Anthony H.J. Paterson

Model for continuous production of solvents from whey permeate in a packed bed reactor using cells of Clostridium acetobutylicum immobilized by adsorption onto bonechar

SummaryA mathematical model has been developed to describe the operation of a packed bed reactor for the continuous production of solvents from whey permeate. The model has been used to quantitate the amounts of different physiological/ morphological types of biomass present in the reactor. The majority of biomass is inert, i.e. it neither grows nor produces solvent. Only relatively small amounts of biomass actively grow (vegetative, non-solvent-producing cells), while even smaller amounts are responsible for solvent production (clostridial, solvent-producing cells).

Production and Uses of Lactose

Lactose has been produced industrially for over 100 years (Dryden, 1992). The objectives of the lactose manufacturer were summed up by Herrington (1934): “In the manufacture of lactose, it is desirable to secure a maximum yield of crystals in a minimum time, and to secure crystals which may be readily washed with a minimum of loss.” These objectives are still valid for the modern lactose manufacturer and this chapter will examine how these objectives might be met.

Secondary Nucleation: Mechanisms and Models

Secondary nucleation is the dominant nucleation mechanism in industrial crystallizers. This work reviews secondary nucleation as it occurs in solution-based crystallization of small organic/inorganic compounds. The review elucidates various mechanisms along with the experimental and analytical techniques used to study them. Based on the review, a refined classification of secondary nucleation mechanism is proposed. Mechanistic models for various secondary nucleation mechanisms are then discussed at length. The review ends with an overview of the metastable zone width for secondary nucleation. The review will be useful to researchers and engineers working on bulk crystallization of small molecules to gain in-depth understanding of secondary nucleation.

A mathematical model for lactose dissolution, part II. Dissolution below the alpha lactose solubility limit

Abstract The rate of dissolution of lactose into water has been shown to be controlled by two different mechanisms, depending on the final concentration of lactose required. If concentrations above the alpha lactose solubility limit are required then the dissolution rate is governed by the first order kinetics of the mutarotation reaction from alpha to beta lactose. At typical room temperatures this reaction is so slow that the rate of dissolution of alpha lactose into solution and the rate of mass transfer away from the surface can be considered instantaneous. At lactose concentrations below the alpha solubility limit, the initial assumption that the rate of mass transfer from the surface to the liquid controlled dissolution, has been shown to be incorrect with experimental dissolution times being much longer than those predicted using a model with the lowest possible mass transfer co-efficient and an instantaneous dissolution of lactose at the surface of the crystal. To account for this discrepancy, a model was proposed that assumed a first order reaction for the dissolution occuring at the surface. Appropriate empirical parameters were fitted to the experimental data at different temperatures and initial particle sizes. It was concluded that the surface reaction of unbinding the bound lactose molecules from the crystal structure controls the rate of dissolution of α-lactose monohydrate crystals below the α-lactose solubility limit at temperatures below 50 °C. The Arrhenius constants of Es = 37 ±3 kJ mole−1 and As = 152 (43–540) m s−1, were determined.

A mathematical model for lactose dissolution

Abstract Many users of lactose crystals have to dissolve the sugar before they can use it in processing. To date, the design of the vessels used to perform this operation has been carried out either on an ad hoc basis or based on past experience. There is therefore a need to define the system in terms of its rate-limiting steps so that appropriate design decisions can be made. Here the relevant literature on lactose dissolution is reviewed and the first-order reaction kinetics for the mutarotation of α-lactose to β-lactose are combined with the appropriate mass transfer equations to model the dissolution process. The resultant predictions are compared with experimental data. Three main mechanistic regions are identified: the first is when saturated solutions of lactose are required, the second is when lactose concentrations between the α-lactose solubility limit and saturated solutions are targeted and the third is when solutions below the α=lactose solubility limit are desired. The model, when modified to allow for the variation in α-lactose solubility with β-lactose concentration, has modelled successfully the first two regions, but fitted only poorly the region below the α-lactose solubility limit.

