D. B. CURLL, JR
`
`Filed Jan. 25, 1959
`
`8 6175.632?
`
`2,251,515,
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`GEMAK 2019
`RECKI'I'I' V. GEMAK
`|PR2020-00186
`
`1
`
`GEMAK 2019
`RECKITT V. GEMAK
`IPR2020-00186
`
`

`

`Patented Aug. 5, 1941
`
`2,251,515
`
`UNITED STATES PATENT OFFICE
`2,251,515
`MANUFACTURE OF ALKALI METAL
`SILICATE‘ SOLUTIONS
`.
`
`Daniel B. Curll, Jr., Marple, Pa., assignor to Phila-
`delphia Quartz Company, Philadelphia, Pa., a
`corporation of Pennsylvania
`
`Application January 23, 1939, Serial No. 252,504
`19 Claims.
`(0:. 23—110)
`'
`
`purification by these methods is due primarily to
`This invention relates to manufacture of alkali
`the high viscosity of commercial silicate solu—
`metal silicate solutions; and it comprises aproc-
`tions. This high viscosity results in a very low
`eSs of preparing solutions of sodium silicate, for
`settling rate for any suspended impurities. Clari-
`example, from the usual silicate glasses which are
`fication of turbid silicate solutions stored in large
`produced by fusion methods; said process com— .5
`tanks is frequently incomplete even after two
`prising preheating water to a temperature of at
`years of storage. The high viscosity also makes
`least about 100° C. and contacting such a silicate
`these solutions difficult to filter, these, difficulties
`glass therewith in the substantial absence of agi—
`being aggravated by the slimy condition of the
`tation, said process resulting in asubstantial sav-
`ing of time in comparison with previous methods 10 filter cakes which tend to clog the filters.
`In
`and in the production of a solution substantially
`order
`to obtain reasonable rates of settling
`free from the usual turbidity and tendency to set—
`and/or filtration, it has been necessary in many
`tle, which is characteristic of the usual commer—
`cases to dilute the silicate solutions which, of
`cial solutions, and also containing less dissolved
`course, necessitates an expensive re-concentra-
`heavy metal impurities either continuously or as 15 tion operation. For these reasons the cost of
`a batch process; all as more fully hereinafter set
`water White solutions in the past has been out
`forth and as claimed.
`of line with'the cost of the more turbid solutions.
`In the usual commercial production of water
`One Of the early methods used for the prepara-
`glaSS and other solutions of sodium silicate, a
`tion of silicate solutions from silicate glasses is
`silicate glass is first produced by fusion methods 20 described in the U. S. patent to Stanton and
`and this glass is then dissolved in water by Vari-
`Vail, No. 1,138,595.
`In this process a bed of sili-
`ous methods. The solutions thus obtained in
`cate glass is introduced into a pressure vessel in
`commercial operation have invariably been more-
`which it is supported by a screen a short distance
`LU
`or-less cloudy or hazy owing to the presence of a _
`from the bottom of the vessel, water is introduced
`small amount of light, finely-divided, suspended _
`into the vessel, this water being then heated by a.
`material having a tendency to settle or to pro—
`steam jacket as well as by direct contact with
`duce “bottoms.” The exact cause for the pres-
`steam at
`its surface, no agitation being em—
`ence of these impurities has not been known.
`ployed. This method operates
`satisfactorily
`These solutions have also contained a consider- 90 When small pressure vessels are employed having
`able quantity of impurities in solution, including ‘1
`_ capacities of the order of 2 to 3 gallons or when
`compounds of iron and titanium. While these
`the pressure vessels are specially COHStl‘uOted in
`impurities are not objectionable in some of the
`order to obtain a uniform distribution of heat.
`many industrial applications in which silicate
`But when vessels of large capacity are employed,
`solutions are used,
`they are particularly objec— n_ the use of a steam jacket produces a steep tem-
`tionable in certain fields, such as textile work and “i? perature gradient between points next to the
`soap making, for example. Even when the sili—
`stEam jacket and interior points. Heating is
`cate solutions are employed in such crude 010-
`very slow and as a result the dissolution of the
`erations as the manufacture of cements and ad-
`glass is very slow. Convection currents set up in
`hosives, it is of advantage to employ clear solu— ,0 such large vessels frequently result in turbid so-
`tions in order to avoid the accumulation of set—
`lutions. The use of this method has therefore
`tlings 0r bottoms in storage tanks and tank cars.
