Sciencemadness Discussion Board

The Neste process: second generation biodiesel

Klute - 5-12-2008 at 02:48

I recently stumbled on a article about a somewhat new process of preparing synthetic biodiesel from triglycerides, producing long chain alcane sinstead of the well-known methyl esters...

http://www.biodieselmagazine.com/article.jsp?article_id=1505...

I find this pretty interesting. Of course it would seem obvious that the amount of energy required to hydrogenate triglycerides to alkanes is much superior to that required by transesterification, so it is still not clear if this really a viable option for an eventual replacement of fossile diesel.

I am more particularily intereste din the chemical aspect of this reaction. The way I see it, the triglycerides are first saturated, then hydrogenolyzed to form fatty alcohols and glycerol. Then I guess they must employ an acidic catalyst that will deshydrate the alcohols to alcenes, which are then reduced to alkanes. The formed glycerol would then be reduced to propane, via acrolein perhaps... What do you guys think? Such a process would require quite harsh conditions..

I know that most fatty alcohols are produced via hydrogenolysis of methyl esters, at least in France, so it must be energetically favourable to run two seperate process (transesterification and hydrogenation) than to directly hydrogenate the triglycerides, at least with the low-pressure process.

If hydrogenating glycerol to propane is economically feasible, how come this isn't already in place to use the never ending stock produced each day by transesterification process?

I'm also supposing the biological balance isn't as favourable as it is with the conventional biodiesel, (the plants consume as much CO2 as is produced by the combustion, at least they say so), owing to the large amount of energy required to push the hydrogenation up to alkanes.. Or maybe they work on super-active catalysts?


Any comments or discussions?

Further info on the NExBTL fuel:

http://en.wikipedia.org/wiki/NExBTL
http://www.climatechange.ca.gov/events/2006-06-27+28_symposi...

Well, there is a rather complete paragraph on the Neste process in the following review:

Synergies between Bio- and Oil Refineries for the Production of Fuels from Biomass
George W. Huber, Avelino Corma,
Angewandte Chemie International Edition; (38), 7184-7201
Link
Quote:

"The first step is the hydrogenation of
the C=C bonds of the vegetable oils. The hydrogenated
vegetable oils then form free fatty acids, diglycerides, and
monoglycerides. [...]
At lower space velocities and temperatures, the free fatty acids, diglycerides, monoglycerides, triglycerides, and
waxes undergo two different pathways to produce normal
alkanes. The first is decarbonylation, which produces normal
liquid alkanes (C17 if from a C18 free fatty acid), CO or CO2,
and propane. This pathway requires the least amount of
hydrogen. Alternatively, triglycerides undergo a dehydration/
hydrogenation pathway to produce a liquid n-alkane (e.g. C18
if from a C18 acid) and propane. The straight-chain alkanes
can undergo isomerization and cracking to produce lighter
and isomerized alkanes. It is likely that organic acids
produced in the hydrotreating process catalyze the isomerization
and cracking reactions. If straight-chain alkanes are
desired, which is typically the case for diesel fuel, then the
isomerization and cracking reactions should be minimized.[...]

Hydrotreating conditions
involved temperatures of 350–4508C, H2 partial pressures of
48–152 bar, LHSVs of 0.5–5.0 h1, and standard hydroprocessing
catalysts including cobalt molybdenum (Co-Mo) and
nickel molybdenum (Ni-Mo).[...]



[Edited on 5-12-2008 by Klute]

[Edited on 5-12-2008 by Klute]

Contrabasso - 11-1-2009 at 02:12

The process that you chose for converting vegetable oil to diesel fuel replacement, is irrelevant! We consume more diesel than we have planet surface to grow the plants! Those plants we process for diesel cannot be used to feed people. -eg Maize feeds people or cattle OR makes liquid fuel.

The need is for a process tolerant of the impurities that second user veg oils carry after use in the food industry.

Early research was done in "Southern Rhodesia" in the days of fuel sanctions. If a farm allocated 33% of it's land to sunflowers then the oil produced would supply the farm's fuel needs. However that is a hot and fertile land area with, then, a low per capita power consumption. Whether bio fuel can ever replace mineral diesel is doubtful.

Klute - 13-1-2009 at 08:26

Well, indeed this isn't a solution for complete replacement of petrodiesel! But it is a much more efficient process than the conventional transesterification, requiring no methanol, and producing only propane, water, and straight chain alkanes, which are more efficient than methyl esters, and generate no NOx, SOx, or CO2 (during combustion, still does produce some during transport and hydrogenation). Apparently, even when used in blends it highly increases cetane number, and reduces emissions.

Obviosuly it isn't a complete solution to fuel crisis, but a much more viable alternative to methyl esters IMHO.

Used cooking oils can be used after treatment by alkali, but what is the life-spand of the catalyst then, I have no idea.

