Synthetic petroleum

[Cirocco]

My bad, I misremembered and wasn't clear enough in my description:

yes, a lot of the reactions are exothermic, but they still need high temperatures to happen at a reasonable rate. Essentially: the reaction produces heat, but it only starts happening at a reasonable rate at high temperatures (200°C and up). So you still need to heat the reactor all the time because even though the reaction is exothermic, you lose heat because you are constantly evacuating the heated products and pushing fresh, "cold" reagents into the reactor. If those reagents are not heated then the reaction slows down and falls to a n

ear standstill. 

As for recycling the energy: it's possible to recycle some heat using heat exchangers, but it's not worth it to try and re-introduce it into the process: it adds too much complexity for very little gain. It's far easier to just burn a bit more gas. That being said, using the waste heat to heat people's homes or some other process that doesn't require super high temperatures is perfectly feasible.

3 hours ago, JebKeb said:

Any byproducts and other wax would be sent to a hydrocracker to be turned into light and heavy naptha, kerosene and gas oil.

Well there's your problem. Waxes are reeeeeaaaaaally hard to crack properly into usable fractions. Heavy hydrocarbon chains, sure, you can crack off a couple carbon atoms from the edges and turn them into lighter fractions and gas (which is usually just burned with a large torch on top of the refinery). But with waxes, you need to selectively crack the heaviest ones down the middle without breaking up the rest of the chain and without cracking the lighter ones. And that is exactly what is so hard: cracking long chains without cracking the small ones into useless, short-chain gasses. Add to that the energy requirements being so restrictive, and there's your explanation for why this process isn't widely used. It's simply still cheaper to just drill it up.

[Sereneti]

and, there are so many uses for waxes..
 

[JebKeb]

On 22/06/2016 at 8:42 PM, Cirocco said:

Well there's your problem. Waxes are reeeeeaaaaaally hard to crack properly into usable fractions. Heavy hydrocarbon chains, sure, you can crack off a couple carbon atoms from the edges and turn them into lighter fractions and gas (which is usually just burned with a large torch on top of the refinery). But with waxes, you need to selectively crack the heaviest ones down the middle without breaking up the rest of the chain and without cracking the lighter ones. And that is exactly what is so hard: cracking long chains without cracking the small ones into useless, short-chain gasses. Add to that the energy requirements being so restrictive, and there's your explanation for why this process isn't widely used. It's simply still cheaper to just drill it up.

Thanks for clarifying what cracking actually is - it's cracking molecules into fractions, not set sizes.

Vacuum distillation would probably be good to seperate out the wax into different grades.

Just being curious, do different conditions during cracking give you different gases?

[Cirocco]

On 6/25/2016 at 0:13 AM, JebKeb said:

Just being curious, do different conditions during cracking give you different gases?

Absolutely, it depends on several factors including but not limited to:

- the type of catalyst

- temperature

- time of exposure to the catalyst and therefore, flowrate through the reactor (higher flowrate = less time for the hydrocarbons to react)

- hydrogen fraction in the mixture

- isomerisation of the molecules you want to crack. Isomerisation means the degree to which the long carbon chains are branched. A hydrocarbon chain can consist of just a bunch of carbons in a line with hydrogens on the edges, but it can also be a line of carbons with a bunch of other lines of carbons branching off of it, kind of like a tree or a root system. High isomerisation means a lot of branching. (this isn't really a process parameter, but it also influences the type of product you get so I included it as well)

 

Now as to how those parameters influence your process:

The type of catalyst: catalysts are usually chosen for their activity. Intuitively, you'd think that high activity is good: high activity means more cracking which means more means more long-chainers broken down to short chains. Problem is that while this is true, your catalysts don't stop there. They'll crack everything they can get their hands on, including those nice new medium-length chains you just made. Therefore, current catalysts almost always have a trade-off: high activity means lots of stuff cracked but low selectivity (i.e. a lot of the stuff that comes out is too short and not usable) whereas lower activity means not that many long chains cracked, but more usable products. The currently used method is, if I recall correctly, to use a medium-activity catalyst, run a purification step, then another cracking and do another 2-3 consecutive steps like that to try and turn a maximum amount of heavier fractions into usable ones. It's energy-intensive but it works. But this problem is also why researchers are trying to look for more selective catalysts that still retain a high activity (like we looked for in my master thesis).

