Shengwei Tang

Effects of Orifice Orientation and Gas-Liquid Flow Pattern on Initial Bubble Size

In many gas-liquid processes, the initial bubble size is determined by a series of operation parameters along with the sparger design and gas-liquid flow pattern. Bubble formation models for variant gas-liquid flow patterns have been developed based on force balance. The effects of the orientation of gas-liquid flow, gas velocity, liquid velocity and orifice diameter on the initial bubble size have been clarified. In ambient air-water system, the suitable gas-liquid flow pattern is important to obtain smaller bubbles under the low velocity liquid cross-flow conditions with stainless steel spargers. Among the four types of gas-liquid flow patterns discussed, the horizontal orifice in a vertically upward liquid flow produces the smallest initial bubbles. However the orientation effects of gas and liquid flow are found to be insignificant when liquid velocity is higher than 3.2 m·s−1 or the orifice diameter is small enough.

Enhanced adsorption of Cu(II) ions on chitosan microspheres functionalized with polyethylenimine-conjugated poly(glycidyl methacrylate) brushes

To enhance the adsorption capacity of crosslinked chitosan (CCS) microspheres towards Cu(II) ions, well-defined poly(glycidyl methacrylate) (PGMA) brushes were grafted onto the surfaces of CCS microspheres via surface-initiated atom transfer radical polymerization (ATRP) for subsequent conjugation of polyethylenimine (PEI). The resultant PEI-grafted CCS (defined as CCS-g-PGMA-c-PEI) microsphere was used as an effective adsorbent to uptake Cu(II) ions from aqueous solution. Success in each functionalization step was ascertained by ATR-FTIR, XPS, SEM and water contact angle measurements. Batch adsorption experiments were performed to determine adsorption kinetics, adsorption isotherms and thermodynamics of Cu(II) ions on the CCS-g-PGMA-c-PEI microspheres. The adsorption equilibrium of Cu(II) ions on the microspheres was found to be rapidly established within 60 min at an optimal solution pH of 5.0, and the adsorption kinetics was well represented by the pseudo-second-order model, together with a significant effect of mass transfer on the Cu(II) adsorption rate. The Langmuir-fitted maximum adsorption capacity was about 3.58 mmol g−1 (229 mg g−1), and the calculated thermodynamic parameters demonstrated an endothermic and spontaneous adsorption process of Cu(II) ions. The PEI-grafted CCS microspheres also exhibited good regenerability and stability for recycle applications. The postulated adsorption mechanism was proposed to account for the adsorption process of Cu(II) ions on the CCS-g-PGMA-c-PEI microspheres.

A Theoretical Model for the Size Prediction of Single Bubbles Formed under Liquid Cross-flow

Abstract The size of initial bubbles is an important factor to the developed bubble size distribution in a gas-liquid contactor. A liquid cross-flow over a sparger can produce smaller bubbles, and hereby enhance the performance of contactor. A one stage model by balancing the forces acting on a growing bubble was developed to describe the formation of the bubble from an orifice exposed to liquid cross-flow. The prediction with this model agrees with the experimental data available in the literatures, and show that orifice size strongly affects the bubble size. It is showed that the shear-lift force, inertia force, surface tension force and buoyancy force are major forces, and a simplified mathematical model was developed, and the detachment bubble diameter can be predicted with accuracy of

Click functionalization of poly(glycidyl methacrylate) microspheres with triazole-4-carboxylic acid for the effective adsorption of Pb(II) ions

Chelating 1,2,3-triazole-4-carboxylic acids were successfully introduced onto the cross-linked PGMA microsphere surfaces by the combination of ring-opening reactions and the click chemistry process between the alkynyl groups of propiolic acid (PA) and the epoxy groups on the surfaces of the PGMA microspheres. The resultant PA-conjugated PGMA microspheres were found to be an effective adsorbent for Pb(II) removal from aqueous solutions. Success in each functionalization step was ascertained by ATR-FTIR, XPS and SEM characterization. Batch and column adsorption experiments were performed to determine the adsorption kinetics, adsorption isotherms and thermodynamics of Pb(II) ions on the as-synthesized microspheres. The Langmuir-fitted maximum adsorption capacity for Pb(II) ions was found to be 69.41 mg g−1 at a solution pH of 5.0, together with the adsorption equilibrium being achieved within 60 min. The thermodynamic studies demonstrated an endothermic and spontaneous adsorption process of Pb(II) ions on the PA-conjugated PGMA microspheres. Column adsorption studies revealed the decrease in the adsorption capacities of the breakthrough and exhaustion points with increasing flow rate. The postulated adsorption mechanism was attributed to the electrostatic interactions from carboxylic groups and chelation or coordination of Pb(II) ions from the triazole moieties, which was facilitated to form a pluralistic potential trap for Pb(II) ions, as confirmed by XPS characterization.

