Non-catalytic Process Research Articles

Application of selective non-catalytic reduction of NOx in small-scale combustion systems

Abstract The selective non-catalytic reduction of NO x has been studied experimentally employing commercial grade urea in a pilot-scale diesel-fired tunnel furnace at 3–4% excess oxygen level and with low ppm of baseline NO x ranging from 65 to 75 ppm within the investigated temperature range. The furnace simulated the thermal behavior of small-scale combustion systems such as small capacity boilers, water heaters, oil heaters, etc., where the operating temperatures remain within the range of 950–1300 K. NO x reductions were studied with the variation of injection temperature, residence time, normalized stoichiometric ratio (NSR) of the reagent, etc. With 5% urea solution, at an NSR of 4, as much as 54% reduction was achieved at 1128 K. The result is quite significant, especially for the investigated level of baseline NO x . The ammonia slip measurements showed that the slip was below 16 ppm at NSR of 4 and optimum temperature of NO x reduction. Finally, the investigations have demonstrated that selective non-catalytic reduction process is quite applicable to the small-scale combustion applications.

Kinetics and mechanism of the oxidation ofL-α-amino-n-butyric acid in moderately concentrated sulfuric acid medium

The reaction kinetics of L-α-amino-n-butyric acid oxidation by permanganate ion have been investigated in moderately strong acid medium using a spectrophotometric technique. In all cases studied an autocatalytic effect, due to Mn+2ions formed as a reaction product, was observed. Both catalytic and noncatalytic processes were determined to be first order with respect to the permanganate ion and the amino acid. The overall rate equation for this process may be written as: [Formula: see text]where k′1and k′2are pseudo-order rate constants for the noncatalytic and catalytic reactions, respectively. The influence of some factors such as temperature and reactant concentration on the rate constants has been studied, and the activation parameters have been calculated. Reaction mechanisms satisfying observations for both catalytic and noncatalytic routes have been presented.Key words: L-α-amino-n-butyric acid, permanganate oxidation, concentrated acidic medium, autocatalysis, free radical intermediates.

Kinetic Investigation of Consecutive-Parallel Reactions in the Non-Catalytic Process of Ethylene Oxide Hydrolysis

A large class of consecutive-parallel addition reactions with a large number of steps has been considered. The system of differential equations describing the kinetics of consecutive-parallel reactions in the non-catalytic process of ethylene oxide hydrolysis has been investigated. By a series of assumptions it is possible to obtain the analytical solution for the distribution of reaction products at non-zero initial conditions. The analytical solution of differential equations as a function of time has been obtained. The comparison between the solutions of the kinetics model with the reported experimental data has shown its sufficient adequacy.

廃木材のガス化・改質による水素リッチ合成ガスの製造(燃焼・ガス化(3),廃棄物処理技術)

The purpose of this study is to establish a super power generation system where hydrogen rich synthesis gas, meeting the limit to the fuel of MCFC (Molten Carbonate Fuel Cell), can be efficiently extracted from biomass via the gasification and reforming technology. For that purpose, the experiments of architectural salvages gasification were performed with a bench scale two-step gasification system. The main influence factors on hydrogen production in the catalytic process and the non-catalytic process were investigated, and temperature was found to be the most important factor. At 950℃, without catalyst employment, the synthesis gas containing above 50% (% V/V) hydrogen was perfectly extracted from feedstock with the suitable selection for the operation parameter of S/C (Steam/Carbon Ratio) and ER (Equivalence Ratio). However, with employing commercial reforming catalyst to the reforming process, the similar result can be generated just at 750℃.

Entrainment and Stability of a Horizontal Gas-Liquid Jet in a Fluidized Bed

Fluid coking is a non-catalytic process where heavy hydrocarbon feed, sprayed using jets into a fluidized bed reactor, cracks upon contacting hot coke particles and produces valuable volatile fractions. It is estimated that the Alberta tar sands contain 1.7 trillion barrels of oil, equivalent to 35% of the world’s crude oil reserves, of which the majority is processed using fluid cokers. Important parameters that affect the yield of fluid cokers include the feed jet stability and therefore its ability to entrain and mix the injected feedstock with the fluidized coke particles. To this purpose, this study investigated the effect of the use of various types of draft tubes, placed downstream of the feed jet to enhance mixing, on solids entrainment and jet stability.Specifically, it has been demonstrated with the use of a gas-liquid and gas-only jet that an optimum distance exists between the nozzle and draft tube for entrainment of solids. For both cases, this optimal distance occurs as the jet touches the draft tube wall. However, for a gas-only jet this occurs at a shorter distances due to the increased angle of expansion. The angles of expansion were confirmed using triboelectric probe measurements. It has also been shown that the shape of the inlet to the draft tube will have an effect on the rate of solids entrainment as will the presence of pulsations in the jet.

