J. Mex. Chem. Soc. 2010, 54(4), 198-203 © 2010, Sociedad Química de México ISSN 1870-249X
Optimization of Ethanol Production Process from Cassava Starch by Surface Response
Leticia López Zamora,* José Amir González Calderón, Evangelina Trujillo Vázquez and Eusebio Bolaños Reynoso
Departamento de Posgrado e Investigación, Instituto Tecnológico de Orizaba. Av. Oriente 9 No. 852, Orizaba, Veracruz 94320. México. email@example.com
Received April 26, 2010; accepted August 20, 2010
Abstract. This work shows the study of the optimization process for producing ethanol from cassava starch based on 22 experimental designs with three central points and using statistical software. This methodology was applied to the stage of saccharification of cas- sava starch by acid hydrolysis as well as to the stage of fermentation using Saccharomyces cerevisiae. From the experimental data of acid hydrolysis, we proposed a first-order kinetic model which presented an average error of 1.87 % compared to the quadratic regression obtained. The development of a semi-continuous process showed a 89.84 % conversion of starch initially considered, yielding an ethanol concentration of 49.76 % Alc/vol. Keywords: Cassava starch, acid hydrolysis, yeast fermentation, response surface, ethanol.
Resumen. En este trabajo muestra el estudio del proceso optimiza- ción de obtención de etanol a partir del almidón de yuca, mediante el planteamiento de un diseño 22 con tres puntos centrales y usando un software estadístico para analizar los resultados. Esta metodolo- gía fue aplicada tanto para la etapa de sacarificación del almidón de yuca mediante hidrólisis ácida como para la etapa de fermentación empleando Saccharomyces cerevisiae. A partir de los datos experi- mentales de la hidrólisis ácida, se propone un modelo cinético de pri- mer orden el cual presentó un error promedio del 1.87 % con respecto a la regresión cuadrática obtenida. El desarrollo de un proceso semi- contínuo mostró una conversión del 89.84 % del almidón inicialmente considerado, obteniéndose una concentración final de etanol del 49.76 % Alc/vol. Palabras clave: Almidón yuca, hidrólisis ácida, fermentación levadu- ra, superficie de respuesta, etanol.
The search for new fuels, both from biological and renewable origin, biodegradable, capable of increasing the performance of automobile engines and the need to reduce emission of gas- ses, have contributed to use anhydrous ethanol (AE) as fuel for commercial gasoline additive worldwide [1, 2].
In recent years, Mexico has considered necessary to do structural reforms that allow further development to face the needs of the energy sector. One energy source that is little mentioned in national projects and has demonstrated its feasi- bility in other regions of the world is the production of ethanol . Ethanol can be used in mixtures with fuels for motor vehi- cles. It can increase the octane index; reducing it between 10 and 15% the CO. Ethanol can be mixed with unleaded gasoline between 10 to 25% without difficulty. Ethanol could therefore replace MTBE (methyl tert butyl ether), an oxygenated prod- uct used in Mexico since 1989, although it has reduced CO2 emissions it has proved to be a groundwater pollutant  and has a carcinogenic effect [5, 6].
Ethanol can be produced from a large number of plants, with a variation, according to the agricultural product, of the yield between the fuel consumed and generated in this process. Among the raw materials there are the fruits and vegetables such as sugar cane and beets, cereals (wheat, corn, sorghum, etc), tubers (potatoes, cassava, etc) and in general, materials from lignocellulosic or organic residues.
The growing prosperity with the use of ethanol as an alter- native to fossil fuels, has created that fermentation technology
must care for several variables involved in the production of ethanol from agro-industrial waste (biomass resource, micro- organisms, types of enzymes, immobilization of the microor- ganism, simultaneous saccharification and fermentation and improved technology) to optimize the efficiency of the process [1, 2, 7, 8, 9, 10, 11, 12].
Cassava starch has several characteristics which favor its industrial use, in general, and in particular as a raw mate- rial in ethanol production. Some characteristics of cassava starch are its high purity, neutral flavor, easy swollen, solu- bility, development of high viscosity and low tendency to retrograde compared with other starches such as potato, rice and corn.
Different treatment and pretreatment to improve the split of cassava starch have been studied with the aim of signifi- cantly improve the overall ethanol yield, such as: ultrasonic pretreatment [13, 14], wet oxidation (WO) pretreatment , combined heat treatment and acid hydrolysis , and alkali steeping , inter alia.
Acid hydrolysis is one in which starch is split by a strong acid. The economic feasibility of this procedure depends main- ly on low costs in raw materials, energy and operating and low investment costs. It has been studied  that the hydrolysis consists of three stages: a) degradation of lignocellulosic mate- rial to fermentable sugars, b) fermentation of sugars into etha- nol and c) purification of ethanol.
The aim of this study was to optimize the acid hydrolysis of cassava starch, determining the kinetic model depending on the concentration of starch and the reaction time and their