catalytic depolymerisation of rubber thompson.pdf8%, 1,2pbd 36% cis 1,4 linkages. method ... stir...
TRANSCRIPT
Stephen Boothroyd, Rebecca Smith, Ezat Khosravi, Richard Thompson
Department of ChemistryDurham University
Catalytic Depolymerisation of Rubber
Contents Motivation
Metathesis Chemistry Basics
Breaking down polybutadienes by Cross-Metathesis
Test reaction on linear PB
Test reaction model cross-linked PB
Trials on SBR
Too good to be true?
Conclusions and outlook
Why?
Main use of rubber is in tyres
Millions of tyres are stockpiled each year due to difficulties in disposing of them
Difficulties due to the high crosslink density
Huge environmental pressure to make tyres reprocessable
without compromising on safety, durability, energy efficiency
The idea Rubber contains double bonds which are available for
further reaction
Use a cross metathesis reaction to break down the rubber network by reacting it with a small olefin
n
Cross Metathesis Rearranges carbon-carbon double bonds
Grubbs Catalyst - ruthenium based metal centre [M]
Reaction proceeds via a metallocyclobutaneintermediate
Number of chain ends is conserved!
Grubbs’ ruthenium catalysts• Most widely used for metathesis reactions
• High functional group tolerance
• Low sensitivity to air and moisture – scaleable!
• 2nd generation is more active than the 1st due to the N heterocyclic (NHC) ligand
1st generation 2nd generation
Experimental ApproachTo carry out cross metathesis reactions on models of
increasing complexity/realism:
1. Linear 1,4-polybutadiene
2. Cross-linked 1,4-polybutadiene
3. Tyre rubber (SBR sheet)
Polybutadiene (PBD)
Polymerise butadiene by 1,2- or 1,4-addition
1,4- PBD has the double bond in the polymer chain
Model material contains a mixture of repeat units.
1,2-PBD trans 1,4-PBDcis 1,4-PBD
Average Mw 280,000 92% 1,4; 8%, 1,2PBD
36% cis 1,4 linkages
Method (E. Khosravi, R.F. Smith)
Dissolve PBD and diester-olefin in DCM
Grubbs ruthenium catalyst (1 mol% per repeat unit)
Stir for 24 hours
2 ml ethyl vinyl ether added and stirred for another 2 hours
Precipitate in methanol
Filter solution
Remove solvent from filtrate & dry
Test reaction on linear PBD: results
Linear PBD can be broken down using the cross metathesis reaction + diester olefin
Changing the diester olefin has little effect- used dimethyl fumarate and dimethyl maleate in reactions
PBD can be broken down without any diester olefin
+?
+?
Test reaction on Model Cross-linked PBD Cross-link PBD with benzoyl peroxide
Generate elastic network (rubber behaviour)
Attempt catalysed breakdown…
10-1
100
101
102
103
100
101
102
103
104
105
106
Breakdown Products
Linear PBD
G, G
/ P
a
/ rad s-1
Crosslinked
Catalysed breakdown of model rubber
Rheology: Transform elastic solid to viscous liquid
GPC: Massive reduction in molecular weight (200 kg/mol to 2 kg/mol)
Both analyses: diester olefin has little effect on breakdown
G1 only
G1 + 1% DM diesterOriginal PBD
Mw / kg.mol-1 / rad.s-1
NMR Chemical Analysis of Breakdown Products
ciscis
cis
cis
trans
trans
trans trans
Cross-linked PBD and 1st
generation Grubbs’ catalyst
PBD
SBR
Styrene-butadiene rubber*
Copolymer of styrene and butadiene
Used in manufacturing tyres
Grubbs’ 2nd generation catalyst
n1,4-PBD
*Sample provided by Stephen Millington, ARTIS
SBR Reacted SBR with dimethyl maleate and Grubbs’ 2nd
generation catalyst at 40°C
SBR in DCM (control), 24 hours at 40°C
SBR broken down to rubber crumb by CM
Process also yields some soluble PBD of low mol wt.
Before reaction After reactionAfter 24 hours
Straight after reaction
After drying
After 24 hoursBefore reaction After ½ hour After reaction
Mass Loss Resulting following heptane swelling test on SBR
Sample % weight loss Error
SBR 11.2 0.2
G2 10% DM 40°C 25 4
G2 10% DM 25°C 16.9 0.9
G2 10% DF 20.5 0.8
G2, no diester 18.3 0.3
Checking for catalyst in rubber
PIXE Elemental analysis
Found 1 Grubbs’ catalyst : 700 butadiene repeat units
5 10 15 20
10
100
Br
Zn
Fe
Ru K
SBR sheet
fit
20HS
fit
Yie
ld
X-ray Energy / keV
Ru L
K
Catalysts work ‘too well’? Catalysts necessary, but diester olefin optional – why? Reaction must conserve chain ends…
So not ‘too good to be true’ – making molecular lassos?
