Roberto Quintana-Solórzano

Sulfur reduction in cracked naphtha by a commercial additive: effect of feed and catalyst properties

Abstract While the use of selective additives and catalysts might be the most economical and easiest solution for refinery operations in reducing the sulfur concentration in catalytic cracked naphtha their effectiveness is still limited. A better knowledge on the chemistry of sulfur compounds under cracking conditions would help to improve the performance of such additives. In this work, the sulfur content (in terms of alkyl-thiophenes and benzothiophene) in cracked naphtha was studied in regard to the feed and catalyst properties and the effect of a commercial sulfur reduction additive. Two equilibrium catalysts (REHY and REUSY) and two feedstock from Isthmus and Maya crude oils were compared in a fluidized fixed bed microreactor. The sulfur content in the naphtha was lower with REHY thus confirming reported trends involving hydrogen transfer and contaminant metals effects. The sulfur compounds contained in the Maya feed were comparatively more reactive than those contained in a conventional Isthmus/Maya (70/30). Assuming that the Maya feed is richer in long chain alkyl-thiophenes it produced proportionally higher amount of C 1 –C 4 alkyl-thiophenes in the naphtha. The additive reduced the amount of C 1 –C 4 alkyl-thiophenes by preventing their formation and producing alkyl-benzothiophenes by hydrocyclization. REHY produced less sulfur-in-naphtha by converting such compounds to H 2 S and light gases. The additive showed a limited effect on naphtha sulfur reduction with either the Maya feed or REHY. An inhibitory effect due to H 2 S adsorption is also proposed to explain this limited effect.

Effect of highly reactive sulfur species on sulfur reduction in cracking gasoline

Abstract Stringent regulations for engine fuels have stimulated R&D work for reducing sulfur in cracked naphtha in the recent years. In order to progress in this issue information on the effect of the chemistry of sulfur compounds under cracking conditions is needed. In this work, hexyl-2-thiol was spiked in a gasoil feed and the effect on sulfur in gasoline was studied with an equilibrium catalyst (Ecat) and a commercial gasoline sulfur reduction additive. Spiked feeds showed lower conversion. The hexyl-2-thiol mainly produced H2S and exhibited a competitive reaction with sulfur compounds contained in gasoil. Higher amounts of sulfur-in-coke were produced with the Ecat-additive blend compared to Ecat thus indicating that the hexyl-2-thiol adsorbs stronger on the additive which can be due to its Lewis acid properties. While the additive moderates the detrimental effect of hexyl-2-thiol on the catalyst activity its activity for sulfur reduction in gasoline was constrained.

Novel SOx removal catalysts for the FCC process: Manufacture method, characterization, and pilot-scale testing

A novel method for preparing SOx removing (ReSOx) catalysts for the fluid catalytic cracking (FCC) process, based on multimetallic layered double hydroxides (LDHs), is presented. The synthesis procedure is industrially feasible and environmentally friendly. Ceria is incorporated in varying amounts as oxidation promoter, to obtain catalysts that are able to work efficiently in either partial or full combustion regenerator modes. The manufacturing process presented herein enables obtaining, by spray drying, microsphere particles with mechanical properties that are adequate for fluidization, without requiring addition of binding agents. The physicochemical properties of the catalysts are examined by several characterization techniques, such as X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). A uniform dispersion of the metal components is observed throughout the particles. Furthermore, the microspheroidal catalysts are tested for the reduction of SOx emissions in a pilot-scale FCC plant, circulating together with a conventional cracking catalyst, during the conversion of a sulphur-containing industrial gas oil obtained from a Mexican refinery. ReSOx catalyst addition to the pilot FCC unit, in only 0.2 wt% of the total catalyst inventory, results in a maximum %SO2reduction of 74–80%. Additionally, the effect of the ReSOx catalyst on the main cracking reactions is studied; it is shown that the disruption of the cracking catalysts activity and selectivity is minimal, at a concentration of 1.5 wt% of the total catalyst inventory. Thus, the use of these SOx removal catalysts appears as a viable, low investment, flexible and effective option for in situreduction of SOx flue gas emissions.

On the influence of particle shape and process conditions in the pressure drop and hydrodynamics in a wall-effect fixed bed

ABSTRACT A low tube-to-particle diameter ratio (dt/de,p) fixed bed, packed with spherical and nonspherical catalyst supports, was used to investigate pressure drop at varying temperature (298–673 K) and inlet pressure (245–294 kPa). The dt/de,p ranged from 3 to 6, namely, a large wall-effect fixed bed, with an average void fraction between 0.38 and 0.61. These conditions pertain to multitubular fixed-bed reactors used for exothermic reactions. The pressure drop was notably influenced by the particle size and morphology as well as temperature. The use of particles with dt/de,p < 5 and relatively large bed void fractions (>0.55) appeared suitable for pressure drop control. The fluid velocity profiles were calculated by applying the Navier–Stokes–Darcy–Forchheimer equation computing the respective permeability parameters with refitted state-of-the-art pressure drop correlations. The fluid flow exhibited different velocity zones across the fixed bed, the highest velocity zone being located near the reactor wall. The axial velocity component was influenced by the catalyst morphology, as well as temperature and inlet pressure.

