Engineering problems in the operation of microspherical chromium oxide/alumina catalysts for the dehydrogenation of paraffins

We analyze the effects of fluidized bed height, circulation ratio, and pressure drop in a reactor on the operational efficiency of a dehydrogenation unit in order to determine the reasons for a decrease in iso-butylene yield and catalyst circulation ratio, leading to an increase in the concentration of by-products at the iso-butane dehydrogenation plant of OAO Nizhnekamskneftekhim, where a mixture of catalysts with different physicomechanical characteristics (abrasion resistance, bulk density, fractional composition) is used to increase the iso-olefin yield. It is revealed that the main reason for the decrease in the olefin yield is the accelerated drop in pressure in the reactor due to a reduction in the free area of the waste-heat boiler tubes and scrubber grids as a result of the formation of hard-to-remove solid sediments consisting of potassium silicate and components of less durable IM-2201 catalysts (e.g., alumina and chromium oxide) on their walls. The sediment accumulation rate is proportional to the IM-2201 catalyst abrasiveness, which increases after a highly durable impregnated catalyst is added. To prevent an undesirable increase in the pressure, it is forbidden to combine catalysts with different physicochemical characteristics, obtained by the technologies of spray drying and support impregnation. In order to use the more durable impregnated chromium oxide/alumina catalysts separately and provide the required fluidized bed height of no less than 45.0% of the total reactor height, it is necessary to improve their aerodynamic properties, and to optimize their fractional composition in particular. The equilibrium catalyst formed during operation and circulating directly in the reactor/regenerator circuit must contain up to 30 wt % of <40-μm granules in order to guarantee the required height and to form a stable fluidized bed with no splashing at a constant level on the device’s upper grid, with less entrainment of fine granules and optimum circulation.     

Development of technology for the production of microspherical alumina support for the alkane dehydrogenation catalyst: II. The influence of hydrothermal treatment conditions on the operational characteristics of microspherical alumina support and chromium oxide/alumina catalyst for the dehydrogenation of iso-butane

For the purpose of improving the mechanical strength and reducing the abrasive activity of micro-spherical chromium oxide/alumina catalysts for the processes of alkane dehydrogenation in fluidized bed, we have developed technology for the production of new highly durable boehmite support with the use of technical aluminum trihydrate as an initial raw material. The technology includes two consecutive stages: the dehydration of aluminum trihydrate and the subsequent hydrothermal treatment of dehydration product into boehmite. Part II covers the results on the influence of conditions for the hydrothermal treatment of aluminum trihydrate dehydration products in an industrial autoclave of special construction on the phase composition, physicomechanical and structural characteristics of boehmite support, the acidic properties of its respective oxide form and chromium oxide/alumina catalyst based on this support and also on the catalytic properties of this catalyst in the reaction of iso-butane dehydrogenation into iso-butylene. It has been shown that differently sized boehmite crystallites and also gibbsite are formed in the volume of microgranule under hydrothermal conditions of χ-Al₂O₃ dehydration depending on a chosen regime (temperature, time). For the production of iso-butane dehydrogenation selective chromium oxide/alumina catalyst with the minimal content of strong acidic sites, catalyzing the cracking reactions, it is necessary to provide such hydration conditions, under which large (43–47 nm) boehmite crystals are formed. The appearance of strong acidic sites is caused by small boehmite crystals and the presence of nonhydrated χ-Al₂O₃ phase. In the absence of the impurity gibbsite phase, the highly durable microgranules of boehmite support and catalyst are formed. The conditions, providing the complete χ-Al₂O₃ hydration into macrocrystalline boehmite, have been defined. The application of the developed two-stage technology gives the iso-butylene yield of 45–49%, the selectivity of 88–90%, and the abrasivity of 0.10 g/(m² h). The given technology for the production of catalyst is realized in an industrial unit with the capacity of 100 t per month at OAO Karpov Mendeleevsk Chemical Plant (Mendeleevsk). Industrial catalyst lots are currently under operation at the Synthetic Isoprene Rubber Plant of OAO Nizhnekamskneftekhim.     

Pilot tests of the microspherical aluminochromium KDI-M catalyst for <Emphasis Type="Italic">iso</Emphasis>-butane dehydrogenation

Results from pilot tests of microspherical aluminochromium KDI-M catalyst mixed with IM-2201 in a large-scale unit (Nizhnekamskneftekhim) for iso-butane dehydrogenation are discussed. Compared to KDI catalyst, its modified analogue KDI-M is more active and selective; the optimized grain-size composition and mechanical strength ensures higher yields of iso-butylene and longer nonstop operation (up to 400 days) of the reactor unit.     

