Oxidative cracking of n-Hexane : a catalytic pathway to olefins

Steam cracking, the major, current existing route for light olefin production, is the most energy consuming process in the chemical industry. The need for an energy efficient processes, urged substantial research work for the development of new catalytic technologies for light olefin production. Steam cracking maximizes ethylene formation and propylene is produced only as a secondary product. The faster increase in demand of propylene than that of ethylene makes steam cracking a less attractive route for the production of propylene. Thus, catalytic pathways that provide for more propylene formation are essential. The present thesis investigates catalytic pathways for n‐hexane cracking, as a model\ud compound of naphtha, in the presence of oxygen. Compared to steam cracking, this work aims towards achieving; (i) lower cracking temperatures making the overall process less energy consuming and (ii) higher selectivities to both propylene and butylenes

Promoting li/mgo catalyst with molybdenum oxide for oxidative conversion of n-hexane

In this work, molybdena-promoted Li/MgO is studied as a catalyst for the oxidative conversion of n-hexane. The structure of the catalysts is investigated with X-Ray Diffraction (XRD) and Raman spectroscopy. The MoO3/Li/MgO catalyst contains three types of molybdena-containing species, the presence of which depend on molybdena loading. At low Mo/Li ratios (i) isolated dispersed [MoO4]2− anionic species are observed. At high Mo/Li ratios, the formation of crystalline lithium molybdate phases such as (ii) monomeric Li2MoO4 and tentatively (iii) polymeric Li2Mo4O13 are concluded. The presence of these lithium molybdates diminishes the formation of Li2CO3 in the catalyst. Subsequently, the catalyst maintains high surface area and stability with time-on-stream during oxidative conversion. Molybdena loading as low as 0.5 wt % is sufficient to induce these improvements, maintaining the non-redox characteristics of the catalyst, whereas higher loadings enhance deep oxidation and oxidative dehydrogenation reactions. Promoting a Li/MgO catalyst with 0.5 wt % MoO3 is thus efficient for selective conversion of n-hexane to alkenes, giving alkene yield up to 24% as well as good stability

Catalytic Oxidative Cracking of Light Alkanes to Alkenes

A review on the catalytic oxidative cracking of light alkanes to alkenes is presented as an alternative route to steam cracking for production of alkenes. Catalytic oxidative cracking is a combination of heterogeneous and homogeneous reactions; the reaction is initiated on the catalyst surface followed by thermal gas phase cracking. The review focuses on the catalytic generation of alkyl radicals at moderate temperatures (550–650 °C) using the Li/MgO system. Comparison with other catalyst systems such as Li/Y2O3, Au/La2O3, Au-SCZ, BiOCl, B2O3/Al2O3, Co-N/Al2O3 and Pt/Al2O3 monoliths is included. Gold supported on sulfated ceria-zirconia catalyst (Au-SCZ) is concluded to be a promising catalyst for further study. In addition to catalytic initiation of radicals, the review discusses alkyl generation using non-equilibrium plasma. Plasma-catalysis in oxidative cracking induces synergy effects and introduces significant improvement in yields of alkenes; however, further understanding of plasma chemistry needs to be elaborated. Minimizing CO2 production and maximizing yields of valuable C2–C4 alkenes remains the bottleneck for the commercialization of oxidative cracking process. Future research should focus on reactor design and on developing optimized reactor-catalyst systems

Catalytic oxidative cracking of hexane as a route to olefins

Catalytic oxidative cracking of naphtha is conceptually an alternative process to steam cracking. The performance of sol–gel synthesized Li/MgO in oxidative cracking of hexane as a model compound of naphtha, has been studied and compared to that of conventionally prepared catalyst. At a temperature as low as 575 °C, Li/MgO shows reasonable hexane conversions (28 mol%) and excellent selectivity to light olefins (60 mol%). It is proposed that hexane activation occurs on the catalyst surface via the Li+O− defect sites, where O− active sites abstract hydrogen from a secondary carbon atom. The formed hexyl radical in gas phase and in the presence of molecular oxygen will then undergo a complex radical chemistry resulting in a product mixture of C1–C5 hydrocarbons (paraffins and olefins) as well as combustion products. Presence of oxygen in the feed is crucial to prevent coking, and to regenerate the catalyst surface through reaction with adsorbed surface hydrogen atoms, thus maintaining catalyst activity. Oxygen also plays a significant role in accelerating radical chemistry in gas phase. Unlike steam cracking, catalytic oxidative cracking results in a relatively higher ratio of high olefins (butylenes + propylene) to ethylene. Thus presence of the catalyst provides a better control over product distribution. Promotion of Li/MgO with MoO3 and Bi2O3 results in considerable improvements in catalyst activity and stability

Antibiotics Contaminated Irrigation Water: An Overview on Its Impact on Edible Crops and Visible Light Active Titania as Potential Photocatalysts for Irrigation Water Treatment

Funding was provided by the WEFRAH (Water-Energy-Food- Health Nexus) initiative at the American University of Beirut (Project number: 25202, Award number: 103763).Sub-therapeutic levels of antibiotics (ABs) are given to animals and poultry to promote growth and reduce disease. In agricultural environments, ABs reach croplands via animal manure used as fertilizer and/or ABs-contaminated water used for irrigation. The continuous discharge of ABs into the ecosystem raises growing concerns on the ABs contamination of edible crops. Tetracyclines (TCs) are among the most widely used ABs around the world. In this review, we discuss the contamination of irrigation water with TCs, its impact on edible crops, and the potential risks of crop contamination with TCs on human health. We propose solar-mediated photocatalytic degradation using Titania (TiO2) photocatalyst as a promising method to remove TCs from irrigation water. The photocatalytic activity of TiO2 can be enhanced by chemical modification to expand its activity under visible light irradiation. Herein, we aim for providing literature-based guidance on developing a visible light–active TiO2-based system to degrade TCs and other ABs in water streams. We include a summary of recent advances on this topic based on three main modification methods of Titania: metal/non-metal/mixed doping, composite formation, and heterojunction construction. Among the investigated photocatalysts, Fe2O3-TiO2/Fe-zeolite and the N-doped TiO2/rGO immobilized composite catalysts were found to be very efficient in the degradation of TCs under visible light irradiation (i.e., 98% degradation within 60 min). Most immobilized TiO2 based composite systems exhibited improved performances and hence we highlight these as efficient, cost effective and ecofriendly photocatalysts for the degradation of TCs in irrigation water.Peer reviewe

Pathway Study on Dielectric Barrier Discharge Plasma Conversion of Hexane

A plasma reactor based on dielectric barrier discharge has been developed for oxidative cracking of hexane to yield olefins at atmospheric pressure. Dissociation of hexane in the presence of oxygen with nonequilibrium plasma state represents complex chemistry, and both conversion and product selectivities differ significantly from the thermodynamic equilibrium state. In order to understand plasma chemistry initiated by electron impact processes, the Boltzmann equation is solved to determine the average electron energy and energy fractions in collision processes. Activation of oxygen in the plasma brings a new route with electron impact dissociation yielding atomic oxygen radicals and initiates oxidative cracking of hexane. Changes in certain features of the dissociation pattern of hexane to yield olefin products with varying parameters such as temperature, oxygen addition, and helium concentration are discusse