Use of a fischer-tropsch derived white oil in food contact applications

The present invention is directed to the use of a Fischer-Tropsch derived white oil in food contact applications. And as a plasticizer for polymer compositions for food contact applications.

EP-A-1 382 639 describes the use of a Fischer-Tropsch derived white oil as a plasticizer in polystyrene compositions. EP-A-1 382 639 indicates that if the polystyrene composition is to be used in food applications, for example coffee cups or food packaging, specific stringent property requirements for the white oil exist. In this respect EP-A-1 382 639 refers to EU Directive 90/128/EEC. According to EU Directive 90/128/EEC based on the recommendation of the Scientific Committee for Food (SCF) of the European Commission and on the results of oral feeding studies carried out at the request of SCF by CONCAWE specifications for white oils derived from petroleum based hydrocarbon feedstocks have been set. The white oil must contain not more than 5% (w/w) mineral hydrocarbons with carbon numbers less than 25, have a kinematic viscosity at 100° C. of not less than 8.5 mm²/s, and an average molecular weight of not less than 480 g/mol. The kinematic viscosity at 100° C. of not less than 8.5 mm²/s and the amount of mineral hydrocarbons with carbon numbers less than 25 in white oils derived from a petroleum based feedstock is linked in this directive.

Applicants have now surprisingly found that if a white oil derived from a Fischer-Tropsch derived hydrocarbon feedstock is used in food contact applications, the white oil does not necessarily need to have a kinematic viscosity at 100° C. of above 8.5 mm²/s (as stipulated by the above EU Directive 90/128/EEC) to result in a content of mineral hydrocarbons with carbon numbers less than 25 of less than 5% (w/w).

Thus, the present invention provides the use of alternative white oils for food contact applications, which are expected to fulfil the requirements for migration limits. To this end the present invention provides the use of a Fischer-Tropsch derived white oil in food contact applications, wherein the Fischer-Tropsch derived white oil has a kinematic viscosity at 100° C. in the range of from more than 2 mm²/s to less than 7 mm²/s, as determined according to ISO 3014, and a content of mineral hydrocarbons with carbon numbers less than 25 of not more than 5% (w/w).

Further it has been found that when the white oils to be used according to the present invention are used as a plasticizer in polymer compositions as compared to white oils having a kinematic viscosity at 100° C. of above 7 mm²/s, this results in an improved fogging behaviour, i.e. a minimized tendency of the polymer compositions to become turbid and hence visibly less attractive. It goes without saying that this is very desirable in e.g. food packages, as the consumer often wishes to be able to see the content of the food package. The minimized tendency further allows an increase in the amount of plasticizer white oil that can be incorporated into a polymer without affecting the clearness of the plasticized polymer composition.

Surprisingly, the compositions according to the present invention show an improved fogging behaviour, i.e. polystyrene compositions for instance are less inclined to turn turbid, while at the same time the white oils as used in the compositions according to the present invention have a content of mineral hydrocarbons with carbon numbers less than 25 of below 5% (w/w) as required by EU Directive 90/128/EEC.

Further, the use of Fischer-Tropsch derived white oils according to the invention is advantageous because they are more easily obtainable than medicinal white oils derived from mineral oils. A further advantage is that the contents of sulphur and nitrogen are nearly zero, due to the nature of the Fischer-Tropsch process.

The person skilled in the art will readily understand what is meant with the term ‘food contact application’. This term includes both direct and indirect food contact. In particular the Fischer-Tropsch derived white oil according to the present invention is used in food processing and food packaging. Some non-limitative examples of food contact applications according to the present invention are food grade lubricants based on said white oils such as compressor oils, heat transfer oils, gear oils, hydraulic fluids, chain oil, greases and hypercompressor oils for use in poly olefin manufacture, for example poly ethylene manufacture. More specifically, the term “food contact applications” refers to polymer compositions for food contact applications.

The person skilled in the art will readily understand what is meant by “white oil”, or more specifically “medicinal white oil”. The white oil may be any type of Fischer-Tropsch derived white oil having a kinematic viscosity at 100° C. of more than 2 mm²/s, and less than 7 mm²/s. It preferably fulfils the requirements for medicinal white oils. General examples of white oils are for instance described in the above referenced EP-A-1 382 639 and in General Textbook “Lubricant Base Oil and Wax Processing”, Avilino Sequeira, Jr, Marcel Dekker Inc., New York, 1994, Chapter 6, pages 141-145.

Preferably, the Fischer-Tropsch derived white oil has a kinematic viscosity at 100° C. of less than 6.5 mm²/s, preferably less than 6.0 mm²/s, more preferably less than 5.5 mm²/s, even more preferably less than 5.0 mm²/s, yet more preferably of less than 4.5 mm²/s, as determined according to ISO 3014. Preferably, the Fischer-Tropsch derived white oil has a kinematic viscosity at 100° C. of and above 2.0 mm²/s, preferably above 2.25 mm²/s, more preferably above 2.4 mm²/s, even more preferably above 2.5 mm²/s, yet more preferably above 3 mm²/s as determined according to ISO 3014. It has been found that if a white oil with a viscosity of 2 mm²/s or below is employed, it will be difficult to incorporate into a polymer, since its use will result in a shear reduction. This requires higher effective shear rates and longer process times, which in turn may lead to degradation of the polymer composition, as well as more complex equipment.

