On-stream Time Research Articles

Small- to medium-scale deep syngas purification: Biomass-to-liquids multi-contaminant removal demonstration

The complete and economic removal of harmful components from biomass gasification-based syngas is a major challenge. A final gas cleaning concept for syngas purification to catalytic synthesis quality was developed as an alternative to organic-solvent scrubbing technologies. The motivation is to present smaller-scale BTL processes with a potentially lower-capex gas cleaning solution. The purpose of this study was to realize and validate the final gas cleaning concept in a real syngas environment and to study longer-term performance of deep gas cleaning. Two successful PDU-scale campaigns in complete biomass-to-liquids production chain were performed. A total on-stream time of 163 h was realized in syngas generated from residual woody- and agro-biomasses, with coupled gas feeding to Fischer-Tropsch synthesis. For S-species removal the final gas cleaning featured a novel hybrid of activated carbon- and ZnO-based bed materials. NH3 and partial CO2 removal was achieved by pressurized water scrubbing. The campaigns employed extensive continuous and non-continuous analysis techniques for the study of syngas impurities such as H2S, COS, NH3, HCN, HCl, benzene and tar. The final gas cleaning process demonstrated flexible deep removal of syngas contaminants of all tested biomass origins, thus achieving similar or better purification levels as conventional wet-scrubbing technologies. The cleaned gas was therefore suitable for catalytic synthesis purposes, demonstrating the technical feasibility of the new final cleaning process in conjunction with optimized hot gas cleaning.

Total and Sustainable Utilization of Biomass Resources: A Perspective.

Feedstock cost is a major variable cost component in conversion to biofuels and chemicals. Consistent feedstock quality is critically important to achieve high product yield and maximum onstream time. Traditionally, raw biomass materials are delivered directly to the biorefineries where they are preprocessed to feedstock prior to being converted to products. Since many types of biomass materials—including agricultural residues, energy crops, and logging residues—are harvested according to growth cycles and optimal harvesting time, just-in-time steady supply of raw biomass to the biorefineries is not possible. Instead, biomass materials are stored, then delivered to the biorefineries as needed. Experience to date indicates that this approach has caused many issues related to logistics, biomass losses due to microbial degradation and fire, and inconsistent feedstock quality due to variability in the properties of as-delivered biomass. These factors have led to high feedstock cost, low throughput, and low product yield for the biorefineries. Idaho National Laboratory has developed a new strategy to address the problems encountered in the traditional approach in biomass feedstock supply, storage, and preprocessing mentioned above. The key components of this strategy are (1) preservation and preconditioning of biomass during storage, (2) utilization of all the biomass, including minor components that are normally considered wastes or contaminants, and (3) maximization of the value of each component. This new approach can be accomplished using feedstock preprocessing depots located near the biomass-production sources.

Production of Motor Fuel from Lignocellulose in a Three-Stage Process (Review and Experimental Article)

A three-stage process for the production of motor fuel (MT) components from lignocellulosic raw materials is described. In the first, pretreatment stage, lignocellulose is subjected to hydrolysis with cellulases followed by fermentation of the resulting sugars into ethanol; then, dilute ethanol solutions are concentrated by membrane vapor separation to obtain 70–80% solutions. At the third stage, aqueous ethanol solutions (water content 0–50%) in the presence of a Pd–Zn/Al2O3/MFI catalyst at 350°C and a space velocity of 0.6 h−1 are converted into alkanes, and С3–С8 olefins and С6–C12 aromatic compounds (MT components). It has been found that water in an amount of up to 30% in ethanol solutions effectively inhibits the detrimental hydrocarbon cracking and catalyst coking processes, thereby leading to a decrease in the formation of undesirable C1 and C2 products and an increase in the catalyst on-stream time to 100 h wherein the yield of the desired fraction is reduced only by 10–15%. The subsequent treatment of the catalyst surface with steam and hydrogen completely restores its catalytic activity.