Successive grafting of poly(hydroxyethyl methacrylate) brushes and melamine onto chitosan microspheres for effective Cu(II) uptake

Cross-linked chitosan (CCS) microspheres tethered with melamine-conjugated poly(hydroxyethyl methacrylate) (PHEMA) brushes were synthesized by combination of surface-initiated atom transfer radical polymerization (ATRP) of HEMA and subsequent covalent immobilization of melamine onto the chain ends of PHEMA brushes. The as-synthesized CCS microsphere was used as a novel adsorbent for effective uptake of Cu(II) ions from aqueous solution. Success in each functionalization step was ascertained by SEM, ATR-FTIR and XPS characterization. Batch adsorption experimental results demonstrated that the adsorption equilibrium of Cu(II) ions on the melamine-grafted CCS microsphere was rapidly established within 20 min, and the adsorption process was found to be governed by intra-particle diffusion and chemisorption processes. The Langmuir-fitted maximum adsorption capacity of Cu(II) ions on the as-synthesized CCS microspheres was as high as circa 4.67 mmol L-1 (299 mg g-1). The calculated thermodynamic parameters revealed an endothermic and spontaneous adsorption process of Cu(II) ions on the melamine-grafted CCS microspheres. XPS spectra revealed that the adsorption mechanism was attributed to coordination (or chelation) interactions between amino (or hydroxyl) groups with cationic Cu(II) ions.

Influences of the [Co2+]/[Co3+] Ratio on the Process of Liquid-phase Oxidation of Toluene by Air

Liquid phase oxidation of toluene is an environmental benign route for the production of benzoic acid. In a φ48mm bubble column reactor, the commercial process of toluene liquid phase oxidation was conducted with Co(CH3COO)2.4H2O as catalyst. The Co(superscript 2+) concentration [Co(superscript 2+)] was determined by extraction spectrophotometry and hereby the Co(superscript 3+) concentration [Co(superscript 3+)] was obtained by mass balance. The results showed that [Co(superscript 3+)] reached the maximum at about 25-30min. [Co(superscript 3+)] increased with increasing Co catalyst amount at total Co concentration＜150 mg•L^(-1) of toluene. The conversion of toluene, yield and selectivity of benzoic acid increased with the increasing [Co(superscript 3+)/Co(superscript 2+)] max. A high [Co(superscript 3+)] and a high [Co(superscript 3+)]/[Co(superscript 2+)] ratio are beneficial to the reaction.

Adsorption/desorption of 2,2,4-trimethylpentane on MCM-36 zeolite functionalized by acidic ionic liquid

AbstractThe facile desorption of products from the reaction sites is crucial to the reaction selectively and catalyst life. In the alkylation process of isobutane and olefine, the product is need to remove from the reaction sites timely so as to inhibit the sequential side reactions and improve the catalyst life. MCM-36 was modified by immobilizing ionic liquid [BTPIm][HSO4] (1-buty-3-(3-triethoxysilane)-propyl imidazolium hydrosulfate) so as to provide an effective way to improve the desorption of product 2,2,4-trimethylpentane from the reaction sites. The adsorption/desorption behaviors of 2,2,4-trimethylpentane on MCM-36 or ionic liquid immobilized MCM-36 were studied systematically by an intelligent gravimetric analyzer. The results showed that a decease adsorption capacity of 2,2,4-trimethylpentane was obtained after grafting [BTPIm][HSO4]. Langmuir–Freundlich model described the adsorption isotherms well. The ionic liquid immobilization led to a low isosteric adsorption heat. It indicated that a weaken interaction between adsorbate and adsorbent was obtained by the grafting of ionic liquid. The kinetics research results showed that the adsorption/desorption process was limited by the surface adsorption step. An increase of desorption rate constant and a decrease of adsorption sites were observed after the IL immobilization. It suggested that the ionic liquid loading was helpful to improve the desorption of 2,2,4-trimethylpentane from the reaction surface.