Derk Willem Frederik Brilman

Gas absorption in an agitated gas-liquid-liquid system

Gas–liquid–liquid systems have gained interest in the past decade and are encountered in several important industrial applications. In these systems an immiscible liquid phase may affect the gas absorption rate significantly. This phenomenon, however, is not completely understood and underlying mechanisms need further study. In this work the well-known Danckwerts-plot technique is used to determine the liquid side mass transfer coefficient kL and the gas–liquid interfacial area a simultaneously in this type of systems. As absorption/reaction system CO2 absorption in a 0.5 MK2CO3 0.5 MKHCO3 buffer solution catalysed by sodium hypochlorite was chosen. Toluene, n-dodecane, n-heptane and 1-octanol were applied as dispersed liquid phases. The Danckwerts-plot could be well used in gas–liquid–liquid systems and from the results it appeared that two types of systems exist; systems that enhance mass transfer and systems that do not enhance mass transfer. Effects at low dispersed phase hold-up were observed to be very strong and are thus important, but were not taken into account in further analysis of the effect of dispersed phase hold-up on mass transfer. In systems where dodecane and heptane were added to the buffer solutions no enhancement of mass transfer was observed. However, the addition of toluene and 1-octanol caused an enhancement of mass transfer that could be well described using a homogeneous model of the shuttle mechanism.

Effective lipid extraction from algae cultures using switchable solvents

a Centro Interdipartimentale di Ricerca Industriale (CIRI), University of Bologna, via S. Alberto 163, Ravenna, Italy. Fax: 0039-0544-937411; Tel: 0039-0544-937353; E-mail: chiara.samori3@unibo.it b Department of Biosystems Engineering, University of Ghent, Ghent, Belgium c Thermo-Chemical Conversion of Biomass Group, Faculty of Science and Technology, University of Twente, Enschede, The Netherlands d Department of Chemistry “Ciamician”, University of Bologna, via F. Selmi 2, 40126 Bologna Italy.

Secondary amines as switchable solvents for lipid extraction from non-broken microalgae

Lipids from algal biomass may provide renewable fuel and chemical feedstock in large quantities. The energy intensity of drying and milling of algae prior to extraction and of solvent recovery afterwards is a major obstacle. The objective is to use switchable solvents to extract oil directly from wet microalgae slurries without the need for drying and milling, and subsequently recover the extracted oil and solvent by simple phase splitting, using CO2 as trigger. In this work secondary amine solvents were investigated for lipids extraction, polarity switching and phase splitting ability upon contacting with CO2. For strain Desmodesmus sp. extraction yields from the wet algal slurries, with and without cell disruption, were comparable with Bligh & Dyer method yields. Oil and solvent recovery via phase separation was realized by CO2 induced phase splitting, making secondary amines a candidate for further development of an energy efficient lipid extraction technology for non-broken microalgae.

Heterogeneous mass transfer models for gas absorption in multiphase systems

Heterogeneous, instationary 2-D and 3-D mass transfer models were developed to study the effect of dispersed liquid-phase droplets near the gas–liquid interface on the local gas absorption rate. It was found among other things that droplets (or particles) influence local mass transfer rates over an area exceeding largely the projection of the droplets on the gas–liquid interface. For a specific application particle–particle interaction was studied and could be described by a single parameter, depending only on the minimum interparticle distance. For gas absorption flux prediction an unit cell must be defined. The sensitivity of the absorption flux to the definition of the unit cell was investigated. Finally, a complete strategy to arrive at gas absorption flux prediction from single particle simulations has been proposed.

A one-dimensional instationary heterogeneous mass transfer model for gas absorption in multiphase systems

For a physically correct analysis (and prediction) of the effect of fine, dispersed phase drops or particles on the mass transfer rate in multiphase systems, it was demonstrated that only 3-D instationary, heterogeneous mass transfer models should be used. Existing models are either homogeneous, stationary or single particle models. As a first step, a 1-D, instationary, heterogeneous multi-particle mass transfer model was developed. With this model the influence of several system parameters was studied and problems and pitfalls in the translation of modeling results for heterogeneous models into a prediction of absorption fluxes are discussed. It was found that only those particles located closely to the gas–liquid interface determine mass transfer. For these particles the distance of the first particle to the gas–liquid interface and the particle capacity turned out to be the most important parameters. Comparisons with a homogeneous model and experimental results are presented. Typical differences in results comparing a homogeneous model with the 1-D heterogeneous model developed in this work could be attributed to a change in the near interface geometry. Future work in this field should therefore be directed towards near interface phenomena. Three dimensional mass transfer models, of which a preliminary result is presented, are indispensable for this.

