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#1 2018-08-01 17:26:57

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
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Sulfuric Acid on Mars

Sulfuric acid is a critical industrial reagant, which finds use in a wide variety of industrial processes.  Global production on Earth is around 180 million tonnes per year (as of 2004, per wiki), which works out to about 30 kilograms per person per year for every person on Earth.   It's worth mentioning that on Mars more will probably be needed.

Anyway, this is a bit of a tangent that came from the Self-Replicating Colony thread that deserves its own thread.  So here we are:

Oldfart1939 wrote:

There hasn't been anywhere near enough concentration on the development of the underlying chemical industry required for a lot of these phantom industries to get started--much less flourish. Everything manufactured from Mars ISRU requires metallurgical extraction or purification of substances extracted from regolith and/or the atmosphere. Until this happens, none of the other associated "industries" have a chance in Hell of working. Everything stated is far more power intensive than a solar farm can provide. Period.

louis wrote:

I agree the chemical industry is vital.  You need probably nearly the full range of gases and chemicals produced on Earth, but obviously in much smaller quantities if we are talking about a small colony of 1000 people.   I was reading that sulphuric acid is the leading industrial chemical. On Earth we produce something like 100 million tonnes per annum.  Proportionately for a colony of 1000 (assuming Earth's population is about 7 billion) that would mean on Mars we would need a maximum of just over 14 tonnes per annum or about 39 kgs per sol. I say maximum but given the nature of a self-replicating colony on Mars the true figure might be much lower.

In a small colony you'd probably produce these chemicals in batches. So maybe you'd maybe make 400 kgs of sulphuric acid every 10 days. Less common chemicals might be produced every 100 days and so on...you'd be working to a detailed schedule of production.

Oldfart1939 wrote:

Your comments re: sulfuric acid are hopelessly naiive. What it takes in order to manufacture sulfuric acid alone is a project beyond the capabilities we have attributed to the colony. First, there's the matter of finding, extracting, and purifying sulfur. That alone is a major industry, and one which isn't going to be accomplished by 75 pioneers. Then after you presumably have Sulfur, the manufacture of Sulfuric Acid is far from trivial. Also necessary is lots of Oxygen, and most assume "you just burn Sulfur in Oxygen." Unfortunately it just doesn't work that way, because that yields SO2, not the SO3 actually needed (this is called "Oleum."). It requires V2O5, Vanadium Pentoxide, as a catalyst. Once Oleum is "in hand," then dissolution in H2O gives Sulfuric Acid. So...you picked a real beauty to espouse manufacturing thereof. Tis entire procedure requires massive amounts of infrastructure. Industrially, this is accomplished on massive plant scale in order to justify the expense of manufacture. The there is the minor matter of making enough plastic boards for conversion into solar panels. Plastics just happen to be another one of my areas of expertise. Even though the reactions "on paper" appear simple, manufacture of polypropylene circuit boards and other associated solid state devise isn't going to be "wished into existence." Plastics manufacture is far more complex and infrastructure intensive than Sulfuric Acid. Cutting to the chase, your estimate of the workforce require for your solar panel construction is really  only about 5-10% manned using your numbers.

So...I really hate to break it to you this way. But...not really. wink

P.S. Just how do I know about Sulfuric Acid? My final orals and that was THE question asked by the inorganic professor on my committee.

Terraformer wrote:

How does the old Lead chamber process compare with the contact process? Would it be easier for a Martian colony to use?

Oldfart1939 wrote:

There is no problem using the lead chamber process other than transporting it to Mars. I can think of several hundred other items which could be equally useful but weighing far less than a lead chamber. The major objection to lead chamber process is contamination of the Sulfuric Acid with measurable amounts of Lead; not what we would want in "Electronics Grade" Sulfuric Acid.

Terraformer wrote:

I wonder if modern glass making could allow glass to be used instead, and for the chambers to be manufactured on Mars?

louis wrote:

I'm not doubting your technical knowledge.