 

Temperature: higher temperature means higher activity, more cracking (though again, often also less selective cracking) but also more coking. Coking is a problem where you essentially "burn" the carbon chains and turn them into soot ("cokes", in the jargon). These cokes then deposit onto the catalyst pellets and effectively clog up the pores into which the long chains insert themselves to be cracked. So again, it's about finding the balance between activity, selectivity and coking. You can regenerate the catalyst by literally burning off the cokes, but this is also detrimental to the catalyst. The less regeneration needed, the better. In short: high temperature means high coking, low selectivity and high activity. Low temperatures means less coking, less activity but higher selectivity.

 

Exposure time (flowrate): As mentioned before: cracking catalysts tend to crack everything they get their hands on. So the longer a molecule spends in the reactor, the more chance it has to be cracked. by adjusting the flowrate and pushing the (gasified) long-chain molecules faster or slower through the reactor, you can favor a certain amount of cracking steps. In short: high flowrate: less cracking but also less overcracking and less useless methane produced. Low flowrate, high cracking, but also more overcracking and more useless methane produced.

 

Hydrogen fraction: (hydro)cracking requires hydrogen: you break apart a C-C bond and stick a hydrogen on each end of the severed bond to get C-H H-C. As with any chemical reaction, you can push the reaction to one side or the other by supplying an overabundance or shortage of one of the reagents (in this case, either long chain hydrocarbons or hydrogen gas). Lots of hydrogen means less coking and more cracking but, as always, also more over-cracking and methane production. Less hydrogen means less cracking but also more coking. You also need to take into account that hydrogen gas costs money and it also has a tendency to activate any sulfur or other impurities in the initial mixture. Sulfur gets turned into H2S-like molecules and those absolutely murder your catalyst. You can literally render an entire reactor useless in minutes if you run highly polluted oil through it.

 

Isomerisation: A bunch of long-chain molecules which are just a single line of carbons stuck together are extremely hard to crack down the middle, they'll just fragment at the edges. As a rule of thumb: the more "branches" a carbon chain has on a certain point, the easier it will break at this branching point. Because of this, the more modern processes of cracking are a two-step process: one reactor first branches (isomerizes) the long chains in the middle(ish) and the second reactor is the actual cracker, in which the long chains will be more easily be cracked in the middle instead of at the edges, because they have more branches down the middle.

 

Petrochemistry is very much a story of percentages. It's almost impossible to get a nice, clean reaction A + B --> C. It's always A + B --> mostly C, but also a bunch of D, E and some F in various percentages. The trick is to try and get as much usable C as possible and minimise or somehow recycle the production of D, E and F.

So in answer to your question: the process parameters influence mostly the degree of cracking of the mixture. And the degree of cracking influences whether you get short-chain gasses or medium to long-chain gasses/liquids. Lots of activity = lots of gasses such as methane, ethane and the like. Less activity = more molecules in the reagions of C10-15 (liquid, usable stuff).

Whew! lots of text! but i was happy to once again dust off my petrochemical knowledge  Hope it helps!

 

Edited June 27, 2016 by Cirocco
better formatting and more logical structure of the post.

[JebKeb]

I've been looking at another method of producing synthetic fuels involving the dehydration of methanol, the Mobil Process.

First, methanol is dehydrated over SiO2 and Al2O3 to yield a mix of methanol and dimethyl ether (isomer of ethanol). Then it's dehydrated completely over ZSM-5 into ethylene and methylene, and oligomerised into a mix of branched paraffins and olefins, napthenes and aromatics. I think the catalyst structure determines the maximum length, so using different zeolite catalysts you could produce kerosene or diesel, as well as petrol.

