Reactor Fouling Research Articles

Correlating Heterogeneities in Support Fragmentation to Polymer Morphology in Metallocene‐Based Propylene Polymerization Catalysis

In the field of olefin polymerization catalysis, metallocenes are heterogenized with methylaluminoxane onto silica supports to yield active catalysts. During olefin polymerization, these silica supports act as a framework to control the fragmentation stage, thereby influencing the final polymer product and preventing reactor fouling and fines formation. This study investigates the influence of different silica supports induced on the final polymer product. To study a broad range of silica supports from an industrial silica database, we utilize a hierarchical clustering method to cluster the supports based on their physical properties. From the clustering method, five supports representing the clusters and an industrial benchmark were analyzed at different polymerization stages using Focused Ion Beam Scanning Electron Microscopy (FIB‐SEM) and Micro‐computed Tomography (MicroCT). This combined FIB‐SEM/MicroCT methodology revealed differences in both fragmentation behavior and polymer morphologies based on structural features, including macropores, mesopores, spray‐dried shells, spray‐dried spheres, and denser shells. The heterogeneity and ideal fragmentation behavior was further assessed by calculating the replication factor of each support, indicating that silica materials containing macropores and spray‐dried shells have an almost ideal replication phenomenon. This multi‐scale analysis revealed new understanding of catalyst fragmentation for different supports.

Homo- and hetero-polymerization of ethylene catalyzed by α-diimine nickel complexes with hydroxyl groups

Heterogeneous olefin polymerization catalysts have received wide interests from academia and industry because their distinct advantages in thermostability, avoidance of reactor fouling and continuous production operations. In this work, hydroxy functional groups are introduced to the α-diimine nickel framework, which can serve as reactive functionality to react with MgCl2/AlRn(OEt)3-n and form ionic anchoring interaction that bind the catalyst strongly to the surface of the supports. These heterogeneous catalysts are highly active in ethylene polymerization to produce polyethylene with higher molecular weight (up to 280.5 × 104 g·mol−1), lower branching density and higher tensile strength (up to 26.7 MPa) than those generated by the homogeneous counterparts. More importantly, the nickel complexes with multiple hydroxy groups lead to high loading capacity on MgCl2/AlRn(OEt)3-n supports, affording polyethylene products with minimum inorganic contamination.

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.

Silica-supported catalyst for the synthesis of low entangled UHMWPE suitable for solid-state processing

Different types of silica (mesoporous, spherical and nano-size particles), pre-activated with methylaluminoxane (MAO), are used to activate and support the bis[N-(3‑tert-butylsalicydene)-2,3,4,5,6-pentafluoroanilinato] titanium(IV) dichloride (FI) complex with the aim to synthesize low-entangled UHMWPE having controlled particle morphology. Through the porosity analysis, nitrogen adsorption and desorption isotherms, a decreased surfaced area of the chosen silica is observed when supported by MAO. From the bonding energy study by XPS, the bonding energy difference of Si and O, between the nano-size silica and in the MAO-nano silica, suggests the formation of Al-O-Si after chemical activation with MAO. Using elementary analysis, ICP-OES and XPS characterization, the aluminum content grafted on the silica surface is found to match with the anticipated amount of MAO on the MAO-Silica/FI catalytic system, indicating a stable grafting after catalyst supporting. From the rheological studies of the polymers, coupled with DSC results using an isothermal crystallization protocol, the resultant entangled state in the semi-crystalline polymers is estimated. The observations are that the entangled state achieved during polymerization from the investigated heterogeneous catalytic systems, is the lowest in PE-MAO-nano silica/FI, increases in PE-MAO-mesoporous silica/FI and is highest in PE-MAO-spherical silica/FI. Silica modification using two different silanes shows significant influence on the catalytic activity, giving lower polymer yield in MAO-modified-mesoporous silica and MAO-modified-nano silica compared to the unmodified MAO-silica. Whereas, no significant spatial effect is observed in the formation of chain entanglement, showing the increased entanglement density of the nascent polymers. By employing heterogeneous catalytic systems, reactor fouling and wall sheeting problems are resolved and the polymers show good morphology replication of the support. The UHMWPE synthesized using the nano silica as support, having the lowest entangled state and loosely packed crystals, can be uniaxially processed in the solid-state to a thin tape having thickness around 34 μm, showing maximum tensile strength of 3.26 N/tex and tensile modulus of 170 N/tex.

