Regeneration of coked catalysts

The intrinsic kinetics of carbon removal from a coked catalyst have been determined. Measurements have also been made of the transient temperature distribution inside a coked catalyst pellet during regeneration. These transient temperature distributions have been compared with predictions based on the sharp interface unreacted core model and on the finite thickness reaction zone model. The experimentally determined values of the maximum temperature rise were found to be in good agreement with the latter model but the sharp interface unreacted core model predicted temperature rises of a very much greater magnitude.     

基于Aspen Plus的气流床煤气化炉三段平衡模型(英文)

A three stage equilibrium model is developed for coal gasification in the Texaco type coal gasifiers based on Aspen Plus to calculate the composition of product gas, carbon conversion, and gasification temperature. The model is divided into three stages including pyrolysis and combustion stage, char gas reaction stage, and gas phase reaction stage. Part of the water produced in the pyrolysis and combustion stage is assumed to be involved in the second stage to react with the unburned carbon. Carbon conversion is then estimated in the second stage by steam participation ratio expressed as a function of temperature. And the gas product compositions are calculated from gas phase reactions in the third stage. The simulation results are consistent with published experimental data.     

高纯氯化氢对电石法PVC失活低固汞催化剂的原位再生

以电石法乙炔氢氯化失活低固汞催化剂为基础,在等温固定床反应器中模拟实际生产转换器单管装置,对失活催化剂通入高纯无水氯化氢气体,研究在氯化氢气体作用下,失活低固汞催化剂的再生效果,并考察再生温度、再生压力、空速以及再生时间对低固汞催化剂再生后汞含量、碘吸附值、四氯化碳吸附值、载体BET比表面积以及催化性能的影响。结果表明,在再生温度220℃、再生压力100 k Pa、空速500 h~(-1)和再生时间60 h条件下,失活低固汞催化剂再生性能最好,再生后乙炔转化率达到99.8%。     

超声辅助熔融草酸法高效绿色再生饱和活性炭

饱和活性炭的高效绿色再生对活性炭在污染物吸附过程中的循环利用是非常重要的。本文利用超声波辅助熔融草酸的方法对饱和活性炭进行高效绿色再生，讨论了温度、时间、超声振幅和固液比对饱和活性炭再生效率的影响。结果表明，在超声辅助作用下，熔融草酸可在20min内使饱和活性炭得到快速再生，再生效率高达94.72%。通过5次吸附-脱附循环后，再生效率仍可达到78.02%，与此同时有机酸的回收率极高，平均达到98.35%，再生过程十分绿色环保。在超声的辅助作用下，强氢键缔合能力的熔融草酸更充分地与焦糖反应，形成草酸-焦糖强氢键缔合体系，降低焦糖与活性炭表面的亲和力，将焦糖解吸，实现活性炭的再生。该法可为绿色高效的活性炭再生方法的研究开发提供新思路。     

Selective Removal of Hydrogen Sulfide from Gases Containing Hydrogen Sulfide and Carbon Dioxide Using Diethanolamine

Abstract

It is sometimes necessary to selectively remove hydrogen sulfide from gases containing carbon dioxide. This may be the case for example in the production of sulfur using the Claus process. When two gases are simultaneously absorbed into a solution containing a reactant with which each gas can react, the rate of absorption of each component is affected by the presence of the other gas. For the absorption of hydrogen sulfide into primary and secondary amines, the reaction which occurs can usually be considered to be instantaneous. An instantaneous reaction is diffusion-limited since the reaction occurs so rapidly that the liquid phase reactant and the absorbed gas cannot coexist in the same region of the liquid. For primary and secondary amines used for gas treatment, the reaction with carbon dioxide is much slower than for hydrogen sulfide and can often be considered to be second order.

In this work the simultaneous absorption of two gases into a liquid containing a reactant with which both gases can react is modeled using penetration theory. It is assumed that one gas reacts instantaneously and the other gas undergoes a second order reaction. Parameters used in the calculations are those available in the literature corresponding to the absorption of hydrogen sulfide and carbon dioxide in diethanolamine.     