`been abandoned in favor of methods employing
`Many attempts have been made to develop satis-
`agitation which are capable of producing more
`factory methods for the elimination of these dim.»
`rapid rates of solution.
`In fact, to the best of
`culties.
`,1; my knowledge, all the commercial methods which
`The methods which have been previously de— " were in use at the time of the present invention
`veloped and used for the clarification of silicate
`employed agitation in order to obtain economical
`solutions have usually involved filtration,
`de—
`rates of solution.
`cantation or chemical treatment.
`It has been
`In the modern commercial processes silicate
`proposed, for example, to add various chemicals r0 glass is digested with water heated by steam un-
`to promote “breaking” or fioc formation, with or 0
`der pressures ranging up to 100 pounds per square
`without a simultaneous heat
`treatment which
`inch. The dissolving vessels are filled with glass
`tends to dissolve the impurities rather than re-
`which is covered with water and then steam is
`moving them from the solution. These prior
`turned on. Agitation is supplied either by ro—
`vl Cl
`methods, however, have failed to produce the de—
`tation of the pressure vessel itself or by use of
`sired results economically. The high cost of '
`stand pipes or other devices serving to induce
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`2,251,515
`irculation. Even with the best circulation ob—
`prior commercial methods. While the usual com-
`tainable, the time required to achieve commercial
`mercial solutions, if heated for long periods of
`concentration is such that it has been found nec-
`time,
`invariably precipitate silica in hydrous
`form, solutions prepared by the new method re—
`essary to employ a quantity of silicate glass in
`main clear under this treatment.
`It was fur-
`large excess of the quantity actually dissolved,
`that is, from about 4-. to 5 times as much glass
`ther found that, when silicate glasses containing
`has been charged into the dissolver as is dis—
`impurities of heavy metals, such as iron and
`solved in each run. This has necessitated the
`titanium, are employed in the process, a very
`use of dissolvers having a capacity much greater
`small quantity of insoluble matter readily set-
`than that which would otherwise have been re-
`tles out. This residue is very dark in color, much
`quired.
`It has required usually from 60 to 90
`darker than the residue obtained from solutions
`minutes for the concentration of the silicate so-
`prepared by conventional dissolving methods.
`It
`lution to build up to the standard strength of
`was found that this matter can be readily re—
`41" Be’., for example.
`moved by simple settling or filtration, leaving a
`In a series of tests which led to the present
`silicate solution substantially clearer than that
`invention, use was made of both commercial size
`obtained by the use of other dissolving methods
`and pilot-plant size dissolvers. A number of
`which include filtration and/or settling. Upon
`interesting facts were discovered.
`It was found
`analysis of various samples of this residue, it was
`that the silicate solutions, obtained with the use
`found that iron and titanium were present in
`of the smaller dissolvers at steam pressures of
`large proportions. The silicate solutions were
`20 to 30 pounds and without agitation, were
`found to be substantially free from these im-
`substantially less cloudy than those obtained
`purities. As stated previously,
`in the silicate
`with commercial dissolvers at 100 pounds steam
`solutions prepared by usual methods, such iron
`pressures and under conditions of agitation.
`and titanium impurities are dissolved and they
`But it was found that, when the steam pressures
`cannot be removed either by filtration or set—
`of
`the commercial dissolvers were reduced to
`tling. Apparently the use of preheated water
`20 to 30 pounds, no improvement resulted.
`It
`without agitation, as in my process, changes the
`was also found that, when agitation was sub—
`iron and titanium impurities in some way to a
`stantially eliminated in the commercial
`dis—
`state in which they can be readily settled out or
`solvers, the clarity of the resulting solutions was
`filtered off from the solution. The cause for this
`improved only slightly while the time required
`peculiar phenomenon is not known. A possible
`for such runs was excessive For example,
`in
`explanation is that, in my process, the silicate
`one run 31/2 hours were required for the concen-
`solution passes so rapidly through the concentra—
`tration to reach 41° Be. in contrast to the usual
`tion range Within which the impurities normally
`operating cycle of 1 hour. Simultaneous reduc—
`present in sand are soluble that these impurities
`tion in steam pressure and the elimination of
`remain in a dense form which settles readily.
