Potassium methoxide
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| General | ||||||||||||||||
| Surname | Potassium methoxide | |||||||||||||||
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| Molecular formula | CH 3 KO | |||||||||||||||
| Brief description |
white to yellowish odorless crystalline powder |
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| properties | ||||||||||||||||
| Molar mass | 70.13 g mol −1 | |||||||||||||||
| Physical state |
firmly |
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| density |
1.7 g cm −3 at 20 ° C |
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| Melting point |
359 ° C |
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| pK s value |
15.5 |
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| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | ||||||||||||||||
Potassium methoxide is the alcoholate of methanol with the counterion potassium and is used as a strong base and as a catalyst for transesterification , especially in the production of biodiesel .
presentation
The synthesis of potassium methoxide on a laboratory scale takes place through the strongly exothermic reaction of metallic potassium with methanol, releasing equimolar amounts of hydrogen .
Of secondary importance for the production of potassium methoxide is the reaction of metal hydrides, such as. B. potassium hydride with methanol.
The exothermic reaction of potassium hydroxide with methanol leads - while avoiding the formation of highly flammable hydrogen gas - in an equilibrium reaction to potassium methoxide and water, which has to be continuously withdrawn from equilibrium in a continuous process.
Also because of the pronounced hygroscopicity of potassium hydroxide, which contains approx. 10% water, the complete removal of the water is critical for the reaction conversion. The significantly higher rate of dissolution of potassium hydroxide in methanol compared to sodium hydroxide is advantageous . On an industrial scale, potassium methoxide is produced by the decomposition of the potassium amalgam formed in the chloralkali electrolysis of potassium chloride by the amalgam process with methanol. Contamination of the resulting potassium methoxide in methanol with metallic mercury can be removed by ultrafiltration . Solid potassium methoxide is obtained by distilling off the methanol.
Because of their simpler presentation and better handling, the solutions of potassium methoxide continuously withdrawn from the amalgam process are preferably used in concentrations of 25 to 32 percent by weight for chemical purposes.
As one of the larger manufacturers of alkali metal alkoxides, Evonik Industries has a capacity of several thousand tons of potassium methoxide solutions per year at its Lülsdorf / Niederkassel site. BASF operates a plant for the production of potassium methoxide in Ludwigshafen.
The displacement of the amalgam process by the ecologically and economically superior membrane process for the production of the bulk chemicals caustic soda and potassium hydroxide calls this standard production process for the production of alkali metal alcoholates into question in the future.
properties
Potassium methoxide is a white to yellowish, hygroscopic, odorless crystalline powder which reacts violently with water to form potassium hydroxide and methanol. The aqueous solutions obtained are strongly basic and have a corrosive and caustic effect. The substance is classified as a flammable solid with a self-ignition temperature of 70 ° C.
The information on human and ecotoxicity of potassium methoxide is based on the properties of the decomposition products potassium hydroxide and methanol during hydrolysis in an aqueous medium.
use
The carbonylation of methanol with carbon monoxide to methyl formate is carried out by strong bases, such as. B. potassium methoxide catalyzed.
The main area of application of potassium methoxide in the form of its 25-32% methanolic solutions is as a basic transesterification catalyst in biodiesel synthesis . Here be triglycerides of plant and animal origin with methanol in the presence of Alkalimetallmethanolaten to the corresponding fatty acid methyl ester ( English fatty acid methyl ester FAME) were reacted. Although potassium methoxide promotes the formation of fatty soaps - here potassium salts of the fatty acids from the triglycerides - more than the (cheaper) sodium methoxide, higher yields are achieved with potassium methoxide. The optimal conditions for biodiesel production from canola oil are given as a concentration of 1.59% by weight potassium methoxide, a reaction temperature of 50 ° C. and a methanol-oil ratio of 4.5: 1. The biodiesel yield is 95.8% with a fatty acid content of 0.75% by weight.
literature
- NY Turova, EP Turevskaya, VG Kessler, MI Yanovskaya (Eds.): The Chemistry of Metal Alkoxides . Springer US, 2002, ISBN 978-0-7923-7521-0 , doi : 10.1007 / b113856 .
Individual evidence
- ↑ a b c Entry on potassium methoxide in the GESTIS substance database of the IFA , accessed on July 23, 2016(JavaScript required) .
- ↑ a b c d Evonik Industries, GPS Safety Summary, Potassium Methylate , accessed on August 12, 2015.
- ↑ a b c OECD : Screening Information Dataset (SIDS) Initial Assessment Report (SIAR) for Potassium methanolate , accessed on August 12, 2015.
- ↑ Entry on Potassium methanolate in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- ↑ AR Ronzio, WB Cook: 4-amino-2,6-dimethylpyrimidine in: Organic Syntheses . 24, 1944, p. 6, doi : 10.15227 / orgsyn.024.0006 ; Coll. Vol. 3, 1955, p. 71 ( PDF ).
- ↑ Chimtek Engineering: Potassium Methylate Production Technology , accessed August 12, 2015.
- ↑ a b J. Ruwwe: Metal alkoxides as catalysts for the biodiesel production . In: Chim. Oggi Chem. Today . tape 26 , no. 1 , 2008, p. 26–28 ( online [PDF]).
- ↑ Patent EP2656905 : dehydration of solutions by ultrafiltration. Registered on April 10, 2013 , published on October 30, 2013 , applicant: Evonik Degussa GmbH, inventors: M. Horn, B. Helpap, M. Thiel, M. Neumann.
- ^ ICF International: Study on EU Implementation of the Minamata Convention on Mercury , accessed August 12, 2015.
- ↑ BN Pattanaik: The advances in processes and catalysts for the production of methyl formate by methanol carbonylation - a review . In: IJCPT . tape 3 , no. 2 , 2013, ISSN 2277-4807 , p. 55-70 .
- ↑ Patent US20140148614 : Process for preparing methyl formats by reaction of methanol with carbon monoxide in the presence of a catalyst system comprising alkali metal formats and alkali metal alkoxide. Registered on November 25, 2013 , published on May 29, 2014 , applicant: BASF SE, inventor: D. Schneider, K.-D. Mohl, M. Schäfer, J. Paschold, JH Teles, S. Rittinger.
- ↑ G. Knothe, J. Krahl, J. Van Gerpen (Eds.): The Biodiesel Handbook, 2nd Edition . AOCS Press, 2010, ISBN 978-1-893997-62-2 .
- ↑ A. Singh, B. He, J. Thompson, J. Van Gerpen: Process optimization of biodiesel production using alkaline catalysts . In: Appl.Eng.Agric. tape 22 , no. 4 , 2006, p. 597–600 , doi : 10.13031 / 2013.21213 ( PDF ( Memento from November 23, 2015 in the Internet Archive )).