Douglas W. Reeve

Model for flux prediction in high-shear microfiltration systems

Abstract A semi-empirical model that predicts permeate fluxes in high-shear microfiltration systems is proposed. The model assumes that non-diffusive transport phenomena are the main mechanisms for the back-transport of particles from the membrane surface to the bulk solution during filtration. It also considers the use of reverse filtration (back-flushing) to control and minimize concentration polarization and fouling. This model incorporates an equation for the transient flux based on a particle mass balance at the membrane surface. The model has been validated by laboratory experiments using two different suspensions: flexographic ink (Φb=0.005) and yeast (Φb=0.01), where Φb is the solid volume fraction in the suspension. The membrane system adopted in this research consists of a bundle of hollow-fiber microfiltration membranes submerged in a tank into which the effluent is introduced. Vacuum is used inside the fiber lumen to create transmembrane pressure differential, and aeration to promote high-shear stress at the membrane surface to minimize concentration polarization and fouling. Periodic reverse filtration (back-flushing) is also used. The experimental validation of the model was carried out by substituting the experimentally determined suspension and operating variables into the model. The results showed good agreement between model prediction and experimental observations.

Sample Contamination in Analysis of Wood Pulp Fibers with X‐ray Photoelectron Spectroscopy

Abstract Contamination of wood pulp fiber samples by the ambient in the x‐ray photoelectron spectroscopy (XPS) analysis was investigated. Various control samples, including platinum foil, cellophane, cellobiose, rayon, cotton, and fully bleached wood pulp fibers, were used for identification and characterization of the contamination sources. It has been found that contaminating material on wood fiber surfaces contains both carbon and oxygen and is responsible for the discrepancy between the true elemental composition of wood pulp fiber surfaces and the composition determined by XPS. A physical model of the contamination has been proposed which allows compensation for the contamination in quantitative analysis of surface lignin by XPS.

Fluorescent Labeling of Lignin in the Wood Pulp Fiber Wall

Abstract Fluorescent labeling of lignin in wood pulp fibers with acridine orange (AO) was investigated. The orthochromatic and metachromatic labeling conditions were explored, and the quantitative aspects of fluorescence analysis were discussed. It was found that with sufficiently low AO concentration, orthochromatic only labeling of lignin could be attained, and the fluorescence intensity of stained pulp fibers could be correlated to the lignin concentration of the pulp. The distribution of lignin across the fiber wall was clearly imaged with confocal laser scanning microscopy (CLSM) after fluorescent staining of pulp fibers.

Engineering leadership: Grounding leadership theory in engineers’ professional identities:

In recent years the US-based National Academy of Engineering and Engineers Canada have urged engineering educators to supplement technical coursework with multiple domains of professional skills development. One such domain is that of engineering leadership. While leadership education is beginning to be infused into some undergraduate engineering programs, it has not yet gained traction as a legitimate field of study. The legitimacy of the field depends on engineers recognizing themselves as members of a leadership profession. Our paper facilitates this process of recognition by grounding leadership theory in the professional experiences of engineers employed by four Canadian engineering-intensive firms. Our constant comparative analysis of qualitative data collected through nine focus groups and seven interviews suggests that engineers are largely resistant to dominant leadership paradigms drawn from other disciplines, but that they do, in fact lead in ways that blend key aspects of their identities with professionally recognized forms of influence. Our compound model of engineering leadership has practical and theoretical implications for engineers, leadership theorists and engineering educators.

Identification and confirmation of traces of chlorinated fatty acids in fish downstream of bleached kraft pulp mills by gas chromatography with halogen-specific detection.

Methyl esters of threo-9,10-dichlorooctadecanoic, threo-7,8-dichlorohexadecanoic, and threo-5,6-dichlorotetradecanoic acids, present in transesterified extracts of filets, gonad, intestinal fat and carcass of white sucker (Catostomus commersoni) sampled in receiving waters of bleached kraft pulp mill effluents, were identified by gas chromatography with halogen-specific detection (XSD). Identification was based on (1) a comparison of the retention times of a sample peak with a prospective reference standard on two stationary phases of very different polarities by spiking, and (2) elution behavior of configurational and positional isomers of dichloro fatty acid methyl esters.

