•CFD method was integrated with factorial design to reveal particle suspension.•Solid-liquid mixing performance of four typical impellers was compared.•Regression models for floating and sinking particles suspension were achieved.•Impeller optimization was proposed upon particle suspension and mixing energy.The present study focuses upon the effect of the impeller on sinking and floating behavior of suspending particles in stirred tank reactor, employing computational fluid dynamics (CFD) simulation where factorial design is used to investigate the main and interaction effects of design parameters on the particle distribution performance of four typical impeller designs. Factorial design results show the effect of diameter and width of the impeller and off-bottom clearance on sinking particles is different from that of floating particles and regression equations for sinking particles and floating particles are achieved separately. Meanwhile, optimal equations which quantitatively reveal the effect of impeller factors on suspension quality and energy input is established for impeller improvement. Besides the development of computational models, the combination of CFD simulation with factorial design method provides a useful approach to gain insight into the suspension behavior of sinking and floating particles, also it guides to optimize the impeller design.Download high-res image (88KB)Download full-size image

•Mutual solubility of 1830 ILs and fuel oil were studied with COSMO-RS calculation.•IL micro-structures were characterized by energy, σ-profile and σ-moment.•Mutual solubility is dependent on ionic structure and vdW and HB interactions.•Mutual solubility between selected ILs and fuel oil were determined experimentally.•[C1pyr]H2PO4 were screened out to perform extractive desulfurization experiments.Extractive and oxidative desulfurization of fuel oil using ionic liquids (ILs) as solvents have been intensively studied recently. In such processes, the mutual solubility of ILs and fuel oil is still a major concern. Less mutual solubility is desired to reduce the loss of ILs and the contamination of fuel oil. To screen the ideal ILs with less mutual solubility with fuel oil and to understand the effects of ILs structural characteristics on the mutual solubility, we employed Conductor-like Screening Model for Real Solvents (COSMO-RS) to calculate the mutual solubility of 1830 ILs and model fuel oil. The influences of ILs structural characteristics such as cationic nature, cationic alkyl chain length, cationic symmetry, anionic nature, anionic alkyl chain length and functional group on the mutual solubility are investigated from micro-level view with σ-profile, σ-moment and COSMO-RS energies. The mutual solubility is strongly dependent on cation or anion species and is highly influenced by van der Waals (vdW) and hydrogen-bonding (HB) energies. Cations with smaller non-polarity, shorter alkyl chain length and less symmetry tend to have weaker vdW energies and smaller mutual solubility, while anions with larger polarity tend to have stronger HB energies and smaller mutual solubility. The functional groups also show remarkable effects on mutual solubility; those functional groups that decrease the non-polarity and vdW energies or increase the polarity and HB energies favor the small mutual solubility. Moreover, experimental determinations of the mutual solubility indicate [C1pyr]H2PO4 is a good solvent for desulfurization. This work provides the theoretical basis to design and select the ILs, which have small mutual solubility with fuel oil.

To screen and use ionic liquids (ILs) as environmental-friendly extractive solvents in removing aromatic sulfur compounds (S-compounds) from fuel oils, the knowledge of their capacity for S-compounds (or solubility of S-compounds in ILs) is very important. In this work, the capacities of 1860 potential ILs (30 anions, 62 cations) for two representative S-compounds of thiophene (TS) and dibenzothiophene (DBT) are calculated using conductor-like screening model for real solvents (COSMO-RS). The influences of cation family, cation alkyl chain length, cation symmetry, anion nature, anion alkyl chain length, and functional group on the capacity are extensively discussed and are understood from microlevel view with σ-profile, σ-moments, and COSMO-RS energies. It is observed that the capacity is very dependent on cation and anion structure characteristics and is in a very wide range (e.g., 10–3∼101 for TS, 10–3∼102 for DBT); the van der Waals (vdW) and hydrogen-bonding (HB) energies have significant effects on the capacity. Increasing the nonpolarity and vdW energies of cation or alkyl chain on anion, or the polarity and HB energies of anion, can favor the capacity. This work is valuable to rationally select or design the ILs for desulfurization of fuel oils.

