Reply #113: There is a huge difference between refereed journals and promotional

[NNadir]

literature. According to this reference:

Impact of Biodiesel Source Material and Chemical Structure on Emissions of Criteria Pollutants from a Heavy-Duty Engine
McCormick, R. L.; Graboski, M. S.; Alleman, T. L.; Herring, A. M.; Tyson, K. S.;
Environ. Sci. Technol.; (Article); 2001; 35(9); 1742-1747

in a refereed journal, biodiesel can vary quite dramatically in particulate output depending on its source. In some cases it exceeds the out put of petroleum derived diesel.

I have actually had occasion, when I was a young man, to attend an autopsy of a lung cancer victim. I recall large carcinomas marbled with black carbon particles. I don't know whether or not he was trying to scare me (I was a teenager who could have conceivably taken up smoking), but when I remarked that the man must of been a smoker, the pathologist informed me that this was not the case at all. The cadaver was that of a man who had merely lived for a long time in New York City. I have never forgotten that, which may be why I so hate air pollution.

Carbon particles are carcinogenic. Biodiesel puts them out, maybe less than ordinary diesels in specific cases, but comparably in many cases. Lineoleic acid, a constituent of some biodiesels has 17 carbon-carbon bonds, including two double bonds in a 1,3 arrangement that could conceivable rearrange under oxidative conditions to give aromatics and benzopyrans and other rather nasty compounds. It is a joke to call this molecule, as some do, an oxygenated compound based on a single ester moiety.

But this is just needling on my side. I prefer biodiesel to petroleum, if only on greenhouse grounds. It is not as desirable in my opinion as DME which has no carbon carbon bonds and consequently gives off no particulates. I am simply stating that biodiesel is no - how does your colleague put it? - risk free panacea.

I like DME for other reasons besides its inordinately clean burn (comparable to natural gas), ease of synthesis, the possibility of making it directly via hydrogenation of carbon dioxide (introducing an industrial carbon cycle). The variety of conditions under which synthesis gas is available, including from carbon dioxide, means it does not depend on specific crops grown in specific areas under constant specific weather conditions. Also the preparation of synthesis gas from biomass uses very nearly 100% of the biologically fixed carbon, it does not distinguish between fatty acids, sugars, and amino acids, as biodiesel does.

In fairness to your side, DME has major drawbacks as well. It is a gas at ordinary temperatures and pressures, and although it is easily liquifiable under pressure, it is at least as dangerous as propane (LPG). This problem can be ameliorated somewhat by adding dimethoxymethane to create a liquid solution, but it is much more prone to accident than biodiesel ever will be. (Dimethoxymethane, like DME itself, has zero carbon carbon bonds.) A very serious drawback to DME in my view is that any scheme to synthesize it will use synthesis gas. There are many environmentally friendly ways to make synthesis gas, from garbage, from biomass etc, but one really objectionable way: From coal. There is no law (existent) that says a DME infrastructure could not be diverted the use of coal as a feedstock. In addition, DME is soluble in water, although undermost spill conditions, it will simply boil away, much as propane does. Also DME is a greenhouse gas. It has a very short half-life in the atmosphere, but this should be a concern nonetheless. If DME is made from atmospheric carbon dioxide sources of course (as biodiesel is 100% of the time) this concern is somewhat ameliorated, but not completely. Undoubtedly DME has a higher greenhouse impact mole for mole than does carbon dioxide.

Overall, I'd still come down in favor of DME, based on my principles of risk minimization. This is because air pollution kills with far greater regularity and constancy than does gas explosions. (I perfectly understand that risk elimination is impossible.)