Diesel Hydrodesulfurization and its Impact on the Fuel Market in Ecuador: A Review

This article examines the hydrodesulfurization process used to produce diesel with low sulfur content in Ecuador. The analysis covers the level of processing in the country, the quality of domestic diesel compared to other nations, and the technical and economic requirements of the process. It also explores the need to modify or upgrade catalysts to achieve deep hydrodesulfurization.. Unfortunately, the review found that sulfur content in Ecuadorian deposits is very high, with 3.53 MMkg produced in 2018. Despite improvements in the country’s refineries, diesel sulfur content has only been reduced to 110 ppm.. Ecuador regulates sulfur emissions through the Ecuadorian standard NTE INEN-1489 (2012). This norm classifies the fuel into three types, diesel #1 (3000 ppm), diesel #2 (7000 ppm), and premium diesel (500 ppm), following the use of diesel both in the industrial and transportation sectors. However, Ecuador seeks to adjust to countries with stricter regulations, such as the European Union. The standard that regulates sulfur emissions in this community is Euro VI, which limits the concentration to 10 ppm. One of the challenges in achieving international standards in the hydrodesulfurization units of the Ecuadorian refineries is to modify or improve the catalytic systems. Trimetallic catalysts, both supported and unsupported, can help overcome this challenge by decomposing the refractory molecules (e.g., dibenzothiophene and 4,6-dimethyldibenzothiophene) found in deep hydrodesulfurization. These catalysts can handle molecules that commonly used catalysts such as CoMo or MoW cannot. Therefore, proposals such as using trimetallic catalysts to achieve deep hydrodesulfurization levels are techno-economic options for Ecuador. Keywords: diesel, sulfur, Ecuador, hydrodesulfurization, refineries, catalyst

Influence of the carbon chain length of a sulfate-based surfactant on the formation of CO 2 , CH 4 and CO 2 –CH 4 gas hydrates

This study investigates how the length of the carbon chain of homologous surfactants affects the amount and growth rate of gas hydrates formed in quiescent CO2/CH4/water systems. The hydrate formation experiments were conducted using sodium alkyl sulfates with different carbon-chain lengths (C8, C10, C11, C12, C13, C14, C16 and C18), at a concentration of 10.4 mol m−3. The CO2:CH4 ratios investigated were 0:100, 25:75, 75:25, and 100:0. Hydrate formation was studied in a batch reactor at an initial subcooling of about 5 K. It was observed to be efficient only for those surfactants that promote the formation of a water-wettable porous hydrate structure, which spreads over the inner sidewalls of the hydrate-formation cell. For the CO2:CH4 ratios of 0:100, 25:75, 75:25 and 100:0, hydrate formation was efficient for the surfactants with respectively 8 to 14, 11 to 13, 11 to 12, and 12 carbon atoms in their alkyl chain. Only the surfactant with 12 carbon atoms was found to promote and accelerate hydrate growth for all the gas-phase compositions tested. The much lesser surfactant effect on hydrate growth rate observed with the increase in the initial CO2 fraction in the gas phase is ascribed to a modification of the adsorption behavior of the surfactant molecules on the hydrate surface, which, as already suggested by Zhang et al. (2010), is probably due to competitive adsorption between the surfactant anions and bicarbonat

CO2 capture by hydrate formation in quiescent conditions: In search of efficient kinetic additives

International audienceAs a preliminary step to the development of a CO2 capture process under high pressure conditions, an experimental kinetic study of CO2 hydrate formation has been carried out in a high-pressure batch reactor, using as water-soluble additives a mixture of tetrahydrofuran (THF) and surfactant (sodium dodecyl sulfate, SDS). Used together and in suitable concentrations, these two additives were found to be very efficient for promoting CO2 capture

Combination of surfactants and organic compounds for boosting CO2 separation from natural gas by clathrate hydrate formation

This study investigates the effects of several combinations of surfactants and organic compounds on the separation of CO2 from a CO2–CH4 gas mixture by clathrate hydrate formation. Seven additives, three surfactants (SDS, SDBS, DATCl) and four organic compounds (THF, 1,3-dioxolane, 2-methyl-tetrahydrofuran and cyclopentane) were tested for various operating conditions and at different concentrations. The influence of these additives on the quantity of gas removed, the selectivity of the separation toward CO2, and the kinetics of hydrate formation were analyzed through experiments in a batch reactor. It was found that a suitable combination of a surfactant and a organic compound can, in some cases, strongly enhance the hydrate crystallization. The best results were obtained with a combination of the additives SDS and THF

