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The impact of water on the partial oxidation of methanol over a FeMo-catalyst

Axelsson, Sarah LU (2015) KET920 20151
Chemical Engineering (M.Sc.Eng.)
Abstract
This diploma work has been performed in collaboration with Johnson Matthey, a company supplying catalysts and technologies, such as formaldehyde plants and catalysts. The aim of the master thesis project was to investigate if and how water impacts the partial oxidation of methanol to formaldehyde over a FeMo-catalyst. The investigation covers how water affects the selectivity to the main product and byproducts and also their formation rates at different reaction conditions. This was investigated by performing various experiments and the data obtained from the experiments was used to fit different rate models found in literature by using a kinetic simulation program called Athena Visual Studios.
Based on earlier performed experiments and... (More)
This diploma work has been performed in collaboration with Johnson Matthey, a company supplying catalysts and technologies, such as formaldehyde plants and catalysts. The aim of the master thesis project was to investigate if and how water impacts the partial oxidation of methanol to formaldehyde over a FeMo-catalyst. The investigation covers how water affects the selectivity to the main product and byproducts and also their formation rates at different reaction conditions. This was investigated by performing various experiments and the data obtained from the experiments was used to fit different rate models found in literature by using a kinetic simulation program called Athena Visual Studios.
Based on earlier performed experiments and literature it is indicated that water might have an inhibitory effect on the reaction of methanol and will reduce the number of available active sites of the catalyst. This could possibly result in lower activity but also lower selectivity to various byproducts.
The experiment and operating conditions have been evaluated as to ensure the data obtained to be intrinsic kinetic data, free from any heat and mass transfer limitations. The models found in literature were based on two common mechanism principles used for catalyst reactions, Langmuir-Hinshelwood which is based on the Langmuir isotherm and also Mars van Krevelen. All models took the water concentration into consideration.
From the experimental results it was a clear trend that the selectivity to formaldehyde in-creased as the water concentration increased. As for the two major byproducts, dimethyl ether and dimethoxymethane, the selectivities decreased as the water concentration increased. The formation rates decreased for all formed products, this being explained by site blockage and site isolation. Based on the results, there were some indications that the catalyst consists of more than one type of active site, which was also indicated in literature. The major byproducts seem to be formed at a more acid site than the site responsible for formaldehyde formation. Basic sites also seem to be present at the catalyst and are indicated to be responsible for CO formation. This makes the Langmuir isotherm invalid since it is based on that the catalyst only consists of one type of active sites. As to obtain a more complete understanding of how water affects the formation rates and selectivities of the various products formed a further investigation is recommended.
Neither of the models was able to describe the kinetics of the various reactions in a successful way; the model based on a combination of the two mechanisms did have the best fit though. This might be caused by several facts, such as not suitable models or limited validity range of various parameters. A new model based on other mechanism theories, which allows for more than one type of active site, is suggested to be further evaluated. (Less)
Popular Abstract (Swedish)
Johnson Matthey Formox är ett företag som designar och säljer fabriker för produktion av kemikalien formaldehyd. Företaget tillverkar även katalysatorer för detta ändamål. För att erbjuda en bra och konkurrenskraftig produkt till sina kunder är företaget måna om att processen skall vara effektiv och framförallt kostnadseffektiv. En del i detta är att kartlägga hur vatten påverkar produktionen av formaldehyd.
Formaldehyd är en av de tjugo mest producerade kemikalierna i världen och den används i en mängd produkter, så som i plaster och plywood. Formaldehyd produceras genom att låta metanol och syre reagera på en katalysator som gör att formaldehyd bildas. Eftersom råvaran metanol är den överlägset största kostnaden vid produktion av... (More)
Johnson Matthey Formox är ett företag som designar och säljer fabriker för produktion av kemikalien formaldehyd. Företaget tillverkar även katalysatorer för detta ändamål. För att erbjuda en bra och konkurrenskraftig produkt till sina kunder är företaget måna om att processen skall vara effektiv och framförallt kostnadseffektiv. En del i detta är att kartlägga hur vatten påverkar produktionen av formaldehyd.
Formaldehyd är en av de tjugo mest producerade kemikalierna i världen och den används i en mängd produkter, så som i plaster och plywood. Formaldehyd produceras genom att låta metanol och syre reagera på en katalysator som gör att formaldehyd bildas. Eftersom råvaran metanol är den överlägset största kostnaden vid produktion av formaldehyd är det av stor vikt att optimera processen och se till att så mycket som möjligt av metanolen reagerar till formaldehyd.
En katalysator är ett ämne som underlättar en reaktion utan att själv bli förbrukad. Katalysatorn som påskyndar reaktionen mellan metanol och syre består av ett pulver som formats som pellets och består av olika metaller. Reaktionen sker på katalysatorytan på specifika platser, så kallade aktiva säten, på vilka metanol och syre sätter sig. Genom att förstå hur katalysatorn fungerar och hur reaktionen sker kan en kostnadseffektiv produktion av formaldehyd uppnås genom att minska risken för bildandet av biprodukter.
