Znd. Eng. Chem. Res. 1995,34, 410-412
410
Refractive Index-Hydrophilic Lipophilic Balance Relationship for Alcohol Ethoxylates Wiedaw Hreczucht “Blachownia”Heavy Organic Synthesis Institute, Kedzierzyn-Koile, Poland
Refractive index-hydrophilic lipophilic balance relationships for ethoxy derivatives of dodecanol, Alfoll214, Liall25, tallow alcohol and nonylphenol were investigated. For each of the mentioned ethoxylates narrow and broad range distribution products were examined. The correlation level over 99% was indicated in each case, and relevant linear equations were established. No influence of homolog distribution on the relationship was found.
Introduction Nonionics are among those surfactants which are the most often manufactured and widely used. It is always important, both for the producer and for the user, to be able to easily control the synthesis process or check product identity. Although ethoxylates are relatively well elaborated analytically, advanced analytical techniques such as chromatography or NMR may not always be available or convenient to use. In the case of routine process control in commercial scale synthesis, for example, quick and simple physicochemical assessment is still appreciated, particularly if it can give desired, synonymous information. Among the most important characteristics of nonionic surfactants, average ethoxylation degree and cloud point are essential. However, some new quality ethoxylates with narrow-range homolog distribution appeared recently on the market, “Novel 11” from Vista Chemical Company and “Rokanol WDH” from Rokita Z.Ch., Poland, among them. The above mentioned characteristics do not distinguish between the narrow and broad range distributed equivalents. Therefore, beside fractional compositions determined chromatographically, another simple parameter would be desirable for that purpose. The refractive index determination was shown earlier by Suster et al. (1987) as a method for indication of average polyaddition degree for alcohol ethoxylates. Its sensitivity to the substrate structure and average ethoxylation degree as well as the possibility of making cheap and easy measurements encouraged a more detailed investigation in relation to ethoxylate homolog distribution type. The purpose of this work was to investigate the refractive index and hydrophilic-lipophilic balance (HLB) relationship of narrow and broad range homolog distribution of ethoxy derivatives of dodecanol, nonylphenol and three basic types of commercial alcohols. It was of interest whether the distribution type can be identified by this way. It might also be considered as an answer t o whether the refractive index determined for a given ethoxylate sample reflects only the amount of the polar ether bounds present in the product mixture despite their distribution. Simple mathematical simulation can show that, if the differences between refractive indexes determined for subsequent homologs in a polydispersed mixture were not constant, the final additive effect should also indicate the existing differences in homolog distribution, in spite of the same average polyaddition degree.
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Correspondence address: Hreczuch Wieslaw, I C s 0 “Blachownia”, 47-220 Kqdzierzyn-Koile, Poland.
0888-5885/95/2634-0410$09.00/0
Table 1. Comparison of the Fractional Compositions of Exemplary Ethoxylate Equivalents with Broad and Narrow Range Homolog Distribution Obtained by Application of NaOH and ‘W-7“Calcium Based Catalyst, Respectively (Fractional Compositions Expressed in mol %) tallow dodecanol Alfoll214 alcohol nonylphenol ingre- ethoxylate ethoxylate ethoxylate ethoxylate dient BRD NRD BRD NRD BRD NRD BRD NRD Wo” 22.5 7.9 17.7 9.3 21.8 14.3 1.6 0.7 W1 W2 W3 W4 W5 W6 W7 W8 W9 W10 W11 W12 W13 W14
N,,
10.6 9.3 8.8 8.4 7.5 6.6 6.2 5.3 4.4 3.5 2.6 1.8 1.3 0.9
6.7 9.7 15.0 16.9 15.7 12.4 8.2 4.5 1.9 0.7
4.1
4.1
12.0 10.8 9.6 8.4 7.4 6.6 5.8 5.4 4.7 3.9 2.7 1.9 1.6 0.8
5.6 9.0 13.8 18.0 17.6 10.4 7.1 4.1 3.0 1.1 0.4
11.1 10.6 10.2 9.0 7.7 7.2
4.3
4.2
3.8
6.0
6.0 3.4 2.6 1.7 1.3 0.9 0.4
5.8 7.6 11.6 15.1 15.2 14.3 8.0 4.5 2.2 0.9 0.4
5.8 15.6 20.1 18.9 14.5 10.3 6.8 3.8 1.8
4.0
3.6 13.0 27.7 24.5 15.4 6.9 3.4 2.4 1.3
0.6
0.6
0.3
0.3 0.2 0.1
3.7
3.6
Wi denotes product fraction of hydrophobe R and ith polyaddition degree. Exemplary fractional compositions of Lial 125 ethoxylates are not considered as the analytical results are not accurate enough.
