Alkane Mixtures Research Articles

Atomistic simulation study of the adsorptive separation of hydrogen sulphide/alkane mixtures on all-silica zeolites

ABSTRACT The selective separation of the aggressive hydrogen sulphide gas from industrial streams is highly important from environmental and economic aspects. Capture of this substance from industrial gases of light hydrocarbons by all-silica zeolites can be an eco-friendly alternative to the other common absorption/adsorption procedures. The adsorption from binary mixtures of hydrogen sulphide and light alkanes (H2S/CH4, H2S/C2H6, and H2S/C3H8) on preselected all-silica zeolites was studied by atomistic simulations, using a recently developed force field for hydrogen sulphide. In addition to four experimental all-silica zeolite frameworks (DDR, CHA, ACO, CAS), three of their hypothetical relatives were also drawn into the investigations. The smaller pore size zeolites (ACO, CAS, and particularly one of the hypothetical zeolites) showed remarkable separation performances under real ambient conditions. Among the examined structural details of the studied frameworks, the calculated realistic pore size distributions proved the most appropriate in attempts to unravel the connection between adsorption selectivities and framework structural properties. The investigations were completed by a necessary demonstration of the translational accessibility of the inner cages of the smaller pore size zeolites.

Process intensification in ternary distillation via comparative grassroots and retrofit designs: A case study of distilling an industrial multicomponent C6 alkane mixture in caprolactam processing

A systematic process intensification method via comparative grassroots and retrofit designs for distillation is proposed. Restricting to the ternary system, a case study of multicomponent C6 alkane separation in caprolactam processing is considered. The existing benchmark flowsheet of direct sequence (DS) features high economic cost but low thermodynamic efficiency. Through the investigation of the composition profile, two middle component remixing peaks and a large feed mismatch are diagnosed as the reasons of inefficiency. To achieve process intensification, potential candidates like side stream column (SSC) and dividing wall column (DWC) are enumerated and evaluated in the grassroots design step. Although DWC performs the best in thermodynamic efficiency, SSC is more preferred for retrofit as its structure is simple but has similar performance. To maximally reuse the existing equipment, two retrofit proposals of either indirect sequence (IS) or SSC are provided based on the grassroots design results. Among them, retrofitted SSC is recommended for long expected lifespan situation, while IS is more suitable for a short one. It is recommended that the proposed process intensification procedure can be extended to other similar processes or systems with more components, through enumerating and comparing the several best but similar grassroots designs with benchmark process.

Separation characteristics of an integrated temperature-controlled micro gas chromatography chip

Compared with traditional laboratory gas chromatograph, portable gas chromatograph has the advantages of fast detection, low power consumption, lost cost and possible applications out of Lab. In this paper, aiming at replacing the traditional column thermostat, we presented a 4 cm · 4 cm micro gas chromatography (μGC) chip with a thickness of about 1 mm and a column length of 3 m integrating the Pt heating wire and snake-shaped temperature sensor, which greatly reduces the power consumption and volume of the portable gas chromatograph without losing the separation performance of the μGC chip. The integrated μGC chip was fabricated by micro electro mechanical systems (MEMS) process and its temperature was controlled in closed-loop by fuzzy proportion integration differentiation (PID) algorithm. Experimental results indicate the temperature control accuracy under constant temperature can be up to ±0.05 °C. When heating to 180 °C, the power consumption is less than 15 W. The chip has good separation properties when it was used to detect 4 kinds of benzenes, 8 kinds of alcohol mixtures and 10 kinds of alkane mixtures.

Biocrude production from orange (Citrus reticulata) peel by hydrothermal liquefaction and process optimization

Hydrothermal liquefaction is a promising anaerobic thermochemical process for the conversion of wet biomass into an energy dense biocrude. In this study, the suitability of orange peel for biocrude production was investigated. The study was carried out at varying temperatures (200 to 300 °C), reaction time (20 to 60 min), and total solids loading (15 to 25%). The optimum operating conditions for recovering maximum biofuel from biomass (28.4 wt%) were found to be 275 °C temperature, 40-min reaction time, and 25% total solids loading. The Box-Behnken design of response surface methodology was used to examine the effect of reaction parameters on biocrude yield and its byproducts and resulted the temperature to be the most effective followed by reaction time and total solids loading. The heating value of biocrude was 32 MJ/kg with flash point of about 93 °C. The obtained biocrude had comparable fuel properties with those of diesel and bio-diesel standards. The GC-MS and FTIR analyses proved biocrude as a complex mixture of alkanes, alkenes, aliphatic and aromatic acids, and alcohols and aqueous phase byproduct as a rich chemical source consisting of esters, alcohols, and ketones which provides a futuristic approach to drop in advanced fuels and chemicals from biocrude.

