Resumo em Inglês:

During rapid ethanol fermentation (2-3 h) of sugar-cane blackstrap molasses, a significant increase in the ethanol yield was frequently observed as fermentation proceeded, eventually leading to yields higher than the theoretical value when the end of the process was approached. In order to explain the above facts, three assumptions were examined: 1. temporary ethanol accumulation within the yeast cells; 2. variation of the dry matter content and/or of the microorganism density during the fermentation; 3. transformation of sugars into undetectable extra-cellular fermentable compounds at the initial stages of the process. Based on the experimental results presented here, the third of the above assumptions seems to explain the observed increase in the ethanol yield.

Resumo em Inglês:

This paper provides a methodology developed for the calculation of the feed rate and of the exit air conditions in an adiabatic rotary dryer, which operates with granular, non-porous solids having only unbound surface moisture. Some aspects related to the algorithm are also discussed in greater detail, such as the behavior of the wet-bulb temperatures along the dryer and the selection of initial values for the iterative loops. The results have been compared with published data from commercial rotary dryers, and predictions compare within 10% of the available data. The methodology can be used to evaluate trends in the behavior of a rotary dryer where the operating parameters vary, and it is useful for the practical engineer, who has to manage several problems commonly encountered in the operation of a rotary dryer installed in a chemical plant.

Resumo em Inglês:

This paper deals with the control of the neutralization processes of the strong acid-strong base and the weak acid-strong base systems using the Generic Model Control (GMC) algorithm. The control strategy is applied to a pilot plant where hydrochloric acid-sodium hydroxide and acetic acid-sodium hydroxide systems are neutralized. The GMC algorithm includes in the controller structure a nonlinear model of the process in the controller structure. The paper also focuses the provides a stability analysis of the controller for some of the uncertainties involved in the system. The rResults indicate that the controller stabilizes the system for a large range of uncertainties, but the performance may deteriorate when the system is submitted to large disturbances.

Resumo em Inglês:

The influence of inoculum preparation on Aspergillus awamori morphology, broth rheology and glucoamylase synthesis in submerged cultures was investigated. A series of runs were performed in fermenters, using initial total reducing sugar concentrations of 20 g/L and 80 g/L. The inocula were prepared in a rotary shaker, at 35oC and 200 rev/min, using a spore concentration of 9.2 x 105 spores/mL and varying both cultivation time and medium pH during the spore germination step. Three types of inocula were used: inoculum cultivated for 24 hours at an initial pH of 5.0, and inocula cultivated for 7 hours at both a pH of 2.5 and a pH of 5.5. Regarding glucoamylase production, the inoculum which provided the best results was shaker cultivated for 7 hours at a pH of 2.5. This inoculum produced glucoamylase of about 1,221 U/L in the fermenter, which was between 20% and 30% higher than those obtained using other inocula.

Resumo em Inglês:

A eucalyptus hemicellulose fraction was hydrolysed by treating eucalyptus wood chips with sulfuric acid. The hydrolysate was used as the substrate to grow Paecilomyces variotii IOC-3764 cultured for 72 or 96 hours. The influence of the inhibitors, nutrients and fermentation time was verified by a 28-4 and, subsequently, a 25-1 fractional factorial design. The effects of the inhibitors (acetic acid and furfural), nutrients (rice bran, urea, potassium nitrate, ammonium sulfate, magnesium sulfate and sodium phosphate) and fermentation time were investigated. The highest yield (10.59 g/L of biomass) was obtained when the microorganisms were cultivated for 72 hours in a medium composed of 30 g/L rice bran, 9.4 g/L ammonium sulfate (2 g/L nitrogen) and 2 g/L sodium phosphate.

Resumo em Inglês:

The relative importance of design variables affecting the fluiddynamic behavior of a fluidized bed reactor for the gas-phase ethylene polymerization is discussed, based on mathematical modeling. The three-phase bubbling fluidized bed model is based on axially distributed properties for the bubble, cloud and emulsion phases, combined with correlations for population balance and entrainment. Under the operating conditions adopted in most industrial processes, the reactor performance is affected mainly by the reaction rate and solids entrainment. Simulation results indicate that an adequate design of the freeboard and particle collecting equipment is of primary importance in order to produce polymeric particles with the desired size distribution, as well as to keep entrainment and catalyst feed rates at adequate levels.

Resumo em Inglês:

The objective of the present work is to study the variation of the electrode distribution potential under electrical conductivity variation of graphite felt RVG 4000 ( Le Carbone Lorraine) when submitted to a mechanical compression. Experimental and theoretical studies show that this electrical conductivity variation can changes the electrode potential distribution E(x) working under limiting current conditions. This may occur when graphite felt is confined in an electrochemical reactor compartment or simply when it is submitted to a force performed by an electrolyte percolation in a turbulent flow. This investigation can contribute to the improvement of electrochemical cells that may use this material as an electrode. Finally, one modification is suggested in the equation that gives the electrode potential distribution E(x) - E(0). In this case the parameter L (thickness in metal porous electrodes) is substituted for Lf = Li (1-j), where j corresponds to the reduction factor of the initial thickness Li.

Resumo em Inglês:

The occurrence of nitrogenous compounds in industrial effluents at concentration levels above legal limits, is a well-known and serious pollution problem for the receiving body. The biological process for the removal of these substances, commonly referred to as ammoniacal nitrogen, is known as nitrification. Bacteria involved are mainly of the genuses Nitrosomonas and Nitrobacter. The aim of the present work was to study the effect of the hydraulic retention time (HRT) on the efficiency of ammonia removal from a petroleum refinery effluent using activated carbon particles as a biofilm support in an airlift bioreactor. The experiments were carried out using HRTs, equal to six, eight and ten hours. The results show that HRT equal to 8 and 10 hours were enough to reduce ammoniacal nitrogen concentration to levels below permited legal limits (5mg/L NH3-N). The reactor nitrifying performance was maximized at 85% removal of ammoniacal nitrogen, for a HRT equal to 10 hours.

Resumo em Inglês:

Acid sugarcane bagasse hydrolyzate was submitted to pH shifts in order to remove toxic compounds from the medium. The hydrolyzate was treated with bases containing mono-, di- or tri-valent cations and H2SO4, and its performance as a fermentation medium was evaluated by the production of xylitol by Candida guilliermondii FTI 20037. The use of bases containing mono-valent cations was not an efficient method of detoxification, and the use of a tri-valent cation did not show any detectable improvement in detoxification. The treated hydrolyzate recovery (in volume) is greatly affected by the utilized base. Treatment using Al(OH)3 and NaOH showed the best hydrolyzate recovery (87.5%), while the others presented a recovery of about 45% of the original hydrolyzate volume. Considering the whole process, best results were achieved by treatment using Al(OH)3 and NaOH which allowed 0.55 g of xylitol produced from each gram of xylose in the raw hydrolyzate.

Resumo em Inglês:

- A group contribution equation of state recently proposed by the authors is used to calculate the activity of solvents in polymer+solvent solutions. The model is based on the generalized van der Waals theory and combines the Staverman-Guggenheim combinatorial term with an attractive lattice gas expression. The results show that the equation correlates the properties of pure solvents and polymers accurately. Furthermore, the equation satisfactorily represents the vapor-liquid equilibrium of solutions containing polymer and solvents of different polarities.