As an attractive and environmentally friendly process for propylene oxide (PO) production, direct epoxidation of propylene (DEP) with molecular oxygen catalyzed by metal-based catalysts such as Ag and Cu has drawn much attention, but remains one of the biggest challenges in chemistry. In this work, the crucial competitive reactions of propylene α-H stripping (AHS) versus the oxametallacycle formation (OMMP formation) using adsorbed atomic oxygen (O*) or adsorbed molecular oxygen (O*) as an oxidant are extensively compared on IB group metal surfaces (Cu, Ag and Au) with varied electronic and structural effects in order to explore the possibility to enhance the PO selectivity by virtue of first-principles calculations. The determining factor for the PO selectivity is quantitatively revealed: it is found that with atomic O*, the AHS pathway was preferred, indicating the reason for low PO selectivity with current catalysts. By contrast, the undissociated molecular O* species is found to prefer to electrophilically attack the C[double bond, length as m-dash]C double bond of propylene and form a special oxametallacycle intermediate (OOMMP) rather than nucleophilically abstracting the α-H. This OOMMP can readily cleave the O-O bond and transform into OMMP. These results demonstrate that the presence of undissociated O* can efficiently promote the PO selectivity. Furthermore, the merit of such a molecular O* mechanism can be rationalized by our quantitative barrier decomposition analyses, which reveal that the lower hydrogen affinity (ΔE) of the O* species dominantly contributes to the limited AHS reaction, and boosts the OMMP selectivity. Therefore, ΔE can be applied as a selectivity descriptor. An efficient strategy to promote PO formation is presented. The insight obtained could pave the way for further development of catalysts for propylene epoxidation.
A novel dinuclear copper complex with tetraglycol aldehyde-phenylalanine Schiff base has been synthesized. It was characterized and formulated as [Cu 2 L(NO 3 )]NO 3 by elemental analysis, magnetic susceptibility, TG-DTA, IR, EPR and 1 H NMR spectra. The obtained complex can be used as a good catalyst for the polymerization of methyl methacrylate (MMA). The optimum polymerization conditions are: MMA/catalyst = 500 (molar ratio); [catalyst] = 7.5×10 −3 mol·L −1 ; dioxane as solvent; 80 ; 6 ℃ h. Polymethyl methacrylate (PMMA) with 80% conversion, 7.2×10 5 viscosity-average molecular weight and 60.5% syndiotacticity was obtained. This complex has also been shown to play an important role in scavenging 2 O i .
The precipitation or block of asphalts, asphaltene and other organics in the porous media near the wellbole will reduce permeability due to change in temperature, pressure and compositions of reservoir oil. Injection of organic aromatic solvents and soaking is one feasible method to remove the precipitates. The objects of this paper are to confect economical and efficient solvents and optimize injected rate, volume and soak time of solvent. To obtain the objects, core flooding experiments by solvents are conducted to select optimum solvents and a simulator to remove the formation damages caused by organic deposition by soaking of aromatic solvents is developed. The influences of different injected rates, volume and soak time of solvent are simulated to improve the permeability of the damaged region. And the permeability is also predicted after soak. A project to remove organic formation damage near the wellbole by injection aromatic solvents started Nov, 1998 at an offshore oil field in China. And the production of the first well increased from 90t/d to 270t/d after injection solvent U-01 selected by core flooding experiments. The simulated results coincide well with the data from the oilfield. Introduction Asphaltenes have been defined as the n-heptane insoluble, but aromatic soluble fraction of crude oil with a condense F structure including significant N/S/O and alkyl groups1,2. And asphalts have been defined as the combination of asphaltenes and resins1. Under normal conditions in the reservoirs, asphaltenes exist in dispersion by the resins peptization. Any changes in temperature, pressure and composition can result in asphaltene precipitation and being deposited. During crude oil production, asphaltenes and asphalts preci-pitation may occur in the wellbore and the vicinity of the wellbore due to changes in temperature, pressure and composition. The problems caused by asphaltene and asphalt precipitation in the tube or wellbore can be easily eliminated by physical or chemical methods. However, the precipitation and deposition of asphaltenes and other organics in the sand will cause formation damage and reduce effective hydrocarbon mobility by a) blocking the pore throats, b) altering the formation wettability from water-wet to oil-wet due to adsorbing onto the rock surfaces and c) increasing hydrocarbon viscosity by nucleating water in oil emulsions3. To remove the asphaltene deposition problems occurred in the formation is rather difficult than those in the tube or wellbore for the paths of hydrocarbon flow in the formation are microporous media compacted and cemented by various minerals with different natures. In general, formation damage caused by asphaltene precipitation and operations such as drilling, completion, workover and stimulation, first occurs in the vicinity of wellbore. However the formation condition near the wellbore is very important where pressure drop of the oilfield mainly depletes. Although the drainage radius may be several hundreds of feet, the effective permeability close to the wellbore has a disproportionate effect on well productivity. According to Roland F. Krueger's study4 for the effect of permeability discontinuity on production performance near wellbore, if the permeability of the formation rock near the wellbore has been damaged to 20% of its original value by some operation to depth of 0.6m, a well treatment that restores the original permeability will increase well productivity by about 100%. On the other hand, if the region doesn't suffer from formation damage, a well treatment that increases the normalized permeability of this undamaged zone by 80% will only a minor effect (about 10%) on the well productivity. Thus, a removal of formation damage in the vicinity of wellbore has significance for improving well productivity. This is so-called elimination of "bottom efficiency" for the wells with formation damage during the production in oilfields.
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