Btp Mid-sem Presentation.pdf

Index 1. 2. 3. 4. 5.

6. 7.

Abstract Introduction Problem statement Literature review Experimental a. Synthesis of catalysts b. Characterization of Catalysts c. Catalytic Activity Study Future plan References

Index Abstract Introduction Problem statement Literature review Synthesis of catalysts Characterization of Catalysts Catalytic Activity Study Future plan References

Abstract In this work, gas-phase alkylation reactions of m-cresol with iso-propanol to form pharmaceutically important product thymol using highly efficient metal ion-exchanged Silica-Alumina framework (SAL) catalysts is reported. Environmentally benign SAL catalysts were prepared by ion-exchange method and characterized by XRD, N 2 sorption, SEM, and TEM techniques. Catalytic activity of the reaction to optimize different reaction parameters like degree of metal loading, reaction temperature, WHSV, reactant mole ratio and catalyst loading to obtain the maximum selectivity to desired product thymol will be investigated in future work.

Introduction... ●

Alkylation of m-cresol with iso-propanol is an important acid catalyzed Friedel-Crafts reaction. The main product is 2-iso-propyl-5-methyl phenol, also known as thymol.

●

Thymol is a precursor of the industrially important pharmaceutical product called menthol, antioxidants, insecticides, insect and animal repellents, fungicides, medical disinfectants, etc

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Other products like iso-propyl 3-methylphenyl ether (IPMCE), 4-isopropyl 3-methylphenol (4I-3MP), 3-isopropyl 5-methylphenol (3I-5MP), dialkylated m-cresols are also widely used as additives in food industry, perfumes, food flavorings, mouthwashes, pharmaceutical and cosmetics.1

Several studies on the iso-propylation of m-cresol have been reported till date using both homogeneous (mineral acids, Lewis acids, etc) and heterogeneous catalysts (mesoporous materials, metal oxides, etc). 2,3 ●

Mineral and Lewis acids possess severe environmental problems as well as low Product selectivity.8

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Metal oxide become rapidly deactivated due to leaching of active metals and pore blocking.

Introduction Need to develop environmentally friendly catalysts with tunable acid densities and pore volumes for the selective production of thymol. Hence, the metal-loaded SAL catalyst with different amount of metal loadings and controlled Bronsted and Lewis acid sites is to be developed. Herein, we report gas phase alkylation of m-cresol with iso-propanol in fixed bed reactor over different metal ion-exchanged SAL catalysts to selectively produce thymol. ●

Different amount of zinc is loaded in multiple ion-exchange steps over SAL catalysts

●

Synthesized catalysts were characterized by using XRD, SEM, TEM, and N2 sorption techniques.

●

Design of experiments (DOE) method is implicated to optimize the process parameters like temperature, reactant mole ratio, WHSV and catalyst loading for this alkylation reaction.

Figure 1: Reaction scheme for alkylation of m-cresol with iso-propanol

Problem Statement For the selective synthesis of thymol, high Lewis acidity is required in the alkylation of m-cresol with iso-propanol. From earlier reports, it is known that among different transition metals exchange with protons present on SAL zeolite, Zn-SAL with high Lewis acidity gave the highest selectivity to thymol. ●

Now determining the amount of zinc on SAL catalysts by multiple ion-exchange steps is important to achieve highest catalytic activity.

●

Moreover, optimization of process parameters is also necessary.

Table 1. Literature review

Reactant

Catalyst

Reaction parameter

Conversion

Selectivity

Reference

Activated alumina

T= 360 0C P= 50 bar t= 4 h

75 (m-cresol)

80

Biedermann et al.4

T= 300 oC, P= 1 bar WHSV= 1.52 h-1

80.9 (m-cresol)

Literature Review m-cresol: propylene m-cresol: iso-propyl acetate (1:3)

Al-MCM-41(55)

83.7

K. Shanmugapria1

m-cresol: IPA (1:4)

Al-MCM-41

T= 300 oC, P= 1 bar WHSV= 1.76 h-1

55 (m-cresol)

75.3

Umamaheshwri et al. 5

m-cresol: IPA (1:4)

Mg-Al hydrotalcites

T= 400 oC, P= 1 bar WHSV=8.6 mol/h-Kg

40 (m-cresol)

80

Velu et.al. 6

m-cresol:IPA (1:5)

ZnAl2O4

T= 255 oC P = 1bar

78.2 (m-cresol)

88.4

Grabowska et al.7

m-cresol: IPA (1:5)

Fe that contains Cr, Si & K oxides

T= 420 oC, P= 1 bar WHSV=1.5 cm3/h

17 (m-cresol)

60

Grabowska et al. 8

m-cresol: IPA (5:1)

UDCaT5 (0.05 g/cm3)

T= 180 oC P= autogenous t= 1 h

92 (IPA)

79

Yadav et al. 9

m-cresol: IPA (1:2)

H-beta zeolite

T= 200 0C, P= 1 bar TOS= 15 min

60 (m-cresol)

40

Nie et al. 10

Experimental: Synthesis of catalysts ●

Ion-exchange method was used to load metal ions on the SAL catalyst.

●

0.05M aqueous solution of metal salt is mixed with SAL catalyst, keeping the liquid to solid ratio 10.

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The mixture was refluxed for 24 h, then filtered, washed and dried at 120 °C for 8h.

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The samples were divided into two parts: the first one is calcined at 540 °C for 4 h whereas the second one is used in the next ion-exchange step.

