Sustainable Iron-Making Using Oxalic Acid: The Concept, A Brief Review of Key Reactions... [View all]

[NNadir]

The paper I'll discuss in this post is this one: Sustainable Iron-Making Using Oxalic Acid: The Concept, A Brief Review of Key Reactions, and An Experimental Demonstration of the Iron-Making Process (Phatchada Santawaja, Shinji Kudo,* Aska Mori, Atsushi Tahara, Shusaku Asano, and Jun-ichiro Hayashi, ACS Sustainable Chem. Eng. 2020, 8, 35, 13292–13301)

There's a rumor going around that coal is dead, often accompanied with the delusional statement that so called "renewable energy" killed it. These statements are Trump scale lies. In the 21st century, has coal proved to be the fastest growing source source of energy, growing in terms of primary energy production by more than 63 exajoules from 2000 to 2018, faster than even dangerous natural gas, which was the next fastest growing source of primary energy, having grown by 50 exajoules from 2000 to 2018, roughly 700% percent faster and 600% faster than so called "renewable energy" in this period, ignoring biomass combustion, and hydroelectricity, the former being responsible for about 1/2 of the six to seven million air pollution deaths each year, the latter having destroyed pretty much every major riverine system in the world.

2019 Edition of the World Energy Outlook Table 1.1 Page 38] (I have converted MTOE in the original table to the SI unit exajoules in this text.)

One of the reasons that coal has grown so fast in this century is that poor people around the world - who basically we pretend don't exist - have not agreed to remain desperately impoverished so rich people in the post industrial Western world can pretend that their "Green" Tesla electric cars are powered by solar cells and wind turbines.

It would be a gross understatement to say that I am "skeptical" that so called "renewable energy" will do anything at all to address climate change. Half a century of cheering for it has done zero to prevent California, Australia, and indeed even the arctic from catching fire.

My least favorite form of so called "renewable energy" is represented by the wind industry, and one of my biggest criticisms of this benighted industry is its high mass intensity, particularly with respect to its high steel requirements, coupled with the short life time on average of wind turbines, typically well under twenty years.

There is essentially no steel that is not made on industrial scale with coal, today: Coal fires convert anthracite coal into coke, with the coke being used to reduce iron, alloying it with carbon, to make steel.

That's a fact. Facts matter.

Even if no energy were produced using dangerous fossil fuels - the use of which is rising, not falling - the problem of steel would remain, although it is possible that we may, to some extent, enter the age of titanium, are well into the age of aluminum, but the electrochemical reduction of both of these metals depend on carbon electrodes made from dangerous fossil fuels, coal coke and petroleum coke respectively.

This dependence is why this paper caught my eye.

From the introduction:

Iron and steel are materials indispensable to modern society. Global crude steel production rose by 3.9% from 1.71 Gt in 2018 to 1.78 Gt in 2019, and continued growth is projected in the years to come.(1) The iron and steel industry is, however, one of the most energy-intensive industrial sectors.(2?7) CO2 emissions from this industry amounted to approximately 2.0 Gt in 2019, accounting for 24% of the total amount emitted directly from industries.(8) The majority of CO2 is generated in the iron-making process, which generally employs a blast furnace (BF). The BF is a sophisticated technology that is used to produce a massive amount of iron continuously. CO2 emissions are unavoidable during this process as the technology relies on fossil fuels, coal in particular, for reducing iron oxides in the iron ore and providing heat to maintain a furnace temperature of up to 2,200 °C.(6,9) Among all energy services and industrial processes, the iron and steel industry, which inevitably relies on fossil fuels, is considered to be in the category of “difficult-to-eliminate emissions”.(7) The development of alternative iron-making technology is thus vital to the global goal of building a sustainable society.

Extensive R&D efforts have been invested in alternative approaches to iron-making from the iron ore, which are largely classified into two types: direct reduction (DR) and smelting reduction processes.(2?6,9?12) In DR, the iron oxides in iron ore are reduced using reducing gas (H2 and CO) produced from natural gas or coal in reactors such as shaft furnaces and fluidized bed reactors. The reduction occurs at temperatures below the melting point of iron, producing so-called direct reduced iron or sponge iron. On the other hand, smelting reduction produces molten iron like a BF using a two-step process consisting of the solid-state reduction, followed by smelting reduction. The developed technologies, e.g., MIDREX for the DR and COREX, FINEX, ITmk3, and Hismelt for the smelting reduction, have been commercialized or are under demonstration.(3,6,13) The advantages of these alternative iron-making processes over BF include the lack of a need for coke, lower CO2 emissions, and lower capital/operation costs. However, they do not address the fundamental problems posed by the use of a BF because of their reliance on fossil fuels and harsh operating conditions. From this viewpoint, there are limited studies on potential sustainable iron-making methods...

