A.#Piovano,#K.#S.#Thushara,#E.#Morra,#M.#Chiesa#and#E ...4...

HOW TO EXPLOIT THE SYNERGY BETWEEN TI3+ AND LEWIS ACIDIC AL3+ SITES ON AL2O3-SUPPORTED ZIEGLER-NATTA CATALYSTS

TO PRODUCE BRANCHED POLYETHYLENE

A. Piovano, K. S. Thushara, E. Morra, M. Chiesa and E. Groppo Department of Chemistry, INSTM and NIS Centre , University of Turin

δ-‐Al2O3 @ 600 °C support

Olefin isomerizaCon and oligomerizaCon

1

Alessandro Piovano, University of Turin – Milan Polymer Days

TiCl4 precursor

Ziegler-‐NaJa catalysis

THE CATALYTIC PROCESS UNDER EXAMINATION

A. Piovano, K. S. Thushara, E. Morra, M. Chiesa, E. Groppo, 2017, in preparaCon



1


TiCl4 precursor

δ-‐Al2O3-‐600/TiCl4 pre-‐catalyst






1


TiCl4 precursor


δ-‐Al2O3-‐600/TiCl4/H2-‐400 catalyst

δ-‐Al2O3-‐600/TiCl4/TEA catalyst




TEA @ R.T. H2 @ 400 °C



1


TiCl4 precursor


δ-‐Al2O3-‐600/TiCl4/H2-‐400 catalyst

δ-‐Al2O3-‐600/TiCl4/TEA catalyst




+ C2H4 ?? + C2H4 ??

TEA @ R.T. H2 @ 400 °C

2


3000 2800

0.1

2

1600 1400 1200

0.1

2

1600 1400 1200

Wavenumber (cm-‐1)

0.1 1

3000 2800Absorbance (a.u.) 0.5

1

110 120 130 140-‐8

-‐6

-‐4

-‐2

0

12

Temperature (°C)

Heat Flow (m

W)

ETHYLENE POLYMERIZATION

FT-‐IR DSC

1. Ethylene conversion on δ-‐Al2O3-‐600/TiCl4/TEA 2. Ethylene conversion on δ-‐Al2O3-‐600/TiCl4/H2-‐400

δ-‐Al2O3-‐600/TiCl4/TEA catalyses the producCon of mainly crystalline HDPE. Polyethylene produced by δ-‐Al2O3-‐600/TiCl4/H2-‐400 reveals a branched nature.

3


CHARACTERIZATION OF THE TWO CATALYSTS

Which is the origin of the different acOvity?

E. Groppo, K. Seenivasan, C. Barzan, Catal. Sci. Technol. 2013, 3, 858.

3





A spectroscopic invesCgaCon…

3






… advantages: ü  idenCficaCon of funcConal groups; ü  evaluaCon of oxidaCon state and

coordinaCon of the metal centres; ü  detecCon of the interacCon

between the acCve sites.

3






… advantages: ü  idenCficaCon of funcConal groups; ü  evaluaCon of oxidaCon state and

coordinaCon of the metal centres; ü  detecCon of the interacCon

between the acCve sites.

… drawbacks: X  heterogeneity of the sites; X  high diluCon of the acCve sites; X  presence of spectator species; X  air sensiCvity.

4


IN SITU FORMATION OF THE PRE-CATALYST

40000 30000 20000 10000

2

1

Kube

lka-‐Mun

k (K.M

.)


1.0

4500 4000 3500 3000 2500 2000 1500 1000

Absorbance (a.u.)


0.2

2

1

DR UV-‐VIS FT-‐IR

TiCl4 grads on alumina reacCng with the OH groups. HCl stabilized by surface Al3+–O2– couples.**

6-‐fold and 4-‐fold Ti4+ sites, having both Cl and O ligands.*

* K. Seenivasan, A. Sommazzi, F. Bonino, S. Bordiga, E. Groppo, Chem. Eur. J 2011, 17, 8648. C. K. Jorgensen, in Orbitals in Atoms and Molecules, Academic Press, London and New York, 1962, pp. 80. ** A. R. McInroy, D. T. Lundie, J. M. Winfield, C. C. Dudman, P. Jones, S. F. Parker, D. Lennon, Catal. Today 2006, 114, 403.

1. δ-‐Al2O3-‐600 2. δ-‐Al2O3-‐600/TiCl4

5


40000 30000 20000 10000

3b

3a

2

1

Kube

lka-‐Mun

k (K.M

.)


1.0

4500 4000 3500 3000 2500 2000 1500 1000

Absorbance (a.u.)