Ultrasound intensified CO2 desorption from pressurized loaded monoethanolamine solutions. I. parameters investigation and modelling

CO2 stripping from loaded monoethanolamine (MEA) aqueous solutions intensified by means of ultrasound was investigated in a lab-scale kettle reboiler with both gas and liquid continuous operations. The reboiler operating conditions were similar to those of a typical industrial reboiler with a pressure of 1 barg, and where the CO2 loading is less than 0.25 mol CO2/mol MEA. Intermittent ultrasound application was tested to find the effects of variables for CO2 stripping from the CO2 loadings 0.20–0.39 mol/mol at pressures up to 1.5 barg. Multi-variate data analysis was employed, and a model was built to explain and find the effects of six variables on CO2 stripping by ultrasound. The six variables include pressure, liquid flow rate, CO2 loading, intensity, frequency and on-stream time of ultrasound. The variable analysis results manifest that the CO2 loading is the significant positive effect variable, pressure is negative on energy saving and CO2 stripping rate and ultrasound parameters have varied effects. Experimental results show that the CO2 stripping rate assisted by ultrasound is 4 times than by heat only when CO2 loading is high, and the best result of specific energy consumption was 2.3 MJ/kg CO2 in the present test conditions.

Mathematical simulation of the formation of liquid products from catalytic cracking gases over a zeolite-containing catalyst modified with Group VI and VIII metals

The kinetics of the formation of liquid products from catalytic cracking gases over a zeolite-containing catalyst in a flow reactor in the temperature range from 260 to 420°C at GHSV = 30–264 h–1 and an on-stream time of 5–25 s has been investigated. A kinetic model for the process proceeding according to a likely scheme is proposed. The rate constants and activation energies of certain reactions involved in the process have been determined. A mathematical model of the process taking into account the mass and heat balances, as well as hydrodynamic conditions, has been developed. The concentration and temperature fields and the pressure over the catalyst bed height have been calculated. The target product yield on has been plotted as a function of the on-stream time.

Carbon dioxide permeation through ceramic-carbonate dual-phase membrane-effects of sulfur dioxide

CO2 perm-selective ceramic/carbonate dual phase membranes are promising in a number of high temperature separation and reaction processes for CO2 capture or process intensification. The stability of these membranes in gas containing SO2 is important for their applications dealing with sulfur containing stream. The present work studies gas permeation performance and stability of Ce0.8Sm0.2O1.9 (SDC)/Li2CO3-Na2CO3 membrane in SO2 containing gas. During CO2 permeation through the SDC/carbonate membrane with feed gas containing SO2, the CO2 permeation flux decreases with on-stream time and the decrease rate increases with the SO2 concentration in the feed gas. The SDC phase remains unchanged after exposure to SO2 containing gas, but the SO2 exposure of the SDC-carbonate dual phase membrane results in formation of sulfate in the carbonate phase in the membrane. The sulfate content in the molten salt phase increases with SO2 concentration in the gas or exposure time. CO2 permeation flux through SDC/carbonate-sulfate dual phase membranes prepared in this work decreases with the increase of the sulfate content in the molten salt phase. The formation of sulfate in the carbonate phase lowers carbonate ion conductivity which becomes the dominant step causing a reduction in CO2 permeance.

Pervaporation Separation of Organic Mixtures by MOF-5 Membranes

Metal organic framework (MOF) membranes have received much attention for gas separation applications, with however limited information about their liquid separation properties. This paper reports a study of permeation and separation of liquid organics by a MOF-5 membrane in pervaporation mode. Multiple high quality MOF-5 membranes were reproducibly prepared by the secondary growth method for various experimental runs. The pervaporation of pure toluene, o-xylene, and 1,3,5-triisopropylbenzene (TIPB) and the separation of their binary mixtures were studied. The permeation flux and separation factors decrease with pervaporation on-stream time and steady state permeation flux could not be reached even after 10 h of pervaporation. The fouling effects do not change the crystalline structure of the MOF-5 membrane. The pervaporation flux with the mixture feed is lower than the pure component flux, and the reduction in the flux decreases with decreasing affinity of the permeating species with MOF-5. The mixture ma...

