CA1302073C - Deicing compositions comprising calcium magnesium acetate double saltand processes for their production - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Compositions which comprise a calcium magnesium ace-tate double salt are useful in deicing compositions. Deicing compositions comprising those compositions and processes for their preparation are described.

Description

~3~2~3 DEICING COMPOSITIONS COMPRISING
CALCIUM MAGNESIUM ACETATE DOUBLE SALT
A~D PROCESSES FOR THEIR PRODUCTIO~

BACK&ROUND OF THE INVENTIO~
Removal and/or melting of snow and ice on roadways, bridges, sidewalks and the like is a major task in many areas.
Various chemicals have been used to assist in the removal and/or melting of snow and ice. Conventional road salt, has been used extensively in part due to its melting ability and also its relatively low cost. However, it has been found that the low cost of salt has been offset in part by the damage to roadways, bridges, underground cables ~such as tele-phone or electrical cables) and the like, not to mention auto-mobiles, caused by its use. Salt's corrosivity has led to dama~e to pavement and to the steel structure of bridges and surrounding structures. Moreover, the accumulation in run-o~f water has caused problems with vegetation. Accumulation in ground water has caused health problems with drinking water due to increased sodium contents. Other salts, such as calcium chloride, have been used; however, calcium chloride too has similar problems and causes accumulation of chloride ion in the environment, which is undesirable.
Accordingly, there has been extensive study on alter-native deicing chemicals which are noncorrosive, environmental-ly acceptable and which are economically practical.
The Federal Highway Administration sponsored an ex-tensive study by the Bjorksten Research Laboratory (BRL) on deicing chemicals. The study's report "Alternative Highway Deicing Chemicals" published March, 1980, identified calcium magnesium acetate (CMA) as a leading candidate for replacing road salt. Since the publication of the BRL report, various groups and individuals have been working on the preparation and testing of deicing agents comprising calcium magnesium acetate, calcium acetate and/or magnesium acetate. (See, e.g., U.S.
Patent ~os.

¢~:

gL3021D73 4,426,308, 4,444,672, 4,511,485 and 4,606,836.) However, preparlng CMA economically on a commercial scale has been a problem. See, e.g., Gancy, Alan B., "Preparat:Lon of Hlgh Quallty Calcium Magneslum Acetate Using a Pilot Plant Process", Federal Hlghway Admlnistratlon (January, 1986). Drled large lumps of CMA ln the product has been a problem, as has unacceptable levels of fugitlve dust from product. See, e.g., "Continuous Productlon Calcium Magneslum Acetate/Sand Deicer"
prepared by Cedarapids Inc. for Iowa Highway Research Board, ~une 3, 1985.
Prevlous processes have exhlblted problems wlth dus~ing of powdered lime and unacceptable levels of acid odor and vapor ln recycled materlal, bed material and e~en product.
Prevlous calcium magnesium acetate-coated sand deicing agents have used a wettlng agent, such as a cement-grinding aid, as a binder. See Unlted States Patent No.
4,588,512 to Rlpple.
United States Patent No. 4,699,725 to Gancy dlscloses magneslum calclum acetate compositlons and processes for their manufacture.
SUMMARY OF THE INVENTION
The present invention is directed to composltlons comprlslng a calclum magne~lum acetate double salt w~lch are useful as delcing compositlons and to processes for preparing sald deic1ng composltlons. In partlcular, the lnvention provldes a compositlon comprlsing less than about 8 percent by welght crystalllne calclum acetate, less than about 8 p~rcent by weight magnesium acetate, about 1 percent to about 3 percent by welght unreacted base, less than about 5 percent by welght water and the remainder being calcium magnesium acetate double salt .

