Effects of surfactants on mass transfer during spray drying

Abstract

A study was conducted to investigate the effects of added surfactants on mass transfer during spray drying. Measurements were made of retention of volatile components and amount of water evaporation at various points near the atomizer inside a spray dryer of pilot plant scale. Experimental data indicate that surfactants can have a substantial effect on transport processes when certain types of liquid solutions are spray dried. Experimental results are interpreted in terms of transport mechanisms and are compared with relevant previous studies on nonspray systems. D. D. Frey C. J. King Department of Chemical EngineeringUniversity of California Berkeley, CA 94720 SCOPESpray drying is widely used for dehydration of liquid foods such as coffee and tea extracts, milk concentrates, and purees. Because of the economic importance of these products, and because of numerous other industrial applications of spray drying, there is growing interest in a better understanding of the mechanisms of mass transfer during spray drying. This knowledge should aid optimization of these processes for minimum cost, for better retention of volatile aroma components, and/or for improving other product quality factors.In spite of the large number of fundamental mass transfer studies to be described below, most previous work dealing with added surfactants has been on idealized systems and does not take into account the following complexities which are characteristic of industrial spray drying: Haven. CT 06520.3. Turbulence and oscillations in drops caused by 4. Effects of drying on the internal motions of drops 5. Formation of a surface crust or a selective-diffusion barrier Notwithstanding the relatively small amount of past work in this area, it is important to understand the effects of surfactants upon spray drying. Many or all liquid foods contain natural surfactants. In situations such as foam-spray drying, it may be necessary to add surfactants to the liquid feed to obtain the desired processing effect. Finally, addition of surfactants may be a convenient means to affect and control mass-transfer rates during spray drying or in other types of spray contacting.For these reasons, an experimental and theoretical investigation was undertaken of the spray drying of surfactant-containing aqueous sucrose and coffee solutions, with acetates as model aroma components. The principal aims of this investigation were to determine the effects of various surfactants on the retentions of highly volatile aromalike components and on the rate of water evaporation in regions close to the nozzle. An aerodynamic model of spray behavior was used to interpret the experimental results. CONCLUSIONS AND SIGNIFICANCEThis study indicates that surfactants can have a large effect on volatiles retention during spray drying. The primary effect of a surfactant appears to be on droplet hydrodynamics and particularly on oscillations, turbulence, and internal circulation in drops. In solutions of high solids content where volatiles losses from drops are small, surfactant...

Spray-Drying of Air–Liquid Interface Sensitive Recombinant Human Growth Hormone

“…It is plausible that given sufficient cumulative contact time, protein molecules will form large aggregates and become insoluble, but those having short overall contact time will form dimers and remain soluble. Polysorbate molecules not only occupy the interface but also slow the fluid movement in the droplets, [24][25][26] thereby reducing the chance for rhGH molecules to be denatured at the interface. These two factors caused by surfactant reduce the contact time of rhGH molecules with the interface.…”

“…One speculation as to how surfactant might smooth out the surface is that the presence of surfactant reduces internal motions and surface turbulence of the droplets during drying. [24][25][26] However, whether reducing the flow motion of the droplets would minimize the formation of a raisin-like surface has yet to be determined.…”

Measurement of droplet interfacial phenomena by light‐scattering techniques

“…Furthermore, if one component is surface-active, the formation of an insoluble monolayer at the interface can reduce the evaporation rate by introducing an interfacial resistance to mass transfer. Frey and King (1986) showed that surfactants can have a substantial effect on mass transfer in spray drying. All of these complications will be examined herein.…”

Absorption of gases into drops

“…The necking phenomena with subsequent detachment occurs in sprays also and should impart oscillation and unsteady internal flow. This may explain the results of Frey and King (1986), who found higher mass transfer rates than those predicted by the Kronig and Brink model. Also, models that predict velocity-dependent mass transfer coefficients do not explain the experimental data.…”