Removal of carbon disulfide: Experimental and modeling results

A mathematical model describing the rate of carbon disulfide (CS₂) removal has been developed. Kinetic studies were carried out in a fixed-bed reactor under atmospheric pressure and a range of temperatures (30-70 °C). The effects of flow rate, CS₂ inlet concentration, temperature and relative humidity were analyzed. A kinetic model based on axial dispersion, external and internal mass-transfer resistances, as well as effects of S deposition on the inner-face of the catalyst was in agreement with the CS₂ experimental breakthrough curves. The mathematical model can be used for process design and scale-up of similar systems.     

Removal of sulfur at high temperatures using iron-based sorbents supported on fine coal ash

This paper deals with the simultaneous removal of H₂S and COS in the temperature range of 400-650 °C at 1 bar by using iron-based sorbents. The iron-based sorbents were prepared using iron oxide and cerium oxide with coal fine ash as the support. Simulated coal gas was used in the sulfidation experiments and 5% O₂ in N₂ gas was used for regeneration of sorbents. Both sulfidation and regeneration experiments have been carried out using a fixed-bed quartz reactor. The product gases were analyzed using a GC equipped with a TCD and a FPD. The results demonstrated that both H₂S and COS can be effectively reduced using the iron-based sorbents supported on fine coal ash. XRD analysis shows that Fe_1−xS phase has formed during sulfidation indicating a high sulfur capacity of the sorbent. The mechanism of the removal of COS simultaneously with H₂S is also discussed.     

Comparison of product selectivity during hydroprocessing of bitumen derived gas oil in the presence of NiMo/Al2O3 catalyst containing boron and phosphorus

A detailed experimental study was performed in a trickle-bed reactor using bitumen derived gas oil. The objective of this work was to compare the activity of NiMo/Al₂O₃ catalyst containing boron or phosphorus for the hydrotreating and mild hydrocracking of bitumen derived gas oil. Experiments were performed at the temperature and LHSV of 340-420 °C and 0.5-2 h⁻¹, respectively, using NiMo/Al₂O₃ catalysts containing 1.7 wt% boron or 2.7 wt% phosphorus. In the temperature range of 340-390 °C, higher nitrogen conversion was observed from boron containing catalyst than that from phosphorus containing catalyst whereas in the same temperature range, phosphorus containing catalyst gave higher relative removal of sulfur than boron containing catalyst. Phosphorus containing catalyst showed excellent hydrocracking and mild hydrocracking activities at all operating conditions. Higher naphtha yield and selectivity were obtained using phosphorus containing catalyst at all operating conditions. Maximum gasoline selectivity of ∼45 wt% was obtained at the temperature, pressure, and LHSV of 400 °C, 9.4 MPa and 0.5 h⁻¹, respectively, using catalyst containing 2.7 wt% phosphorus.     

Dynamic relaxation characteristics of Matrimid polyimide

The dynamic relaxation characteristics of Matrimid^® (BTDA-DAPI) polyimide have been investigated using dynamic mechanical and dielectric methods. Matrimid exhibits three motional processes with increasing temperature: two sub-glass relaxations (γ and β transitions), and the glass—rubber (α) transition. The low-temperature γ transition is purely non-cooperative, and displays an identical time-temperature response to both the dynamic mechanical and the dielectric probes with a corresponding activation energy, E_A = 43 kJ/mol. The β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. Comparison of dynamic mechanical and dielectric data for the β process suggests that the dynamic mechanical test (E_A = 156 kJ/mol) is sensitive to a broader, more strongly correlated range of sub-glass motions as compared to the dielectric probe (E_A = 99 kJ/mol). Time-temperature superposition was used to establish mechanical master curves across the glass-rubber (α) relaxation, and these data could be described using the Kohlrausch-Williams-Watts function with an exponent value, β_KWW = 0.34. The corresponding shift factors were used as the basis of a cooperativity plot for the determination of dynamic fragility. The relation between fragility index (m = 115) and β_KWW for the Matrimid polyimide was in good agreement with the wide correlation reported in the literature.     

Use of a dispersed iron catalyst for upgrading extra-heavy crude oil using methane as source of hydrogen

The use of an iron dispersed catalyst, derived from Fe₃(CO)₁₂, for extra-heavy crude oil upgrading using methane as source of hydrogen was studied. The upgrading reactions were carried out batchwise in a stainless-steel 300 ml Parr reactor with 250 ppm of Fe at a temperature of 410-420 °C, a pressure of 11 MPa of CH₄, and a residence time of 1 h. In the presence of Fe₃(CO)₁₂, the reaction of Hamaca extra-heavy crude oil led to a reduction of two orders of magnitude in the viscosity (from 500 to 1.3 Pa s), 14% reduction in sulfur content, and 41% conversion of the >500 °C fraction in the upgraded product with respect to the original crude. The iron catalyst was isolated from the coke produced from the upgrading reaction and was analyzed by XPS, EDAX, and Mössbauer spectroscopy. The results indicated the presence of a Fe-V mixed sulfide species with a composition ca. (Fe_0.6V_0.4)_zS, where z is in the range 0.8-0.9.     