Some chemicals will be easier than others. But for a colony of 1000 the quantities would certainly be small and could be manufactured in small scale facilities.

Modern solar panel factories produce MWs of solar panel capacity with v. few workers. Producing 300 sq. metres a week would not require much human involvement.  Remember, it's a batch process so human workers can move from one part of the process to the next.

Oldfart1939 wrote:

Please don't use the old "dismissive statement" ploy here. Making ANY chemicals in larger than benchtop scale quantities will require major infrastructure and the technical know-how to make it work. By making such statements, you automatically overlook the nuts and bolts of running ANY manufacturing operation. It's sort of "Well, we now have Sulfuric acid in a reactor. Now what do we do with it?" I'm referring to the additional transfer equipment and safety measures; personal protective equipment, containers, acid resistant pumps, etc., etc., etc. The answer will be to transport Pfaudler or DeDietrich chemical reactors to Mars, along with the necessary temperature control equipment; steam plants; chillers; process piping; rupture discs; overflow receivers; support brackets; filters; centrifuges; huge holding tanks. You should really make a visit to a real chemical plant before making these statements. Sorry you don't like my rebuttal, but I live in the real world.

Terraformer wrote:

Scaling down a process doesn't mean scaling down the cost, complexity, or labour requirement. Think of it like cooking. Making a curry for one person doesn't allow you to cut out ingredients, and you can't do it ten times as fast as making it for ten people. You need a stove however many people you make it for - you can't use a kitchen that's ten times cheaper when only making it for one, since you need the same equipment.

louis wrote:

OK this is a thought experiment and it depends what you mean by "major infrastructure".

Obviously you need a lot of energy.  I've suggested a 1000 person colony would need a large energy infrastructure of perhaps 300,000 sq metres of PV panels.

I've been to a few large industrial facilities in my time. The striking thing about the more modern ones is often how few people are involved.

You are not wrong to point to the complexity. But then a 1000 strong Viking community in Greenland in the 1100s would have been pretty complex.  You couldn't write down everything they did in half an hour.

You reference centrifuges and acid-holding tanks...these are technologies that will cross over several technologies. Likewise as I previously pointed out re industrial robot arms - they are common to a huge range of applications these days.

I would be happy to consider in detail the complexities of making a batch of 400 kgs of sulphuric acid every 10 sols on Mars, if you want to lead the discussion...e.g. going through mining processes, purification, creating and maintaining feedstocks, and following through the various processes that lead to safe storage of sulphuric acid.

So here we are!  More thoughts to follow.


-Josh

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#2 2018-08-01 19:17:04

SpaceNut
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Re: Sulfuric Acid on Mars

We have had a few topics that were the use of acids to create regolith soil, pull ore appart for its minerals but its not a natural chemical combination that we would want to make use of....

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#3 2018-08-01 19:21:35

louis
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Re: Sulfuric Acid on Mars

I think it would be useful to take one v. important strand of industrial production - producing sulphuric acid - and look in detail at what that requires, not just the process but also the manufacture of machines that support the process.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#4 2018-08-01 20:46:19

kbd512
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Re: Sulfuric Acid on Mars

Why can't we just go to Venus and get all the sulfuric acid we can handle?

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#5 2018-08-01 22:14:37

SpaceNut
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Re: Sulfuric Acid on Mars

Yes use mars glass containers to contain it on its trip back to mars...
That implies commerce.

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#6 2018-08-01 22:49:31

Oldfart1939
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Re: Sulfuric Acid on Mars

OK. My point towards which I was moving was effective  utilization of available manpower and resources. I personally, would not want to see the colony be submerged in manufacture of in situ solar panels--there's a lot more work which needs to be accomplished in other areas.
But our admin has started this thread, & Sulfuric Acid is a staple of the modern chemical industry.

Let's start with the basic chemistry:

     S  + O2  ------------------>  SO2, which is Sulfurous Acid when dissolved in water;  H2SO3. Not at all useful.


