Life cycle of hydroprocessing catalysts and total catalyst management

Hydroprocessing catalysts based on Ni, Co, Mo and W are used in various refinery processing applications where several deactivation mechanisms become of importance (coke formation, active phase sintering, metals deposition, poisoning) in the catalyst's life cycle. The life cycle of commercial hydroprocessing catalysts is very complex and includes the catalyst production, sulfidation, use, oxidative regeneration followed by re-sulfidation and reuse or, if reuse is not possible, recycling or disposal. To understand the changes in catalyst properties taking place during a life cycle, the catalyst quality in the different stages can be best monitored by using advanced analytical techniques. The catalyst's life cycle is further complicated by numerous technical, environmental and organizational issues involved. In principle, different companies can be involved in each of the life cycle steps. Leading catalyst manufacturers, together with specialized firms, offer refineries a total catalyst management concept, starting with the purchase of the fresh catalyst and ending with its final recycling or disposal. Total catalyst management includes a broad range of services, ensuring optimal timing during the change-out process, reliable, smooth and safe operations, minimal downtime and maximum catalyst and unit performance.     

Studies on recycling and utilization of spent catalysts: Preparation of active hydrodemetallization catalyst compositions from spent residue hydroprocessing catalysts

Spent catalysts form a major source of solid wastes in the petroleum refining industries. Due to environmental concerns, increasing emphasis has been placed on the development of recycling processes for the waste catalyst materials as much as possible. In the present study the potential reuse of spent catalysts in the preparation of active new catalysts for residual oil hydrotreating was examined. A series of catalysts were prepared by mixing and extruding spent residue hydroprocessing catalysts that contained C, V, Mo, Ni and Al₂O₃ with boehmite in different proportions. All prepared catalysts were characterized by chemical analysis and by surface area, pore volume, pore size and crushing strength measurements. The hydrodesulfurization (HDS) and hydrodemetallization (HDM) activities of the catalysts were evaluated by testing in a high pressure fixed-bed microreactor unit using Kuwait atmospheric residue as feed. A commercial HDM catalyst was also tested under similar operating conditions and their HDS and HDM activities were compared with that of the prepared catalysts. The results revealed that catalyst prepared with addition of up to 40 wt% spent catalyst to boehmite had fairly high surface area and pore volume together with large pores. The catalyst prepared by mixing and extruding about 40 wt% spent catalyst with boehmite was relatively more active for promoting HDM and HDS reactions than a reference commercial HDM catalyst. The formation of some kind of new active sites from the metals (V, Mo and Ni) present in the spent catalyst is suggested to be responsible for the high HDM activity of the prepared catalyst.     

A review of recent advances on process technologies for upgrading of heavy oils and residua

The term hydroconversion is used to signify processes by which molecules in petroleum feedstocks are split or saturated with hydrogen gas while tumbling boiling ranges and impurities content from petroleum fractions. Hydroprocessing is a broad term that includes hydrocracking, hydrotreating, and hydrorefining. To meet the gradual changes in petroleum stipulate, in particular a reduced demand for heavy fuel oil, advanced technologies for residue hydroprocessing are now extremely necessary. A refining process is needed for treating heavy petroleum fractions (atmospheric or vacuum oil residue) in the presence of catalysts and hydrogen at high pressure. In this article the different technologies for residua processing: thermal, catalytic fixed and ebullated types of hydroconversion are reviewed and discussed. A possibility of combining the advantages of these technologies together with suitable catalyst with enhanced and controlled cracking activity is also analyzed.     

