C6 Fraction Research Articles

Asymmetric carbon-bridged diphosphine based chromium complexes for selective ethylene tri-/tetramerization with high thermal stability

Asymmetric alkylphosphanyl carbon-bridged diphosphine Ph2PC = CPR1(R2)-type L1-L5 ligand has been observed to have a distinct effect on the catalytic performance of the corresponding Cr(III) based catalysts in ethylene oligomerization. Precatalyst 1, bearing diethylphosphanyl moiety, exhibited a high catalytic activity of 3628 kg·g−1·h−1 accompanied by 65.5% high C8 selectivity. Precatalyst 2 having diisopropylphosphanyl group afforded remarkably high catalytic activity of 4833 kg·g−1·h−1 with 91.8% combined (C6 + C8) product selectivity. Precatalysts 1–2 also showed good thermal stability and offer high catalytic activity at the high reaction temperature. Precatalyst 3 with sterically encumbered dicyclohexylphosphanyl substituent mainly offers C6 selectivity at the expense of the C8 fraction. Precatalyst 5 having isopropylphosphanyl moiety afforded poor catalytic activity and high C6 selectivity. Density functional theory (DFT) calculations of precatalyst 2 showed that the rate-determining step in the trimerization pathway of the catalyst may face a low energy barrier and therefore produce more C6 fraction.

A rational approach towards selective ethylene oligomerization via PNP-ligand design with an N-triptycene functionality.

Novel PNP ligands bearing an N-triptycene backbone were developed and evaluated for selective ethylene oligomerization. Upon activation with MMAO-3A, the pre-catalyst mixture containing Cr(acac)3/ligand efficiently promotes ethylene tetramerization with remarkably high productivities (up to 1733 kg gCr-1 h-1) and C8 olefin selectivities (up to 74.1 wt%). More importantly, ligands with a PNP moiety connecting at the 1- or 1,4-position of the triptycene molecule could achieve exceptionally high alpha (1-C6 + 1-C8) selectivities, exceeding 90 wt%, as a result of high 1-C6 purity (>90 wt%) in the C6 fraction. Based on comparative catalytic studies employing various PNP ligands with or without an N-triptycene backbone, we illustrate the fact that a rational design of PNP ligands with an optimum degree of steric profile around the N-center could provide C6 cyclics controlled highly α-selective ethylene oligomerization.

Techno‐economic and life‐cycle assessment of a wood chips‐based organosolv biorefinery concept for production of lignin monomers and oligomers by base‐catalyzed depolymerization

AbstractMore wood for technical valorization is to be expected in Europe over the coming years, due to climate change and the bark beetle. To further independence from fossil‐fuel resources a novel approach to the base‐catalyzed depolymerization (BCD) of organosolv lignin into monomers and oligomers, while maximizing yields and minimizing coke formation, was scaled up in a theoretical wood‐based biorefinery with a yearly input of 40 000 t of wood chips. Other process steps were modeled from the literature. A novel work‐up approach was evaluated under laboratory conditions, implemented, and compared with a simulation‐based pervaporation technique. The life‐cycle assessment (LCA) showed that the biorefinery provided a significantly lower global warming potential (GWP) (excluding biogenic carbon) than its fossil counterparts. Moreover, the majority of impacts on the other midpoint categories was also smaller than for the fossil reference. However, after allocating the GWPs, it was evident that subsequent conversion of the C6 fraction to value‐added products is necessary for optimal results. The discounted cash flow analyses for the biorefinery setups (40 to 400 kt year–1) showed that they were not profitable with prices based on fossil references. However, when using higher prices/t from the literature, such as €1615 for monomers, €2000 for oligomers, and €510 for C6 sugars, a positive net present value could be reached at approximately 100 000–120 000 t processed annually. Hence, the conclusion was that a biorefinery utilizing wood not only brings environmental benefits and a reduction in the use of fossil resources but can also be financially beneficial. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd

