Biomass Derived Mesoporous Carbon for the Capture of Sulfur Dioxide.

[NNadir]

The paper I'll discuss in this post is this one: Facile Preparation of Biomass-Derived Mesoporous Carbons for Highly Efficient and Selective SO2 Capture (Shuguang Deng et al Ind. Eng. Chem. Res. 2019, 58, 14929−14937)

The dangerous fossil fuel and dangerous biomass waste dumped into the atmosphere, familiarly called "air pollution," kills seven million people per year, according to best estimates, suggesting that "air pollution" is too gentle a term to describe the realities of the situation.

Air pollution as a generic term does not in general describe the specific health effects of its constituents, these include particulates, specific carcinogens, generally planar aromatic species like benzofurans, benzodioxins, other polycyclic aromatic hydrocarbons, and inorganic species, particularly carbon particulates, heavy metals including but limited to lead and mercury, as well as acidic gases like nitrogen dioxide, sulfur dioxide, sulfur trioxide, ozone, and of course, possibly the worst of all forms of dangerous fossil fuel waste over the long term, carbon dioxide.

From the general reading I've done over the years, it seems that the component responsible for the most deaths over the short term, other than those resulting from climate change, are the carbon particulates, which may include the polycyclic aromatic hydrocarbons. However none of these gases are trivial in their health effects, and any one of them easily outweigh the health consequences of things popular with small minds, like say, Fukushima, or abandoned uranium mine tailings.

The paper attached here refers to one of the smaller killers among the air pollutants, albeit, again, not at all a trivial killer, since the death toll for air pollution is enormous, sulfur dioxide.

Sulfur dioxide is toxic in its own right, but in air, it is easily oxidized to sulfur trioxide, SO3, which is generally the whitish component of heavily polluted air that one can see pretty much in any major city of the world, particularly on hot days lacking wind. Sulfur trioxide is strictly the anhydride of sulfuric acid, which is a very strong acid, meaning that when exposed to water it forms sulfuric acid, which is obviously toxic and corrosive. It is a component of acid rain, along with nitric acid, which forms from a pollutant also associated with the combustion of dangerous fossil fuels, the nitrogen oxides NO, and NO2 in the presence of oxygen and water.

Sulfur dioxide is produced by the combustion of pretty much any untreated dangerous fossil fuel although there are ways to remove sulfur from the fluid dangerous fossil fuels dangerous natural gas and dangerous petroleum, albeit at expense. If the dangerous fossil fuel is coal which has been the fastest growing source of energy in the 21st century despite whatever lie you may have told yourself (or heard) about coal being dead, the sulfur dioxide (or sulfur trioxide) must be removed after combustion using a scrubber, also at added expense. In the 1970's, scrubbers were added to many coal plants in the United States because many lakes in the Northeast United States were becoming so acidic that nothing could live in them, because of sulfuric acid.

We are now killing bodies of water, including the oceans, with carbonic acids, although to a limited extent sulfur oxides and nitrogen oxides are very much involved in acidification, because we have done nothing effective to address the rising use of dangerous fossil fuels except to prattle on endlessly about how wonderful solar and wind energy are, even though they have proved, after the expenditure of trillions of dollars on them, useless at addressing the rising use of dangerous fossil fuels, acidification of bodies of water, and climate change.

You know the old shibboleth, don't you, sometimes attributed, dubiously, to Albert Einstein? The definition of insanity is doing the same thing over and over again and expecting a different result.

Sulfur dioxide is also produced by the production of many materials, chiefly metals. If one is refining copper, or zinc - the latter also being an ore having the the important industrial elements gallium and indium as side products - the ores are generally sulfides. The metals are produced by roasting them - with heat provided by dangerous fossil fuels - and oxidizing the sulfide to sulfur dioxide which is then dumped in our favorite waste dump, the planetary atmosphere. Steel, including steel made to make all those wonderful massive posts for wind turbines that will be landfill twenty or thirty years from now, also requires significant amounts of coke, which is made by roasting coal while releasing sulfur dioxide both from heating the iron ore and by burning coal to produce the heat.

If one needs to produce redundant systems, say to make copper for a generator for a wind turbine as well as copper for a generator for a dangerous natural gas plant that will run when the wind isn't blowing, one needs to use twice as much as a material as one would otherwise use, meaning that the material derived air pollution will be twice as great as it would if one just built the gas plant, or better yet, if one were actually interested in producing clean energy rather than pretending to produce clean energy, a nuclear plant. (The reason that nuclear energy is cleaner than all other forms of energy is its high energy to mass ratio.)

