De invloed van de samenstelling van binaire mengsels op het schotelrendement in rectificatiekolommen

The effect of composition on plate efficiencies for binary mixtures of ethanol and water, n-heptane and methylcyclohexane, and methylcyclohexane and toluene was studied experimentally in an adiabatic distillation column of 3.8 cm internal diameter containing 9 sieve plates. Accurate data concerning the vapour-liquid equilibrium curves were required for the calculation of Murphree plate and point efficiencies. This led to the use of the test for internal consistency of vapour-liquid equilibrium data as introduced by Harington, which was extended to P constant, T variable and corrected for differences from an ideal gas of the vapour phase. An exact graphic method to evaluate the vapour-liquid equilibrium from boiling point composition data of binary mixtures was derived.The observed point efficiencies on overall gas basis seemed to vary markedly with composition in low and high concentrations. It was demonstrated that these variations could not be attributed to lack of precision in the equiibrium data, interference with the column operation by sampling, variation in physical properties with composition, or a variation in stripping or rectifying factor mV/L with concentration.The point efficiencies at total reflux seemed to be a function of the corresponding driving forces for mass transfer in the gas phase.<p/

Het TNO-onderzoek op het gebied van de biotechnologie

Bericht voor de persbijeenkomst op maandag 26 april 1982 in het kader van de 'toekomstige biotechnologie-activiteiten van TNO'. Prof Thijssen was voorzitter van de Dwarsverband biotechnologie TNO en directeur ITC

Freeze concentration of food liquids

Freeze concn. of aq. solns. consists of 2 successive steps, namely the crystn. of a part of the water and the sepn. of the ice crystals from the liq. conc. The selectivity of the process is solely detd. by the sharpness of the ice-liq. sepn. For a max. phase sepn. in centrifuges the sp. area of the ice crystals must be as small as possible. The sharpness of sepn. in presses and in wash columns is insensitive to crystal size, crystal size distribution, and crystal shape. The capacity of all these separator types, however, sharply increases with a decrease of the sp. area of the crystals. Crystallizer design and operating conditions consequently must be directed to the formation of large uniform and shperical crystals. Process variables influencing crystal growth rate and crystal nucleation are discussed. A stirred crystallizer cooled by a crystal-free, strongly supercooled feed stream is reported to produce spherical crystals with a mean diam. of about 1 mm. Because of their excellent sepn. performance wash columns are preferred over filter centrifugals and presses. [on SciFinder (R)

Goed(koop) produkt via vriesconcentratie

Volumereductie bij vloeibare voedingsmiddelen op conventionele wijze, dat wi( zeggen door verdamping of omgekeerde osmose, resulteert in een geringere esthetische waarde van het gereconstitueerde eindprodukt. Dit is het gevolg van het verloren gaan van allerlei aroma-stoffen en andere belangrijke ingredienten. Bovendien zijn dergelijke processen energie-intensief. Het vriesconcentratieproces zoals ontwikkeld. door prof.dr.ir. H.A.C. Thijssen (TU Eindhoven) wordt al 20 jaar door Grenco toegepast. Het is een commercieel aantrekkelijk alternatief voor de conventionele methoden. Recente ontwikkelingen op het gebied van vriesconcentratie onderstrepen de technische mogelijkheden van het proces op grootschalig niveau. Het gereconstitueerde produkt heeft nagenoeg dezelfde smaak, kleur, textuur en hetzelfde aroma als het oorspronkelijke produkt, terwijl aanzienlijke energiebesparingen worden bereikt

Concentration processes for liquid foods containing volatile flavours and aromas

Three concentration processes are technically feasible for the selective dewatering of liquid food, viz. evaporation with aroma recovery, freeze concentration and reverse osmosis. Concerning quality preservation the freeze concentration is superior to the other two processes. the process is not yet developed to full technical maturity, however. It seems likely that in the coming years it will deprive the established evaporation process of its monopoly position. Reverse osmosis has not yet passed the laboratory scale stage. Because membranes with acceptable permeabilities are not very selective, it can be expected that their technical application in dewatering aroma‐containing liquid foods will remain restricted to some specialties. The costs of concentration are about the same for evaporation and freeze concentration. the higher investment costs of the latter process are partially offset by lower costs of energy. Depending upon the capacity and yearly operation hours the costs vary between ±5 and ±15 per ton water removal. Reverse osmosis may become competitive at more than 100 operation days per year

Freeze concentration of food liquids

Freeze concn. of aq. solns. consists of 2 successive steps, namely the crystn. of a part of the water and the sepn. of the ice crystals from the liq. conc. The selectivity of the process is solely detd. by the sharpness of the ice-liq. sepn. For a max. phase sepn. in centrifuges the sp. area of the ice crystals must be as small as possible. The sharpness of sepn. in presses and in wash columns is insensitive to crystal size, crystal size distribution, and crystal shape. The capacity of all these separator types, however, sharply increases with a decrease of the sp. area of the crystals. Crystallizer design and operating conditions consequently must be directed to the formation of large uniform and shperical crystals. Process variables influencing crystal growth rate and crystal nucleation are discussed. A stirred crystallizer cooled by a crystal-free, strongly supercooled feed stream is reported to produce spherical crystals with a mean diam. of about 1 mm. Because of their excellent sepn. performance wash columns are preferred over filter centrifugals and presses. [on SciFinder (R)

Retention of aroma components in extractive drying of aqueous carbohydrate solutions

A new drying technique, extractive drying, has been studied experimentally. The retention of the components methanol, n‐propanol and n‐pentanol in extractive drying of a model liquid food was investigated. The model liquid food consisted of an aqueous solution of mixtures of dextrin and malto‐dextrin, to which the alcohols were added in low concentrations. As extraction liquid polyethylene glycol (PEG) 400 was used. The solution to be dried was dispersed in the PEG in the form of droplets. High losses of the alcohols were found when the feed droplets were distorted upon contact with the extraction liquid. This distortion does not occur when the viscosity of the feed solution is higher than approximately 150 cP. For such feed solutions, containing 40% water and on dry basis 25% dextrin and 75% malto‐dextrin, very high aroma retentions were found. The effects observed agree with the selective diffusion theory

A simple model describing the effect of axial mixing on countercurrent mass exchange

By means of a model the effect of axial dispersion on mass transfer in countercurrent contactors is described. The mixing is represented by a cascade of a number of ideal mixers in each phase. The separation performance-characterized by the number of external transfer units, ∫ dC/(C* C)-is in a simple analytical way related to the extraction factor, mFx/Fy, to the number of internal transfer units, kox.a.L/vx, and to the number of ideal mixers in each phase. The number of external transfer units calculated with this model is in good agreement with the results of the longitudinal dispersion model as presented by Miyauchi and Vermeulen. The simplicity of the model enables rapid slide rule calculations and provides rapid recognition of the factors limiting the separation performance