A ZSM-5 zeolite-based catalyst for oligomerization of the butane–butylene fraction

The effect of localization of acid sites and the nature of the modifier metal on the activity, selectivity, and operation stability of a ZSM-5 zeolite-based catalyst in the oligomerization of the butane–butylene fraction (BBF) has been examined. It has been shown that the selective poisoning of acid sites on the external surface of zeolite crystals reduces coking and increases the yield of the desired gasoline fraction. Introduction of a promoter metal insignificantly affects the catalytic properties of the zeolite. Among Zn, Ga, and La, gallium appears to be the best modifier, which provides an increase in the yield of the desired gasoline fraction by 0.9%. As a result of the study, a BBF oligomerization catalyst has been developed that ensures a threefold increase in the catalyst on-stream time and a 7% increase in the yield of the gasoline fraction as compared with its commercial counterpart.

Glycerol steam reforming on supported Ru-based catalysts for hydrogen production for fuel cells

Glycerol steam reforming on Ru and Ru–Me (Me = Fe, Co, Ni, and Mo) catalysts supported on yttria, ceria–zirconia, and γ-alumina is studied at high temperatures for the production of hydrogen for fuel cell applications. The nature of the support notably affects the catalytic properties of these catalysts resulting in significant enhancements of the H2 production turnover rate and product selectivity on the reducible yttria and ceria–zirconia supported Ru-based catalysts via facilitation of the water–gas shift reaction. The acidic γ-alumina supported Ru-based catalysts demonstrate a low H2 production turnover rate with a high CO product selectivity and also favor the formation of C1–C2 hydrocarbons. Differently, the promotion effects due to Fe, Co, Ni, and Mo on the bimetallic Ru–Me catalysts are limited with only small increases in the glycerol conversion turnover rate for the Ru–Ni, Ru–Mo, and Ru–Co catalysts. The alumina supported Ru-based catalysts are deactivated by a significant extent with increasing on-stream time due to coking. The carbon deposition is insignificant on the yttria and ceria-zirconia supported catalysts, but moderate deactivation occurs due to sintering of the dispersed metal clusters. Influenced by the surface MoOx species that hamper sintering of the surface metal clusters and by the Y2O3 support that prevents coking on the catalyst, the Ru–Mo/Y2O3 catalysts exhibit superior catalytic stability against deactivation.

Thermodynamic stability of coke-generating compounds formed on the surface of platinum dehydrogenation catalysts in their oxidation with water

Results of thermodynamic analysis and mathematical simulation of the deactivation of a platinum dehydrogenation catalyst by coke-generating compounds are presented. An approach to increasing the catalyst on-stream time has been proposed, suggesting implementation of a procedure for calculating the optimal flow rate of water fed to the reactor to maintain the conditions of thermodynamic equilibrium of the coke formation reaction and oxidation of intermediate condensation products with water.

Effect of reaction temperature on activity of Pt- and Ru-substituted lanthanum zirconate pyrochlores (La2Zr2O7) for dry (CO2) reforming of methane (DRM)

