GEK Wiki / Alcohols
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Alcohols

Page history last edited by jay 9 years, 5 months ago

The Alcohols:

The combustion of an oxygenated fuel creates reactive oxygen species (ROS) which are highly reactive free radicles at a lower flame temperatures. When an oxygenated fuel is added to the less efficient mixed chain-length range  of hyrdocarbon fuels this greatly enhances the combustion efficiency of the fuel leading to a much lower soot production.

 

Methyl Alcohol:

Methanol is less thermodynamically favorable than creating higher alcohols and hydrocarbons which typically requires a higher compression temperature of the syn gas (30-50 atm). However, less water is created than that of hydrocarbons and higher alcohols from synthesis gas. Conversions of methanol into gasoline (Mobil process) and higher alcohols (Union Carbide process) are much more thermodynamically favorable and have a higher selectivity of carbon chain-lengths than direct higher alcohol synthesis or Fischer-Tropsch.

 

Catalysts for methanol include zinc oxide (ZnO) and copper oxide (CuO). Aluminum oxide is used as a support in earlier technologies. In the more recient and more efficient lower pressure slurry technologies, aluminum is used in smaller amounts as a promotor, and in direct dimethyl ether (DME) production, it is used as a dehydrator as Al2O3.

 

 

 

Higher Alcohols:

Ethyl Alcohol:

Biological:

The majority of the technologies converting syngas from biomass to ethanol are biological conversions using fermentation or enzymes. Biological process are much slower in their reaction rates, although much more selective towards ethanol than metal catalysts.

Metal Catalysts:

Most of the metal catalysts that are being used to selectively produce ethanol from syngas have high reaction temperatures and pressures making it less conventional. Slurry technologies of silica gel with suspended catalysts allow reactions at lower temperatures and pressures. (specifics to be added soon.)

Iowa State University is using syngas from biomass to produce ethanol at reasonable temperatures and pressures using carbon-based nano-particles from graphite that carry a transition metal with high yields. Hopefully in the near future they will reveal a less vague and more technical article.

 

Mixed Alcohols

The technology to create higher alcohols are less specific in their selectivity. They are made with Fischer-Tropsch catalysts (Fe, Co, Ni, and Ru oxides) with mixed oxides of Cr, Mo, Cu, and Zn.

"Ex:  A catalyst composition of Cr2O3/MnO/Rb2O (1:0.85:0.42), with the synthesis gas consisting of CO and H2 at 400C and 200 atm was converted to liquid products consisting of 42% methanol, 38% higher alcohol (mostly ethanol), and 15% aldehydes and acetals" (SERI).

 

Water

The very basic reaction of syngas to alcohols:

methyl alcohol:   CO + 2H2 --> CH3OH

ethyl alcohol:      2CO + 4H2 --> C2H5OH + H2O

propyl alcohol:    3CO + 6H2 --> C3H7OH + 2H2O

etc.

 

The production of C2 and higher alcohols always will produce at least one water molecule as the 'unused' oxygen is liberated from the carbon monoxide to creat a C-C bond. This 'unused' oxygen will go to create water in the already highly water soluble alcohol mixture. Because water has a high affinity to the lower chain alcohols, a lot of energy (exactly how much?) is needed to separate the alcohol/water mixture during distillation.

*Dehydrating salts can be used and then baked in the sun? Not economical for a large industry, and I haven't seen much on this really, but it would be cool if this worked really well on a small scale.

 

Materials:

Methanol is the most corrosive alcohol. It acts as a weak acid, and interestingly it acts as its own oxidizer and reduction agent. This characteristic can be seen in the newer Direct Methanol Fuel Cells (DMFC).

 

Always check the compatability of plastics and metals with the alcohol fuels, especially methanol. Because methanol has been used in the biodiesel industry, recently there has been an increase in materials and products that are resistant to methanol.

Chemical Compatability and Resistance Charts

CAT Pumps Compatability Chart

 

LPMeOH (TM): http://www.google.com/patents/about?id=icYYAAAAEBAJ&dq=lpmeoh

 

 

 

 

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