the oxidation of cyclohexane in a capillary

The Oxidation of Cyclohexane in a Capillary R. Jevtic, P.A. Ramachandran, M. P. Dudukovic Chemical Reaction Engineering Laboratory Motivation Nylon -6,6 Source: http://www.uni-regensburg.de O 2 HNO 3 + Caprolactam & Adipic acid KA -mixture >120 C ~15 bars OH O + KA oil >120 C ~8-15 bars adipic acid Traditional cyclohexane oxidation (“1st step”) process operates at: 3-8% cyclohexane conversion 85% selectivity to cyclohexanol and cyclohexanone adiabatic condition Two possible modifications to improve the current process: 1. Selectively oxidize cyclohexane directly to adipic acid in one step, or 2. Increase volumetric productivity in the first step without sacrificing selectivity toward cyclohexanol and cyclohexanone Goals Improved understanding and quantification of the effect of oxygen availab ility the effect of the reactor type on rates and selectivity in cyclohexane oxidation V R =50 ml D =2.1 mm Results Summary 2003-2006: 61 papers; 32 in Chinese and 21 in English * Source: SciFinder The interest in cyclohexane oxidation has not diminished in years: Experimental set up: capillary reactor (D=2.1 mm), T= 160 0 C, P=15 atm, Q L =0.1-1.0 ml/min Concentrations of the products obtained experimentally are an order of magnitude lower that those obtained by PFR model (conversion at 20 min (model)=36% conversion (exp) = 4%). Figure 1. Comparison of experimental and modeling results for cyclohexanol (ROH) and cyclohexanone (RO) concentrations in cyclohexane oxidation in the capillary at 160ºC and 15 atm without the use of a catalyst. Figure 2. Experimental and modeling results for cyclohexanol (ROH) and cyclohexanone (RO) concentrations obtained in the capillary reactor at 160ºC and 15 atm. Mass transfer coefficient used in the model was an order magnitude lower then the one predicted from the correlations available in the literature. Taylor flow in a capillary: • 3 different mixers used. • Similar results observed-Taylor flow erratic and almost independent of the gas and the liquid flow rates used 1 2 3 Gas flow rate: 1.2 ml/min Liquid flow rate: 3.6 ml/min (nylon tubing, 1/8’’ OD) 57 . 0 19 . 1 111 . 0 SLUG TP GL GL L u a k ﬁlm L cap L GL a k a k a k ) ( Mass transfer correlation for Taylor flow: Bercic and Pintar, 1997Van Baten and Krishna, 2004 a k GL 0.001s -1 to 0.08 s -1 If smaller (than predicted by correlations from the literature) mass transfer coefficient is used, agreement between model and experimental results gets better. Mass transfer might be the reason for the discrepancies between the model and the experimental results Design, set up and the experimental study in the capillary reactor is completed. There is discrepancy between model and experimental results, which is, most likely, due to poor mass transfer in the capillary Better mixing of gas and liquid is needed. References 1. Schaefer, R.; Merten, C.; Eigenberger, G., Autocatalytic Cyclohexane Oxidation in a Bubble Column. The Canadian Journal of Chemical Engineering 2003, 81, (741-748). 2. Bercic, G.; Pintar, A., The role of gas bubbles and liquid slug lengths on mass transport in the Taylor flow through capillaries. Che. Eng. Sci. 1997, 52, (21/22), 3709-3719. 3. Kreutzer, M. T.; Du, P.; Heiszwolf, J. J.; Kapteijn, F.; Moulijn, J. A., Mass transfer characteristics of three-phase monolith reactors. Chem. Eng. Sci. 2001, 56, (21-22), 6015-6023. 4. van Baten, J. M.; Krishna, R., CFD simulations of mass transfer from Taylor bubbles rising in circular capillaries. Chemical Engineering Science 2004, 59, (12), 2535-2545. L i i i L i G G V c H p a k dz dp RT V u ) ( NR k k ki i i i L i L r c H p a k dz dc u 1 ) ( Mass transfer correlation for Taylor flow in a capillary used Kinetics from Kharakova et al, 1989 A small improvement in the product yield can lead to significant impact on the process economics.