The world's largest consumer of coal because it is also the world's largest producer of steel, is China. The authors of this paper are Chinese. Nearly half of the papers written in journals published by the American Chemical Society are Chinese. They don't hate science as much as we do.

By the way, one often hears extremely noxious statements that all of our environmental problems are China's fault because China produces more carbon dioxide (marginally) than the United States. This is simply racist nonsense for several reasons: First China makes the metals for our so called "green" stuff, and until recently Chinese workers and children were suffering vast health effects to engage in "green" "recycling" of our electronic and plastic waste, and finally because the average per capita carbon dioxide emissions of Chinese citizens and energy consumption of Chinese citizens is about 1/10th that of average smug American logging on to the Cleantechnia website to read delusional bull about consumerist junk like Tesla electric cars and how hydrogen can be produced from wind and solar energy.

By the way, 99% of the hydrogen produced on this planet is produced from dangerous natural gas. This was true in 1980. It is true in 2019.

In theory, but not in practice, hydrogen can be produced from sulfur dioxide, a topic on which I'll touch briefly here, but right now, it isn't. In terms of the magic words "percent" so widely used when we wish to lie to ourselves about how wonderful so called "renewable energy" is, in 1980 world production of energy from wind, solar, tidal and geothermal energy which generates so much electricity to run computer servers to say how great wind, solar, tidal and geothermal energy are, was close to zero percent of the world energy supply. In 2017, according to the most recent data available in from the international energy agency, IEA 2017 World Energy Outlook, Table 2.2 page 79, these were producing 1.82% of the world's energy. According to this same document, in the year 2000, again in magic "percent talk," dangerous fossil fuels were responsible for 80% of the world's energy supply. In 2017 dangerous fossil fuels were responsible for 81% of the world's energy. The "percent talk" is intended to be misleading and it is. World energy consumption rose by 164.83 exajoules according to the World Energy Outlook from 2000 to 2019, which is the equivalent of adding 166% of a United States to this energy disaster.

So we better know what the hell we're going to do with sulfur dioxide.

From the introduction to the paper written by Chinese scientists:

The flue gas emissions generated by coal-fired power plants and the petroleum refining industry contain large amounts of SO2 that is recognized as the major source of acid rain, fog, and haze.1,2 The traditional flue gas desulfurization technologies via limestone-scrubbing or wet-sulfuric-acid methods are effective, but the exhaust gases usually still retain as much as 400 ppm of SO2.3,4 Even such a small amount of SO2 would react with organo-amine solutions of the following CO2-scrubbing process, causing permanent solvent activity loss.5 Thus, the development of cutting-edge flue gas desulfurization and purification technologies has attracted great attention, especially for the removal of trace SO2 contaminant from flue gases and other SO2-containing gases. The physical adsorption of SO2 by porous materials has been regarded as a promising approach for efficient and low-cost deep desulfurization. Traditional porous materials including zeolites,6 porous polymers,7 and mesoporous silica8 have exhibited a low energy penalty in adsorption-based gas mixture separation processes. Unfortunately, these materials generally suffer from relatively low adsorption capacity or selectivity. Recently, metal−organic frameworks (MOFs) have been employed as an emerging SO2 adsorbent with excellent capacity and selectivity.9,10 However, the high fabrication cost, low synthesis yields, and irreversible structure degradation after exposure to SO2 have severely limited their large-scale implementation.

The Chinese scientists have an idea: They propose to use porous carbon to capture the sulfur dioxide.

Porous carbons have been considered as potent candidates for practical gas separation and purification, owning to their intrinsic advantages such as low fabrication cost, excellent structure stability, and high surface property amendment ability.11,12 However, considering the acidic nature of CO2 and SO2 molecules, and much lower concentration of SO2 than that of CO2 in flue gas (CO2: 15%, v/v; SO2: ∼3000 ppm), it is very challenging to efficiently remove SO2 from CO2 with a high selectivity. With the increasing requirements for SO2 adsorption and separation, it is urgent to develop efficient porous carbon adsorbents with high adsorption capacity and selectivity...13

