A Technology for Saving Energy in Ethanol Production
May. 10 de 2012
By: Ángela María Betancurt Jaramillo, Unimedios
Sugarcane, molasses, corn, wheat, rye and wood are some of the raw materials used to make ethanol, a chemical compound also known as ethyl alcohol, present in diverse fermented beverages, particularly wine and beer, and with wide–ranging applications in the chemical, pharmaceutical and food industries.
As a biofuel, ethanol is quite competitive with oil and has made it possible to decrease dependence on that hydrocarbon. One of its advantages is that it is derived from vegetable sources, which reduces its impact on the environment.
Ethanol is obtained through the fermentation of raw materials (crop products), as follows: the solution of sugars and nutrients from the crop products nourishes a type of yeast, which transforms the mixture into ethanol. This mixture, which is the product of the fermentation, goes through a process of separation in distillation columns to obtain concentrated ethanol, followed by a dehydration phase to take out any remaining water, which produces ethanol suitable for fuel.
Although the conventional system has been able to satisfy current ethanol demand in Colombia –estimated at 1.5 million liters per day for mixture with gasoline–, its manufacture requires the consumption of huge amounts of energy and water while generating vinasse, which is a byproduct of distillation that is highly contaminating for the environment.
"In this country, ethanol is seen as a short and long-term solution for fuels, which is why its industrial production has been encouraged. However, new technologies are needed to reduce energy consumption and production costs", according to Mario Andrés Noriega Valencia, from the Research Group on the Application of New Technologies (Grupo de Investigación en Aplicación de Nuevas Tecnologías - Giant) at the Universidad Nacional de Colombia in Manizales.
In search of a solution to these problems, the Giant group designed a fermentation process using membrane technology (tubular filters), that makes it possible to capture and selectively remove the ethanol while retaining the flow of untransformed sugars, water, salts and organic material.
To reach their goal, the members of the Giant group made membranes that remove five times more ethanol than the commercially available ones, thereby decreasing the investment of capital in the process.
Researcher Miguel Ángel Gómez García explains that "economic studies show that one of the problems facing industrial implementation of membrane technology in this country is the cost of the filters. The ones that we make locally are more economical and have a removal velocity and selectivity regarding the ethanol that makes them attractive for this type of process".
In this way, the new system for obtaining ethanol begins with a concentrated sugar solution that, thanks to the presence of the yeast, is transformed into ethanol, which is then simultaneously removed by the membranes along with a water fraction.
The mixture that has been removed is obtained with a 30% concentration of ethanol during the fermentation stage, whereas in the conventional process this concentration is just 7%. There is therefore a 35% savings in energy consumption during the purification process.
This occurs because the membranes, in contrast to other distillation processes, make it possible to achieve high energy efficiencies that considerably reduce consumption.
"The amount of membrane that must be used in this new fermentation system is approximately 1/5 as much as in the conventional system, thus reducing operational and capital costs. For example, to produce 100,000 liters per day requires approximately 35,000 m2 of the commercial membranes, whereas using those developed at the UN, only 7,000 m2 are needed" affirms the professor and director of the project at the UN in Manizales, Javier Fontalvo Alzate.
In addition to being a continuous fermentation process (with no time lapses in its manufacture), it provides greater control over the manufacture of the alcohol. The scale of the size of the fermentation equipment is smaller, so that it is easier to transport. The process makes it possible to produce four times more ethanol with less energy, which is reflected in 2.5 times more alcohol. Also, because less water is removed during distillation, there is a corresponding decrease in the volume of vinasse, another environmentally favorable aspect.
The filters have a useful life of approximately 4 years, and their wear does not imply changing them but rather making adjustments to the process.
While the savings in production costs are significant, both because of the characteristics of the membranes as well as the savings in energy consumption and low environmental impact of the process, the cost of implementation for a company interested in the system is also attractive.