A simplified mathematical modeling for thermo-catalytic decomposition of methane over carbon black catalyst in a fluidized bed reactor

A mathematical model for thermo-catalytic decomposition of methane over carbon black catalysts in a fluidized bed was proposed. The simplified isothermal, uniform flow model was considered and implemented into a computer code to predict the reactor performance. The experiment of methane decomposition into hydrogen and carbon was carried out in a fluidized bed of I.D of 0.055 m and height of 1.0 m. The range of reaction temperature was 850–900 °C, gas velocity was 1.0–3.0 U _mf , and catalyst loading was 50–200 g. The reaction parameters for model equation were determined from the curve fittings and the comparison of experimental data with simulation results showed good agreement for fluidized bed reactor system. From the simulation results, the fluidized bed performance with different operating conditions were obtained, and this simple model can be used to predict the performance of a larger scale fluidized bed reactor and also in determining the optimum operating conditions.     

Hydrogen production by catalytic decomposition of methane over carbon catalysts in a fluidized bed

A fluidized bed reactor made of quartz tube with an I.D. of 0.055 m and a height of 1.0 m was employed for the thermocatalytic decomposition of methane to produce CO₂ — free hydrogen. The fluidized bed was used for continuous withdrawal of the carbon products from the reactor. Two kinds of carbon catalysts — activated carbon and carbon black — were employed in order to compare their catalytic activities for the decomposition of methane in the fluidized bed. The thermocatalytic decomposition of methane was carried out in a temperature range of 800–925°C, using a methane gas velocity of 1.0–3.0 U _mf and an operating pressure of 1.0 atm. Distinctive difference was observed in the catalytic activities of two carbon catalysts. The activated carbon catalyst exhibited higher initial activity which decreased significantly with time. However, the carbon black catalyst exhibited somewhat lower initial activity compared to the activated carbon catalyst, but its activity quickly reached a quasi-steady state and was sustained over time. Surfaces of the carbon catalysts before and after the reaction were observed by SEM. The effect of various operating parameters such as the reaction temperature and the gas velocity on the reaction rate was investigated.     

Development of technology for the production of microspherical aluminum oxide supporter for the paraffin dehydrogenation catalyst

For the purpose of improving the mechanical strength and to reduce the abrasive activity of microspherical chromoalumina catalyst for the paraffin dehydrogenation in fluidized bed, technology, using technical aluminum trihydrate as an initial raw material and including consecutive stages of Al(OH)₃ dehydration and hydrothermal processing of its product into boehmite, has been developed for the production of highly durable boehmite supporter. As applied to the iso-butane dehydrogenation into iso-butylene, microspherical chromoalumina catalysts, which are synthesized with the use of boehmite supporter, exceed their known industrial analogous in activity, selectivity and physicomechanical properties. The technology of supporter and iso-butane dehydrogenation catalyst is realized at OAO Karpov Mendeleevsk Chemical Plant (Mendeleevsk) for the production with the capacity of 100 t per month. Industrial catalyst lots are under operation at the Synthetic Isoprene Rubber Plant of OAO Nizhnekamskneftechim. The given article consists of two parts. In the first one, investigation results are presented for the changes in technical properties of Al(OH)₃ during its dehydration in an industrial continuous baking drum-type furnace. The changes in physicomechanical characteristics of granules at the dehydration stage are caused by phase transformations of gibbsite and boehmite, by crystalline structure rearrangements in the volume of microgranules and do not depend on mechanical loads in a baking furnace and on porous structure changes. The conditions of gibbsite complete phase change into the two-phase boehmite-χ-Al₂O₃ mixture with minimal reduction in the microgranules strength have been determined: T _av = 435−475°C, ν_THA = 170 kg/h, and τ_av = 0.8 h.     

Performance studies of various cracking catalysts in the conversion of canola oil to fuels and chemicals in a fluidized-bed reactor