Det är sedan tidigare känt att vatten också kan sätta sig på de aktiva sätena på katalysatorn och därför blockera dessa genom att hindra metanol från att sätta sig på de aktiva sätena. Resultatet blir att mindre formaldehyd kan bildas. Vad som också noterats vid tidigare experiment är att mängden biprodukter reduceras, vilket är en önskvärd effekt.
För att studera hur vatten påverkar reaktionerna som sker i reaktorn har en mängd experiment genomförts där vattenhalten, metanolhalten samt reaktionstemperaturen varierats. Detta för att uppnå en komplett bild av hur vattens påverkan ser ut. Den laborativa uppställningen efterliknade en verklig process fast i mycket mindre skala. Resultatet från dessa försök var att katalysatorns aktivitet minskade då vattenhalten ökade, det vill säga att vatten hindrar bildandet av både formaldehyd och flera biprodukter. Dessa resultat uppnåddes för både låg och hög reaktionstemperatur. Det verkade dock som att bildandet av biprodukter reduceras mest vid ökad vattenhalt. Detta kan bero på att fler metanolmolekyler behöver vara nära varandra på katalysatorytan för att biprodukterna ska bildas, jämfört med bildandet av formaldehyd då endast en metanolmolekyl behövs.
Detta resultat leder till att bildandet av formaldehyd främjas. Ju mer formaldehyd som bildas av metanolen desto mindre blir produktionskostnaden. En reducerad mängd biprodukter är dessutom bättre för miljön då mindre kolföreningar behöver förbrännas i reningsanläggningen och därmed släpps mindre koldioxid ut i naturen.
Dessa inledande experiment indikerar en positiv inverkan av att tillsätta vatten, men för att se hur effekterna blir i en riktig process behöver fler experiment utföras i större skala. (Less)
Please use this url to cite or link to this publication:
author
Axelsson, Sarah LU
supervisor
organization
course
KET920 20151
year
type
H2 - Master's Degree (Two Years)
subject
keywords
kemiteknik, chemical engineering
language
English
id
7442654
date added to LUP
2015-06-24 11:34:05
date last changed
2015-06-24 11:34:05
@misc{7442654,
  abstract     = {This diploma work has been performed in collaboration with Johnson Matthey, a company supplying catalysts and technologies, such as formaldehyde plants and catalysts. The aim of the master thesis project was to investigate if and how water impacts the partial oxidation of methanol to formaldehyde over a FeMo-catalyst. The investigation covers how water affects the selectivity to the main product and byproducts and also their formation rates at different reaction conditions. This was investigated by performing various experiments and the data obtained from the experiments was used to fit different rate models found in literature by using a kinetic simulation program called Athena Visual Studios. 
Based on earlier performed experiments and literature it is indicated that water might have an inhibitory effect on the reaction of methanol and will reduce the number of available active sites of the catalyst. This could possibly result in lower activity but also lower selectivity to various byproducts.
The experiment and operating conditions have been evaluated as to ensure the data obtained to be intrinsic kinetic data, free from any heat and mass transfer limitations. The models found in literature were based on two common mechanism principles used for catalyst reactions, Langmuir-Hinshelwood which is based on the Langmuir isotherm and also Mars van Krevelen. All models took the water concentration into consideration. 
From the experimental results it was a clear trend that the selectivity to formaldehyde in-creased as the water concentration increased. As for the two major byproducts, dimethyl ether and dimethoxymethane, the selectivities decreased as the water concentration increased. The formation rates decreased for all formed products, this being explained by site blockage and site isolation. Based on the results, there were some indications that the catalyst consists of more than one type of active site, which was also indicated in literature. The major byproducts seem to be formed at a more acid site than the site responsible for formaldehyde formation. Basic sites also seem to be present at the catalyst and are indicated to be responsible for CO formation. This makes the Langmuir isotherm invalid since it is based on that the catalyst only consists of one type of active sites. As to obtain a more complete understanding of how water affects the formation rates and selectivities of the various products formed a further investigation is recommended.
Neither of the models was able to describe the kinetics of the various reactions in a successful way; the model based on a combination of the two mechanisms did have the best fit though. This might be caused by several facts, such as not suitable models or limited validity range of various parameters. A new model based on other mechanism theories, which allows for more than one type of active site, is suggested to be further evaluated.},
  author       = {Axelsson, Sarah},
  keyword      = {kemiteknik,chemical engineering},
  language     = {eng},
  note         = {Student Paper},
  title        = {The impact of water on the partial oxidation of methanol over a FeMo-catalyst},
  year         = {2015},
}