Comparison of furfural and biogas production using pentoses as platform

Coffee cut-stems (CCS), a biomass with high lignocellulosic content, is a coffee crop waste after bean harvesting. The main application of this material is as fuelwood for farmers, disregarding their carbohydrate content for biotechnological processes. In these terms, this work aims to compare three process scenarios for the experimental valorization of C5 fraction from CCS to produce biogas and furfural with and without the ethanol production from remaining C6 fraction under biorefinery concept. Therefore, an experimental stage was performed to obtain these products, based on a previous diluted acid pretreatment. The hydrolysate fraction was used to produce furfural and biogas, achieving yields of 0.34 g of furfural/g xylose and 81.1 mL of CH4 per gram of volatile solids. Concerning the solid fraction after acid pretreatment, it was used to produce ethanol with a previous enzymatic hydrolysis. After fermentation, 0.47 g of ethanol/g of glucose (92% of the theoretical yield) was obtained. These experimental results were fed to simulation models in order to compare three scenarios in technical, economic and environmental terms. As the main results, from technical point of view, the biogas production presents the lowest energy requirements. From the economic perspective, the furfural production presents a prefeasibility at the base scale of processing (e.g., 12.5 ton h−1). Meanwhile, the biogas scenario needs a processing capacity >22.5 ton h−1 to achieve the economic prefeasibility. In the biorefinery case, the positive economic performance is found at processing scales above 83 ton h−1. This work concludes that the C5 sugars platform is identified as a potential alternative for the generation of furfural and biogas, however, in this case a multiproduct biorefinery system is not always the best option to valorize biomass given the very high scale required and the economic indicators.

In situ formed Cr(III) based silicon-bridged PNS systems for selective ethylene tri-/tetramerization

In-situ formed and activated chromium(III) catalysts based on silicon-bridged PNS (Si-PNS) ligands of the form Ph2PN(R1)Si(CH3)2S(R2) have been investigated for selective ethylene tri-/tetramerization. Ligand substituents at the backbone N and S atoms have been realized to have a marked impact on the product selectivity in these systems. Ligands having the substituents such as cyclohexyl (in ligand 3), ortho-tolyl (in ligand 5) or ethyl (in ligand 6) at backbone S, and a low steric bulk moiety (isopropyl) at backbone N in these ligands favor tetramerization of ethylene and respectively deliver 75%, 76% and 66% C8 selectivity. Ligands having higher steric bulk substituents like 2,6-diisoprpylphenyl (in ligand 1) or cyclopentyl (in ligand 2) at backbone N, and a cyclohexyl moiety at backbone S in these ligands promote trimerization of ethylene and produce C6 fraction. While the ortho-tolyl moiety at backbone S and a 2,6-diisopropylphenyl substituent at backbone N completely diminish the C6 and C8 selectivity in ligand 4 based system and produce higher oligomers. DFT calculations revealed that the sterically relaxed ligand 3 provide a facile and energetically favorable route for C8 formation, while sterically encumbered substituents tend to block the formation of C6 and C8 fractions in ligand 4 based system.

Biodegradation of light hydrocarbon(C5-C8) in shale gases from the Triassic Yanchang Formation, Ordos basin, China