Preparation of CuY catalyst using CuCl2 as precursor for vapor phase oxidative carbonylation of methanol to dimethyl carbonate

Cu^IY catalyst was prepared by heating the mixture of CuCl₂ and acidic Y zeolite under flowing nitrogen and characterized by TG/DTG, XRD and elementary analysis techniques. The experimental result indicate that when the heating temperature was from 350 °C to 500 °C, the CuCl₂ of the CuCl₂ and acidic Y zeolite mixture sample decompose to CuCl and Cl₂ gas, then the produced CuCl reacted with the Brønsted acid center H⁺ of Y zeolite to form Cu^IY catalyst by the solid-state ion-exchanged reaction. The amount of ion-exchanged Cu^I in the Cu^IY catalyst reached the maximum of 0.1 mol/g when the heating temperature was 650 °C, and the catalyst exhibited the best catalytic activity, the conversion of methanol (C_MeOH), the selectivity and the space-time yield of dimethyl carbonate (S_DMC and STY) reached 4.36%, 74.55% and 97.32 mg/(g h), respectively.     

H2S retention with Ca-based sorbents in a pressurized fixed-bed reactor: application to moving-bed design

The H₂S retention with Ca-based sorbents in a pressurized fixed-bed reactor (1 MPa) has been analyzed, obtaining the breakthrough curves with a dolomite and two different limestones, different particle size (+0.8-1.0, +1.25-1.6, and +1.6-2.0 mm), and both at calcining (1173 K) and non-calcining conditions (1123 K). The effect of the stoichiometric time in the breakthrough curves has been analyzed varying the bed length, the gas velocity and the sorbent fraction in the bed. From these results, the conversion and H₂S concentration profiles in the transition zone and the length of unused bed (LUB) have been determined. H₂S retention in fixed-bed until concentration close to the given by the thermodynamic equilibrium was obtained using dolomite or limestone at calcining conditions, and dolomite at non-calcining conditions. The results of H₂S retention in a fixed-bed reactor has been applied to the calculus of the minimum height of a countercurrent moving-bed reactor to obtain the maximum H₂S retention with the minimum amount of sorbent. A mathematical model was developed to predict the experimental results obtained in the fixed-bed reactor, which was also valid for the design of countercurrent moving-bed reactors for gas desulphurization.     

Optimum operating conditions for a two-stage gasification process fueled by polypropylene by means of continuous reactor over ruthenium catalyst

We studied fuel gas production by means of pyrolysis and steam reforming of waste plastics for applications in solid oxide fuel cells. More specifically, we evaluated the effects of pyrolytic gasification temperature, catalyst content, steam reforming temperature, and weight hourly space velocity for a Ru catalyst used in a 60 g h^− 1-scale continuous experimental apparatus, which consisted of a tank reactor for pyrolysis and a packed-bed catalytic reactor for steam reforming. Polypropylene (PP) pellets were used as a model waste plastic. Ru/γ-Al₂O₃ catalysts with two different Ru contents were investigated. To suppress residue formation, the optimum operating temperature of the pyrolyzer was 673 K. To ensure suppressed coke formation, sufficient carbon conversion to gaseous products, and minimized heat loss from the reactor, the optimum operating conditions for the reformer were determined to be 903 K and 0.11 g-sample g-catalyst^− 1 h^− 1 with a 5 wt.% Ru/γ-Al₂O₃ catalyst. The composition of the gas produced with the 5 wt.% catalyst was almost the same as that predicted by chemical equilibrium laws, and it was applicable for a direct hydrocarbon fuel cell.     

