Roberto C. Giordano

Bioelectricity versus bioethanol from sugarcane bagasse: is it worth being flexible?

BackgroundSugarcane is the most efficient crop for production of (1G) ethanol. Additionally, sugarcane bagasse can be used to produce (2G) ethanol. However, the manufacture of 2G ethanol in large scale is not a consolidated process yet. Thus, a detailed economic analysis, based on consistent simulations of the process, is worthwhile. Moreover, both ethanol and electric energy markets have been extremely volatile in Brazil, which suggests that a flexible biorefinery, able to switch between 2G ethanol and electric energy production, could be an option to absorb fluctuations in relative prices. Simulations of three cases were run using the software EMSO: production of 1G ethanol + electric energy, of 1G + 2G ethanol and a flexible biorefinery. Bagasse for 2G ethanol was pretreated with a weak acid solution, followed by enzymatic hydrolysis, while 50% of sugarcane trash (mostly leaves) was used as surplus fuel.ResultsWith maximum diversion of bagasse to 2G ethanol (74% of the total), an increase of 25.8% in ethanol production (reaching 115.2 L/tonne of sugarcane) was achieved. An increase of 21.1% in the current ethanol price would be enough to make all three biorefineries economically viable (11.5% for the 1G + 2G dedicated biorefinery). For 2012 prices, the flexible biorefinery presented a lower Internal Rate of Return (IRR) than the 1G + 2G dedicated biorefinery. The impact of electric energy prices (auction and spot market) and of enzyme costs on the IRR was not as significant as it would be expected.ConclusionsFor current market prices in Brazil, not even production of 1G bioethanol is economically feasible. However, the 1G + 2G dedicated biorefinery is closer to feasibility than the conventional 1G + electric energy industrial plant. Besides, the IRR of the 1G + 2G biorefinery is more sensitive with respect to the price of ethanol, and an increase of 11.5% in this value would be enough to achieve feasibility. The ability of the flexible biorefinery to take advantage of seasonal fluctuations does not make up for its higher investment cost, in the present scenario.

Evaluation of immobilized lipases on poly-hydroxybutyrate beads to catalyze biodiesel synthesis

Five microbial lipase preparations from several sources were immobilized by hydrophobic adsorption on small or large poly-hydroxybutyrate (PHB) beads and the effect of the support particle size on the biocatalyst activity was assessed in the hydrolysis of olive oil, esterification of butyric acid with butanol and transesterification of babassu oil (Orbignya sp.) with ethanol. The catalytic activity of the immobilized lipases in both olive oil hydrolysis and biodiesel synthesis was influenced by the particle size of PHB and lipase source. In the esterification reaction such influence was not observed. Geobacillus thermocatenulatus lipase (BTL2) was considered to be inadequate to catalyze biodiesel synthesis, but displayed high esterification activity. Butyl butyrate synthesis catalyzed by BTL2 immobilized on small PHB beads gave the highest yield (≈90 mmol L(-1)). In biodiesel synthesis, the catalytic activity of the immobilized lipases was significantly increased in comparison to the free lipases. Full conversion of babassu oil into ethyl esters was achieved at 72 h in the presence of Pseudozyma antarctica type B (CALB), Thermomyces lanuginosus lipase (Lipex(®) 100 L) immobilized on either small or large PHB beads and Pseudomonas fluorescens (PFL) immobilized on large PHB beads. The latter preparation presented the highest productivity (40.9 mg of ethyl esters mg(-1) immobilized protein h(-1)).