Then I noticed that the Fischer-Tropsch process is practically decomposing CO into C and O and hydrogenating these into water and methylene, which then oligomerises into straight-chain paraffins and olefins. 

So, could you make an "advanced FT process" which uses the first few steps of FT through Co, then oligomerises the products over a zeolite catalyst providing much easier refining? Also, by blending the mixes of Co and different zeolites could you change the composition of the syncrude?

[Cirocco]

On 7/1/2016 at 10:46 AM, JebKeb said:

So, could you make an "advanced FT process" which uses the first few steps of FT through Co, then oligomerises the products over a zeolite catalyst providing much easier refining? Also, by blending the mixes of Co and different zeolites could you change the composition of the syncrude?

When you say Co, do you mean carbon monoxide or a Cobalt catalyst? Or something else entirely?

[JebKeb]

On 05/07/2016 at 7:20 PM, Cirocco said:

When you say Co, do you mean carbon monoxide or a Cobalt catalyst? Or something else entirely?

Cobalt catalyst. I am using the formula of things.

[JebKeb]

Let's just shift back to the low-temp FT process.

It appears to produce around 55% water, 40% hydrocarbons and 5% oxygenates. These hydrocarbons are around half/half paraffins and olefins. I was thinking, could you use a hydrotreating unit to turn olefins and alcohols into paraffins? I'm pretty certain we could easily hydrogenate the olefins, but adding H2 to alcohols I am wondering about.

CH3CH2OH + ? H2 -> 1,2

1 - CH3CH2OH3 -> CH3CH3 + H2O

2 - CH3 + CH4 + OH -> CH3OH + CH4

CH3OH + H2 -> CH4 + H2O

 

Is this in anyway possible?

[PB666]

On July 9, 2016 at 5:19 AM, JebKeb said:

Let's just shift back to the low-temp FT process.

It appears to produce around 55% water, 40% hydrocarbons and 5% oxygenates. These hydrocarbons are around half/half paraffins and olefins. I was thinking, could you use a hydrotreating unit to turn olefins and alcohols into paraffins? I'm pretty certain we could easily hydrogenate the olefins, but adding H2 to alcohols I am wondering about.

CH3CH2OH + ? H2 -> 1,2

1 - CH3CH2OH3 -> CH3CH3 + H2O

2 - CH3 + CH4 + OH -> CH3OH + CH4

CH3OH + H2 -> CH4 + H2O

 

Is this in anyway possible?

Nope, I believe that is a SN2 rxn, for water to be a leaving group r-ch2-oh2+ off of the ethanolium ion, it will exist as a specific ion a neutral ph of less than 10-7m. Sulfuric acid cause a condensation with this as a leaving group forming diethyl ether. 

CH3: has and extremely low pka. It will pull a hydrogen off of anyhthing, including basic ammonia.  CH. is a free radical, it will pull hydrogen off water or geneally any labile hydrogen. CR3+ is a SN2 intermediate, it tends to be fabored if R is not H. Free radicals can exist during cracking, adding a source of hydrogen breaks larger molecules, particularly with branched alkanes.  Addition of hydrogen to a mixture that has unstable aromatics tends to favor cyclic alkanes or branched alkanes. 

CH3-OH plus HBr forms Metyl bromine and water. This can be treated the borohydride to form methane, with ammonia to from methyl amine. 

[todofwar]

50 minutes ago, PB666 said:

Nope, I believe that is a SN2 rxn, for water to be a leaving group r-ch2-oh2+ off of the ethanolium ion, it will exist as a specific ion a neutral ph of less than 10-7m. Sulfuric acid cause a condensation with this as a leaving group forming diethyl ether. 

