Cogenerating Thermochemical Hydrogen While Recovering Waste Copper.

[NNadir]

Last edited Sat Feb 24, 2018, 05:47 PM - Edit history (1)

The paper from the primary scientific literature to which I'll refer is this one:

Co-production of Hydrogen and Copper from Copper Waste Using a Thermochemical Cu–Cl Cycle (Farrukh Khalid* , Ibrahim Dincer, and Marc A. Rosen, Energy and Fuels, 2018, 32 (2), pp 2137–2144)

There are many hydrogen cycles known, water splitting thermal cycles. The CuCl2 cycle is just one of them, other examples include the much studied sulfur-iodine cycle and variations, various cerium cycles (which include carbon dioxide splitting options), zinc cycles...etc...etc.

I've dreamt up a few variations on my own, although I have no idea whether they would actually work.

In general, they all feature the possibility of high thermal efficiency, since they are easily coupled to thermal processes for electricity generation, the generation of heat for chemical processing, and the production of pure oxygen that may be utilized for closed combustion systems that will not involve smokestacks and will, to the extent that oxygen is used to combust biomass, allow for the recovery of carbon dioxide from the atmosphere for its removal.

One limitation of these cycles involves materials science, although we have in recent decades developed some spectacularly refractory materials and others are clearly on the horizon.

One of the problems that humanity faces however is the depletion of important elements in the periodic table, including some in the popular, but spectacularly failed, so called "renewable energy" industry, which is in fact, is neither "renewable" nor sustainable for precisely this reason.

When elements are distributed, as in "distributed energy" their recovery involves energy, and the more diffuse they are, the more distributed they are, the more energy is required to reconcentrate them into a recoverable and useful form. This is a consequence of the second law of thermodynamics, which cannot be repealed by the legislature of California (where such repeal is often proposed, albeit usually "by 'such and such' a date, when conveniently, the people voting on the repeal will be either out of office or dead) or by any other legislature or even by any ersatz or real dictator, orange or otherwise.

The dilution of elements or molecules is known as "the entropy of mixing."

An essential element in our modern life is copper, which is ever more critical particularly because of the sloppy ways we use it, in low capacity utilization systems such as wind turbines, which, since they require redundancy as well as the use of large mass collection systems, and when these systems turn into landfill, the recovery of copper in them will require energy.

That's why this paper is of interest.

From the introduction:

The use of energy plays an important part in the progress of any country. With increasing populations and rising living standards in many countries, the demand for energy is growing. The present dependence upon fossil fuels to meet most of this energy demand and the challenges associated with fossil fuels has led to research around the world to develop environmentally benign energy sources, such as renewable and nuclear. During the past decade, there has been an increasing interest in the development of large-scale non-fossil hydrogen production technologies, particularly coupled with renewable and nuclear process heat/waste heat, which leads to clean hydrogen production with almost negligible life cycle emissions and, hence, minimized environmental impact. In this regard, thermochemical and/or electrochemical processes with a renewable or nuclear option offer an environmentally friendly option.(1-5)

I agree with part of the last statement. Nuclear energy is environmentally friendly, but in my oft expressed opinion, so called "renewable energy" is not.

Hydrogen is not an acceptable fuel, but it an extremely useful captive intermediate where it can be utilized to make sustainable fuels - my personal favorite being dimethyl ether, DME - via the hydrogenation of carbon dioxide (or monoxide).

The introduction continues:

A number of thermochemical cycles have been investigated(6-8) to produce hydrogen from water. However, most of these cycles operate at over 800°C. The relatively lower temperature (550 °C) requirement and use of inexpensive chemicals make the copper–chlorine (Cu–Cl) thermochemical cycle a promising process for hydrogen production. To build large-scale hydrogen production facilities based on this cycle, some challenges need to be resolved. First, the difficulty in separation of CuCl and CuCl2 from the spent anolyte in the electrolytic step needs to be addressed. Second, some copper crossover is observed in the electrolyzer membrane, resulting in degradation of the electrolyzer performance. One of the possible ways to achieve better kinetics and integration is the introduction of a high-temperature electrolysis step in the Cu–Cl cycle. Such a high-temperature electrolysis step needs to be thoroughly examined in terms of feasibility and practical viability.

Copper is one of the most widely used metals in the world, with applications including energy technologies, electronic devices, electricity transport, and coin production. With advances in electrical and electronic technology and decreases in prices, the use of such equipment has increased.(9, 10) This has led to increases in copper waste, especially in the industrial world,(11) posing a worldwide challenge for safe disposal.(12, 13) There are numerous methods available to recycle copper from copper waste, such as pyrometallurgy and hydrometallurgy.(14-17) However, each process has drawbacks. For instance, the energy consumption is very high and the temperature requirement is high (more than 1273 K) in pyrometallurgy...

Here, from the paper, is a schematic of the particular copper chloride cycle the authors envision. Note that their cycle requires an electrical input, but not all cycles, not even all copper chloride cycles, do:



Their purpose in including electricity is to reduce the temperatures required. With advances in materials science, this may not be necessary.