Metal solution precursors: their role during the synthesis of MoVTeNb mixed oxide catalysts

Synthesized via the slurry method and activated at high temperature (873 K), MoVTeNb multimetallic mixed oxides are applied to catalyze the oxidative dehydrogenation of ethane to ethylene (ODHE). Mixed oxides typically contain M1 and M2 crystalline phases, the relative contribution of these phases and the respective catalytic behaviour being notably influenced by the preparation conditions of the metallic aqueous solution precursor, given the complexity of the chemical interactions of metal species in solution. Thus, detailed in situ UV-vis and Raman studies of the chemical species formed in solution during each step of the synthetic procedure are presented herein. The main role of vanadium is to form decavanadate ions, which interact with Mo species to generate an Anderson-type structure. When niobium oxalate solution is added into the MoVTe solution, a yellow-coloured gel is immediately formed due to a common ion effect. When liquid and gel phases are separated, the M1 crystalline phase is produced solely from the gel phase. Attention is also devoted to the influence and role of each metal cation (Mo, V, Te and Nb) on the formation of the active M1 crystalline phase and the catalytic behaviour in the ODHE. The catalyst constituted mostly of M1 crystalline phase is able to convert 45% of the fed ethane, with a selectivity to ethylene of around 90%.

Controlling the redox properties of nickel in NiO/ZrO2 catalysts synthesized by sol–gel

NiO–ZrO2 samples were prepared by the sol–gel method adjusting the nickel content to 3 and 10 wt% and varying the calcination temperature from 500 to 700 °C. The solids were characterized by X-ray diffraction, ultraviolet-visible diffuse reflectance spectroscopy (UV-vis DRS), X-ray photoelectron spectroscopy, high resolution transmission electron microscopy (HRTEM) and scanning and transmission electron microscopy (STEM). For the sample with 3 wt% Ni, diffraction lines related to cubic zirconia were only detected when calcined from 500 to 650 °C, a NiO crystalline phase as well as the transition phase from cubic to tetragonal zirconia appeared when calcined at 700 °C. UV-vis DRS and HRTEM results indicated the presence of a highly dispersed NiO phase at the nanometric scale throughout the main zirconia crystalline phase. The NiO crystalline phase was already detected for the sample with 10 wt% nickel content calcined at 500 °C. The NiO–ZrO2 interaction was modified by reducing the hydrolysis rate during synthesis leading to a sample with a high dispersion of Ni throughout ZrO2, thus modifying the reducibility of NiO. The NiO–ZrO2 samples were catalytically tested for the oxidative dehydrogenation of ethane as a model reaction. Prior to reaction, the calcined catalysts were pre-treated in situ under reducing and oxidant atmospheres to study their redox properties. As the NiO–ZrO2 interaction modifies the electronic properties of both nickel oxide and zirconia, ethane conversion and ethylene selectivity were strongly influenced not only by the nickel content and calcination temperature but also by the in situ pre-treatment before reaction. This effect was particularly evident in the sample prepared with a modified hydrolysis rate, which changed the redox properties of the NiO species.

On the effect of a high reactive sulfur species on sulfur reduction in gasoline

Varying solutions are available for reducing the amount of sulfur contained in gasoline from fluid catalytic cracking units (FCCUs). However, the use of selective catalysts or additives can be the easiest to implement and potentially represent the most cost effective solution. In order to improve overall performance a better understanding of the effects of the feed properties on catalyst activity is needed. In this work we study the effect of a high reactive sulfur compound on the sulfur distribution in cracked products. Experiments were carried out in a fixed fluidized bed reactor using a REUSY equilibrium catalyst (Ecat), a commercial additive for gasoline sulfur reduction and an industrial feed spiked with hexane-2-thiol. The acidity of the materials was studied using FTIR spectra of chemisorbed pyridine. With spiked feeds both Ecat and the additive exhibited lower cracking activity indicating that the hexane-2-thiol had a strong poisoning effect on the materials acid sites. The effect of the type of acidity of the materials used is discussed and a selective adsorption of hexane-2-thiol on Lewis acid sites is proposed to explain the observed results. Similar trends were generated with a high sulfur feed derived from a Mayan crude oil thus leading to the conclusion that the presence of nonthiophenic sulfur compounds in the feed might have a strong negative effect on sulfur reduction. The potential use of an alumina material, possessing Bronsted and Lewis acidity, for sulfur reduction is presented and discussed.