Assessing the production of first and second generation bioethanol from sugarcane through the integration of global optimization and process detailed modeling

Abstract There is a worldwide effort to make economically feasible the use of lignocellulosic biomass for production of biofuels. In sugarcane industry, cane juice (sucrose) is fermented for bioethanol production. Sugarcane bagasse is used as fuel in cogeneration systems, to produce steam and electric power to the plant, and the surplus of electric power may be delivered to the grid. The hydrolysis of bagasse to produce second generation ethanol poses a challenge: how much bagasse can be diverted, since the process must continue energetically self-sufficient. This work presents a computational tool developed within an equation-oriented process simulator that couples the simulation of first and second generation bioethanol production with a global optimization algorithm. The tool was robust, optimizing the steady state process in any economic scenario and for different process configurations. Four case studies are presented, and their implications on process internal demands and on the surplus electrical power are discussed.

Kinetic model for whey protein hydrolysis by alcalase multipoint-immobilized on agarose gel particles

Partial hydrolysis of whey proteins by enzymes immobilized on an inert support can either change or evidence functional properties of the produced peptides, thereby increasing their applications. The hydrolysis of sweet cheese whey proteins by alcalase, which is multipoint-immobilized on agarose gel, is studied here. A Michaelis-Menten model that takes into account competitive inhibition by the product was fitted to experimental data. The influence of pH on the kinetic parameters in the range 6.0 to 11.0 was assessed, at 50oC. Initial reaction-rate assays in a pHstat at different concentrations of substrate were used to estimate kinetic and Michaelis-Menten parameters, k and KM. Experimental data from long-term batch assays were used to quantify the inhibition parameter, KI. The fitting of the model to the experimental data was accurate in the entire pH range.

Lignocellulose pretreatment technologies affect the level of enzymatic cellulose oxidation by LPMO

Sugarcane bagasse, corn stover, and wheat straw are among the most available resources for the production of cellulosic ethanol. For these biomasses we study the influence of pre-treatment methods on the chemical composition, as well as on the subsequent reactions of enzymatic hydrolysis and oxidation of cellulose. The applied pre-treatment methods are organosolv, hydrothermal, and alkaline. Hydrothermally pretreated wheat straw gave the highest cellulose conversion with 80% glucose yield and 0.8% oxidized cellulose products. Recent studies have shown that lignin is able to boost the activity of the cellulose oxidizing enzyme lytic polysaccharide monooxygenase (LPMO). The highest activity of LPMO was observed for the hydrothermally pretreated biomasses, which also contained the highest level of lignin. All hydrolyses were done at high dry matter levels using a commercial enzyme preparation containing hydrolytic and oxidative enzymes.

Immobilization of trypsin on chitosan gels: Use of different activation protocols and comparison with other supports

Trypsin was immobilized on chitosan gels coagulated with 0.1 or 1 M NaOH and activated with glutaraldehyde or glycidol. The derivatives were characterized by their recovered activity, thermal (40, 55 and 70 degrees C) and alkaline (pH 11) stabilities, amount of enzyme immobilized on gels for several enzyme loads (8-14 mg(protein)/g(Gel)) and compared to agarose derivatives. Enzyme loads higher than 14 mg(protein)/g(Gel) can be immobilized on glutaraldehyde derivatives, which showed 100% immobilization yield and, for loads up to 8 mg(protein)/g(Gel), 100% recovered activity. Activation with glycidol led to lower immobilization yields than the ones obtained with glutaraldehyde, 61% for agarose-glyoxyl (AgGly) with low grade of activation and 16% for the chitosan-glyoxyl (ChGly), but allowed obtaining the most stable derivative (ChGly), that was 660-fold more stable than the soluble enzyme at 55 and 70 degrees C-approximately threefold more stable than AgGly. The ChGly derivative presented also the highest stability during incubation at pH 11. Analyses of lysine residue contents in soluble and immobilized trypsin indicated formation of multipoint bonds between enzyme and support, for glyoxyl derivatives.