2ia73 The deicing compositions of the present invention comprise substantially pure CMA double salt which is substan-tially free from crystalline calcium acetate, magnesium acetate and unreacted magnesium hase.
In one embodiment, these compositions comprise CMA
double salt which is substantially anhydrous. By "substantial-ly anhydrous" is meant comprising less than about 5 percent water [or less than about 0.45 mole water per each mole of calcium or magnesium; e.g., if a CMA double salt had the approximate empirical formula of CaMg25C2H302)6, then the double salt would have less than 1.35 mole water per mole CMA
double salt]. Preferred are compositions comprising less than about 2.5 percent by weight water (compositions with the above-noted empirical formula would have 0.65 mole water per mole or about 0.21 mole water per mole calcium or magnesium). Our Eindings are in contrast to teachings that desirably CMA compo-sitions have 3 to 4 moles water per mole magnesium (thus, a CMA
composition having a calcium:magnesium ratio oE 1:2 would have about 6 to 8 moles water or about 20 to 25 percent by weight water). See U.S. Patent ~o. 4,694,725 to GancyO
It is believed that the CMA double salts of the present invention have the approximate empirical formula:
CaxMgy(c2~3o2)2(x+y) where x = 3 to 4 and y = 7 to 6. Accordingly, the calcium:magnesium ratios may range from about 4:6 to about 3:7, preferably from about 3:6 to about 3:7.
The compositions of the present invention comprise substantially pure CMA double salt which is substantially free of crystalline CA and crystalline MA as evidenced by ~-ray diffraction. These compositions are also substantially free of amorphous (as well as crystalline) MA and free of unreacted magnesium base as determined by thermogravametric analysis-gas chromatography-mass selective detector ("TGA-GC-MSD"). ~That technique takes evolved gases through thermogravametric analy-sis and subjects them to gas chromatography using a mass ~3~ 73 selective detector set at 20-200 atomic mass units. See Examples 14 and 15 for further description).
A comparison of the X-ray diffraction patterns of the compositions of the presen-t invention (see FIGS. 7C, 7D and 7G) to CA, MA, and other CMA compositions (see FIGS. 7A, 7B, 7G, and 7F) and the TGA-GC-MSD spectra of the present invention (see FIGS. 6A, FIGS. 8A to 8D, and FIGS. 9A to 9D) with those from CA~ MA~ a physical mixture of CA and MA and other CMA
compositions ~see FIGS. 5A to 5C/ 6B, 6C, FIGS. 10A to 10D, FIGS. llA to llD, and FIGS. 12A to 12D) show tha-t the CMA
double salts of -the present invention are distinctly different from those other compositions.
The CMA double salt described herein has different properties than either calcium acetate or magnesium acetate or a physical mixture of the -two. For instance this CMA double salt differs in solubility in water from ei-ther calcium acekate and/or magnesium acetate. Laboratory studies indicate that this CMA double salt is much less soluble in water than either CA or MAo Furthermore, this CMA double salt appears to have a characteristic crystalline structure as evidenced by analytical techniques such as X-ray crystallography (see procedure described in Example 16 and FIGS. 7C, 7D, and 7F) and TGA-GC-MSD analysis (see procedure described in Examples 15 and FIG. 6A and FIGS. 8A to 8D and FIGS. 9A to 9D)~
Moreover, these deicing compositions show improved ice melting behavior over what would be expected by a mixture of calcium acetate and magnesium acetate on a molar basis.
This is surprising in view of the aforenoted poor solubility in water of CMA double salt.
According to a preferred embodiment of the present invention CMA double salt compositions are provided which comprise substantially isodimensional pellets which have bulk densities of at least 40 pounds per cubic foot particle specific gravities greater than 1.2, and attrition of less than about 3 percent ~as measured by ASTM D 4058-81)~ Other ~i ~302al73 - 5 -- 61936-184g superior handling characteristics of these compositions include having a Eairly even size distribution, and being low in dust and low in acetic acid odor. Thus, the deicing compositions of the present inve~tion m3y be d~stri~ute~ using conventiona~
machinery for distributing deicing chemical such as roaa salt.
Moreover, due to this relatively high bulk density, these de-icing compositions are not prone to blowing away once applied to snow or ice, unlike previously used compositions co~prising CMA. (See "High Sierra Is Site For Caltrans CM~ Tests," Roads lQ & Bridges, June 1987, pp. 48-49.) In one embodiment these deicing compositions comprise a plurality of layers of a CMA composition of the present in-vention on discrete substrate particles. Such substrate parti-cles may optionally comprise a traction aid and/or CMA parti-cles.
The present invention also provides processes for preparing a calcium magnesium acetate double salt which is substan-tially free Erom crystalline calcium acetate, magnesium acetate and unreacted magnesium base which comprise (a) prepar-ing an aqueous mixture of calcium and magnesium base ("CMbase") having a calcium:magnesium ratio of from about 4:6 to about 3:7, preferably from about 3:6 to about 3:7 which com-prises about 40 percent by weight water; (b) simultaneously mixing at once the mixture of step (a) with from about 70 per-cent to about 110 percent of the stoichiome-tric amount of acetic acid, the resulting mixture having at least about 50 percent by weight water to give a CMA slurry; and aging the slurry of step (c) to allow substantially complete reaction of the calcium and magnesium bases with acetic acid; and drying pelletizing slurry of step (c). By "stoichiometric amount" is meant the number of moles of acetic acid (or acetate) needed to react completely with calcium or magnesium ion, or two moles acetic acid (acetate) for each mole of calcium and magnesium ion.
In a preferred embodiment of the process of the ~3~73 present invention, in step (b) about 70 percent to about 95 percent, more preferably about 90 percent, of the stoichio-metric amount of acetic acid is added at once, after mixing the pH is measured (diluting the CMA slurry 1 part slurry to 2 parts water before measuring the pH) and if above about 8 to 8.5, is adjusted to about 7 to about 8.5, preferably about 7.5 to about ~3 by the addition of additional acetic acid. Option-ally, if too low a pH is obtained (about 6-1/2) it may be increased to the more preferred range by adding re-slurried CMA
dust (from dust collection means, see page 19) in water.
In a preferred embodiment of the process of the present invention, a continuous process is employedO In such a continuous process, the slurry is aged by allowing it to flow tnrough a reactor train that has sufficient residence time to allow for comple-te reaction of the CM base with acetic acidO
Suitable residence times are in the range of about 3-1/2 or hours. Longer residence times may be used if desired.
We have discloséd that hot slurries have advantageous handling properties. Since the reaction between the CM base and acetic acid is exothermic, slurry temperatures in the range of about 130F to 150F or greater may be obtained due to the heat of reaction alone. However, if the temperature of the slurry begins to fall below that range, it is advantageous to heat the slurry to at least 130F to 150F, preferably to about 170F to about 200F. Temperatures above 200F may be used if desired.
In the processes of the present invention we have found that by mixing at once the CM base and acetic acid in essentially stoichiometric amounts in a reasonably dilute aqueous medium and then aging the resulting slurry, substan-tially complete reaction is obtained and a CMA double salt composition is obtained that is substantially free from unreac-ted magnesium base and is substantially anhydrous and also, according to data obtained by X-ray diffraction and TGA-GC-MSD, is substantially free from either calcium acetate and magnesium ~3~2~73 - 7 - 61936-1~48 acetate per se. This resul-t is surprising in that processes disclosed by others produce products having substantial amounts of unreacted magnesium base and/or substantial amounts of cal-cium acetate and/or magnesium acetate as determined by the above-noted analytical methods. (See FIGS. 6B, 6C, lOA to lOD, llA to llD, and 12A to 12D.) As noted above, the CMA double salt prepared accord-ing to the processes of a preferred embodiment of the present invention is substantially anhydrous, having on the order of less than about 5 weight percent, preferably less than about 2.5 weight percent water (or less than about 0.45 mole, prefer-ably less than about 0.21 mole, water per each mole calcium and magnesium). This is in contrast to teachings that CMA composi tions desirably have 3 to 4 moles water per mole magnesium, and thus, at least about 6 to 8 moles water. See, e.g., U.S.
Patent No. 4,699,725 to Gancy.
Preferred are CMA slurries having a slightly alkaline pH. More preferred are slurries having a pH of about 7 to 8.5.
Especially preferred are slurries having a pH of about 7.5 to about 8. Such slurries yield deicing compositions having an advantageous alkaline pH's which decrease damage to pavement surfaces. Also such slurries decrease the production of over-size particles in the distributing and drying steps and also advantageously decrease acetic acid emissions which must be controlled for environmental reasons.
In one embodiment o~ the process of the present in-vention the drying and pelletizing s-tep comprises disbributing the CMA slurry in a thin layer on discrete substrate particles and drying the substrate particles. The substrate particles may comprise either an inert support, such as for example a traction aid, fertilizer (such as urea, ammonium phosphate, phosphate rock or the like) or other aggregate; or preformed AEC particles. The distributing and drying steps may be re-peated to give a plurality of thin layers of AEC until the deicing agent particles reach the desired particle size. To be ~302(~73 fluid and pumpable, said slurry generally contains about at least 50~ by weight water. Preferred are slurries containing from about 55% to about 6~ water. Preferably, the slurry of step (b) is heated to a temperature of about 100F to about 250F; more preferably, to a temperature of about 170~F to about 200F. Slurries having lower moistures may need to be heated to higher temperatures in order to be Eluid and pump-able. The distributing and drying steps may be performed at substantially the same time.
Various materials may be used as the substrate upon which the CMA slurry is distributed. Preferred substrates include traction aids and preformed CMA particles.
Accordingly, the above processes provide particulate CMA double salt deicing compositions of sufficiently high den-sity that they penetrate ice rapidly and have a uniformity in size, substantially isodimensional shape, and pellet hardness such that a maximum of deicing effectiveness is obtained with a minimum of dust problems during handling and application.
The deicing compositions prepared according to the above processes are substantially isodimensional and may have particle sizes in a wide or narrow size range with an average si7e that is large or small as desired.
For example, deicing compositions may be prepared having a size range as small as 48 Tyler mesh (about 0.295 mm diameter) to about 0.371(5) inches (about 9.5 mm diameter). In one embodiment the size is in the -5 to +28 mesh size range.
Such particle sizes are preferred due, in part, to their ease of use with conventional machinery for the distribution of deicing compositions.
Product size may be controlled by selecting an appro-priate mesh si~e product screen. For example, a 7-mesh product (fines) screen may be used to meet a specification of 90~ +8 mesh; a 7-1/2-mesh screen may be used to meet a specification of 90% minimum +9 mesh.

