Jeffrey G. Weissman

Structures of niobium pentoxide and their implications on chemical behavior

Abstract The many structures of bulk niobium pentoxide can be grouped into the low-temperature and high-temperature forms, with the latter being more ordered. The crystallization behavior, however, is influenced by starting materials, impurities, and interactions with another component. These interactions affect both the physical (mobility) and chemical (reducibility, acidity) properties of catalytic systems containing niobium pentoxide.

Titania-zirconia mixed oxide aerogels as supports for hydrotreating catalysts

Abstract Supercritical fluid (SFC) extraction was used to make aerogels of TiO 2 , ZrO 2 and two TiO 2 /ZrO 2 mixed oxides, having surface areas from two to five times greater than their conventionally prepared equivalents; additionally the mixed oxides have higher surface acidities than the two single component oxides. Heat treatments, either during catalyst preparation or reactor testing, always resulted in small to significant decreases in surface areas in the aerogel-containing samples. These samples were used as supports for Mo-Ni catalysts for the hydroprocessing of gas oil in a pilot-plant scale reactor. The high ZrO 2 containing materials were found to be unstable under reaction conditions and were nearly inactive; in contrast, the high TiO 2 containing catalysts, while somewhat unstable, are more active on a surface area basis than Al 2 O 3 or conventional TiO 2 equivalent supported Mo-Ni catalysts. This improvement is attributed to properties inherent in the SCF prepared supports; these results also indicate that support acidity contributes to hydrotreating activity.

Niobia-alumina supported hydroprocessing catalysts: relationship between activity and support surface acidity

Abstract Two classes of MoNi catalysts, surface niobium-aluminum oxides and mixed niobium-aluminum oxides, were examined for hydroprocessing of gas-oils. Niobia containing surface and mixed oxides are known to have increased surface acidities as compared to the component oxides; support surface acidity, in turn, may enhance gas-oil sulfur and nitrogen removal activities. Maximum rates of sulfur and nitrogen removal occurred for surface oxide catalysts containing 5 wt.-% Nb 2 O 5 , corresponding to the NbAl surface oxide support composition reported to have the highest Lewis acidity. Maximum activities, normalized on a surface area basis, occurred at a support composition of 80 wt.-% Nb 2 O 3 for the mixed oxide series. Surface acidities of the Nb 2 O 5 A1 2 O 5 supports were measured by temperature programmed reaction study of adsorbed [180]ethanol; the desorption temperature of the ether dehydration product is a relative measure of Lewis acidity. Using this method, the highest surface acidity was found on the mixed oxide supports containing 80 wt.-% Nb 2 O 5 . For both series of catalysts, the compositions exhibiting the greatest degree of hydrotreating activity improvement corresponded to those exhibiting the highest surface acidity. Addition of niobia to alumina readily permits surface modifications to hydroprocessing catalysts for obtaining maximum hydroprocessing activity.

Review of processes for downhole catalytic upgrading of heavy crude oil

Abstract Unlike conventional refinery processing, downhole upgrading involves implementing catalytic processes in oil-bearing geologic formations. In this way impurities contained in heavy crude oil can possibly be left in the ground or easily separated during oil production, providing an improved crude oil feed for refineries. Additionally, value or viability can be added to an otherwise uneconomic or remote heavy oil deposit. In order to successfully produce improved quality oil via a downhole upgrading project, several processing steps are anticipated: placement of catalysts into an appropriate downhole location, mobilization of reactants over the catalyst bed, and creation of processing conditions necessary to achieve a reasonable degree of catalytic upgrading. Each of these steps has been proven by past application; their combination into a unified below-ground process remains problematic. Downhole processing differs from surface processing in that brine, high steam partial pressures and low hydrogen partial pressures need to be accommodated in the downhole setting. There are no reports of significant downhole catalytic upgrading of crude oil, although examples of thermal upgrading are noted. However, available technology should be amenable to conducting a successful process. Upgrading of heavy crude oil at anticipated downhole processing conditions has been successfully proven in the laboratory. Recently published literature with immediate pertinence to the problems of downhole catalytic upgrading is reviewed with the goal of stimulating research and providing directions for future investigations.