Upload: aileen

Post on 05-Jan-2016

47 views

Category:

Documents

2 download

Report

Download

Tags:

Embed Size (px):

DESCRIPTION

O. H. O. O. 2. H. N. O. Caprolactam. +. 3. +. & Adipic acid. >120 C. >120 C. ~15 bars. KA. -. mixture. ~8-15 bars. KA oil. adipic acid. Motivation. Results. Mass transfer correlation for Taylor flow:. Bercic and Pintar, 1997. Van Baten and Krishna, 2004. - PowerPoint PPT Presentation

TRANSCRIPT

Page 1: The Oxidation of Cyclohexane in a Capillary

The Oxidation of Cyclohexane in a CapillaryR. Jevtic, P.A. Ramachandran, M. P. Dudukovic

Chemical Reaction Engineering Laboratory

Motivation

Nylon -6,6Source: http://www.uni-regensburg.de

O2 H N O

3+Caprolactam

& Adipic acid

KA - mixture

>120 C

~15 bars

O HO

KA oil

>120 C

~8-15 barsadipic acid

Traditional cyclohexane oxidation (“1st step”) process operates at: 3-8% cyclohexane conversion 85% selectivity to cyclohexanol and cyclohexanone adiabatic condition

Two possible modifications to improve the current process:

1. Selectively oxidize cyclohexane directly to adipic acid in one step, or

2. Increase volumetric productivity in the first step without sacrificing selectivity toward cyclohexanol and cyclohexanone

Goals

Improved understanding and quantification of

the effect of

oxygen availabili

the effect of the reactor

type

on rates and selectivity in cyclohexane oxidation

VR=50 mlD =2.1 mm

Results

Summary

2003-2006: 61 papers;

32 in Chinese and 21 in English

* Source: SciFinder

The interest in cyclohexane oxidation has not diminished in years:

Experimental set up: capillary reactor (D=2.1 mm), T= 1600C, P=15 atm, QL=0.1-1.0 ml/min

Concentrations of the products obtained experimentally are an order of magnitude lower that those obtained by PFR model (conversion at 20 min (model)=36% conversion (exp) = 4%).

Figure 1. Comparison of experimental and modeling results for cyclohexanol (ROH) and cyclohexanone (RO) concentrations in cyclohexane oxidation in the capillary at 160ºC and 15 atm without the use of a catalyst.

Figure 2. Experimental and modeling results for cyclohexanol (ROH) and cyclohexanone (RO) concentrations obtained in the capillary reactor at 160ºC and 15 atm. Mass transfer coefficient used in the model was an order magnitude lower then the one predicted from the correlations available in the literature.

Taylor flow in a capillary:

• 3 different mixers used. • Similar results observed-Taylor flow erratic and almost independent of the gas and the liquid flow rates used

1 23

Gas flow rate: 1.2 ml/minLiquid flow rate: 3.6 ml/min(nylon tubing, 1/8’’ OD)

57.0

19.1111.0

SLUG

TPGLGL L

uak filmLcapLGL akakak )(

Mass transfer correlation for Taylor flow:

Bercic and Pintar, 1997 Van Baten and Krishna, 2004

akGL 0.001s-1 to 0.08 s-1 If smaller (than predicted by correlations from the literature) mass transfer coefficient is used, agreement between model and experimental results gets better.

Mass transfer might be the reason for the discrepancies between the model and the experimental results

Design, set up and the experimental study in the capillary reactor is completed.

There is discrepancy between model and experimental results, which is, most likely, due to poor mass transfer in the capillary

Better mixing of gas and liquid is needed.

References

1. Schaefer, R.; Merten, C.; Eigenberger, G., Autocatalytic Cyclohexane

Oxidation in a Bubble Column. The Canadian Journal of Chemical

Engineering 2003, 81, (741-748).

2. Bercic, G.; Pintar, A., The role of gas bubbles and liquid slug lengths on

mass transport in the Taylor flow through capillaries. Che. Eng. Sci. 1997,

52, (21/22), 3709-3719.

3. Kreutzer, M. T.; Du, P.; Heiszwolf, J. J.; Kapteijn, F.; Moulijn, J. A., Mass