Bret H. Howard

Development of membranes for hydrogen separation: Pd coated V–10Pd

Abstract Numerous group IVB and VB alloys were prepared and tested as potential membrane materials, but most of these materials were brittle or exhibited cracking during hydrogen exposure. One of the more ductile alloys, V–10Pd (at.-%), was fabricated into a thin foil (107 μm thick) composite membrane coated with 100 nm of Pd on each side. The material was tested for hydrogen permeability, resistance to hydrogen embrittlement, and long term hydrogen flux stability. The hydrogen permeability ϕ of the V–10Pd membrane was 3·86×10–8 mol m–1 s–1 Pa–0·5 (average of three different samples) at 400°C, which is slightly higher than the permeability of Pd–23Ag at that temperature. A 1400 h hydrogen flux test at 400°C demonstrated that the rate of metallic interdiffusion was slow between the V–10Pd foil and the 100 nm thick Pd coating on the surface. However, at the end of testing, the membrane cracked at 118°C because of hydrogen embrittlement.

Improved benzene production from methane dehydroaromatization over Mo/HZSM-5 catalysts via hydrogen-permselective palladium membrane reactors

The effectiveness of hydrogen-permselective palladium membrane reactors for non-oxidative methane dehydroaromatization (MDA) over 4 wt% Mo/HZSM-5 catalysts was investigated as a function of weight hourly space velocity (WHSV) at 700 °C and atmospheric pressure. CH4 conversion and aromatic product yield decrease with increasing WHSV from 750 to 9000 cm3 gcat−1 h−1. C6H6 is the main C-containing product at and below 3000 cm3 gcat−1 h−1 whereas C2H4 dominates the C-product distribution at higher WHSVs. Due to selective removal of H2 from the reaction products in catalytic membrane reactors, C6H6 yield is significantly improved over the whole WHSV range compared to those obtained in fixed-bed reactors. H2 recovery is strongly influenced by WHSV as it decreases from 48.3% at 750 cm3 gcat−1 h−1 to 6.8% at 9000 cm3 gcat−1 h−1. There exists a trade-off between catalytic activity and H2 recovery, which results in the maximum enhancement (~360%) in C6H6 yield at 3000 cm3 gcat−1 h−1. At this intermediate space velocity, the largest concentration of H2 is found in the retentate stream and helps alleviate coke accumulation particularly on HZSM-5. Carbon is deposited on the inner surface of the membrane reactor portion in contact with the catalyst bed and transports to the outer surface, thus causing H2 permeability to decrease over the 15 h reaction period.

Recovering Rare Earth Elements from Aqueous Solution with Porous Amine–Epoxy Networks

Recovering aqueous rare earth elements (REEs) from domestic water sources is one key strategy to diminish the U.S.s foreign reliance of these precious commodities. Herein, we synthesized an array of porous, amine-epoxy monolith and particle REE recovery sorbents from different polyamine, namely tetraethylenepentamine, and diepoxide (E2), triepoxide (E3), and tetra-epoxide (E4) monomer combinations via a polymer-induced phase separation (PIPS) method. The polyamines provided -NH2 (primary amine) plus -NH (secondary amine) REE adsorption sites, which were partially reacted with C-O-C (epoxide) groups at different amine/epoxide ratios to precipitate porous materials that exhibited a wide range of apparent porosities and REE recoveries/affinities. Specifically, polymer particles (ground monoliths) were tested for their recovery of La3+, Nd3+, Eu3+, Dy3+, and Yb3+ (Ln3+) species from ppm-level, model REE solutions (pH ≈ 2.4, 5.5, and 6.4) and a ppb-level, simulated acid mine drainage (AMD) solution (pH ≈ 2.6). Screening the sorbents revealed that E3/TEPA-88 (88% theoretical reaction of -NH2 plus -NH) recovered, overall, the highest percentage of Ln3+ species of all particles from model 100 ppm- and 500 ppm-concentrated REE solutions. Water swelling (monoliths) and ex situ, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) (ground monoliths/particles) data revealed the high REE uptake by the optimized particles was facilitated by effective distribution of amine and hydroxyl groups within a porous, phase-separated polymer network. In situ DRIFTS results clarified that phase separation, in part, resulted from polymerization of the TEPA-E3 (N-N-diglycidyl-4-glycidyloxyaniline) species in the porogen via C-N bond formation, especially at higher temperatures. Most importantly, the E3/TEPA-88 material cyclically recovered >93% of ppb-level Ln3+ species from AMD solution in a recovery-strip-recovery scheme, highlighting the efficacy of these materials for practical applications.

Gasification and Associated Degradation Mechanisms Applicable to Dense Metal Hydrogen Membranes

Dense metal membranes have been identified as a promising technology for post-gasifier forward water-gas shift (WGS) membrane reactors or post-shift membrane separation processes. It is known that both major and minor gasification effluent constituents can have adverse effects on the mechanical and chemical stability of potential metal membranes. With this in mind, the scope of this chapter is to provide introductions to the gasification process and dense metal membranes, and the possible degradation mechanisms that dense metal hydrogen membranes may encounter in gasification environments. Degradation mechanisms of interest include catalytic poisoning, oxidation, sulfidation and hydrogen embrittlement. Additionally, the influence of in-situ and post-WGS gas compositions and CO conversions on the aforementioned degradation mechanisms will be addressed.

Passive detection of Pb in water using rock phosphate agarose beads

In this study, passive detectors for Pb were prepared by immobilizing powdered rock phosphate in agarose beads. Rock phosphate has been used to treat Pb-contaminated waters and soil by fixing the metal as an insoluble pyromorphite mineral. Under lab conditions, Pb was rapidly adsorbed from aqueous solution by the beads over time, consistent with the acidic dissolution of rock phosphate, the precipitation of pyromorphite within the pore space of the agarose gel matrix, and surface exchange reactions. Net accumulation of Pb occurred when beads were exposed to simulated periodic releases of Pb over time. Under field conditions, beads in mesh bags were effective at detecting dissolved Pb being transported as surface runoff from a site highly contaminated with Pb. Rates of Pb accumulation in beads under field conditions appeared to be correlated with the frequency of storm events and total rainfall. The rock phosphate agarose bead approach could be an inexpensive way to carry out source-tracking of Pb pollution, to verify the successful remediation of sites with Pb-contaminated soil, and to routinely monitor public water systems for potential Pb contamination.

CO2 Interaction with coals of different mineral and moisture content

To improve our understanding of the role of moisture and mineral matter with respect to CO2 sequestration in unmineable coal semns, we investigated sorption and swelling behavior of several Eastern and Western US coal samples, pmiicularly, cuttings from San Juan Basin (Fruitland) site of the Southwest Regional Pminership and crushed-coal samples of the Central Appalachian Basin (Russell County, VA) coal seam received from the SECARB pminership. The CO2 55°C sorption isotherm measurements have been completed for moist (as received) and dried samples representing the well probes. The results are summarized versus mineral matter and moisture content.