The removal of nitrogen-compounds (N-compounds), e.g. basic and neutral species, from fuel oils is necessary because of their inhibiting effect on the hydrodesulfurization process. In this work, the extractive denitrogenation performance of four dicyanamide-based ionic liquids (ILs) with different cationic characteristics, i.e., aromatic 1-butyl-3-methylimdazolium dicyanamide ([BMI][N(CN)2]) and 1-ethyl-3-methylimdazolium dicyanamide ([EMI][N(CN)2]), cyclic ethylated tetrahydrothiophenium dicyanamide ([S2][N(CN)2]), and tetrahedral ethyldimethylsulfonium dicyanamide ([EtMe2S][N(CN)2]), is investigated using basic pyridine and neutral carbazole as representative N-compounds. These ILs are capable of effectively extracting the N-compounds from the fuel oils with carbazole being more efficiently extracted than pyridine; also, aromatic imidazolium ILs exhibit better performance than cyclic thiophenium and tetrahedral trialkylsulfonium ILs in the order [BMI][N(CN)2] > [EMI][N(CN)2] > [S2][N(CN)2] > [EtMe2S][N(CN)2]. Under ambient conditions, 1:1 (w/w) IL:oil, the N-content in the raffinate phase of the carbazole-containing fuel oil is undetected after <5 min of contact with [BMI][N(CN)2] and [EMI][N(CN)2], while 96.8% and 84.3% N-extraction efficiency is obtained after contact with [S2][N(CN)2] and EtMe2S][N(CN)2] respectively; for pyridine-containing fuel oil, the N-extraction efficiency in the aforementioned ILs is 72.7%, 69.1%, 63.5% and 59.8%, respectively. Compared with other ILs reported, the extractive performance of these ILs is competitive. [BMI][N(CN)2] is selected as a representative IL to undergo a series of parallel experiments to determine the influence of IL:oil mass ratio, temperature, initial N-content, and multiple extractions; a recyclability test is also performed. This work may present a new approach to fuel denitrogenation.

In this work, the extractive and oxidative deep desulfurizations of model fuel oils using a low-viscosity ionic liquid, i.e., 1-ethyl-3-methylimidazolium dicyanamide ([C2mim][N(CN)2]), are investigated. [C2mim][N(CN)2] is capable of effectively extracting thiophene (TS) and dibenzothiophene (DBT) from oils. The sulfur content in the raffinate phases is only ∼10 ppm after a few extraction steps. A short extraction equilibrium time of <5 min is observed. The extraction operation is insensitive to temperature, and it can be effectively performed at or around room temperature. Unexpectedly, the oxidative removal of DBT by such a dicyanamide-based ionic liquid is not effective and is not as good as the corresponding extraction operation. Such an undesirable oxidative desulfurization is understood at a molecular level from ab initio calculations, and it may be ascribed to the strong intermolecular interaction between CH3COOH or CH3COOOH and [C2mim][N(CN)2] phase. Therefore, such a dicyanamide-based ionic liquid is efficient for direct extractive desulfurization, while it is less efficient for oxidative desulfurization.

Ionic liquids (ILs), a new class of green solvents, have recently been undergoing intensive research on the removal of thiophenic sulfur species (e.g., dibenzothiophene) from fuels because of the limitation of the traditional hydrodesulfurization method in removing these species. In this work, deep oxidative desulfurization of diesel fuels by six functional acidic ILs are studied, in which ILs are used as both extractant and catalyst, and 30 wt % H2O2 solution as oxidant. These ILs include both Lewis acidic species such as 1-butyl-3-methylimidazolium chloride/2ZnCl2 ([C4mim]Cl/2ZnCl2 and [C4mim]Cl/ZnCl2) and Brønsted acidic species such as 1-methyl-3-ethylcarboxylic acid imidazolium hydrogen sulfate ([CH2COOHmim]HSO4), 1-methyl-3-(butyl-4-sulfinate) imidazolium hydrogen sulfate ([SO3H–C4mim]HSO4), [Hmim]HSO4, and [C4mim]HSO4 where different acidic groups such as −H, −COOH, and −SO3H are appended to the cations. Except for [CH2COOHmim]HSO4, both Brønsted and Lewis acidic ILs are capable of effectively removing dibenzothiophene from model diesel fuels, where 100% sulfur removal is obtained for [C4mim]Cl/2ZnCl2 and [SO3H–C4mim]HSO4. The effects of temperature, molar ratio of O/S, mass ratio of IL/oil, and IL regeneration on desulfurization are investigated systematically for [C4mim]Cl/2ZnCl2 and [SO3H–C4mim]HSO4. The desulfurization ability is not sensitive to the mass ratio of IL/oil, which is desired for reducing IL dosage in industrial application; the ILs can be recycled six times with merely a negligible loss in activity. [C4mim]Cl/2ZnCl2 can reduce the sulfur content in real commercial diesel fuel from 64 to 7.9 ppm with a sulfur removal of 87.7%; however, it is not too effective for coke diesel fuel with high initial sulfur content of 5380 ppm. This work tends to show that diesel fuels can be purified to sulfur-free or ultralow sulfur fuels by further deep oxidative desulfurization by using ILs after hydrodesulfurization.