Synthesis of α-Diimine Complex Enabling Rapidly Covalent Attachment to Silica Supports and Application of Homo-/Heterogeneous Catalysts in Ethylene Polymerization.

For covalent attachment-supported α-diimine catalysts, on the basis of ensuring the thermal stability and activity of the catalysts, the important problem is that the active group on the catalyst can quickly react with the support, anchoring it firmly on the support, shortening the loading time, reducing the negative impact of the support on the active centers, and further improving the polymer morphology, which makes them suitable for use in industrial polymerization temperatures. Herein, we synthesized a α-diimine nickel(II) catalyst bearing four hydroxyl substituents. The hydroxyl substituents enable the catalyst to be immobilized firmly on silica support by covalent linkage in 5-10 min. Compared with the toluene solvent system, the homogeneous catalysts show high activity and thermal stability in hexane solvent at the same conditions. Compared with homogeneous catalysts, heterogeneous catalysis leads to improvements in catalyst lifetime, polymer morphology control, catalytic activity, and the molecular weight of polyethylene (up to 679 kg/mol). The silica-supported catalysts resulted in higher melting temperatures as well as lower branching densities in polyethylenes. Even at 70 °C, the polyethylene prepared by S-CatA-2 still exhibits dispersed particle morphology, and there is no phenomenon of reactor fouling, which is suitable for industrial polymerization processes.

Effect of Hydrothermal Carbonization on Fuel and Combustion Properties of Shrimp Shell Waste

Shrimp shell is a popularly consumed seafood around the globe which generates a substantial quantity of solid wet waste. Hydrothermal carbonization (HTC) could be a viable pathway to convert wet shrimp shell waste into energy-dense hydrochar. The present study aims to assess the fuel properties, physicochemical attributes, and combustion properties of shrimp shell hydrochar generated with a wide range of HTC temperatures (110–290 °C). Results showed that a rise in carbonization rate results in a decline in mass yield to as low as 25.7% with the increase in HTC temperature. Thermogravimetric analysis indicates shrimp shell hydrochars to be more thermally stable than raw dried feedstock. Results from the bomb calorimeter report a maximum HHV of 27.9 MJ/kg for SS-290, showing a 13% increase in energy densification compared to raw shrimp shell. The slagging and fouling indices determined for the hydrochars further assisted in addressing the concern regarding increasing ash content changing from 17.0% to 36.6%. Lower ratings of the slagging index, fouling index, alkali index, and chlorine content for hydrochars at higher temperature indicate the reduced probability of reactor fouling during combustion. The findings of the analysis demonstrate that HTC is a promising approach for transforming shrimp shell waste into a potential fuel replacement.

Heterogenization Strategies for Nickel Catalyzed Synthesis of Polyolefins and Composites