Dry catalytic partial oxidation of diesel-fuel distillates into syngas

Volatile compounds distilled below 205 °C from diesel fuel are reformed into synthesis gas by dry catalytic partial oxidation using porous membrane reactors, eliminating complex liquid-fuel injectors and fuel-air mixers, greatly simplifying reformers for applications with solid-oxide fuel cells and NO_x traps. For distillates utilizing 20 wt% of the diesel fuel, 88 mol% of the carbon is converted into CO and 75 mol% of the hydrogen into H₂. Rationale is as follows: Long-chain n-alkanes such as n-hexadecane, with normal boiling point, 286.5 °C, but autoignition temperature, 205 °C, are the least thermally stable hydrocarbons in diesel fuel. If attempts are made to vaporize diesel fuel under oxygen-lean conditions without precautions, long-chain n-alkanes crack at autoignition temperatures forming radicals that initiate polymerization. By eliminating more troublesome compounds by distillation, and by effusing cooler air through porous ceramic membranes to react radicals with oxygen, carbon deposition is largely suppressed. A perovskite catalyst, fed pre-heated air at >900 °C, provides a reservoir of mobile lattice oxygen to react with adsorbed carbon. In continuous runs of 72 h, carbon deposition was negligible in the reactor, on the catalyst, and in the exhaust, except for minor graphite deposited onto walls near the catalytic hot zone.     

Mechanistic investigations of single-walled carbon nanotube synthesis by ferrocene vapor decomposition in carbon monoxide

The single-walled carbon nanotubes (SWCNTs) were synthesized by the carbon monoxide disproportionation reaction on Fe catalyst particles formed by ferrocene vapor decomposition in a laminar flow aerosol (floating catalyst) reactor. On the basis of in situ sampling of the product collected at different locations in the reactor, kinetics of the SWCNT growth and catalyst particle crystallinity were studied. Catalyst particles captured before SWCNT nucleation as well as inactive particles were determined to have cementite (Fe₃C) phase, while particles with γ- and α-Fe phases were found to be embedded in the SCWNTs. The growth rate in the temperature range from 804 to 915 °C was respectively varied from 0.67 to 2.7 μm/s. The growth rate constant can be described by an Arrhenius dependence with an activation energy of E_a = 1.39 eV, which was attributed to the carbon diffusion in solid iron particles. CNT growth termination was explained by solid-liquid phase transition in the catalyst particles. A high temperature gradient in the reactor was found to not have any effect on the diameter during the SWCNT growth and as a result on the chirality of the growing SWCNTs.     

Heterogeneous catalyzed biodiesel production from Moringa oleifera oil

In this study, biodiesel was produced from Moringa oleifera oil using sulfated tin oxide enhanced with SiO₂ (SO₄²⁻/SnO₂-SiO₂) as super acid solid catalyst. The experimental design was done using design of experiment (DoE), specifically, response surface methodology based on three-variable central composite design (CCD) with alpha (α) = 2. The reaction parameters studied were reaction temperature (60 °C to 180 °C), reaction period (1 h to 3 h) and methanol to oil ratio (1:6 to 1:24). It was observed that the yield up to 84 wt.% of Moringa oleifera methyl esters can be obtained with reaction conditions of 150 °C temperature, 150 min reaction time and 1:19.5 methanol to oil ratio, while catalyst concentration and agitation speed are kept at 3 wt.% and 350-360 rpm respectively. Therefore this study presents the possibility of converting a relatively new oil feedstock, Moringa oleifera oil to biodiesel and thus reducing the world's dependency on existing edible oil as biodiesel feedstock.     

Kinetic resolution of 4-phenyl-2-azetidinone in supercritical carbon dioxide

The lipase-catalysed kinetic resolution of rac-4-phenyl-2-azetidinone was investigated in supercritical carbon dioxide (scCO₂). Water (0.5 mol equivalent) was used as nucleophilic donor. The effects of pressure and temperature were studied in a batch reactor (internal volume: 30 mL). The optimum pressure and temperature of the β-lactam ring-opening reaction proved to be 14 MPa and 70 °C. Under optimum conditions, full conversion was achieved in 120 h. The resulting (R)-β-phenylalanine (ee ≥ 98%) and (S)-4-phenyl-2-azetidinone (ee ≥ 99%) could be easily separated by scCO₂ extraction of the (S)-β-lactam and subsequent washing of the enzyme with hot water to recover the amino acid.     

Efficient oxidative desulfurization (ODS) of model fuel with H2O2 catalyzed by MoO3/γ-Al2O3 under mild and solvent free conditions

An efficient process to remove organic sulfur compounds from model fuel has been explored. Dibenzothiophene (DBT) and 4, 6-dimethyldibenzothiophene (4, 6-DMDBT) can be completely oxidized into their corresponding sulfones by H₂O₂ over 14 wt.% MoO₃/γ-Al₂O₃ catalyst under mild conditions in 15 min. The effects of solvent, initial sulfide concentration, loading of MoO₃ and amount of catalyst on oxidative removal of DBT were studied. The employments of solvents have decreased the reaction rate of DBT, which can be attributed to the competitive adsorption between the sulfide and solvent. The oxidative reactivity increases in the order of thiophene (Th) < benzothiophene (BT) < DBT < 4, 6-DMDBT. The catalyst can be regenerated by methanol washing at 333 K.     