Studies were conducted at atmospheric pressure at temperatures in the range of 400–500°C and fluidizing gas velocities in the range of 0.37–0.58 m/min (at standard temperature and pressure) to evaluate the performance of various cracking catalysts for canola oil conversion in a fluidized-bed reactor. Results show that canola oil conversions were high (in the range of 78–98 wt%) and increased with an increase in both temperature and catalyst acid site density and with a decrease in fluidizing gas velocity. The product distribution mostly consisted of hydrocarbon gases in the C₁–C₅ range, a mixture of aromatic and aliphatic hydrocarbons in the organic liquid product (OLP) and coke. The yields of C₄ hydrocarbons, aromatic hydrocarbons and C₂–C₄ olefins increased with both temperature and catalyst acid site density but decreased with an increase in fluidizing gas velocity. In contrast, the yields of aliphatic and C₅ hydrocarbons followed trends completely opposite to those of C₂–C₄ olefins and aromatic hydrocarbons. A comparison of performance of the catalysts in a fluidized-bed reactor with earlier work in a fixed-bed reactor showed that selectivities for formation of both C₅ and iso-C₄ hydrocarbons in a fluidized-bed reactor were extremely high (maximum of 68.7 and 18 wt% of the gas product) as compared to maximum selectivities of 18 and 16 wt% of the gas product, respectively, in the fixed-bed reactor. Also, selectivity for formation of gas products was higher for runs with the fluidized-bed reactor than for those with the fixed-bed reactor, whereas the selectivity for OLP was higher with the fixed-bed reactor. Furthermore, both temperature and catalyst determined whether the fractions of aromatic hydrocarbons in the OLP were higher in the fluidized-bed or fixed-bed reactor.     

Characteristics of carbon dioxide hydrogenation in a fluidized bed reactor

Characteristics of CO₂ hydrogenation were investigated in a fluidized bed reactor (0.052 m IDxl.5 m in height). Coprecipitated Fe-Cu-K-Al catalyst (d_ρ=75–90 Μm) was used as a fluidized solid phase. It was found that the CO₂ conversion decreases but the CO selectivity increases, whereas the space-time-yield attains maximum values with increasing gas velocity. The CO₂ conversion has increased, but CO selectivity has decreased with increasing hydrogenation temperature, pressure or H₂/CO₂ ratio in the fluidized bed reactor. Also, the CO, conversion and olefin selectivity appeared to be higher in the fluidized bed reactor than those of the fixed bed reactor. Presented at the Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University     

Effect of the nature of silicon oxide structures on the activity of an alumina-chromium catalyst in the reaction of iso-butane dehydrogenation

The formation of silicon oxide structures in the composition of an alumina-chromium catalyst for the dehydrogenation of iso-butane is studied by means of nitrogen adsorption, XRD analysis, solid-state ²⁹Si NMR spectroscopy, temperature-programmed desorption of ammonia, and UV-Vis and Raman spectroscopy. It is established that 0.5–1.2 wt % silicon was distributed on the catalyst surface in the form of Si(OSi)₄ structures. As the silicon content was increased to 2.2–3.6 wt %, Si(OSi)₃(O-) structural elements were present on the surface in addition to Si(OSi)₄. The formation of silicon oxide structures on the catalyst surface was responsible for an increase in the concentration of Cr(III) ions and a decrease in the surface acidity; the activity and selectivity of the catalysts in the reaction of iso-butane dehydrogenation increased.     

Reaction performance of FCC slurry catalytic cracking

The condensation of heavy hydrocarbon causes the coke formation inside the disengager vessel. Slurry oil is the heaviest component of FCC hydrocarbon products and most likely to be condensed to form coke. Converting slurry to lighter hydrocarbons can alleviate coke formation. The slurry cracking experiments were carried out in a confined fluidized bed reactor. The results showed that the crackability of slurry was lower than that of FCC feedstock, due to the difference of their properties. About 30 wt.% heavy oil remained in the product after the slurry was cracked, but its end point declined and the heavier component decreased. The comparison of slurry cracking results at different reaction temperatures and regenerated catalyst contents indicated that the appropriate operating conditions for slurry conversion were the reaction temperature of 500 °C and the regenerated catalyst content within 25–50 wt.%.     

Autothermal CO2 reforming of methane over NiO–MgO solid solution catalysts under pressurized condition: Effect of fluidized bed reactor and its promoting mechanism

The effect of fluidized bed reactor in autothermal CO₂ reforming of methane over NiO–MgO solid solution catalysts was investigated by comparing with fixed bed reactor. Methane conversion to syngas was drastically enhanced by using a fluidized bed reactor. The catalyst was reduced and oxidized repeatedly in fluidized bed reactor during the reaction. The enhancement of methane conversion is related to the catalyst reducibility.     

Experimental Investigations of Catalytic Partial Oxidation of Methane to Synthesis Gas in Various Types of Fluidized‐Bed Reactors

The partial oxidation of methane to synthesis gas over Ni/α‐Al₂O₃ catalysts (1 and 5 wt.‐% Ni loading, 71–160 and 250–355 μm particle diameter) was investigated in different types of fluidized‐bed reactors, i.e., the bubbling fluidized bed (FlB), the spout fluid bed (SFB) and the internally circulating fluidized bed (ICFB). A methane‐to‐oxygen ratio of 2:1 was used in all experiments and the temperature was varied between 700 and 800 °C. Gas velocities and catalyst masses were adjusted to assure a stable and controllable reactor operation. A nearly isothermal operation was established in all reactors. The thermodynamic equilibrium values were achieved in the FlB and SFB reactor whereas in the ICFB reactor slightly lower conversions and selectivities were obtained. Taking the direct scale‐up concept of the ICFB reactor into account, significant higher space‐time yields were obtained in this reactor than in the industrial‐scale bubbling fluidized‐bed reactor. No increase of the space‐time yield in comparison to the FlB was obtained in the SFB reactor.     