A Mathematical Model Of Solar Drying Of Rice

Abstract A mathematical model describing the heat and moisture transfer within a solar drying system of rice was formulated. A numerical solution using MATLAB was implemented due to the many coupled PDEs and nonlinear algebraic equations. The model was checked for a range of the space steps and by comparison to analytical solutions for completed situations and was shown to contain no significant numerical errors. After estimating the best values and uncertainties of the system inputs the model was validated by comparison with experimental data for solar drying of rice. It was shown to be a very good mechanistic tool with advantages of simplicity and practical accuracy. The model accurately predicted the drying time and the temperature, and moisture content (MC) within the bed during drying except when a polystyrene drying pad was used. However, the model did not predict the experimental bed water activity (relative humidity) consistently well.

Effect of Fines on Agglomeration in Spray Dryers: An Experimental Study

Agglomeration in spray dryers occurs by overlapping the spray patterns of multiple liquid nozzles and the airstreams containing recycled fine powder. In this work, the role of the recycled fines stream is explored by measuring the extent of agglomeration. Two scales are investigated, a small-scale dryer with nominal capacity of ~ 1 kg/h and a pilot-scale dryer of ~ 75 kg/h. Experiments were designed to investigate a number of parameters at three levels: low, medium and high about midpoints that represent typical operation at each scale. These operating points are representative of those available, or potentially available, to operators of agglomerating spray dryers: spray flow rate, spray solids concentration, spray droplet size, powder flow rate, and powder particle size. Drying conditions were kept as constant as possible and all experiments used skim milk powder. A measure of success, called the agglomeration efficiency, was developed based on examining the agglomerated product size distribution relative to the spray and fines. The efficiency reflects the proportion of particles sizes that disappear from the spray size distribution and then appear in the agglomerated product after the fines have been censored from it. Comparisons were made between the reference case of natural agglomeration when the dryer was run without fines, and later forced agglomeration trials with fines. These confirm that fines addition does promote agglomeration. Trials containing fines show that the extent of agglomeration depends principally on the mass flux ratio of fines to spray followed by the particle size of the fines; this can be linked to the probability of interaction between spray and fines in the turbulent interaction zone. The concentration of the spray liquid has a weaker effect on influencing forced agglomeration, but has a major influence on the final product particle size because high solids concentrations promote natural agglomeration when sprays interact. This relates to the development of surface stickiness which influences the success of collisions. The two scales of dryer have the same trends and approximately scale.

Effects of Different Solar Drying Methods on Drying Time and Rice Grain Quality

Paddy rice was sun dried in Cambodia in 2004 using a range of methods practiced by local rice farmers. For each treatment in the experiment, a grain sample at about 22% moisture (typical harvest moisture content) was sun dried between 8 a.m. and 4 p.m. During experiments, the grain moisture content was measured at regular intervals. The grain varieties used, bed depths, stirring of the grain, bulk tempering after drying and the drying pads had significant effects on the drying time. Drying was faster when bed depth was reduced, regularly stirred but not shaded or covered and when the drying was carried out on a porous pad. Damage to the dried grain was reduced when the bed was thin, stirred and shaded and when the drying was slow on pads with less air circulation.

Milks and Milk Concentrates: Surface Tension Measurement

Surface tension is an important property of milk concentrates because it affects atomisation in spray drying. A Krüss tensiometer and Wilhelmy plate were used to measure surface tension. Skim milk and whole milk were tested at a range of solids concentrations and were compared with the surface tension of standard and reconstituted milks. It was found that surface tension was affected more by temperature than by fat content or solids concentration. The surface tensions for concentrates correspond to published values for standard milks below 60°C, but above 60°C, the surface tension increases markedly, which can be attributed to changes in the milk chemistry. The difficulty associated with using the Wilhelmy plate method is the time taken to perform each measurement, which allows a skin to form and reduces the accuracy of the measurements.

Transformation of lactose for value-added ingredients

Abstract: Lactose, as a raw material in whey, is currently available in quantities that far exceed the demand for the product. This means that lactose is inexpensive relative to the costs of other dairy products. This chapter looks at the sources of lactose, the reasons behind why there was a recent spike in lactose price and the range of different derivatives that people have considered as ways of using lactose. Tagatose seems to be the product with the most potential to develop into a significantly large market that will use significant amounts of lactose.