Evaluation of SO2 oxidation and fly ash filtration by an activated carbon fluidized-bed reactor: The effects of acid modification, copper addition and operating condition

It is expected that the simultaneous removal of acid gases and particles from flue gas, using a single process and at the same temperature, will become an economical, and thus, desirable option. Accordingly, this study investigates the potential for the utilization of a fluidized-bed adsorbent/catalyst reactor for the simultaneous removal of SO₂ and fly ash from simulated flue gas. The operating conditions for the evaluation include: (1) different pre-treatments of the adsorbent/catalyst, (2) the operating parameters of adsorption/filtration and (3) the effects of simultaneous adsorption/filtration through the fluidized-bed reactor. Based on the experimental data gathered, the Brönsted acid sites were formed on the surface of activated carbon (AC) support materials after modification with nitric or sulfuric acid and it acted as anchor. This characteristic accounts for the promotion of the effects of dispersion and adsorption of the adsorbent/catalyst. Moreover, the addition of copper facilitated the oxygen transfer of SO₂ to the carbon matrix. The concentration of SO₂ removed by the fluidized-bed adsorbent/catalyst reactor decreased from 17.9 to 14.2 mg SO₂/g of adsorbent after exposure to a high concentration of fly ash. Therefore, an acid-pre-treatment of the adsorbent/catalyst is required to hasten the removal of SO₂ in the simulated flue gas. Our result shows that the acidic groups may facilitate the adsorbent/catalyst removal of SO₂ when there exist high concentrations of fly ash in the flue gas.     

Preparation and selection of Fe-Cu sorbent for COS removal in syngas

A series of iron-based sorbents prepared with iron trioxide hydrate, cupric oxide by a novel method was studied in a fixed-bed reactor for COS removal from syngas at moderate temperature. In addition, the sorbents mixed with various additives in different ratios were tested. The effects of additive type and ratio on the breakthrough capacity and desulfurization performance, as well as the influence of operating conditions on sulfidation behavior of the sorbent, were investigated. The simulate gas contained 1% COS, 5% CO₂, 20%–30% CO and 60%–70% H₂. The outlet gases from the fixed-bed reactor were automatically analyzed by on-line mass spectrometry, and the COS concentration before breakthrough can be kept steady at 1 ppmv. The result shows that the breakthrough sulfur capacity of the sorbent is as high as 25 g-S/100 g. At 700 K and space velocity of 1000 h⁻¹, the efficiency of sulfur removal and breakthrough sulfur capacity of the sorbent increase with the increase of copper oxide with an optimum value. The result shows that the species and content of additives also affect desulfurization performance of the sorbent.     

Electroless immobilization and electrochemical characteristics of nickel hexacyanoruthenate film at an aluminum substrate

The surface of an aluminum (Al) electrode was modified with a thin film of nickel hexacyanoruthenate (NiHCR) as a novel electrode material. The modification procedure of Al surface, includes two consecutive procedures: (i) the electroless deposition of metallic nickel on the Al electrode surface from NiCl₂ solution, and (ii) the chemical transformation of deposited nickel to nickel hexacyanoruthenate films in solution of 20 mM K₃[Ru(CN)₆] + 0.5 M KNO₃. Cyclic voltammogram of the modified Al electrode showed a well-defined redox reaction due to [Ni^IIRu^III/II(CN)₆]^1−/2− system. The effects of different supporting electrolytes and solution pH were studied on the electrochemical characteristics of the modified electrode. The diffusion coefficients of K⁺ and Na⁺ cations in the film (D), the transfer coefficient (α), and the charge transfer rate constant at the modifying film/electrode interface (k_s), were calculated in the presence of both K⁺ and Na⁺ cations. The stability of the modified electrode was investigated under various experimental conditions.     

Influence of temperature and relative humidity on performance and CO tolerance of PEM fuel cells with Nafion-Teflon-Zr(HPO4)2 higher temperature composite membranes

The carbon monoxide (CO) poisoning effect on carbon supported catalysts (Pt-Ru/C and Pt/C) in polymer electrolyte membrane (PEM) fuel cells has been investigated at higher temperatures (T > 100 °C) under different relative humidity (RH) conditions. To reduce the IR losses in higher temperature/lower relative humidity, Nafion^®-Teflon^®-Zr(HPO₄)₂ composite membranes were applied as the cell electrolytes. Fuel cell polarization investigation as well as CO stripping voltammetry measurements was carried out at three cell temperatures (80, 105 and 120 °C), with various inlet anode relative humidity (35%, 58% and 100%). CO concentrations in hydrogen varied from 10 ppm to 2%. The fuel cell performance loss due to CO poisoning was significantly alleviated at higher temperature/lower RH due to the lower CO adsorption coverage on the catalytic sites, in spite that the anode catalyst utilization was lower at such conditions due to higher ionic resistance in the electrode. Increasing the anode inlet relative humidity at the higher temperature also alleviated the fuel cell performance losses, which could be attributed to the combination effects of suppressing CO adsorption, increasing anode catalyst utilization and favoring OH_ads group generation for easier CO oxidation.     

