High-temperature Steam Treatment Research Articles

Carbohydrate Reactions During High-Temperature Steam Treatment of Aspen Wood

Aspen wood was treated with steam at different time-temperature severity factors. Analysis of the amounts of acids released revealed a relationship between the acidity and the formation of furfural and hydroxymethyl furfural as degradation products from carbohydrates. It is suggested that two concurrent or consecutive mechanisms are responsible for the observed results: a homolytic cleavage and an acid hydrolysis of glucosidic linkages in the polysaccharides. By preimpregnating the wood with alkali, hydrolysis can be eliminated, resulting in a much cleaner depolymerization of the polysaccharides without any further acid-catalyzed degradation. The enzymatic digestibility of the steam-treated wood material for the formation of glucose was compared with that of steam-exploded wood. A more efficient route for glucose production from steam-exploded wood was found as long as the biomass-pretreated material was homogeneous and without shives.

Influence of silicate ratio and high-temperature steam treatment of pentasil on its acid and catalytic properties in conjugate conversion of lower alkanes and methanol

The influence of aluminum content in the zeolite matrix of Pentasil on its acid and catalytic properties in conjugate conversion of lower alkanes and methanol was studied.

An Effective Catalyst for Syngas-to-Dimethyl Ether Process with Steamed Zeolite HMCM-49 as Dehydration Component

Abstract The HMCM-49 zeolites before and after steam treatment were commingled with methanol synthesis catalyst to perform the single-step syngas-to-dimethyl ether process. The high temperature steam treatment meliorated the acidity of HMCM-49 zeolite, and consequently enhanced the selectivity to dimethyl ether significantly by reducing the formation of by-products like carbon dioxide and hydrocarbons.

Incorporation of Titanium into H-ZSM-5 Zeolite via Chemical Vapor Deposition: Effect of Steam Treatment

Ti-ZSM-5 prepared by secondary synthesis, from the reaction of H-ZSM-5 with vapor phase TiCl 4 , was characterized with several physicochemical techniques including FT-IR and UV/VIS-DRS. It was found that zeolite structure, surface area and pore volume did not change, and the framework aluminum could not be replaced by titanium atom during the secondary synthesis of Ti-ZSM-5. The incorporation of titanium into the framework might be due to reaction of TiCl 4 with the silanol groups associated with defects or surface sites. The formation of extra-framework titanium could not be avoided, unless the samples were further treated by water vapor at 550 °C or higher temperature. High temperature steam treatment of Ti-ZSM-5 prepared by chemical vapor deposition with TiCl 4 was efficient to prevent the formation of non-framework titanium species. Ti-ZSM-5 zeolites prepared in this work contained only framework titanium species and exhibited improved catalytic property close to TS-1 prepared by hydrothermal synthesis.

Effect of high-temperature steam treatment of high-silica zeolites of the ZSM-5 type on their acidity and selectivity of formation of lower olefins from straight-run naphthas

The effect of high-temperature steam treatment of high-silica zeolites of the ZSM-5 type on their acidity and selectivity of formation of lower olefins from straight-run naphthas was studied.

Steam tolerance of Fe/ZSM-5 catalyst for the selective catalytic reduction of NOx

This article reports the effects of steam on the activity and stability of Fe/ZSM-5 for the selective catalytic reduction of NO withiso-butane. When the feed contained 10% of H2O, the de-NOx activity was maintained if the temperature was above the maximum conversion temperature. However, when the temperature was below the maximum conversion temperature, the catalytic activity decreased. The effect of high temperature steam treatment on the stability was also examined. After the steam treatment, the activity of Fe/ZSM-5 decreased due to the dealumination of ZSM-5 and the migration of Fe ion isolated in the ion exchange site to form ferromagnetic iron agglomerate. The physicochemical properties of the fresh and deactivated catalysts were monitored by ESR,27Al MAS NMR, XPS, XRD, TPR and FT-IR spectroscopy.

Steam deactivation of CoZSM-5 NO x reduction catalysts

The effects of high-temperature steam treatment on the activity and selectivity of CoZSM-5 catalysts for the selective catalytic reduction of NO with methane have been examined. Loss of activity and selectivity on steam treatment is due to framework dealumination of the zeolite, causing an irreversible change in the coordination state of the Co 2+ ions. Pre-exchange of the zeolite with La 3+ cations inhibits the dealumination while stabilizing the catalysts.

State of aluminium in hydrothermally dealuminated MFI zeolite

27 Al Magic-angle spinning (MAS) NMR, 29Si MAS NMR, X-ray diffraction (XRD), FTIR and water adsorption have been used to investigate the state of aluminium after steam treatment of MFI zeolite. Dealumination and removal of silanol groups, as well as a transformation of the zeolite symmetry, have been observed. The signal (50 ppm) of tetrahedrally coordinated framework aluminium disappears at a lower temperature (< 1040 K) steam treatment and then reappears at a higher temperature. The framework aluminium is first observed to be extracted by steam to form extraframework aluminium species (with 0 ppm chemical shift) at a high temperature. With further steam treatment, the aluminium is changed to another form, which has the same chemical shift as that of framework aluminium. XRD, 29Si MAS NMR and FTIR confirm that the framework symmetry of the sample is monoclinic with high crystallinity, and the signals of framework aluminium and silanol groups are removed. From water adsorption data, two increases in hydrophobicity can be found in the sample treated with steam at different temperature, the first at 770 K and the second at 1030 K. This result is consistent with the change in the 27Al MAS NMR spectra. The 27Al MAS NMR spectrum shows that the newly formed aluminium species, after high-temperature steam treatment, is not Al2O3, based on the different chemical shift. Aluminium on MFI zeolite and on amorphous silica, after impregnation with Al3+, acts like framework aluminium during hydrothermal treatment. This result indicates that the newly formed aluminium species is in the form of Si—O—Al dispersed on the outer surface of the zeolite.