`agitation produced no improvement. It was noted
`My further tests with this new method of dis-
`that, with a semi—commercial dissolver, com-
`solving silicate glasses have shown that
`this
`mercial gravities were obtained within a period
`method does not require the use of a large
`of only 30 to 40 minutes which indicated clearly
`excess of silicate glass in order
`to obtain a
`that some unknown factor was ailecting the re-
`reasonably rapid rate of solution. Even though
`sults.
`In the attempt to discover the cause for
`the theoretical quantity of glass is employed,
`these differences in results, obtained with dis—
`which is required to produce a solution of a given
`solvers of different size, one run was attempted
`strength this glass will dissolve completely within
`in a. small dissolver without the use of agitation
`a period which is usually shorter than that re-
`and with the water preheated under pressure to
`quired in previous methods in which a lame ex-
`a temperature of 170° C.
`In this run the sur-
`cess of glass has been employed.
`prising result was obtained that; with the use of
`It has been found that the presence of an
`water preheated in this manner, the solution built
`excess of silicate glass in the dissolver, while not
`up to commercial gravities within a period of
`essential
`in my new method,
`is advantageous
`only 5 to '7 minutes. And when this new pre-
`in that the dissolving cycle is reduced. For ex-
`heating method was employed with a commercial
`ample, in one run, in which a commercial dis-
`size dissolver then, for the first time, wholly com-
`solver was charged with a silicate glass, contain-
`parable results were secured, and the effect of the
`ing 1 mole of cho to 3.2 moles of 8102, the
`capacity of the dissolver was eliminated. A dis-
`dissolver being charged with 4 times the quan-
`solving period of from 5 to 7 minutes was ob—
`tity of glass theoretically required to produce the
`tained as with the smaller dissolver.
`It is be-
`commercial gravity of 41° Bé.,
`the water em-
`lieved that this is the first
`time that such a
`ployed being at a temperature of 170° C., a dis-
`short dissolving period has been obtained in a
`solving cycle of only 7 minutes was required.
`large dissolver either with or without the use of
`After the withdrawal of the resulting solution,
`agitation.
`this dissolver was charged with preheated water
`When the silicate solution, obtained by the use
`without the addition of silicate glass. The sec-
`of preheated water, as described, Was examined
`ond dissolving cycle was found to be only slight-
`for turbidity and tendency to settle, the further
`ly longer than the first but, in the case of the
`surprising fact was discovered that this solution
`third cycle, in which the ratio of silicate glass
`was substantially free from cloudiness or haze.
`present to that dissolved had been reduced to 211,
`In other experiments with preheated water it
`it required 20 minutes to complete a dissolving
`was found that, when silicate glasses of high
`cycle. This forms a convenient way to conduct
`purity are employed and agitation is avoided,
`my process, that is, to repeatedly treat the same
`water white, stable silicate solutions can be ob—
`glass batch, until the time required for the liq-
`tained directly from the dissolver without any
`uid to reach the desired concentration indicates
`clarifying treatment and with a dissolving period
`that recharging is necessary. The formation of
`of only 5 to 10 minutes.
`It was also found that
`“stickers” can be prevented by maintaining steam
`silicate solutions prepared by this method are
`pressure on the dissolver between cycles. When
`substantially more stable than those prepared by
`the quantity of silica glass in the dissolver has
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`2,251,515
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`been substantially lowered, as at the end of the
`third cycle, for example, the pressure can be
`reduced for the introduction of a new charge of
`glass.
`If a small sticker should form in this
`operation, it is quickly dissolved by the preheated
`water used in the next cycle.
`It has been found
`that stickers dissolve much more quickly in my
`process than in those in which the water is
`heated in contact with the glass. These results
`indicate that it is of considerable advantage to
`employ an excess of the silicate glass in the new
`process, although, even without the use of such
`an excess,
`in comparison with prior methods,
`the new method is capable of producing a quality
`of silicate solution heretofore unattainable and
`in a shorter timeeperiocl. Of course, the dissolv—
`ing rate depends upon the temperature employed
`as well as upon the fineness of the-subdivision
`of the silicate glass.