The slug flow behavior of polyethylene particles polymerized by Ziegler-Natta and metallocene catalysts

We investigated the flow behavior of polyethylene particles polymerized by Ziegler-Natta catalyst and Metallocene catalyst. The employed polymer particles were linear low-density polyethylene (LLDPE), and average particle size was 600 Μm. Different flow behavior of polymer particles in a fluidized bed was observed with different polymerization catalysts in the bubbling and slugging flow regimes. The flow behavior determined from the pressure drop fluctuation in the lower and upper section of the bed was analyzed with statistical methods. Presented at the Int’/Sym. on Int’l Symp. on Chem. Eng. (Cheju, Feb. 8–10, 2001), dedicated to Prof. H. S. Chun on the occasion of his retirement from Korea University.     

Hydrogen production from fluidized bed steam reforming of hydrocarbons

Steam reforming of methane, kerosene and heavy oil over a nickel/alumina commercial catalyst and other materials such as limestone, dolomite and iron ore, was studied using a 5 cm i.d. fluidized bed reactor. The effects of operating parameters on conversion, hydrogen yield, product gas composition and elutriation of fine catalysts were investigated. It was found that a fluidized bed is flexible enough to handle various feedstocks, including hydrocarbons heavier than naphtha, because it permits the addition of catalyst to, or withdrawals of, coked catalyst from the bed. The yield of hydrogen obtained from fluidized bed steam reforming of heavy oil at 800‡C over limestone was similar to that obtained over commercial nickel-based catalyst. This indicates that limestone could be a promising catalyst for the production of hydrogen from heavy oil. However, hydrogen yield decreased with reaction time in the experiments using the limestone catalyst. The main cause of the decrease in hydrogen yield was elutriation of fine catalysts from the bed during the reaction.     

Comparative study between fluidized bed and fixed bed reactors in methane reforming combined with methane combustion for the internal heat supply under pressurized condition

The effect of catalyst fluidization on the conversion of methane to syngas in methane reforming with CO₂ and H₂O in the presence of O₂ under pressurized conditions was investigated over Ni and Pt catalysts. Methane and CO₂ conversion in the fluidized bed reactor was higher than those in the fixed bed reactor over Ni_0.15Mg_0.85O catalyst under 1.0 MPa. This reactor effect was dependent on the catalyst properties. Conversion levels in the fluidized and fixed bed reactor were almost the same over MgO-supported Ni and Pt catalysts. It is suggested that this phenomenon is related to the catalyst reducibility. On a catalyst with suitable reducibility, the oxidized catalyst can be reduced with the produced syngas and the reforming activity regenerates in the fluidized bed reactor. Although serious carbon deposition was observed on Ni_0.15Mg_0.85O in the fixed bed reactor, it was inhibited in the fluidized bed reactor.     

Transformation of propane,n-butane and n-hexane over H3PW12O40 and cesium salts. Comparison to sulfated zirconia and mordenite catalysts

Over H₃PW₁₂O₄₀ and its acidic cesium salts at 250°C, alkane transformations occur through the mechanisms previously proposed for sulfated zirconia and mordenite catalysts: propane is mainly transformed into butanes through a trimerization–isomerization–cracking process, n-butane into isobutane, propane and pentanes through a dimerization–isomerization–cracking process, n-hexane into methylpentanes and 2,3-dimethylbutane through a monomolecular mechanism. With all the samples, n-butane transformation is initially much faster than propane transformation, the difference in rate increasing significantly with the Cs content: from 25 times with H₃PW₁₂O₄₀ to 350 times with Cs_2.4H_0.6PW₁₂O₄₀. On the other hand, n-hexane transformation is 2.3 to 7 times faster than n-butane transformation. A decrease in acid strength and in acid site density with Cs introduction is proposed to explain the increase in the rate ratios. For all the reactions, sulfated zirconia pretreated at 600°C is 2–3 times more active than the heteropolycompounds. HMOR10 which is the most active catalyst for n-hexane transformation is the least active for n-butane and especially propane transformation. This very low activity of mordenite for these bimolecular processes can be related to particularities of its pore system: bimolecular reactions are strongly unfavoured in the narrow non-interconnected channels of this zeolite. This revised version was published online in August 2006 with corrections to the Cover Date.     