A comparative study for heavy oil hydroprocessing catalysts at micro-flow and bench-scale reactors

CoMo and NiMo catalysts were prepared and the catalytic activities were evaluated in fixed bed micro-flow and bench-scale reactors with different feed composition. Experiments were conducted at conditions close to those that exist in the industrial practice. Due to the different nature of the feeds, the conditions were varied with respect to both evaluation scales. The fresh and spent catalysts were characterized. Spent catalyst textural properties indicated that catalysts were deactivated and the surface area and pore volume dropped by 20–60%. The adsorption–desorption hysteresis of spent catalysts indicated that cylindrical pores are deactivated at the pore mouth and played an important role in modification by either closing one end of the pore or forming a narrow neck pore, which is indicative of the formation of “ink-bottle” type pores. Thus, the deposition of metal and carbon takes place preferentially at the pore entrance, which causes pore mouth plugging. These results are also supported by the SEM–EDAX analysis, where metal and carbon depositions are evident and taking place at the superficial region of a catalyst particle. The increase in absolute area of hysteresis is based on the catalyst's average pore diameter: the higher the average pore diameter, the lower the area of the spent catalyst. The activity and deactivation of the catalyst are discussed on the basis of catalyst porosity and deposited metal characterization. The composition of catalysts varies, considering two applications in a multi-reactor system: a CoMo catalyst for the first reactor, and a NiMo in the second reactor; the former is supported on γ-Al₂O₃ and the latter on TiO₂/Al₂O₃. As a comparison, the CoMo catalyst exhibited better hydrogenolysis while the NiMo catalyst showed better hydrogenation activity in both micro-flow and bench-scale reactors. It appears that there is a moderate effect of TiO₂ content in support on Ni and V hydrodemetallization (HDM) while hydrodeasphaltenization (HDAs) and hydrodesulfurization (HDS) activities were slightly improved when a partially hydrotreated feed, which contains more refractory compounds than virgin feedstock, was employed.     

Advances on the development of novel heterogeneous catalysts for transesterification of triglycerides in biodiesel

This paper describes experimental work done towards the search for more profitable and sustainable alternatives regarding biodiesel production, using heterogeneous catalysts instead of the conventional homogenous alkaline catalysts, such as NaOH, KOH or sodium methoxide, for the methanolysis reaction. This experimental work is a first stage on the development and optimization of new solid catalysts, able to produce biodiesel from vegetable oils. The heterogeneous catalytic process has many differences from the currently used in industry homogeneous process. The main advantage is that, it requires lower investment costs, since no need for separation steps of methanol/catalyst, biodiesel/catalyst and glycerine/catalyst. This work resulted in the selection of CaO and CaO modified with Li catalysts, which showed very good catalytic performances with high activity and stability. In fact FAME yields higher than 92% were observed in two consecutive reaction batches without expensive intermediate reactivation procedures. Therefore, those catalysts appear to be suitable for biodiesel production.     

Titanium-based solid catalysts for transesterification of methyl-methacrylate by 1-butanol: the homogeneous catalysis contribution

Titanium-based solid catalysts were prepared according to two different procedures. In order to improve the stability of the SiOTi bond in the titanium grafted silica catalysts, the surface remaining hydroxyl groups were passivated to prevent the titanium leaching by SiOTi bond solvolysis. This was performed by grafting trimethoxy-silane groups on isolated silanols of silica, after or before metal grafting. The synthesised materials were characterised by FT-IR spectroscopy, and their catalytic properties evaluated in the reaction of transesterification of methyl-methacrylate (MMA) with 1-butanol (BuOH) in liquid phase to produce butyl-methacrylate (BuMA). An important titanium leaching (18–35%) was always detected with all the solid catalysts.

Investigation of the behaviour of Ti(OBu)₄ as homogeneous catalyst for very small concentrations of titanium was carried out in order to evaluate the catalytic contribution of the active dissolved species. We demonstrate here that the catalytic activity is mainly due to the homogeneous catalysis.     

Using new packages for modelling, equation oriented simulation and optimization of a cogeneration plant

The development and testing of an equation-oriented (EO) mathematical model for the optimization of heat and power systems using a new state-of-the-art sequential quadratic programming (SQP) method called filterSQP has been reported in an earlier paper. The model has been extended to include combined cycle cogeneration plants (CCCPs), the economic optimization of which involves adding equipment investment, cost functions and operating cost models to the stream and unit operation models of the earlier paper. These systems are of substantial industrial interest and are substantially larger than those in Rodríguez-Toral et al., Computers and Chemical Engineering, August 2000. Their size and complexity required the use of a new flexible modelling system (FMS) recently created within our research group. FMS can be used to set up large systems of equations, create networks to be modelled and give starting guesses easily for problems of any size. Also, FMS is able to interact with solvers for EO simulation and optimization, which have been developed here and elsewhere. A number of EO simulation and optimization examples, from simple unit operations to a whole real cogeneration plant involving a commercial gas turbine with 1275 variables and equations, are used to demonstrate the applicability of the CCCP model and the modelling package.     