Downhole heavy crude oil hydroprocessing

Abstract Several processing options are being proposed to accomplish near well-bore, downhole (in-situ) hydroprocessing of heavy crude oils. These processes are designed to pass crude oil over a fixed bed of catalyst, the catalyst being placed by conventional reservoir engineering methods. The presence of water or brine and the need to provide heat and reactant gases in a downhole environment impose challenges not present in conventional processing. In order for an in-situ process to be successful, there is a need to assess if hydroprocessing reactions under these unusual conditions are possible; and if so, how much upgrading can be obtained at processing conditions that can reasonably be obtained in an in-situ environment. Both continuous flow and batch reactor systems were used for assessing in-situ hydroprocessing of heavy crude oils. Processing conditions, including oil/water ratios, temperatures, pressures, and hydrogen flow-rates, were those expected to be achievable in a downhole environment. For the particular heavy Middle-Eastern crude oil studied, hydrodesulfurization follows pseudo-first order kinetics; activity is not catalyst dependent but instead appears to be limited by the reactivity of the feed. Additionally, from 20 to 30% of the sulfur contained in this particular crude oil consists of thermally labile sulfur; the amount of which removed remains constant provided a minimum processing temperature is attained. Density of the product decreases almost linearly with increasing reaction temperature. Reduction of hydrogen partial pressure results in a decrease in hydrodesulfurization, probably due to hydrogen starvation. Upgrading reactions occur in a sufficiently short contact time to allow for conventional oil-well production rates. These results indicate that in-situ hydroprocessing is feasible from reaction and catalyst standpoints.

Characterization and aging of hydrotreating catalysts exposed to industrial processing conditions

Abstract Several series of commercial alumina supported nickel-molybdenum and cobalt-molybdenum hydrotreating catalysts were exposed to differing degrees of reaction lengths and severities using a variety of naphtha and gas-oil feeds. Fresh and used catalysts were characterized by gas-oil desulfurization and denitrogenation activity, chemical analysis of deposits, porosimetry, and high-resolution transmission electron microscopy; in addition, deposits on the catalysts were characterized by carbon-13 nuclear magnetic spectroscopy. Deactivation was primarily by suppression of active sites by carbon containing deposits on the support. Changes in MoS 2 structure, as observed by HRTEM, do not appear to contribute to activity changes. Two types of carbon deposits were observed: processing with gas oils leads to deposition of a compact carbon, resulting in substantial loss in nitrogen removal activity but only slight loss in sulfur removal activity; at higher loadings this dense carbon deposit affects both sulfur and nitrogen removal activities, but nitrogen removal is reduced to a greater extent. Processing with naphthas results in deposition of less dense carbon, which reduces nitrogen and sulfur removal by the same amount, the extent of which is proportional to carbon loading. Comparison of different catalysts deactivated in the same commercial environment permits insights into those factors important to preventing activity loss.

FT-IR analysis of borate-promoted NiMo/Al2O3 hydrotreating catalysts

A series of boron-modified commercial NiMo/Al2O3 hydrotreating catalysts have been characterized by IR analysis of adsorbed NO and pyridine and by gas-oil sulfur- and nitrogen-removal activities. Sulfur removal activity was found to correlate with the 1690 cm−1 (Mo(NO)22+) band in the NO adsorption spectra. Nitrogen removal activity was found to be dependent on support Bronsted acidity as measured by the density of the pyridinium band at 1540 cm−1 in the pyridine adsorption spectra. At higher boron loadings, over 1.8 wt.% boron, the presence of bulk borate phases results in poor catalytic performance.

Preparation of niobia/silica mixed oxide model thin films

Model thin films of niobia/silica (Nb2O5/SiO2) were prepared by radio-frequency sputtering and, subsequent to different calcination conditions, found to have structures which are similar to their high-surface-area counterparts.