0.2

23a

3b

1

Isolated Ti centers and TiCl3-‐like clusters.* Isolated Ti3+6c sites, without alkyl groups.***

Fingerprints of alkyl groups deriving from TEA.** Chemisorbed HCl is removed, Al3+ sites exposed on the surface.***

* R. J. H. Clark, J. Chem. Soc., 1964, 417-‐425. ** S. Kvisle and E. RyJer, Spectrochim. Acta A, 1984, 40, 10, 939-‐951. *** A. Piovano, K. S. Thushara, E. Morra, M. Chiesa, E. Groppo, Angew. Chem. Int. Ed. 2016, 55,37, 11203-‐11206

1. δ-‐Al2O3-‐600 2. δ-‐Al2O3-‐600/TiCl4 3a. δ-‐Al2O3-‐600/TiCl4/TEA 3b. δ-‐Al2O3-‐600/TiCl4/H2-‐400 DR UV-‐VIS FT-‐IR

IN SITU FORMATION OF THE CATALYST

6


0 5 10 15 20 25 300

5

10

15

20

25

30

ν2[M

Hz]

ν1[MHz]0 5 10 15 20 25 30

0

5

10

15

20

25

30

ν2[M

Hz]

ν1[MHz]

Ti3+ SURROUNDING

Q-‐BAND HYSCORE EPR T = 10 K B0=1243.5 mT

Weak hyperfine interacCon of Ti3+ with remote 27Al nuclei, from either alumina support or TEA co-‐catalyst. Strong hyperfine coupling of Ti3+ with 27Al nuclei through the directly coordinated anions: direct proof for the presence of Ti3+-‐Cl-‐Al linkages.

δ-‐Al2O3-‐600/TiCl4/TEA δ-‐Al2O3-‐600/TiCl4/H2-‐400

7


P. Cossee, J. Catal., 1964, 3, 1, 80-‐88.

SCHEME OF REACTION

Polymerization on δ-Al2O3-600/TiCl4/TEA

Although the catalyst acCvaCon process at a molecular level is sCll unclear, the hypothesis of polymerizaCon mechanism broadly accepted dates back to 1964, to the so called “Cossee-‐Arlman mechanism”:

8


?

SCHEME OF REACTION

Polymerization on δ-Al2O3-600/TiCl4/H2-400

9


M. C. Baird, Chem. Rev. 2000, 100, 1471.

Al3+ Lewis acid catalytic activity toward C2H4 conversion

Al3+ Lewis acid sites act as iniCators for ethylene oligomerizaCon through a carbocaConic mechanism.

SCHEME OF REACTION


A. Piovano, K. S. Thushara, E. Morra, M. Chiesa, E. Groppo, Angew. Chem. Int. Ed. 2016, 55,37, 11203-‐11206

Ti3+ and Al3+ sites in close proximity each other act in a concerted fashion to synergisCcally boost the conversion of ethylene into branched polyethylene, using ethylene as the only feed and without any acCvator.

SCHEME OF REACTION

Polymerization on δ-Al2O3-600/TiCl4/H2-400

10

11


δ-‐Al2O3-‐600/TiCl4/TEA and δ-‐Al2O3-‐600/TiCl4/H2-‐400 catalysts are two extremes starCng from the same pre-‐catalyst.

CONCLUSION AND PERSPECTIVES

11


δ-‐Al2O3-‐600/TiCl4/TEA and δ-‐Al2O3-‐600/TiCl4/H2-‐400 catalysts are two extremes starCng from the same pre-‐catalyst. Is it possible to obtain intermediate catalysts?


11


δ-‐Al2O3-‐600/TiCl4/TEA and δ-‐Al2O3-‐600/TiCl4/H2-‐400 catalysts are two extremes starCng from the same pre-‐catalyst. Is it possible to obtain intermediate catalysts? Set of catalysts to finely tune the properCes of the polymer:

§  Molecular weight distribuCon §  Branching degree §  Length of branches


Mechanical ProperCes

Workability


THANKS TO:

Dr. Elena Groppo Dr. K. S. Thushara

Prof. Mario Chiesa Dr. Elena Morra

Dr. Jarmo Lindroos

Prof. Silvia Bordiga Prof. Adriano Zecchina

This work has been supported by the ProgeJo di Ateneo/CSP 2014 (Torino_call2014_L1_73).

A.#Piovano,#K.#S.#Thushara,#E.#Morra,#M.#Chiesa#and#E ...4...

Documents

Transcript of A.#Piovano,#K.#S.#Thushara,#E.#Morra,#M.#Chiesa#and#E ...4...