Technical Specifications

FILTRATION DEFINITIONS

  • FILTRATION

It is a physical process which consists of separating the two phases(solid-liqulid,liquid-liquid,solid-gas,liquid-gas)using an adequate filtration mean,according to the sample’s nature.

  • FILTER

It is the appliance or the system used to carry out the filtration process.

  • FILTRATION MEAN

It is the porous material where the phases separation is achieved.

KINDS OF FILTRATION

The phases we can separate in a filtration process can be:

  • SOLID-LIQUID:

Retention of the solid particles in order to clean a liquid sample.
Example: A water sample to determine solids in suspension.

  • LIQUID-LIQUID:

Separation of one watery phase from an organic one.
Example: A mix of oil and water with a phase separator paper.

  • SOLID-GAS:

Retention of solid particles which are in a gas.
Example: Atmospheric emissions test using quartz thimbles.

  • LIQUID-GAS:

Retention of watery particles which are in a gas.
Example: Blowing tasks using a PTFE filter.

FILTRACION’S OBJECTIVE:

  • EFFICACY:

Remove the harmful phase of the sample and recover the useful phase with the highest clean grade possible.

  • SPEED:

Complete the filtration process in the least time possible.

  • FINANCES:

Complete the filtration process with the lowest cost possible.

FACTORS AFFECTING THE FILTRATION

The factors which intervene in the filtration process are diverse and complex.

  • NATURE OF THE PHASES BEING SEPERATED
  • Particles in the sample:
  • SHAPE
  • SIZE
  • ELECTRICAL CHARGE
  • Sample’s nature:
  • SURFACE TENSION
  • VISCOCITY
  • pH
  • NATURE OF THE FILTRATION MEAN
  • RETENTION OF THE FILTRATION MEAN
  • CHARGE CAPACITY
  • FILTRATION SURFACE
  • FILTER’S FORMAT
  • PRESSURE DIFFERENTIAL OF THE FILTRATION MEAN
  • PHYSICAL CONDITIONS OF THE FILTRATION
  • PRESSURE DIFFERENTIAL OF THE FILTRATION MEAN

5.FACTORS AFFECTING THE FILTRATION

PARTICLE’S SIZE

  • pH

In 1909 the Danish chemist Sorensen defined the hydrogen potential(pH) as the negative logarithm of the hydrogen ions activity.

pH=-log10(aH+)

The pH has a scale from 0 to 14,being the dissolutions with pH lower than 7,acids;and the ones with higher pH than 7,basics.

The sample’s pH affects quickly and directly the filtration mean’s integrity, reason why it is necessary to consult the chemistry compatibility tables of the different filtration means regarding to the nature of the samples.

  • LOAD CAPACITY:

The load capacity of a filter defines the amount of particles that a filtration mean is able to retain, using different mechanisms, before arriving to the clogging state.

The filters with a higher load capacity are the depth filters, usually they are thick filter papers and with low density.

  • SURFACE OF THE FILTRATION

It is an important parameter, since of it depends the premature clogging of the filtration mean and the speed of the filtration process.

If we have in mind to filtrate a very dirty sample, the best option is to increase the diameter of the filtration mean.

For example: a filter of 47mm diameter will clog four times earlier than one of 90mm diameter.

  • FILTER’S FORMAT:

The laboratory filter papers can be flat or folded.

  • FILTER’S FORMAT:

The laboratory filter papers can be flat or folded.

  • Flat: used in Buchner funnels, filtration equipments or folded in quadrant when using conical funnels.
  • Folded : used in conical funnels.

The folded filters have the advantage of doing the filtration process more quickly tan the flat papers, since with their folds they let the liquid to be separated from the funnel’s wall and so it lets the air through, letting the liquid exit from funnel.

  • PRESSURE DIFFERENTIAL OF THE FILTRATION EQUIPMENTS

We often need a pressure differential between the entrance of the filtration equipment's and the exit of the liquid so as to get the wished effects.

It is not the same to do a filtration under the atmospheric pressure than forcing it by vacuum or pressure.

STRUCTURE OF THE FILTRATION MEANS

CELLULOSE FILTER PAPERS

QUANTITATIVE FILTER PAPER

DIATOMACEOUS FILTER PAPER

FILTER SHEETS

PHYSICAL PARAMETERS OF THE FILTRATION MEANS

  • CELLULOSE FILTER PAPERS(I)
  • Weight in grams: shows the filter paper weight in g/m2 .That is to say,the weight in grams of a sheet 100x100cm.
  • Thickness: it is the measure of the paper sheet thickness in mm.
  • Surface: A filter paper can have three kinds of surfaces: smooth, creped or embossed.
  • Vel. Filtration: It lets us know the water volume able to go through a filtration mean, by time and area units.
  • Content in ash: Calculated from the difference of weight between the calcinated residue obtained at 8000C and the sample’s weight when it is completely free of moisture. It is expressed in %.
  • CELLULOSE FILTER PAPERS(II)
  • Resistance in moist state: It shows the resistance of a moistened filter paper. A filter paper can be ordinary or hardened.
  • Pore diameter: Calculated by a pore meter Coulter kind. The units is the µm(micron or micrometer).It is calculated using a Gaussian bell curve chart with the distribution of the different pore sizes.
  • Fracture resistance: A 10cm2 filter paper area is undergone to a increasing pressure. At the moment of break, the pressure is determined. It is expressed in N/cm2

CHOOSING THE ADEQUATE FILTER(FILTER PAPERS)

LABORATORY FILTRATION SYSTEMS

  • Atmospheric pressure:
  • With folded papers - Glass funnel
  • Vacuum:
  • Flat papers - Buchner funnel
  • Disposable equipments - Polycarbonate equipments
  • Membranes, glass fiber - Biosart
  • Filtration pad - Kitasato flask
  • Pressure:
  • Pressure tank - 142 or 293 mm. dish
  • Syringe filters - 4, 15 or 25 mm.
  • Holders - 13, 25 or 47 mm.
  • Sartobrand cartridge