New Developments

diagram: benzene to phenol

Nitrous Oxide

One reaction that is being developed on a commercial scale is the AlphOx process developed by Solutia and the Boreskov Institute of Catalysis in Moscow. This has been running as a pilot plant since 1996 and may come on stream commercially in the next few years.

This reaction uses nitrous oxide (N2O) as the oxidising agent, which reacts with Benzene in the vapour phase to give phenol and nitrogen. The process uses metal modified zeolite catalysts, such as V2O5/ MoO5/ ZSM-5 and Fe2O3/ MoO3/ ZSM-5, which transfer atomic oxygen, from the decomposition of the N2O on their surface, to benzene. The active catalyst appears to be the metal species occupying the pores in the zeolite structure.

This reaction is of particular value to Solutia, as they are a major producer of hexanedioic acid (adipic acid), used in nylon production, and N2O is produced is a by-product. This cannot simply be released into the atmosphere, as it is a pollutant under strict control, so its use to make phenol removes the need to treat it as waste, and generates a valuable product.

Biomass

Though pure benzene and phenol will continue to be petrochemical products for the foreseeable future, one area where the use of biomass feedstock is already making an important contribution is in the production of phenol-based resins used in wood panel products like plywood, medium density fibreboard (MDF) and laminates.

Heating the biomass, mainly softwood waste, produces a pyrolysis oil which, although containing a mixture of many phenol-based materials, can be used to make phenol-methanal resins without requiring further purification, as it can still form the cross-links. It is generally used in a 50-50 mixture with pure phenol.

The lack of a purification stage reduces the energy needed, and the gases and charcoal also produced can be used as fuel for heating the biomass. Cost savings can be as high as 25%.
Research aimed at increasing the proportion of biomass feedstock to 100% for this particular application is being undertaken.

Microreactor Technology

In future, many chemicals including phenol may be produced in relatively small reactors about the size of a large desktop.

One potential micro-reactor to produce phenol involves the use of a small diameter (2 mm), porous tube of alumina coated with a layer of palladium metal. A mixture of benzene and oxygen is fed through the tube, and hydrogen gas is passed over the tube.
diagram: micro-reactor for producing phenol by oxidation of benzene

The tube is heated to 150 - 250°C. Hydrogen permeates though the alumina tube, and is converted to atomic hydrogen by the palladium catalyst. The hydrogen atoms react with oxygen gas, releasing oxygen atoms, which in turn react with the benzene forming benzene epoxide. This isomerises to phenol.

diagram: benzene to phenol
The boiling points of phenol (182°C) and benzene (80°C) mean that phenol is easily separated from unreacted benzene, and the final liquid phenol is in a highly pure form.

Researchers claim that this method saves on capital cost, reduces energy use, reduces waste, and can easily be scaled up by adding more tubes, effectively using a modular approach. One single micro-reactor could produce up to 100,000 tonnes per year. The technology can also be applied to the manufacture of other materials.

 

 

 

Oxidation of Benzene

The direct oxidation of benzene can be achieved using several different oxidising agents, but none of these have yet proved economically viable on a large scale. Considerable research is going on into finding catalysts, which might allow the direct oxidation of benzene to phenol.

 

 

 

 

 

 

 

 

 

photo: forestry work

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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