Dry (CO2) reforming of methane (DRM) is a highly endothermic reaction (ΔH=+59.1kcal/mol) producing syngas (H2 and CO) with the H2/CO ratio of ~1. DRM requires reaction temperatures above ~800°C for complete equilibrium conversion to CO and H2, and is inevitably accompanied by carbon deposition. Here we examine lanthanum zirconate (La2Zr2O7) pyrochlores, with the larger trivalent cation La and a smaller tetravalent cation Zr occupying A and B sites, respectively. Three catalysts are tested: La2Zr2O7 [LZ] and two pyrochlores in which Zr in the B-site has been isomorphically partially substituted with (a) Ru (2.00wt%) [LRuZ] and (b) Pt (3.78wt%) [LPtZ]. The levels of substitution by weight correspond to identical atomic levels of substitution at the B-site. Here, activation energies are determined as a function of Ru or Pt substitution on the B-site. The results show that activation energies based on both CH4 and CO2 reaction rates are much lower for LRuZ than LPtZ. Conversion of CH4 (XCH4) and CO2 (XCO2) was greater for LRuZ compared to LPtZ at 525°C, 575°C, and 625°C throughout an on-stream time of 600min. After each 600-min run, temperature programmed oxidation (TPO) showed that total carbon formation decreased with increasing reaction temperature, although the stability of the deposited carbon increased with increasing reaction temperature.

Physicochemical and catalytic properties of iron- and indium-containing zeolites

The influence of the preparation procedure of Fe- and In-containing zeolites on their physicochemical and catalytic properties in methanol conversion to hydrocarbons and the upgrading of the straight-run gasoline fraction of crude oil has been studied. The introduction of In and Fe into a zeolite increases the on-stream time of the catalysts in methanol conversion and increases their selectivity for the formation of alkenes and isoalkanes. Zeolites containing iron and indium nanopowders are the most effective catalysts for the manufacturing of high-octane gasolines from straight-run gasoline.

Catalytic Studies toward Synthesis of 2,6-Dimethylnaphthalene from 1-(p-Tolyl)-2-methylbutane

In this work experiments have been performed in order to study the synthesis of 2,6-dimethylnaphthalene (DMN) via dehydrocyclizing 1-(p-tolyl)-2-methylbutane over Pt/SiO2, V/Ca/Al2O3, and unimpregnated or potassium-impregnated Cr2O3/Al2O3 catalysts. The obtained liquid product mixture consisted of 1,6-cyclization products (dimethylnaphthalenes) and dealkylated 1,6-cyclization products (2-methylnaphthalene and naphthalene), 1,5-cyclization products (trimethylindanes and -indenes), and fragmentation products (mainly p-xylene and 3-(p-tolyl)-propylenes) and 1-(p-tolyl)-2-methylbutenes. Among 10 possible DMN isomers 1,5-, 1,6-, 2,6-, and 2,7-DMN were identified. Metal catalysts V/Ca/Al2O3 (5 wt % vanadium) and Pt/SiO2 (1 wt % platinum) were slightly more active than unimpregnated commercial Cr2O3/Al2O3. After 1 h on-stream time the conversion of 1-(p-tolyl)-2-methylbutane was 96 mol % when the artificial contact time (1/weight-hourly space velocity (WHSV)) was 5.7 h at 783 K over unimpregnated Cr2O3/Al2O3. Po...

Methanol Conversion to Dimethyl Ether over H-SAPO-34 Catalyst

The process of methanol conversion to dimethyl ether over an H-SAPO-34 molecular sieve was studied, using the catalyst as synthesized or formulated in an alumina matrix. The experiments were performed on the temperature interval 100−250 °C, liquid space velocities of 1−5 h−1, and pressures between 1 and 10 bar. The results evidenced a high catalytic activity of the H-SAPO-34 molecular sieve, providing in these conditions a practically total methanol transformation to dimethyl ether. Also, a special run, performed at 180 °C, with an output composition close to chemical equilibrium, showed no significant change of catalyst activity during an on-stream time of 50 h, this proving a good stability and resistance to deactivation. A published rate expression for the methanol dehydration reaction was selected and adapted to describe the experimentally observed process kinetics.