~3~ 3 Definitions As used herein, the following terms have the Eollow-ing meanings, unless expressly stated to the contrary.
The term "slurry" indicates a solution of a soluble substance possibly above the saturation point for the soluble substance, whether or not the solution contains non-soluble suspended material. (See, e.g., U.S. Patent ~o. 3,333,297).
For example, an AEC slurry may comprise an AEC solution or a solution comprising both dissolved, undissolved AEC, and unre-acted raw materials.
The term "alkaline earth" refers to elements in GroupIIa of the Periodic Table, and includes, for example, beryl-lium, calcium, magnesium, strontium, barium, radium, and the like.
The term "alkali metal" refers to metallic elements in Group Ia of the Periodic Table and includes, for example, lithium, sodium, potassium, rubidium, cesium, francium, and the like.
The term "AE base" refers to alkaline earth or alkali metal bases or mixtures thereof which are capable of reacting with a carboxylic acid to form a carboxylate salt. Typical AE
bases include oxides, hydroxides, carbonates and the like of the alkaline earth and alkali metal elements. Such AE bases may contain one or more of the individual alkaline earth or alkali metal elements in various combinations and molar ratios.
The term "calcium and magnesium base" or "CM base"
refers to AE bases wherein said alkaline earth or alkali metal portion comprises calcium, magnesium or mixtures thereof.
The term "magnesium base" refers to AE bases where said alkaline earth or alkali metal portion comprises magne-sium.
The term "AEC" refers to alkaline earth or alkali metal carboxylates or mixtures thereof where the carboxylate group has from 1 to 4 carbon atoms. The term AEC includes Xi ~L3~ 73 single sal-ts sueh as calcium acetate, magnesium acetate, and potassium ace~ate as wel~ as mixed salts such as calcium magne-sium ace-tate as well as physical mixtures or produc-ts of co-crystallization of single and/or mixed salts.
The term "CA" or "calcium acetate" refers -to both anhydrous calcium acetate and its hydrates.
The term "MA" or "magnesium acetate" refers to bo-th anhydrous magnesium acetate and its hydrates.
The term "calcium magnesium acetate" or "CMA" refers to calcium magnesium acetate compositions having the empirical formula CawMgz(Acetate)2(w+z), where w is moles calci-um and z is moles magnesium and thus refers to calcium magnesium acetate compositions which may have essentially any molar ratio of calcium to magnesium.
The term "ealeium magnesium ~eetate double salt" or "CMA double salt" refers to a salt of ealeium ma~nesium aeetate wherein both ealeium and maynesium are coerystallized together and do not comprise a physical mixture of calcium acetate and magnesium acetate, said salt having an empirical formula con-sistent with that noted above for CMA. It is believed that theCMA double salt has the following approximate empirical formu-la:
CaxMgy(Acetate)2(x+y), where x = 3 to 4 and y = 7 to ~
The terms "caleium magnesium ratio" or "caleium to magnesium ratio" refer to the ratios of moles ealcium to moles magnesium.
Unless stated otherwise, all percents refer to per-cent by weight.
The term "traetion aid" refers to materials whieh help improve traction when applied to a slippery surfaee.
Thus, the term includes inert supports which have good antislip properties and includes materials such as sand, crushed lime-stone, pulverized corncobs, nutshells (such as walnut shells, peean shells, almond shells or the like), expanded shale, vermieulite, pumiee, cinders, other substantially insoluble ~r ~30;~73 minerals with good antislip properties, or the like.
The term "mesh" re~ers to mesh sizes determined according to the Tyler standard sieve series.
The -term "slurry pH" refers to the pH of the CMA
slurry as measured by diluting one part slurry to two parts water.
BRIEF DESCRIPTION OF THE DRAWI~GS
.
FIG. 1 is a schematic drawing showing the steps of one embodiment of the present invention.
FIG. 2 is an elevational view of semi-diagrammatic character which shows a combined distributor-dryer apparatus used in one embodiment of the process of the present inven-tion.
FIG. 3 is a longitudinal section through the drum element of FIG. 2 and its end appurtenanees.
FIG. 4 is a transverse sectional view of the drum element of FIG. 2.
FIG. 5A is a chart showing the TGA-GC-MSD speetrum for crystalline calcium acetate hemihydrate.
FIG. 5B is a chart showing the TGA-GC-MSD spectrum for crystalline magnesium acetate tetrahydrate.
FIG. 5C is a chart showing the TGA-GC-MSD spectrum for a physical mixture of crystalline calcium aeetate and crystalline magnesium acetate tetrahydrate having a 1:1 weight ratio.
FIG. 6A is a chart showing the TGA-GC-MSD speetrum for a CMA double salt sample of the present invention having sample ~o. ~8105-02-6.
FIG. 6B is a chart showing the TGA-GC-MSD spectrum for a CMA sample prepared according to U.S. Patent No.
4,606,836, having a 1:1 ealcium:magnesium ratio and sample No.
B8105-40-3.
FIG. 6C is a chart showing the TGA-GC-MSD spectrum for a CMA sample prepared according to U.S. Patent No.
4,606,836, having a 3:7 ealeium:magnesium ra-tio and sample No.
B8105-40-5.

