Andrzej B. Jarzębski

A benchmark study on the thermal conductivity of nanofluids

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

Very stable silica-gel-bound laccase biocatalysts for the selective oxidation in continuous systems.

Cerrena unicolor laccase was immobilized by adsorption and covalent bonds formation on silica-gel carriers, functionalized with different organosilanes and surface densities. The effects of protein concentration, pH value of the coupling mixture and the enzyme purity on immobilization efficiency of the best carrier, moderately modified (0.75 mmol/g carrier) with 3-aminopropyltriethoxysilane were investigated. Activity of the best biocatalysts, expressed in ABTS oxidation, was 4028 U/mL of the carrier or 3530 U/mg of bound protein. Properties of immobilized laccase were determined to find excellent thermal stability improvement; t(1/2) for freely suspended enzyme was 2-3 min at 80 degrees C, whereas after immobilization over 100 min. Kinetic experiments in both batch and packed-bed reactors gave only four times lower k(cat)/K(m) value than for the native enzyme. A packed-bed reactor with silica-gel-bound laccase beads appeared to be very efficient in ABTS oxidation and its exceptional potentials were shown in the continuous decolorization of indigo carmine for 18 days without loss in activity. This system offers perfect ability to degrade recalcitrant dyes, but we can also envisage its use, with ABTS acting as a mediator, in regeneration of nicotinamide cofactors.

Modelling of oscillatory behaviour in continuous ethanol fermentation

SummaryIt is shown that a tri-compartment cell population model with kinetics predicting decrease of product inhibition with decrease in substrate concentration can portray all dynamic situations observed in continuous ethanol fermentations depending on substrate concentration, from sustained oscillations to completely stable cultures.

Nickel-alumina composite aerogel catalysts with a high nickel load: a novel fast sol-gel synthesis procedure and screening of catalytic properties

AbstractNickel–aluminacompositeaerogelswithlargenickelloadingweresynthesizedusinganovelcomplexingagent-assisted sol–gel procedure to obtain materials displaying very large and open internal surface area, easily ac-cessible for large molecules and demonstrating excellent catalytic properties. They were tested in the followingreactions:(i)hydrogenationofpropeneand1-butene,(ii)methanizationofcarbondioxide,(iii)isometizationof1-butene,(iv)dehydrogenationofcyclohexane,(v)conversionofequimolarmixtureofCOandNOtoCO 2 andN 2 .Fullconversions and 100% selectivities were obtained in reactions (i), (ii), (iv) and (v) and an equilibrium composi-tioninreaction(iii).ThesecatalystsshowednopyrophoricactivityonexposingtoairevenatNicontentaslargeas50wt%. 2003ElsevierScienceB.V.Allrightsreserved. 1. IntroductionThenickel-basedcatalystsareofconsiderableindustrialinterest,especiallyforreactionssuchashydrogenationofaromaticsandunsaturatedhy-drocarbons, CO 2 =CH 4 reforming and reductionoffunctionalgroups[1–5],andaluminaismostoften used as nickel support. Quite often thesecatalystscontainaconsiderablenickelload,wellinexcessof10%(w/w)[2,5],toensureapropersurfacedensityandsizeofmetalclusters.How-ever,carbondepositionoverthemetallicandtheacidsidesofthesupportandNiparticlelossandsinteringathightemperatures,facilitatedbyhighnickelloadings,leadtocatalystsdeactivation.Itis well documented that this carbon depositiondecreaseswiththeincreaseinbasestrengthofthecatalystsandtheadditionoflantanium,magne-sium or molybdenium oxides has been foundparticularlyusefultodiminishthiseffect[3,6,7].

Potentials and Prospects for Application of Supercritical Fluid Technology in Bioprocessing

Abstract Recent investigations on the application of supercritical (SC) fluid technology in bio- and food chemistry are reviewed. The gas-antisolvent crystallization and rapid expansion of SC fluid emerge as attractive methods for micron-size particle formation. Also gaining ground is enzymic catalysis in SC CO 2 , which offers the possibility of integrated synthesis-product recovery processes. These processes, successfully tested on a laboratory scale, need further scale-up and optimization. Supercritical CO 2 has proven to be unfriendly, or even toxic, for living microorganisms, which precludes direct fermentation in dense CO 2 but does not rule out other useful applications.