There are many routes to oxalic acid with carbon dioxide as a starting material; one can come across papers along these lines regularly, some of which involve electrochemical reduction. Oxalic acid is moderately toxic, and is frequently utilized in commercial wood preservative products because it suppresses the viability of microorganisms that hydrolyze cellulose and lignin, the main constituents of wood. Famously the inability of the American Chestnut tree to synthesize oxalic acid when compared to the ability of the Chinese Chestnut to produce this biotoxin, led to the near extinction of the former. (Recently there has been promising work to insert oxalic acid generating genes into American Chestnuts.)

Oxalic acid is the simplest diacid, having the formula C2H2O4. It may be thought of as dimer formed by the elimination of two hydrogens from formic acid, the simplest carboxylic acid.

The overall scheme of this oxalic acid iron reduction scheme is shown in the following graphic from the paper:



The caption:

Figure 1. Concept of iron-making process proposed in this study. OA: oxalic acid.

The authors note that among many acids designed to solvate iron oxides - which are clearly insoluble in water - is in fact oxalic acid, although mineral acids are more commonly utilized in this process.

They write:

During leaching, iron is chelated by the organic acids and selectively removed from the material in a stable form. Among the organic acids, oxalic acid has been studied extensively and suggested to be the most effective acid for this purpose due to its high acid strength and good complexing ability...

...There are several factors affecting the rate of iron dissolution. Among them, pH of the initial solution, acid concentration, and temperature have been intensively studied.(17?24,26,28,30?32) The rate of iron dissolution is maximized when the pH of the oxalic acid solution is in the range of 2.5–3.0 because bioxalate anions (HC2O4–), which are responsible for iron dissolution, are the most abundant species in this range.(24,27,28) However, the pH of 2.5–3.0 is difficult to control with oxalic acid due to its low concentration, corresponding to 1–3 mmol/L, and, moreover, the low concentration is often insufficient for iron oxide removal. Therefore, the oxalic acid solution is typically prepared with the addition of its alkali salt as a buffering agent...

Dissolution is improved with the application of heat, which is unsurprising.

It is known that iron oxalate complexes can be reduced photochemically - this reaction has been used in actinometric devices - but the rate is slow, so the authors examine pyrolysis of the complex.

Thermal treatment of metal oxalates is an approach used to synthesize nanocrystalline metals or metal oxides. Fe(II) oxalate dihydrate is the typical precursor, and its thermal behavior has been investigated in some reports.(50?54)Figure 2 presents mass release curves for pyrolysis of Fe(II) oxalate dihydrate under a flow of N2 or 50% H2/N2, analyzed in this study. Upon heating, Fe(II) oxalate dihydrate starts to release water, forming anhydrous Fe(II) oxalate that is thermally stable up to around 300 °C. At higher temperatures, Fe(II) oxalate pyrolyzes with the release of CO and CO2 to form metallic iron, iron oxides, or iron carbides. The chemical form and composition of the iron product are significantly influenced by the atmosphere during the occurrence of pyrolysis. Although the reaction mechanism that determines the chemical form is still contested, most studies have identified FeO as the primary product during pyrolysis under an inert atmosphere, which was also confirmed in Figure 2 by the relative mass of 39.9%, corresponding to the generation of FeO, above 420 °C.

Figure 2:



The caption:

Figure 2. Mass release curves of Fe(II) oxalate dihydrate in the pyrolysis under a flow of N2 or H2/N2 (50%): sample 5 mg, heating rate 10 °C/min, and gas 300 mL/min.

The authors avoid the hand waving "we're saved!" nonsense that often accompanies popular descriptions of lab scale processes when discussing the reduction of carbon dioxide to oxalic acid:

Oxalic acid has been synthesized on a large scale worldwide. Because demand is not necessarily high, the synthetic route and feedstock used differ by countries and companies according to their situation. The employed feedstock has been sugars (e.g., starch and sucrose), CO, ethylene glycol, and propylene.(55) Alternatively, there has been no industrial process that uses CO2 as the feedstock, and only a few academic works have reported successful synthesis despite its attractiveness. This clearly shows the technical difficulty of CO2 activation in forming C–C bonds.

A robust approach to the reductive coupling of CO2 is electrochemical conversion.(56?58) For example, atmospheric CO2 is spontaneously captured and electrochemically converted into oxalate over copper complex, mimicking the natural photosynthetic transformation of CO2.(59) However, electrochemical conversion requires costly catalysts and organic solvents, which are unlikely candidates as an industrial method to produce cheap oxalic acid and iron. A recent report by Banerjee and Kanan(60) stood out in this regard, revealing the generation of oxalate only by heating cesium carbonate in the presence of pressurized H2 and CO2. The carbonate anion was replaced by formate anion from CO2. Then, the formate anion was coupled with CO2 to selectively form cesium oxalate with a yield of up to 56% (with respect to the carbonate), including other carboxylates at 320 °C and 60 bar. Nevertheless, the technical development of CO2 utilization for oxalic acid synthesis is still in its infancy.