.

2~'73 FIG. 7~ is a chart s~owing the X-ray diffraction pattern for crystalline calcium acetate hemihydrate.
FIG. 7B is a chart showing the X-ray diffraction pattern for crystalline magnesium acetate tetrahydrate.
FIG. 7C is a chart showing the X-ray diffraction pa-ttern for a CMA double salt sample of the present inven~ion, having sample No. B8105-02-5.
FIGo 7D is a chart showing the X-ray diffraction pattern Eor a CMA double salt sample of the present invention 10 having sample No. B8105-02-6.
FIG. 7E is a chart showing the X-ray diffraction pattern for CMA sample having a calcium:magnesium ratio o-E 1:1 and having sample No. B8105-02-4.
FIG. 7F is a chart showing the X-ray diffraction pattern -for CMA sample having a calcium:magnesium ratio of 3.3:6.7, prepared at low temperature and having sa~lple No.
B5669-23-2.
FIG. 7G is a chart showing the X-ray diffraction pattern for a CMA double salt sample of the present invention having without the superimposed crystalline CA peak points.
FIGS. 8A to 8D are charts showing TGA-GC-MSD spectra for a CMA double salt sample of the present invention prepared according to the process described in Example 10.
FIGS. 9A to 9D are charts showing TGA-GC-MSD spectra for a CMA double salt sample of the present invention prepared according to the process described in Example lOA.
FIGS. lOA to lOD are charts showing TGA-GC-MSD
spectra for a commercial CMA sample from Verdugt.
FIGS. llA to llD are char-ts showing TGA-GC-MSD
spectra for a CMA sample having a calcium:magnesium ratio of 2:8 prepared according to U~S. Patent No. 4,699,725.
FIGS. 12A to 12D are charts showing TGA-GC-MSD
spectra for a CMA sample having a calcium:magnesium ratio of 1:2 prepared according to U.S. Patent No. 4,699,725.

~1 ~31t)~ 1)73 DETAILED DESCRIPTION OF THE INV~NTION
The CMA double salt compositions produced according to the present invention are produced according to our process which comprises preparing a fluid, pumpable C~A slurry and then drying and pelletizing the CMA slurry, Preferably the CMA
slurry is dried and pelletized by distribu-ting CMA slurry hav-ing a temperature of at least about 130F to about 150F, pre-ferably from about 170F -to 200F, in a thin layer onto dis-crete substrate particles (which may optionally comprise CMA or a traction aid) and drying the substrate particles to give a particulate (or pelletized) deicing composition.
Production of CMA Slurry Typically, the CMA slurry is prepared by mixing CM
base, acetic acid and water, preferably in an agitated vessel.
Preferably CM base and water are first mixed, to give a Elow-able aqueous C~ base mixture, typlcally comprising at least about 40 percent by weight water; then acetic acid is added.
The CM base is reacted with a sufficient stoichiometric amount of acetic acid to give a CMA slurry having a pH which provides complete reaction of CM base and minimal acid vapor loss and also results in a CMA composition with low corrosivity. Pre-ferably, the ratio of acetic acid to CM base is carefully adjusted to give substantially complete reaction of CM base and to minimize volatilization of unreacted acid during the subse-quent distributing and drying steps. Accordingly, preferably su~ficient acetic acid is added to react with the CM base to give a CMA slurry with a pH of about 7 to about 8.5, more pre-ferably from about 7.5 to 8.0 (when diluted 1 part slurry to 2 parts water) which is substantially free of acid odor. Option-ally, reslurried CMA dust collec-ted by dust collection means (during the distributing and drying step) may be added to the slurry. Such addition may increase the slurry pH above 8.5, without the undesirable increase in insolubles otherwise usual-ly seen at pH's above about 8.5. Such slurries result in a finished CMA product having a pH of about 9 to about 10 (when diluted 1 par-t product to 9 parts water).

~31~12~73 Slurries having low pH's (about 5 -to 6) may result in increased production of oversized product during the distribu-ting and drying steps and in unacceptably high acetic acid emissions from an environmental standpoint. Such slurries may result in products of unacceptable corrosivity and which cause discoloration and scaling of pavement surfaces when used for deicing.
Sufficient water is added, either alone or as part of the acetic acid solution, to give a fluid, pumpable slurry which does not solidify. Slurries having insufficient water may abruptly solidify, particularly if heated. We have found that if a slurry contains less than about 50% by weight water (on the order of about 30 moles water per mole CMA), excessive thickening of the slurry may occur at about 170F. As lower slurry moistures are employed, the resulting slurry must be heated to a higher temperature. Accordingly, preferred are slurries having at least about 50% water. Particularly prefer-red are CMA slurries having from about 55% to about 68% water.
Although CMA slurries having greater amounts of water may be used, such additional water later must be removed in the drying step and thus slurries having higher water contents may be less economical and disadvantageous due to increased drying costs.
Also, using lower slurry moistures may require heating the resulting slurry to a higher temperatura before the distribu-ting and drying steps.
Suitable CM bases include oxides, hydroxides, carbon-ates and the like of calcium, magnesium or mixtures thereof in various molar ratios.
Preferred CM bases include dolomitic lime, hydrated dolomitic lime, preferably Type S hydrated dolomitic lime and magnesium oxide.
Preferred CM bases are those which are low in those impurities, such as iron and aluminum, which form insoluble acetate salts.