Loop
formation
CM with 1,2
(vinyl) groups
Planned
reaction
Conclusions Cross metathesis reaction can break down PBD to
oligomers.
SBR can be broken down using Grubbs’ catalyst and diesterMain product = rubber crumb
Also get ~15% PBD oligomer
CM reaction has potential to be used to recycle rubber
Outlook / Future Directions Very promising route to PBD oligomer and/or crumb from rubber
Need to optimise in a ‘greener’ solvent
Repolymerise and establish reprocessed rubber properties.
Commercialise process – industrial partners wanted!
Smith, Boothroyd, Khosravi, Thompson, Green Chemistry. (ASAP) DOI: 10.1039/C5GC03075G
Free Access Until 11/5/16
Rheology
0
1
2
3
4
5
6
0 0.5 1 1.5 2 2.5 3
Gʹ/Gʺ(Pa)
log Ang. Freq (rad/s)
Cross-linked PBD log G ʹ
Cross-linked PBD log Gʺ Product
log G ʹ
Product log Gʺ
Deformation and flow behaviourFrequency sweeps, 20 °CGʹ=storage modulus, Gʺ= loss modulus
Gel permeation chromatography (GPC)
Retention volume/ mL
Linear PBD before reaction
After reactionCross-linked PBD product
Linear PBD product
8.0 10.0 12.0 14.0 16.0 18.0
Reaction Reference PBD grade/ molecular
weight(kDa)
Diester Type Grubbs’ Catalyst
generation
Double bond ratio of
polymer:diester
Outcomes
01 1.5 DF 1st 3:1 Major breakdown of PBD, mostly soluble in methanol
02 1.5 DF 2nd 3:1 Major breakdown of PBD, completely soluble in methanol
03 1.5 - 1st 1:0 Major breakdown of PBD but with large PDI
04 1.5 DF 2nd 3:1 Major breakdown of PBD, heating had no effect on the product
Reaction Reference PBD grade/ molecular
weight(kDa)
Diester Type Grubbs’ Catalyst generation Double bond ratio of
polymer:diester
Outcomes
05 420 DF 1st 3:1 Major breakdown of PBD, completely soluble in methanol
06 420 DF 2nd 3:1 Major breakdown of PBD, completely soluble in methanol
07 420 DF 1st 100:1 Major breakdown of PBD, mostly soluble in methanol
08 420 DF 2nd 100:1 Major breakdown of PBD, mostly soluble in methanol
09 420 DF 1st 200:1 Major breakdown of PBD, little difference to 07
10 420 DM 1st 3:1 Major breakdown of PBD, mostly soluble in methanol
11 420 DM 2nd 3:1 Major breakdown of PBD, mostly soluble in methanol
12 420 - 1st 1:0 Major breakdown of PBD, completely soluble
13 Cross-linked DF 1st 100:1 Broken down to same extent as linear PBD
14 Cross-linked DM 1st 100:1 Broken down to same extent as linear PBD
15 Cross-linked - 1st 1:0 Broken down to same extent as linear PBD
16RT Rubber crumb DM 1st 10:1 Appeared unchanged, Ru chemically bonded
16H Rubber crumb DM 1st 10:1 Appeared unchanged, Ru chemically bonded
17RT Rubber crumb - - 1:0 Appeared unchanged
17H Rubber crumb - - 1:0 Appeared unchanged
18RT Rubber crumb DM 1st 10:1 Appeared unchanged, Ru chemically bonded
18H Rubber crumb DM 1st 10:1 Appeared unchanged, Ru chemically bonded
19 Rubber crumb DM 2nd 10:1 Swelling tests show large weight loss
20RT SBR DM 2nd 10:1 Crumb product
20H SBR DM 2nd 10:1 Crumb product large weight loss in swelling test
21RT SBR - - 1:0 Swelled during reaction
21H SBR - - 1:0 Swelled during reaction
22 SBR DF 2nd 10:1 Crumb product, Ru chemically bonded, large wt loss in swelling
test
23 SBR - 2nd 1:0 Crumb product
24 420 DM 1st 3:1 Completely broken down within 2 hrs
25 420 DM 2nd 3:1 Almost completely broken down within 2 hrs
26 SBR DM 2nd 10:1 Crumb product after 21/2 hrs at RT