`In order to compare the clarity of the silicate
`solutions obtained by my method with those ob-
`tained in ordinary commercial practice,
`three
`different runs in a commercial dissolver were
`made by my method using three different com—
`mercial
`silicate glasses
`containing different
`amounts of impurities and having slightly differ-
`ent characteristics. The glasses had a ratio of
`NazO to Si02 of 1 to 3.2 and the silicate solu—
`tions obtained had gravities of 41” Be. When
`tested for clarity the three solutions obtained
`were found to test 30.2 cm., 28 cm. and 26 cm.,
`respectively, these figures representing the depth
`of solution through which an operator could ob-
`serve a black line on a white background, the
`bottom of the testing tube being held 5 inches
`above the line. When these solutions were al—
`IOWed to stand in a tank having a diameter of 6
`' feet and a height of 10 feet for 24 hours, each
`measured over 36 cm., being water clear.
`In
`comparison with these results it was found that
`a solution, prepared in the same dissolver by the
`usual commercial method employing agitation
`and a high-quality silicate glass having the same"
`silica ratio and the same gravity, had an initial
`clarity of only 1 cm. This solution, after stand-
`ing a week in a tank of the same dimensions
`as that employed previously, had a clarity of 1.5
`cm. Even after standing for three months the
`clarity of this solution was found to be only 3.9
`cm. These results are representative of solu-
`tions produced by present commercial practice.
`Silicate solutions prepared by present practice,
`including a special clarification by filtering or
`“breaking,” normally have clarities of about 25
`cm. by the same test.
`It is therefore evident
`that my process produces directly solutions hav-
`ing an initial clarity which is slightly greater
`than that obtained by present methods employ-
`ing special clarification procedures and that this
`clarity becomes substantially improved by the
`simple procedure of permitting the solutions to
`settle for 24 hours.
`In a further commercial test on my method,
`using a silicate glass, having a silica ratio of
`1Na20:2.5GSi02 and containing a large quantity
`of impurities, a solution having a gravity of 50°
`Bé. was prepared. The initial clarity of this so—
`lution was found to be 12 cm. but upon standing
`48 hours,
`the clarity was found to be over 36
`cm.
`It is, of course, well recognized that a sili-
`cate solution of this high gravity, prepared by
`usual commercial methods, cannot be clarified
`either by filtering or “breaking” without dilu-
`tion. The present method therefore enables a
`water clear solution of this type to be prepared
`
`by the use of a ,short settling step of only 48
`hours duration as the only clarifying procedure—
`a result which is impossible by prior art commer—
`cial methods.
`It is evident from the above discussion that
`the mechanism of the dissolving process, which
`takes place upon the dissolution of silicate glasses,
`is but little understood. This process undoubt—
`edly involves such phenomena as hydration,
`swelling, gel formation, hydrolysis, flocculation
`and peptization. Our knowledge of these phe-
`nomena individually leaves much to be desired.
`But in those cases where all or at least more than
`one are involved simultaneously our knowledge
`is, to say the least, highly empirical.
`The cause for the various unexpected results
`obtained in my new process is not evident. There
`are several possible explanations. The use of
`preheated water in the present process insures
`that the temperature inside the dissolver shall be
`substantially uniform, corresponding throughout
`to the temperature of the steam above the body
`of water.
`In the prior methods, wherein the '
`water is heated in the dissolver while in con—
`tact with the silicate, it appears at least possi—
`ble that pockets are formed in the broken sili-
`cate glass which never reach the desired tem-
`perature even though the pressure above the Wa—
`ter eventually reaches that of the steam line.
`Non-uniformity of temperature would imply non-
`uniformity of concentration. This may account
`for the increased rate of solution in the present
`process.
`The cause, for the elimination of turbidity in
`the silicate solutions, obtained by the present
`process is not evident.
`It appears that one cause
`for the turbidity in silicate solutions produced
`by prior methods is the circulation of dilute
`solutions of silicate in contact with the silicate
`glass.
`ese dilute solutions may leach out the
`alkali
`from the silicate glass
`leaving more
`siliceous portions which, when agitation is em-
`ployed, may become dispersed through the solu—
`tion as agglomerates of silica.
