Validation of a low field Rheo-NMR instrument and application to shear-induced migration of suspended non-colloidal particles in Couette flow

Nuclear magnetic resonance rheology (Rheo-NMR) is a valuable tool for studying the transport of suspended non-colloidal particles, important in many commercial processes. The Rheo-NMR imaging technique directly and quantitatively measures fluid displacement as a function of radial position. However, the high field magnets typically used in these experiments are unsuitable for the industrial environment and significantly hinder the measurement of shear stress. We introduce a low field Rheo-NMR instrument (¹H resonance frequency of 10.7MHz), which is portable and suitable as a process monitoring tool. This system is applied to the measurement of steady-state velocity profiles of a Newtonian carrier fluid suspending neutrally-buoyant non-colloidal particles at a range of concentrations. The large particle size (diameter >200μm) in the system studied requires a wide-gap Couette geometry and the local rheology was expected to be controlled by shear-induced particle migration. The low-field results are validated against high field Rheo-NMR measurements of consistent samples at matched shear rates. Additionally, it is demonstrated that existing models for particle migration fail to adequately describe the solid volume fractions measured in these systems, highlighting the need for improvement. The low field implementation of Rheo-NMR is complementary to shear stress rheology, such that the two techniques could be combined in a single instrument.

A process for energy-efficient high-solids fed-batch enzymatic liquefaction of cellulosic biomass

The enzymatic hydrolysis of cellulosic biomass is a key step in the biochemical production of fuels and chemicals. Economically feasible large-scale implementation of the process requires operation at high solids loadings, i.e., biomass concentrations >15% (w/w). At increasing solids loadings, however, biomass forms a high viscosity slurry that becomes increasingly challenging to mix and severely mass transfer limited, which limits further addition of solids. To overcome these limitations, we developed a fed-batch process controlled by the yield stress and its changes during liquefaction of the reaction mixture. The process control relies on an in-line, non-invasive magnetic resonance imaging (MRI) rheometer to monitor real-time evolution of yield stress during liquefaction. Additionally, we demonstrate that timing of enzyme addition relative to biomass addition influences process efficiency, and the upper limit of solids loading is ultimately limited by end-product inhibition as soluble glucose and cellobiose accumulate in the liquid phase.

Reactors for High Solid Loading Pretreatment of Lignocellulosic Biomass

The review summarized the types, the geometry, and the design principle of pretreatment reactors at high solid loading of lignocellulose material. Among the reactors used, the explosion reactors and the helical stirring reactors are to be considered as the practical form for high solids loading pretreatment operation; the comminution reactors and the extruder reactors are difficult to be used as an independent unit, but possible to be used in the combined form with other types of reactors. The principles of the pretreatment reactor design at high solid loading were discussed and several basic principles for the design were proposed. This review provided useful information for choosing the reactor types and designing the geometry of pretreatment operation at the high solids loading.

The role of endoglucanase and endoxylanase in liquefaction of hydrothermally pretreated wheat straw

The role of endocellulases and endoxylanase during liquefaction and saccharification of hydrothermally pretreated wheat straw was studied. The use of a flow-loop setup with in-line magnetic resonance imaging enabled frequent measurements of viscosity at 55°C during saccharification at 6% total solids content. Viscosity data were complemented with off-line measurements of fiber lengths and release of soluble sugars. A clear correlation between fiber attrition and a decrease in viscosity was found. Fiber lengths and viscosity dropped quickly within the first hour and then stagnated, while sugar yields increased substantially thereafter, illustrating that liquefaction and saccharification are separate mechanisms. Both endoglucanase and endoxylanase were shown to have a significant effect on viscosity during liquefaction while the addition of endoxylanase also increased sugar yield.

MRI of plants and foods

The importance and prospects for MRI as applied to intact plants and to foods are presented in view of one of humanity's most pressing concerns, the sustainable and healthy feeding of a worldwide increasing population. Intact plants and foods have in common that their functionality is determined by complex multiple length scale architectures. Intact plants have an additional level of complexity since they are living systems which critically depend on transport and signalling processes between and within tissues and organs. The combination of recent cutting-edge technical advances and integration of MRI accessible parameters has the perspective to contribute to breakthroughs in understanding complex regulatory plant performance mechanisms. In food science and technology MRI allows for quantitative multi-length scale structural assessment of food systems, non-invasive monitoring of heat and mass transport during shelf-life and processing, and for a unique view on food properties under shear. These MRI applications are powerful enablers of rationally (re)designed food formulations and processes. Limitations and bottlenecks of the present plant and food MRI methods are mainly related to short T2 values and susceptibility artefacts originating from small air spaces in tissues/materials. We envisage cross-fertilisation of solutions to overcome these hurdles in MRI applications in plants and foods. For both application areas we witness a development where MRI is moving from highly specialised equipment to mobile and downscaled versions to be used by a broad user base in the field, greenhouse, food laboratory or factory.

The effect of mixing on the liquefaction and saccharification of cellulosic fibers

The enzymatic hydrolysis of cellulosic material is a key step in the biochemical routes for production of renewable fuels and chemicals. This must be performed at high solids to be economically viable. High solids operations creates numerous processing challenges, most importantly the limitations due to mass transfer and poor mixing of enzymes in the cellulose suspensions. We use magnetic resonance imaging (MRI), a cylindrical penetrometer, and HPLC to demonstrate the importance of spatial homogeneity in the distribution of enzyme on the rates of liquefaction of the substrate and in the suspension mechanical strength. Our results show that the largest mechanical strength changes occur in a narrow interval of time during the initial stages of conversion. Differences in enzyme concentration distribution occurring at the centimeter-scale produced order of magnitude differences in liquefaction and saccharification rates, supporting the hypothesis that mixing quality has a major influence in both liquefaction and saccharification rates.