The Synthesis and Chemical Structures of Tetrameric Lignin Model Compounds

ABSTRACT In order to study the reaction of high molecular weight residual lignin in pulp with chlorine dioxide, three types of tetrameric lignin model compounds were designed and synthesized. All three tetramers contain diphenylmethane condensation - type structures but 1 also contains a biphenyl structure and 3 contains β-arylether linkages. Synthesis of tetramer 1 involved oxidative coupling of vanillin followed by reduction and condensation with an excess of creosol under alkaline conditions. Tetramer 2 was prepared by the condensation of vanillin with formaldehyde followed by reduction and condensation as for tetramer 1. Preparation of tetramer 3 was accomplished by condensation of a dimer containing a β-aryl ether linkage with formaldehyde.

Initial Delignification and Cellulose Degradation of Conventional and Ethanol-Assisted Ozonation

Abstract It has been proposed that the initial regime of pulp ozonation is a diffusion controlled process, due to the low solubility of ozone and its very fast reaction with lignin. However, whether the process is governed by diffusion on a fibre wall scale (macro diffusion control), on a (micro)fibril scale (micro diffusion control), or by reaction with lignin located on the fibre surface followed by diffusion control is an open question. In order to address this, a 31 kappa Hemlock kraft pulp impregnated with acidified (pH = 2.0) water or acidified (pH = 2.0) ethanol-water (70% w/w) was ozonated at high consistency in a differentially operated packed bed reactor. The cellulose degradation and pulp delignification rates were determined from the change in pulp viscosity and kappa number with ozonation time. Transmission electron microscopy (TEM) was used to visualize the lignin distribution of KMnO4 stained fibre walls. The TEM pictures clearly show reacted lighter regions at exposed fibre surfaces, which...

Chlorination of linoleic acid

Abstract Aqueous chlorination of linoleic acid gave a mixture of tetrachlorostearic acid, trichlorohydroxystearic acid and dichlorohydroxystearic acid of linoleic acid in relative percentages of 49%, 38% and 13% respectively. Treatment of threo-cis-cis-9,10,12,13-diepoxystearic acid with HCl gave a mixture of tetrahydrofuranyl ethers and dichlorohydrins in relative percentages of 24% and 76%. A separate synthesis of trichlorohydroxystearic acid is described. Products were identified by infrared spectrometry (IR), nuclear magnetic resonance spectroscopy (NMR) and negative methane chemical ionization mass spectrometry (NCl). Chlorohydrins were confirmed by their conversion to epoxides by NaOH.

Evaluation of Halogen‐Specific Detector (XSDTM) for Trace Analysis of Chlorinated Fatty Acids in Fish

Abstract The applicability of a halogen‐specific detector (XSD™, manufactured by OI Analytical) was evaluated for GC analysis of chlorinated fatty acid methyl esters (FAMEs) that are present at trace levels in transesterified fish extract, a complex matrix consisting of similar but nonchlorinated compounds. A characteristic of the XSD working principle is that thermal electron emission, negative surface ionization and positive surface ionization are all operative in a concerted manner. While the XSD is not superior to other GC detectors in terms of signal‐to‐noise, its merit is in its high selectivity (106) and low detection limit (2 pg Cl) for chlorinated fatty acids, and ease of operation and maintenance. Its reasonably wide linear range (up to 10 ng Cl) is desirable for trace analysis of chlorinated FAMEs. A major drawback of this detector is a certain degree of peak broadening and peak tailing of eluted compounds with concentrations larger than ∼1 ng Cl/µL in the injected solution even though this value does not exceed the upper limit of the XSD linear range. Nevertheless, in trace analysis of chlorinated compounds, the concentrations of analytes are usually well below 1 ng Cl/µL. Parallel use of the XSD and a universal detector such as FID in gas chromatography is useful for optimizing operation conditions for trace analysis and simultaneously analyzing nonchlorinated major components.

Enrichment of Trace Chlorinated Species in a Complex Matrix of Fatty Acids Using HPLC in Conjunction with Gas Chromatography‐Halogen Specific Detection

Abstract Due to the similarity in chemical and physicochemical properties between analytes (chlorinated fatty acids) and matrix compounds (nonchlorinated fatty acids), conventional cleanup procedures were not successful in analysis of chlorinated fatty acids in extracts of freshwater fish. A new approach was devised of utilizing reversed‐phase high performance liquid chromatography (HPLC) for its high separation power, and the halogen specific detector (XSD) for its high selectivity for organochlorine. The bulk of nonchlorinated matrix was removed by HPLC fractionation, and target chlorinated analytes were selectively enriched. The enrichment effect was assessed by a universal detector, a flame ionization detector (FID). Methyl esters of chlorinated fatty acids were completely nondetectable prior to HPLC fractionation, but were present as moderate or small, yet discernible, peaks after the HPLC enrichment. This enrichment method is efficient with good selectivity, reproducibility, and predictability.