`It is evident that
`this condition is intensified in' the usual process
`wherein the water is heated in contact with the
`silicate glass under conditions of agitation. The
`rate of solution is Iowand a considerable time is
`required to bring the dissolver up to its maxi-
`mum temperature. But lack of circulation can—
`not be the only explanation of the improved
`results secured by the present invention, since
`even with the most careful
`temperature and
`pressure control and a jacketed vessel which will
`give a minimum circulation. large scale opera-
`tions consistently yield turbid solutions.
`The ‘Ibottoms Which are formed in present
`commercial silicate solutions are always highly
`siliceous. They usually analyze between ’70
`to
`eo'per cent SiOz with small amounts of NazO
`and a relatively high proportion of dalcium,
`magnesium and aluminum.
`It appears probable
`that precipitates of this nature may be caused
`by the formation of agglomerates of silica re-
`sulting from the selective leaching of alkali
`from the silicate glass or from hydrolysis of the
`solution. . In my process either or both of these
`factors may be suppressed by the rapid solution
`of the silicate.
`'
`It is also possible that the turbidity usually
`present in silicate solutions may be caused by
`the precipitation of complex silicates which may
`ta‘ke place at intermediate temperatures and
`concentrations. The preheating of
`the water
`may cause the solution in the dissolver to pass
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`on
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`2,251,515
`apidly through the concentration range in
`which such a precipitation may take place. And
`it is obvious that in my process the tempera-
`tures throughout the dissolving cycvle are main-
`tained at a, maximum value.
`But whatever the explanation for the advan—
`tageous results obtained by the present process,
`the facts remain as stated. These favorable re-
`sults are obtained only when preheated water is
`employed in combination with a quiescent con—
`dition in the dissolving zone during the dissolv-
`ing cycle. This implies the absence of boiling
`in the pressure vessel which can be accomplished,
`of course, by a pressure of steam or air above
`the liquid.
`If preheated Water
`is agitated
`throughout the cycle, turbidity results While, if
`cold water is employed at the start of the cycle
`and no agitation is used, the resulting solution
`Will be found turbid and in addition the dissolv—
`ing cycle will be unduly prolonged.
`It is advantageous to avoid agitation as far as
`possible in my process even when the solution
`is being Withdrawn from the dissolver. This
`can be accomplished by maintaining a pressure
`of air or other inert gas or of steam, above the
`silicate solution while it is being withdrawn, in
`order to prevent the silicate solution from boil-
`ing when in contact with the glass.
`Ilf
`the
`solution is permitted to boil While being with—
`drawn,
`the resulting mechanical action causes
`the suspension of a fine sediment which, how-
`ever, quickly settles, being thus distinguished
`from the turbidity which is always present when
`cold water is heated in contact with silicate
`glass in regular commercial dissolvers.
`It has
`also been found that, if the solution boils dur-
`ing Withdrawal from the dissolver, this tends to
`make the residual glass in the dissolvcr stick
`together or to cake.
`In order to eliminate all boiling in the pres-
`sure vessel it is sometimes necessary, when heat—
`insulated vessels are employed, to provide ini—
`tially an interior pressure which is somewhat
`higher than the vapor pressure of
`the pre-
`heated water which is introduced. The cause ‘
`for this is the development of heat on solution,
`which depends upon the fineness of the silicate
`as well as its composition. This heat of solu-
`tion tends to heat the water, and thus raise the
`vapor pressure of the liquid, more rapidly than
`the boiling point of the liquid is raised due to
`the resultant increase in concentration. Boiling
`of the liquid will therefore result unless a slight
`excess pressure is maintained in the pressure
`vessel, that is, a pressure slightly above the Vapor '
`pressure of the pre—heated water. A convenient
`way of preventing this initial tendency to boil
`is
`to pass
`the preheated water
`from the
`heater to the dissolver before it has reached the
`temperature corresponding to the steam pres-
`sure employed in heating it. Then, if full steam
`pressure is maintained in the dissolver, this is
`sufficient
`to prevent boiling. The introduction
`of steam into the dissolver before the preheated
`water is introduced serves to preheat the silicate
`glass. This results in the substantial elimi-
`nation of convection currents which would be
`produced if the preheated Water should be con-
`tacted with a relatively cold silicate glass.