ConspectusPolyolefin is one of the most common synthetic polymers. However, most polyolefins are nonpolar materials, which leads to poor compatibility with polar materials, thus limiting their application in some fields. Polar functionalized polyolefins can lead to significantly improved dyeability, adhesiveness and compatibility with polar fillers, and can realize customized properties of polyolefin materials. Transition-metal-catalyzed coordination copolymerization of olefin and polar functionalized comonomers represents a direct and potentially economic route to synthesize polar-functionalized polyolefin materials, which has attracted great attention in recent decades. Literally hundreds of nickel and palladium catalysts have been synthesized and investigated in olefin-polar monomer copolymerization to achieve high copolymerization efficiency by tuning the molecular structures of the catalysts. In particular, earth-abundant and low-cost nickel-based catalysts hold great potential for industrial applications. However, most research efforts focus on homogeneous copolymerization catalysts, while the industrially preferred heterogeneous systems have remained largely unexplored. With the objective of bridging this gap, our group has recently developed a series of heterogenization strategies for the synthesis of high-performance heterogeneous nickel catalysts taking advantage of hydrogen bond anchoring, ionic anchoring, coanchoring, cocatalyst, and ionic cluster formation. These strategies involve known or easily accessible catalysts, can be easily adapted to various catalytic systems, and can lead to simultaneous enhancement in all copolymerization parameters such as thermal stability, activity, comonomer incorporation ratio, and copolymer molecular weight versus the homogeneous counterparts. In addition, the performance of the catalysts can be tuned by changing the type of the support, thereby facilitating the discovery of high-performance heterogeneous nickel catalysts. Most importantly, great product morphology control can be achieved. This is desirable for industrial polymerization processes because it avoids reactor fouling and results in significant improvements in the safety and operational efficiency of the polymerization processes. Finally, these heterogenization strategies give access to high-performance polyolefin materials (polar-functionalized polyolefins, polar-functionalized polyolefin in-reactor blends and polyolefin-based functional composites) with custom-made properties. Compared with melt blending, polyolefin composites obtained by heterogeneous catalytic in situ polymerization have better material properties. By using functional fillers, customized polyolefin composites with high performance can be prepared in situ. These polyolefin-based materials have potential applications in many fields, such as electrical and thermal conductivity, photodegradation, flame retardancy, barrier, etc. It is expected that the continuous research on the copolymerization mechanism/catalysts, heterogenizatioin strategies and material properties of polar functionalized polyolefins and their composites will eventually achieve commercialization of nickel-catalyzed production of polyolefins and composites.

Fouling resistance study in industrial tubular reactor for low density polyethylene production

Fouling is the development and buildup of unwelcome elements on the surface of processing equipment. Fouling study in LDPE production via tubular reactor is very important with regard to safety, economic and productivity. However, the fouling study in LDPE production was rarely reported in the literature due to complex chemical reaction and reactor configuration. In this work, the overall heat transfer coefficient (U) computed by component’s physical properties (method 1) and log mean temperature difference of plant data (method 2) were studied. The U obtained from the correlation method is larger than plant data. The U variations obtained from industrial data were employed in this work to determine the maximum reactor fouling resistance Rfmax. The Rf reaction zone is significantly lesser than the Rf cooling zone.The fouling investigation utilized fouling resistance (Rf) as the fouling measurement. Rf is signified by the alteration of U dynamically over ten hours. The Rfmax achieved is 50.0 cm2.s.K/cal. The Rfmax value obtained were then applied as a constraint for the optimization study.

Emulsion Polymerization Strategy for Heterogenization of Olefin Polymerization Catalysts

Heterogenization of homogeneous metal catalysts on solid supports has been widely studied for product morphology control in ethylene polymerization. In this contribution, an emulsion polymerization strategy was introduced to achieve heterogenization of various imino-based nickel olefin polymerization catalysts. A series of polymeric microspheres were prepared through emulsion copolymerization of vinyl-functionalized imino ligands with comonomers such as styrene or methyl methacrylate. The corresponding heterogeneous nickel catalysts demonstrated superior properties in ethylene polymerization and copolymerization with methyl 10-undecylenate. Their catalytic properties can be controlled by tuning the comonomer type, composition, and particle size. Most importantly, this strategy can achieve product morphology control and avoid reactor fouling while generating polyethylene products with minimum inorganic contamination. In addition, the introduction of polymer microspheres can improve the mechanical properties and surface properties of polyolefin products.

Self-seeded coprecipitation flow synthesis of iron oxide nanoparticles via triphasic reactor platform: Optimising heating performance under alternating magnetic fields

Liquid-liquid segmentation is a common method to prevent reactor fouling when synthesising nanoparticles in flow, despite limiting synthetic protocols to single reagent addition steps before segmentation. This work demonstrates how a modular triphasic (gas–liquid–liquid) flow reactor platform overcomes this limitation, facilitating a continuous and fouling-free four-step co-precipitation flow synthesis of iron oxide nanoparticles (IONPs) for magnetically induced hyperthermia cancer treatment (MHCT). For this and other biomedical applications water-based IONP syntheses such as co-precipitation are favoured, but producing IONPs > 10 nm as needed for MHCT remains challenging. To overcome this size barrier for co-precipitation syntheses, a seeded growth co-precipitation strategy was employed here for the first time. After demonstrating the synthesis in batch, a triphasic flow reactor was developed to translate the multistep batch protocol into flow. Nitrogen gas was used to space the liquid–liquid segmented slugs evenly, enabling self-synchronised solution addition into the aqueous slugs dispersed in heptane. Three additions of the iron precursor solution followed by citric acid solution addition formed the seeds, grew them to larger IONPs and stabilised them. The flow platform was used for screening of the synthetic parameters to optimise the IONP heating performance in an alternating magnetic field, hence investigating their potential as MHCT heating agents. The optimal reactor settings identified made it possible to continuously synthesise 0.46 gIONPs/h colloidally stable IONPs in the aqueous phase of size ∼15 nm. The fouling-free flow reactor operated at short overall residence times (<5 min) using just ferric and ferrous salts, sodium carbonate and citric acid. The IONPs exhibited high heating performance, with an intrinsic loss power up to 3.76 nH m2 kgFe-1.

