No abstract

The direct conversion of crude oil to light olefins is considered one the cheapest and most reliable sources of petrochemical primary feedstocks. Unlike in the past when refineries operated to produce mainly transportation fuels, such as gasoline and diesel, many refineries worldwide are considering tandem production of both fuels and chemicals (particularly, light olefins). To achieve this, refining technology, process optimization, and catalyst formulations may have to be reconfigured. Developing active and selective catalysts for crude oil cracking that fit into the current refinery system will go a long way in saving cost and time. In this review, catalyst formulations for the conversion of crude oil to light olefins have been discussed under the classifications: zeolite components, tuning of zeolite porosity, and matrix materials. USY has been the common zeolite that is used in the cracking of hydrocarbons to gasoline fractions, and ZSM-5 has the desired shape selectivity for cracking of paraffins in gasoline fractions to light olefins. At the same time, its low hydrogen transfer activity does not consume a large amount of generated light olefin, resulting in improvement of light olefin production. Various modifications of ZSM-5 composition have shown improvement in the light olefin yield. The wide range of hydrocarbons in crude oil makes pore size tuning of the zeolite especially important. Matrix materials generally increase the attrition resistance, hydrothermal and chemical stability, metal entrapment ability, coke resistivity, and fluidizable catalyst formation. However, they can also affect (positively or negatively) catalyst arrangement and active site properties, which makes careful selection very important.

Tetramerization of ethylene by chromium catalysts stabilized with functionalized N -aryl phosphineamine ligands C 6 H 4 ( m -CF 3 )N(PPh 2 ) 2 ( 1 ), C 6 H 4 ( p -CF 3 )N(PPh 2 ) 2 ( 2 ), C 6 H 4 ( o -CF 3 )N=PPh 2 -PPh 2 ( 3 ), and C 6 H 3 (3,5-bis(CF 3 ))N(PPh 2 ) 2 ( 4 ) was evaluated. The parameter optimization includes temperature, co-catalyst, and solvent. Upon activation with MMAO-3A, the new catalyst system especially with m -functional PNP ligand ( 1 ) exhibited high 1-octene selectivity and productivity while giving minimum undesirable polyethylene and C 10 + olefin by-products. Using PhCl as a solvent at 75 °C led to a remarkable α-olefin (1-C 6 + 1-C 8 ) selectivity (>90 wt %) at a reaction rate of 2000 kg·g Cr –1 ·h –1 . Under identical conditions, analogous PNP ligands bearing −CH 3 , −Et, and −Cl functional moieties at the meta position of the N -phenyl ring displayed significantly lower reactivity. The catalyst with p -functional ligand ( 2 ) exhibited lower activity and comparable selectivities, while the Cr/PPN (with ligand 3 ) system gave no noticeable reactivity. The molecular structure of the precatalyst ( 1 -Cr), exhibiting a monomeric structural feature, was elucidated with the aid of single-crystal X-ray diffraction study.

Dissipative particle dynamic (DPD) simulations were performed to study the interfacial properties such as interfacial tension, area compressibility, stress profile, and conformation of surfactant at the water/octane interface. Experimental studies of the interfacial tension (IFT) in water/octane/surfactant systems were conducted using the pendant drop method. The IFT results of DPD agree semiquantitatively with experimental measurements. Three surfactants with different head groups and same alkyl tail, sodium dodecyl sulfate (SDS), dodecyltrimethyl­ammonium bromide (DTAB), and dodecyl­dimethylamine oxide (DDAO), were selected to study the effect of headgroup structure. The efficiency of surfactants from DPD follows the same order of experimental results DDAO > SDS > DTAB. The DDAO surfactant is more ordered at the interface with a high area compressibility which indicates more highly packed monolayer. The effect of salts and temperature at water/octane/SDS surfactant at the interface were investigated. The addition of salts in the systems stretched and ordered the SDS surfactant more at the interface; as a result, the area compressibility increased. Temperature has little effect on the orientation of the SDS surfactant at the interface, and the area compressibility decreased with increasing temperature.