   2 S  + 3O2 ----------------->  2 SO3, or Oleum  (Sulfuric Anhydride); dissolved in water is Sulfuric Acid.
                       V2O5
Some form of catalysis is required, but Vandium Pentoxide is THE choice in industry.

Here's the synopsis from Free Patents Online :http://www.freepatentsonline.com/2394426.html

This is NOT a process where "building a small scale unit" will really be of much use. As I mentioned on the previous thread, the entire process is VERY infrastructure intensive. That, in general, means very cost intensive, especially when it must undoubtedly be built on Earth and subsequently transported to Mars. This is probably orders of magnitude more complex than many of the other chemical processes we need there, i.e. Sabatier synthesis of Methane, or Moxie extraction of atmospheric Oxygen.

The real "kicker" will be finding deposits of elemental Sulfur as the feedstock for this hypothetical nascent chemical industry.

Bottom line: "It ain't gonna' happen anytime soon."

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#7 2018-08-01 23:01:12

SpaceNut
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Re: Sulfuric Acid on Mars

Sulfur was detected by the rovers and landers
https://en.wikipedia.org/wiki/Composition_of_Mars
https://en.wikipedia.org/wiki/Ore_resources_on_Mars

DISTRIBUTION OF SULFUR ON THE SURFACE OF MARS …
https://www.lpi.usra.edu/meetings/lpsc2010/pdf/2174.pdf

planetary science - Mars: Readily usable sulfur for sulfur ...
https://space.stackexchange.com/questio … r-concrete

Minerals to build with seem well distributed and as you indicated come with a mass cost and expense from earth to be able to using them.
Access to low hanging fruit of the most used should be first.

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#8 2018-08-01 23:33:59

JoshNH4H
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From: Pullman, WA
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Re: Sulfuric Acid on Mars

Wikipedia list three processes for producing Sulfuric Acid: The contact process, the wet sulfuric acid process, and the lead chamber process.

The processes are not identical, but basically for all of them you start with sulfur or hydrogen sulfide, oxidize it to Sulfur dioxide and then sulfur trioxide, and then slowly dissolve that with water.  They will react to form sulfuric acid.

The main difference between the lead chamber process and the two more modern processes seems to be the method by which SO2 is oxidized to SO3.  In the older process, Nitrogen Dioxide (a very reactive radical that is also moderately hard to produce) is used because the reaction is pretty fast.  It seems like at some point in the early 20th century they realized that a Vanadium Oxide (V2O5) catalyst will allow you to use regular oxygen and that process is now preferred for reasons that I think also hold on Mars.

Mars is generally regarded as being a sulfur-rich planet.  Table One in this paper suggests that Martian soil in the Ares Valles (where Pathfinder landed) is roughly 5% SO3 by mass.  The map at the end of this paper suggests that pathfinder landed in a particularly high-sulfur region of the planet, but that there is sulfur in various places on the planet.

Now there's a couple caveats.  The data in that paper comes from the Gamma Ray Spectrometer aboard Mars Reconnaissance Orbiter and has limited resolution both spatially (it looks like tens of kilometers or more) and in its ability to probe into the regolith (perhaps no more than 30 centimeters depending on soil composition).  You could have a deposit of pure sulfur 1 kilometer wide and it might not show up.  Likewise, the entire planet below the first meter of regolith could be sulfur and it wouldn't show on this map (we know for other reasons that this is not the case).

Anyway, I think it's most likely that the SO3 in this map is actually sulfates and not pure SO3 sitting around ready to be extracted, which is a shame for this purpose.

I'll think some more about sources of sulfur tomorrow.


-Josh

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#9 2018-08-02 02:44:29

Terraformer
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Re: Sulfuric Acid on Mars

Are there other catalysts which can be used for the contact process, or are we limited to just V2O5?


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#10 2018-08-02 02:51:24

Oldfart1939
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Re: Sulfuric Acid on Mars

Please note that I stated "elemental Sulfur," not in the form of sulfates, or other inorganic molecules. Having to obtain Sulfur by any other method than what is done here on Earth (steam injection into almost pure Sulfur deposits), is highly inefficient and adds an enormous energy burden on top of an already energy consumptive process. The complexity is becoming almost overwhelming as a result. In the chemical industry, complexity = expense.