Stabilization of CuZSM-5 NOx reduction catalysts with lanthanum

The effects of high temperature steam treatment on the activity and selectiv ity of CuZSM-5 catalysts for the selective catalytic reduction of NO with propene have been examined. Loss of activity and selectivity on steam treatment is due to framework dealumination of the zeolite, which causes migration of Cu out of the zeolite pores to the external surface. Pre-exchange of the zeolite with La3+ cations inhibits the dealumination, preventing migration of Cu to the surface and allowing the catalyst to retain high activity and N2 selectivity after steam treatment. The deactivation of the catalysts was monitored using X-ray powder diffraction, magic angle spinning27Al and29Si nuclear magnetic resonance, X-ray photoelectron spectroscopy and ion scattering spectroscopy.

Electron Microscope Investigation of Mesopore Formation and Aluminum Migration in USY Catalysts

Combined high resolution electron microscope (HREM) and analytical electron microscope (AEM) investigations have been used to study the formation and evolution of mesopores in hydrothermally dealuminated ultrastable Y (USY) materials. The HREM results give clear evidencc for an inhomogeneous formation and distribution of the 5- to 50- nm defect regions attributed to mesopores. Such features are characteristic of extended hydrothermal treatment. In regions with high defect concentration, mesopores coalesce to form channels and cracks, which ultimately define the boundaries of fractured crystallite fragments. At these boundaries, a dark band is often observed which is highly enriched in aluminum, while within the mesopore itself, aluminum appears to be deficient. These dark bands are observed both in a neat USY material subjected to several cycles of steam acid treatment and in a high-temperature steam-deactivated USY fluid catalytic cracking (FCC) catalyst. Individual grains of both the neat USY and the dealuminated USY catalyst exhibit extreme fracturing into small crystallites of dimensions 20 to 50 nm. The fracturing is attributed to the nonequilibrium nature of the high-temperature steam treatments which characterizes accelerated deactivation procedures in the laboratory.

Supported transition metal oxides as acid cracking catalysts: Periodic trends and their relationship to activity and selectivity

Surface phase oxides bonded to a support such as alumina have not been recognized previously to have acid cracking activities in the league of amorphous silica-alumina to the best of our knowledge. In this paper the relative gas-oil cracking activities of all Group IV, V, and VIB oxides supported on alumina (including alumina and rhenia on alumina) are reported. All of the supported oxides are at a surface coverage about one-third that of a monolayer. Tungsten oxide and niobium oxide on alumina have been identified as solid acids with high activity; while molybdenum oxide and rhenium oxide on alumina lead to high coke and gas make even with steam present as a cofeed in the cracking test. The periodic trends of cracking activity are those expected from the charge-to-radius ratio of the metal cation. This class of surface phase oxide solid acids has a wide range of activities (two orders of magnitude) and may prove useful for matching acid strength to specific reactions. In addition, this class of solid acids maintains surface area and cracking activity following high temperature steam treatment, in contrast to many conventional solid acid catalysts.

Effects on activity of superhigh-silica cracking catalysts from high-temperature treatment with air and steam

The authors study the influence of conditions of high-temperature air and steam treatment in cracking a hydrocarbon feedstock and in regenerating the catalyst on the activity of SHS zeolites and catalysts based on these zeolites. A TsVM-361 SHS zeolite was used in the studies. The conditions of catalyst activation, the procedures used to monitor the degree of crystallinity and the method of determining the activity in the model reaction of nheptane cracking are described. The authors found that steam treatment of the SHS zeolites reinforces the hydrophobic properties of their surface, and this leads to a decrease in the n-heptane conversion on the SHS catalyst to be a factor of approximately 4. By varying the conditions of a special calcination in air and subsequent steaming with unsaturated steam, and also varying the paraffin feedstock mass velocity, a satisfactory level of stability of activity can be brought about.

Disulphide Bond Breakdown in Wool during High–temperature Steam Treatments

The extent to which cystine residues react when wool is steamed at temperatures above 10077deg;C was found to be very dependent on the pH of the wool and the temperature of the treatment, but was less sensitive to variations in the time of treatment. Extending the wool by up to 20% had no significant effect on cystine reactivity.Lanthionine was detected in the steamed wool in amounts which corresponded, approximately mole for mole, with the cystine losses recorded for the same samples, thus indicating that, under these conditions, even when the wool is at pH 3 0, almost all the cystine undergoing modification is converted to lanthionine. Measurements of the urea–bisulphite solubility of steamed wool provided indirect evidence of lanthionine formation.A new method of estimating lanthionine in protein hydrolysates, based on one–dimensional thin–layer chromatography combined with measurements of spot areas, is described.