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Screening of optimal pretreatment and reaction conditions for the isomerization-cracking of long paraffins over Pt/WO3–ZrO2 catalysts

Paper ID Volume ID Publish Year Pages File Format Full-Text
41784 45900 2010 10 PDF Available
Title
Screening of optimal pretreatment and reaction conditions for the isomerization-cracking of long paraffins over Pt/WO3–ZrO2 catalysts
Abstract

Pretreatment and reaction conditions for the isomerization-cracking of long paraffins over commercial Pt/WO3–ZrO2 catalysts were screened. Optimal conditions were seeked for the production of short, high octane branched paraffins for the gasoline pool. n-C16 was used as a model molecule. The reaction over the acidic catalyst was used to adjust the size of the molecules to the boiling range of gasolines and to add branching in order to increase the octane number of the product. These adjustments had to be done while minimizing the production of light gases and getting a stable activity level.With respect to the pretreatment it was confirmed that the best calcination temperature of the tungstate oxoanion promoted hydroxides was 800 °C. Optimality was mostly related to the activity level. The optimum temperature coincides with the appearance of small WO3 crystallites which are thought to be center for creation of Brönsted acid sites in the presence of platinum and hydrogen.Regarding the reaction conditions, increasing temperature values augmented the conversion but also increased the cracking. Therefore optimum values were found at moderate temperature given the high reactivity of the feed. Space velocity values were analyzed with attention to the liquid C5+ yield, the selectivity to branched isomers and the stability of the catalysts. Best yields to branched naphtha products were obtained with Pt/WO3–ZrO2 at WHSV = 18 h−1. The catalyst coking rate was a function of the H2/hydrocarbon ratio. A value of 6 was enough to attain a stable conversion value on Pt/WO3–ZrO2. The values of liquid yield as a function of pressure displayed a volcano pattern that was rationalized in terms of a non-classical bifunctional mechanism of reaction.High pressure values increased the concentration of Brönsted acid sites and hence the activity. Too high pressures enhanced hydrocracking and decreased the liquid yield.The results indicate that in general terms Pt/WO3–ZrO2 at moderate reaction conditions transforms a paraffinic heavy cut into a branched isomerizate that can be added to the gasoline pool to improve the quality properties. It was however found that under some conditions the octane gain is inversely proportional to the yield of light gases indicating that a high RON isomerizate can only be got at the expense of the liquid yield.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (57 K)Download as PowerPoint slideResearch highlights▶ Pt/WO3–ZrO2 catalysts and moderate reaction conditions isomerize-crack long paraffins into gasoline compounds. ▶ Too high temperature and pressures produce excessive cracking. ▶ Results point to the existence of non-classical bifunctional metal–acid mechanism. ▶ Under some reaction conditions a high RON isomerizate can only be got at the expense of the liquid yield.

Keywords
Tungsten–zirconia; Reaction conditions; Hexadecane; Cracking; Isomerization; Gasoline
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Screening of optimal pretreatment and reaction conditions for the isomerization-cracking of long paraffins over Pt/WO3–ZrO2 catalysts
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 387, Issues 1–2, 20 October 2010, Pages 35–44
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us