The Influence of Active Phase Loading on the Hydrodeoxygenation (HDO) of Ethylene Glycol over Promoted MoS2_{2}/MgAl2_{2}O4_{4} Catalysts

The hydrodeoxygenation (HDO) of ethylene glycol over MgAl$_{2}$O$_{4}$ supported NiMo and CoMo catalysts with around 0.8 and 3 wt% Mo loading was studied in a continuous flow reactor setup operated at 27 bar H$_{2}$ and 400 °C. A co-feed of H2S of typically 550 ppm was beneficial for both deoxygenation and hydrogenation and for enhancing catalyst stability. With 2.8-3.3 wt% Mo, a total carbon based gas yield of 80-100 % was obtained with an ethane yield of 36-50 % at up to 118 h on stream. No ethylene was detected. A moderate selectivity towards HDO was obtained, but cracking and HDO were generally catalyzed to the same extent by the active phase. Thus, the C2/C1 ratio of gaseous products was 1.1-1.5 for all prepared catalysts independent on Mo loading (0.8-3.3 wt%), but higher yields of C1-C3 gas products were obtained with higher loading catalysts. Similar activities were obtained from Ni and Co promoted catalysts. For the low loading catalysts (0.83-0.88 wt% Mo), a slightly higher hydrogenation activity was observed over NiMo compared to CoMo, giving a relatively higher yield of ethane compared to ethylene. Addition of 30 wt% water to the ethylene glycol feed did not result in significant deactivation. Instead, the main source of deactivation was carbon deposition, which was favored at limited hydrogenation activity and thus, was more severe for the low loading catalysts

Hydrodeoxygenation (HDO) of aliphatic oxygenates and phenol over NiMo/MgAl2_{2}O4_{4}: Reactivity, inhibition, and catalyst reactivation

This study provides new insights into sustainable fuel production by upgrading bio-derived oxygenates by catalytic hydrodeoxygenation (HDO). HDO of ethylene glycol (EG), cyclohexanol (Cyc), acetic acid (AcOH), and phenol (Phe) was investigated using a Ni-MoS$_{2}$/MgAl$_{2}$O$_{4}$ catalyst. In addition, HDO of a mixture of Phe/EG and Cyc/EG was studied as a first step towards the complex mixture in biomass pyrolysis vapor and bio-oil. Activity tests were performed in a fixed bed reactor at 380–450 °C, 27 bar H2, 550 vol ppm H2S, and up to 220 h on stream. Acetic acid plugged the reactor inlet by carbon deposition within 2 h on stream, underlining the challenges of upgrading highly reactive oxygenates. For ethylene glycol and cyclohexanol, steady state conversion was obtained in the temperature range of 380–415 °C. The HDO macro-kinetics were assessed in terms of consecutive dehydration and hydrogenation reactions. The results indicate that HDO of ethylene glycol and cyclohexanol involve different active sites. There was no significant influence from phenol or cyclohexanol on the rate of ethylene glycol HDO. However, a pronounced inhibiting effect from ethylene glycol on the HDO of cyclohexanol was observed. Catalyst deactivation by carbon deposition could be mitigated by oxidation and re-sulfidation. The results presented here demonstrate the need to address differences in oxygenate reactivity when upgrading vapors or oils derived from pyrolysis of biomass

Modeling gravitational collapse of rectangular granular piles in air and water

The present paper is concerned with the two-dimensional collapse of piles of granular materials, a problem analogous to the classical dam break problem in hydraulics. This study is intended to aid in the development of constitutive equations and modeling procedures that can be applied to predict various flows involving high concentration liquid-particle mixtures. We consider the granular collapse as a test problem and attempt to validate our modeling by comparing our predictions with previously published granular collapse experiments. The time-dependent evolution of the collapsing granular piles is calculated by making use of COMSOL, a commercial finite element code that is designed to handle a wide variety of Multiphysics problems. We begin by considering the collapse of a rectangular block of dry granular material and calculate the temporal evolution of the free surface by making use of the Level Set method. Good agreement is found between these predictions and the laboratory experiments of Balmforth and Kerswell (2005). The collapse of granular material submerged in a water is then investigated using a Mixture Model approach. The experiments of Rondon et al. (2011) revealed drastically different collapse periods depending upon whether the initial pile was in a loose or a dense, compacted state. The simple Mixture Model approach gave reasonably good predictions of the Rondon et al. (2011) experiments for the case of initially loose piles that collapsed in about a second, but it was unsuccessful in simulating the collapse of the initially dense piles that were observed by Rondon et al. (2011) to take around 30-40 s. Some simple empirical modifications to the material constitutive behavior were able to roughly predict such long collapse times, but a more comprehensive and detailed investigation of the phenomenon is warranted. \ua9 2013 Elsevier Ltd. All rights reserved.Peer reviewed: YesNRC publication: Ye

