Ethylene Oligomerization Research Articles

Chromium Catalysts for Selective Ethylene Oligomerization Featuring Binuclear PNP Ligands.

A series of novel binuclear PNP ligands based on the cyclohexyldiamine scaffold were synthesized for this study. The experimental results showed that positioning the two PNP sites at the para-positions of the cyclohexyl framework led to a significant enhancement in the catalytic activity for selective tri/tetramerization of ethylene. The PNP/Cr(acac)3/MAO(methylaluminoxane) catalytic system exhibited relatively high catalytic activity (up to 3887.7 kg·g-1·h-1) in selective ethylene oligomerization with a total selectivity of 84.5% for 1-hexene and 1-octene at 40 °C and 50 bar. The relationship between the ligand structure and ethylene oligomerization performance was further explored using density functional theory calculations.

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

Chromium-based selective ethylene tri-/tetramerization catalysts supported by two-carbon bridged diphosphine ligands

The effect of backbone-substituent of carbon-bridged diphosphine ligands of the type {Ph2PC(COOR)=C(COOR)PPh2} on the catalyst performance in ethylene oligomerization has been explored. The Cr precatalyst supported by the ligand {Ph2PC(COOMe)=C(COOMe)PPh2} (L1) achieved a high activity of 1800 kg/g Cr/h with a total selectivity of 90.8 % toward 1-hexene (77.3 %) and 1-octene (13.5 %) when activated with MMAO-3A. The catalytic system based on these ligands exhibited considerably high thermal stability, maintaining high activity even at 100 oC.

Zirconia-incorporated yttria with a Lewis pair of acid–base surface sites for chemoselective dehydration of alcohols into alpha olefins

Alpha olefins are currently made by ethylene oligomerization to a broad range of carbon number. An alternative conversion is selective alcohol dehydration in which the conventional catalyst development focused on the addition of any basic components into acidic supports. We herein demonstrated that the Zr4+ addition to Y2O3 (acid-to-base addition) was more effective than the Y3+ addition to ZrO2 in alcohol dehydration to alpha olefins. The zirconia-incorporated yttria with 4 mol% Zr (named 4ZIY) was structurally more stable than the yttria-stabilized zirconia (YSZ) counterpart. Moreover, the 4ZIY showed a high purity of alpha olefins when various C4 and C6 alcohols were used. Catalyst characterization works revealed that the 4ZIY contains a large amount of strong Lewis base sites, which is associated with oxygen vacancy, with a little Lewis acid sites. Consequently, the 4ZIY is suggested to have the favorable acid–base pair for the conversion of alcohols to alpha olefins.

Nickel-containing catalysts for ethylene conversion to motor fuel components and light alkenes

Polyfunctional Ni-containing catalysts supported on the B2O3-Al2O3 and MoO3-Al2O3 were prepared by a sequential impregnation. They were evaluated in ethylene conversion to C5+ alkenes or propylene. The catalysts were characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, Fourier transformed infrared spectroscopy of adsorbed CO, UV-VIS diffuse reflectance spectroscopy, temperature programmed reduction and temperature-programmed desorption of NH3. NiO/B2O3-Al2O3 samples containing Ni2+ cations chemically bonded to the acid support are the most effective catalysts for ethylene oligomerization. The NiO/MoO3-Al2O3 catalyst activity in the ethylene conversion to propylene is related with the presence of ethylene dimerization active sites, i.e. Ni2+ cations bonded to the support acidic sites, and active sites of metathesis in the form of monomolybdate species.

Front Cover: Ethylene Oligomerization: Unraveling the Roles of Ni Sites, Acid Sites, and Zeolite Pore Topology through Continuous and Pulsed Reactions (ChemCatChem 5/2024)

Front Cover: Ethylene Oligomerization: Unraveling the Roles of Ni Sites, Acid Sites, and Zeolite Pore Topology through Continuous and Pulsed Reactions (ChemCatChem 5/2024)

Ethylene trimerization using half‐sandwich titanium‐based catalysts supported on mesoporous silica modified with ionic liquids