`It is evident from the above that my new
`process results in a number of unexpected re-
`sults, the more important of which are that the
`process substantially reduces the dissolving cycle
`required to produce a silicate solution of given
`concentration, the resulting solution is substan-
`
`tially less cloudy and more stable upon heat-
`ing, the solution can be substantially freed from
`any impurities of iron, titanium, etc., by simply a1-
`lowing it to settle for a short time, and the new
`method can be conducted with the use of theo-
`retical quantities of silicate glass without pro-
`longing the dissolving cycle beyond that em-
`ployed in prior processes. Needless to say these
`results are of great importance from the stand—
`point of the purity of the product as well as
`cost of production.
`In addition my process has several incidental
`advantages one of which is that the silicate glass
`does not require crushing to the same degree of
`fineness as that used in prior processes.
`It also
`is not necessary to use quenched or hydrated
`glass. Glass in blocks as large as 4" x 4” x 8"
`have been used successfully in my process.
`In
`fact the rate of solution is so rapid that the
`expense of crushing to a finer size is usually not
`warranted. Another incidental advantage of my
`process is that the water employed to dissolve
`the silicate can be heated at less expense in a
`separate vessel in which either direct or indirect
`heating can be employed. Since a dissolver
`cannot be fired directly without danger of scal-
`ing, it is evident that greater efficiency can be
`obtained by preheating the water in a separate
`vessel
`in which direct firing can be used.
`It
`will also be noted that my process can be con-
`ducted Without substantial consumption of steam.
`Owing to the very high rate of solution which
`is obtained in my process it is possible to con—
`duct
`this process continuously. This was not
`considered feasible prior to the present invention.
`owing to the long dissolving cycle and the as—
`sumption that some agitation Was desirable. The
`continuous process can be conducted either by
`passing preheated water through a series of pres—
`sure vessels containing silicate glass, the vessels
`being replaced by freshly charged vessels as the
`original vessels become exhausted, or by passing
`the preheated water through a rather deep bed
`of silicate glass contained in a single pressure
`Vessel, this bed of silicate being replenished at
`intervals by the introduction of fresh silicate
`glass, through a pressure lock, for example.
`In
`this continuous process it is important that the
`preheated water be passed through the silicate
`glass Very slowly in order to avoid agitation as
`far as possible. The water can be introduced
`either at the top or at the bottom of the pres—-
`sure vessel but it has been found best to introduce
`the preheated Water at the top of the dissolver,
`allowing the liquid to flow downwardly over the
`silicate glass to be drawn on at full concentra-
`tion at the bottom.
`The benefits of the present invention can be
`realized in part even though the water used to
`dissolve the silicate glass is preheated only slight—
`ly. Thus, it is possible to preheat the water to a
`temperature of about 100° C. or above, for ex—
`ample, and to conduct further heating within
`the pressure vessel. And it is possible to use rela—
`tively low temperatures of 100° C. or slightly
`above in my process producing dissolving cycles
`of from 60 to 90 minutes.
`I have found, how-
`ever, that the most practical operatinor range is
`from about 150—200“ C. This range is selected
`because a sufficiently high rate of solution is
`obtained to make the process very economical,
`that is, dissolving cycles of 7 to 10 minutes are
`obtained which are about as rapid as can be con—
`veniently handled by an operator. Above this
`range of temperature, pressures would be re-
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`quired which would involve special construction
`of pressure equipment and special piping. At
`lower temperatures the dissolving period increas—
`es.
`It is obvious, of course, that silicate glasses
`having various ratios of NazO to si02 can be
`used in my process. The larger the proportions
`of NazO in these glasses, the shorter the dis-
`solving period.
`My invention can be described in somewhat
`greater detail by reference to the accompanying
`drawing which shows, more or less diagrammati—
`cally, an assembly of apparatus elements with
`which my process can be conducted.
`In this
`showing the figure represents an elevational View
`with certain parts broken away to show details.
