acetylation of starch in supercritical co2

7/26/2019 Acetylation of Starch in Supercritical CO2

1/37

| 1

H. Muljana, F. Picchioni, L.P.B.M. Janssen and H.J. Heeres

Chemical Engineering Department

University of Groningen

The Netherlands

Acetylation of Starch in Supercritical CO2


2/37

| 2

Outline

Introduction

Objectives Why supercritical CO2

Experimental results and discussion

Exploratory process studies

Fundamental studies

Solublity

Conclusions

Acknowledgement


3/37

Green chemical reaction engineering at RUG

Catalytic biomass conversions

Biofuels Platform chemicals

Bio based (performance) materials

Catalytic pyrolysis oil upgrading

Biodiesel fromJatropha Curcas

hydroxymethylfurfural levulinic acid methanol diols phenolics

Novel polymers from valerolactone

St a r ch a n d cel l u l o se m od i f i ca t i o n


4/37

| 4

General

Objective:

Study potential ofsupercritical CO2assolventfor starchmodification reactions

Literature data:

Remarkably little known on modification chemistry inscCO2

Landmark

patent:R.

Harris,

S.

H.

Jureller,

J.

L.

Kerschner,

P.

T.

Trzasko,

and

R.

W.

Humphreys,U.S.Patent,5977348(1999)

Introduction


5/37

| 5

Why use supercritical solvents

Liquid like density and gas like diffusivity

Supercritical conditions for sCO2 relatively mild: Pc = 73 bar, Tc = 31 oC Green properties: non toxic, relatively inert, non flammable

Easy of separation

High pressure equipment required Complex phase behaviour for mixtures

Properties Gas Supercritical

fluid

Liquid

(kg m-3) 1 100 800 1000

(Pa s) 0.001 0.005 0.01 0.05 0.1

D (m2 s-1) 1. 10-5 1.10-7 1.10-9


6/37

Introduction

(a) (b)

(c) (d)


7/37

Introduction

Approach:

Perform modification reactions in scCO2

System: model reaction, acetylation selected

Approach: screening and focussed studies

Fundamental studies on starch-scCO2 interactions

(solubility, gelatinization); Experimental and modeling


8/37

| 8

Introduction

Model reaction : Acetylation of starch

Native starch Starch acetate

Reactants : acetic anhydride

Catalyst : alkaline salt catalyst(NaOH, NaOAc, Na2CO3)


9/37

| 9

Introduction

Reaction network:


10/37

| 10

Introduction

Drawbacks current aqueous processes:

Solids content limited to 35- 42%-w Lowering of selectivity for starch acetate due to hydolysis (SAA)

High costs associated with water removal in work-up scetion

Lab scale

High DS and SAApossible, however application of pyridine,DMSO instead of water

Toxic, high environmental impact

Supercritical CO2 ??


11/37

| 11

Experimental Setup

Pmax 350 bar


12/37

Process studies; initial screening

Process variables

Pressure: 8-25 MPa

Fixed

Temperature (90C)

Catalyst (NaOAc)

Output

Degree of substitution (DS) Acetic anhydride conversion (Xaah)

Selectivity to desired starch acteylation reaction (Ssa)


13/37

| 13

4000 3500 3000 2500 2000 1500 1000 500 0

Transmitan

ce(%)

Wavelength (cm-1)

1612 cm-1

1723 cm

-1

1609 cm-1

a

b

Product analyses: FT-IR


14/37

Product analyses: NMR

01234567

(b)

ppm

(a)

Acetylgroup


15/37

Product analyses: SEM

Native potato starch Acetylated starch


16/37

| 16

0

0.05

0.1

0.15

0.2

0.25

0.3

80 100 150 200 250 285Pressure (bar)

DS

Selectivity

Optimization study- Effect of pressure

DS max : 150 bar

SAAn max : 150 bar

Literature [1]:rates maximal near the criticalpoint of mixture

T = 90 C

1. Savage, P. E., Gopalan, S., Mizan, T. I., Martino, C. J.& Brock, E. E. (1995),AIChe Journal, 41, 1723-1778.


17/37

| 17

0

0.05

0.1

0.15

0.2

0.25

0.3

80 100 150 200 250 285

Pressur e (bar)

DS

Selectivity


Critical point mixture


18/37

Overview supercritical properties

Table 2.The critical region of AAH-CO2 mixtures at different temperatures

No T

(oC)

Critical region

(MPa)

yAAH

1 50 9.4 9.8 0.08

2 70 12.4 12.6 0.09

3 90 14.5 14.8 0.09


19/37

Effect of starch particle size

Table 3. Comparison of the DS for various starch particle sizes at different reaction conditions

a.fractionated with specified sieve trays, b.determined by laser diffraction c.Experiments at 50 oC, 8 MPa , d.Experiments

at 90oC, 15 MPa

Particle

sizesa

Average Particle Size

(dv)b

Condition Ic Condition II

d

(m) (m) DS DS

36 - 45 43.64 0.21 0.51

45 - 56 52.33 0.18 0.48

56 - 63 62.55 0.18 0.46

> 63 73.5 0.15 0.29

Mainly surface reaction, intra particle mass transfer limited


20/37

Catalyst screening

P: 15

MPa T: 90C

C/Sratio 0.1mol/mol

t 1

h

Catalyst basicity plays

a role

NaOAc exception?