Reaction of 4‐(N,N‐Dimethylaminophenyl)magnesium Bromide with Palladium Tetrakis(triphenylphosphine).

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalytic Gasification of Sawdust Derived from Various Biomass

A systematic study is conducted for the steam gasification of biomass materials (cellulose, Cedar, and Aspen) using temperature-programmed gasification (TPG) and constant-temperature gasification (CTG) methods in order to produce H2-rich gas. The performance of catalyst (CaO) was also studied by varying the catalyst loading from 0 to 8.9 wt % during TPG and CTG processes. The TPG and CTG experiments showed that the use of CaO as a catalyst reduced the maximum gasification temperature by ∼150 °C. Also, the rate of H2 and cumulative H2 productions were increased with the impregnation of CaO in cellulose, Cedar, and Aspen during TPG and CTG processes. In TPG, the rate of production of H2 was increased from 0.21 to 0.38 cm3 (STP)/min/(0.04 g of sample) when 5.5 wt % CaO was impregnated in cellulose. Higher CaO loading of 8.9 wt % did not improve H2 production. In CTG, the rate of H2 production and cumulative production of H2 increased from 0.18 to 0.31 cm3 (STP)/min and from 11 to 14 cm3 (STP)/(0.04 g of sample) when 5.5 wt % CaO was impregnated in cellulose. The rate of production and cumulative production of H2 from Cedar and Aspen were significantly higher than those from cellulose for catalytic as well as for noncatalytic TPG and CTG processes. Total fuel yield, H2, and carbon yields were also significantly increased with the impregnation of CaO in cellulose, Cedar, and Aspen.

Demonstration of real biomass gasification drastically promoted by effective catalyst

The gasification of cedar wood using highly efficient Rh/CeO 2/SiO 2(60) catalyst and air as a gasifying agent has been investigated in a continuous feeding fluidized bed gasifier at low temperatures (823–973 K). Regarding the carbon conversion and syngas formation, Rh/CeO 2/SiO 2(60) catalyst exhibited much better results than conventional Ni and dolomite catalysts, and the non-catalytic process. The performance of Rh/CeO 2/SiO 2 was very dependent on the loading amount of CeO 2; in this case 60% CeO 2 on SiO 2 was the most suitable. In the case of the most effective catalyst, Rh/CeO 2/SiO 2(60), no severe deactivation was observed even in the longer reaction time (4 h). The catalyst developed in the cellulose gasification is also applicable to the gasification of real biomass (wood powder).

Evolution of Processes for Synthesis Gas Production: Recent Developments in an Old Technology

The manufacture of gas mixtures of carbon monoxide and hydrogen has been a vitally important part of chemical technology for about a century. Originally, such mixtures were obtained by the reaction of steam with incandescent coke and were known as “water gas”. Used first as a fuel, water gas soon attracted attention as a source of hydrogen and carbon monoxide for the production of chemicals, at which time it gradually became known as synthesis gas. Eventually, steam reforming processes, in which steam is reacted with natural gas (methane) or a petroleum naphtha over a nickel catalyst, found wide application for the production of synthesis gas. A modified version of steam reforming known as autothermal reforming, which is a combination of partial oxidation near the reactor inlet with conventional steam reforming further along the reactor, improves the overall reactor efficiency and increases the flexibility of the process. Noncatalytic partial oxidation processes using oxygen instead of steam also found wide application for synthesis gas manufacture, with the special feature that they could utilize low-value feedstocks such as heavy petroleum residua. In recent years, catalytic partial oxidation employing very short reaction times (milliseconds) at high temperatures (850−1000 °C) is providing still another approach to synthesis gas manufacture, as Professor Lanny Schmidt and his students have shown in their pioneering exploratory research in this area. (See, for example, Hickman and Schmidt Science 1993, 259, 343.) Here, we consider some crucial issues in catalytic partial oxidation and report some new data with a bearing on these issues. Nearly complete conversion of methane, with close to 100% selectivity to H2 and CO, can be obtained with a Rh monolith under well-controlled conditions. Experiments on the catalytic partial oxidation of n-hexane conducted with added steam give much higher yields of H2 than can be obtained in experiments without steam, a result of much interest in obtaining hydrogen-rich streams for fuel cell applications.

