1,4-Dioxane A Current Topic for Household Detergent and Personal Care Formulators

Transcription

1 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 100 th AOCS Annual Meeting, May 6, 2009

2 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. Photo purchased from

3 What is 1,4-Dioxane? 1,4-Dioxane

4 Not to Be Confused with Dioxin Dioxin 1,4-Dioxane is not the same as dioxin.

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

6 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. Photo purchased from

7 Where Does 1,4-Dioxane Come From? RO H + M + OH - RO - + M + + H 2 O Feedstock Catalyst EO RO CH2 CH 2 O - EO RO CH2 CH 2 O CH 2 CH 2 O - RO (CH 2 CH 2 O) n H Ethoxylate H + EO etc. 1,4-Dioxane is not easily formed under conditions of alkaline catalyzed ethoxylation of fatty alcohols.

8 Where Does 1,4-Dioxane Come From? Most 1,4-Dioxane is produced during the sulfation of ethoxylated alcohols to make AES. The thin film sulfation reaction with SO 3 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.

9 SO 3 Sulfation of Alcohol Ethoxylates (AE) R-(EO) n -OH + SO 3 R-(EO) n -OSO 3 H Reaction occurs under strongly acidic conditions. O O OSO 3 - ROSO 3 H + NaOH ROSO 3 Na Neutralization of the AES acid should occur promptly after sulfation to minimize decomposition and to reduce by-product formation.

10 Formation of 1,4-Dioxane by Excess SO 3 1,4-Dioxane can be formed from ethoxymers with >1 mole of EO when excess SO 3 is used.

11 Factors Influencing the Level of 1,4-Dioxane During the Sulfation of AE to Make AES Process and Equipment Factors SO 3 : AE feed mole ratio Reactor loading %SO 3 concentration in air Residence time of AES acid prior to neutralization De-aeration and stripping of AES paste Feedstock Compositional Factors Average degree of ethoxylation PEG and moisture content EO adduct distribution

12 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 Composite SO 3 : AE feed mole ratio %SO 3 concentration in air Reactor 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)

13 AE Feedstock for Experimental Design Study Feedstock Analysis: C 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

14 1,4-Dioxane vs. Loading & Mole Ratio at 3% SO 3 Constant Factor: 3% SO 3 in air Loading Mole Ratio Mole Ratio & Reactor Loading Then ,4-Dioxane 1,4-Dioxane 1,4-Dioxane Mole Ratio Loading

15 1,4-Dioxane vs. Loading & Mole Ratio at 4% SO 3 Constant Factor: 4% SO 3 in air Reactor Loading Mole Ratio 1,4-Dioxane Mole Ratio Loading Then ,4-Dioxane 1,4-Dioxane Loading Mole Ratio

16 1,4-Dioxane vs. SO 3 Concentration & Mole Ratio Constant Factor: 0.92 Reactor Loading SO 3 Conc Mole Ratio Mole Ratio & SO 3 Concentration Then ,4-Dioxane 1,4-Dioxane 1,4-Dioxane Mole Ratio SO 3 Conc

17 1,4-Dioxane vs. SO 3 Concentration & Reactor Loading Constant Factor: 0.99 Mole Ratio (Slight excess of AE) Loading SO 3 Conc Reactor Loading SO 3 Concentration Then ,4-Dioxane 1,4-Dioxane 1,4-Dioxane SO 3 Conc Loading

18 Color vs. SO 3 Concentration and Mole Ratio Constant Factor: 0.92 Reactor Loading Mole Ratio SO 3 Conc SO 3 Concentration Then Klett Color Klett Color Klett Color Low color is a very important quality parameter for AES for personal care formulations. SO 3 Conc Mole Ratio

19 Color vs. SO 3 Concentration and Reactor Loading SO 3 Concentration 0.99 Mole Ratio Loading Then SO 3 Conc 1,4-Dioxane & Klett Color Conditions which yield low color (i.e. low SO 3 concentration), will generally yield low levels of 1,4- Dioxane. Loading SO 3 Conc 1,4-Dioxane 1,4-Dioxane Klett Color Klett Color SO 3 Conc Loading SO 3 Conc Loading