Activation of a Palladium-Based Catalyst by Hexafluoroisopropanol for Polyketone Synthesis via Homogeneous Solution Polymerization

Polyketone (PK) is a promising material because of its superior qualities as an engineering plastic and the direct use of CO. It is typically produced using slurry polymerization techniques, which cause reactor fouling and low bulk density product. Here, solution polymerization of CO/ethene/propene with high-molecular-weight products (240.3 kDa) and high catalytic activity (36.1 kg PK·g–1 Pd·h–1) was achieved utilizing a mixture of hexafluoroisopropanol (HFIP) and methanol. Both the activity and Mw are an order of magnitude higher than those reported in the literature. HFIP was able to activate the palladium-based precatalyst without using any strong acid. The 31P NMR, single-crystal X-ray diffraction, and density functional theory analysis prove that HFIP decreased the coordination between palladium and the acetate ligands of the precatalyst without the disassociation of the acetate. Furthermore, the active centers in the HFIP system were more stable than that in the catalytic system with strong acid.

Unprecedented Mechanical Properties in Linear UHMWPE Using a Heterogeneous Catalytic System

Several homogeneous postmetallocene complexes are known to produce weakly entangled ultrahigh-molecular-weight polyethylene (disentangled UHMWPE) under controlled polymerization conditions leading to ultimate mechanical properties. Major challenges in using a homogeneous catalyst system exist such as reactor fouling and uncontrolled polymer morphology, which could be addressed by heterogenization of the single-site complex. In such a scenario, a heterogeneous catalytic system that can synthesize ultrahigh-molecular-weight polyethylene with a reduced number of entanglements, to an extent that the mechanical properties are equivalent to those obtained using a postmetallocene catalyst in a homogeneous condition, remains a challenge. Herein, a magnesium chloride based in situ formed activator/support, MgClx/EtnAly(2-ethyl-1-hexoxide)z, is employed with a highly active bis[N-(3-tert-butylsalicylidene)pentafluoroanilinato] titanium(IV) dichloride (Cat. 1) for the synthesis of ultrahigh-molecular-weight polyethylene with a reduced number of entanglements. A novel route is adopted to make a nano-support that allows tailoring of the entangled state and control over the resultant morphology without reactor fouling and wall sheeting, thus providing the feasibility of pursuing the polymerization via a continuous process. The synthesized nascent polymer shows the formation of single crystals of linear UHMWPE, identifying the fold surface and crystal thickness and suggesting a low entangled state. The topological differences with the commercial entangled sample are identified by chain diffusion from the noncrystalline to crystalline region via solid-state NMR, following melting kinetics via DSC, and transformation of the nonequilibrium melt into the equilibrium state via rheology. Thus, the obtained disentangled crystals can be compressed in the solid state, without melting, to an extent that the macroscopic forces can be transferred to the molecular level. This allows the desired chain orientation for securing the ultimate tensile modulus (>200 N/tex) and tensile strength (>4.0 N/tex) in the synthesized low entangled linear polyethylene having a weight average molar mass exceeding a million grams per mole. These mechanical properties are equivalent to those perceived using a homogeneous catalytic system and are the first of their kind reported in a polymer synthesized using a heterogeneous catalytic system.