~3C1~73 Suitable forms of acetic acid include both dilute acetic acid solutions (as low as about lO percent) and concen-trated acetic acid such as glacial acetic acid and acetic acid solutions having intermediate concentrations. The acetic acid used herein may be produced by chemical or by alternative methods such as fermentation oE cellulosic materials by micro-organisms and the like. Acetic acids produced by alternative me~hods such as ~icrobial fermentation may have cost advantages over more concentrated acetic acid produced by conventional methods used in the chemical industry which might outweight the economic disadvantages of possible increased drying costs due to their diluteness and thus the need to evaporate more water to obtain a dry product.
Preferred acetic acids include glacial acetic acid.
The CMA slurry is aged to allow complete reaction of CM base with acetic acid. Even when using reactive CM bases which have relative short reaction times with acetic acid, it is preferred to age the slurry. This may be done by allowing it to flow through a reactor train of several vessels before reaching the drying and pelletizing step~ Reactor trains hav-ing residence times of about 3.5 to 4 hours provide more than sufficient time to allow complete reaction of CM base and acetic acid. Reactor trains having longer residence times, on the order of about 10 to about 13 hours, or more, may be used if desired.
Production of De ng Composition from CMA Slurry Preferably, a fluid, pumpable CMA slurry is heated to a temperature of about 100F to about 250F, preferably to at least about 150F, more preferably from about 170F to about 200F. We have surprisingly found that heating the CMA slurry to a relatively high temperature, preferably from about 170F
to about 200F improves efficiency in the subsequent distribu-ting step and thus yield. Moreover, we have found that in preparing CMA, maintaining a high slurry temperature results in production of a higher proportion of the CMA as CMA double ~3~2~73 - 16 - ~1936-1848 salt. In addition, when slurries are not hea-ted to a suffi-ciently high temperature, for example, less than about 100F, in the distributing s-tep much oE the slurry may go to dus-t rather than to forming a thin layer on substrate particles.
Such dust must be collected in a high efficiency dust collector such as a baghouse or wet scrubber and then is generally re-cycled, generally with additional water. Thus, the overall amount of water which must be removed in the drying step in-creases which increases manufacturing costs.
Moreover, we have discovered that another beneficial effect of operation with high slurry temperature was that the hardness of the CMA coating increased by 50~ for high slurry temperature operation compared to low slurry temperature opera-tion. This increase in the hardness of the CMA coating provid-ed a product that can better withstand degradation to form dust and fines during shipping and storage oE the product.
As noted previously, the CMA slurry must contain sufficient water so that it remains fluid and pumpable and does not solidify. Such slurries generally contain at least about 50% water. Particularly, preferred are slurries having about 55~ to about 68% water. Low slurry water content may also result in formation of higher dust and fines in the distribut-ing step. Higher than required slurry water contents may result in increased drying costs and reduced manufacturing efficiency.
In one embodiment the process of -the present inven-tion the CMA slurry is distributed onto discrete substrate particles to give a thin layer of CMA on substrate particles.
Atomizing air of from about 0 to 100 psig, preferably from about 0 to about 20 psig, may be used. We have surprisingly found that not using additional atomizing air in distributing the slurry on the substrate particles results in increased production and also decreased the amount of the slurry that went to dust and fines. Preferably, said thin layer of CMA
substantially surrounds said substrate particles and forms a ~.~