结炭B-02催化剂烧炭再生本征动力学模型

以工业两段绝热床中运行近4000h的结炭B—02催化剂为研究对象,利用内循环无梯度反应器,求得催化剂烧炭再生本征动力学模型.由于催化剂中的结炭是多核芳烃,因此可简单地以碳氧化和氢氧化的动力学方程表征烧炭再生动力学模型.碳氧化动力学方程为-dN_c/N_Cdt=K_Cp_(O_2)~(0.3)(N_C/N_C)~1.3式中,一段催化剂 K_C=13.37exp[-78.97×10~3/(RT)]二段催化剂 K_C=96.54exp[-89.30×10~3/(RT)]氢氧化动力学方程为-dN_H/N_Hdt=K_H(N_H/N_H)~1.1式中,一段催化剂 K_H=0.48exp[-39.04×10~3/(RT)]二段催化剂 K_H=4.79exp[-52.03×10~3/(RT)]     

Interface species and effect of hydrogen on their amount in the CO oxidation on Au/ZnO

A FTIR study of the CO oxidation on Au/ZnO from 90 to 300 K in the absence and in the presence of hydrogen has been performed. An insight on the origin of deactivation during CO oxidation at room temperature and on the regeneration effect of hydrogen is given. FTIR spectra show that at 90 K only carbonylic species on the metallic particles and on the support cations are produced. Carbonates and/or carbonyls at the interface between the metal and the oxide are produced by increasing the temperature from 90 to 300 K. The presence of hydrogen in the mixture inhibits in some extent the formation of transient intermediates and of stable carbonates adsorbed on the support. The amount of stable species at the interface is reduced as a consequence of the lowered basicity of the reactive oxygen species at the borderline between the metal and the oxide.     

活性炭催化过氧化氢氧化脱附其表面吸附的二苯并噻吩

主要研究了活性炭催化过氧化氢氧化脱附其表面吸附的二苯并噻吩。比较了使用H₂O₂水溶液,H₂O₂+HCOOH水溶液和H₂O₂+CH₃COOH水溶液对活性炭进行催化氧化再生的性能,并考察了催化条件对活性炭再生性能的影响。结果表明：3种不同的催化氧化再生方法都能使活性炭获得不同程度的再生,其中,使用H₂O₂+HCOOH水溶液进行催化氧化再生的活性炭再生效果最好,达90％以上。使用H₂O₂+HCOOH水溶液对活性炭进行再生时,H₂O₂浓度、HCOOH浓度、反应温度和时间对活性炭再生性能均有影响,选择合适的催化条件,可使再生性能达到最佳。     

CO and H2 oxidation on a platinum monolith diesel oxidation catalyst

This paper presents experimental and modelling results for the oxidation of mixtures of hydrogen and carbon monoxide in a lean atmosphere. Transient light-off experiments over a platinum catalyst (80 g/ft³ loading) supported on a washcoated ceramic monolith were performed with a slow inlet temperature ramp. Results for CO alone agree with earlier results that predict self-inhibition of CO; that is an increasing light-off temperature with increasing CO concentration. Addition of hydrogen to the feed causes a reduction in light-off temperature for all concentrations of CO studied. The most significant shift in light-off temperature occurs with the addition of small amounts of hydrogen (500 ppm, v/v) with only minor marginal enhancement occurring at higher hydrogen concentrations. Hydrogen alone in a lean atmosphere will oxidise at room temperature. In mixtures of hydrogen and CO, the CO was observed to react first until a conversion of about 50% was observed, at which point the conversion of hydrogen rapidly went from 0 to 100%.

Simulations performed using literature mechanistic models for the oxidation of these mixtures predicted that hydrogen ignites first, followed by CO, a direct contradiction of the experimental evidence. Upon changing the activation energy between adsorbed hydrogen and oxygen, the CO was observed to oxidise first, however, no enhancement of light-off was predicted. The effect cannot be explained by the mechanistic model currently under discussion.     

REGENERATION PROTOCOLS FOR FIXED BED REACTORS DEACTIVATED BY COKE

Coked catalyst in fixed bed reactors is regenerated by passing hot air mixed with a non-reacting diluent (like steam(. The concentration of oxygen in the regenerating stream is increased from the beginning of the regeneration following a so called regeneration protocol, in order to minimize the regeneration time but still maintaining the maximum temperature within the reactor below permissible level. In this paper, we have modelled the low temperature regeneration in fixed bed reactors and have suggested general regeneration protocols, suitable for wide range of process conditions

A pseudo-homogeneous model is developed to simulate regeneration of fixed bed reactors. The model accounts for major industrially important issues like, non-uniform coke deposition along the reactor length, hydrogen content (with faster burning of hydrogen) of coke and incomplete combustion of coke. Detailed qualitative understanding of the regeneration process and the role of protocol is developed. Specific guidelines were evolved and discussed to aid process engineers to select better regeneration protocol. One worked example of regeneration of fixed bed reactors is included     

Regeneration of Activated Carbon Loaded with Toluene by Supercritical Carbon Dioxide

Abstract

Activated carbon loaded with toluene was regenerated by supercritical carbon dioxide. The adsorptive capacities after several regeneration cycles were still close to that of virgin carbon and remained stable. The effects of temperature, pressure, and flow rate on regeneration efficiency were studied. It was found that the operations at higher pressures were more favorable for regeneration, but the optimal operating temperature depended on pressure. The interphase mass transfer resistance was insignificant during regeneration. A one-parameter mathematic model assuming linear desorption kinetics is proposed which agrees well with the experimental data. The adsorption rates of activated carbon regenerated by the supercritical regeneration method and the steam regeneration method are compared in this study. It was found that the supercritical regeneration method is superior to the steam regeneration method.     

