Double-Slit Model for Partially Wetted Trickle Flow Hydrodynamics

A Double-Slit Model Developed Can Predict the Frictional Two-Phase Pressure Drop, External Liquid Holdup, Pellet-Scale External Wetting Efficiency, and Gas - Liquid Interfacial Area in Cocurrent Downflow Trickle-Bed Reactors Operated under Partially Wetted Conditions in the Trickle Flow Regime. the Model, an Extension of the Holub Et Al. (1992, 1993) Mechanistic Pore-Scale Phenomenological Approach, Was Designed to Mimic the Actual Bed Void by Two Inclined and Interconnected Slits: Wet and Dry Slit. the External Wetting Efficiency is Linked to Both the Pressure Drop and External Liquid Holdup. the Model Also Predicts Gas - Liquid Interfacial Areas in Partially Wetted Conditions. an Extensive Trickle-Flow Regime Database Including over 1,200 Measurements of Two-Phase Pressure Drop, Liquid Holdup, Gas - Liquid Interfacial Area and Wetting Efficiency, Published in 1974-1998 on the Partial-Wetted Conditions, Was Used to Validate the Modeling Approach. Two New Improved Slip-Factor Functions Were Also Developed using Dimensional Analysis and Artificial Neural Networks. High-Pressure and -Temperature Wetting Efficiency, Liquid Holdup, Pressure Drop, and Gas - Liquid Interfacial Area Data from the Literature on the Trickle-Flow Regime using Conventional Monosized Beds and Catalyst Bed-Dilution Conditions Were Successfully Forecasted by the Model

Discriminating Trickle-Flow Hydrodynamic Models: Some Recommendations

The Forecasting Ability of Five One-Dimensional (1-D) Two-Fluid Phenomenological Models for Liquid Holdup and Two-Phase Pressure Drop in Trickle-Flow Reactors Was Evaluated using the Most Comprehensive Trickle-Flow Regime Database. All of These Models, Namely, the Permeability Model, the Slit Model, the Extended Slit Model, the 1-D CFD Model, and the Double-Slit Model Can Be Used to Predict Liquid Holdup. among Them, the Permeability and the Slit Models, Because of a Much Simpler Structure, Are Recommended. the Extended Slit Model based on Iliuta Et Al. (Ind. Eng. Chem. Res. 1998, 37, 4542) Shear and Slip Constitutive Relationships Can Be Employed for Two-Phase Pressure Drop Predictions. When the Knowledge of Wetting Efficiency Becomes Essential at Very Low Liquid Flow Rates, the Double-Slit Model is Recommended

A comparative study of biodegradation of vinyl acetate by environmental strains

Four Gram-negative strains, E3_2001, EC1_2004, EC3_3502 and EC2_3502, previously isolated from soil samples, were subjected to comparative studies in order to select the best vinyl acetate degrader for waste gas treatment. Comparison of biochemical and physiological tests as well as the results of fatty acids analyses were comparable with the results of 16S rRNA gene sequence analyses. The isolated strains were identified as Pseudomonas putida EC3_2001, Pseudomonas putida EC1_2004, Achromobacter xylosoxidans EC3_3502 and Agrobacterium sp. EC2_3502 strains. Two additional strains, Pseudomonas fluorescens PCM 2123 and Stenotrophomonas malthophilia KB2, were used as controls. All described strains were able to use vinyl acetate as the only source of carbon and energy under aerobic as well as oxygen deficiency conditions. Esterase, alcohol dehydrogenase and aldehyde dehydrogenase were involved in vinyl acetate decomposition under aerobic conditions. Shorter degradation times of vinyl acetate were associated with accumulation of acetic acid, acetaldehyde and ethanol as intermediates in the culture fluids of EC3_2001 and KB2 strains. Complete aerobic degradation of vinyl acetate combined with a low increase in biomass was observed for EC3_2001 and EC1_2004 strains. In conclusion, P. putida EC1_2004 is proposed as the best vinyl acetate degrader for future waste gas treatment in trickle-bed bioreactors

Removal of gaseous toluene using immobilized Candida tropicalis in a fluidized bed bioreactor

A pure yeast strain Candida tropicalis was immobilized on the matrix of powdered activated carbon, sodium alginate, and polyethylene glycol (PSP beads). The immobilized beads were used as fluidized material in a bioreactor to remove toluene from gaseous stream. Applied toluene loadings were 15.4 and 29.8 g/m3 h in Step 1 and Step 2, respectively, and toluene removal was found above 95% during the entire operation. A continuous pH decline was observed and pH of the suspension was just above 6 in Step 2 but no adverse effects on treatment efficiency were observed. The CO2 yield values were found to be 0.57 and 0.62 g-\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$C_{{{\text{CO}}_{2} }} /{\text{g-}}C_{\text{toluene}}$$\end{document} in Step 1 and Step 2, respectively. These values indicate that a major portion of toluene-carbon was channeled to yeast respiration even at higher toluene loading. In conclusion, immobilized C. tropicalis can be used as a fluidized material for enhanced degradation of gaseous toluene

The prevalence of autosomal dominant polycystic kidney disease (ADPKD): A meta-analysis of European literature and prevalence evaluation in the Italian province of Modena suggest that ADPKD is a rare and underdiagnosed condition