Linear alpha olefins (LAOs) are produced industrially via ethylene oligomerization using catalytic methods. The cost‐effective separation process has sparked significant interest in the selective oligomerization of ethylene to produce alpha‐olefins, including 1‐hexene (1‐C6), in multi‐product commercial processes. In addition, the utilization of immobilized catalysts is crucial because of their reduced environmental impact, ease of catalyst separation, recyclability, and transportability. Furthermore, the use of immobilized catalysts simplifies the purification process, making it easier to isolate pure products. In the present study, mesoporous silica (MS) was first modified with ionic liquids (ILs) consisting BF4− and Br− counter‐anions to prepare IL‐BF4@MS and IL‐Br@MS, respectively. Then 12 catalysts were synthesized through immobilization of the half‐sandwich catalysts with different bridges on the surface of MS, IL‐Br@MS, and IL‐BF4@MS and characterized by BET, TGA, and SEM–EDX‐Mapping analyses. UV–Visible spectroscopy showed a tetrahedral structure for the synthesized complexes. The activity and selectivity of the catalysts for the production of 1‐hexene were studied under specific conditions, including an ethylene pressure of 8 bar, a temperature of 40 °C, and an Al/Ti ratio of 1:2000. The C1‐IL‐BF4@MS immobilized catalyst with cyclohexane middle bridge immobilized on MS modified with IL‐BF4 revealed the highest activity (1199 kg 1‐C6 molTi−1·h−1) at a catalyst concentration of 1.5 μmol. The lowest activity (138 kg 1‐C molTi−1·h−1) was obtained for both C3@MS and C4@MS catalysts.

Synthesis and application of chromium complexes based on 4,5-bis(diphenylphosphanyl)-<i>H</i>-1,2,3-triazole ligands to obtain higher С<sub>10</sub>–С<sub>18</sub> olefins

Objectives. To synthesize 4,5-bis(diphenylphosphanyl)-H-1,2,3-triazole ligands and new chromium complexes based on them, in order to obtain a fraction of higher C10–C18 alpha-olefins from ethylene.Methods. The Schlenk technique was used to obtain the target chromium complexes. Diphenylphosphanyl triazole ligands can be characterized by nuclear magnetic resonance spectroscopy. The composition of the final products was confirmed by elemental analysis. The liquid phase of the oligomerization reaction was studied by gas chromatography.Results. L1–L9 ligands were obtained, and K1–K9 chromium complexes were synthesized based on the correspondent ligands using commercially available chromium (III) trichloride tris(tetrahydrofuran). The K1–K9 complexes thus obtained were tested in the process of ethylene oligomerization.Conclusions. Chromium complexes based on 4,5-bis(diphenylphosphanyl)-H-1,2,3-triazoles K1–K9 were produced in high yields using the Schlenk technique. It was found that systems based on the K4–K7 and K9 complexes enable the ethylene oligomerization process to be carried out with a sufficiently high level of productivity. It was shown that the introduction of a dialkyl zinc derivative increases the performance and selectivity of the catalytic system for the target fraction.

Effect of ligand structure and metal center on ethylene oligomerization with N, N′ Schiff base late transition complexes: experiments and calculations

A series of N, N’ bis(pyridine-imine) Schiff base late transition metal (Fe, Co, and Ni) complexes with different ligand structures and catalytic active sites were synthesized. Ethylene oligomerization results showed that bis(pyridine-imine) iron complex had the highest catalytic activity (10.8 × 105 g/mol Fe h), and the catalytic activity of cobalt complex was the lowest (2.5 × 105 g/mol Co h); nickel complex had the highest selectivity toward high carbon olefins (28.6%), while the iron complex had the lowest (0.2%). The structure-activity relationship between the catalyst structure and catalytic properties for ethylene oligomerization was further studied by density functional theory (DFT) calculations. The bis(pyridine-imine) iron complex had the highest energy gap value and the most stable catalyst structure, which was more conducive to oligomerization; and the N–M–N bond of the nickel complex had the smallest bond angle, which was beneficial for chain growth. Based on the Cossee mechanism, a mechanism for ethylene oligomerization catalyzed by bis(pyridine-imine) metal complexes was proposed. To further study the micro reaction process of ethylene oligomerization, a molecular model of pyridine imine nickel complex and its catalytic ethylene oligomerization reaction path were proposed. The structure and energy of the reaction intermediate and transition state were calculated using DFT. The molecular model of the nickel complex had a lower ethylene insertion barrier and β-H elimination of energy barriers, indicating that the molecular model of the pyridine imine nickel complex had ethylene oligomerization active centers.

Catalytic Synthesis of Butene-1 and Hexene-1 in the Homogeneous Oligomerization of Ethylene in the Presence of Nickel Complexes Based on N-Heteroaryl-Substituted α-Diphenylphosphinoglycines

Catalytic Synthesis of Butene-1 and Hexene-1 in the Homogeneous Oligomerization of Ethylene in the Presence of Nickel Complexes Based on N-Heteroaryl-Substituted α-Diphenylphosphinoglycines

A Continuous-Wave EPR Investigation into the Photochemical Transformations of the Chromium(I) Carbonyl Complex [Cr(CO)4bis(diphenylphosphino)]+ and Reactivity with 1-hexene.