Ionic liquids (ILs) show good performances in SO2 separation science, e.g., SO2 capture from high-temperature flue gas or separation from gas mixtures. In this work, the mechanism of capturing SO2 by three guanidinium-based ILs, 1,1,3,3-tetramethylguanidinium lactate ([tmgHH][L]), 1,1,3,3-tetramethylguanidinium bis(trifluoromethylsulfonyl)imide ([tmgHH][Tf2N]), and 1,1,3,3-tetramethylguanidinium tetrafluoroborate ([tmgHH][BF4]), is investigated by using molecular dynamic simulation and ab initio calculation. The results of condensed phase molecular dynamic simulation for the mixtures of SO2 and these three ILs indicate the similar SO2 organization and interaction among them; SO2 may organize around [tmgHH]+ while it favorably organizes around the anions through Lewis acid−base interaction. Gas phase ab initio calculations show that [tmgHH][L] chemically interacts with SO2 while [tmgHH][Tf2N] and [tmgHH][BF4] do not, which is supported by the earlier FT-IR and 1H NMR data and is also consistent with the experimental result of a much higher absorption capability of [tmgHH][L] for SO2 than the latter two. The anion plays a key role in the chemical interaction between [tmgHH][L] and SO2, the S atom is bonded to the N atom on −NH2 of [tmgHH]+, and some products with aminosulfate or aminosulfinic acid fragment may be formed. This work shows that IL structures should be carefully tailored for their final application in SO2 capture.

Four low-viscosity ionic liquids (ILs) based on the dicyanamide anion ([N(CN)2]−), i.e., 1-butyl-3-methylimdazolium ([BMI][N(CN)2]), 1-ethyl-3-methylimdazolium ([EMI][N(CN)2]), ethylated tetrahydrothiophenium ([S2][N(CN)2]) and ethyldimethylsulfonium ([EtMe2S][N(CN)2]), have been investigated to determine their extraction capability for thiophene (TS) and dibenzothiophene (DBT) from model fuel oils. Aromatic imidazolium is more efficient than cyclic thiophenium and tetrahedral trialkylsulfonium; specifically, the S-extraction ability follows the order [BMI][N(CN)2] > [EMI][N(CN)2] > [S2][N(CN)2] > [EtMe2S][N(CN)2], with DBT being more efficiently extracted than TS. The S-extraction of [BMI][N(CN)2] has been investigated as a representative with respect to the influence of extraction temperature, IL:oil mass ratio, initial S-content, multiple extractions and reusability, along with its mutual solubility in oil. The percentage of S-removal from gasoline and diesel fuel were 48.5 and 68.7%, respectively, in a single extraction at 25 °C, 1:1(w/w) IL:oil, 5 min; the S-content in gasoline decreased from 599 ppm to 4 ppm after 5 extraction cycles and in diesel fuel decreased from 606 ppm to an undetectable value after 4 cycles. The mutual solubility is not pronounced and the extraction efficiency is not conspicuously changed after 6 regeneration cycles. It is worth noting that a short extraction time of < 5 min is observed for all the ILs at room temperature, which is understood by their low viscosities and effective mass transfer. This work may offer a new option for the deep desulfurization of fuel oils.

A series of Cu/SiO2 catalysts with copper loadings ranging from 17.8 to 42.2 wt% were prepared by the sol–gel method and evaluated for the hydrogenolysis of diethyl oxalate to ethylene glycol. The physicochemical properties of these catalysts were systematically characterized by means of different techniques. It is found that copper loadings have great influence on the catalytic performance; the catalyst with a copper loading of 37.8 wt% exhibited the best activity and ethyl glycol selectivity. The sol–gel derived catalyst was superior in catalytic performance to the catalyst prepared by the deposition precipitation method, a result due to the presence of finely dispersed copper phyllosilicate.

Owing to some desirable properties, ionic liquids (ILs) have attracted increasing interests and applications in many domains. Unfortunately, however, they generally have much higher viscosities than conventional molecular solvents, which result to some problems of handling or transferring in chemical processing. ILs with lower viscosity are desired. Therefore, understanding the relationship between micro-structure and macro-viscosity along with a comprehensive viscosity data is important for the synthesis and rational design of ILs with low viscosity. In this work, a comprehensive collection of viscosity data covering the period of 1983–2009 is conducted on the pure imidazolium-based ILs, and quantitative structure–property relationship (QSPR) study is performed for four selected data sets. The four correlations are obtained with R2 > 0.93, and quantum-chemical descriptors gave significant contributions. The cation–anion electrostatic interaction has the significant effects on the viscosity of imidazolium-based ILs, while other interactions (e.g., interionic hydrogen-bond, van der Waals) or micro-characteristics (e.g., molecular orbital, electronic population, dipole moment, volume, shape, branching degree, symmetry) also give some effects.

The liquid phase hydrogenation of furfuryl alcohol (FA) to tetrahydrofurfuryl alcohol (THFA) on a series of new special supported Ni catalyst was experimentally studied while the raw material and the product were analyzed by a set of on-line GC. The reactor used in the experiment was a continuous stirred autoclave with volume of 500 mL. The operating conditions studied in the experiments were opted as the following ranges: temperature within 433–453 K, pressure within 3.0–4.0 MPa, catalyst loading 20 g/L and the stirring rate at about 1000 rpm. The experimental results show that, under the operation conditions mentioned above, the hydrogenation of FA in the presence of the catalyst QD3 can lead to a high FA conversion above 99.9% and a high selectivity of THFA higher than 98.3% within 3.5 h.