Abstract: Evidence based on the molecular, carbon and hydrogen isotopic composition of shale gas has shown that the biodegradation level of the Yanchang Formation shale gas decreases markedly with increasing depth in some parts of the Ordos basin. The compositions of a suite of 30 shale desorbed gases from the Upper Triassic Yanchang Formation, Ordos basin, China, were analyzed in order to assess the effect of variable levels of biodegradation on the distribution of light hydrocarbons in the shale gas and to investigate the effect of biodegradation on common light hydrocarbon parameters. By comparison and analysis of the gas chromatograms of shale desorbed gas from different depths, a series of light hydrocarbon parameters reflecting biodegradation were established. The results indicate that the order of preferential biodegradation of light hydrocarbon fractions (C5-C8) is C5>C6>C7≈C8 and that the C6 fraction composition is n-Hexane (nC6)>2-methypentane (2-MP) ≈3-methypentane (3-MP)> Methylcyclopentane (MCP)>2,3-Dimethybutane (2,3-DMB)>2,2-Dimethybutane (2,2-DMB)>Cyclohexane (CH). There are three main controls on the susceptibility to biodegradation of light hydrocarbons: carbon skeleton, degree of alkylation, and position of alkylation. If the carbon skeleton is the same, a higher degree of alkylation represents a stronger ability to resist biodegradation. If the degree of alkylation is the same, those alkanes with larger carbon skeletons are more resistant to biodegradation. Finally, light hydrocarbon fractions with two methyl groups in the same position are more resistant to biodegradation than hydrocarbons with two methyl groups in different positions. Most of the light hydrocarbon parameters were influenced by biodegradation, except the Mango parameters K1and K2.

B(C6F5)3 Promotes the catalytic activation of [N,S]-ferrocenyl nickel complexes in ethylene oligomerization

The synthesis of new methallyl-ferrocenyl-thiazoline-nickel complexes [1-(2-thiazolin-2-yl)-2-(R-thio)-ferrocene-κ2N,S]-(η3-methallyl)nickel(II) [Y] (1-3, R = Me, i-Pr, Ph, Y = BF4-4, R = Me, Y = BAr´4-) by reaction with 2-ferrocenyl-2-thiazoline ligands L1–3 with [Ni-(η3-(CH2)2CMe)Cl]2 in presence of fluoroborate salts (Y = BAr´4-; BF4-) is reported. The complexes 1–4 were obtained in high yields, and characterized by 1H, 13C, 19F and 11B NMR, FTIR. The X-Ray diffraction analysis of 4 confirmed the formation of a single isomer containing a nickel center coordinated to L1 in a bidentate [N,S] fashion and to a η3-methallyl ligand. These complexes catalyzed efficiently the ethylene oligomerization when tris(pentafluorophenyl)borane (BCF) was used as co-activator. All catalytic precursors produced C4 and C6 fractions. Complex 1 showed higher activity with TOF 3006 h-1 at room temperature with selectivity of 86% to C4 fraction. In contrast, catalyst 2 was more selective to the formation of 1-butene, but with low activity. DFT-Computational studies of complex-BCF adducts show than these species behave as frustrated Lewis pairs, mainly stabilized by long-range interactions enhancing the acceptor character of the complexes. Structural modifications over the sulfanyl group tune the acceptor character of Ni center, affecting their catalytic performance.

A Selective Chromium Catalyst System for the Trimerization of Ethene and Its Coordination Chemistry

AbstractIn this paper a novel ligand of the type [PNPNH] is presented for the application in a new homogeneous highly selective ethene trimerization system for the formation of 1‐hexene, which consists of the chromium source CrCl3(thf)3, the ligand Ph2PN(iPr)P(Ph)N(iPr)H (1), and Et3Al as an activator in toluene. The excellent characteristics of this new system, e.g. very high selectivity to C6 with highest purity of the C6 fraction (>99 % 1‐hexene), activity on a constant level on a long timescale, use of small amounts of Et3Al as a cheap activator, and only very low production of PE, make it to a hot candidate for industrial application. Its organometallic background gives an indication of the nature of the active catalyst species.

OLIGOMERIZATION OF ETHENE OVER SEVERAL CATALYST BEDS CONSISTING OF BOTH Ni/SiO<SUB>2</SUB>·Al<SUB>2</SUB>O<SUB>3</SUB> AND BPO<SUB>4</SUB>

The oligomerization of ethene was investigated over several catalysts involving Ni/SiO2·Al2O3(Ni/SA) and BPO4. The oligomerization of ethene activity of SA or BPO4 was very low, while that of Ni/SA was very high. Butene was predominantly observed over Ni/SA, while no product was observed over BPO4. Combined use of Ni/SA and BPO4 was more effective for promoting the ethene oligomerization than Ni/SA, especially for increasing C6 fraction. 1-Butene as C4 products in the ethene oligomerization was mainly obtained in the presence of Ni/SA alone, while an equilibrium mixture of n-butene was formed using Ni/SA and BPO4 together, suggesting that the isomerization of n-butene formed from ethene occurs over BPO4.

