1,4-Dioxane –A Current Topic for Household Detergent

and Personal Care Formulators

L. Matheson and G. Russell -

SASOL N.A.B. MacArthur and W. B. Sheats

-

Chemithon

100th

AOCS Annual Meeting, May 6, 2009

1,4-Dioxane: What Are The Issues?

Recent reports suggest that 1,4-Dioxane has been detected at measurable levels (1 to 100ppm) in some personal care products.

1,4-Dioxane is recognized as a toxic substance that should be controlled.

The source of 1,4-Dioxane has been inaccurately reported.

The reality is:1,4-Dioxane is not a significant by-product of the base-catalyzed ethoxylation of fatty alcohols. 1,4-Dioxane is a controllable by-product of the highly acidic sulfation process to make AES.

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What is 1,4-Dioxane?

1,4-Dioxane

Not to Be Confused with Dioxin

Dioxin

1,4-Dioxane is not the same as dioxin.

The focus of this presentation is on how and where 1,4-

Dioxane is created and what can be done to control its formation.

However, it should be noted that thorough risk assessments of 1,4-Dioxane exposure from cleaning products have been conducted.

Good examples can be found at: www.heraproject.com

HERA (Human and Environmental Risk Assessment) is a voluntary industry program to carry out risk assessements

on household cleaning product ingredients.Alcohol Ethoxylates Version 1.0. (2007, May)Alcohol Ethoxysulphates – Human Health Risk Assessment – Draft. (2003, January)

Risk from 1,4-Dioxane Exposure in Household and Personal Care Products

Where Does 1,4-Dioxane Come From?

Recent publications suggest 1,4-Dioxane is formed through ethoxylation of fatty alcohols.

However, in-house evaluation of alcohol ethoxylates produced by Sasol North America shows <5ppm of 1,4-Dioxane in the ethoxylates used in household and personal care products.

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Where Does 1,4-Dioxane Come From?

RO H + M+OH- RO- + M+ + H2OFeedstock Catalyst

EORO CH2 CH2O-

EO RO CH2 CH2 O CH2 CH2 O-

EO etc.

H+RO (CH2CH2O)nH

Ethoxylate

1,4-Dioxane is not easily formed

under conditions of alkaline catalyzed ethoxylation of fatty alcohols.

Most 1,4-Dioxane is produced during the sulfation of ethoxylated alcohols to make AES.

The thin film sulfation reaction with SO3

occurs under highly acidic conditions.

This has been recognized for some time, and control methods are practiced in the Industry.

Assuming that active levels of any one ingredient in personal care products are about 10%, then the 1,4-

Dioxane in the final product would be diluted by a factor of 10 from that of the starting ingredient.

Where Does 1,4-Dioxane Come From?

SO3 Sulfation of Alcohol Ethoxylates (AE)

R-(EO)n

-OH + SO3

R-(EO)n

-OSO3

H

Reaction occurs under strongly acidic conditions.

Neutralization of the AES acid should occur promptly after sulfation to minimize decomposition and to reduce

by-product formation.

OO

OSO3-

ROSO3

H + NaOH ROSO3

Na

Formation of 1,4-Dioxane by Excess SO3

1,4-Dioxane can be formed from ethoxymers

with >1 mole of EO when excess SO3

is used.

Factors Influencing the Level of 1,4-Dioxane During the Sulfation of AE to Make AESProcess and Equipment Factors

SO3 : AE feed mole ratioReactor loading%SO3 concentration in airResidence time of AES acid prior to neutralizationDe-aeration and stripping of AES paste

Feedstock Compositional Factors Average degree of ethoxylationPEG and moisture contentEO adduct distribution

1,4-Dioxane Study by Chemithon and Sasol

Objective: Sulfate an alcohol ethoxylate and generate response surfaces showing dependence of 1,4-Dioxane on process conditions for making AES.