Modeling Metal-Catalyzed Polyethylene Depolymerization: [(Phen)Pd(X)]+ (X = H and CH3) Catalyze the Decomposition of Hexane into a Mixture of Alkenes via a Complex Reaction Network

The ternary Pd complexes [(phen)Pd(H)]+ (1-Pd) and [(phen)Pd(CH3)]+ (5-Pd) (where phen = 1,10-phenanthroline) both react with hexane in a linear ion trap mass spectrometer, forming the C–H activation product [(phen)Pd(C6H11)]+ (3-Pd) and releasing H2 and CH4, respectively. Density functional theory (DFT) calculations agree well with the experiments in predicting low barriers for these reactions proceeding via a metathesis mechanism. Species 3-Pd undergoes extensive fragmentation, or cracking, of the hydrocarbon chain when sufficient energy is supplied via collision-induced dissociation (CID), resulting in the extrusion of a mixture of alkenes, methane, and hydrogen. DFT calculations show that Pd chain-walking from α (terminal carbon) to β and from β to γ positions can proceed with barriers sufficiently below those required for chain cracking. The fragmentation reactions can be made catalytic if 1-Pd and 5-Pd produced by CID of 3-Pd are allowed to react with hexane again. Ni complexes largely mirrored the chemistry observed for Pd. Both 1-Ni and 5-Ni reacted with hexane, forming 3-Ni, which fragmented under CID conditions in a fashion similar to 3-Pd. In contrast, only 5-Pt reacted with hexane to form 3-Pt, which fragmented predominantly via sequential losses of H2.

Steric Effects in the Catalytic Tandem Isomerization‐Hydrosilylation Reaction

AbstractThe selective synthesis of linear silanes from remote alkenes is reported. Four new silane‐thioether bidentate proligands [SiMe2H(o‐C6H4SR)] (R=iBu, pentyl, benzyl, neopentyl) have been synthesized and used to form unsaturated and cationic 16‐electron hydrido‐silyl‐RhIII complexes. These compounds are efficient catalysts for the tandem catalytic alkene isomerization‐hydrosilylation reaction at room temperature under solvent‐free conditions. The different size of the substituent on the sulfur atom results on a difference in the activity of this tandem reaction. Experimental observations demonstrate that the isomerization process is the rate‐determining step of this catalytic transformation. This process would be of value to the chemical industry because mixtures of internal aliphatic olefins are substantially cheaper and more readily available than the pure terminal isomers.

Modeling Sorption and Diffusion of Alkanes, Alkenes, and their Mixtures in Silicalite: From MD and GCMC Molecular Simulations to Artificial Neural Networks

AbstractMolecular dynamics (MD) in canonical (NVT) statistical ensemble and grand canonical‐Monte Carlo (GCMC) simulations along with artificial neural network (ANN) techniques are used for the study of diffusion and sorption characteristics of small alkanes, alkenes, and their mixtures in silicalite. In particular, sorption isotherms and self‐diffusion coefficients of alkanes (ethane to hexane), alkenes (ethene to hexene), and the respective alkane–alkene mixtures (consisting of the same number of carbon atoms) in silicalite are studied. The findings are directly compared with recent magic‐angle spinning pulsed field‐gradient nuclear magnetic resonance experimental diffusivity measurements and are in close agreement. Furthermore, new results are provided for the alkane–alkene systems. The sorption data from GCMC simulations, the self‐diffusivity calculations from the MD simulations along with available experimental data are used for the development of ANN predictive modeling procedures in order to give generic sorption and diffusion predictions for pure alkanes, alkenes in different input values of fugacity, temperature, and sorbate loadings at the minimum computational resources and time. Finally, structural characteristics for pure alkane, alkenes, and alkane–alkene mixtures when confined in the silicalite framework are computed revealing sorption domains and siting preferences.