21/37

Systematic process studies

T: 50-90C

P: 8- 25 MPa C/S: 0.1-0.5 (mol/mol)

AAH/S: 4.35 time: 1 h

Catalyst: K 2CO3

22 experiments

Output analysed by non-linear regression


22/37

Results

Max DS: 0.5


23/37

Results

AAH intake as additional variable Catalyst intake as additional variable

Pressure shows an optimum


24/37

| 24

Solubility of sCO2 in starch

Definition solubility :S = (mCO2 dissolved)/mpolymer

Experimental method : Gravimetric : Magnetic Suspension

Balance (MSB)

Range : max T = 473 K, max P = 50MPa

MSB schematic drawing (Nalawade S, 2005)


25/37

| 25

Solubility Study: Results

Sstarch acetate

> Snative

DS SA: 0.5

Muljana et al. Accepted for publication in Polymer Engineering and Science


26/37

Solubility data; comparison

Polymer Pressure Temperature Solubility

(MPa) (oC) (mg CO2/g sample)

Polystyrene (PS) 0 - 9.5 40 30.9 134

2 - 19.8 100 12.7 - 121.8

Poly(ethylene terephthalate)(PET) 0- 39.5 80 0 38

0 - 39.5 120 0 - 32.5

5 - 30 120 9.1 - 37.2

Polypropylene (PP) 5 - 10 40 29.9 - 54.2

5 - 10 120 22.6 - 43.8

Poly(butylenes succinate)(PBS) 1 - 9.9 50 9.8 73

2.3 - 19.9 120 21.7 - 176.1Polycaprolactone (PCL) 8 - 20 50 29.3 - 1637.9

Poly(L-lactide)(PLLA) 10.73 - 29.9 50 190 - 699.5

Starch 2-16 120 8-31

Starch acetate 2-26 120 14-80


27/37

FT-IR measurements for SA at high pressure

S starch acetate> S native

Lewis acid baseinteraction


28/37

| 28

Concluding Remarks

sCO2 is a suitable solvent for starch acetylation reactions

DS is tunable with pressure

Highest DS values at critical points of mixture

Reactions are intra-particle mass transfer limited

In the range T = 120oC and P = 20 300 bar : Max S native : 31 mgCO2/g starch Max S starch acetate : 79 mgCO2/g starch

S starch acetate > S native


29/37

Acknowledgement

Sjoerd van der Knoop

Danielle Keyzer Prof. Z. Knej (University of Maribor)

AVEBE for stimulating discussions


30/37

| 30


31/37

080908 | 31

Good performance of scCO2

Acetylation Study Results

T , DS T, SAA


32/37

080908 | 32

Acetylation Study Effect of pressure and temperature

0 50 60 70 80 90 100

0,00

0,05

0,10

0,150,20

0,25

0,30

0,35

0,40

0,45

0,50

0,55

50 deg C

70 deg C

90 deg C

DS

Pressure (bar)

P , DSconstant

Working at higherpressure (P > 100 bar)

0 50 60 70 80 90 100

0,00

0,02

0,04

0,06

0,08

0,10

0,12

0,14

0,160,18

0,20

0,22

0,24

50oC

70oC

90oC

SAAn

Pressure (bar)


33/37

Determination of supercritical properties

(a) (b) (c) (d)

(e) (f) (g) (h)


34/37

080908 | 34

Gelatinization study (1) DSC Results

T > , P >, DG >

P : 80 bar 250 bar


35/37

080908 | 35

Gelatinization study (2) XRD results

P , broader amorphous region

P (bar)

Degree of

crystallinity

Relative

crystallinityNative 0.132 1.00

80 0.125 0.94

150 0.108 0.82

250 0.102 0.77

P , Crystallinity , DG


36/37

080908 | 36


b. 150 bar, 24 h, DS = 0.61

a. 150 bar, 1 h, DS = 0.29 b. 200 bar, 1 h, DS = 0.23

d. 200 bar, 24 h, DS = 0.31


37/37

Rationalise

Liquid phase

AAH

Catalyst

DissolvedCO2

Possibly

some water

AA

Gas phase

Mainly

scCO2

Dissolved

AAH

StarchParticle

Water

AAH

Catalyst

AA

Dissolved

CO2

Gas-liquid-solid Supercritical -solid

Supercriticalphase

CO2

AAH

Catalyst

Possibly

some water

AA

StarchParticle

Water

AAH

Catalyst

AA

Dissolved

CO2

acetylation of starch in supercritical co2

Documents