Purification of capsular polysaccharide from Streptococcus pneumoniae serotype 23F by a procedure suitable for scale-up

Streptococcus pneumoniae is a pathogenic encapsulated bacterium, which causes pneumonia, bacteraemia and meningitis. Capsular polysaccharide conjugated to a carrier protein has been widely used as a vaccine antigen. Serotype 23F is one of the prevalent worldwide pneumococci. A simple and efficient method for capsular polysaccharide serotype 23F purification that can easily be scaled‐up was developed. This method consisted of using culture broth obtained by tangential microfiltration through a 0.22 μm membrane, broth microfiltrate concentration by tangential ultrafiltration in a 30 kDa spiral membrane, fractional ethanol precipitation (28–60%), nuclease and proteinase treatment, and concentration/diafiltration in a 30 kDa cassette membrane. The final polysaccharide recovery was 89%. The final protein and nucleotide contamination was 1.5% (w/w) and 0.3% (w/w) respectively. The final pure polysaccharide meets the requirements of the World Health Organization and residual proteinase was not found in the final product.

Performance of a continuous Taylor–Couette–Poiseuille vortex flow enzymic reactor with suspended particles

Vortex flow reactors (VFRs) are a good option when fragile particles are present in the medium, due to their gentle but efficient stirring characteristics. However, the presence of a by-pass stream may deteriorate the reactor performance, and particles of inadequate density may either settle down or clog the reactor outlet. This work assessed the performance of an enzymic VFR. Fructose–glucose isomerization, catalyzed by immobilized glucoisomerase was the test reaction, taking advantage of the negligible changes that it causes on the medium viscosity. Intra- and extra-particle mass transfer effects were avoided. Reactor geometry (radius ratio η=0.677 and aspect ratio Γ=18.30) and residence time were selected aiming at possible applications of the device as a bioreaction and/or adsorption system. Visualization experiments confirmed that the vortices’ cores stop their axial displacement when the rotation of the inner cylinder is increased. Intermediate rotations were the most detrimental to reactor performance, due to by-pass effects. Vortex agitation is very gentle, causing no detectable damage to shear-sensitive particles.

Distribution of suspended particles in a Taylor–Poiseuille vortex flow reactor

Vortex flow reactors (VFRs) are specially suited to work with shear-sensitive particles, due to the gentle and efficient stirring characteristics of Taylor vortices. For heterogeneous VFRs, the distribution of the solid phase must be accounted for in detail. This work presents residence-time distributions (RTDs) of agarose gel particles (Φ av =214 μm), suspended in different liquid solutions. Reactor porosity was 90%. The mass transfer coefficients of a lumped-parameter model of the reactor are estimated from residence time distributions of a tracer. The VFR has radius ratio η=0.664 and aspect ratio Γ=14.9. Axial flow rates were selected to provide a mean residence time of 1850 s, adequate for many applications. Minimum rotation rates of the inner cylinder were imposed by suspended particles homogeneity criteria. The VFR operational region was: 0.0645<Re ax <0.592 and 98<Re θ <3820, corresponding to very high values of the ratio Re θ /Re ax (between 5293 and 6236). Under these conditions, the vortices were stationary, and circumvented by a by-pass stream. The results indicate that the gel particles are unevenly distributed in the vortex core and by-pass regions. Mean residence times for the particles are substantially greater than for the liquid. The mathematical model presented in this paper can accommodate this behavior, using a partition coefficient for the solid phase.

Recent trends in the modeling of cellulose hydrolysis

This work reviews recent trends in the modeling of cellulose hydrolysis, within the perspective of application of kinetic models in a bioreactor engineering framework, including scale-up, design and process optimization. From this point of view, despite the phenomenological insight that mechanistic models can provide, the expectation that more detailed approaches could be a basis for extrapolations to different substrates and/or enzymatic pools is still not fulfilled. The complexity of the lignocellulosic matrix, the different mechanisms of catalytic action, the role of mass transfer limitations and the deviations from ideal mixing are important difficulties for the modeler, which will continue to impose more conservative approaches for scale-up. Nevertheless, the search for more robust models is a very important task, provided that the engineer is aware of their limitations. Data-driven, non-mechanistic models such as artificial neural networks, perhaps in combination with other approaches in the so-called hybrid models, is also a promising alternative.