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For multiple ion-exchanges, the above steps were repeated and the calcined samples were designated as Zn-SAL-N, where N is the ion-exchange step number.11

Experimental: Characterization of Catalysts The average crystallite size (t) of the catalysts is calculated by Debye-Scherrer formula: t = kλ/βcosθ Where, k = shape factor = 0.9, λ = X-ray wavelength of Cu Kα radiation (1.54Å), θ = Braggs diffraction angle, Β = full width at half maximum height (FWHM) of the diffraction peak. The average crystallite sizes are: H-SAL = nm Zn-SAL-I = nm Zn-SAL-II = nm Zn-SAL-III = nm Zn-SAL-IV = nm Figure 2: XRD pattern of the prepared catalysts

Experimental: Characterization of Catalysts BET Surface Area by N2 sorption The surface area and micropore volume of the catalysts used in this work were measured by N 2 sorption techniques. The exchange of proton in SAL with Zn2+ cations decrease the surface area and micropore volume due to the preferential location of exchanged Zn2+ inside the micropore of the SAL. Table 2. Textural properties of the prepared catalysts Catalyst

Specific surface area, SBET (m2 g-1)

Total pore volume (P/Po=0.99) (cm3 g-1)

Micropore volume (cm3 g-1)

Average pore diameter (nm)

H-SAL

382.2249

0.869204

0.127030

59.5675

Zn-SAL-I

367.6021

0.703383

0.113158

76.5374

Zn-SAL-II

327.7957

0.691148

0.094418

84.3389

Zn-SAL-III

309.1342

0.641033

0.093935

86.9456

Zn-SAL-IV

298.8266

0.610004

0.07734

89.6532

Experimental: Characterization of Catalysts Scanning Electron Microscopy (SEM) SEM images of all the catalysts revealed a polygonal morphology. In Zn-SAL, most of the Zn is present in agglomerated form and the agglomeration increases with increase in the zinc content.

Figure 3. SEM images of catalysts (a) H-SAL, (b) Zn-SAL-I, (c) Zn-SAL-II, (d) Zn-SAL-III, and (e) Zn-SAL-IV

Experimental: Characterization of Catalysts Transmission Electron Microscopy (TEM) TEM image of H-SAL revealed its high dispersion due to high aluminium content present in it. Whereas, when the zinc ions were ion-exchanged on H-SAL, the aggregation of the particles was observed

Figure 4: TEM images of catalysts (a) H-SAL and (b) Zn-SAL-I

Experimental: Characterization of Catalysts Energy Dispersive X-ray (EDX) Figure 5 shows the EDX spectrum of H-SAL and Zn-SAL-I samples. In H-SAL, the elements Si, Al, O, C and Cu were detected. Whereas Si, Al, O, Zn, C, and Cu elements were detected in the sample Zn-SAL-I. This confirms the loading of Zn on SAL.

Figure 5: EDX analysis of catalysts (a) H-SAL and (b) Zn-SAL-I

Experimental: Catalytic Activity Study Design of Experiment An experimental design using response surface methodology (RSM) is used to optimize the process parameters in this continuous alkylation to minimize rigorous experimental procedures and conserve the catalyst. The parameters, namely, temperature, reactant mole ratio, catalyst loading, and WHSV on the conversion of m-cresol and yield of thymol will be optimized using Box–Behnken design. Table 3. Parameter levels and coded values used in the experimental design.

Range and levels Factors

Symbols -1

0

+1

Temperature (°)

X1

200

250

300

WHSV (h-1)

X2

1.68

2.8

3.92

Reactant mole ratio

X3

1

2

3

Catalyst loading (g)

X4

0.5

1.0

1.5

Table 4. Experimental design using Box–Behnken method Run Temper Catalyst Number ature WHSV Loading

Reactant m-cresol Selectivity mole ratio Conversion to Thymol

1

0

0

-1

-1

2

-1

0

-1

0

3

0

-1

-1

0

4

0

1

-1

0

5

1

0

-1

0

6

0

0

-1

1

7

-1

0

0

-1

8

0

-1

0

-1

9

0

1

0

-1

10

1

0

0

-1

11

-1

-1

0

0

12

-1

1

0

0

13

0

0

0

0

14

0

0

0

0

Run Temper Number ature WHSV

Catalyst Loading

Reactant m-cresol Selectivity mole ratio Conversion to Thymol

15

0

0

0

0

16

1

-1

0

0

17

1

1

0

0

18

-1

0

0

1

19

0

-1

0

1

20

0

1

0

1

21

1

0

0

1

22

0

0

1

-1

23

-1

0

1

0

24

0

-1

1

0

25

0

1

1

0

26

1

0

1

0

27

0

0

1

1

Future Plan 1. Acidity estimation of the catalysts using ammonia-TPD and pyridine-FTIR technique. 2. Optimization of reaction parameters like temperature, WHSV, feed mole ratio and catalyst loading for this reaction. 3. Development of kinetic model for this reaction.

References 1. Shanmugapriya K. et. al., J. Catal. 2004, 224 (2), 347-357. 2. Zapata P.A. et. al., J. Am. Chem. Soc. 2012, 134, 857. 3. Yadav G.D. et. al., Microporous Mesoporous Mater. 2006, 89 (1–3), 16. 4. Biedermann W. et. al., Process for preparing thymol, US4086, 1978, 283. 5. Umamaheswari V. et. al., Journal of Catalysis, 2002, 210, 367. 6. Velu S. et. al., Research on Chemical Intermediates, 1998, 4 (6), 657. 7. Grabowska H. et. al., Applied Catalysis A: General, 2001, 220, 207–213. 8. Grabowska H. et. al, Res. Chemcial Intermed. 2001, 27, 281. 9. Yadav G.D. et. al., J. Phys. Chem. A, 2005, 109, 11080. 10. Nie L. et. al., Applied Catalysis A: General, 2012, 447, 14. 11. Afreen G. et. al., Molecular catalysis, 2017, 441, 122. 12. Marakatti V.S. et. al., RSC Adv. 2015, 5, 14286.