Thermostability and esterification activity ofMucor javanicus lipase entrapped in silica aerogel matrix and in organic solvents

The lipase ofMucor javanicus (nowM. circinelloides) entrapped in silica matrix by the sol-gel method esterified primary and secondary alcohols with conversions ranging from 30 to 35% and 10 to 15%, respectively. Loss in activity of the preparations after incubation at 100°C for 1 h with petroleum ether, dodecane, 1-heptanol or oleyl alcohol was about half of that observed for the native lipase.

DRAG AND MASS TRANSFER IN SLOW NON-NEWTONIAN FLOWS OVER AN ENSEMBLE OF NEWTONIAN SPHERICAL DROPS OR BUBBLES

An approximate solution for the slow motion of an ensemble of spherical drops through a power law fluid is obtained using Happels free-surface cell model. It is shown that the drag coefficient decreases with decrease of the flow index and that this reduction is more significant at low voidage and large viscosity ratio parameter. The effect of the pseudoplastic anomaly on the mass transfer rate is more pronounced at low voidage for large values of viscosity ratio parameter, unlike the case of a single spherical drop The present analysis covers the whole range of values of viscosity ratio parameter from infinity (an assemblage of solid spheres) to zero (a swarm of bubbles) and reduces to the solutions for those cases already known The results for the motion of an ensemble of spherical drops also provide the basis for proposing a tentative expression for the expansion of liquid-liquid fluidized bed at low Reynolds number.

Alkaline lipase from Pseudomonas fluorescens non-covalently immobilised on pristine versus oxidised multi-wall carbon nanotubes as efficient and recyclable catalytic systems in the synthesis of Solketal esters

In order to produce effective and recyclable catalysts for enantioselective transesterification in the industrial applications, alkaline lipase from Pseudomonas fluorescens was non-covalently immobilised (ca. 6 wt%) on pristine multi-wall carbon nanotubes (MWCNTs) and oxidised MWCNTs (O-MWCNTs) using an adsorption technique. Mesoporous silica modified with n-octyl groups was used as a reference support. Irreversible transesterifications of three vinyl esters (acyl donors) by racemic Solketal with a chromatographically (GC) traced kinetics were selected as model reactions. The undertaken comparative studies revealed that different morphology and chemical functionalisation of the supports led to various enzyme loadings, catalytic activities and enantioselectivities. MWCNT-lipase emerged as the exceptionally active (yield up to 98%, t=1h, 1320 Ug(-1), i.e. 9 times more active than native enzyme) whereas lipase immobilised on O-MWCNTs as the most enantioselective system, particularly for longer acyl chain esters (e.e. up to 72% after 30 min at yield of 20%, 340 Ug(-1)). Moreover, the activity of all nanotube-based catalysts after 10 cycles of transesterification remained practically unchanged. The differences in performance of MWCNTs and O-MWCNTs as solid supports were found to be based on geometry of pores, dominating hydrophobic interactions and absence/presence of the surface polar groups. Due to an excellent activity and reusability of the nanotube-lipase catalysts one can propose (O-)MWCNT as supports of a prospective industrial relevance.

Immobilization of an integral membrane protein for biotechnological phenylacetaldehyde production

Styrene oxide isomerase (SOI) has previously been shown to be an integral membrane protein performing a highly selective, hydrolytic ring opening reaction of epoxides to yield pure aldehydes. Earlier studies had also shown a high sensitivity of SOIs toward their product phenylacetaldehyde which caused an irreversible inhibition and finally complete loss of activity at higher aldehyde concentrations. Here we report on the covalent immobilization of a styrene oxide isomerase (SOI) on SBA-15 silica carriers. The production of the SOI from a Rhodococcus strain was optimized, the enzyme was enriched and immobilized, and finally the biocatalyst was applied in aqueous as well as in two-phase systems. Linkage of the protein to epoxide or amino groups on the SBA-based carriers led to relatively poor stabilization of the enzyme in an aqueous system. But, improved stability was observed toward organic phases like the non-toxic phthalate-related 1,2-cyclohexane dicarboxylic acid diisononyl ester (Hexamol DINCH) which here to our knowledge was used for the first time in a biotechnological application. With this two-phase system and the immobilized SOI, 1.6-2.0× higher product yields were reached and the lifetime of the biocatalyst was tremendously increased.

Remarks on some properties of the equation of heat transfer in multichannel exchangers

Abstract Some properties of the equation of heat transfer in n -channel mixed parallel and counter-flow exchangers are discussed. It is shown that the matrix of coefficients A is of rank n − 1, and the necessary and sufficient condition for A to have two zero latent roots is given.