My bottom line comment: use the weight of "stuff" required to bring in multiple Megawatt nuclear reactors and forget the massive solar farms which have limited lifetimes and are totally unusable during dust storm blackouts. This is the pragmatist approach; use what we can implement immediately with existing technology and have a reliable power system from the get-go.

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#11 2018-08-02 02:55:08

Oldfart1939
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Re: Sulfuric Acid on Mars

My chemical engineer who built much of the apparatus I needed in the last plant where I worked before my retirement had a comment he always gave management when asked if we could "do" a certain plant process: "All it takes is time and money." Getting a Sulfuric Acid plant built, up and running will either take a LOT of time, or a LOT of money; probably BOTH.

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#12 2018-08-02 08:17:17

knightdepaix
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Re: Sulfuric Acid on Mars

Why do we need sulfuric acid in the first place? Does the fact that industries on Earth need the acid mean that it is needed on Mars on the onset of immigration?

For existence, chlorine in the form of perchlorate has been confirmed and fluorine in minerals suggested. On Earth, hydrochloric acid can etch metal surface and various acids of fluorine and hexafluorate are used in producing aluminium and silicon metals from ores. Smelting iron ores need carbon monoxide. The rocks after extracting iron metal provide the calcium oxide. Then the conventional smelting for iron can begin.

Also in terms of plastics, silicones can be used extensively because carbon, hydrogen, oxygen and silicon elements are available.

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#13 2018-08-02 09:37:05

knightdepaix
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Re: Sulfuric Acid on Mars

I am taking about more or less chemistry here. Can hydrogen peroxide solution be used to oxidize dissolved concentrated sulfur dioxide? After the oxidation in solution, a concentrated sulfuric acid solution is achieved; however, using chlorine or oxygen oxoacids welcomes contamination.

Hydrogen peroxide itself can be made by combining hydrogen and oxygen using organic catalyst. Hydrogen and oxygen themselves can come from various sources.

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#14 2018-08-02 09:55:19

Terraformer
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Re: Sulfuric Acid on Mars

I did think that, but according to Wikipedia, Hydrogen Peroxide is even harder to make than Sulfuric Acid.


"I guarantee you that at some point, everything's going to go south on you, and you're going to say, 'This is it, this is how I end.' Now you can either accept that, or you can get to work." - Mark Watney

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#15 2018-08-02 11:02:34

JoshNH4H
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Re: Sulfuric Acid on Mars

Hi Oldfart1939,

Please note that I stated "elemental Sulfur," not in the form of sulfates, or other inorganic molecules. Having to obtain Sulfur by any other method than what is done here on Earth (steam injection into almost pure Sulfur deposits), is highly inefficient and adds an enormous energy burden on top of an already energy consumptive process. The complexity is becoming almost overwhelming as a result. In the chemical industry, complexity = expense.

I hear you and agree that elemental sulfur would be ideal, I was just trying to have a quick look at the available sulfur resources.  If there's elemental sulfur available, presumably we will use it (unless there's Oleum in the regolith, in which case we presumably will skip the oxidation step and use that).  However, I imagine you would agree that, all else being equal, if there is no elemental sulfur to be had and only sulfates are available, we could find a way and it would not by itself halt settlement.

On the topic of regolith oleum, by the way, this article (pdf download)  basically says that there are sulfates but not free SO3.  This makes a lot of sense, and it means that SO3 is listed basically for convenience of description.  Oh well.

My bottom line comment: use the weight of "stuff" required to bring in multiple Megawatt nuclear reactors and forget the massive solar farms which have limited lifetimes and are totally unusable during dust storm blackouts. This is the pragmatist approach; use what we can implement immediately with existing technology and have a reliable power system from the get-go.

I don't think I agree with this, for a few reasons. 