gL3i[ 12 [)73 - 17 - 61936-184~
substantially continuous layer. The layered substrate parti-cles are then dried. The layered substrate particles may be recycled through the distributing and drying steps adding addi-tional thin layers of CMA with each distribu~ting and drying cycle to give a plurality of CMA layers on said substrate particles until the desired particle size for the deicing composition is obtained.
Suitable substrate particles may be inert supports such as, for example, traction aids, fertilizer (such as urea, ammonium phosphate, phosphate rock or the like), or other aggregates, or preformed CMA particles. Particularly preferred substrate particles include sand, especially sand of -10 to +20 mesh size, and preformed CMA particles. Preformed CMA parti-cles may be obtained by crushing deicer compositions having layers of C~A on substrate such as that prepared by the present process and separating CMA material from inert support (if any). Preformed CMA particles may be provided by recycling a set portion of product of desired size to obtain oversized particles which are then crushed to provide a supply of pre-formed CMA particles.
The distributing and drying steps optionally may becarried out simultaneously, such as by distributing a thin layer of CMA slurry on substrate particles in the presence of a heated gas or said distributing and drying steps may be per-formed separately in sequence.
In one preferred embodiment the distributing and drying steps are performed substantially simultaneously. In this embodiment, the slurry is distributed onto a dense falling curtain of substrate particles in the presence of a heated gas (such as air). The heated gas contacts the substrate particles at substantially the same time as the slurry is distributed in a thin layer on the substrate particles. Droplets of slurry are distributed on the substrate particles, and the water flashed off leaving a thin coating of dry CMA on substrate particles. The flowrate and temperature of the heated gas are ~3/02073 controlled such t'nat the water from -the thin layer of CMA
slurry on the substrate particles is flashed off. Optionally, undersized substrate particles are recycled through the combin-ed distributing and drying step to give additional layers of CMA as necessary to give the desired particle size for the substantially isodimensional product. Where preformed CMA
particles comprise the substrate, product size or oversize particles may be crushed to obtain a continuous supply of pre-formed C~A particles or undersized particles may be used with-out crushing.
The layered substrate particles may be screened toremove fines which may be recycled to receive additional layers of CMA; oversized material may be fed to a suitable crusher.
Since the present process may be used to prepare deicing agents having various ratios of individual alkaline earths and alkali metals, the type and amount of alkaline earth or alkali metal base is controlled to give the desired content of individual alkaline earths and alkali metals. Accordingly, the alkaline earth bases used herein are controlled to give deicing compositions comprising CMA double salt having a cal-cium to magnesium ratio of about 4:6 to about 3:7, preferably about 3:6 to about 3:7.
FIG. 1 illustrates one embodiment of the process of the present invention.
In FIG. 1, water is fed through line 10, which has a suitable means for the control of rate of flow into mix tank 12. Simultaneously, CM base ("AE Base No. 1") through line 14 and, if more than one CM base is used, CM base No. 2 ('tAE Base No. 2") through line 16 are fed into tank 12. If additional CM
bases are used, they may be fed into tank 12 through additional feed lines. The mixture overflows through line 18 into option-ally agitated reactor 22. Acetic acid ("carboxylic acid"~ is fed through line 20 into reactor 22 whereby it reacts with the CM base to give a CMA slurry. The CMA slurry over-flows through line 24 into surge tank 26. Dust recovered from dust collector ~02~73 - 19 - 61936-1~4~
~6 is fed into surge tank 26 with additional water, if indicat-ed. Heating means 28 heats the slurry in surge tank 26. Suit-able heating means 28 include a steam jacket, steam coil or other heating means. Heated CMA slurry is pumped from surge tank 26 through line 30 through atomizing nozzles 32 so posi-tioned in contactor 34 so that the sprayed slurry impinges on a dense curtain of substrate particles cascading from lifters 36 in contactor 34. Substrate particles enter contactor 34 through line 38 or CMA layered substrate through recycle line 40. The layered substrate particles are dried in dryer 42. A
stream of gas is drawn through line 44 into heating means 46 ~where it is heated by natural gas or other suitable heating means) and then the heated gas is drawn through line 48 into dryer 42. In one preeerred embodiment contactor and dryer means are combined so that substrate particles are dried immediately aEter coating (see FIGS. 2 to 4). In another embodiment contactor and dryer means are separate. Layered substrate exits dryer 42 -through line 50 and goes into sepera-tor means 52. Separator means 52 removes fines which are removed and returned through line 54-40 to contactor 34 for additional coating. Oversize material goes through line 56 into crusher 58 (suitable crushers include hammermill or roll crushers) and then is returned through line 60-40 to contactor 34. Product is withdrawn through line 62 and then sent to shipping or storage. (Where substrate particles comprise CMA
particles, optionally a set portion of product may be recycled to contactor 34 to obtain oversized material which is then crushed to generate CMA substrate particles.) Al-ternately, product may be cooled in a rotary drum cooler or fluid bed cooler or other suitable cooling means.
Substrate particles are continuously fed through line 38 (or recycle 40) into contactor 34. Adjustments are made in the quantity of material in contactor 34 and the internal configuration of contactor 34 to minimize the ~' ( ~3~Z~73 61g36-1794 return of discharge particles and to provide the most uni~orm level coating on each particle.
Air and dust are removed from dryer 42 through line 64. Dust is recovered in dust collector means 66. Suitable dust collector means 66 include, for example, a baghouse, wet scrubber or other conventional dust removing systems. Air is discharged to the atmosphere (outside) through line 68.
Recovered dust collected in dust collector means 66 is returned through line 70 to surge tank 26. (Alternatively, where dust collector means comprise a wet scrubber, a CMA dust and water mixture may be returned to mix tank 12 throuyh a conduit.) In the process for preparing the deiclng compositions of our invention, elther preformed or undersized CMA particles or inert support, including traction aids, may be used as substrate particles.
Figures 2 to 4 show a combined distributor-dryer apparatus suitable for use with a preferred embodiment of the present invention. That apparatus is more fully described in United States Patent ~o. 3,333,297 to Tytus et al.
In brief, the combtned distributor-drying apparatus shown in Figures 2 to 4 includes hollow elongated drum 102 which is mounted for rotation. Substrate enters drum 102 through conduit 104. Vanes 106 help feed substrate delivered by conduit 10~ toward vanes 108 whlch line drum 102. Vanes 108 are shown in cross section in Figure 4. CMA slurry is delivered through conduit 110 to spray nozzle 112. Atomizing air pressures of about 0 to about 100 psig, preferably from about 0 to about 20 psig, may be used. It ls especia1ly preferred that no additional atomizing air is used with the atomizing nozzle. We have found that not using additional atomizing air decreased the amount of slurry that went to dust ~0 B

1302~73 61936-179~
and fines. This is surprising, since it was thought tha~
atomizing air of about 20 to 80 psig air pressure on spray nozzles was required to keep coated substrate product from sticking to the lifters and to aid slurry in adhering to ~3021[173 substrate particles. A hot gas i5 supplied to the drum by conduit 113. As drum 102 rotates, vanes 108 act to shower substrate particles in curtains vertically and longitudinally of the drum said curtains moving across the drum. Slurry is sprayed through nozzle 112 on the plurality of traveling cur-tains of substrate particles distributing a thin layer on the particles which is dried by the hot drying gases passing through the drum. The spraying and drying action is repeated as the substrate particles traverse drum 102 to reach dam 114 at the exit end of drum 102. Manifold 116 receives bo-th hot gases and substrate particles. Substrate particles enter receiving means 118 from where they are sized~ and if indica-t-ed, recycled into drum 102.
In another embodiment of the process of the present invention, separate distributing and drying means are employed.
Suitable apparatus for separate distributing means include drum granulators, pan granulators, pug mills and other conventional granulating and pelletizing machinery. Suitable separate dry-ing means include rotary drum and fluid bed dryers as well as other conventional means for drying pelleted or granulated materials. Such apparatus are used with sufficient substrate particles to give a rolling bed of substrate particles upon which the slurry may be distributed. Such apparatus is adjust-ed to give a sufficient recycle ratio to provide build-up of layers on substrate particles to give the desired si~e pro-duct.
Continuous Preparation of CMA Double Salt In a preferred embodiment of the present invention, substantially pure CMA double salt which i5 substantially free from unreacted magnesium base and is substantially anhydrous is produced by a continuous process.
Water and calcium and magnesium bases (such as cal-cium oxide, magnesium oxide and dolomitic lime) are continuous-ly mixed to give an a~ueous CM base mixture. Sufficlent water is added to give a flowable mixture, at least about 40 percent by weight water.