Catalytic conversion of model compounds of plastic pyrolysis oil over ZSM-5

Mechanistic investigation of the catalytic conversion of model compounds for plastic pyrolysis oil (1-octene, octadiene, octane, and toluene) over ZSM-5 in a fixed-bed reactor was studied. 1-Octene breaks down into smaller olefins, which undergo further cracking, oligomerization, cyclization, and hydrogen transfer to eventually produce benzene, toluene, xylene (BTX), coke, and hydrogen. The effect of contact time on 1-octene conversion was further investigated and compared with thermodynamics analyses to elucidate the reaction network. Under the reaction conditions (500 °C, 1 atm), octadiene undergoes thermal coking, significantly contributing to reactor fouling. The products from octane cracking are similar to the products from 1-octene conversion whereas toluene undergoes disproportionation, dealkylation and coking. The analysis of spent catalyst showed long-chain hydrocarbons created by oligomerization reactions filled the pores and covered the surface of the catalyst. When mesoporous ZSM-5 is used instead of conventional, product selectivity is maintained for 70 h in time-on-stream experiments.

On the Elucidation of Polymer Fouling Mechanisms and Ethylene Decomposition in High‐Pressure LDPE Tubular Reactors

AbstractIn high‐pressure free‐radical ethylene polymerization tubular reactors, fouling often occurs due to polymer deposition onto the reactor's wall surface. This results in a decrease in the overall heat transfer coefficient. Note that a high‐pressure tubular reactor must be capable of removing about half of the generated polymerization heat to the cooling water flowing into the reactor's jackets. Therefore, reactor fouling can have serious implications including decrease of heat removal rate and monomer conversion, increase in the overall initiator(s) consumption, change of polymer quality, decline of reactor's safe operation, and significant economic losses due to lower plant productivity and longer reactor maintenance periods. In rare cases, the loss of reactor's heat removal capacity may result in the appearance of local hot spots that eventually can trigger ethylene decomposition. In the present review paper, the fundamental physical and chemical phenomena regarding polymer fouling and ethylene decomposition in high‐pressure low density polyethylene (LDPE) reactors are critically discussed. The effects of shear rate, polymer molecular weight, and wall surface energy on polymer adsorption and desorption are analyzed. Moreover, the effect of characteristic initiator decomposition and micromixing times and process conditions on initiator dispersion, polymer fouling, and ethylene decomposition are assessed.

SiO2‐Supported Ni(II) and Fe(II) Catalysts Bearing Sodium‐Sulfonate Group for Olefin Polymerization†

Comprehensive SummaryHeterogeneous catalysts have been dominant for industrial polyolefin production, offering many distinct advantages, such as controlling the morphology of the polymer and preventing reactor fouling. In this contribution, we designed several types of imine ligands bearing sodium‐sulfonate ionic groups and the corresponding nickel/iron catalysts. These catalysts could be immobilized on SiO2 with strong affinity and high catalyst loadings. The SiO2‐supported catalysts behaved better than their homogeneous counterparts during ethylene polymerization with extremely high activity (2.6 × 104 kg·mol−1·h−1) and high thermal stability. In addition, the supported nickel catalysts generated free‐flowing polyethylene with high molecular weight (Mn up to 2.65 × 103 kg·mol–1) and excellent morphology control, indicating no reactor fouling due to the leaching of catalyst. Moreover, for copolymerization, immobilized nickel catalysts showed a higher tolerance of polar monomers, and the efficient copolymerization of ethylene with undecylenic acid was achieved with high activity (450 kg·mol−1·h−1) and a high incorporation ratio (up to 12.3%).

Optimization of Slurry Loop Reactors by Understanding the Complex Mesoscale Structure of Liquid–Solid Flow

Slurry loop reactors have been extensively used in chemical industry, for example, ethylene copolymerization. A classical engineering problem is the timely removal of reaction heat which would otherwise cause particle swelling and aggregation, and thus reactor fouling, operation instability, or even blockage, imposing a high safety risk in production. Lack of knowledge on the mesoscale information of particle swelling and aggregation poses great challenge on the prediction of the macroscale behavior. A swelling-dependent two-fluid model was developed and applied for reactor optimization in this work to account for the evolution of mesoscale structures. The simulation resolves the particle aggregation and plug accumulation in the upstream of the pump and the upper horizontal pipe, revealing the fundamental of reactor blockage. The mesoscale structure, when developing to a certain extent, can cause a sharp increase of pump power consumption. This structure can be characterized by the growth and threshold of the plug volume. Based on this mesoscale understanding, a reactor optimization scheme was heuristically proposed to minimize or eliminate the plug regions by employing two pumps and two cycles.