A new Navier-Stokes and Darcy's law combined model for fluid flow in crossflow filtration tubular membranes

Numerical simulations were performed for laminar fluid flow in a porous tube with variable wall suction, a model of a crossflow filtration tubular membrane. The variable wall suction is described by Darcy's law, which relates the pressure gradient within a flow stream to the flow rates through the permeable wall. The feed stream in the tube, which flows mainly tangentially to the porous wall, is modelled by the Navier-Stokes equations. A method of coupling the Navier-Stokes and the Darcy equations in a solution scheme was considered to develop a fluid dynamic model of crossflow filtration. The governing equations were solved numerically using a finite difference scheme. The solution depends on both the Reynolds axial and filtration number. Some assumptions adopted in simplified models are discussed.     

Supported alkali catalysts for steam gasification of carbonaceous residues from petroleum

Steam reforming of petroleum residues was investigated at 1173 K and atmospheric pressure in a fluidized-bed flow system using a series of alumina-supported catalysts of alkali metal compounds. The catalytic activity increased with decreasing ionization potential of the catalytic alkali metals: Cs >; K >Na >Li. Catalysis was elucidated in terms of an oxygen transfer mechanism proposed for the catalysis by alkali metal compounds in graphite-or char-steam reaction.     

Preparation and characterization of inexpensive heterogeneous catalysts for air pollution control: Two case studies

Relatively inexpensive heterogeneous catalysts for two reactions of great importance in air pollution control, NO reduction and VOC combustion, were prepared and characterized. Apart from their common practical goal and the frequent need for simultaneous removal of air pollutants, these reactions share a similar redox mechanism, in which the formulation of more effective catalysts requires an enhancement of oxygen transfer.

For NO reduction, supported catalysts were prepared by adding a metal (Cu, Co, K) using ion exchange (IE) and incipient wetness impregnation (IWI) to chars obtained from pyrolysis of a subbituminous coal. The effects of pyrolysis temperature, between 550 and 1000 °C, on selected catalyst characteristics (e.g., BET surface area, XRD spectrum, support reactivity in O₂) are reported. For IE catalysts, the surface area increased in the presence of the metals while the opposite occurred for IWI catalysts. For the Co-IE catalysts, the highest surface area was obtained at 700 °C. The XRD results showed that, except for Cu (which exhibited sharp Cu⁰ peaks), the catalysts may be highly dispersed (or amorphous) on the carbon surface. For the C–O₂ reaction the order of (re)activity was K  Co > Cu for IE catalysts and K > Cu > Co for IWI catalysts. For NO reduction the orders were K > Co > Cu (IE catalysts) and Cu > Co > K (IWI catalysts). In all cases the catalytic (re)activity for NO reduction was lower than that exhibited for the C–O₂ reaction. The K-IE and Cu-IWI catalysts appeared to be the most promising ones, although further improvements in catalytic activity will be desirable. Some surprising results regarding CO and CO₂ selectivity are also reported, especially for Co catalysts.