Firstly, I had in my head that we were talking about a time when bulk imports from Earth aren't happening so much anymore.  I hear what you're saying about specialized equipment that—even on Earth—only has one or two manufacturers and I will try to think through what that means for an indigenous Martian chemicals industry in this thread. 

Secondly, I don't agree with your claim about nuclear power on the merits.  In the past, I was a strong pro-nuclearite, and I still think nuclear power is an excellent solution for utility-scale power pretty much everywhere.  Having said that all of the research dollars and enthusiasm these days is going to solar, and we have seen some genuinely impressive developments in PV, CSP, and power storage in the past couple decades.  I think when selecting a power system, it's important to acknowledge that both solar and nuclear can work.  Once you've acknowledged that, the choice becomes much more low-stakes.  If I had been put in charge 30 years ago, I would have directed almost all the research dollars to nuclear and I'm sure we would see fantastic results there.  Instead, almost all the research dollars went to solar, which has consequently improved by orders of magnitude.

In 1996 Dr. Zubrin looked at this and said that solar power is just not there, and he staked the viability of his Mars Direct mission on the political will to construct and use an SP-100 reactor.  Maybe in 1996 he was right.  Maybe for a first mission he's still right.  But it's not 1996 and we’re not talking about a first mission.  In the last 22 years solar has improved by leaps and bounds while nuclear has not.  Basically, what I’m saying is that we’re in a space where both technologies will work and the choice between them is dominated by other things that are hard to quantify: Political considerations (People love solar and are scared of nuclear—I am not making a value judgment here), Regulation (Minimal for solar and maximal for nuclear), and Development cost (it’s expensive to develop a new kind of nuclear reactor, not as expensive to space-harden solar panels and batteries that already exist).

Thirdly, and perhaps most importantly, I think it's a mostly irrelevant question in this thread.  It's critically important that the settlement have reliable electrical and thermal power, of course, but as long as the power is clean and reliable the machines won't care where it comes from.

My chemical engineer who built much of the apparatus I needed in the last plant where I worked before my retirement had a comment he always gave management when asked if we could "do" a certain plant process: "All it takes is time and money." Getting a Sulfuric Acid plant built, up and running will either take a LOT of time, or a LOT of money; probably BOTH.

This is something of which I have no doubt.  But it will need to be done sooner or later and it's an interesting topic.


-Josh

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#16 2018-08-02 11:06:36

Oldfart1939
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Re: Sulfuric Acid on Mars

To all: we really don't need to reinvent the wheel. The chemistry of Sulfuric Acid production is well documented, and straightforward--given easy access to the key starting materials. But--that is the real problem here. Sulfur "has been identified" on Mars, but not in the readily accessible form needed.

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#17 2018-08-02 11:29:57

JoshNH4H
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Re: Sulfuric Acid on Mars

I would say a big part of what happens in a thread like this is that we as a group learn about how sulfuric acid is produced on Earth and think about the ways in which those methods will have to change to adapt to life on Mars.  Not everyone has your experience smile


-Josh

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#18 2018-08-02 12:28:04

Oldfart1939
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Re: Sulfuric Acid on Mars

Just to clarify: I have been an advocate of using BOTH technologies for Mars, but have become somewhat polarized by the unwillingness of others to adapt an eclectic solution. My view of power generation is I don't care to see the Martian landscape become a giant solar farm as far as the human eye can see. I actually consider both solar farms and wind farms to be producing a different environmental impact: visual pollution.

Last edited by Oldfart1939 (2018-08-02 12:28:46)

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#19 2018-08-02 14:37:29

louis
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Re: Sulfuric Acid on Mars

An interesting video on the contact process.

https://www.youtube.com/watch?v=_zj3bMjFclA

At 0:57 there's a photo of the factory site with the various parts highlighted in series - quite useful to imagine how that could be scaled down.

It's simple enough for me to understand! And I don't see anything there that can't be scaled down for a small colony on Mars.

The more difficult parts of the process are probably sourcing the sulphur and vanadium (which also would require processing of course) and producing an air analogue (or would oxygen do by itself? -  probably...). 

