Another Discussion of Biomass Derived Anodes to Replace Petroleum Coke in Aluminum Production.
The paper I will discuss in this post is this one: Renewable Biomass-Derived Coke with Texture Suitable for Aluminum Smelting Anodes (Yaseen Elkasabi*† , Hans Darmstadt‡, and Akwasi A. Boateng, ACS Sustainable Chem. Eng., 2018, 6 (10), pp 13324–13331)
This is a follow up to recent post in this space, Can Biocoke Address the Anode CO2 Problem (Owing to Petroleum Coke) for Aluminum Production?
I don't buy into the pop enthusiasm for so called "renewable energy," since I am aware of the demonstrated fact - the demonstration being the concentration of carbon dioxide in the planetary atmosphere rising at an unprecedented rate despite the "investment" of trillions of dollars on this pixilated adventure - that so called "renewable energy" has not worked, is not working and will not work to address climate change.
Thus, the subtext of my previous post was an inferential attack on this pop enthusiasm, since I noted that the construction of so called "renewable energy" infrastructure is metal (and, just as bad, concrete intensive) and that two of the most important structural metals, specifically steel and aluminum, both depend on access to coke made from dangerous fossil fuels, coal based coke in the case of steel, petroleum based coke in the case of aluminum.
Ironically I am somewhat less hostile to what is clearly the most dangerous form of so called "renewable energy," biofuels than I am to wind and solar, even though biomass combustion is responsible for about half of the seven million air pollution deaths each year. (Recent publications however suggest that while the overall death toll from air pollution is rising significantly, both the fraction caused by biomass and the absolute numbers associated with biomass related deaths are falling, probably owing to improvements in stoves in impoverished areas. Impoverished areas are areas where "renewable energy" never really went away after largely being abandoned by the wealthier population beginning in the early 19th century, when the invention of steam engines made it possible to drain coal mines. Pretty much all of the increasing death toll related to air pollution derives from the rising use of dangerous fossil fuels.)
The reason that I'm less hostile to biomass than I am to wind and solar is that I believe it is technologically feasible to utilize (some) biomass to capture some of the dangerous fossil fuel waste carbon dioxide from our currently unrestrictedly utilized waste dump for it, the planetary atmosphere.
Although abandoning the "renewables will save us" fantasy will prevent massive surges in the demand for steel and aluminum - at what will be in my view an unacceptable environmental cost - the abandonment will not in any way eliminate the demand for steel and aluminum. The best it can do is to keep it steady.
By use of a well known and sometimes industrial chemical reaction, the Boudouard reaction, I have actually come to believe that it might be possible to run aluminum plants (with their electrical demand coming from nuclear energy, as well as thermal energy for the reduction of carbon dioxide by thermochemical splitting) as carbon negative enterprise. I referred obliquely to this in my earlier post on this subject.
In that post I discussed the use of carbon anodes containing a fraction of biochar, wood thermally decomposed by heating in the absence of oxygen to make biocarbon that could be mixed into petroleum coke to reduce the carbon impact of aluminum production.
The paper cited at the outset of this post, by contrast, uses bio-oil to make carbon anodes.
Bio-oils are made by the destructive distillation of biomass in the absence of oxygen. Since biomass contains largely cellulosic polymers made up of chains of sugars and lignins, largely ether linked catecholic aromatics, bio oils tend to contain a fair amount of oxygen. Although they can be utilized in combustion, including combustion in engines, they tend not to be very stable. They oxidize to organic acids which not only burn poorly, but are prone to take up water as well as to be corrosive.
The current paper suggests a better use for biooils.
From the introduction to the paper:
Although proposed in the literature,(8) use of biomass char in electrodes is not performed commercially. According to laboratory studies,(9,10) partial replacement of petroleum coke by biomass char resulted in poorer anode properties. The anode density decreased, whereas anode resistivity and oxidation increased. This was attributed to low char bulk densities and to the presence of inorganic compounds (such as Na and K) which catalyze anode oxidation. While methods exist for removal of inorganic compounds from biomass char,(11) the low bulk density remains an issue. Pressurized pyrolysis, in a manner similar to ablative reactors, can increase the char bulk density,(12) but costs have yet to be determined. Furthermore, biomass char usually has an amorphous texture.(13) Anodes containing fillers with these textures have a high coefficient of thermal expansion (CTE),(14) making them susceptible to thermal shock cracking.(15) In anodes, isotropic coke can only be used as a blend component, but not exclusively.(16) It can be summarized that the poor performance of biomass char in anodes has several reasons: inorganic compounds present in biomass report to the char and during carbonization, the developing char does not pass through a liquid phase required for the development of the desired graphite-like, anisotropic texture...
The authors propose to use bio-oils prepared pyrolytically from several sources, guayle (creosote bushes), willow, switch grass, hardwood and - how ironic is this - horseshit, which they more politely euphemize as "horse litter."
Briefly, they heat their biomass in a fluidized sand bath at 500C in a stream of flowing nitrogen.
The oils distill out, and then are heated under argon at temperatures between 200 and 300 C, then "coked" in an oven at 900C.
It is found that the resulting cokes contain considerable elemental impurities. These can and do end up in the aluminum prepared in the cryolite electrolyzer utilized in the Hall Process, and can impact the quality of the aluminum.
Elements found in the biomass are calcium, vanadium, sodium, silicon and nickel at levels in the hundreds of parts per million, and zinc, manganese and titanium at concentrations an order of magnitude lower.
Potassium is also prominent in hardwood sources.
Horseshit contains large amounts of phosphorous, and the authors thus reject its use, since phosphorous content in anodes leads to higher electricity costs and in aluminum degrades its properties.
Alkali metals like potassium and calcium are said to increase the rate of oxidation of anodes and thus are undesirable, as is calcium - although calcium chloride is the working electrolyte in the FFC process for electrolytic titanium reduction (instead of croylite in the Hall process.)
Here's some pictures of the anode materials:
The caption:
The caption:
The caption:
Like the authors who produced the subject paper in my last post on this subject, these authors actually make electrodes that are only partially biological with respect to the carbon in the anodes.
The caption:
Although the authors here do not make a large enough sample to perform the standard tests for anodes used in the aluminum industry, the do some electrical measurements, such as "I V" curves, current vs. voltage:
The caption:
For some reason this graph lacks a key. It will probably show up in a "corrections" paper in this journal in the future.
The authors thus conclude:
The amount of aluminum produced by humanity is huge. I personally hope that this materials science effort will continue, since it is increasingly exigent to ban the use of dangerous fossil fuels and switch to nuclear energy.
This sort of thing offers some small hope for the future.
I wish you a pleasant day tomorrow.
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