20 Free Oil vs. SO 3 Concentration and Mole Ratio Constant Factor: 0.92 Reactor Loading Mole Ratio Mole Ratio SO 3 Conc Then Free Oil Free Oil Free Oil Conditions which give lower 1,4-Dioxane generally yield high free oil levels. SO 3 Conc Mole Ratio

21 How to Minimize 1,4-Dioxane in AES 1. Proper Conditions for Thin Film SO 3 Sulfation SO 3 to AE mole ratio of 1.0 or lower SO 3 concentration in air at 3% Reactor loading at ~1 kg/hr - cm 2. Properly Designed Thin Film Sulfation Equipment

22 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.

23 AES Stripping System for 1,4-Dioxane Removal AES Paste Steam Steam Stripper Cond 1,4-Dioxane Destruction Product AES

24 1,4-Dioxane Removal in Stripper Stripper Outlet 1,4-Dioxane (ppm wt 100% Act. Basis) 72% Active AES with 100ppm Inlet

25 How to Minimize 1,4-Dioxane in AES 1. Proper Conditions for Thin Film SO 3 Sulfation SO 3 to AE mole ratio of 1.0 or lower SO 3 concentration in air at 3% Reactor loading at ~1 kg/hr - cm 2. Properly Designed Thin Film Sulfation Equipment Sulfation reactor and subsequent neutralization De-aeration and stripping of neutralized 70% active AES paste 3. Appropriate Choice of AE Feedstock

26 Laboratory Studies on 1,4-Dioxane Formation Sulfation with excess SO 3 Ethoxylate Feedstock Characteristics Degree of Ethoxylation Content of High Mole PEG By-Product Content of High Mole EO Adducts

27 The Effect of SO 3 / AE Mole Ratio ,4-Dioxane (ppm) Mole Ratio of SO 3 /ETO

28 1,4-Dioxane vs. EO Adduct Length in AES 2,500 2,000 ppm 1,4-Dioxane (100% active basis) , , C12 EO Adduct Chain Length ` Ethoxylate comparisons are on equimolar basis, sulfated at 1.03 mole ratio.

29 Formation of 1,4-Dioxane by Excess SO 3 Excess SO 3 finds few unreacted hydroxyl groups and attacks ether oxygens instead. Higher EO adducts have more sites to attack.

30 1214GC (70:30) Alcohol EO Adduct Distributions Weight % EO 2 EO 3 EO 1214GC-1 10 Wt% 5 EO 1214GC-2 25 Wt% 5 EO 1214GC-3 39 Wt% 5EO EO Mole Adducts

31 EO Adduct Distributions for 1214GC-2 Mole Ethoxylates, NRE vs. BRE Weight % BRE NRE BRE 25 Wt% 5 EO NRE 11 Wt% 5 EO EO Mole Adducts

32 Effect of By-Product PEG in AE PEG comes from residual water present during ethoxylation. H 2 O + EO HO CH 2 CH 2 O H Ethylene Glycol + more EO HO O O O O O O O O O O O O O OH Typical PEG by-product in 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)

33 Effect of Moisture in Sulfation Feed H 2 O + SO 3 (gas) H 2 SO 4 (liquid) H 2 O combines with SO 3 and forms H 2 SO 4 H 2 SO 4 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.

34 How to Minimize 1,4-Dioxane in AES 1. Proper Conditions for Thin Film SO 3 Sulfation Mole ratio of 1.0 or lower SO 3 concentration in air at 3% Reactor Loading at ~1 kg/hr - cm 2. Properly Designed Thin Film Sulfation Equipment Sulfation reactor and subsequent neutralization Stripping of neutralized 70% active AES paste 3. Appropriate choice of AE feedstock Minimize high mole EO adducts Low PEG and low moisture levels in AE

35 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.