Zeolites as Catalyst Supports for Hydrocarbon Oxidation Reactions: Comparison
Please note this is a comparison between versions V3 by Lindsay Dong and V2 by Lindsay Dong.

Catalytic oxidation is a key technology for the conversion of petroleum-based feedstocks into useful chemicals (e.g., adipic acid, caprolactam, glycols, acrylates, and vinyl acetate) since this chemical transformation is always involved in synthesis processes. Zeolites are microporous, crystalline aluminosilicate materials known since 1756 when the stilbite structure was identified by the Swedish mineralogist Crönstedt. Zeolites and other related porous materials can be supports for organometallic or metallic active species. These materials are the most studied supports due to their combined properties of mechanical and thermal stability that allows it an easy regeneration and recycling. 

  • hydrocarbon oxidation reactions
  • zeolites
  • hierarchical zeolites
  • immobilized catalyst

1. Industrial Hydrocarbon Oxidation Reactions

Catalytic oxidation reactions are of high industrial relevance since many important commodities have synthesis paths involving oxidation. To understand their relevance, it can just refer to adipic acid, with a global production of over 4 million tons and expect to exceed a $8 billion USD global market by 2025 [1].
When addressing hydrocarbon oxidation reactions, there are several significant industrial applications. The direct oxidation of alkanes is an attractive alternative to oxidation via olefins; however, only two industrial processes have been implemented, and other alkanes oxidations are only at the research or pilot plant status. One of these reactions is the production of maleic anhydride from n-butane (Figure 1).
Figure 1. Maleic anhydride synthesis from n-butane oxidation.
This process uses supported (VO)2P2O7 as heterogenous catalyst and achieves high weight yields (ca. 95%) replacing a previous method with benzene. In both methods, butane (or benzene) is fed into a stream of hot air, and the mixture passes through a catalyst bed at high temperature. Fixed, fluidized, and transport bed reactors technologies have been implemented in different industrial plants to address different technical difficulties [2].
Another example of alkane oxidation but in the liquid phase with homogeneous catalysis is the oxidation of cyclohexane into a mixture of cyclohexanol and cyclohexanone (also known as KA oil), which are intermediates in the manufacture of nylon-6 and nylon-6,6. KA oil is mainly obtained through the oxidation of cyclohexane using air or peroxide as the oxidant agent. In the present industrial conditions, liquid phase oxidation of cyclohexane is achieved at about 165 °C and O2 pressures of 8–15 bar in the presence of manganese or cobalt naphthenates as catalysts (Figure 2). To avoid oxidative side reactions, a short retention time is used to assure 80–85% selectivity; thus, the conversion is limited to 10–11% per cycle, requiring separation and refeeding of the unconverted cyclohexane. Additionally, the currently used homogeneous catalysts are difficult to separate from the reaction media, leading to serious environmental pollution. [3]


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