Chromium complexes containing a bis(diphenylphosphino) ligand have attracted significant interest over many years due to their potential as active catalysts for ethylene oligomerisation when combined with suitable co-catalysts such as triethylaluminium (TEA) or methylaluminoxane (MAO). While there has been considerable attention devoted to the possible reaction intermediates and the nature of the Cr oxidation states involved, the potential UV photoactivity of the Cr(I) complexes has so far been overlooked. Therefore, to explore the photoinduced transformations of bis(diphenylphosphino) stabilized Cr(I) complexes, we used continuous-wave (CW) EPR to study the effects of UV radiation on a cationic [Cr(CO)4(dppp)]+[Al(OC(CF3)3)4]- complex (1), where dppp represents the 1,3 bis-(diphenylphosphino)propane ligand, Ph2P(C3H6)PPh2. Our preliminary investigations into the photochemistry of this complex revealed that [Cr(CO)4(dppp)]+ (1) can be readily photo-converted into an intermediate mer-[Cr(CO)3(κ1-dppp)(κ2-dppp)]+ complex (2) and eventually into a trans-[Cr(CO)2(dppp)2]+ complex (3) in solution at room temperature under UV-A light. Here, we show that the intermediate species (2) involved in this transformation can be identified by EPR at much lower temperature (140 K) and at a specific wavelength (highlighting the wavelength dependency of the reaction). In addition, small amounts of a 'piano-stool'-type complex, namely [Cr(CO)2(dppp-η6-arene)]+ (4), can also be formed during the photoconversion of [Cr(CO)4(dppp)]+ using UV-A light. There was no evidence for the formation of the [Cr(L-bis-η6-arene)]+ complex (5) in these UV irradiation experiments. For the first time, we also evidence the formation of a 1-hexene coordinated [Cr(CO)3(dppp)(1-hexene)]+ complex (6) following UV irradiation of [Cr(CO)4(dppp)]+ in the presence of 1-hexene; this result demonstrates the unprecedented opportunity for exploiting light activation during Cr-driven olefin oligomerisation catalysis, instead of expensive, difficult-to-handle, and hazardous chemical activators.

Experimentally-based Fe-catalyzed ethene oligomerization machine learning model provides highly accurate prediction of propagation/termination selectivity.

Linear α-olefins (1-alkenes) are critical comonomers for ethene copolymerization. A major impediment in the development of new homogeneous Fe catalysts for ethene oligomerization to produce comonomers and other important commercial products is the prediction of propagation versus termination rates that control the α-olefin distribution (e.g., 1-butene through 1-decene), which is often referred to as a K-value. Because the transition states for propagation versus termination are generally separated by less than a one kcal mol-1 difference in energy, this selectivity cannot be accurately predicted by either DFT or wavefunction methods (even DLPNO-CCSD(T)). Therefore, we developed a sub-kcal mol-1 accuracy machine learning model based on several hundred experimental selectivity values and straightforward 2D chemical and physical features that enables the prediction of α-olefin distribution K-values. As part of our model, we developed a new ad hoc feature that boosted the model performance. This machine learning model captures the effects of a broad range of ligand architectures and chemically nonintuitive trends in oligomerization selectivity. Our machine learning model was experimentally validated by prediction of a K-value for a new Fe phosphaneyl-pyridinyl-quinoline catalyst followed by experimental measurement that showed precise agreement. In addition to quantitative predictions, we demonstrate how this machine learning model can provide qualitative catalyst design using proximity of pairs type analysis.

Selective linear ethylene oligomerization over nickel-containing zeotypes with tetravalent framework heteroatoms

Nickel-containing Lewis acidic zeolites as highly selective ethylene oligomerization catalysts.

Sulfonic acid-modified MOFs as heterogeneous bifunctional catalysts for ethylene oligomerization at room temperature without cocatalysts

Ethylene oligomerization plays an important role in industrial production.

Microkinetic modeling of the homogeneous thermal oligomerization of ethylene to liquid fuel-range hydrocarbons

Microkinetic model quantitatively captures conditions under which thermal oligomerization of ethylene leads to broad product distribution of linear alkenes with both even and odd carbon numbers.

