The effects of mixing on the enzymatic hydrolysis of lignocellulosic biomass

Biorefining of lignocellulosic biomass into biofuels and chemicals can help replace fossil resources and decrease anthropogenic greenhouse gas emissions. This thesis is focused on the effects of mixing on the enzymatic hydrolysis of pretreated biomass. Two different types of biomass were studied: softwood (Norway spruce and Scots pine), and the energy grass giant reed. Before enzymatic hydrolysis, the biomass was pretreated by either steam or sulfite pretreatment. The first part of the work concerns the connection between particle morphology and rheology of pretreated biomass, how such properties change during the course of enzymatic hydrolysis, and how the changes are influenced by reactor mixing. The second part examines the effects of mixing in stirred tank reactors on the enzymatic hydrolysis of different pretreated materials, and also attempts to explain the mechanisms behind the observed phenomena.The particle size reduction during enzymatic hydrolysis of steam pretreated spruce was primarily driven by reactor agitation. In the case of steam pretreated giant reed the particle size was mainly reduced by enzymatic hydrolysis. The rapid reduction in particle size of giant reed coincided with a rapid liquefaction. For steam pretreated softwood, the viscosity in fact increased at the beginning of enzymatic hydrolysis, followed by a gradual decrease during the remainder of the hydrolysis. This interesting phenomenon was in part linked to the type of pretreatment used on the softwood biomass. In contrast to steam pretreated softwood, the viscosity of sulfite pretreated spruce decreased rapidly during enzymatic hydrolysis. Efficient viscosity reduction in sulfite pretreated spruce was also achieved with very low doses of pure endoglucanase enzymes (0.1 mg protein per g glucan) without significant glucose release.The effect of mixing on the enzymatic hydrolysis was in part determined by the viscosity of the pretreated biomass. For steam pretreated spruce at low solid loading, decreasing the agitation rate had little effect on the the enzymatic hydrolysis. However, if the viscosity was increased by the addition of a thickening agent, the effect of agitation was much larger. For a substrate that underwent rapid initial viscosity reduction, such as steam pretreated giant reed, the enzymatic hydrolysis was almost independent of agitation rate. Another important factor determining the effect of mixing on the enzymatic hydrolysis was the level of product inhibition. If the glucose and cellobiose concentrations were high, as during high solid hydrolysis of steam pretreated spruce, low agitation rate had a large negative effect on the enzymatic hydrolysis. However, if the product concentration was kept low, as during SSF, the effect of agitation was much weaker. Overall, the results indicate that the decrease in hydrolysis rate occurred due to increased local product inhibition, caused by mass transfer limitations in the stagnant zones, formed in the reactor volume when under low intensity mixing. The rate of enzymatic hydrolysis appeared to be determined by flow regime, i.e. Reynolds number, rather than specific mixing power input. This implies that the negative effects of low agitation rate will be less of a problem in larger reactors

Experiments on transformation thermodynamics: Molding the flow of heat

It has recently been shown theoretically that the time-dependent heat conduction equation is form-invariant under curvilinear coordinate transformations. Thus, in analogy to transformation optics, fictitious transformed space can be mapped onto (meta-)materials with spatially inhomogeneous and anisotropic heat-conductivity tensors in the laboratory space. On this basis, we design, fabricate, and characterize a micro-structured thermal cloak that molds the flow of heat around an object in a metal plate. This allows for transient protection of the object from heating, while maintaining the same downstream heat flow as without object and cloak.Comment: 10 pages, 4 figure

Scattering problems in elastodynamics

In electromagnetism, acoustics, and quantum mechanics, scattering problems can routinely be solved numerically by virtue of perfectly matched layers (PMLs) at simulation domain boundaries. Unfortunately, the same has not been possible for general elastodynamic wave problems in continuum mechanics. In this paper, we introduce a corresponding scattered-field formulation for the Navier equation. We derive PMLs based on complex-valued coordinate transformations leading to Cosserat elasticity-tensor distributions not obeying the minor symmetries. These layers are shown to work in two dimensions, for all polarizations, and all directions. By adaptative choice of the decay length, the deep subwavelength PMLs can be used all the way to the quasi-static regime. As demanding examples, we study the effectiveness of cylindrical elastodynamic cloaks of the Cosserat type and approximations thereof

Optically assisted trapping with high-permittivity dielectric rings: Towards optical aerosol filtration