A more promising approach would be other biomass to fuel, including none-alimentary feedstocks, as this is indeed a major moral dilema: steal food from the hungry poor to give fuel for the rich?!

Best way would be combining waste-treatment by bacteria, and using th eformed biomass to make fuel! Even if only biogass would be produced, some kind of oligomerisation process to form higher alkanes would make this viable for liquid fuels.

I really feel that this should be a major task for the actual chemists, getting rid of this condemned self-destructing petrodiesel dependancy...

Combining biofuels and Pantone technology would be a real solution for tomorow, but I guess I'm been utopic here... The petrol companies will never tolerate loosing their control and income, even if this means stopping/diverting technology evolution...

Anyway, i was ratehr interested in the chemistry aspect, and obtaine dall my answers from the Angw. Chem. Article.

Considering the construction of a 800 000 ton/year plant in Singapour, combined with two actual 170 000 ton/year plants in Finland, it seems we will have some NexBTL in our reservoirs soon (at least in Europe)... So long, methyl esters.

not_important - 14-1-2009 at 04:16

Quote:
If hydrogenating glycerol to propane is economically feasible, how come this isn't already in place to use the never ending stock produced each day by transesterification process?

It's be worked on, as has hydrogenation of glycerol to propandiol and propanol, as well as conversion to H2 + CO2;which can be used to make methanol, or in the case you're talking about make propane and hydrogenate the oils. It's new stuff, most of the papers seem to be 4-6 years old. Propane is fairly cheap, I suspect the conversion of glycerol to propane using hydrogen made from natural gas is not economic, it would take the use of some of the glycerol as a hydrogen source to make it competitive - maybe.

See pages around the one here http://tinyurl.com/89qlv9
Quote:
and generate no NOx, SOx, or CO2 (during combustion, still does produce some during transport and hydrogenation). Apparently, even when used in blends it highly increases cetane number, and reduces emissions.


In comparison to rockoil diesel, not to fatty acid methyl ester diesel. I doubt it produces no NOx, standard ester biodiesel doesn't produce SOx either. Much of the soot from diesel is due to the aromatics content, which the biological fat/oil derived fuels don't have.
Quote:
Used cooking oils can be used after treatment by alkali, but what is the life-spand of the catalyst then, I have no idea.


Resulting in fatty acid salts that must be dealt with. Reactive distillation can produce the esters from FFA containing oils with no extra treatment and no waste. It also produces a much higher quality glycerol, the standard alkali catalysed transesterfication produces low grade glycerol and waste salts.
Quote:
A more promising approach would be other biomass to fuel, including none-alimentary feedstocks, as this is indeed a major moral dilema: steal food from the hungry poor to give fuel for the rich?!

Best way would be combining waste-treatment by bacteria, and using th eformed biomass to make fuel! Even if only biogass would be produced, some kind of oligomerisation process to form higher alkanes would make this viable for liquid fuels.


The problem with biofuels is the low density of production. A half watt per square meter is around the European norm, the tropics run around 1 watt with the potential to read between 1.5 and 2 watts/sqm with intensive cultivation, fertilier application, and genetic modifications. There is considerable debate as to how much of the energy produced ends up being used to produce the crop.

At 5 km/kWh for BEVs, you need at least 400 sq meters in Europe to travel 1 km, that should be modified by the fuel-to-plug efficiency, or for ICE cars by the fuel-to-wheel efficiency. Pure electric vehicles getting their power from large modern power plants are roughly twice as efficient as modern diesel engine vehicles burning the fuel; the BEV efficiency goes up for urban driving where regenerative braking becomes important. Say about 40% fuel-to-wheel for BEV, 20%*oil (meaning less than 20%) conversion efficiency for diesels.

For the U.S., the waste fats and oils amount to maybe 3% or so of the vehicle fuel consumption. Converting sewage and garbage to methane would produce more, maybe 1/3 their natural gas consumption or less than 1/5 their petroleum consumption; however the energy losses in converting methane to higher alkanes are significant and the more direct conversions tend to give highly branched isomers which do not make good diesel fuel; but may work OK in conventional gasoline engines.
Quote:
Combining biofuels and Pantone technology would be a real solution for tomorow, but I guess I'm been utopic here... The petrol companies will never tolerate loosing their control and income, even if this means stopping/diverting technology evolution...


Ah, Pantone ...
Quote:
"I've known Paul for about 20 years. He is always talking about some huge development about to unfold that he is involved with. Most of the time nothing happens."
(Told in phone conversation to Sterling Allan on March 20, by a source who will remain anonymous.)

"It's always 'next week' some huge demo is going to happen, but 'next week' never happens. He's told me that at least 15 times." (someone else)

"He's told me that 500 times!" (yet someone else)


While PAC is real, it does not offer efficiency increases anywhere near what Pantone claims. And the petroleum companies still control the refineries to convert fats and oils into alkane diesel fuel; the size of the plant tends to be an important part of efficiency.