One of the most important chemical reactions industrially - for better or for worse - is the production of styrene, which is of course, the chemical precursor for the widely used plastic polystyrene.
Humanity produces about 7 million tons of polystyrene per year. It is widely used in a large number of consumer products, including, but not limited to, insulation for our wonderful modern sustainable energy efficient homes. It is of course, also used in disposable coffee cups and stuff like that.
Polystyrene, because of its high level of chemical stability, actually represents a huge environmental problem, particularly in seawater, but it is not my point to cheer for polystyrene, but simply to make another point about the conversion of the most important energy waste form now facing humanity, carbon dioxide, into a commodity chemical. Such use would serve to lower the propensity for simply dumping it into humanity's favorite waste dump, the planetary atmosphere.
The paper from the primary scientific literature I will discuss tonight is written by Chinese chemists and was published last year. The reference is ChemSusChem 2011, 4, 341 – 345. This journal is devoted to "sustainable chemistry."
The title of the paper is "V2O5/Ce0.6Zr0.4O2-Al2O3 as an Efficient Catalyst for the Oxidative Dehydrogenation of Ethylbenzene with Carbon Dioxide."
Briefly...
...some excerpts from the paper:
Vanadium has been widely used in catalysis because metal oxide- supported vanadia can catalyze many industrially important reactions, such as oxidation reactions.[1, 2] The activity of the supported vanadia is highly dependent on the specific oxide support[1–3] as a result of the so-called strong metal oxide–support effect. Although many researchers have attempted to gain insight into the catalytic mechanism, by using theoretic (sic) calculations and various characterization techniques, it is not yet fully understood.[4] Thus, the design of a high-performance supported vanadia catalyst, especially one with a high degree of stability, is still a challenge. The oxidative dehydrogenation of hydrocarbons (ODH) to alkenes is industrially important for various large-volume synthetic polymers. Because ODH with molecular oxygen as oxidant is a promising solution, many efforts have been reported.[ 5] Based on the concepts of dehydrogenation and selective catalytic oxidation of hydrogen, the commercial SMART process for the oxidative dehydrogenation of ethylbenzene was developed. This process co-feeds oxygen and steam in series reactor system.[5a, b] To overcome safety problems that result from mixing oxygen and light hydrocarbons, a novel idea to remove the dehydrogenation product of hydrogen by using reducible lattice oxygen was proposed,[5c–h] and a high-performance catalyst for the selective combustion of hydrogen in the presence of light hydrocarbons has been developed.[5e–h] Alternatively, ODH using CO2, being a soft oxidant without the problem of deep oxidation, is very attractive because it may open up new directions for oxidation reactions,[6] and create a new route for ODH.
Putting oxygen into a reactor with a hot organic molecule is, um, a little dangerous, as they point out.
Anyway, their new catalyst reportedly works quite well to substitute carbon dioxide for oxygen in this reaction, a much safer deal.
The reaction proceeds at 550C and the carbon dioxide is reduced to carbon monoxide, which is, of course, a useful synthetic intermediate for zillions of purposes. It can, for instance, be used to make motor fuels. The other side product is water.
Suppose that all of the styrene produced on earth were produced by this reaction. It can be shown that since 7 million tons of styrene are produced each year, the use of this reaction would require about 2 million tons of carbon dioxide each year.
For a sense of scale, humanity currently dumps about 30 billion tons of carbon dioxide per year in its favorite waste dump, Earth's atomosphere.
But this is just one application for the utilization of carbon dioxide as a commodity chemical intermediate.
Recently, as I've reported elsewhere, the great chemist George Olah has written of the need for a closed industrial carbon cycle. (The obvious input required is energy.)
Anthropogenic Chemical Carbon Cycle for a Sustainable Future.
This is the kind of approach that would be involved.
The reaction is actually much safer than the type of chemistry that is widely used for this sort of thing right now.
It's esoteric, but it's also kind of cool.
Have a nice day tomorrow.
