Paraffin waxes (Fischer-Tropsch), isomerization

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

3rd May and 13th May 2005

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: guideline study on Gas-to-liquids (GTL) substance covering the carbon range from C15 to C50

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Date of inspection: December 2002; Date of certificate: February 2003

Type of method:

flask method

Key result

Water solubility:

3.1 mg/L

Temp.:

20 °C

pH:

6.3 - 6.4

Details on results:

The preliminary results indicated that the test material was essentially insoluble in water and that the loading rate had no influence on the final analysed TOC concentration. Therefore the definitive test was performed at a single loading rate only, that of 1.0 g/l.

Preliminary test:

The preliminary results indicated that the test material was essentially insoluble in water and that the loading rate had no influence on the final analysed TOC concentration. Therefore the definitive test was performed at a single loading rate only, that of 1.0 g/l.

Definitive test

The TOC concentrations (mg/l) of the sample solutions are shown in the following table:

Solution	Total Organic Carbon Content (TOC in mg/l)
Sample 1A	3.7
Sample 1B	4.4
Sample 2A	1.4
Sample 2B	1.7
Sample 3A	3.1
Sample 3B	3.5
Water blank	0.6

As the water blank represented a significant contribution towards each sample TOC content, it has been subtracted from the definitive test overall results.

The results and sample treatment summary are shown in the following table:

Sample Number	Time Shaken at ~ 30ºC (hours)	Time Equilibrated at 20ºC (hours)	TOC Content (g/l)	Solution pH
1	24	24	3.5 x 10^-3	6.4
2	48	24	<1.0 x 10^-3	6.2
3	72	24	2.7 x 10^-3	6.3

Mean concentration:    3.1 x 10^-3 g/l at 20.0 ± 0.5 ºC (not including Sample 2, which was below the limit of quantification applied to the procedure)

Range:                         <1.0 x 10^-3 to 3.5 x 10^-3 g/l

Discussion:

Due to the test material being a very complex mixture of hydrocarbons, and it also being essentially insoluble in water, analysis of the sample solutions was performed monitoring the TOC content of the sample solutions only.

The preliminary water solubility test indicated that the column elution method should have been performed as the solubility was less than 1x10^-2 g/l. However, due to the physical nature of the test material, it was not possible to use this method; experience has shown that liquid test materials coated onto glass beads cause these beads to adhere together forming a plug within the column and thus preventing water circulation.

Conclusions:

The water solubility of the test material has been determined to be 3.1 mg TOC/l of solution at 20.0 ± 0.5°C.
Interpretation of results: slightly soluble (0.1-100 mg/L)

Executive summary:

The determination was carried out for 'Paraffin waxes (Fischer-Tropsch), full-range, C15-50 - branched and linear' using the flask method, Method A.6 of Commission Directive 92/69/EEC (which constitutes Annex V of Council Directive 67/548/EEC).

Due to the test material being a very complex mixture of hydrocarbons, and it also being essentially insoluble in water, analysis of the sample solutions was performed monitoring the TOC content of the sample solutions only.

The preliminary water solubility test indicated that the column elution method should have been performed as the solubility was less than 1x10^-2g/l. However, due to the physical nature of the test material, it was not possible to use this method; experience has shown that liquid test materials coated onto glass beads cause these beads to adhere together forming a plug within the column and thus preventing water circulation.

The definitive test was based on the preliminary test. Mixtures of the test material and the glass double-distilled water were added to three seperate flasks. After addition of glass double-distilled water to the flasks, they were shaken at approximately 30 deg C and after standing at 20 deg C for a period of not less than 24 hours, the contents of the flasks were centrifuged at 13500 rpm for ca. 20 minutes. The pH of each solution was measured.

The water solubility of the test material was determined to be 3.1 x 10 ^-3 g TOC/l of solution at 20.0 +/- 0.5 deg C.

Description of key information

- water solubility of the closely related (liquid) substance GTL waxy raffinate [C15-50; CAS 848301-87-1, EC 482-130-1] covering the low molecular weight fraction of the registration substance up to C50 [determined using the flask method, EU Method A.6]: 3.1 mg TOC/L at 20.0 ± 0.5°C (arithmetic mean of two determinations at pH 6.3 - 6.4);

- as the water solubility decreases with increasing carbon chain length, it can be safely concluded that the corresponding result for the (solid) registration substance containing higher molecular weight constituents (C25 - C150, about 30-55% >C50) should be < 3.1 mg TOC/L at 20.0 ± 0.5°C;

- as key result, a water solubility of approx. 1 mg TOC/L (rather < 1 mg TOC/L) is applied for the registration substance [which is supported by a test result for the closely related (liquid) substance GTL base oil (CAS 848301-69-9, EC 482-220-0), consisting of linear and branched alkanes (paraffins) with a small amount of cycloalkanes in the carbon range from C18 to C50; see supporting study];

- waxes, just as the registration substance, are insoluble in water, but soluble in organic, non-polar solvents

Key value for chemical safety assessment

Water solubility:

1 mg/L

at the temperature of:

20 °C

Additional information

Measured data are not available for the registration substance itself.

However, reliable data of the closely related substance GTL waxy raffinate (C15-50; CAS 848301-87-1, EC 482-130-1) can be used to address the endpoint that is suitable to draw conclusions on the water solubility of the registration substance [in terms of total organic carbon (TOC) contained in water].
The water solubility of the closely related (liquid) test item GTL wax raffinate - consisting of linear and branched alkanes (paraffins) in the carbon range from C15 to C50 and covering the low molecular weight fraction of the registration substance up to C50 - was determined to be 3.1 mg TOC/L at 20.0 ± 0.5°C.
Since water solubility decreases with increasing carbon chain length, it can be safely concluded that the corresponding result for the (solid) registration substance containing higher molecular weight constituents (C25 - C150, about 30-55% >C50) should be < 3.1 mg TOC/L. Therefore, a water solubility of about 1 mg TOC/L (rather < 1 mg TOC/L) is applied as key result for the (solid) registration substance [which is supported by a test result for the closely related (liquid) substance GTL base oil (CAS 848301-69-9, EC 482-220-0), consisting of linear and branched alkanes (paraffins) with a small amount of cycloalkanes in the carbon range from C18 to C50; see supporting study].

 

Predicted water solubility values, calculated using a validated QSAR method, are available for individual constituents of the substance GTL waxy raffinate [C15-50; CAS 848301-87-1, EC 482-130-1]. Predicted water solubility is in the range <1.0E-04 to 2.7E-04 mg/l. Based on the identical predicted results for individual constituents in the carbon range, C30-50, a water solubility of <1.0E-04 mg/l can also be considered for the higher molecular weight constituents of the registration substance (>C50).

It should be noted that the predicted water solubilities will differ when the substances are present in a mixture, as the registration substance:

• The actual water solubility of a component in a mixture will decrease, as the total water solubility of an ideal mixture is proportional to the sum of the water solubilities of the mole fractions of each individual component (Banerjee 1984).


• Components that are normally solid under environmental conditions when part of a mixture may have lower melting points (and therefore be in a liquid state) and increased vapour pressure and water solubility (Banerjee 1984).

^{Source: Banerjee S. 1984. Solubility of organic mixtures in water. Environmental Science & Technology 18:587–591.}