For food applications the Fischer-Tropsch derived white oil preferably has a content of mineral hydrocarbons with carbon numbers less than 25 of not more than 5% (w/w) and a 5 wt % recovery boiling point of above 391° C. according to ASTM D 2887.

Preferably, the Fischer-Tropsch derived white oil preferably has a content of mineral hydrocarbons with carbon numbers less than 25 of not more than 5% (w/w), preferably below 3% (w/w), more preferably below 1% (w/w). Further, the Fischer-Tropsch derived white oil preferably has 5 wt % recovery boiling point of above 400° C. The Fischer-Tropsch derived oil preferably has a Saybolt colour of greater than +25 and preferably equal to +30. The content of polar compounds is preferably less than 1 wt % and the content of non-cyclic isoparaffins is preferably between 75 and 98 wt %. The ultra violet (UV) adsorption spectra values as measured according to ASTM D 2269 is preferably less than 0.70 in the 280-289 nm spectral band, less than 0.60 in the 290-299 nm spectral band, less than 0.40 in the 300-329 nm spectral band and less than 0.09 in the 330-380 nm spectral band as according to FDA 178.3620 (c). The pour point of the oil is preferably below −10° C. and more preferably below −15° C. The CN number as measured according to IEC 590 is preferably between 15 and 30.

The content of Fischer-Tropsch white oil as plasticizer in a polymer composition may range from 0.1 wt % to 10 wt %, more suitably from 0.5 to 8 wt %, yet more suitably from 1 to 5 wt %, and most suitably from 2 to 3 wt %. The exact amount of the Fischer-Tropsch derived white oil depends on the desired properties of the composition, as well as on the viscosity of the Fischer-Tropsch derived white oil and the molecular weight and composition of the polymer.

Preferably, the content of the Fischer-Tropsch derived white oil in the polymer composition is in the range from 0.1 wt % to 3 wt % for a Fischer-Tropsch derived white oil having a kinematic viscosity at 100° C. of from 4.5 mm²/s to 7 mm²/s, while a Fischer-Tropsch derived white oil having a kinematic viscosity at 100° C. of from more than 2 mm²/s to below 4.5 mm²/s may preferably be present in an amount from 0.1 to 8 wt %, more suitably from 0.1 to 5 wt %, and most suitably from 0.1 to 3.5 wt %, all in view of the turbidity of the final composition at ambient temperature in the case of polystyrene as polymer.

Further it is preferred according to the present invention that the Fischer-Tropsch white oil has a kinematic viscosity at 40° C. of less than 55 mm²/s, preferably less than 45 mm²/s, more preferably less than 40 mm²/s, even more preferably less than 35 mm²/s, most preferably less than 30 mm²/s according to ISO 3014.

Further, the Fischer-Tropsch white oil preferably has a flash point below 270° C., preferably below 260° C., more preferably below 250° C., and above 220° C., preferably above 225° C., more preferably above 230° C. according to ISO 2592.

The Fischer-Tropsch derived white oil according to the present invention is preferably obtained by the following process. The preferred process comprises (1) a Fischer-Tropsch synthesis step, (2) a hydrocracking/hydroisomerisation step on (part of) the Fischer-Tropsch synthesis product followed by (3) a pour point reducing step of (a fraction of) the product of the hydroprocessing step. Either solvent or catalytic dewaxing may achieve reduction of pour point in step (3). The desired medicinal or technical white oil having the desired viscosity can be isolated from said dewaxed product by means of distillation. Optionally the oil is hydrofinished or subjected to an adsorption treatment in order to improve its colour. Examples of these process steps are illustrated for the below preferred embodiment.

The thus obtained Fischer-Tropsch derived white oil is then blended in an additional step (e) with the polymer.

The Fischer-Tropsch synthesis step may be performed according to the so-called commercial Sasol process, the commercial Shell Middle Distillate Process or by the non-commercial Exxon process. These and other processes are for example described in more detail in EP-A-776 959, EP-A-668 342, U.S. Pat. No. 4,943,672, U.S. Pat. No. 5,059,299, WO-A-9 934 917 and WO-A-99/20720. Most of these publications also describe the above-mentioned hydroisomerisation/hydrocracking step (2).

A preferred process in which high yields of medicinal or technical white oils having a kinematic viscosity at 100° C. (vK@100) ranging from more than 2 mm²/s to less than 7 mm²/s, can be obtained is by:

(a) hydrocracking/hydroisomerisating a Fischer-Tropsch derived feed, wherein weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms in the Fischer-Tropsch derived feed is at least 0.2 and wherein at least 30 wt % of compounds in the Fischer-Tropsch derived feed have at least 30 carbon atoms;
(b) separating the product of step (a) into one or more lower boiling distillate fraction(s) and a higher boiling white oil precursor fraction;

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