...Oil-tea is a unique edible oil and popular functional food in China, and oil-tea shells (OTS) account for ∼60% of the camellia fruit on a wet weight basis.16,17 Huge amounts of OTS are produced in southern China annually, and as a lignocellulosic waste, OTS are often discarded directly but without effective utilization. Herein, we prepare OTS-derived porous carbons via a facile one-step activation method. The pore structures could be tuned by altering the porogen/OTS ratio and activation temperature. The as-prepared carbons possess a large surface area, suitable pore size, and abundant basic adsorption sites. An excellent SO2 adsorption capacity of 10.7 mmol g−1 is achieved at 298 K and 1 bar with an outstanding SO2/CO2, SO2/CH4,

A description of their process:

2.2. Synthesis of OTS-Derived Porous Carbons. The porous carbons were synthesized from oil tea shells (OTS, Hunan Academy of Forestry, China) and ground in a coffee grinder (KRUPS F203) to obtain a fine powder. In a typical synthesis procedure, 1.0 g of OTS powder was mixed with 3.0 g of zinc chloride (ZnCl2) in 150 mL of deionized (DI) water. The solution was heated at 110 °C with magnetic stirring until a slurry was obtained. Subsequently, the slurry was placed in a horizontal tube furnace, and the temperature was ramped from room temperature to 650 and 750 °C for 1 h in N2 gas flow (300 sccm). After they were cooled to room temperature, the products were washed with HCl solution to remove impurities and then dried at 80 °C. The obtained porous carbons were denoted BC-X-Y, where X refers to the impregnation ratio of ZnCl2/OTS and Y stands for the activation temperature. For a comparison, a plain sample was prepared by calcination at 650 °C, denoted as OTSC. The schematic illustration of the synthesis process is presented in Figure 1a.

I like the part about the coffee grinder, which gives an idea of the laboratory scale of this work. Often, when we hear breathless stuff about solar and wind breakthroughs - I've been hearing these so called "renewable energy" breakthroughs since I was a young man and I am far from young now, and so called "renewable energy" is still useless - the issue of scale is ignored. All of the massive wind turbines grinding up the avian ecosystem throughout the world, all of the toxic solar stuff that will be electronic waste in 20 years, do not even remotely approach the scale of dangerous fossil fuels, the use of which is surging.

Figure 1 from the paper:



The caption:

Figure 1. (a) Schematic illustration of synthesis process and application; SEM images of (b) raw OTS and (c) BC-3-650, and (d) TEM images of BC-3-650.

Some graphical analytical results of the porous carbon:



The caption:

Figure 2. (a) XRD patterns, (b) Raman patterns, (c) N2 adsorption–desorption isotherms at 77 K, and (d) NLDFT pore size distribution curves of BC-X-650.

The caption:

Figure 3. N 1s spectra of (a) BC-3-650, (b) BC-4-650, and (c) BC-4-650. O 1s spectra of (d) BC-3-650, (e) BC-4-650, and (f) BC-4-650.

Some graphics about the performance of the porous carbon at removing sulfur dioxide from gas streams produced by the combustion of dangerous fossil fuels:



The caption:

Figure 3. N 1s spectra of (a) BC-3-650, (b) BC-4-650, and (c) BC-4-650. O 1s spectra of (d) BC-3-650, (e) BC-4-650, and (f) BC-4-650.

The caption:

Figure 4. (a) SO2 adsorption isotherms of OTSC, BC-X-650, and CMK-3 at 298 K. (b) SO2 adsorption isotherms at 313 and 333 K of BC-X-650. (c) SO2, CO2, CH4, and N2 adsorption isotherms at 298 K for BC-3-650. (d) IAST-predicted adsorption selectivity of SO2 over CO2, CH4, and N2 at 298 K.

The caption:

Figure 5. (a) Breakthrough curves and cycle test of SO2/CO2 (0.02 (v)/99.8 (v)) binary mixture. (b) Breakthrough curves of simulated flue gas. (c) Breakthrough curves and cycle test of simulated flue gas with water vapor on BC-3-650 at 298 K and 1 bar.

A cartoon about the mechanism by which the porous oil tea derived carbon works:



The caption:

Figure 6. Cluster model of SO2 adsorption on different BC surfaces: (a) SO2/BC; (b) SO2/OH-BC; (c) SO2/NO-BC; and (d) SO2/NO&OH-BC. All lengths are given in angstroms. Gray, red, blue, yellow, and pink spheres denote C, O, N, S, and H atoms, respectively.

