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Fuels and Chemicals from Biomass:
Condensation of Short AldehydesPDF
  • Introduction
  • Objective & Approach
  • Experimental
  • Results
  • Conclusions

Introduction & Motivation

The increased price of petroleum over the past several years, coupled with concerns regarding stability of the source of petroleum, has generated interest in producing liquid transportation fuels domestically, both from increased drilling as well as alternative sources, such as biomass.

Transesterification of vegetable oils produces biodiesel, but also has the byproduct of glycerin. Something must be done with the glycerin apart from discarding it. One option is to convert it to liquid transportation fuels as well.

Fast pyrolysis of biomass also produces small aldehydes which, by themselves, offer little in the way of value. If they were combined with other aldehydes in addition and condensation reactions, the final product may also be valuable as a liquid transportation fuel.

propanal

 

Objectives & Approach

Glycerol is decomposed to short, reactive compounds, including short aldehydes.

Vapor phase aldehydes are passed over basic catalysts to increase their molecular weight by coupling reactions.

Higher molecular weight yields lower vapor pressure suitable for gasoline.

glycerol-short aldehydes

 

Catalyst preparation

Zeolite NaX is ion-exchanged with Potassium and Cesium to generate a solid catalyst with stronger basic sites than NaX. Acid sites are leveraged to assist ring-closing reactions, resulting in a self-limiting reaction scheme, preventing excessively heavy compound from forming.

 

 

 

 

 

 


 

Conversion vs. Time on stream

Alkali-exchanged zeolites are more active than traditional basic catalysts. Proper ion selection results in greatly improves stability.

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Pictures of feed & trimer products in zeolite window

aldehyde-zeolitetrimer-zeolite

 

Proposed mechanism

Consecutive aldol addition over acidic or basic sites, followed by dehydration, results in higher molecular weight compounds, decreasing the volatility and increasing the compatibility with the petroleum fuel pool.

mechanism

After three small molecules have combined with each other, the acid-catalyzed ring closure reaction prevents further additions, preventing formation of undesirable heavy compounds.

mechanism2

Conclusions

Short aldehydes from glycerol decomposition may be combined to higher molecular weight compounds over solid basic catalysts.

Further study is required to understand the mechanism so it may be optimized.