Catalytic Total Oxidation of Methane. Part II. Catalytic Processes to Convert Methane: Partial or Total Oxidation

The introduction of solid catalysts into a traditionally non-catalytic free-radical process such as combustion occurred in recent years under the influence of environmental pressures. The major applications of catalytic combustion are two-fold: at low temperatures to eliminate volatile organic compounds (VOCs) and at high temperatures (>1000°C) to reduce NOx emission from gas turbines, jet motors, etc. It is the high temperature application that is reviewed here. Some recent developments in high-temperature catalytic combustion are trend setters in catalysis and hence of particular interest. For instance, novel materials are being developed for catalytic applications above 1000°C for sustained operation longer than one year. Where material/catalyst developments are still inadequate, systems engineering is coming to the rescue by developing multiple-monolith catalyst systems and the so-called hybrid (catalytic + thermal) reactors.

Reaction of 4-(N, N-dimethylaminophenyl)magnesium bromide with palladium tetrakis(triphenylphosphine)

The influence of reaction conditions on catalyzed by Pd(PPh3)4 cross-coupling of 4-N,N-dimethylaminophenylmagnesium bromide with 4-bromobenzonitrile in tetrahydrofuran was investigated. The yield of the product of the catalytic process, 4-N,N-dimethylamino-4'-cyanobiphenyl, and of the main product of noncatalytic process, 4-N,N-dimethylaminophenyl 4'-bromophenyl ketone, is mainly governed by the order of introduction of reagents and catalyst into the reaction zone. Experimental observations and analysis of side products suggested conclusions on the processes resulting in deactivation of the catalyst.

Application of polyoxotungstates as environmental catalysts: wet air oxidation of acid dye Orange II

The catalytic effect of two Keggin-type polyoxotungstates, namely H 4SiW 12O 40 and Na 2HPW 12O 40, on the wet air oxidation of azo dye Acid Orange 7 (AO7; C dye=248 μM) at varying reaction temperatures ( T=160–290 °C at P H 2O= 0.6–3.0 MPa, respectively) was examined. Arrhenius parameters for catalytic and non-catalytic wet air oxidation were obtained in terms of temperature dependent AO7 and TOC abatement kinetics. To get a further insight into the dominant reaction pathway of the catalytic and non-catalytic wet air oxidation processes, isopropyl alcohol and bromide (300 μM) were added as OH scavengers. Obtained results revealed an important homogenous contribution for WAO of AO7 (Arrhenius parameters E a=84 kJ mol −1 and A=5.6×10 7 min −1). However, mineralization (TOC removal) was noticeably influenced by the investigated polyoxotungstates ( C catalyst=140 μM) and the activation energy decreased from 40 kJ mol −1 in the absence of catalyst to only 28 kJ mol −1 (PW 12 3−) and 22 kJ mol −1 (SiW 12 4−). The catalytic processes were appreciably less sensitive to the presence of OH scavengers than uncatalyzed wet air oxidation implying that polyoxotungstate-catalyzed wet air oxidation did not solely depend upon a free radical type reaction mechanism. The obtained results tend to support the free radical chain mechanism to account for Orange dye degradation only for uncatalyzed wet air oxidation.

Problems of nonlinear fluid dynamics in industrial plants

A series of oxidation tests was carried out on a small-scale blowing unit fed with two different visbreaker (VB) bitumens, and with two straight-run (SR) soft bitumens for reference. The purpose was to study the possibility of applying the blowing process to VB feeds, and to evaluate process kinetics and product characteristics. The results showed that industrial blowing of VB bitumens is feasible and that the rate of reaction can be expressed by a first order equation with respect to change in softening point. Production of distillate oils was quite high, especially when iron trichloride was used as a catalyst; in industrial application it is suggested that VB bitumens may be oxidized without any catalyst, the kinetics of the non-catalytic process being satisfactory. Air consumption was unsteady compared with the SR operation, and plugging of the air coil was more frequent.

The effect of carbon additives on the mesophase induction period of Athabasca bitumen