The paper's conclusion:

In summary, this work reports the successful preparation of OTS-derived porous carbons via a facial one-step method for selective SO2 adsorption. A moderate pore size and functional groups are both critical for SO2 adsorption. The obtained carbons are mesoporous with pore sizes centered at 4−6 nm with a large specific surface area of 1449 m2 g−1. The DFT calculations confirmed that the presence of −OH and −NOx groups in the carbon framework endows a strong interaction for SO2 adsorption and selectivity. As a result, BC-3-650 exhibited outstanding high SO2/CO2 (32), SO2/CH4 (127), and SO2/N2(2349) selectivities with an excellent SO2 adsorption capacity of 10.7 mmol g−1 at 298 K and 1 bar. As further conformed by the dynamic breakthrough experiments, BC-3-650 exhibited an outstanding SO2 separation ability with SO2/CO2 binary gas mixtures and mimicked flue gas stream. Moreover, even with the presence of water vapor, an almost intact performance and excellent recycling stability were confirmed. Thus, the facile prepared porous adsorbents is a potential material for the efficient SO2 removal especially at ultralow pressures.

This is a fine paper. I like it a lot. Although this work has been performed on a coffee grinder scale, were it go industrial, and the heat for its processes provided by nuclear heat, it would represent something that I think may be necessary for future generations after they clean up our disgusting mess that we generated while cruising mindlessly to the "Cleantechnia" website where we could validate the pretty lies we tell ourselves, and they're not little lies; they're big lies: This technology would sequester carbon by using it.

And let's get real. The economic viability of a process if it is to be sustainable is not to build huge waste dumps, for carbon dioxide or anything else. It is to convert waste into products, to close the mass cycles.

One may ask, though, if the world were to get less stupid and embrace nuclear energy as opposed to endlessly caterwauling with endless selective attention to nuclear energy's imperfections while seven million people die every year because our fantastic embrace of the wait for Godot, the grand renewable energy nirvana that has not come, is not here and will not come, why would we need to capture sulfur dioxide, since we would not be using coal, or oil, or dangerous natural gas.

I want dangerous fossil fuels banned. I think we need to do so on an emergency basis, although it's clear no one cares what I think.

My recent interest in sulfur dioxide stems from one of the conversations I had with my son during our travels back from his internship, a ten hour trip. We were discussing thermochemical cycles.

One of the oldest known and most studied thermochemical cycles is the sulfur-iodine cycle, which involves thermally splitting hydrogen iodide gas into hydrogen and elemental iodine, reacting the resultant iodine after separating it from the hydrogen with sulfur dioxide and water to produce sulfuric acid, and heating the resultant sulfuric acid to its decomposition point to produce oxygen and sulfur dioxide. The net result of this cycle, which is much more thermodynamically efficient than electrolysis, is to split water into oxygen and hydrogen.

I'm not fond of this particular thermochemical cycle, although it is widely studied and is probably the most advanced thermochemical cycle - in terms of understanding and research - of all of them. My concern has been about mass transfer. Iodine has a molecular weight of 254 grams/mole, 258, if one uses slightly radioactive Iodine-129 available from used nuclear fuels. Hydrogen has a molecular weight of 2 grams per mole. I think this is a problem.

But while chatting with my son, a better way of addressing this problem occurred to me. I'm not sure it hasn't occurred to someone else; probably it has; very few of my original ideas prove to be original at all, which I regard as a comforting thing. Anyway, I wanted to share this idea with my son because he is way smarter than I am, will clearly enjoy better opportunities than I have, is developing into a fine young scientist, and I very much encourage him to use his fine mind to save what will be left to save in his times should humanity ever turn away from its increasing investment in, and fondness for, deliberate ignorance.

I will die soon enough, and if I have an idea that may be good, if I share it with him, it may prove useful in a distant time if he steals it, which I encourage him to do.

One of the issues with the oxygen product of the sulfur iodine thermochemical cycle is the separation of two gaseous products, sulfur dioxide from oxygen, and the possibly ersatz "new" idea I had revolved around this separation as well as the reduction of the significance of the mass transfer problem. However, in order to utilize the oxygen produced to capture carbon dioxide from the air, to be environmentally acceptable, the sulfur dioxide must be completely removed from it. Further, if the means to do this is the oxyfuel combustion of biomass or even biomass reforming, biomass contains significant sulfur from methionine and cysteine in proteins and from other constituents in biomass. Sulfur is an essential element for living things, which is why dangerous fossil fuels, which derived from living things, contains it.

Therefore technologies for the removal of sulfur dioxide, including trace sulfur dioxide, are important, and even if this work was intended to mildly reduce the massive noxious results of the use of dangerous fossil fuels, it may have applications in areas intended to arrest, completely, their use.

I hope you'll have a very pleasant weekend.