Waste heat could be an issue in an enclosed facility on Mars. Presumably the heat could be vented or could be used to heat water for use in the colony. I think however any industrial sites would be located well away from the home and agricultural habs...so if you were doing that you might have to pipe the water quite a way. Might not be worth the effort of installing piping.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#20 2018-08-02 14:42:02

louis
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From: UK
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Re: Sulfuric Acid on Mars

Just to add to that video in my previous post -

The largest plant in the world produces 300,000 tonnes per year of sulphuric acid.  For a colony of 1000, we are talking about producing a max of 14 tonnes per annum.


Let's Go to Mars...Google on: Fast Track to Mars blogspot.com

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#21 2018-08-03 07:01:58

Oldfart1939
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Re: Sulfuric Acid on Mars

Sulfuric acid is the "Mother of all Chemical Industry." That said, the 14 Tonnes Louis suggests is trivial amount for al the suggested uses. Look at the chemistries of making all the plastics and other chemicals to be extracted/processed from Martian regolith.

If I were going to build such a plant here on Earth, I would initially raise about $100 Million--for starters--then get the engineers working on plant design. This is NOT a trivial process. But again, nothing done with Mars in mind is trivial; neither is the associated cost.

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#22 2018-08-03 09:03:19

knightdepaix
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Registered: 2014-07-07
Posts: 230

Re: Sulfuric Acid on Mars

louis wrote:

Waste heat could be an issue in an enclosed facility on Mars. Presumably the heat could be vented or could be used to heat water for use in the colony. I think however any industrial sites would be located well away from the home and agricultural habs...so if you were doing that you might have to pipe the water quite a way. Might not be worth the effort of installing piping.

With thermal energy storage, waste heat could be stored away and producing electricity to the grid for the use of all colonists. Not to mention smelting Mars' ore need energy which can come from waste heat. Water desalination on Earth can use waste heat, too.

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#23 2018-08-03 16:59:22

SpaceNut
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From: New Hampshire
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Posts: 18,195

Re: Sulfuric Acid on Mars

Strong and weak acids are important to know, both for chemistry class and for use in the lab. There are very few strong acids, so one of the easiest ways to tell strong and weak acids apart ..

Complete List of Inorganic Acids & List of Common Organic Acids


The focus will not be the complete list but those with common purposes.

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#24 2018-08-03 23:01:51

JoshNH4H
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From: Pullman, WA
Registered: 2007-07-15
Posts: 2,526
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Re: Sulfuric Acid on Mars

Oldfart1939 wrote:

Just to clarify: I have been an advocate of using BOTH technologies for Mars, but have become somewhat polarized by the unwillingness of others to adapt an eclectic solution. My view of power generation is I don't care to see the Martian landscape become a giant solar farm as far as the human eye can see. I actually consider both solar farms and wind farms to be producing a different environmental impact: visual pollution.

I'm mostly in agreement, I think: Nuclear could work for maybe 50 kWe and above, and solar theoretically for pretty much any amount of power from 1 W to 1 TW (Actually, covering 100% of Mars' surface in panels should generate around 5 petawatts of power, but that's not going to happen any time soon).

As far as visual pollution--I don't disagree entirely (although having recently driven cross-country the giant wind farms in SD, WY, and MT are quite stunning in their way), but that seems like a relatively low concern on the order of priorities.  It's not all that hard to transmit electrical power over long distances, either, so if the local population doesn't want their views spoiled by their solar power plants they could certainly set them up a hundred km or more from the population center for a relatively small expenditure of resources.  In the far future I could see the great volcanoes of Tharsis becoming big industrial production centers due to their relative immunity to dust storms and lower atmospheric haze; on the other hand there exists a specific need for conservation in the peaks of some of the Solar System’s biggest mountains.

knightdepaix wrote:

Why do we need sulfuric acid in the first place? Does the fact that industries on Earth need the acid mean that it is needed on Mars on the onset of immigration?

