1. A separation disc adapted to being fitted in a milk separator comprising a rotor, to being rotatable together with the rotor about an axis of rotation and to forming together with other separation discs which are fitted in the rotor substantially coaxially with the axis of rotation, wherein spacing members are arranged to keep adjacent separation discs in the stack at mutual axial spacing such that the separation discs form between them narrow flow gaps for milk which is to be separated during operation of the milk separator by means of centrifugal force, the separation disc comprising; a truncated substantially conical portion and an annular flange element which is connected to the conical portion at a smallest radius defined thereby, the annular flange element extends therefrom radially inwards substantially perpendicular to the axis of rotation; the separation disc defines a hole which surrounds the axis of rotation and which forms in the stack of separation discs a flow passage which extends axially through the stack of separation discs to lead away cream separated from the milk; the flange element delimits an axial throughflow cross-section for the flow passage for the cream; the flange element has a radial extent corresponding to at least 10% of the radial extent of the substantially conical portion, and the inner radial edge of the flange element is provided with a number of recesses distributed along the circumference of the edge and adapted to protrusions on a column which is connected to the rotor and which extends coaxially through the stack of separation discs, so that the recesses and the protrusions provide polar guidance and centering for the separation discs relative to the column and the rotor; the recesses are formed so that the protrusions fill substantially the whole of the recesses and that the radial extent of the recesses corresponds to at least 20% of the radial extent of the flange element, the column protrusions being adapted to entraining the cream during operation of the milk separator.
2. A separation disc according to claim 1, wherein the radial extent of the flange element corresponds to at least 15% of the radial extent of the conical portion.
3. A separation disc according to claim 1, wherein the radial extent of the flange element corresponds to 20-50% of the radial extent of the conical portion.
4. A separation disc according to claim 1 wherein the radial extent of the flange element corresponds to about 35% of the radial extent of the substantially conical portion.
5. A separation disc according to claim 1 wherein the flange element is adapted together with the column to delimiting the throughflow cross-section of the flow passage so as to result in a minimum flow velocity for the cream through the flow passage.
6. A separation disc according to claim 1 wherein the recesses are formed so that the protrusions fill substantially the whole of the recesses and that the recesses have a substantial radial extent corresponding to at least 50% of the radial extent of the flange element.
7. A separation disc according to claim 1 wherein the recesses are formed so that the protrusions fill substantially the whole of the recesses and that the recesses have a radial extent corresponding to substantially the whole of the radial extent of the flange element.
8. A separation disc according to claim 1 wherein the flange element comprises spot-shaped spacing members.
9. A separation disc according to claim 1 wherein the flange element comprises linear spacing members which extend radially along a major portion of the radial extent of the flange element.
10. A separation disc according to claim 1 wherein the conical portion has distribution holes adapted to leading and distributing the milk into respective flow gaps in the stack of separation discs during operation of the milk separator.
11. A separation disc according to claim 1 wherein the conical portion is provided with spot-shaped spacing members.
12. A separation disc according to claim 1 wherein the conical portion is provided with linear spacing members.
13. A milk separator comprising a rotor rotatable about an axis of rotation and a plurality of stacked separation discs positioned in and rotatable with the rotor, the separation discs being arranged substantially coaxially with the axis of rotation; a portion of the stacked separation discs being configured as described in claim 1.
The claims below are in addition to those above.
All refrences to claim(s) which appear below refer to the numbering after this setence.
1. A process to prepare a base oil having a viscosity index of between 80 and 140 starting with a feedstock that is either a distillate or a de-asphalted oil by
(a) contacting the feedstock in the presence of hydrogen with a sulphided hydrodesulphurisation catalyst comprising nickel and tungsten on an acid amorphous silica-alumina carrier, and
(b) performing a pour point reducing step on the effluent of step (a) to obtain the base oil.
2. The process according to claim 1, wherein the sulphided hydrodesulphurisation catalyst has a hydrodesulphurisation activity of higher than 300%, wherein the hydrodesulphurisation activity is expressed as the yield in weight percentage of C4-hydrocarbon cracking products when thiophene is contacted with the catalyst under standard hydrodesulphurisation conditions, wherein the standard conditions consist of contacting a hydrogen-thiophene mixture with 200 mg of a 30-80 mesh catalyst at 1 bar and 350\xb0 C., wherein the hydrogen rate is 54 mlmin and the thiophene concentration is 6 vol % in the mixture.
3. The process according to claim 2, wherein the hydrodesulphurisation activity of the catalyst is lower than 40% .
4. The process according to claim 3, wherein the hydrodesulphurisation catalyst is obtained in a process wherein nickel and tungsten where impregnated on the acid amorphous silica-alumina carrier in the presence of a chelating agent.
5. The process according to claim 4, wherein the alumina content of the hydrodesulphurisation catalyst is between 10 and 60 wt % as calculated on the carrier alone.
6. The process according to claim 5, wherein the silica-alumina carrier has an n-heptane cracking test value of between 310 and 360\xb0 C., wherein the cracking test value is obtained by measuring the temperature at which 40 wt % of n-heptane is converted when contacted, under standard test conditions, with a catalyst consisting of said carrier and 0.4 wt % platinum.
7. The process according to claim 6, wherein the silica-alumina carrier has an n-heptane cracking test value of between 320 and 350\xb0 C.
8. The process according to claim 7, wherein the catalyst comprises between 2-10 wt % nickel and between 5-30 wt % tungsten.
9. The process according to claim 8, wherein the surface area of the hydrodesulphurisation catalyst is between 200 and 300 m2g.
10. The process according to claim 9, wherein the total pore volume of the hydrodesulphurisation catalyst is above 0.4 mlg
11. The process according to claim 10, wherein between 5 and 40 volume percent of the total pore volume of the hydrodesulphurisation catalyst is present as pores having a pore diameter of more than 350 \u212b.
12. The process according to claim 11, wherein the feedstock in step (a) contains more than 700 ppm sulphur.
13. The process according to claim 12, wherein the feed to step (a) is first subjected to a hydrodesulphurisation step prior using the feed in step (a) when preparing a base oil having a viscosity index of greater than 120.
14. The process according to claim 13, wherein the catalyst in step (a) comprises between 0.1 and 8 wt % of a molecular sieve.
15. The process according to claim 14, wherein the molecular sieve is zeolite Y, ultrastable zeolite Y, ZSM-12, zeolite beta or mordenite molecular sieve.
16. The process according to claim 15, wherein step (b) is performed by means of solvent dewaxing.
17. The process according to claim 15, wherein step (b) is performed by means of catalytic dewaxing.
18. The process according to claim 17, wherein the dewaxing catalyst is selected from the group consisting of a catalyst composition A comprising a silica bound and dealuminated PtZSM-12, a catalyst composition B comprising a silica bound and dealuminated PtZSM-22, and a catalvst composition C comprising a silica bound and dealulninated PtZSM-23.
19. The process according to claim 18, wherein the dewaxing catalyst is a silica bound and dealuminated PtZSM-12.