Bifurcation and its implications for a novel autothermal circulating fluidized bed membrane reformer for the efficient pure hydrogen production

The present investigation is a prelude to the experimental exploration of Static Bifurcation Behavior (SBB) in a novel Autothermal Circulating Fluidized Bed Membrane Reformer (ACFBMR) for pure hydrogen production by steam reforming of heavy hydrocarbons. Important impacts of a wide range of design and operating parameters on the reformer performance are explored with two reformer configurations. One is with the catalyst regeneration before the gas-solid separation and another is with the catalyst regeneration after the gas-solid separation. For both configurations there are three steady states (multiplicity of the steady states, static bifurcation behavior). The system behavior in the bifurcation region is quite complex and defies the simple logic of non-autothermal processes. For the first configuration, on the branch of upper temperature steady state the carbon formation and deposition on the nickel catalyst is highest, while the net hydrogen yield is highest on the branch of lower temperature steady state. For the second configuration, the conversion of heptane is always 100%. In the multiplicity region, the order of net hydrogen yield from high to low is the middle, upper and lower temperature steady states, while the order of reformer exit carbon flow rate from high to low is the lower, middle and upper temperature steady states. Efficient production of pure hydrogen for fuel cells requires fundamental and practical understanding of their bifurcation behaviors.     

Combustion of coke deposits in a catalyst pellet

A model of catalyst pellet regeneration is presented that accounts for the separate combustion reactions of the hydrogen and the carbon in the coke. The complete structure of the burn-off time with respect to several system parameters is given. It is shown that there are values of initial coke weight fraction and pellet size that give minimum burn-off time. The model indicates that the combustion of the deposited coke is limited by diffusion at higher temperatures than previously thought, and it predicts relatively high temperature differences between the solid particles and the fluid phase at low levels of conversion for some range of the model parameters.     

Steady-state modeling and bifurcation behavior of circulating fluidized bed membrane reformer-regenerator for the production of hydrogen for fuel cells from heptane

The production of hydrogen for fuel cells by steam reforming of heptane is investigated in a Circulating Fluidized Bed Membrane Reformer-Regenerator (CFBMRR) system (A.I.Ch.E. Journal 49(5) (2003) 1250). Palladium based hydrogen permselective membranes are used for hydrogen removal and dense perovskite oxygen permselective membranes are used for oxygen introduction. A series of pseudo-steady-state simulations show that when the catalyst is not regenerated, the circulating nickel reforming catalyst deactivates quickly and the “half catalyst activity life” for efficient production of hydrogen is quite short, especially at high temperatures. Efficient continuous catalyst regeneration can keep the catalyst activity high (∼1.0). With continuous catalyst regeneration, autothermal operation for the entire adiabatic reformer-regenerator system is achievable when the exothermic heat generated from the catalyst regenerator is sufficient to compensate for the endothermic heat consumed in the riser reformer. This type of autothermal operation becomes less likely at high steam to carbon feed ratios. This is due to the fact that carbon deposition rate decreases leading to the decrease of autothermal circulating feed temperature and energy-based hydrogen yield (adiabatic hydrogen yield in autothermal reformer-regenerator system). Multiplicity of the steady states for the reformer is possible for this configuration. With the steam to carbon feed ratio as the bifurcation parameter, multiplicity occurs between the two bifurcation points 1.444 and 2.251 mol/mol. In this multiplicity region, the energy-based hydrogen yield at the upper steady state with high regenerator output temperature is surprisingly the lowest one. While it is the highest one at the lower steady state with low regenerator output temperature. The maximum energy-based hydrogen yield is about 15.58 moles of hydrogen per mole of heptane fed at the lower steady-state when steam to carbon feed ratio is very close to the bifurcation value of 1.444 mol/mol. After removing the sweep gas steam by downstream cooling and de-humidification, the product hydrogen from steam reforming of hydrocarbons can be used for fuel cells with high purity (∼100%).     

Deactivation and regeneration of Pt/Al2O3 catalysts during the hydrodechlorination of carbon tetrachloride

Deactivation and regeneration of Pt/Al₂O₃ catalysts during the hydrodechlorination of carbon tetrachloride were studied. The effect of reactant partial pressures and temperature on the catalyst deactivation was investigated. A deactivation model with residual activity was developed to quantify the kinetic deactivation parameters. The effect of the regeneration atmosphere was also investigated. Regeneration under air allowed for the full recovery of the catalytic performance of fresh catalysts while treatments under flowing hydrogen resulted in a superior catalytic performance, increasing both the initial and residual activities. This was ascribed to a combined effect, redispersion of the metallic phase and formation of surface defects.     