Chemical Ecology, Biochemistry, and Molecular Biology of Insect Hydrocarbons.

Insect cuticular hydrocarbons (CHCs) consist of complex mixtures of straight-chain alkanes and alkenes, and methyl-branched hydrocarbons. In addition to restricting water loss through the cuticle and preventing desiccation, they have secondarily evolved to serve a variety of functions in chemical communication and play critical roles as signals mediating the life histories of insects. In this review, we describe the physical properties of CHCs that allow for both waterproofing and signaling functions, summarize their roles as inter- and intraspecific chemical signals, and discuss the influences of diet and environment on CHC profiles. We also present advances in our understanding of hydrocarbon biosynthesis. Hydrocarbons are biosynthesized in oenocytes and transported to the cuticle by lipophorin proteins. Recent work on the synthesis of fatty acids and their ultimate reductive decarbonylation to hydrocarbons has taken advantage of powerful new tools of molecular biology, including genomics and RNA interference knockdown of specific genes, to provide new insights into the biosynthesis of hydrocarbons.

Study of molecular radii of pseudobinary liquid mixtures by ultrasonic velocity and density

During recent past, ultrasonic velocity has been a very interesting subject due to its usefulness in studying molecular interactions in several types of liquid mixtures. Various attempts have been made to utilize the significance of thermodynamic properties computed by using ultrasonic velocity and related data in studying numerous acoustic relations.In the present work, an effort has been made to compare the radius of molecules of different liquids and their mixtures. In ternary liquid mixtures under study, the first component taken is polar and the other two components are non-polar in nature i.e. they are the mixture of alkanes which in turn are considered as second component. Thus, the ternary mixtures under study are being treated as pseudobinary mixtures. The associated thermodynamic properties of these liquid mixtures are being applied on different acoustic relations. Applicability and authentication of different acoustic relations for calculation of the molecular radii in liquid mixtures is likewise been done, where Rao's relation is found to be the finest.

Separation of alkane and alkene mixtures by metal–organic frameworks

Metal–organic frameworks hold great promise for the separation of alkane and alkene mixtures in light of their diverse structures, high porosity, and tunable pore dimensions and surface functionality.

Method of Calculation for Determining the Temperature Self-Ignition of Gas-Air Mixtures of Alkanes at Atmospheric Pressure

Method of Calculation for Determining the Temperature Self-Ignition of Gas-Air Mixtures of Alkanes at Atmospheric Pressure

Systematic Analysis Reveals Thermal Separations Are Not Necessarily Most Energy Intensive

Summary At the industrial level, separation of a variety of mixtures is predominantly carried out by thermally driven processes such as distillation. Nevertheless, the current literature seems to suggest that much is to be gained by replacing these processes with alternative non-thermal methods, which will potentially require a fraction of the energy used by distillation. This is primarily due to the widespread perception that thermal separation processes, particularly those that involve vaporization, are highly energy intensive. However, this belief is not well founded, because it is based on extrapolation from comparisons in the literature, many of which make ad-hoc assumptions and result in incorrect conclusions. Our analysis shows that this confusion arises because the processes utilize different types of energy: heat and electricity. Here, we present a consistent framework that enables a fair comparison between different processes that consume different forms of energies. Using this framework, we refute the general perception that thermal separation processes are inherently the most energy intensive and conclusively show through the examples of two challenging mixtures constituting components with low relative volatilities, that distillation processes, when run properly, can consume remarkably lower fuel than non-thermal membrane alternatives, which have often been touted as more energy efficient.

