Adsorbents bone char

V. R. Deitz, Bibliography of Solid Adsorbents Bone Char Research Project, Inc., J. M. Brown, Secretary-Treasurer, care Revere Sugar Refinery, 333 Medford Street, Charlestown 29, Mass., p. xx (1944). 

Fig. XVII-29. Nitrogen isotherms the volume adsorbed is plotted on an arbitrary scale. The upper scale shows pore radii corresponding to various relative pressures. Samples A, Oulton catalyst B, bone char number 452 C, activated charcoal F, Alumina catalyst F12 G, porous glass S, silica aerogel. (From Ref. 196).

The refining effect of ion exchange treatment is of sufficient magnitude to permit the elimination of a substantial portion of activated carbon, or bone char requirement. At least a portion of the cost of operation of the ion exchange unit is thus paid for by the savings in requirement of color adsorbent. 

Figure 15.1. Processes for making adsorbents, (a) Flowsketch of a process for making molecular sieve adsorbents, (b) Process for reactivation of bone char, (c) Silica gel by the BASF process. The gel is formed and solidifies in air from sodium silicate and sulfuric acid, then is washed.free of sodium sulfate with water (Ullmann, Encyclopedia of Chemical Technology, Verlag Cliemie, Weinheim, Germany).

After activated carbon has become saturated with a vapor or an adsorbed color, either the vapor can be steamed out, condensed, and recovered (Fig. 2), or the coloration can be destroyed and the carbon made ready for reuse. The oldest example of this process uses the decolorizing carbon long known as bone char, or bone black. This consists of about 10% carbon deposited on a skeleton of calcium phosphate [Ca3(P04)2] and is made by the carbonization of fat-free bones in closed retorts at 750 to 950°C. 

To achieve a pH of 6 or lower for the effluent from a char filter, it is necessary to acid temper the rebumed bone char after it has been returned to the filter, i.e., to treat the char with dilute acid. It is evident, therefore, that bone char is not well adapted, in this respect, to dextrose refining. Consequently, one obvious direction in which an improvement in the conventional process could be made would be the devising of an adsorbent which would buffer on the acid side of neutrality instead of on the alkaline side. 

Finally, it is essential that adsorbents proposed for sugar refinery use be capable of regeneration in existing equipment, and preferably at the same temperature as bone char in order that the proposed adsorbent can be added to the service char as make-up. To fulfil this latter requirement it is also necessary that the proposed adsorbent be of such a nature that it will not react chemically with bone char in filters or kilns, since such reaction would almost certainly be deleterious to both adsorbents. 

Inspection of Figure 4 shows that the two adsorbents are equally efficient decolorizers of the number 13 soft sugar at a residual color of 5.2%. Above this residual color bone char, and below it Synthad, is the more efficient. For the Cuban raw the residual color for equal efficiencies is 1.7%. It is evident that a decision as to which adsorbent is the better decolorizer should be based both on the character of the sugar and on the ratio of adsorbent used to sugar treated. Even when these factors are taken into account, quantitative predictions of refinery performance cannot be made. In the laboratory, the adsorbents and the liquors were allowed to reach an approximate equilibrium. In the refinery, equilibrium is never attained. Before the laboratory color measurements were made, the liquors were all buffered to the same pH value. Char... 

The effect of carbon content has already been discussed generally, but it should be noted that if carbon is allowed to accumulate in the pores of the adsorbent it will block them quite as effectively as will inorganic impurities, and hence contribute to the deterioration. That moderate variations in carbon content have no effect on the rate of deterioration of adsorbents is shown in Figure 7, which presents results of some of the laboratory tests made on the adsorbents during the full-scale comparison of Synthad and bone char, to which reference has already been made.4... 

Pore volume distributions for the adsorbents into cycle 1 of Figure 7 are shown in Figure 10, Curves 1 and 2. If the bone char had merely lost pore volume and area as a consequence of retained impurities partially... 

These observations appear to indicate that although the Synthad referred to in Figures 7 and 10 was initially much more coarsely porous than the bone char, it would be desirable to produce a synthetic adsorbent still more coarsely porous. That progress in this direction is being made is shown by curve 3 of Figure 10. 

Carbon adsorbents have traditionally been used for removal of coloration in the clarified effluent liquor. The general carbon adsorbents, which may be bone char, granular carbon, or powdered carbon products, are used in either a fixed-bed operation or a moving-bed process. These carbons are regenerated at intervals to maintain their effectiveness. 

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