In its infancy.

Given my personal focus on the utility of fission products, I note that hot cesium is one of the most prominent fission products, especially when freshly captured from used nuclear fuels. In addition, gamma radiation is known to produce carbon dioxide radicals, which may well accelerate this process.

But it's a very long way from here to there...

In any case, the authors experimentally (lab scale) use both photochemical and pyrolytic reduction of iron oxalate.

The following table shows the composition of the iron in each case.



XRD (X-ray diffraction) of the two processes:



The caption:

Figure 3. XRD pattern of feedstock and solid products from photochemical reduction (SSTP2) and pyrolytic reduction (SSTP3).

Scanning electron microscope (SEM) images of the product:



The caption:

Figure 4. SEM image of feedstock and solid products from photochemical reduction (SSTP2) and pyrolytic reduction (SSTP3).

In these graphics IO-A and IO-B refer to two different natural iron ores; CS refers too "converter slag" which represents iron recovered that would otherwise be waste.

Yields:



The caption:

Figure 5. Iron recovery at each step of conversion.

A graphic representation of the dissolution process using oxalic acid:



All papers on processes have to make a stupid genuflection to the idea that solar energy will save the world, even though it won't:

The caption:

Figure 7. Photochemical reduction of dissolved iron with solar simulator at 180 klx and room temperature: time-dependent change of conversion to FeC2O4·2H2O and Fe2+ or Fe3+ concentration.

An attempt to build a plant around this idea would be to deliberately build a plant that is a stranded asset for large periods of a twenty four hour day, not to mention days when it rains, snows, or the sky is occluded by the smoke of uncontrolled fires because solar energy did not address climate change even after trillions of dollars and worldwide screams of cheering.



The caption:

Figure 7. Photochemical reduction of dissolved iron with solar simulator at 180 klx and room temperature: time-dependent change of conversion to FeC2O4·2H2O and Fe2+ or Fe3+ concentration.

On that score, a schematic of batch productivity:



The caption:

Figure 8. Iron productivity as functions of reaction time and iron concentration in a batch operation.

Excerpts of the conclusion and caveats against "We're saved!"

A three-step iron-making process was proposed and investigated using different types of iron-containing materials. The experimental results showed promising performance as an iron-making method. The chemical selectivity of iron dissolution and photochemical reduction enabled the obtainment of product iron with a purity of 80.5–99.7 wt % (on a metal basis) from the feedstocks consisting of 33.9–93.3 wt % iron. The highest temperature used for completing the reduction to metallic iron was only 500 °C due to the pyrolysis characteristics of Fe(II) oxalate. On the other hand, the iron dissolution step determined primarily the overall yield and purity of the produced iron. Ca and Mg reacted with oxalic acid to form water-insoluble oxalates, causing its shortage for the iron dissolution. Transition metals such as Mn were inevitably included in the produced iron. As a result, iron recovery from CS, having high contents of these unwanted metals, was limited to 15.8%. The iron recoveries from IO-A and IO-B were 91.5 and 88.3%, respectively. The proposed method also allowed for the use of powdered ore, which has not been the feedstock in conventional iron-making except for the smelting reduction. The availability of diverse feedstocks will be a great advantage considering the decreasing quality of iron ore globally...

...A consideration is necessary for particle sizes of the feedstock iron ore, Fe(II) oxalate, and iron product. In the present experiment, fine particles of feedstock with sizes below 38 ?m were used to avoid possible influences of mass transfer on the iron dissolution. Fe(II) oxalates, obtained in the photochemical reduction, were also fine powders in the order of micrometers. In large-scale practical applications, technical difficulties would be found in feeding into and recovering from reactors for such small particles. Another concern is that small sizes of reduced iron product cause a low resistance to spontaneous ignition, which is also a problematic property of direct reduced iron.

The synthesis of oxalic acid from CO2 is vital to process sustainability. Direct synthesis is an emerging area of research but has a long way to go to become an industrial technology. Indirect synthesis via CO or biomass is a realistic option if a conversion system with economic and energetic rationality is found. It is also important to confirm the generation of CO2 and CO from iron-making, according to the proposed stoichiometry, and to design reactors that enable their recovery...

It's a cool paper on an area of research that I would certainly think is merited, not that anyone cares what I think.

Have a nice weekend. Please be safe and respect the safety of others.