CLEANING METHOD FOR MEMBRANES

1. Method for cleaning porous membranes suitable for use in oil refining processes comprising the regular treatment of said membranes by applying the steps of: a) backblowing with gas when the flux has reduced to less than 95% of the maximum flux, i.e. the flux through the membrane immediately after cleaning; b) backflushing with edible oil, when the maximum flux rate measured after backblowing with a gas, has diminished to less than 90% of the top flux, i.e. flux through the membrane when it is used for the first time; c) treating the membranes with alkaline material when the maximum flux rate measured after backflushing with oil, has diminished to less than 90% of the top flux; wherein the method is used for a cleaning in place, with the proviso that said method does not involve the use of organic solvents to clean the membranes. 2. Method according to claim 1, wherein step (a) of backblow with gas is carried out at a frequency of more than once every 8 hours. 3. Method according to claim 1 or 2 wherein step (b) of backflushing with oil is carried out at a frequency of more than once every 14 days. 4. Method according to any one of claims 1-3 wherein step (c) of treating with alkaline material is carried out at a frequency of more than once every 7 months. 5. Method according to any one of claims 1-3 wherein step (c) of treating with alkaline material is carried out at a frequency of more than once every 6 weeks. 6. Method according to one or more of the claims 1-5 wherein step (b) of backflushing with oil is performed with hot non-winterized oil. 7. Method according to one or more of the claims 1-6 wherein the alkaline treatment is performed with a solution that comprises one or more compounds selected from the group of caustic soda, surfactants, detergents. 8. Method according to one or more of the claims 1-7 wherein the porous membranes are microfilters having an average pore diameter of 0.05-5 (m. 9. Method according to one or more of the claims 1-8 wherein the membranes are in the form of a module that consists of a housing comprising a package of hollow fibres made of a symmetric, synthetic polymer membrane, preferably Polyvinylidene Fluoride (PVDF), said membranes having an average pore diameter of 0.2-0.9 (m. 10. Method according to one or more of the claims 1-9 wherein the oil with which the membranes are backflushed is the same as the oil to be refined. 11. Method according to one or more of the claims 1-10 wherein step (a) of backblowing with