Preparation and High Performance of La2O3−V2O5/MCM-41 Catalysts for Ethylbenzene Dehydrogenation in the Presence of CO2

A series of La2O3−V2O5/MCM-41 catalysts with high specific surface area were prepared by means of incipient wetness impregnation for the dehydrogenation of ethylbenzene to styrene using CO2 as oxidant. At 600 °C, the conversion of ethylbenzene and selectivity to styrene over 10La15V/MCM-41 after an on-stream time of 4 h was about 86.5 and 91.0%, respectively. The properties of the catalysts before and after the reaction were characterized using techniques such as X-ray diffraction, specific surface area, Fourier transform infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed desorption, and oxidation. The high catalytic activity and stability of 10La15V/MCM-41 during dehydrogenation of ethylbenzene is attributed to an optimized La/V atomic ratio. The accumulation of amorphous carbon species on the external surface of La2O3−V2O5/MCM-41 is the cause for catalyst deactivation.

Effects of acidification and basification of impregnating solution on the performance of Mo/HZSM-5 in methane aromatization

Abstract The effects of acidification and basification of ammonium heptamolybdate solution during impregnation of HZSM-5 on the catalytic performance of Mo/HZSM-5 in methane dehydro-aromatization have been investigated. At reaction temperature of 700 °C and GHSV = 1600 ml h −1 g −1 , a 2 wt.% Mo/HZSM-5 prepared with H 2 SO 4 -acidified solution gave a high aromatics yield of 7.2% but the catalytic activity declined drastically with time on-stream. A 2 wt.% Mo/HZSM-5 prepared with NH 3 -basified solution showed both high activity (7.1% aromatics yield) and good stability. With a rise in reaction temperature, the 2 wt.% Mo/HZSM-5 prepared with NH 3 -basified solution gave increased initial aromatics yields of 10.2 and 15.5% at 750 and 800 °C, respectively. The extent of catalyst deactivation with on-stream time increased with increasing reaction temperature or reactants space velocity but was less severe compared to that over a similar catalyst prepared without pH adjustment of the impregnation solution. The catalyst stability could be further improved by adding an appropriate concentration of CO 2 or O 2 in the reactant stream. With 5.6 vol.% O 2 or 9.6 vol.% CO 2 in the methane feed, steady aromatics yield of ca. 8.4% at 800 °C and 1600 ml h −1 g −1 was obtained for a period of 6 h.

A process for a high yield of aromatics from the oxygen-free conversion of methane: combining plasma with Ni/HZSM-5 catalysts

A process for a high yield of aromatics and co-produced hydrogen from the oxygen-free conversion of methane using a two-stage plasma-followed-by-catalyst (PFC) reactor at atmospheric pressure and low temperature is reported. Pure methane and a methane and hydrogen mixture as the feed gas for the two-stage PFC process were investigated, respectively. Using the methane and hydrogen mixture as the feed gas into the two-stage PFC reactor, Ni/HZSM-5 catalysts keep stable catalytic activity for a much longer on-stream time than that using pure methane as the feed gas. The maximum aromatic yield may be achieved using low Ni-loading Ni/HZSM-5 catalysts and at a suitable catalyst temperature.

XPS, XAES, and TG/DTA characterization of deposited carbon in methane dehydroaromatization over Ga–Mo/ZSM-5 catalyst

The catalytic dehydroaromatization of methane over 3.0%Mo/HZSM-5 and 0.1%Ga–3%Mo/HZSM-5 catalysts were reported. The nature of deposited carbon was characterized by means of XPS, XAES, TG/DTG, HRTEM, and DTA techniques. In XAES study, the type of deposited carbon was characterized based on the fine structures of d N/d E spectra. The results confirm that the sp 2/sp 3 bonding ratio of coke species increases with on-stream time, suggesting that the deposition of heavier aromatic-type carbon is the main reason for catalyst deactivation. The addition of gallium to 3.0%Mo/HZSM-5 enhances the adsorption of CO x species as well as the formation of alkene (such as ethylene). Therefore, the Ga-modified 3%Mo/HZSM-5 catalyst is more active and stable than the unmodified one.

