CHEMICAL ENGINEERS have found they can use the Fischer-Tropsch process to produce alcohols and aldehydes, in a breakthrough they claim could save energy and costs for industry.
The conventional route for producing alcohols and aldehydes begins with various steps of crude oil processing and refinement to form olefins. These are then reacted with carbon monoxide and hydrogen at high pressures and temperatures between 40–200°C in what is known as hydroformylation – or the oxo process – to produce aldehydes. These are used in resins and fragrances or as intermediates for the synthesis of a variety of chemical compounds. The majority of aldehydes from hydroformylation are hydrogenated into alcohols for use as fuel additives, plasticisers, lubricants and detergents.
A team of researchers at Washington State University, US, have developed a catalyst made of cobalt, manganese and potassium that they claim can build alcohols and aldehydes from hydrogen and carbon monoxide in a much simpler one-step Fischer-Tropsch process.
“The catalyst preparation is really important,” says research team leader Norbert Kruse. “And the chemistry aspect is wonderful: starting with only two gases, we end up with a technically useful liquid that you usually obtain only after a number of steps in petrochemical refining. I think there is a good chance for industrial implementation.”
The team says the results of its research opens the door for designing a flexible “one-pot heterogeneous process” that allows them to selectively produce aldehydes or alcohols by varying the ratios of hydrogen and carbon monoxide at a constant total pressure of 40 bar.
“This has rarely been done so far,” said Kruse. “It was most intriguing to see how easily you can influence the relative amounts of chemicals you produce without changing the length of the hydrocarbon scaffold.”
High-pressure catalytic tests were carried out using grammes of reactants in a fixed-bed plug-flow reactor at 200°C.
Kruse tells The Chemical Engineer that shifting from traditional homogenous catalysis to heterogenous catalysis will save costs by eliminating the need to separate the catalyst from the reactants and products.
“However, while our synthesis route is simple and straightforward, aldehydes and alcohols are produced with varying hydrocarbon chain length which have to be sorted by applying common methods of separation – unit operations. It is difficult to make a quantitative estimation of the costs and savings of our technology as compared to hydroformylation at this point in time.”
While the selectivity has been tuned to over 95% for either product, it is not the only relevant process parameter.
“In most cases, including ours, selectivity and activity run counter [to one another] when varying the temperature,” says Kruse. “So, one has to make a compromise between selectivity and reasonable activity. Having said this, I would assess our results as impressive from the chemical point of view, and close to industrially-relevant from the engineering point of view.”
The team is now working to increase yields and the lifetime of the catalysts.
The researchers have patented the method and started working with industry partners to commercialise their method.
Nature Communications: doi.org/brpg
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