Syngas production from methane reforming with CO2/H2O and O2 over NiO–MgO solid solution catalyst in fluidized bed reactors

Catalyst performance of NiO–MgO solid solution catalysts for methane reforming with CO₂ and H₂O in the presence of oxygen using fluidized and fixed bed reactors under atmospheric and pressurized conditions was investigated. Especially, methane and CO₂ conversion in the fluidized bed reactor in methane reforming with CO₂ and O₂ was higher than those in the fixed bed reactor over Ni_0.15Mg_0.85O catalyst under 1.0 MPa. In contrast, conversion levels in the fluidized and fixed bed reactor were almost the same over MgO-supported Ni and Pt catalysts. It is suggested that the promoting effect of catalyst fluidization on the activity is related to the catalyst reducibility. On a catalyst with suitable reducibility, the oxidized and deactivated catalyst can be reduced with the produced syngas and the reforming activity regenerates in the fluidized bed reactor during the catalyst fluidization. In addition, the catalyst fluidization inhibited the carbon deposition.     

A new alkylate production process

A new technology for alkylation on solid AlkiRAN-GPN catalyst with process performance characteristics and an attained material balance competitive with existing sulfuric and hydrofluoric acid alkylation technologies is presented. Data on the effect such parameters as temperature, pressure, iso-butane: olefin ratio, and feedstock hourly space velocity (FHSV)) have on the process’s performance characteristics are given, and their optimum values are recommended. It is shown that using a sectioned reactor at a constant inlet iso-butane: olefin ratio ensures a higher internal ratio of these components and an increase in the total concentration of alkylate in the reaction products at a specified internal iso-butane: olefin ratio. This also lengthens the period of catalyst interregeneration with no losses in the process’s productivity and selectivity. The use of a zeolite based on faujasite in the rare-earth element–calcium form (REECaHY) and ultrastable zeolites as catalysts is substantiated. Higher values of olefin conversion and the alkyl gasoline yield are observed when these zeolites are used. To test the new technology, a demonstration plant of iso-butane alkylation with olefins on heterogeneous catalysts with an alkylate production capacity of 1 t/day is constructed. The results from studies are to be used in developing the basic design of an industrial plant. The construction of the first industrial plant of alkylation on a heterogeneous catalyst with an alkyl gasoline production capacity of 100000 t/year is planned at AO Gazprom Neft Moscow Oil Refinery.     

生物质催化气化实验研究

在常压流化床上进行了生物质在水蒸气条件下的实验研究。实验装置主体由常压流化床反应器和固定床催化裂解反应器组合而成。生物质原料为木屑,焦油裂解催化剂分别选用煅烧白云石和镍基重整催化剂。实验结果表明,H2/CO(H/C)的摩尔比随着气化温度、水蒸气质量/生物质质量（S/B）的升高迅速增加,但催化裂解温度变化对H/C的影响较小。另外,在催化裂解反应器中使用催化剂种类不同,H/C也不同。本文采用两段催化裂解,一段催化剂采用煅烧白云石,二段采用镍基催化剂,焦油裂解率达到96.70％。采用两段催化裂解,不但可以提高焦油的裂解率,增加了H2和CO收率,净化生物质裂解气,而且可以防止镍基重整催化剂失活,延长其使用寿命。     

Oxidative dehydrogenation of butenes over Bi‐Mo and Mo‐V based catalysts in a two‐zone fluidized bed reactor

The oxidative dehydrogenation of a 1‐butene/trans‐butene (1:1) mixture to 1,3‐butadiene was carried out in a two‐zone fluidized bed reactor using a Mo‐V‐MgO and a γ‐Bi₂MoO₆ catalyst. The significant operating conditions temperature, oxygen/butene molar ratio, butene inlet height, and flow velocity were varied to gain high 1,3‐butadiene selectivity and yield. Furthermore, axial concentration profiles were measured inside the fluidized bed to gain insight into the reaction network in the two zones. For optimized conditions and with a suitable catalyst, the two‐zone fluidized bed reactor makes catalyst regeneration and catalytic reaction possible in a single vessel. In the lower part of the fluidized bed, the oxidation of coke deposits on the catalyst as well as the filling of oxygen vacancies in the lattice can occur. The oxidative dehydrogenation reaction takes place in the upper zone. Thorough particle mixing inside fluidized beds causes permanent particle exchange between both zones. © 2016 American Institute of Chemical Engineers AIChE J, 63: 43–50, 2017