CH3: has and extremely low pka. It will pull a hydrogen off of anyhthing, including basic ammonia.  CH. is a free radical, it will pull hydrogen off water or geneally any labile hydrogen. CR3+ is a SN2 intermediate, it tends to be fabored if R is not H. Free radicals can exist during cracking, adding a source of hydrogen breaks larger molecules, particularly with branched alkanes.  Addition of hydrogen to a mixture that has unstable aromatics tends to favor cyclic alkanes or branched alkanes. 

CH3-OH plus HBr forms Metyl bromine and water. This can be treated the borohydride to form methane, with ammonia to from methyl amine. 

These flow reactors don't tend to be aqueous, and there aren't intermediates in SN2 reactions, you're thinking SN1. I'm not familiar with these catalysts, but I believe you can oxidatively add an alcohol to a metal, than beta hydride eliminate and reductively eliminate to give water and ethylene. Ethylene will then oligomerize easily enough. 

[PB666]

3 minutes ago, todofwar said:

These flow reactors don't tend to be aqueous, and there aren't intermediates in SN2 reactions, you're thinking SN1. I'm not familiar with these catalysts, but I believe you can oxidatively add an alcohol to a metal, than beta hydride eliminate and reductively eliminate to give water and ethylene. Ethylene will then oligomerize easily enough. 

There are some complex metal reactions that involved mercury, lead, copper, ect catalyst. i wouldn,t even call sn1 stable, by intermediates i mean transition state, since his chemistry was pretty mucked up i didn't think i needed to go into detail. In addition i should point out that if you are running high temperature metal catalyzed reactions, you are simply going to get a mess. 

[todofwar]

1 hour ago, PB666 said:

There are some complex metal reactions that involved mercury, lead, copper, ect catalyst. i wouldn,t even call sn1 stable, by intermediates i mean transition state, since his chemistry was pretty mucked up i didn't think i needed to go into detail. In addition i should point out that if you are running high temperature metal catalyzed reactions, you are simply going to get a mess. 

Not necessarily. Cu doped zeolite is used for partial alcohol oxidation, it's fairly selective based on pore size. And maybe high temperatures are bad, but metal catalysts can give you beautiful selectivity under the right conditions. 

[PB666]

2 hours ago, todofwar said:

Not necessarily. Cu doped zeolite is used for partial alcohol oxidation, it's fairly selective based on pore size. And maybe high temperatures are bad, but metal catalysts can give you beautiful selectivity under the right conditions. 

 The papers i see online are in rhe 1 - 10% range... what is your source, and dont give me a research gate link?. 

 

[JebKeb]

What about as a kind of visbreaker, could we use a hydrocracker to isomerise and crack the heavy hydrocarbons in LTFT syncrude? Also, would that hydrogen force it's way inbeween the e.g. CH3 and OH to give us methane and water from methanol?

[JebKeb]

Well, it looks like everything has been cleared up and chemistry has been sorted out. I'll be starting a new thread soon, with a summary of the entire concept. That will probably be the thread where everything is ironed out and economics are explored. I'll link to it in the next post.

[JebKeb]

I appear to have forgotten a LOT.

I've got several VERY important things to know. Firstly, what is the product composition in FCC product? 

Next, how would I remove longer alcohols from the syncrude? I have 2 methods.

• Add solvent to the syncrude. Seperate the solvent, water and light alcohols in a reflux drum. Deoxygenated syncrude heads onto the distillation column.
• Seperate water and light alcohols in a reflux drum. Send through a hydrotreater which splits the C-O bonds in alcohols using hydrogen, and also hydrogenates olefins into paraffins. (Olefins lead to aromatic formation in FCC and catalytic reforming, my spies tell me, so more paraffins would be desirable.)

Fjnally, what other oxygenates are found in LTFT syncrude? Sasol appears to have ketones as well as alcohols in their diagrams.

Edited July 20, 2016 by JebKeb

[rtxoff]

I just ran into this:

https://news.uic.edu/breakthrough-solar-cell-captures-co2-and-sunlight-produces-burnable-fuel