Mechanistic Investigation of the Pyrolysis of Brown Grease

The conversion of brown grease using pyrolysis reactions represents a very promising option for the production of renewable fuels and chemicals. Brown grease forms a mixture of alkanes, alkenes, and ketones at a temperature above 300°C at atmospheric pressure. This work is a computational study of the detailed reaction mechanisms of brown grease pyrolysis using DFT methodology. Prior experimental investigations confirmed product formation consistent with a set of radical reactions with CO2 elimination, as well as ketone by product formation, CO forming reactions, and formation of alcohols and aldehydes as minor byproducts. In this work, computational quantum chemistry was used to explore these reactions in greater detail. Particularly, a nonradical pathway formed ketone byproducts via the ketene, which we refer to as Pathways A1 and A2. Radical formation by thermal decomposition of unsaturated fatty acids initiates a set of reactions which eliminate CO2, regenerating alkyl radicals leading to hydrocarbon products (Pathway B). A third pathway (Pathway C) is an alternative set of radical reactions, resulting in decarbonylation and formation of minor byproducts. The results of the calculations are in good agreement with recent experimental studies.

Applying Raman Microspectroscopy to Evaluate the Effects of Nutrient Cations on Alkane Bioavailability to Acinetobacter baylyi ADP1.

Contamination with petroleum hydrocarbons causes extensive damage to ecological systems. On oil-contaminated sites, alkanes are major components; many indigenous bacteria can access and/or degrade alkanes. However, their ability to do so is affected by external properties of the soil, including nutrient cations. This study used Raman microspectroscopy to study how nutrient cations affect alkanes' bioavailability to Acinetobacter baylyi ADP1 (a known degrader). Treated with Na, K, Mg, and Ca at 10 mM, A. baylyi was exposed to seven n-alkanes (decane, dodecane, tetradecane, hexadecane, nonadecane, eicosane, and tetracosane) and one alkane mixture (mineral oil). Raman spectral analysis indicated that bioavailability of alkanes varied with carbon chain lengths, and additional cations altered the bacterial response to n-alkanes. Sodium significantly increased the bacterial affinity toward decane and dodecane, and K and Mg enhanced the bioavailability of tetradecane and hexadecane. In contrast, the bacterial response was inhibited by Ca for all alkanes. Similar results were observed in mineral oil exposure. Our study employed Raman spectral assay to offer a deep insight into how nutrient cations affect the bioavailability of alkanes, suggesting that nutrient cations can play a key role in influencing the harmful effects of hydrocarbons and could be optimized to enhance the bioremediation strategy.

Modeling the Fluid-Phase Equilibria of Semifluorinated Alkanes and Mixtures of (n-Alkanes + n-Perfluoroalkanes) with the SAFT-γ Mie Group-Contribution Approach

The SAFT-γ Mie group-contribution approach is extended to describe the fluid-phase behavior and excess properties of mixtures of linear alkanes and perfluoroalkanes, as well as the properties of th...

Partial oxidation of light alkanes in microchannel

In this work, we conducted an experimental study of partial oxidation of fuel gas, consisting of a mixture of light C1-C4 alkanes, in an annular microreactor with a catalyst deposited on the inner wall of the channel with a carbon/oxygen ratio equal to one. The experiments were carried out at different contact times in the temperature range of the reactor of 450-750°C.

Kinetic separation of C4 olefins using Y-fum-fcu-MOF with ultra-fine-tuned aperture size

The separation of C4 olefin mixtures into pure components is one of the most challenging processes in chemical industries. Adsorption-based separation, using ultra-microporous materials, is considered as a viable alternative to reduce the operating cost of the currently employed but energy intensive distillation technique. The understanding of structural properties-relationships for C4 olefins separation using solid state materials is still lacking particularly for microporous materials with purely cage-based structures. Herein, the adsorptive separation of C4 olefins (butene isomers and 1,3-butadiene) by the microporous MOF, Y-fum-fcu-MOF, containing octahedral and tetrahedral cages with triangular pore aperture size (≈4.7 Å), is studied. The adsorption capacities of the MOF for C4 olefins were assessed by measuring the single component adsorption isotherms at 30 °C which led to very similar equilibrium adsorption uptakes at saturation for the components (excluding isobutylene). However, adsorption breakthrough curves collected at 25 °C and Pulse Gas Chromatography experiments, conducted to define the guest–host affinity at very low concentration (Henry’s region), evidenced kinetically driven separation of C4 olefins by Y-fum-fcu-MOF. In fact, a strong relation between pores window size, kinetic diameter of the components and their adsorption behavior was observed. The breakthrough capacity decreases at increasing molecular size, allowing the separation of cis- and trans-2-butene despite the quite similar adsorption enthalpies for these components (42.0 and 37.7 kJ/mol, respectively).