13~Z073 The CM base mixture and from about 70 percent to about 110 percent of the stoichiometric amount of acetic acid are simultaneously added together to give a steady state of about 1.8 mole (90 percent of the stoichiometric amount) acetic acid per each mole of calcium and magnesium. If too little acid is added, or the acid is added at too slow a rate, side products may form and precipitate out ~for e~ample, calcium acetate as a white precipitate and magnesium acetate as an amorphous precipitate).
Additional acetic acid is added, as needed, to main-tain a slurry pH of about 7 to 8.5, preferably -Erom about 7.5 to 8. Slurry pH is monitored, after diluting the slurry, one part slurry to two parts water, the pH of the thusly diluted slurry is measured.
The slurry is then aged for period of -time sufficient to allow ionization of the ace-tic acid ~nd substantially com-plete reaction. This aging may be accomplished by the slurry flowing through a series of vessels so that the combined resi-dence times are sufficient for substantially complete reaction.
We have found that residence times on the order of about 3.5 to 4 hours are sufficient; longer residence times (on the order of about 10 to about 15 hours) may be used. The heat of reaction of CM base with acetic acid may give slurry temperatures above 150F and in the preferred range of about 170F and 200F, however, during the aging step it may be desirable to heat the slurry to maintain its temperature in the preferred range and maintain its fluidity.
After aging, the slurry is heated (if necessary) to a temperature of about at least 150F, preferably to about 170F
to about 200F. The slurry is then distributed on substrate particles and dried as described above.
Calcium Magnesium Acetate Double Salt The compositions of the present invention which comprise substantially pure crystalline CMA double salt having a calcium to magnesium ratio of about 1:2 exhibit certain ~~~ .

~311~073 proper-ties which are different from not only CA, MA, and physi-cal mixtures of CA and MA, but also from other CMA compositions which are made by other processes and are not substantially pure crystalline CMA double salt.
The substantially pure crystalline CMA double salt of the present invention is substantially free of crystalline CA
and crysta~line MA, as evidenced by X-ray di-ffraction. The X-ray diffraction technique is described in Example 16. The substantial absence of CA is evidenced by the subs-tantial absence of the most intense peaks of crystalline CA at about 5.2 and 7.4 two-theta. The substantial absence of crystal-line MA is evidenced by the substantial absence of the most intense peak of crystalline MA at about 12.5 to 13 two-theta.
Instead, the characteris-tic very strong double peak in the range of two-theta 8.7S to 10.5 are observed Eor the crystal-line double salt; these peak positions are centered at about 9.1 and 9.8 two-theta.
The amount of crystalline CA and MA impurities can be estimated from the X-ray diffraction patterns. To do so, the peak intensities for the CMA peaks located at about 9.1 and 9.8 are added together and compared to the peak intensities for the CA peaks located at about 5.2 and 7.4~ plus two times the peak intensity for MA centered at about 12.7 two-theta.
Substantially pure crystalline CMA double salt has the percent-age of -these impurity peaks relative to the sum of the two CMA
peaks equal to less than about 8~, preferably less than about 5%.
The substantially pure crystalline CMA double salt of the present invention is also substantially free of amorphous (and crystalline) MA and free of unreacted magnesium base, as determined by TGA-GC-MSD. This technique takes the evolved bases from thermogravimetric analysis (TGA) and subjects them to gas chromatography using a mass selective detector (TGA-GC-MSD) set at 15 to 200 atomic mass units.
When monitoring the TGA-GC-MSD at the mass for C02 ,~

13~20~73 and/or acetone as discussed in Examples 14 and 15, the substan-tial absence of MA is evidenced by the substantial absence of peaks at 29 to 35 minutes, i.e., about 290 to 350C~ At the same time, unreacted magnesium base, either Mg(OH)~ or magnesi-um oxide hydrate, gives a peak at about 300C, when present.
Amounts greater than about 1 weight percent of unreacted mag-nesium base, relative to CMA, can be detected by this tech-nique. Unreacted base is observed in some of the products produced by the direct reac-tion process disclosed by others, but not in the products produced using the slurry process of the present invention.
The amount of MA and magnesium base impurities can be calculated from the TGA-GC-MSD. To calculate the amount of MA
impurity, monitor the evolved acetone spectrum. The area under the peaks from about 29 to 35 minutes (about 290 to 350C), which correspond to the M~ impurity, is compared to the area under all the acetone peaks from 20 to ~5 minutes (200 to 450C). The MA acetone evolution as a percent of the total acetone evolution can thus be determined. The substantially pure crystalline CMA double salt has no more than 5 percent of this MA impurity, as calculated in this manner. To calculate the amount of magnesium base impurity, monitor the evolved water spectrum. The area under the peak coming off at about 300~C corresponds to the water from magnesium hydroxide or magnesium oxide impurities. Substantially pure crystalline CMA
double salt has this percentage of magnesium base impurity at less than about 3 weight percent of the CMA, preferably at less than about 1 percent.
As described above, the substantially pure CMA double salt of the instant invention is substantially free of all of the following: crystalline CA; crystalline and amorphous MA;
and unreacted magnesium base.
more specifically, this substantially pure CMA double salt mee-ts the following criteria:

~ .