Nickel catalysts for the preparation of functionalized polyolefin materials

<p indent="0mm">As the largest class of thermoplastic polymers, polyolefin materials have wide applications and huge annual production. The introduction of even a small amount of polar functional groups into the polyolefins could excise great control over important material properties. As the most direct and economic strategy, the coordination-insertion copolymerization of olefin with polar-functionalized monomers can enable molecular-level control of the copolymer microstructures. This represents one of the biggest challenges in this field, and is recognized as one of the last “holy grails” in this field. Late transition metal catalysts have attracted much attention in the direct copolymerization of olefin with polar monomers for the synthesis of functionalized polyolefin materials. In this field, research efforts have been devoted to palladium catalyst systems, which have been investigated thoroughly in the past few decades. In contrast, the utilization of less-expensive and earth-abundant nickel catalysts has received much less attention and is much more challenging, mainly due to the higher oxophilicity and lower polar group tolerance of the nickel metal versus palladium metal. However, the field of nickel-catalyzed copolymerization of olefins with polar monomers has witnessed rapid developments in recent years. This perspective mainly focuses on the work concerning nickel-catalyzed olefin copolymerization and summarizes the following subjects: First, we summarize the design and development of different nickel catalyst systems for the copolymerization of olefins with polar monomers, including α-diimine nickel, salicylaldimine nickel, various [N,O] nickel, phosphine-sulfonate nickel, phosphine-phenolate nickel and [P,C/N/P=O] nickel systems. We focus on their ligand design and catalytic properties (activity, copolymer molecular weight, comonomer incorporation, etc.) in these copolymerization reactions. In addition to the above-mentioned homogeneous nickel systems, we also summarize various heterogeneous nickel catalysts for the copolymerization of ethylene with polar monomers. Heterogeneous catalysts offer many distinct advantages, such as controlling the morphology of the copolymer product and preventing reactor fouling in the copolymerization processes. Second, we discuss some of the unique properties of the polar-functionalized polyolefin materials bearing various polar functional groups. These polar-functionalized polyolefin materials show great mechanical properties along with excellent antioxidant, self-healing, flame retardant properties, etc. Notably, there have been very few studies on the properties of functionalized polyolefins prepared by nickel catalysts, due to the inferior properties of nickel catalysts in the copolymerization reactions. Considering the recent developments of various high-performance nickel catalyst systems, more efforts should be directed towards this research field. Finally, we discuss problems and challenges in this field, and propose some promising research directions: (1) The design of new nickel catalysts with further improved catalytic properties, with special focus on expanding the scope of applicable olefins and polar monomers (ethylene, propylene, carbon monoxide, various polar monomers); (2) the development of new heterogeneous nickel catalysts and new supporting methods that could achieve product morphology control and enable continuous polymerization process by preventing reactor fouling; (3) the systematic studies on the properties of functionalized polyolefin materials with the aim of developing high-end applications. Although the research history of nickel-catalyzed copolymerization to access functionalized polyolefin materials is relatively short, we believe that it will become an important leading direction in the field of polyolefins.

Effects of fluid film properties on fouling in biphasic flow systems

Flow chemistry has the potential to enhance the large-scale accessibility of precision-engineered nanomaterials. While reactor fouling presented a major challenge in precision control, the liquid–liquid segmented flow method has been demonstrated to reduce or even eliminate it. However, guidelines for properly selecting materials and designing parameters in such systems are currently lacking. For these reasons, the present study investigated two biphasic flow systems for continuous gold nanoparticle (AuNP) synthesis. Visual observations showed no evidence of fouling in the silicone oil–water flow system, but some localized fouling was observed in the heptane-water flow system. The results indicated the silicone oil–water system gave a 50% lower polydispersity index and a 25% higher reaction yield due to fouling mitigation. We investigated two important factors of the continuous phase for fouling reduction: liquid film continuity and film thickness. Film continuity was evaluated by temperature-controlled contact angle measurements and the film dewetting velocity; And film thickness was estimated using two different mathematical models. It was concluded that the formation of a continuous oil film of thickness higher than the maximum surface asperities, as was the case only for the silicone oil–water flow system, is critical to eliminate fouling in continuous AuNP synthesis.