浸渍活性炭脱除H2S的反应动力学

提出了浸渍活性炭脱除Ｈ２Ｓ的反应过程机理模型，认为脱硫过程主要是Ｈ２Ｓ在活性炭的吸附水膜内离解后被活化的Ｏ２分子以及活性氧原子氧化生成单质硫逐渐沉积在活性炭表面，同时应用最小二乘法回归实验数据得到了脱硫动力学方程ｄＷｓ／ｄｔ＝ｋ１ｋ２／ａｐｏ２／ｐＨ２Ｓ／１＋ｋ２ｐｏ２×（１－αＷｓ）＾２其中动力学参数ｋ１＝３．７５３×１０＾５ｅｘｐ「－３００６．５／Ｔｒ」ｋ２／０．２６３ｅｘｐ「１９４５．６／Ｔ     

Structural properties of water around uncharged and charged carbon nanotubes

Studying the structural properties of water molecules around the carbon nanotubes is very important in a wide variety of carbon nanotubes applications. We studied the number of hydrogen bonds, oxygen and hydrogen density distributions, and water orientation around carbon nanotubes. The water density distribution for all carbon nanotubes was observed to have the same feature. In water-carbon nanotubes interface, a high-density region of water molecules exists around carbon nanotubes. The results reveal that the water orientation around carbon nanotubes is roughly dependent on carbon nanotubes surface charge. The water molecules in close distances to carbon nanotubes were found to make an HOH plane nearly perpendicular to the water-carbon nanotubes interface for carbon nanotubes with negative surface charge. For uncharged carbon nanotubes and carbon nanotubes with positive surface charge, the HOH plane was in tangential orientation with water-carbon nanotubes interface. There was also a significant reduction in hydrogen bond of water region around carbon nanotubes as compared with hydrogen bond in bulk water. This reduction was very obvious for carbon nanotubes with positive surface charge. In addition, the calculation of dynamic properties of water molecules in water-CNT interface revealed that there is a direct relation between the number of Hbonds and selfdiffusion coefficient of water molecules.     

低温脱硫剂的研究进展

介绍了国内外低温脱硫剂的研究现状。阐述了应用于低温条件下的活性炭、氧化铁和氧化锌等单一组分脱硫剂的脱硫机理、动力学模型及再生方法。总结了脱硫剂结构、原料气组成和工艺条件等因素对硫化氢脱除效果的影响。简述了复合脱硫剂的研究进展及工业化应用情况。展望了低温脱硫剂的研究前景。     

Studies in char gasification—I A lumped model

The gasification of char in a steam-oxygen fluidized bed was studied. The char was assumed to be composed of base carbon and ash. The gaseous compounds found were limited to CO, CO₂, H₂, H₂O, O₂ and CH₄. As the oxygen and hydrogen were assumed not to co-exist, the bed was divided into a shallow combustion zone where the carbon combustion would take place and a gasification zone where no oxygen would be found. A lumped model for the gasification zone was formulated. The thickness of the combustion zone was assumed to be negligible compared to the total height of the reactor. All chemical changes in the gasification zone were described by three reactions: steam gasification, carbon hydrogasification and water-gas shift reaction. The gases and the solids in the gasification zone were assumed to be at uniform temperature. From the results of the model calculations it was concluded that one should use the fairly complicated empirical kinetic expressions developed by Johnson for reliability over a wide range of pressures and residence times. The effects of the reactor pressure, the char residence time and the amount of oxygen in the feed on the gasifier performance were analysed.     

High-temperature desulphurization of low-CV fuel gas

Experimental results on desulphurization of synthesized low-CV fuel gas using Western Kentucky No.9 gasifier coal ash as the sorbent are presented; oxides of iron in the ash react with the hydrogen sulphide, and ferrous and ferric sulphides are formed. Fixed beds of ash, held at 1000 K, removed 99% of the hydrogen sulphide at a concentration of 1.25% and a throughput of 2000 h⁻¹. Increasing temperature, pressure, sulphide concentration and space velocity increased the sorption capacity of the ash markedly. In the conditions tested, results were consistent with diffusion control from laminar flow. Spent ash was regenerated by passing air through the beds, when sulphur dioxide was evolved and ferric oxide reformed. Potentials for other chemical reactions were examined by chemical equilibrium; the gases hydrogen, carbon dioxide, carbon monoxide and water react during desulphurization and their concentrations reach equilibrium. It is suggested that gasifier coal ashes having significant iron content are suitable sorbents for high-temperature desulphurization from synthetic low-CV fuel gases derived from coal.