Controlling the transport, trapping, and filtering of nanoparticles is important for many applications. By virtue of their weak response to gravity and their thermal motion, various physical mechanisms can be exploited for such operations on nanoparticles. However, the manipulation based on optical forces is potentially most appealing since it constitutes a highly deterministic approach. Plasmonic nanostructures have been suggested for this purpose, but they possess the disadvantages of locally generating heat and trapping the nanoparticles directly on surface. Here, we propose the use of dielectric rings made of high permittivity materials for trapping nanoparticles. Thanks to their ability to strongly localize the field in space, nanoparticles can be trapped without contact. We use a semi-analytical method to study the ability of these rings to trap nanoparticles. Results are supported by full-wave simulations. Application of the trapping concept to nanoparticle filtration is suggested.Comment: 5 figure

Invisible waveguides on metal plates for plasmonic analogues of electromagnetic wormholes

We introduce two types of toroidal metamaterials which are invisible to surface plasmon polaritons (SPPs) propagating on a metal surface. The former is a toroidal handlebody bridging remote holes on the metal surface: It works as a kind of plasmonic counterpart of electromagnetic wormholes. The latter is a toroidal ring lying on the metal surface: This bridges two disconnected metal surfaces i.e. It connects a thin metal cylinder to a flat metal surface with a hole. Full-wave numerical simulations demonstrate that an electromagnetic field propagating inside these metamaterials does not disturb the propagation of SPPs at the metal surface. A multilayered design of these devices is proposed, based on effective medium theory for a set of reduced parameters: The former plasmonic analogue of electromagnetic wormhole requires homogeneous isotropic magnetic layers, while the latter merely requires dielectric layers.Comment: 17 figure

Survey of gas-liquid mass transfer in bioreactors

Bioreactors are becoming more important in the production of biobased products such as proteins, medicines, and renewable fuels. The economic viability of these processes is dependent on the bioreactor\u27s ability to aid the microorganism and provide a friendly environment. One of the important microorganism requirements is proper gas concentrations so that the microorganism has the necessary inputs for proper metabolism. These gas concentrations are obtained and maintained through optimized gas-liquid mass transfer and mixing, also known as hydrodynamics. Other bioreactor responsibilities include damage mitigation and bioreactor volume utilization. A proper bioreactor design should also maximize profitability through ease of use, maintenance, and construction. This thesis work provides a survey of gas-liquid mass transfer theories, applications, and dependencies in major bioreactor and several novel designs. The major reactor designs include the stirred tank bioreactor, bubble column, airlift bioreactor, and fixed bed bioreactor. Variations of these major designs are also considered such as the slurry bubble column, internal- and external-loop airlift, draught-tube bioreactor, and trickle, packed, and flooded bed bioreactor. Since the microorganisms used in biological processes are diverse, a best or preferred bioreactor design is not feasible. Rather, bioreactor options can be presented based on the microorganism properties and production scale. Stirred tank bioreactors generally produce the largest gas-liquid mass transfer rates, but they also tend to cause high shear rates and variations, which can be very harmful to microorganisms. The impeller often limits the operating range, scale, process time, especially with non-Newtonian liquids. The bubble column and internal-loop airlift bioreactor have similar gas-liquid mass transfer rates; however, the bubble column has significant backmixing while the airlift bioreactor has lower bioreactor volume utilization. The external-loop airlift bioreactor provides more process and mixing control and generally has lower shear rates, but the attainable gas-liquid mass transfer rate and volume utilization tend to be lower. The fixed bed bioreactors protect and support microorganisms very well. On the other hand, the phase flow rates are much lower than in the other bioreactor designs. In other words, each bioreactor design has important advantages and disadvantages, and the microorganism may very well determine the optimal design. The bioreactor designs may be described as complementary rather than competitive. Each design and design variation has been implemented to fill a void caused by the original form. This design mentality has led to highly complex bioreactor relationships and the inability to identify the single best bioreactor because that was not the intent. Future research and development can be taken into two different directions. First, a design variation could be approached with the clear intent of superiority for biological processes. Such a device could possible use a mixture of airlift and stirred tank bioreactor attributes. Second, research could be oriented towards the continued niche creation. Each design improvement would be implemented with the intent of improving a certain bioreactor attribute or application with a specific type of microorganism. For example, the fixed bed bioreactor research could investigate new packing that would provide better support and shear protection for very sensitive microorganisms such mammalian cells

Hall-effect sign-inversion in a realizable 3D metamaterial

In 2009, Briane and Milton proved mathematically the existence of three-dimensional isotropic metamaterials with a classical Hall coefficient which is negative with respect to that of all of the metamaterial constituents. Here, we significantly simplify their blueprint towards an architecture composed of only a single constituent material in vacuum/air, which can be seen as a special type of porosity. We show that the sign of the Hall voltage is determined by a separation parameter between adjacent tori. This qualitative behavior is robust even for only a small number of metamaterial unit cells. The combination of simplification and robustness brings experimental verifications of this striking sign-inversion into reach.Comment: 9 figures, 7 page