Experimental demonstration of the reverse flow catalytic membrane reactor concept for energy efficient syngas production. Part 1: Influence of operating conditions

In this contribution the technical feasibility of the reverse flow catalytic membrane reactor (RFCMR) concept with porous membranes for energy efficient syngas production is investigated. In earlier work an experimental proof of principle was already provided [Smit, J., Bekink, G.J., van Sint Annaland, M., Kuipers, J.A.M., 2005a. A reverse flow catalytic membrane reactor for the production of syngas: an experimental study. International Journal of Chemical Reactor Engineering 3 (A12)], but compensatory heating was required and problems related to the mechanical strength of the powder-based YsZ catalyst and the steel filter were reported. Therefore, in Part 1 the performance of a Rh - Pt / Al 2 O 3 catalyst with improved mechanical strength and porous Al 2 O 3 membranes with excellent temperature resistance was tested in an isothermal membrane reactor. For this purpose a novel sealing technique was developed that could withstand sufficiently high pressure differences and temperatures. Very high syngas selectivities close to the thermodynamic equilibrium could be achieved for a considerable period of time without any increase in pressure drop and without any decrease in syngas selectivity. Using the Rh – Pt / Al 2 O 3 catalyst, several experiments were performed in a RFCMR demonstration unit and the influence of different operating conditions and design parameters on the reactor behaviour was investigated. It is shown that very high syngas selectivities (up to 95%) can be achieved with a maximal on-stream time of 12 h, without using any compensatory heating and despite inevitable radial heat losses. In Part 2 a reactor model is discussed that can well describe the experimental results presented in this part.

Pretreatment options for large scale SWRO plants: case studies of OF trials at Kindasa, Saudi Arabia, and conventional pretreatment in Spain

Kindasa Water Services (KWS) currently operates an RO facility at Jeddah Port on the Red Sea in Saudi Arabia, using conventional pre-treatment, to provide a 14 mld output. Due to an increasing requirement for treated water services, a contract has recently been placed with Weir Westgarth for a new desalination facility to expand the capacity of RO treated water from 14 to 40.5 mld (3.7 to 10.7 MGD). The original system has operated well for most of the time since it was brought into supply in 2000. However, occasional poor quality conditions have occurred during storms, or periods of algal bloom, which have resulted in SDI's to the RO exceeding target levels. Accordingly, an interest was expressed in utilizing ultrafiltration (UF) as an alternative to conventional pre-treatment, to improve RO feed quality, and guarantee on-stream time. The UF trial was highly successful in achieving stable membrane permeability and a consistent filtrate SDI when operated under optimized process conditions. Utilizing ferric chloride dosing, with acidification, the trial has operated at a flux of 95 LMH, and at a transmembrane pressure of 0.15–0.20 bar. The recovery was 94%. An average SDI of 2.2 has been obtained in the UF filtrate, approximately 2 units better than the existing conventional treatment. By utilizing an air enhanced backwash on a regular basis, the trial has shown that filtrate SDI's of less than 3.0 can be obtained at all times, even under the poor feed quality conditions that occur during algal blooms. In the final phase of the trial, we have been able to obtain UF filtrate SDI values well below 2. Hydranautics has gained experience with UF pre-treatment to RO in 3 other case studies in the Gulf of Mexico, the Red Sea, and the Mediterranean. In each case, OF was demonstrated to provide excellent pre-treatment to RO, with no RO cleaning required in 6-month trial periods. In addition, the Integrated Membrane System guarantee offered by Hydranautics for the UF-RO system minimizes process risk for all parties. This paper will review the data from the UF trial at Kindasa, and from the three other case studies mentioned above. The benefits for the RO facility at Kindasa will be quantified with regard to both technical and commercial parameters. We will also mention the experiences encountered in Spain in different sites as Carboneras 123,000 m 3/d SWRO with conventional pre-treatment and Las Palmas 371,000 m 3/d SWRO with conventional pre-treatment.