Screening method for Enzyme-based liquefaction of corn stover pellets at high solids.

Liquefaction of high solid loadings of unpretreated corn stover pellets has been demonstrated with rheology of the resulting slurries enabling mixing and movement within biorefinery bioreactors. However, some forms of pelleted stover do not readily liquefy, so it is important to screen out lots of unsuitable pellets before processing is initiated. This work reports a laboratory assay that rapidly assesses whether pellets have the potential for enzyme-based liquefaction at high solids loadings. Twenty-eight pelleted corn stover (harvested at the same time and location) were analyzed using 20 mL enzyme solutions (3 FPU cellulase/ g biomass) at 30 % w/v solids loading. Imaging together with measurement of reducing sugars were performed over 24-hours. Some samples formed concentrated slurries of 300 mg/mL (dry basis) in the small-scale assay, which was later confirmed in an agitated bioreactor. Also, the laboratory assay showed potential for optimizing enzyme formulations that could be employed for slurry formation.

Power consumption evaluation of different fed-batch strategies for enzymatic hydrolysis of sugarcane bagasse.

The minimization of costs in the distillation step of lignocellulosic ethanol production requires the use of a high solids loading during the enzymatic hydrolysis to obtain a more concentrated glucose liquor. However, this increase in biomass can lead to problems including increased mass and heat transfer resistance, decreased cellulose conversion, and increased apparent viscosity with the associated increase in power consumption. The use of fed-batch operation offers a promising way to circumvent these problems. In this study, one batch and four fed-batch strategies for solids and/or enzyme feeding during the enzymatic hydrolysis of sugarcane bagasse were evaluated. Determinations of glucose concentration, power consumption, and apparent viscosity were made throughout the experiments, and the different strategies were compared in terms of energy efficiency (mass of glucose produced according to the energy consumed). The best energy efficiency was obtained for the strategy in which substrate and enzyme were added simultaneously (0.35 kg(glucose) kWh⁻¹). This value was 52% higher than obtained in batch operation.

Enzymatic Hydrolysis of Pretreated Sugarcane Straw: Kinetic Study and Semi-Mechanistic Modeling.

Although there are already commercial-scale productions of second generation (2G) ethanol, focusing efforts on process optimization can be of key importance to make the production cost-effective in large scale. In this scenario, mathematical models may be useful in design, scale-up, optimization, and control of bioreactors. For this reason, the aim of this work was to study the kinetics of the enzymatic hydrolysis of cellulose from sugarcane straw. Experiments using hydrothermally pretreated sugarcane (HPS) straw (195 °C, 10 min, 200 rpm) with and without alkaline delignification (4 % NaOH m/v, 30 min, 121 °C) were carried out in shake flasks (50 °C, pH 5.0, 200 rpm). Solid load was varied in a range of 0.8 to 10 % (m/v), in initial velocity and long-term assays. Enzyme concentration (Cellic®CTec2) was varied from 5 to 80 filter paper unit (FPU) gcellulose (-1). It was possible to fit Michaelis-Menten (MM), modified MM, with and without competitive inhibition by glucose, and Chrastil models. Chrastil model and modified MM with inhibition (both suitable for heterogeneous system, with high resistance to internal diffusion) showed more appropriate than pseudo-homogeneous MM model. The fitted models were able to identify key features of the hydrolysis process and can be very useful within the perspective of bioreactors engineering.

Mixing design for enzymatic hydrolysis of sugarcane bagasse: methodology for selection of impeller configuration.

One of the major process bottlenecks for viable industrial production of second generation ethanol is related with technical-economic difficulties in the hydrolysis step. The development of a methodology to choose the best configuration of impellers towards improving mass transfer and hydrolysis yield together with a low power consumption is important to make the process cost-effective. In this work, four dual impeller configurations (DICs) were evaluated during hydrolysis of sugarcane bagasse (SCB) experiments in a stirred tank reactor (3 L). The systems tested were dual Rushton turbine impellers (DIC1), Rushton and elephant ear (down-pumping) turbines (DIC2), Rushton and elephant ear (up-pumping) turbines (DIC3), and down-pumping and up-pumping elephant ear turbines (DIC4). The experiments were conducted during 96 h, using 10 % (m/v) SCB, pH 4.8, 50 °C, 10 FPU/g biomass, 470 rpm. The mixing time was successfully used as the characteristic parameter to select the best impeller configuration. Rheological parameters were determined using a rotational rheometer, and the power consumptions of the four DICs were on-line measured with a dynamometer. The values obtained for the energetic efficiency (the ratio between the cellulose to glucose conversion and the total energy) showed that the proposed methodology was successful in choosing a suitable configuration of impellers, wherein the DIC4 obtained approximately three times higher energetic efficiency than DIC1. Furthermore a scale-up protocol (factor scale-up 1000) for the enzymatic hydrolysis reactor was proposed.

Effect of the carbon sources on the growth kinetics of Cephalosporium acremonium in the Cephalosporin C production process

The growth phase of Cephalosporium acremonium ATCC 48272 was analized in the batch production process of cephalosporin C. Two media were used: one containing glucose and sucrose as main sources of carbon and energy, and the other containing only glucose. The consumption rate of glucose to form biomass was much higher in medium containing only glucose. The behavior in both media could be satisfactorily explained though simulation of a model which included inibition of glucose comsumption by sucrose in the classical Contois kinetics.