Laboratory filtration

A laboratory filtration study is to be carried out at constant rate. The basic equation (Cook, 1984) comes from the relation... 

Laboratory filtration investigations are of three main kinds ... 

Vacuum and pressure laboratory filtration assemblies are shown in Figure 11.7. Mild agitation with air sometimes may be preferable to the mechanical stirrer shown, but it is important that any agglomerates of particles be kept merely in suspension and not broken up. The test record sheet of Figure 11.8 shows the kind of data that normally are of interest. Besides measurements of filtrate and cake amounts as functions of time and pressure, it is desirable... 

ASTM D-5452. Standard Test Method for Particulate Contamination in Aviation Fuels by Laboratory Filtration. 

Filtration. There have been many developments in the field of filtration, but the use of filter paper, gauze, cotton or glass wool along with a suitable funnel still fills the requirements for most clinical laboratory filtrations. 

The centrifuge is very useful in many laboratory filtrations when reasonably small quantities of material are handled (under 100 ml). The centrifuge is capable of effecting very rapid filtration because of the large force exerted on the material. In a typical small centrifuge with a radius of 10 cm and operating at 1,200 rpm, the force is 160 times that of gravity. 

Example 30.2. Laboratory filtrations conducted at constant pressure drop on a slurry of CaCOj in H2O gave the data shown in Table 30.2. The filter area was 440 cm, the mass of solid per unit volume of filtrate was 23.5 g/L, and the temperature was 25°C. Evaluate the quantities a and as a function of pressure drop, and fit an empirical equation to the results for a. 

A dead-ended laboratory filtration apparatus is relatively simple. It consists of a vacuum rated filter flask, large filter funnel with perforated plate, and a filter paper disk covering the perforations. The filter paper should be wetted and vacuum applied to hold the paper against the funnel while a precoat water slurry of filter aid is applied to the funnel to create a precoat layer of approx 0.5 in. thickness. Additional filter aid should be added to the fermentation broth and well mixed before pouring broth onto the funnel. Amount of filter aid added depends on the broth characteristics, but a typical starting point would be 50 g/L of broth. 

Preliminary sample evaluation and review of processing records often provides useful information as to the nature of the problem. In the case of haze or precipitates present in small amounts, it may be necessary to concentrate the latter by either centrifugation or filtration. Most laboratory filtration units utilize 47-mm membranes. Alternatively, syringe filters equipped with a filter disk of appropriate pore size may also be used. For general purposes, 1-5-pm cellulose acetate filters are useful. Alternatively, the bottle may be stood upright for several hours and the precipitate pipetting directly off the bottom. 

Industrial filtration equipment differs from laboratory filtration equipment only in the amount of material handled and in the necessity for low-cost operation. A typical laboratory filtration apparatus is shown in Fig. 14.2-1, which is similar to a Buchner funnel. The liquid is caused to flow through the filter cloth or paper by a vacuum on the exit end. The slurry consists of the liquid and the suspended particles. The passage of the particles is blocked by the small openings in the pores of the filter cloth. A support with relatively large holes is used to hold the filter cloth. The solid particles build up in the form of a porous filter cake as the filtration proceeds. This cake itself also acts as a filter for the suspended particles. As the cake builds up, resistance to flow also increases. 

A laboratory filtration study has been carried out at constant rate. The filtration time tf in hours) required to build up a specific cake thickness has been correlated as... 

D7321 Particulate contamination of B1 00 and biodiesel blends by laboratory filtration EN 14104 Acid value... 

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