Experimental Section The following hydrophobic substrates were used for ethoxylate synthesis: n-dodecanol containing 98%of the pure ingredient, Alfol 1214 (Ziegler alcohols), Lial 125 (oxo alcohols), tallow alcohols containing 29% of C16 and 60% of c18 alcohols as the main components, and nonylphenol, which was 95% pure. Broad range distribution (BRD) ethoxylates were synthesized with NaOH as the catalyst, whereas narrow range distribution (NRD) ethoxylates were obtained using the unconventional (calcium based) catalyst, W7”, commercially produced in the “Blachownia”ICSO, Kqdzierzyn-Koile, Poland. All the ethoxylates (except as mentioned otherwise) were synthesized separately in a 2 dm3 autoclave, equipped with a heating mantle, cooling coil, and mechanical stirrer. Substrate alcohol was mixed with the desired amount of catalyst (0.2-0.3 wt %) and placed in the reactor. The reaction was carried out at 160 and 180 “Cfor BRD and NRD ethoxylates, respectively, until a desired amount of oxirane was introduced. The reaction mixture was then kept for 30 min at the reaction temperature. After cooling, the reaction product was discharged and weighed.
0 1995 American Chemical Society
Ind. Eng. Chem. Res., Vol. 34,No. 1,1995 411 1.5200 1.5100
1
Equation for nonvlphenol ethoxvlates: Y = -0.00219019 X + 1.50952 Coef of dedermination, R-squared = 0.99062
1.5000 1.4900
$J
1.4800
0
.-
Dodecanol, NRD
.$ 1.4700
1
0
1.4600
Nonylphenol, BRD Nonylphenol,NRD
1.4500 1.4400 1.4300 1.4200
Y =0.00171052'X+ 1.428 Coef of determination, R-squared= 0.99474
*-I
0
1
I
I
I
I
I
10 12 14 16 16 20 HLB Figure 1. HLB-refractive index (at 50 "C) relationship for dodecanol and nonylphenol ethoxylates.
1.4540 1.4560
4
2
6
8
Equation for Ab11214 ethoxyletes, BRD and NRD Y 0.00154988 x + 1.42838 Cod of dotemination, R-squared = 0.985238
1
V
(3
1.4380 1.4360 --
Talbw alcohol, BRD
Talbw alcohol, NRD I
1
I
I
Dodecanol ethoxylates were obtained in a one-batch process where separate samples were taken periodically during the synthesis. The differences in fractional composition between ethoxylate counterparts with broad and narrow range homolog distribution obtained with NaOH and "-7" catalyst respectively are demonstrated by a few examples presented in Table 1. Fractional compositions of the ethoxylation products were determined chromatographically according to the method described earlier by Hreczuch et al. (1993). Refractive indexes were determined on the Abbe type refractometer a t 50 "C. Cloud points were determined according to the international standard method, reference number IS0 1065: 199UE). A sample of 5.00 g of surfactant was diluted in 45 g of an aqueous 25% ( d m ) solution of nbutyldiglycol. The final solution was heated until it was completely opaque and next allowed to cool slowly while
,
I
stirring. The temperature a t which the opacity disappeared was marked as the cloud point. Average ethoxylation degrees (except dodecanol ethoxylates) were calculated from synthesis weight balance. Average ethoxylation degrees of dodecanol ethoxylates were determined by an appropriate NMR technique described by Hammond and Kubik (1994). HLB indexes were calculated from the formula found by Griffin (1955):
HLB = (44A/(5Mw))x 100 where A is the average ethoxylation degree and M, is the average molecular weight of the ethoxylate. Results and Discussion The first surfactant groups investigated are NRD and BRD dodecanol ethoxylates. As shown in Figure 1,their HLB-refractive index relationships show good correla-
412 Ind. Eng. Chem. Res., Vol. 34, No. 1, 1995 100 -
90
80 70
*
60 -
9
*
50
40
Ethoxylates o f
D
A
0
-
7
30 20
Alfol 1214, BRD
+
Alfol 1214, NRD
0
Lial 125, BRD
A
Lial 125, NRD
0
Tallow alcohol, BRD
Tallow alcohol, NRD
A
-
4
6
8
10 HLB
12
14
16
Figure 3. HLB-cloud point relationship for Alfol 1214, Lial 125, and tallow alcohol ethoxylates.