Supercritical water gasification of sewage sludge: gas production and phosphorus recovery

In this study, the feasibility of the gasification of dewatered sewage sludge in supercritical water (SCW) for energy recovery combined with P-recovery from the solid residue generated in this process was investigated. SCWG temperature (400°C, 500°C, 600°C) and residence time (15min, 30min, 60min) were varied to investigate their effects on gas production and the P recovery by acid leaching. The results show that the dry gas composition for this uncatalyzed gasification of sewage sludge in SCW mainly comprised of CO2, CO, CH4, H2, and some C2-C3 compounds. Higher temperatures and longer residence times favored the production of H2 and CH4. After SCWG, more than 95% of the P could be recovered from the solid residue by leaching with acids. SCWG combined with acid leaching seems an effective method for both energy recovery and high P recovery from sewage sludge.

Recycling nutrients in algae biorefinery

Algal fuel cells: Repeated nutrient recycling is demonstrated by reusing the aqueous phase obtained from the hydrothermal liquefaction (HTL) of microalgae. This is achieved, for the first time, by performing a complete set of four continuous growth–HTL cycles. Results show similar growth rates in each cycle, the potential of nutrient reduction, as well as cell morphology changes. This study demonstrates progress towards the standalone operation of algae biorefineries

Experimental study of the effect of bubbles, drops and particles on the product distribution for a mixing sensitive, parallel-consecutive reaction system

For stirred multiphase reactors the effect of a dispersed (gas, liquid or solid) phase on the product distribution for a mixing sensitive reaction was tested. Turbulence modification due to the presence of dispersed-phase particles has been reported frequently in literature, but the extent of the effect in a stirred multiphase reactor was not clear. In this work the well-known mixing sensitive diazo-coupling reaction system was selected to investigate the influence of the changes in the turbulent kinetic energy spectrum on the product distribution. This reaction system was found to be suitable to study the influence of a dispersed (gas, liquid or solid) phase. The Engulfment model could describe the single-phase experiments and describes reasonably well the multiphase experiments when the effective dispersion properties are implemented. For the liquid–liquid dispersions effects of de-localization of the reaction zone were encountered, due to Naphthol extraction by the dispersed phase. The Engulfment model was extended to incorporate mass transfer and the first experimental and simulation results are promising. Additional, experimental and theoretical, research studying the combined effects of the mass transfer rate and the mixing rate for the liquid–liquid dispersions is highly desired.

Stability of a Benzyl Amine Based CO2 Capture Adsorbent in View of Regeneration Strategies

In this work, the chemical and thermal stability of a primary amine-functionalized ion-exchange resin (Lewatit VP OC 1065) is studied in view of the potential options of regenerating this sorbent in a CO2 removal application. The adsorbent was treated continuously in the presence of air, different O2/CO2/N2 mixtures, concentrated CO2, and steam, and then the remaining CO2 adsorption capacity was measured. Elemental analysis, BET/BJH analysis, Fourier transform infrared spectroscopy, and thermogravimetric analysis were applied to characterize adsorbent properties. This material was found to be thermally and hydrothermally stable at high temperatures. However, significant oxidative degradation occurred already at moderate temperatures (above 70 °C). Temperatures above 120 °C lead to degradation in concentrated dry CO2. Adding moisture to the concentrated CO2 stream improves the CO2-induced stability. Adsorbent regeneration with nitrogen stripping is studied with various parameters, focusing on minimizing the moles of purge gas required per mole of CO2 desorbed.

Gas-liquid-liquid reaction engineering : the Koch synthesis of pivalic acid from iso- and tert-butanol; Reaction kinetics and the effect of a dispersed second-liquid phase

In gas–liquid–liquid reaction systems with fast parallel and consecutive reactions the effects of mass transfer and mixing on the product yield can be significant. The Koch synthesis of pivalic acid, using sulfuric acid as catalyst, was chosen to study these effects. Reaction kinetics and the effect of the catalyst-phase composition have been investigated by using isobutanol as reactant. For studying the effect of an immiscible liquid phase on the reaction products obtained, the more reactive tert-butanol was used. Pivalic acid can be produced from isobutanol using sulfuric acid as a catalyst solution with 2-methylbutanoic acid as main byproduct, if gas–liquid mass transfer limitations are excluded. The selectivity towards 2-methylbutanoic acid is generally less than 20% and decreases strongly with decreasing acidity. The reaction is first order in isobutanol and dehydration is likely to be rate determining. The presence of pivalic acid and isobutanol strongly reduces the apparent reaction rate constant by decreasing the solution acidity (Ho). For the industrially applied backmixed reactors in the Koch synthesis, this may imply that these operate at much lower values for Ho. On addition of an immiscible heptane phase, the reaction products are extracted to some extent and this adds to maintaining a high catalyst solution acidity. Using tert-butanol, the yield and pivalic acid selectivity was found to depend strongly on CO transport to the reaction zone through gas–liquid mass transfer and mixing. The presence of an immiscible heptane phase increased the product yield and selectivity towards pivalic acid significantly.