CO2 enclathration in the presence of water-soluble hydrate promoters: Hydrate phase equilibria and kinetic studies in quiescent conditions

Clathrate hydrates have potential applications in various domains and particularly for CO2 capture where the search for additives able to speed up hydrate formation is of scientific, technological and economical interest. This study investigates the potentialities of two additives used in combination for enhancing CO2 enclathration rates: a surfactant (sodium dodecyl sulphate; SDS) and an organic compound (tetrahydrofuran; THF). Experiments performed in batch and in semi-continuous reactor configuration, reveal that this combination of additives efficiently promotes hydrate formation, allowing a full water-to-hydrate conversion despite the quiescent-forming conditions used. The possible action mechanisms of this combination of additives are analyzed and discussed on the basis of experimental data of hydrate phase equilibria (with and without additives), visual observations, and kinetics experiments

Effect of the concentration and carbon chain length of a sulfate-based surfactant on hydrate formation kinetics

This paper reports an experimental study on the effect of the concentration and the carbon chain length of surfactants on the formation kinetics of gas hydrates in a quiescent CO2/CH4/water system. Sodium alkyl sulfates with different carbon chain length (C8, C10, C12, C14, C16 and C18) were tested at different concentrations. The experiments were conducted in a batch configuration, at a temperature of 275 K and with an initial gas pressure of about 3.3 MPa. For each system studied, hydrate crystallization was triggered by suddenly injecting a small amount of THF (4,000 ppm) directly into the surfactant solution in contact with the gas-hydrate-former phase at 275 K and 3.3 MPa. The long induction time for hydrate formation usually observed for these systems at the pressure and temperature conditions used in this study was thus eliminated. The experimental results show that, of the six surfactants tested, only the sodium dodecyl (C12) sulfate efficiently promotes the formation of CO2-CH4 binary hydrate under quiescent conditions. A minimum concentration of 500 ppm of the C12 surfactant was however necessary to obtain a beneficial effect on hydrate formation, and the rate of hydrate crystallization was observed to level off for the surfactant concentrations higher than 3,000 ppm. For the systems containing the C8 and C10 surfactants, which have a Krafft temperature lower than 275 K, the presence or absence of micelles in the surfactant solution does not have any effect on the hydrate formation kinetics

Séparation du co2 d'un mélange co2-ch4 par cristallisation d'hydrates de gaz (influence d'additifs et effet des conditions opératoires)

La séparation du CO2 d'un mélange de gaz par cristallisation d'hydrates de gaz est un procédé qui pourrait à terme présenter une alternative intéressante aux techniques conventionnelles de capture du CO2. L'objectif de cette thèse était d'évaluer le potentiel de ce procédé "hydrates" pour séparer le CO2 d'un mélange CO2-CH4 riche en CO2. Nous avons étudié en particulier la sélectivité de la séparation vis-à-vis du CO2 et la cinétique de cristallisation des hydrates, ainsi que l'effet d'additifs thermodynamiques et cinétiques (et de certaines de leurs combinaisons) sur ces deux paramètres pour différentes conditions opératoires (pression, température, concentrations). Les expériences de formation/décomposition d hydrates ont été réalisées en mode "batch" dans un réacteur haute pression faisant partie d'un pilote expérimental conçu et construit entièrement pendant cette thèse. Un modèle semi-empirique a été également développé pour estimer le taux de conversion de l eau en hydrate et la composition des différentes phases en présence (hydrates, liquide et vapeur) à l'équilibre. Les résultats obtenus montrent que l'association du sodium dodécyl sulfate (SDS), utilisé en tant que promoteur cinétique, avec du tétrahydrofurane (THF), utilisé en tant que promoteur thermodynamique, permet d'obtenir des résultats intéressants en terme de quantité d'hydrates formés et de cinétique de formation. La sélectivité de la séparation vis-à-vis du CO2 reste cependant trop faible (en moyenne quatre molécules de CO2 piégées dans la structure de l'hydrate pour une de CH4) pour envisager d utiliser ce procédé "hydrates" à plus grande échelle afin de séparer le CO2 de ce type de mélange de gaz.The separation of CO2 from a gas mixture by crystallization of gas hydrates is a process that could eventually provide an attractive alternative to the conventional techniques used for CO2 capture. The aim of this thesis was to evaluate the potential of this "hydrate" process to separate CO2 from a CO2-CH4 gas mixture, rich in CO2. We have studied in particular the selectivity of the separation toward CO2 and the hydrate crystallization kinetics. The effects of thermodynamic and kinetic additives (and some additive combinations) on these two parameters for different operating conditions (pressure, temperature, concentrations) were evaluated. Hydrate formation and dissociation experiments were performed in "batch mode in a high pressure reactor, and with an experimental pilot rig designed and built entirely during this thesis. A semi-empirical model was also developed to estimate the water to hydrate conversion and the composition of the different phases (hydrates, liquid and vapor) at equilibrium. The results show that the combination of sodium dodecyl sulfate (SDS) used as a kinetic promoter, with tetrahydrofuran (THF) used as a thermodynamic promoter, provides interesting results in terms of both the amount of hydrates formed and the hydrate formation kinetics. The selectivity of the separation toward CO2 remains too low (an average of four CO2 molecules trapped in the hydrate structure for one of CH4) to consider using this "hydrate" process on a larger scale to separate CO2 from such a gas mixture.PAU-BU Sciences (644452103) / SudocSudocFranceF