New highly active and selective Et oligomerization catalysts based on cationic diamide zirconium complexes

Group 4 complexes based on the diamide ligand, [Me3CN(SiMe2)2NCMe3]2−, have been investigated as possible catalysts for olefin conversions. The dialkyl complexes, (Me2SiNCMe3)2ZrR2 (R = CH2Ph, Me), were converted into zwitterionic (X-ray: {Me2SiNCMe3}2Zr(η1-Bz){ηn-BzB(C6F5)3}), or cationic mono-alkyl compounds by reaction with B(C6F5)3 or borate reagents. These electrophilic species catalyzed ethylene oligomerization, affording highly linear alpha-olefins under mild conditions (C6 fraction > 99.5% 1-hexene at 50°C, 6 bar). The highest activities (290 Kg/g Zr.h) were obtained in toluene solvent using tri-iso-butylaluminium (TIBA) as scavenger. The catalyst exhibited activity decay in alkane solvent, which was countered by replacement of TIBA by more crowded trialkylaluminium scavengers or branched alkylaluminoxane scavengers. The product consisted primarily of linear alpha-olefins (LAO) with low levels of remote-branched AO's. These are formed by successive insertion of higher olefin and one or more ethylenes in a growing chain, followed by chain transfer.

Change in the distillation of automobile gasolines by addition of light hydrocarbons

1. To meet requirements with regard to distillation data and saturated vapor pressure of winter and northern grades of automobile gasolines, we may use as the light components of the fuel butane, isopentane, isomerizate, and the light fractions of straight-run and gas naphtha, or various mixtures of these components. 2. The authors have plotted the decrease in the 10 and 50% distillation temperatures of base gasolines with differing distillation data versus the amount of butane and 23–62 and 34–67°C light hydrocarbon fractions added. These graphs enable us to calculate the necessary amounts of components for obtaining northern, winter, and summer grades of automobile gasolines with distillation data in line with requirements. 3. The paper gives data characterizing the change in the IBP of base gasolines due to compounding with butane and other light hydrocarbon fractions. 4. It is shown that butane has little effect, and a mixture of C4, C5, and C6 fractions virtually no effect, on the decrease in the 90% distillation temperature and the FBP of base gasolines. 5. Addition of 1% of butane, isopentane, the straight-run 23–62°C fraction, and the 34–67°C gas-naphtha fraction increases the saturated vapor pressures of base gasolines (with saturated vapor pressure of 100 to 400mm Hg) by 35–40, 14–7, 12–5.5, and 9-3.5 mm Hg, respectively. 6. A lower limit of the saturated vapor pressure of winter grades of automobile gasolines of 500 mm Hg may be obtained if the 10% distillation temperature is not more than 50°C.

On the catalytic hydrocondensation of carbon monoxide with olefins and their hydropolymerization under the action of carbon monoxide and hydrogen

1. It was shown by the method of capillary gas-liquid chromatography that the composition of the C5 and C6 fractions of the products of hydropolymerization of ethylene under the action of carbon monoxide at 190° on a cobalt catalyst depends upon the presence of a promoter (ZrO2 +MgO) and especially upon the nature of the carrier. 2. Kieselguhr as the carrier promotes the formation of larger amounts ofβ-olefins in comparison with clay. 3. The quantitative ratio of hydrocarbons of normal and iso-structure is ∼2∶1 in the C5 fraction and ∼ 1∶1 in the C6 fraction, independent of the composition of the catalyst.