In VOC combustion, the effect of the nature of ion B (Fe and Ni) on the partial substitution of ion A (Ca for La) in ABO₃ perovskites (e.g., LaFeO₃ and LaNiO₃) and on their catalytic activity was studied. The perovskite-type oxides were characterized by means of surface area measurements, XRD, temperature-programmed desorption (TPD) and temperature-programmed reduction (TPR). The effect of partial substitution of La³⁺ by Ca²⁺ was more significant for the La_1−xCa_xFeO₃ perovskites. In this case, the electronic perturbation is compensated by an oxidation state increase of part of Fe³⁺ to Fe⁴⁺. The TPD results revealed that, at higher substitution levels, oxygen vacancies are also formed to preserve electroneutrality. For the La_1−xCa_xNiO₃ perovskites, the characterization results showed no evidence of large differences in electronic properties as calcium substitution increases. The La_1−xCa_xNiO₃ perovskites exhibited lower activity than the simple LaNiO₃ perovskite, whereas for the La_1−xCa_xFeO₃ substituted perovskites the most active catalyst (exhibiting the lowest ignition temperature) was obtained at the highest substitution level, La_0.6Ca_0.4FeO₃.

The performance of both groups of catalysts is briefly discussed in terms of redox processes, in which the interplay between oxygen transfer and electron transfer requires further elucidation for the improvement of catalytic activity.     

High-throughput preparation and screening of rhenium oxide-alumina catalysts in olefin metathesis

High-throughput (HT) experimentation in heterogeneous catalysis exemplifies a multidisciplinary approach to address in an efficient manner different aspects of catalyst development – from synthesis to testing and characterization. The present work reports on preparation systems for rapid parallel synthesis of well defined heterogeneous catalysts and catalyst screening in olefin metathesis. Metathesis of ethene and but-2-ene to propene was chosen as a test reaction. The influences of various parameters such as rhenium oxide loading, catalyst calcination conditions, catalyst pre-treatment, as well as the reaction temperature and contact time on the catalytic performance are discussed. Sample characterization by UV–vis and FT-IR gave an evidence for the formation of active surface perrhenate species, very sensitive to humidity and pre-treatment conditions applied.     

Heterogeneous basic catalysts as alternatives to homogeneous catalysts: reactivity of Mg/Al mixed oxides in the alkylation of m-cresol with methanol

Mg/Al mixed oxides, obtained by decomposition of hydrotalcite-like precursors, represent interesting heterogeneous catalytic systems for basic-catalyzed reactions, as an alternative to environmentally unfriendly homogeneous catalysts. The reactivity of these oxides was evaluated using the methylation of m-cresol as a test reaction and relationships between catalytic performance and chemical–physical features were established. The basicity of the samples was evaluated by CO₂ adsorption and thermal-programmed-desorption. The presence of Al in the mixed oxides considerably affected the density and the strength of the basic sites with respect to MgO. These basic properties in turn influenced the catalytic performance of the materials. Under the reaction conditions used in the present work, medium strength basic sites played the major role in the reaction.     

Influence of the activation temperature on the metal accessibility in model three-way catalysts

The influence of the reduction temperature on the accessibility of the metallic surface was studied on model ceria-alumina supported platinum or rhodium catalysts. For a 0.5% Pt-Ce/Al solid, the H/M values, deduced from hydrogen irreversible chemisorption, decrease deeply with T_r, the reduction temperature, from 60% at T_r = 300°C to 19% at T_r = 500°C. This can be attributed to strong interactions between ceria and platinum, since, the initial H₂ chemisorption could be restored after reoxidation. The presence of BaSO₄ in the support accelerates the loss of metallic area, because of sulfur poisoning of the platinum surface. For T_r = 300°C, the dispersion values were in agreement with those deduced from FTIR spectroscopy of adsorbed CO. In the case of rhodium, a 37% H/M dispersion was obtained, which did not change when T_r was increased from 300 to 500°C. For two industrial Pt-Rh three-way catalysts, the behaviour was found similar to that of platinum, the amount of chemisorbed hydrogen decreasing for T_r > 350°C. Thus, in the three-way catalysts characterization, the maximum metal accessibility is obtained after a reduction at 300°C.     

Determining the environment of transition metal ions in zeolitic catalysts: A combined computational and synchrotron-based study of nickel ions in zeolite-Y

Computer modelling techniques are used to investigate the local structure of the zeolite framework around Ni²⁺ ions in the S_I sites of Ni exchanged zeolite-Y. Our calculations show that there are pronounced inward relaxations (0.4 Å–0.6 Å) of the surrounding oxygen ions. The results allow a detailed rationalisation of recent EXAFS and diffraction studies on this zeolite.     