Experimental Design:

Three Factorial Design -

Central CompositeSO3 : AE feed mole ratio%SO3 concentration in airReactor loading (kg/hr-cm of wetted reactor surface)

Response Measurements 1,4-Dioxane (ppm in 100% active product)Klett Color (5% active basis, 40mm path)Free Oil (wt% in 100% active product)Sodium Sulfate (wt% in 100% active product)

AE Feedstock for Experimental Design StudyFeedstock Analysis:

C1412-3 Ethoxylate –

KOH catalyzed linear, primary C12 and C14 alcohol ethoxylated to approximately 3 moles

Ave Moles EO: 2.8

Ave MW: 329

Wt.% Free Alcohol: 12.1

Wt.% PEG: 0.8

ppm 1,4-Dioxane: 0.1

ppm Moisture: 260

1,4-Dioxane vs. Loading & Mole Ratio at 3% SO3

------Then------

Constant Factor: 3% SO3 in air

Loading

Loading

Mole Ratio

Mole Ratio

1,4-Dioxane

1,4-

Dio

xane

Mole Ratio&

ReactorLoading

1,4-Dioxane

1,4-Dioxane vs. Loading & Mole Ratio at 4% SO3

Mole Ratio

Mole Rati

o

Loading

Loading

1,4-Dioxane

1,4-

Dio

xane

Constant Factor: 4% SO3 in air

Reactor Loading

Mole Ratio

1,4-Dioxane

------Then------

1,4-Dioxane vs. SO3 Concentration & Mole Ratio

SO3 Conc

SO 3Conc

Mole Ratio

Mole Ratio

1,4-Dioxane

1,4-

Dio

xane

Constant Factor: 0.92 Reactor Loading

------Then------

Mole Ratio&

SO3Concentration

1,4-Dioxane

1,4-Dioxane vs. SO3 Concentration & Reactor Loading

Loading

Loading

SO3 Conc

SO3 Conc

1,4-Dioxane

1,4-

Dio

xane

Constant Factor: 0.99 Mole Ratio(Slight excess of AE)

SO3Concentration

ReactorLoading

------Then------

1,4-Dioxane

------Then------

Color vs. SO3 Concentration and Mole Ratio

Low color is a very important quality parameter for AES for personal care formulations.

Mole Ratio

Mole Ratio

SO3 Conc

SO3 Conc

Klett C

olor

Kle

ttC

olor

Constant Factor: 0.92 Reactor Loading

SO3Concentration

KlettColor

Color vs. SO3 Concentration and Reactor Loading

0.99 Mole RatioLoading

Loading

SO3 Conc

SO3 Conc

1,4-Dioxane

1,4-

Dio

xane

Loading

Loading

SO3 Conc

SO3 Conc

Klett C

olor

Kle

ttC

olor

Conditions which yield low color (i.e. low SO3 concentration), will generally yield low levels of 1,4-

Dioxane.

SO3Concentration

1,4-Dioxane &

Klett

ColorThen

Free Oil vs. SO3 Concentration and Mole Ratio

Conditions which give lower 1,4-Dioxane generally yield

high free oil levels.

Mole Ratio

Mole Ratio

SO3 Conc

SO3 Conc

Free Oil Fr

ee O

il

Constant Factor: 0.92 Reactor Loading

Mole Ratio

------Then------

Free Oil

How to Minimize 1,4-Dioxane in AES

1.

Proper Conditions for Thin Film SO3

SulfationSO3

to AE mole ratio of 1.0 or lowerSO3

concentration in air at 3%Reactor loading at ~1 kg/hr -

cm

2.

Properly Designed Thin Film Sulfation Equipment

1,4-Dioxane Reduction by Stripping AES Paste

Reduction of 1,4-Dioxane content in neutral 70% AES paste can be accomplished by stripping.

The reduction factor (Inlet 1,4-Dioxane/Outlet 1,4-Dioxane) in a single stripping stage depends on the weight ratio of stripping steam to AES paste employed.

Reduction ratios from 2 to 10 can be achieved economically.

De-aeration of 70 wt% active AES paste occurs simultaneously upon stripping.

AES Stripping System for 1,4-Dioxane Removal

Steam

Cond

Steam

1,4-DioxaneDestruction

Product AES

AES Paste

Stripper

1,4-Dioxane Removal in Stripper

72% Active AES with 100ppm Inlet

Stri

pper

Out

let 1

,4-D

ioxa

ne

(ppm

wt 1

00%

Act

. Bas

is)

How to Minimize 1,4-Dioxane in AES

1.

