Filters, blocking porous

The fi-compound is dissolved in 50 c c. pure dry ether, and dry hydiogen chloride is passed in with constant shaking to prevent the delivery tube from becoming blocked. Colourless crystals of the hydrochloride of the /3-o ime separate and aie filtered and washed with dry ether and then placed in a separating funnel and covered with a layer of ether. A. concentrated solution of sodium carbonate is gradually added with constant shaking until no further effervescence is observed. Sodium chloride is precipitated and the /3-oxime dissolves in the ether. The ether extract is sepaiated, dehydrated over sodium sulphate, and the ether remoi ed as rapidly as possible at the ordinary temperature by evaporation in vacuo. The residue crystallises, and when pressed on a porous plate leaves a mass of small silky needles, m. p. 126—130A It may be re-... 

Coarse (dP = 50-100 pm) porous disks are the most frequently applied diffusers in large-scale drinking water treatment systems (Masschelein, 1994). They are seldom used in industrial waste water treatment applications. The reason is that blocking or clogging can easily occur, e. g. by means of precipitation of chemicals, like carbonates, aluminum or ferrous oxides, manganese oxides, calcium oxalate or organic polymers. This is also valid for ceramic filter tubes, which are sometimes used as mass transfer systems in drinking water applications. 

Industrial cells are mainly bipolar consisting of a large number of individual plate cells connected back to back and coupled in blocks according to the filter press principle. If the electrolysis is carried out under pressure, the energy consumption can be reduced by 20%. Further recent developments are the use of porous electrodes, high temperature steam electrolysis and the SPE-process (solid polymer electrolyte). Heavy water, D2O, can be produced as a byproduct in water electrolysis through enrichment in the electrolyte. 

Clogging depends more on particle size than the intensity of the turbidity. Coarse particles form a porous layer on the filter surface and cause litde clogging. Finer particles penetrate the filter layer and block it rapidly. 

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. 

It has been stated that a filter medium is a porous (or at the very least semi-permeable) barrier placed across the flow of a suspension to hold back some or all of the suspended material. If this barrier were to be very thin compared with the diameter of the smallest particle to be filtered (and perforated with even sized holes), then all the filtration would take place on the upstream surface of the medium. Any particle smaller than the pore diameter would be swept through the pores, and any particle larger than that (assuming the particles to be rigid) would remain on the upstream surface. Some of the larger particles, however, would be of a size to settle into the individual pores and block them. The medium surface would gradually fill with pores blocked in this way, until the fluid flow reduced to below an acceptable level. At this point filtration would be stopped and the medium surface would be brushed or scraped clean (although many automatic filters have their surface continuously brushed or scraped). 

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