The ability of solid carbonaceous material to retard the formation of coke during thermal cracking and hydrocracking of heavy hydrocarbons is well known. In this study, we used in-situ microscopy (hot-stage) to obtain additional mechanistic information on whether fine coke and fullerene soot particles retard the growth of mesophase during thermal cracking of Athabasca bitumen, thus reducing the possibility of fouling in preheaters and furnaces. The findings from this study could also have application in other non-catalytic thermal processes such as visbreaking and coking. In the absence of additives in the Athabasca bitumen feed, the formation of mesophase occurred after 61 and 67 min (measured from room temperature) at reaction temperatures of 450°C and 440°C, respectively. The addition of solid coke (ca. 5 wt.%) from a commercial delayed coking operation shortened the mesophase formation time to almost 45–50 min under similar conditions. The coke, having surface area of only 1.65 m 2/g, resulted in enhanced bitumen fluidity and large-textured mesophase. These observations were rationalized based on the ability of delayed coker coke to release hydrocarbons into the bulk fluid during thermal cracking. Light hydrocarbons released from coke may have changed the solvating power of the liquid phase in bitumen and promoted phase separation, resulting in a shorter induction period. In contrast, adding small amounts of fine fullerene soot (ca. 1 and 5 wt.%) delayed the appearance of mesophase significantly under similar conditions. The ability of fullerene soot to physically absorb the mesophase precursors into its pore structure led to an increase in the apparent viscosity of the bulk phase, which is known to reduce mesophase size and prolong the induction period. Consistent with this, the induction period was prolonged an additional 10 min when the soot surface area was increased from 152 to 208 m 2/g. The increase in induction period is significant with respect to reaction times and suggests that these fullerene soot materials could be effective in allowing for increased severity and liquid products yield from visbreaking, with less likelihood of fouling in the preheater tubes and furnace walls.

Thermal N 2O decomposition in regenerative heat exchanger reactors

The decomposition of nitrous oxide (N 2O), which may be carried out either catalytically or thermally, is a reaction of considerable environmental significance. A novel non-catalytic process for the destruction of nitrous oxide emissions is presented. Experimental studies on a laboratory scale demonstrate that a selective removal of N 2O can be achieved in a purely thermal conversion step within the temperature range of 800°C–1000°C without adversely affecting the NO x levels in the gas. The new process is also suitable for the treatment of lean waste gas streams, since the integrated heat recovery, for instance in a regenerative reverse flow reactor, permits simple, robust autothermal operation with the recovery of useful heat whilst circumventing the danger of additional NO x formation. Further studies deal with the simultaneous occurrence of both homogeneous and heterogeneous reactions in the N 2O decomposition process and their interaction. The stability limits in the operation of a flow reversal reactor could well offer a useful practical means of discriminating between the relative contributions of the two types of reaction and of identifying coupling mechanisms, as the combined system exhibits parametric sensitivities and thermokinetic instabilities, such as ignition–extinction phenomena and multiple periodic steady states, which depend on the underlying structure of the reactive processes. The concepts involved are illustrated using the results of preliminary model simulations. The stability structure of the system can be analysed expediently using a combination of dynamic simulation and an asymptotic countercurrent reactor model.

Study on wet air oxidation of aqueous ferrous cyanide solution catalyzed by three metal salts

The catalytic wet oxidation (CWO) process with Cu2+, Mn2+, and Ce2+ as catalysts, respectively, was applied to investigate the degradation of ferrocyanide (Fe(CN)64-) solution. For the conversions of Fe(CN)-64- during the noncatalytic wet oxidation (WO) process up to 99.9% was attained after a reaction time of 70 min. The COD removal efficiency was observed as only 38% in a noncatalytic oxidation; however, it could be enhanced to 75%, 61%, and 50% in the presence of Cu2+, Mn2+, and Ce2+, respectively. Both noncatalytic and catalytic wet oxidation processes of Fe(CN)-64- solution were considered to be a two-step reaction at pH 9.0 and temperatures of 433-473 K. The oxidation rate was initially fast, followed by a slow step, which did obey first-order kinetics with respect to chemical oxygen demand (COD). Both the 2+ and Ce2+ catalyzed oxidation showed a significant effect on the reduction of activation energy during the first reaction of the WO runs.

Catalyzed gasification of active carbon by oxygen: influence of catalyst type, temperature, oxygen partial pressure and particle size

A thermogravimetric study of the oxygen gasification of a commercial active carbon using Co, Ni and Cu as catalysts has been carried out. This follows a previous study of the influence of the particle size, gas volumetric flow rate, initial sample weight temperature and oxygen partial pressure an non-catalytic gasification. The results show that for T < 500 °C; P02 < 1 atm; D p < 0.4 mm, Q v > 50 cm3 min−1 and M o < 75 mg the gasification of the active carbon with oxygen is controlled by the chemical reaction. The presence of a catalyst increases in all cases the reaction rate, both temperature and catalyst concentration showing a very positive influence. The activity of the different catalysts follows the order: Co > Cu > Ni. A kinetic study applied to both types of gasification has allowed the activation energy and the reaction order with respect to oxygen and the catalyst to be determined. In all cases both the activation energy and the Arrhenius pre-exponential factor are lower in the catalytic gasification. This brings about the existence of an isokinetic point for the catalytic and the non-catalytic processes, which were also determined. © 2000 Society of Chemical Industry