一种新型常温常湿一氧化碳消除催化剂的研制

采用沉淀法制备了一种新型的银铜型CO消除催化剂,考察了沉淀方法、沉淀剂种类、银铜比例对催化剂活性的影响,对这种新型催化剂进行了结构表征。结果表明该银铜型催化剂在常温、常湿条件下表现出优良的催化性能,具有较强的抗湿性。     

新型沸石分子筛的研究进展及其在FCC催化剂中的应用

介绍了用于FCC催化剂中的几种新型沸石分子筛的结构特征,并综述了其研究进展,以及在FCC催化剂中应用时,存在的问题和前景展望。根据目前炼油技术的需求多样化,指出特种分子筛催化材料的技术发展趋势。     

Activity of solid catalysts for biodiesel production: A review

Heterogeneous catalysts are promising for the transesterification reaction of vegetable oils to produce biodiesel. Unlike homogeneous, heterogeneous catalysts are environmentally benign and could be operated in continuous processes. Moreover they can be reused and regenerated. However a high molar ratio of alcohol to oil, large amount of catalyst and high temperature and pressure are required when utilizing heterogeneous catalyst to produce biodiesel. In this paper, the catalytic activity of several solid base and acid catalysts, particularly metal oxides and supported metal oxides, was reviewed. Solid acid catalysts were able to do transesterification and esterification reactions simultaneously and convert oils with high amount of FFA (Free Fatty Acids). However, the reaction rate in the presence of solid base catalysts was faster. The catalyst efficiency depended on several factors such as specific surface area, pore size, pore volume and active site concentration.     

Alloying in platinum-based catalysts for gasoline reforming: A general structural proposal

Platinum/alumina catalysts have been used for many years in the process of gasoline octane upgrading normally referred to as reforming. It is now standard industrial practice to add another element to the catalyst, which may be chosen from many parts of the periodic table, and which acts to prolong the life and improve the selectivity of the catalyst. Additives in use include gallium, germanium, iridium, tin, rhenium and chromium. It is proposed that each of these components alloys with the platinum, but in such a way that the exposed surface of the catalyst particles continues to be wholly platinum. The alloying element is enriched in the immediate subsurface layer, and modifies the properties of the catalyst through an electronic interaction.     

A new method for electrochemical screening basedon the rotating ring disc electrode and its applicationto oxygen reduction catalysts

A new method for electrochemical characterization of composite electrode materials is reported. A paste of the catalytic material in Nafion® is coated on a rotating ring disc electrode (RRDE) to partially simulate the working environment of a proton exchange membrane (PEM)/electrode composite as used in, for example, water electrolysis or PEM fuel cell operation. This allows direct comparison of a wide range of candidate electrocatalysts in a reproducible manner. Problems specific to these volumic electrodes are accommodated satisfactorily by rational modification of the standard expressions used in RRDE analysis. The value of the method is illustrated in studies of various cobalt complexes which show promise in dioxygen reduction; namely, cobalt tetramethoxyphenylporphyrin (CoTMPP), cobalt phthalocyanine (CoPC), and cobalt cyclam (CoCy), supported on a range of particulate carbons BP2000, Printex XE 2 and Vulcan XC-72. Typical electrochemical parameters have been measured or estimated, including half-wave potentials (E1/2), Tafel slopes (b), activation currents (Ia) and the average number of electrons transferred (n). The nature of the complex itself and the carbon support have a strong influence on electrode behaviour. Ligands with more aromatic character give better performance. Dramatic improvements in performance result from heat pretreatment, which is tentatively attributed to the formation of dimeric cobalt species via thermally-induced aggregation. In terms of the four electron reduction (to water), the best result was obtained for CoTMPP on Printex XE2 and rationalized on the basis of popular current views on the mechanism and catalyst functionality. CoPC on BP2000 is unusual in showing a strong change in n with reduction potential. Product selectivity ranges between mainly hydrogen peroxide (n=2) and water (n=4) with increasing overpotential.