| dc.description.abstract | The biosurfactants displays an alternative to the use of synthetic surfactants,
especially when considering their advantages of less toxicity, greater biodegradability and
stability. Among these biosurfactants, the rhamnolipid, produced by Pseudomonas aeruginosa,
has been presenting itself as one of the most notable biosurfactants as a result of its high
performance and applicability in advanced petroleum recovery. However, the large scale
application of rhamnolipids has been a challenge to companies since the costs of production are
high, due to, mainly, the downstream purification process. Therefore, in this study the production
of rhamnolipid by a strain of Pseudomonas aeruginosa was investigated and optimized. The
Plackett-Burman design was used to select the variables that affect significantly the production
yield of the biosurfactant and the Central Composite design was used to optimize the rhamnolipid
production. Afterwards, the kinetic modeling was performed, in which four non-structural models
were tested, and the parameters were optimized through the genetic algorithm and the numeric
discretization by the Runge-Kutta method. The biosurfactant produced was characterized and
evaluated regarding its capacity of being used in the Microbial Enhanced Oil Recovery (MEOR),
finally, the influence of the purification stage was investigated in the rhamnolipid ability to
increase oil production after the convencional recovery process. The results indicated that the
optimal values of temperature, pH, carbon/nitrogen rate, glycerol concentration and time
(variables selected through the statistical experimental design) are, respectively, 30.17°C, 7.37,
32.35, 9.36% (v/v) and 10.26 days. The biosurfactant produced also presented a excellent
emulsification rate, approximately 67% for the n-hexane and 69% for the petroleum, and a
capacity of reducing the water superficial tension from 72 to 35.26 mN/m in a c.m.c of 127 mg/L.
Furthermore, the rhamnolipid also presented a good stability to wide ranges of pH and salinity.
Such characteristics configured the rhamnolipid as a good candidate to the application in MEOR.
The kinetic parameters, of four non-structural models, for the experimental data of four
rhamnolipid production curves were optimized by the genetic algorithm method and the main
result demonstrated that the Monod model is the best predicting the data, with values of µmáx
equal to 0.06 h-1
, KS equal to 50.8 g/L, YX/S equal to 0.43 g/g and YP/X equal to 0.017 g/g. At last,
with the tests of advanced recovery, it was demonstrated that the rhamnolipid can efficiently
recover the oil, obtaining the best result for a biosurfactant concentration 100% above the c.m.c
and petroleum with a API Gravity of 21.90, which was able to achieve a total recovery of
50.45±0.79%, of which 11.91±0.39% corresponds to the MEOR. Moreover, it was evidenced that
the biodegradability of the rhamnolipid did not represent a desavantage and that bigger
investments in purification processes for the biosurfactant would be dispensable, since the
biosurfactant was able to maintain its ability of increasing the oil recovered factor, even after two
months of production. Also, the non-purificated rhamnolipid presented higher recovery factors
when compared with the purificated, for all three types of oils studied. | |