Hydrogenation and dehalogenation of aryl chlorides and fluorides by the sol–gel entrapped RhCl 3–Aliquat 336 ion pair catalyst

The SiO 2 sol–gel entrapped ion pair [(C 8H 17) 3NMe] +[RhCl 4 . nH 2O] −, generated from RCl 3 .3H 2O, Aliquat 336® and Si(OMe) 4 catalyzes at 80°C and 16 atm. H 2, the hydrogenation of aryl fluorides and chlorides to give halogen-free hydroaromatics. Fluorobenzenes initially yield fluorocyclohexanes which eliminate HF, in a non-catalytic process, followed by hydrogenation of the cyclohexenes. In contrast, chlorobenzenes are first dehalogenated to the corresponding benzene derivatives, that in a second step are hydrogenated to cyclohexanes. Aryl bromides undergo dehalogenation and hydrogenation as well, but only in the presence of a free radical scavenger. The catalyst in these reactions is leach-proof and recyclable with little or no loss in activity.

Degradation of maleic acid in a wet air oxidation environment in the presence and absence of a platinum catalyst

Over a temperature range of 415–478 K, the catalytic and non-catalytic degradation of an aqueous solution of maleic acid (0.03 M) has been studied both in the presence of oxygen and under an inert atmosphere (nitrogen). These reactions were first-order for maleic acid. The non-catalytic oxidation reaction was zero-order in oxygen over a partial pressure range of 0.4–1.4 MPa. The apparent activation energies for the non-catalytic removal of maleic acid under both a nitrogen (66.7 kJ mol −1) and an air (131.5 kJ mol −1) environment have been calculated. The use of 0.5 wt.% platinum on γ-alumina catalyst significantly enhanced the degradation rate of maleic acid. A kinetic expression was developed accounting for both homogeneous and heterogeneous routes in maleic acid elimination. Although maleic acid removal was zero-order for oxygen concentration, the presence of oxygen is shown to result in significant chemical oxygen demand (COD) removal in both the catalytic and the non-catalytic process. Finally, the stability of a platinum catalyst has been tested for eight consecutive runs without any noticeable loss in catalyst activity.

Dechlorination of p-chlorophenol on a Pd/Fe catalyst in a magnetically stabilized fluidized bed; Implications for sludge and liquid remediation

p-Chlorophenol is dechlorinated using a Pd/Fe bimetallic micro-size catalyst in a magnetically stabilized fluidized bed (MSFB) reactor. The catalyst is used in both powder form ( d c =7 μm) and entrapped in alginate beads ( d b =2.0 mm). The dechlorination reaction is performed in aqueous solution containing p-chlorophenol with and without the presence of soil particles (20% w/w). Several important operating parameters involved in this complex chemical process are studied: Pd/Fe weight ratio, the extent of palladization or the ratio of Pd (Fe) interface area to the amount of chlorine to be removed, system pH, and dissolved O 2. Important process resistances including formation of Fe(OH) 2, Fe(OH) 3, and hydrogen gas bubbles, which are dependent on the mentioned operating parameters, are identified for accurate representation of the overall reaction kinetics. Pseudo first-order kinetics ( k=3.81±0.08 m 3/kg min) with first order deactivation of catalyst ( k d=0.12 1/min) are found to excellently represent dechlorination chemical reaction. Once the chemical kinetics were defined, the active Pd/Fe catalyst was entrapped in alginate beads for use in a magnetically stabilized fluidized bed. Diffusion constraints ( D e =8.0×10 -10 m 2/s) through the bead material (1.5% alginate +98.5% H 2O) are not severe and are reported as being approximately 85–90% of the diffusivity measured in water (Shishido et al., Chem. Engng. Res. Design: Trans. Inst. Chem. Eng. 73(6), 719–725, 1995; Oyaas et al., 1995a Biotechnol. Bioengng 47, 492–500). It can be further moderated by decreasing the size of the beads and by using a nano size Pd/Fe catalyst particles (Wang and Zhang, 1997). Overall, the Pd/Fe bimetallic catalyst has been shown to effectively dechlorinate p-chlorophenol both as a powder and entrapped in 2 mm alginate beads. Integration of the catalyst entrapped in the beads with the MSFB introduces a novel method for the treatment of difficult to handle materials, and toxic compounds. The MSFB and alginate beads are shown to be an excellent engineering platform which can be implemented in a variety of catalytic and non-catalytic liquid-solid reaction processes.