Using electrocoagulation-electroflotation technology to treat synthetic solution and textile wastewater, two case studies

The purpose of this study was to investigate the effects of the operating parameters, such as pH, initial concentration (C_i), duration of treatment (t), current density (j), interelectrode distance (d) and conductivity (κ) on the treatment of a synthetic wastewater in the batch electrocoagulation (EC)-electroflotation (EF) process. The optimal operating conditions were determined and applied to a textile wastewater. Initially a batch-type EC-EF reactor was operated at various current densities ranging from 11.55 to 91.5 mA/cm² and various electrode gaps (1, 2 and 3 cm). For solutions with 300 mg/L of silica gel, good turbidity removal (89.6%) was obtained without any coagulant when the current density was 11.55 mA/cm², and with initial pH at 7.6, conductivity at 2.1 mS/cm: the treatment time was hold for 10 min and the electrode gap was 1 cm. Application of the optimal operating parameters on a textile wastewater showed a high removal efficiency for the following variables: suspended solid (SS) 85.5%, turbidity 76.2%, biological oxygen demand (BOD₅) 88.9%, chemical oxygen demand (COD) 79.7%, and color over 93%.     

Synthesis, characterization and performance of CuO/La2O3 composite catalyst for ammonia catalytic oxidation

This work considers the oxidation of ammonia (NH₃) by selective catalytic oxidation (SCO) over a CuO/La₂O₃ composite catalyst at temperatures between 150 and 400 °C. A CuO/La₂O₃ composite catalyst was prepared by co-precipitation of copper nitrate and lanthanum nitrate at various molar concentrations. This study also considers how the concentration of influent NH₃ (C₀ = 1000 ppm), the space velocity (GHSV = 92,000 l/h), the relative humidity (RH = 12%) and the concentration of oxygen (O₂ = 4%) affect the operational stability and the capacity for removing NH₃. The catalysts that were characterized using FTIR, XRD, UV-Vis, BET and PSA, have shown that the catalytic behavior is related to the copper (II) oxide, while lanthanum (III) oxide may serve only to provide active sites for the reaction during a catalyzed oxidation run. The experimental results show that the extent of conversion of ammonia by SCO in the presence of the CuO/La₂O₃ composite catalyst was a function of the molar ratio. The ammonia was removed by oxidation in the absence of CuO/La₂O₃ composite catalyst, and around 93.0% NH₃ reduction was achieved during catalytic oxidation over the CuO/La₂O₃ (8:2, molar/molar) catalyst at 400 °C with an oxygen content of 4.0%. Moreover, the effect of the reaction temperature on the removal of NH₃ in the gaseous phase was also monitored at a gas hourly space velocity of under 92,000 h^− 1.     

Mass transfer limitations on fixed-bed reactor for Fischer-Tropsch synthesis

Mass transfer limitations on fixed-bed for Fischer-Tropsch synthesis were investigated by changing synthesis gas superficial velocity, catalyst pellet size, and catalyst amount. To study external mass transfer limitation, synthesis gas superficial velocity was changed from 8.47 × 10^− 4 m s^− 1 to 3.39 × 10^− 3 m s^− 1. As a result, the synthesis gas superficial velocity of 3.39 × 10^− 3 m s^− 1 was most suitable for hydrocarbon chain growth resulting to liquid hydrocarbon formation. In case of internal mass transfer limitations, the effects of catalyst pellet size and catalyst amount (W_cat/F) were discussed. The large catalyst pellet showed higher C₅₊ selectivity and a lower α value compared to the small pellet because of more severe internal mass transfer limitations of α-olefin and long-chained hydrocarbons in the large pellet, respectively. Catalyst amount (W_cat/F) was inversely proportional to the internal mass transfer limitation because increased catalyst amount gave more time for liquid hydrocarbon products to diffuse from the catalyst pellet and, therefore, the catalyst amount of 4.5 g (W_cat/F = 45 g_cat min L^− 1) was most appropriate for liquid hydrocarbon formation.