In situ injection of THF to trigger gas hydrate crystallization: Application to the evaluation of a kinetic hydrate promoter

This paper investigates an original method to efficiently trigger gas hydrate crystallization. This method consists of an in situ injection of a small amount of THF into an aqueous phase in contact with a gas-hydrate-former phase at pressure and temperature conditions inside the hydrate metastable zone. In the presence of a CO2–CH4 gas mixture, our results show that the THF injection induces immediate crystallization of a first hydrate containing THF. This triggers the formation of the CO2–CH4 binary hydrate as proven by the pressure and temperature reached at equilibrium. This experimental method, which “cancels out” the stochasticity of the hydrate crystallization, was used to evaluate the effect of the anionic surfactant SDS at different concentrations, on the formation kinetics of the CO2–CH4 hydrate. The results are discussed and compared with those published in a recent article (Ricaurte et al., 2013), where THF was not injected but present in the aqueous phase from the beginning and at much higher concentration

CO2 Removal from a CO2–CH4 Gas Mixture by Clathrate Hydrate Formation Using THF and SDS as Water-Soluble Hydrate Promoters

This study investigates the use of hydrate formation to separate the CO2 from a CO2–CH4 gas mixture in the presence of water-soluble additives—tetrahydrofuran (THF) and/or sodium dodecyl sulfate (SDS)—at low concentrations. The influence of additive concentration and process operating conditions on the gas enclathration kinetics, the quantity of gas removed, and the selectivity of the separation are studied under quiescent hydrate-forming conditions in a batch reactor. Gas consumption and enclathration occur at high rates only when the two additives are used in combination. Similarly to what has been observed with pure CO2, the proposed mechanism is that a mixed hydrate of structure sII containing THF forms first, which triggers the formation of CO2–CH4 binary gas hydrate of structure sI. However, the gas separation was found not to be selective enough to the CO2 for envisaging any practical application

CO2 enclathration in a semi-continuous quiescent hydrate-forming reactor operated with pure CO2 and water soluble additives.

CO2 capture by gas hydrates is now considered as a promising alternative to classical separation processes, especially in applications when the inlet gas is available at high pressure and CO2 is to be reinjected in a geological formation. In a continuous process, forming the gas hydrates under quiescent (or unstirred) conditions would be very interesting for many reasons, including economical and safety aspects, even though the technical challenge is then to achieve high water conversion and high hydrate formation rates. The laboratory experiments presented here show that this challenge can be met by using a low concentration of appropriate water-soluble additives. These experiments extend to semicontinuous (or semi-batch) conditions a previous series of experiments conducted in a closed vessel using as additives a combination of a small quantity – in or below the percent range – of a surfactant (sodium dodecyl sulfate) and an organic compound (tetrahydrofuran). An almost complete conversion of water into hydrates is reached in a reasonable amount of time despite the quiescent conditions used. Enhanced capture kinetics and possible actions mechanisms of this combination of two additives are analyzed and discussed on the basis of experimental equilibrium curves, visual observations, kinetics data, hydrate formation rate and final water conversion