For existence, chlorine in the form of perchlorate has been confirmed and fluorine in minerals suggested. On Earth, hydrochloric acid can etch metal surface and various acids of fluorine and hexafluorate are used in producing aluminium and silicon metals from ores. Smelting iron ores need carbon monoxide. The rocks after extracting iron metal provide the calcium oxide. Then the conventional smelting for iron can begin.

It's true that if all you need is a strong acid, HCl and H2SO4 are both strong acids.  However, they actually differ substantially in strength:  The ka of HCl is 1.3e6, while that of H2SO4 is 1.0e3.  This doesn't mean that HCl is 1000 times stronger than H2SO4 exactly but it certainly does like to dissociate more (Not 1000 times more, though, it has to do with the dissociation constant, etc.)

There are other differences too.  HCl is a gas at STP while H2SO4 is a liquid.  I've read that you can't really use HCl as a solution above 37% concentration (12.5 M) because it's too volatile and evaporates.  H2SO4, on the other hand, is liquid all the way up to 100% concentration (18.5 M).  There are other applications where HCl is bad, too: In electrolysis applications, HCl will be electrolyzed before water; If you put HCl into water and supply a voltage, it will produce H2 and Cl2 gas, not H2 and O2.  This is not the case for H2SO4, which has a higher standard electrode potential.

Then there's questions of neutralization: Chloride salts are generally soluble in water, while sulfate salts are generally insoluble.

Now on the other hand, it seems reasonable to think that it may be cheaper to produce H2SO4 than HCl (on Earth).  The production process for H2SO4 is basically a combustion process, with a special catalyzed combustion step in the middle and then a hydration step.

On the other hand, HCl is made by an electrolytic process.  As I mentioned, the chloride ion will be oxidized before oxygen in aqueous solution.  I believe it is most often produced by electrolysis of a NaCl solution in water.  The electrodes produce H2 and Cl2, with Na+ and OH- remaining in solution.  In theory, you could recover most of the energy by combining the H2 and Cl2 in a fuel cell to form HCl.  In practice I do not believe there are any fuel cells that can handle the hydrochloric acid solution produced as a byproduct and the energy is lost.  On the plus side I suppose you also get NaOH out of it, which is afaik the most important strong base out there.


-Josh

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#25 2018-08-04 00:52:17

JoshNH4H
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Re: Sulfuric Acid on Mars

Oldfart1939 wrote:

Sulfuric acid is the "Mother of all Chemical Industry." That said, the 14 Tonnes Louis suggests is trivial amount for al the suggested uses. Look at the chemistries of making all the plastics and other chemicals to be extracted/processed from Martian regolith.

If I were going to build such a plant here on Earth, I would initially raise about $100 Million--for starters--then get the engineers working on plant design. This is NOT a trivial process. But again, nothing done with Mars in mind is trivial; neither is the associated cost.

Agreed that louis's estimate is an extreme lowball, possibly 100 times too low.  It doesn't make sense to use world averages because any martian settlement would have resource consumption similar to or exceeding that of the developed world and high industrial production.  This is basically a recipe for very high usage of industrial chemicals.  Louis appears to also have an incorrect figure for global mean production, which on a per-person basis is roughly twice as large as the numbers he is using.

I do wonder where that $100 million number comes from.  I'm not disagreeing, per se, but it seems like a lot.  That's roughly 1000 engineer-years of money.  I think it's defensible, depending on scale, to spend less money on developing the plant and accept lower operating efficiency/higher operating costs (either higher labor input per unit product than strictly necessary or lower quality product, or both), and improve the plant incrementally as population and demand expand.  Experience is the best teacher anyway.

Does anyone have information about sulfur or sulfides on Mars?  I've done a bit of preliminary research and it's clear that there's plenty of sulfates, but I haven't found any references to free sulfur or sulfides which Oldfart1939 has pointed out are much preferable.  It wouldn't necessarily surprise me if they didn't exist because of the oxidizing environment but it would complicate the sulfuric acid production process.


-Josh

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