Оптимальное управление процессом протекания каталитической реакции

The article is devoted to the development of an algorithm for determining the optimal operating parameters of a catalytic reaction. Statements of optimal control problems are formulated, in which the temperature and time of the reaction act as control parameters. To solve them, a genetic algorithm with real coding is given. The efficiency of the algorithm is confirmed by the results of numerical experiments for the ethylene oligomerization reaction.

A study of Ni(ii) catalyzed ethylene oligomerization and dimerization with various N∩N ligands: structure/reactivity/selectivity relationships

The Cossee–Arlman mechanism of nickel-catalyzed oligomerization and dimerization with various N∩N-type ligands was studied using the DFT method.

A comparison of the catalytic activities of oxovanadium(IV) and cobalt(II) complex compounds in the oligomerization of ethylene

The polymerization and oligomerization of olefins, especially ethylene, is a process of great industrial and scientific importance in polymer chemistry. Catalysts are an essential part of this reaction, and a new report of a catalyst improving this process is worthy of special attention. During this study, nine complex compounds based on oxovanadium(IV) and cobalt(II) ions in combination with organic ligands, e.g., dipicolinic acid, 2,2′-bipyridine, iminodiacetic acid, diglycolic acid, thiodiacetic acid, 1,10-phenanthroline were synthesized. The compound [VO(tda) · 0.5 H2O] is a new complex not previously reported in the literature, and its synthesis and structure are described in this article. The high catalytic activity values in other oligomerization processes in other olefins led us to use the synthesized compounds as precatalysts in the oligomerization reaction. Subsequently, their catalytic activity was also calculated in this process. The obtained oligomerization products were then analyzed by IR, MALDI-TOF-MS, TG, DSC, and SEM techniques to characterize the obtained products and verify the correctness of the oligomerization reaction. Based on the obtained data, the catalytic activity values were compared and the most active catalyst was selected. The best catalyst was a cobalt(II) compound containing an iminodiacetic acid anion and 2,2′-bipyridine in its structure. However, all complexes can be classified as highly active and active catalysts for ethylene oligomerization. The presented studies show novel catalysts that have in their structure other metal ions than those most commonly used in the literature so far. Additionally, coordination compounds of this type have not been previously used in ethylene oligomerization. Moreover, these studies are a source of knowledge on the correlation between catalyst structure and catalytic activity value, thanks to which they provide essential information necessary for the design of next-generation catalysts used for ethylene oligomerization and polymerization.

Computer-aided ligand screening to develop polymer-free catalyst in Cr-catalyzed ethylene oligomerization

Preventing the formation of undesirable polymer in ethylene oligomerization is a major challenge since the presence of these insoluble materials can cause severe reactor fouling. Based on previous experimental data, the concomitant formation of these solid compounds can be divided in two types. Detailed discussion in combination with mathematical analysis revealed that the low-molecular weight waxes (low-Mw waxes) are most likely the tail products of the Schulz-Flory distribution while high-molecular weight polyethylene (high-Mw PE) may be catalyzed by multiple active sites independent from the oligomerization cycle. Controlling the Schulz-Flory coefficient (K value) to remain in a lower range is crucial in achieving plentiful C4–C8 components and inhibiting polymer formation at the same time. Attempting to predict the K value, the energetic disparities of key transition states which control 1-butene selectivity have been extracted as a chemical descriptor to establish a general model. Promising ligands derived from computer-aided screening are expected to avoid the inherent waxes formation. Plausible strategies for the elimination of external polymerization sites are also suggested. The combination of them may provide a chance to develop more polymer-free catalysts to meet the requirements of industrial manufacturing.

Synthesis of straight-chain C49H100 alkane using a modular splicing strategy

Ultra-long n-alkanes are highly valuable in both scientific research and as major constituents of specialty high-melting-point waxes. Unlike conventional methods (e.g., Fischer–Tropsch (FT), ethylene oligomerization, and polyethylene cracking) typically resulting in wide n-alkane distributions, the elaborate design strategy presented herein allows the direct synthesis of pure, long n-alkanes using a modular splicing method with acetone, furfural, and fatty acid anhydrides or acyl chlorides as bio-blocks. The herein approach is based on a simple four-step catalytic reaction scheme involving C–C chain elongation and C–O bond activation. The synthesized pure n-alkanes had a carbon chain length as high as C49 (total yield of 49%). The synthesis approach also allows to selectively prepare n-alkanes with even and odd carbon numbers ranging from C15 to C49. This process represents a great breakthrough in the synthesis of long-chain pure n-alkanes, surpassing the carbon number limitations reported in previous methodologies.