ADPKD is erroneously perceived as a not rare condition, which is mainly due to the repeated citation of a mistaken interpretation of old epidemiological data, as reported in the Dalgaard's work (1957). Even if ADPKD is not a common condition, the correct prevalence of ADPKD in the general population is uncertain, with a wide range of estimations reported by different authors. In this work, we have performed a meta-analysis of available epidemiological data in the European literature. Furthermore we collected the diagnosis and clinical data of ADPKD in a province in the north of Italy (Modena). We describe the point and predicted prevalence of ADPKD, as well as the main clinical characteristics of ADPKD in this region

Techno-economic assessment of membrane assisted fluidized bed reactors for pure H2 production with CO2 capture

This paper addresses the techno-economic assessment of two membrane-based technologies for H2 production from natural gas, fully integrated with CO2 capture. In the first configuration, a fluidized bed membrane reactor (FBMR) is integrated in the H2 plant: the natural gas reacts with steam in the catalytic bed and H2 is simultaneously separated using Pd-based membranes, and the heat of reaction is provided to the system by feeding air as reactive sweep gas in part of the membranes and by burning part of the permeated H2 (in order to avoid CO2 emissions for heat supply). In the second system, named membrane assisted chemical looping reforming (MA-CLR), natural gas is converted in the fuel rector by reaction with steam and an oxygen carrier (chemical looping reforming), and the produced H2 permeates through the membranes. The oxygen carrier is re-oxidized in a separate air reactor with air, which also provides the heat required for the endothermic reactions in the fuel reactor. The plants are optimized by varying the operating conditions of the reactors such as temperature, pressures (both at feed and permeate side), steam-to-carbon ratio and the heat recovery configuration. The plant design is carried out using Aspen Simulation, while the novel reactor concepts have been designed and their performance have been studied with a dedicated phenomenological model in Matlab. Both configurations have been designed and compared with reference technologies for H2 production based on conventional fired tubular reforming (FTR) with and without CO2 capture. The results of the analysis show that both new concepts can achieve higher H2 yields than conventional plants (12-20% higher). The high electricity consumptions of membrane-based plants are associated with the required low pressure at the retentate side. However, the low energy cost for the CO2 separation and compression makes the overall reforming efficiency from 4% to 20% higher than conventional FTR with CO2 scrubbing. FBMR and MA-CLR show better performance than FTR with CO2 capture technology in terms of costs mainly because of lower associated CAPEX. The cost of H2 production reduces from 0.28 €/NmH23 to 0.22 €/NmH23 (FBMR) and 0.19 €/NmH23 (MA-CLR)

Reversible Aging in Asphalt Binders

X-ray diffraction, optical microscopy, and mass spectrometry techniques were used in an attempt to clarify the morphological and chemical features that are responsible for reversible aging processes that occur in asphalt binders during conditioning at low temperatures. The reversible aging term is used in this paper to capture all reversible processes (i.e., wax crystallization, free volume collapse, asphaltene aggregation, etc.) that lead to a reduction in low-temperature rheological and fracture performance. Crystalline content and asphaltene aggregate size at ambient temperatures, as measured by X-ray diffraction on thin asphalt films, are identified as two factors that correlate reasonably well with the reversible aging tendency at low temperatures. A coarse and unstable colloidal state for the asphaltene fraction is also identified as an important contributor to reversible aging. It was found that the saturates fraction has a particularly significant role in the aging process, with those asphalts containing higher amounts of linear paraffin losing more in terms of rheological performance. This important phenomenon is responsible for significant fracture distress in asphalt pavements in northern climates and therefore deserves further investigation. Some of the air-blown asphalts investigated in this study were found to show a high crystalline content and a coarse phase morphology and concurrent tendency for reversible aging during cold conditioning. This may be due to the crude source(s) employed, the chemistry of the air-blowing process, or resulting phase changes. Other air-blown binders did not show these features while they were still susceptible to reversible aging. Hence, the reason for this behavior appears to be due to multiple processes which are at present only poorly understood

Integrated aqueous-phase glycerol reforming to dimethyl ether synthesis A novel allothermal dual bed membrane reactor concept

BIOVERT+PFODimethyl ether (DME) production from glycerol via an integrated process involving aqueous-phase glycerol reforming to biosyngas combined with DME synthesis into an allothermal dual-bed membrane reactor was analyzed numerically. The system combines two separate enclosures, a fixed-bed water perm-selective membrane DME synthesis unit and a gas-liquid-solid fixed-bed aqueous-phase glycerol reforming unit. Exothermic DME synthesis provides heat to endothermic aqueous-phase glycerol reforming which in return produces biosyngas for DME synthesis. The two-scale, non-isothermal, unsteady-state model developed for the integrated system accounts for a detailed gas/gas-liquid dynamics whereupon DME synthesis/aqueous-phase glycerol reforming kinetics, thermodynamics, thermal effects and variable gas flow rate due to chemical/physical contractions were accounted for. The integrated process is intended to minimize abundant glycerol by-product streams via an energy efficient alternative for producing DME. It presents an opportunity to improve the economics of green DME synthesis by cost reduction of biosyngas production while improving thermal efficiency of DME synthesis. (C) 2012 Elsevier E.V. All rights reserved