Identification of Unique Aldehyde Dimers in Sorghum Wax Recovered after Fermentation in a Commercial Fuel Ethanol Plant

AbstractSorghum wax can be extracted from the surface of sorghum (Sorghum bicolor) kernels. It is composed mostly of a mixture of unsaturated C28 and C30 alkanes, fatty acids, fatty alcohols, and fatty aldehydes. Like carnauba wax, sorghum wax is a hard wax with a high melting point and it has potential edible and industrial applications. The yield of sorghum wax from the surface of sorghum kernels is 0.2–0.5 g of wax per 100 g of kernels. Sorghum wax can also be recovered from the “distillers oil” which is obtained after fermentation of sorghum (milo) or sorghum/corn blends in dry grind fuel ethanol plants. This distillers sorghum wax can potentially be obtained in yields of up to 10% by chilling the distillers oil to precipitate the wax and then recovering it via centrifugation or filtration. Like sorghum kernel wax, distillers sorghum wax is mainly composed of C28 and C30 alkanes, alcohols, and aldehydes in the molecular weight (MW) range of 350–450. However, we found that 7–49% w/w of distillers sorghum wax is composed of larger wax components with MW of 799–912. Analysis via high‐resolution atmospheric pressure chemical ionization mass spectrometry (APCI) and gas chromatography with electron ionization mass spectrometry (GC/MS‐EI) resulted in exact mass data and fragmentation patterns that suggested that these high MW compounds are monounsaturated fatty aldehyde dimers, likely formed by aldol condensation. Further confirmation supporting the GC/MS data for the aldol reaction was obtained by comparison with similar aldol products.

Analysis and optimisation of a novel ‘almond-refinery’ concept: Simultaneous production of biofuels and value-added chemicals by hydrothermal treatment of almond hulls

For the first time, this work investigates the achievability of developing a biorefinery concept around almond hulls by hydrothermal treatment (HTT), thoroughly scrutinising the influence of the temperature (200–300 °C), pressure (100–180 bar), time (20–180 min) and solid loading (5–25 wt%). This process allowed the conversion of almond hulls into four main products: gas (2–13%), bio-oil (2–12%), aqueous (4–69%) and hydro-char (17–89%). The gas consisted of a mix of H2, CO2, CO and CH4 with a LHV fluctuating from 1 to 13 MJ/m3 STP. The bio-oil comprised a mixture of alkanes, aldehydes, ketones, phenols, furans, benzenes and nitrogen compounds with a HHV between 21 and 31 MJ/kg. The solid product resembled an energetic hydro-char material (HHV 21–31 MJ/kg), while the aqueous effluent comprised a mixture of value-added chemicals, including saccharides and small oxygenated compounds. The production of biofuels can be maximised at 256 °C and 100 bar, using a 5 wt% solid loading for 157 min, conditions at which 43% of the original feedstock can be converted into an elevated energy-filled bio-oil (11% yield, 30 MJ/kg), along with a high energetic hydro-char (32% yield, 29 MJ/kg). Regarding value-added chemicals, up to 10% of the almond hulls can be converted into a bio-oil with a high proportion (45%) of phenolic species at 250 °C and 144 bar with a solid loading of 5 wt% for 167 min. In comparison, a sugar-rich (81 C-wt%) solution can be produced in high yield (54%), by treating a 24 wt% suspension at 252 °C and 180 bar for 153 min. Therefore, the versatility, novelty and intrinsic green and holistic nature of this ‘almond-refinery’ concept exemplify a landmark achievement in future energy and chemicals production from biomass, which might help render the complete bio-refinery for almond hulls more cost-effectively and ecologically feasible.

Cover Picture: The density characteristics of CO2 and alkane mixtures using PC‐SAFT EoS (Greenhouse Gas Sci Technol 5/2020)

Cover Picture: The density characteristics of CO₂ and alkane mixtures using PC‐SAFT EoS (Greenhouse Gas Sci Technol 5/2020)