Iminopyridyl ligands bearing polyethylene glycol unit for nickel catalyzed ethylene polymerization

Influence of polyethylene glycol unit on nickel catalyzed ethylene polymerization have attracted increasing interest. The Lewis basic oxygen atoms on polyethylene glycol group can form interactions with Lewis acidic metal additives. In this contribution, a series of iminopyridyl ligands (L-O1, L-O2 and L-O3) bearing polyethylene glycol units and corresponding nickel complexes (Ni-O1, Ni-O2 and Ni-O3) were designed, synthesized and characterized. By the activation of alkylaluminium cocatalysts, the nickel complexes and their corresponding MgCl2-supported nickel precatalysts (Ni-O1-Mg, Ni-O2-Mg and Ni-O3-Mg) were investigated in catalytic homogeneous and heterogeneous ethylene polymerization, respectively. The molecular weight of products increased with the number of oxygen atoms on polyethylene glycol unit increasing. The introduction of the MgCl2 support resulted in much higher molecular weights and much lower branched densities of polyethylenes than those of products generated in the homogeneous polymerizations. The polymers generated in heterogeneous polymerizations have excellent polymer powder morphology to prevent reactor fouling, facilitating potential industrial applications.

AL – Mansuriya gas fields associated liquid and its role to increase the potential capacity of gasoline fuel in Daura oil refinery

Hydrotreating processing is commonly used to remove platforming catalyst poisons from straight run or cracked naphthas prior to charging to the platforming Process unit. It can be seen that the primary function of the naphtha Hydrotreating Process can be characterized as a “Clean up” Operation. The catalyst used in the Naphtha Hydrotreating Process is composed of an alumina base impregnated with compounds of cobalt or nickel and molybdenum. The catalyst is insensitive to most poisons which affect dehydrogenation reactions. A relatively high percentage of carbon on the catalyst does not materially affect its sensitivity or selectivity. Volumetric recoveries of products depend on the sulfur and olefin contents [1].&#x0D; The Naphtha Hydrotreating Process is a catalytic refining process employing a selected catalyst and a hydrogen-rich gas stream to decompose organic sulfur, oxygen and nitrogen compounds contained in hydrocarbon fractions. In addition, hydrotreating removes organo-metallic compounds and saturates olefinic compounds.&#x0D; Organo-metallic compounds, notably arsenic and lead compounds, are known to be permanent poisons to platinum catalysts. "The complete removal of these materials by Hydrotreating processing gives longer catalyst life in the platforming unit.&#x0D; Sulfur, above a critical level, is a temporary poison to platforming catalysts and causes an unfavorable change in the product distribution. Organic nitrogen is also a temporary poison to platforming catalyst. It is an extremely potent one, however, and relatively small amounts of nitrogen compounds in the Platformer feed can cause large deactivation effects, as well as the deposition of ammonium chloride salts in the platforming unit cold sections.&#x0D; Oxygen compounds are detrimental to the operation of a Platformer. Any oxygen compounds which are not removed in the hydrotreater will be converted to water in the platforming unit, thus affecting the water/ chloride balance of the platforming catalyst. Large amounts of olefins contribute to increase coking of the platforming catalyst. Also, olefins can poly­merize at platforming operating conditions which can result in exchanger and reactor fouling.&#x0D; The Naphtha Hydrotreating Process makes a major contribution to the ease of operation and economy of platforming. Much greater flexibility is afforded in choice of allowable charge stocks to the platforming unit. Because this unit protects the platforming catalyst, it is important to maintain consistently good operation in the Hydrotreating Unit.&#x0D; In addition to treating naphtha for Platformer feed, naphthas produced from thermal cracking processes, such as delayed coking and visbreaking, are usually high in olefinic content and other contaminants, and may not be stable in storage. These naphthas may be hydrotreated to stabilize the olefins and to remove organic or metallic contaminants, thus providing a marketable product.