`The shell of the dissolver is shown at I, this
`shell being broken away to show the bed of sili-
`cate glass 2 supported a short distance from the
`bottom by means. of the screen 3. At the top
`of the bed of silicate glass a spreader fl is shown
`which serves to distribute the silicate glass as
`it is introduced through the pressure lock device
`shown generally at 5. This pressure lock is pro-
`vided with valves 6 and 'I at the bottom and
`the top, respectively, and also with a steam or
`air connection 8. A funnel 9 is employed for
`feeding the silicate glass to the pressure lock.
`This pressure lock is maintained full of silicate
`glass and, when additional glass is required in the
`dissolver,
`the lower valve is opened while the
`upper valve remains closed. Steam or air pres-
`sure may be applied to the interior of the look
`by opening the valve ID. The dissolver is pro‘
`vided with a steam or air connection at II, with
`preheated water connections I2 and I3, and with ’
`draw-offs for the silicate solution at I4 and I5.
`The water preheater I6, which may be steam
`heated and of the so-called “open” or “closed'
`type or which may be fired directly, is provided
`with water inlet I1 and steam inlet I8 while an »
`air outlet is provided at I9. The preheated water
`is withdrawn from the bottom of this preheater
`at 20 and may be passed through lines I2 or IE
`to the heater in accordance with the setting of
`If valve 2! is closed, while "
`the valves 2| and 22.
`valves 22, 23 and 24 are open, the preheated
`water passes in at the bottom of the dissolver
`and out through the outlet 15, whereas if the
`valves 22 and 24 are closed and if valves l4, 2|
`and 23 are open, the preheated water enters the
`top and leaves at the bottom, of the dissolver.
`The operation of the dissolver shown in the
`figure is believed to be obvious from the preceding
`description.
`In the batch process it
`is only
`necessary to fill the dissolver with silicate glass
`and then to introduce the preheated water
`through one of the connections I2 and I3 while
`the dissolver is maintained under a pressure or
`air or steam at least suflicient to correspond to
`the temperature of the preheated water and suf-
`ficient to prevent boiling of the water as it en—
`ters the dissolver. The water can be introduced
`either under pressure or by gravity. The water
`should flow into the dissolver slowly in order that
`there may be a minimum of agitation. As soon
`as commercial gravities are reached by the solu—
`tion, it can be withdrawn through the draw-off
`14, full steam pressures being advantageously
`maintained over the solution as it is being with-
`drawn in order to prevent boiling.
`When a continuous process is employed, the
`preheated water may be introduced at the bottom
`through the connection I3 and withdrawn at I5
`but it is somewhat more advantageous to in—
`troduce the preheated water at the top through
`
`2,251,515
`the connection I2, the solution being removed
`from the bottom of the dissolver through the
`outlet I4 as rapidly as commercial gravities are
`secured, the dissolver being maintained substan—
`tiallyrfull of liquid. Additional silicate glass can
`be introduced at intervals in order to maintain
`the dissolver substantially full of glass.
`In the
`absence of a pressure lock, a semi-continuous
`process may be employed, the equipment being
`shut down while fresh silicate glass is introduced
`to replace that dissolved.
`In a specific embodiment of the present process,
`I made use of a diSSUlVel‘ having a diameter of
`40 inches and a height of 6 feet. This was sub-
`stantially filled with a commercial silicate glass
`having a ratio of 8102 to Na20 of about 3.2.
`Steam under a pressure of 100 pounds per square
`inch was introduced into the dissolver and then
`the dissolver was filled with water preheated to
`a corresponding temperature (170° C.) , this water
`being slowly passed in at the bottom. The solu—
`tion was tested at rather frequent intervals and
`it was found that a gravity of 41° Bé. was secured
`in about '7 minutes. At this point the solution
`was withdrawn from the dissolver while full
`steam pressure was maintained in order to pre-
`vent the solution from boiling during withdrawal.
`The resulting solution was found to be substan-
`tially clear but close examination revealed the
`presence of a small amount of dense, dark-colored
`matter in suspension which settled rapidly yield-
`ing a crystal clear solution. This solution was
`decanted from the precipitate and, after standing
`for several days, it was still found to be entirely
`free from any precipitate.
`While I have described what I consider to be
`the best embodiments of my process, it is evident
`that many modifications can be made in the spe-
`cific procedures disclosed without departing from
`the purview of my invention.
`In its broad scope
`my invention comprises the production of a sili-
`cate solution by contacting a silicate glaSS with
`water which has been pre