tion in a wide range of average polyaddition degrees, despite the homolog distribution type. The data presented in Figure 1 cover dodecanol ethoxylates in the range of their HLBs from 4.1 (average ethoxylation degree, Nav.= 1.1)up to 16.7 (Nav.= 21.3). Distinct cloud point determination for the respective ethoxylates is only possible in the temperature range below 90°C, which responds to an HLB of about 15 (Nav,= 12). Consequently, after being determined experimentally, the refractive index of an ethoxylate sample can be used for description of its HLB in a much broader range than in the case of cloud point. Nonylphenol ethoxylates exhibit also linear refractive index-HLB dependence without distinguishing the homolog distribution type (Figure 1). However, contrary to the aliphatic alcohol ethoxylates the refractive indexes of the alkyl-aryl derivatives decrease with increasing HLB and shift to remarkably higher values. Alfol 1214, Lial 125, and tallow alcohol ethoxylates were considered in further investigation as representative products commonly found on the market. A relationship similar to that from Figure 1shows that, for a given HLB level, increasing average molecular weight of a substrate alcohol caused refractive indexes of its ethoxy derivatives to increase as well (Figure 2). For a given alcohol substrate its NRD and BRD ethoxylates were also put in one line. Quite similar results were found when cloud point was related to HLB for the same products (Figure 3). It was confirmed in this paper that the refractive index of an ethoxylate sample can serve as a reliable parameter for its HLB or average polyaddition degree control as well as an indicator of substrate type in ethoxylation product. Furthermore, its sensitivity to average ethoxylation degree extends far more than for any other technique of cloud point determination.
It might also be concluded that refractive index and cloud point (determined according to IS0 1065) do not describe homolog distribution in an ethoxylation product. They can only reflect the additive effect of an increasing total amount of the polar ether bounds present in an ethoxylation product which is the same in the NRD and BRD equivalents.
Literature Cited Griffin, W. C. Calculation of HLB values of nonionic surfactants. Am. Perfum. Essent. Oil Rev. 1955, 65, 26-29. Hammond, E. C.; Kubik, K. D. Determination of Ethylene Oxide Content in n-Alcohol Ethoxylates by Proton Nuclear Magnetic Resonance Spectroscopy'. J. Am. Oil Chem. SOC.1994,71,113115. Hreczuch, W.; Krasnodebski, Z.; Szymanowski, J. Effect of Narrowing Oxirane Adduct Distribution on Some Properties of Ethoxylated Alcohol-Based Sulfosuccinic Acid Halfesters. J . Am. Oil Chem. SOC.1993, 70, 707-710. International Standard. Non-ionic surface-active agents obtained from ethylene oxide and mixed non-ionic surface active agents-Determination of cloud point. IS0 1065:1991(E). Suster, A.; Grebennikova, A. I.; Ahmetianov, I. S.;. Trubenko, L. L. Ob ispolzovanii nekatoryh fiziEeskih charakteristik dla kontrola proizvodstva oksietilirovannyh spirtov. (The Use of Some Physicochemical Characteristics for the Control of the Production of Ethoxylated Alcohols.) NTZS Neftepererubotka 1987,3,30-32. Received for review May 26, 1994 Revised manuscript received October 24, 1994 Accepted November 7, 1994" IE940336F Abstract published in Advance ACS Abstracts, December 1, 1994.