Proper Conditions for Thin Film SO3

SulfationSO3

to AE mole ratio of 1.0 or lowerSO3

concentration in air at 3%Reactor loading at ~1 kg/hr -

cm

2.

Properly Designed Thin Film Sulfation EquipmentSulfation reactor and subsequent neutralizationDe-aeration and stripping of neutralized 70% active AES paste

3.

Appropriate Choice of AE Feedstock

Laboratory Studies on 1,4-Dioxane Formation

Sulfation with excess SO3

Ethoxylate Feedstock CharacteristicsDegree of Ethoxylation

Content of High Mole PEG By-Product

Content of High Mole EO Adducts

The Effect of SO3 / AE Mole Ratio

0

100

200

300

400

0 0.2 0.4 0.6 0.8 1 1.2

Mole Ratio of SO3/ETO

1,4-

Dio

xane

(ppm

)

1,4-Dioxane vs. EO Adduct Length in AESppm 1,4-Dioxane (100% active basis)

0 0

408212

812

1858 17822093

1285

0

500

1,000

1,500

2,000

2,500

0 1 2 3 4 5 6 7 8

C12 EO Adduct Chain Length

`

Ethoxylate comparisons are on equimolar

basis, sulfated at 1.03 mole ratio.

Formation of 1,4-Dioxane by Excess SO3

Excess SO3

finds few unreacted

hydroxyl groups and attacks ether oxygens

instead.Higher EO adducts have more sites to attack.

0

5

10

15

20

25

30

35

40

45

0 2 4 6 8 10 12 14

1 EO2 EO3 EO

1214GC (70:30) Alcohol EO Adduct Distributions

EO Mole Adducts

Wei

ght %

1214GC-1 10 Wt% ≥

5 EO1214GC-2 25 Wt% ≥

5 EO1214GC-3 39 Wt% ≥

5EO

0

5

10

15

20

25

30

0 2 4 6 8 10 12 14 16

BRE

NRE

EO Adduct Distributions for 1214GC-2 Mole Ethoxylates, NRE vs. BRE

EO Mole Adducts

Wei

ght %

BRE 25 Wt% ≥

5 EONRE 11 Wt% ≥

5 EO

Effect of By-Product PEG in AE

HOO

OO

OO

OO

OO

OO

OO

OH

PEG comes from residual water present during ethoxylation.

Typical PEG by-product in 1412-3 ethoxylate

•Less than 0.8 weight % PEG in AE

•Ave. MW of 750 for PEG (17 EO units) compared to 435 for alcohol ethoxylate (3 EO units)

H2 O + EO HO CH2 CH2 O H+ more

EOEthylene Glycol

Effect of Moisture in Sulfation Feed

H2

O + SO3 (gas) H2

SO4 (liquid)

H2

O combines with SO3

and forms H2

SO4

H2

SO4 condenses as liquid droplets and forms localized excess of sulfating agent.

Over-sulfation and heat of reaction can lead to increased formation of 1,4-Dioxane.

How to Minimize 1,4-Dioxane in AES

1.

Proper Conditions for Thin Film SO3

SulfationMole ratio of 1.0 or lowerSO3

concentration in air at 3%Reactor Loading at ~1 kg/hr -

cm

2.

Properly Designed Thin Film Sulfation EquipmentSulfation reactor and subsequent neutralizationStripping of neutralized 70% active AES paste

3.

Appropriate choice of AE feedstockMinimize high mole EO adductsLow PEG and low moisture levels in AE

Conclusions

The main source of the 1,4-Dioxane reported in household and personal care products is from the sulfation of AE to produce alcohol ether sulfates (AES).

Our data shows only 5ppm or less 1,4-Dioxane can be attributed to the original alcohol ethoxylate feedstock.

The use of proper sulfation equipment, optimum process conditions, and good quality AE feed should produce AES containing less than 100ppm of 1,4-Dioxane on 100% active basis.

Stripping of the 70% AES paste can reduce the 1,4-Dioxane levels even further.