µl/g of NS50013 (cellulose complex) and NS50010 (β-glucosidase cocktail) respectively. The sugar recovery obtained is competitive with current best available technologies i.e. (Sundaram and Muthykumarappan, 2016).

In a second stage, we synthesize a process for the production of biobutanol from corn stover including the use of novel technologies such as pervaporation to improve the yield from biomass and reducing the by-products by means of AB fermentation. The processes consists of four sections, pretreatment, hydrolysis, fermentation-pervaporation system and product purification. We use the experimental results to determine the yield of the pretreatment and hydrolysis. A hybrid simulation using EXCEL to develop black box kind of models for the experimentally validated units and ChemCAD has been performed to evaluate the technoeconomic feasibility of this process.

The results show an investment of 186 MM� and a butanol production cost of 1.09 �/kg for a 27 kt/y plant. The yield to butanol is 0.21 kg/kg of biomass resulting, altogether, in a fuel closer to become competitive versus second generation bioethanol and fossil based fuels in terms of yield and cost.

References

Durre, Biobutanol: an attractive biofuel Biotech. J., 2 (2007), pp. 1525â??15234

M.S. Madihah, A.B. Ariff, K.M. Sahaid, A.A. Suraini, M.I.A. Karim (2001) Direct fermentation of gelatinized sago starch to acetoneâ??butanolâ??ethanol by Clostridium acetobutylicum. World J. Microbiol. Biotechnol. 17 (2001), pp. 567â??576

Martín, M., Grossmann, I.E. (2011) Process optimization of FT- Diesel production from biomass. Accepted Ind. Eng. Chem Res, 50 (23),13485â??13499

Martín, M.; Grossmann, I.E. (2014) Simultaneous dynamic optimization and heat integration for the co-production of diesel substitutes: Biodiesel (FAME & FAEE) and glycerol ethers from algae oil. Ind. Eng. Chem. Res. 53, 11371-11383

Qureshi, N., Hans P. Blaschek. Production of Acetone Butanol Ethanol (ABE) by a Hyper-Producing mutant strain of Clostridium beijerinckii BA101 and recovery by Pervaporation. Biotechnol.Prog. 1999, 15, 594-602.

Sundaram, V., Muthukumarappan. K., Influence of AFEXTM pretreated corn stover and switchgrass blending on the compaction characteristics and sugar yields of the pellets. Industrial Crops and Products 83 (2016) 537â??544.