Their particular cycle relies on the oxidation of chlorine gas at 950K with water (steam) to give HCl gas and oxygen, and the HCl gas is reacted with copper wastes to generate hydrogen and cuprous chloride (copper (I) chloride) and hydrogen at around 770K, a temperature at which the cuprous chloride is a liquid, simplifying mass transfer. This liquid is electrochemically disproportionated into copper metal and cupric chloride (CuCl2 - copper (II) chloride) and the latter is thermochemically decomposed at 883 K to give chlorine gas and copper metal.

Here's a schematic of the electrochemical step:



Here's a photograph of the actual lab scale operating system:



I used to love putting stuff together that looked like that when I was in the lab. It makes one feel all "sciency." (Sometimes modern instrumentation can look too clean to be fun.)

There's a nice discussion of the thermodynamics in the paper, as well as a simple graphic that shows the story:



The caption:

Figure 6. Specific exergy destruction and exergy efficency of the various steps of the proposed Cu–Cl cycle.

A number of other graphics in the paper discuss optimization of the temperatures for each step. The interested reader may refer to the original either by subscription or by traveling to a good scientific library.

Note that the electrochemical portion may not be strictly necessary, depending on process parameters, and indeed on chemistry. A well known variant of copper based thermochemical cycles is the copper bromide cycle, and indeed iodide cycles also are possible.

Usually at this point someone will mention cost, usually in the context of declaring that "nuclear energy is too expensive" among other distorted views by which anti-nukes morph into Ayn Rand type Laissez Faire capitalists, usually with a healthy dollop of selective attention.

So called "renewable energy" is not cheap unless it is isolated from the environmentally questionable necessity for redundant back up whenever the sun isn't shining - sunlight is widely reported to disappear for various amounts of time depending on latitude and season - and the wind isn't blowing.

The reality is that the back up - despite all the horseshit about Elon Musk's (and other) unsustainable batteries - is dangerous natural gas, also reported as being "cheap."

It's "cheap" only if someone other than the user pays for cleaning up the trash it leaves behind, for example, carbon dioxide, radioactive flowback water, permanently leaching spent fields, etc.

The people consigned to pay for these clean ups are not the users; it is rather all future generations, our children, our grandchildren, their children, their great grandchildren etc.

The fact is that the dangerous fossil fuel industry is simply allowed to dump its waste directly into the planetary atmosphere without restriction, and without cost, while cleaner forms of energy, notably nuclear energy, are required to show that they can contain all by products indefinitely, over as long a period as stupid people can imagine, even though nuclear materials have a spectacular record of not killing many people, while fossil fuel waste kills millions upon millions of people year after year after year after year with little comment.

Because of this situation, so called "natural gas" is described as being "cheap" even though it is no such thing.

In recent weeks I've been reading about the history of human slavery in this country; a horrible story that is very difficult to read. Sometimes I have to put the books I'm reading down weeping; they're too painful to read but innocent people were required to live these events.

It is hard not to express profound disgust at the generations of white Americans of those times in which human slavery was legal in this country, and the twisted mentality that sought to perpetuate this great crime for many unimaginably cruel generations.

And then I think about how future generations might regard our generation, and I'm not comforted by the thought.

Since all current schemes to stop dumping the dangerous fossil fuel waste carbon dioxide into our favorite waste dump, the planetary atmosphere, have all failed, future generations will be required to clean up our garbage, this while having fewer resources than our generation enjoyed - and squandered - with complete disregard for them.

To get resources, they'll have to dig through our garbage, and probably face huge health risks in doing so. It's hard to think they'll think kindly on us any more than I think kindly on the purveyors of human slavery in the United States.

Maybe processes described in this paper might help a little, but irrespective of leaving them with the paltry record of such unscaled experiments they will be totally in their rights, in my view, to view us with as much or more disgust as I - more than a century later - view the slaveholders and their enablers, North, South, and everywhere else.

Have a pleasant Sunday tomorrow.

[Eko]

1. Why dont they use

Nuclear as the backup to renewable sources?

[eppur_se_muova]

2. "Electrochemical disproportionation" ? Had to think about that for a minute.

Glad I did; it's an interesting concept. In this case, just don't let the chlorine escape, but let it react with liquid CuCl. Not all that different from capturing Cl2 with alkali, and disp'n to chlorate and chloride.

Wish I could get past the paywall. Maybe xopy it at the U. library, **IF** they have paper copies (I'm not betting on it).

[NNadir]

3. Some options on access...

The first if you want electronic access and are near a University is to check with the librarian. Many libraries have open access computers for public access, although one needs to find out where they are sometimes. There may be limited use times but I generally can cover what I need in less than an hour.

Some libraries charge a fee which may or may not be nominal. I pay Princeton for access, although even Princeton has some free options albeit for limited periods.

The ACS offers 50 free papers to members. If you are not a member, but would like to consider it, and need a sponsor, PM me. They also have inexpensive packages for members for up to 500 papers.

Most of my posts here are from ACS journals because those are the ones I read, but basically I can read almost any piece of scientific literature I want with just two libraries. Rarely I have to email my son at his university for something more esoteric.