Collapse of rectangular granular blocks

The collapse of bulk granular materials is of increasing importance in many applications in engineering and geophysics including processing of oil-sands and analysis of avalanches and landslides. The present work is primarily aimed at modelling of the deposition of tailings. This requires predicting the geometry of stable granular heaps, which poses a particular difficulty to available CFD models. In this paper we introduce a new plasticity model for the frictional stresses within the bulk granular material. The numerical simulations employ a two-fluid, one the granular material and the other the surrounding fluid, mixture approach to model the two-phase fluid-granular flow. Solution of the governing equations is carried out using COMSOL code. Results for two cases with small and large aspect ratios are presented. The results show the evolution of the internal flow and shape of the granular heap. The simulations examine the role of the height-to-length ratio on the final shapes. The results include comparisons between the present computations and available experimental measurements.Peer reviewed: YesNRC publication: Ye

Viscosities of heavy oils-in-toluene and partially deasphalted heavyoils-in-heptol in the study of asphaltenes self-interactions

Interparticle interactions of the soluble asphaltenes in partially deasphalted heavy oils in toluene-heptane (heptol) mixtures are compared to those of several heavy oils diluted in toluene only. Viscosity-volume fraction (eta-Phi) relationships for the heavy oils and bitumen in toluene were almost identical. However, the asphaltenes in toluene associated and scaled differently from its source oil. Four classical viscosity models were used to describe the data, and scaling was interpreted on the basis of asphaltenes association, as in macromolecular interactions, The Pal-Rhodes model showed deviation from sphericity with solvation constants for heavy oils in toluene and C-5 asphaltenes in toluene, at 1.4-1.6 and 3.7, respectively. The Krieger-Dougherty (KH) model indicated high interparticle interaction factors, and maximum packing factors of similar to 1 suggested polydispersity. Neither models fit the data for deasphalted oils. The Leighton-Acrivos model showed that W the maximum packing fraction (Phi(max)) for all oils was similar, (ii) the asphaltenes alone in toluene had the highest self-associations, and (iii) the deasphalted oils showed Phi(max) values close to the theoretical values (0.58). From the Einstein equations, intrinsic viscosities [eta] of deasphalted oils in heptol gave aspect ratios (length to radius, L/R) of the asphaltenes at 10 (i.e., rodlike molecules). The K-H model gave [eta] of similar to 4 and L/R approximate to 3.5 for heavy oils in toluene; however, for asphaltenes in toluene, the model gave [eta] approximate to 10.6 and L/R approximate to 5.8 (i.e., less-rodlike molecules)

Evidence for Detachment of Indigenous Bacteria from Aquifer Sediment in Response to Arrival of Injected Bacteria

Two bacterial strains isolated from the aquifer underlying Oyster, Va., were recently injected into the aquifer and monitored using ferrographic capture, a high-resolution immunomagnetic technique. Injected cells were enumerated on the basis of a vital fluorescence stain, whereas total cell numbers (stained target cells plus unstained target and antigenically similar indigenous bacteria) were identified by cell outlines emanating from fluorophore-conjugated antibodies to the two target strains. The arrival of injected bacteria at the majority of monitored sampling ports was accompanied by simultaneous temporary increases in unstained cell counts that outnumbered the injected bacteria by 2- to 100-fold. The origin and mechanism of appearance of the unstained cells are considered

Data from: Ecological and evolutionary diversification within the genus Carex (Cyperaceae): consequences for community assembly in subarctic fens

The concept of limiting similarity predicts that closely related taxa are less likely to co-occur than expected by chance. The degree to which the phylogenetic relatedness in plant communities is in accord with limiting similarity has been little tested at the scale where the consequences of adaptive differentiation during speciation should be most evident: the scale of neighboring, congeneric plants within a community. To quantify species co-occurrence patterns in relation to environment, we sampled sedge species, their rooting level relative to the water table, and the water pH in 2,124 0.25 m² quadrats distributed across 29 subarctic fens in the central Labrador Peninsula. We estimated phylogenetic relationships using four DNA regions (ETS, ITS, matK, trnL-trnF) for all species of Carex (42), Eriophorum (6), and Trichophorum (2) in the region, of which 21, four, and two, respectively, occurred in the sampled fens. We demonstrate that closely related species of Carex are less likely to co-occur than expected by chance using 1) a probabilistic method to test the significance of pairwise co-occurrence patterns of species, and 2) linear mixed modeling to relate these patterns to phylogenetic relationships and ecological tolerances along gradients of substrate pH and rooting level in relation to the water table. The results also indicate that suites of species with significant mutual pairwise co-occurrence belong to distant lineages within the Cariceae-Dulichieae-Scirpeae clade of Cyperaceae and have stabilizing niche differences. We suggest that niche differentiation during the evolution and diversification of a clade of wetland Carex species over the past few million years, especially during the dynamic glacial cycles of the Pleistocene, has resulted in diverse sedge communities that share space and resources in harsh northern peatland habitats