Tese
Produção biotecnólogica de ácido succínico a partir de casca de arroz
Fecha
2013-12-16Registro en:
BEVILAQUA, Daiane Balconi. Biotecnological production of succinic acid from rice husks. 2013. 124 f. Tese (Doutorado em Química) - Universidade Federal de Santa Maria, Santa Maria, 2013.
Autor
Bevilaqua, Daiane Balconi
Institución
Resumen
Rice husk is a subproduct of the food industry, rich in carbohydrates, which can be partially
fractionated and converted into fermentable sugars. In this work, it was investigated the best
conditions for the conversion of the residual biomass, rice husks, into succinic acid, an
important start molecule for the synthesis of the chemo-pharmaceutical industry.
With the goal of the separation of lignin and transformation of cellulose and hemicellulose
into sugars, the rice husks were submitted, initially, to acid hydrolysis, in autoclave and in
pressurized polytetrafluoroethylene reactor. The hydrolysis conditions were optimized by
factorial design for the pressurized acid hydrolysis; temperature, time and acid catalyst
concentration (HCl or H2SO4) were evaluated. For the acid hydrolysis in autoclave, it was
optimized the ratio rice husks mass: acid volume, time and concentration of HCl or H2SO4.
It was observed that the sugar production by using autoclave was lower than by the
pressurized hydrolysis system, needing further concentration of the hydrolysate for the
subsequent fermentation step. The best results were obtained with the polytetrafluoroethylene
reactor, by 59 bar, with HCl 0,26 mol L-1, at 175°C and reaction time of 46 min, yielding 19.0
g L- 1 of glucose and 3.01 g L- 1 of xylose.
The efficiency of different detoxification methods of the hydrolyzed rice husk were evaluated;
the combined method of pH adjustment plus adsorption on active carbon was the most
effective by eliminating inhibitors, without appreciable reduction of the sugar concentration.
The detoxified hydrolysate was sterilized and adjusted at pH 7 and fermented with A.
succinogenes at 37 ° C, in anaerobic medium, occurring the conversion of the two main
monosaccharides, glucose and xylose, into succinic acid.
The nutrient concentration and the agitation rate of the medium were also optimized by
factorial design. As a result, after 54 h of static fermentation, the hydrolysate was
supplemented with 8.40 g L-1 yeast extract and 1.40 g L -1 of NaHCO3, to yield 59.9% succinic acid. Almost all of the sugar at this time was consumed and converted to succinic
acid; at the same time, acetic and formic acid are formed, but, in low concentrations related to
the production of succinic acid, not compromising the yield of the process.
For the succinic acid extraction and purification, the fermentate was submitted to the solid
phase extraction procedure; cartridges with different extraction phases were tested, and
among them, the ion exchange one was the only effective, with recoveries up to 96%. After
solid phase extraction, the eluted solution, containing 12.05 g L- 1 succcinic acid, was
lyophilized, and crystals of succinic acid with 80.7% (m m- 1) were obtained.
The raw material used in the bioprocess has no commercial value, representing a zero cost
carbon source, which reveals itself adequate to the succinic acid production by fermentation
with A. succinogenes, after hydrolysis.
The use of the residual rice husk can contribute to the mitigation of the environmental impact
resulting from the illegal discharge in the environment.