~3~ai73 1. It is substantially free of crystalline CA and crystalline MA, as evidenced by its X-ray diffraction pattern, i.e., the sum of the impurity peaks for CA and MA relative to the sum of the two intense CMA peaks (as discussed above) is less than about 8~, preferably less than about 5%.
2. It is substantially free of amorphous (and crystalline) MA and free of unreacted magnesium base, as deter-mined by TGA-GC-MSD, i.e., the MA acetone evolution is less than 5 percent of the total acetone evolution; and the magnesi-um base impurity (as measured by water evolution at about300C) is less than about 3 weight percent, pre~erably less than 1 weight percent of the CMA sample.
The substantially pure CMA double salt compositions show a distinctive pattern when subjected to TGA-GC-MSD analy-sis (see FIG. 6A) as compared with crystalline CA, crystalline MA, and a physical mixture o~ crystalline CA and M~ (see FIGS.
5A, 5B and 5C respectively) or as compared with CMA composi-tions prepared by other processes ~see FIGS. 6B and 6C).
The TGA-GC-MSD analyses depicted in FIGS. 5A to 5C
and FIGS. 6A to 6C plot the relative ion abundance of acetone and carbon dioxide (the main decomposition products of acetate) over time at a constant heating rate of lOD/minute. The carbon dioxide abundance was scaled down by a factor o~ 3 in order to match the scale of acetone abundance to show the fine structure of the GC-MSD chromatogram. Further description of this proce-dure is found in Examples 14 and 15.
FIG. 5A depicts the TGA-GC-MSD analysis for crystal-line CA hemihydrate. Basically, CA decomposes upon heating to give acetone and calcium carbonate; calcium carbonate further decomposes to give carbon dioxide. ~ote that only small amounts of carbon dioxide are de-tected during the time frame plotted. Most of the carbon dioxide is evolved at a higher temperature (about 600 to 800DC) than that reflected in FIG.
5A.
FIG. 5B depicts the TGA-GC-MSD analysis for Xl ~3~73 crystalline MA. MA behaves much like CA, except that magnesium carbonate decomposes at lower temperatures and the evolved CO2 is thus detected during t'he time frame plotted.
FIG. 5C depicts the TGA-GC-MSD analysis for a physi-cal mixture of CA and MA. The mixture was prepared by grinding CA and MA together with a 1:1 weight ratio.
FIG. 6A depicts -the TGA-GC-MSD analysis for a CMA
double salt according to -the present invention. A comparison with the analyses shown in FIGS. 5A, 5B and 5C show that -this sample contained a minimum amount of residual CA and MA. With a proposed decomposition mechanism or reaction scheme as follows:

Ca~Mgy(C2~32)2(X~y) ~ xCaC03 ~ yMgO +
2(x~y)CH3COCH3 ~ YCO2 ~at 300-500C) xCaCO3 ~ xCaO ~ xCO2 (at 500-800C) Assuming the above scheme, the x/y ratio from the TGA data is calculated to be 0.55 which is in good agreement o~ the elemen-tal analysis result of that sample of 0.52. Accordingly, theTGA-GC-MSD analysis would indicate that the sample was substan-tially pure calcium magnesium acetate double salt with a cal-cium to magnesium mole ratio of about 1 to about 2.
FIG. 6B depicts the TGA-GC-MSD analysis of a CMA
sample having a calcium to magnesium acetate ratio of about 1:1 which was prepared according to the process disclosed in U.S.
Patent No. 4,606,836 (a "direct reaction" process). From a comparison with FIG. 5A and FIG. 6A, it may be seen that that sample contained a substantial amount of residual CA, as evi-denced by the peaks monitored at the molecular weight of ace-tone at about 40 and 42 minutes.
FIG. 6C depicts the TGA-GC-MS~ analysis of a CMA
sample having a calcium to magnesium ratio of 3:7 which was prepared according to the same direct reaction process as the sample of FIG. 6B. This sample is also not of the present ~1 t~

~3~ )73 6193~-18~8 invention. From a comparison with FIGS. 5A, 5B and 6A, it may be seen that the sample contained substantial amounts of both residual CA and MA.
~ hen subjected to analysis by powder X-ray diffrac-tion, the crystalline CMA double salt of the present invention has a characteristic pattern as compared with crystalline CA
and crystalline MA and CMA compositions which are not substan-tially pure CMA double salt. (5ee FIGS. 7A to 7G.) The X-ray diffraction pat-terns depicted in FIGS. 7A
to 7F show that crystalline CA, crystalline MA and CMA double salt all exhibit characteristic X-ray diffraction patterns.
Further description of the methodology is set forth in Example 16. Table XIII summarizes the peak positions for CMA double salt of the present invention.
FIG. 7A depicts the X-ray diffraction pat-tern for crystalline CA hemihydrate, with two strongest peaks at two-theta about 5.2 and about 7.4.
FIG. 7B depicts the X-ray diEfraction pattern for crystalline MA tetrahydrate. It shows -the strongest peak at two-theta 12.5 to 13. Amorphous MA shows a strong broad diffraction peak centered at about 10 two-theta.
FIG. 7C depicts the X-ray diffraction for a CMA
double salt according to the present invention. Overlapped on this chart are sharp vertical lines for the peak positions corresponding to crystalline CA. The double salt exhibits a characteristic very strong double peak in the range of two-theta 8.75 to 10.5. These peaks are centered at about 9.1 and 9.8. The strongest crystalline MA peak is absent, indica-ting that the sample appears to contain substantially no resi dual crystalline MA. The very low intensity peaks coinciding with the two-theta range of the two strongest CA peaks (at 5.2 and 7.4) indicate that this sample contained only very small amounts of residual crystalline CA and thus appears to comprise substantially pure CMA double salt.

X

~l3~2073 FIG. 7D also depicts the X-ray diffraction of a CMA
double salt according to the present invention with crystalline CA peaX points superimposed. The sample exhibits the strong double peak in the range of two-theta 8.75 to 10.5 character-istic of the CMA double salt. The absence of the strongest crystalline MA peak coupled with the presence of only very low intensity peaks coinciding with the two-theta range for the strongest crystalline CA peaks would indicate that this sample contained subs-tantially pure CMA double salt with substantially no residual crystalline MA, and only very small amounts of crystalline CA.
FIG. 7E depicts the X-ray diEfraction pattern of a CMA sample not of the present invention having a calcium to magnesium molar ratio of 1 to 1 which was prepared by the slurry process of Example 7. The diffraction pattern of this sample exhibits the double peak characteristic of CMA double salt, but also exhibits peaks of moderate intensity correspond-ing to the two-theta values of the two strongest peaks of crystalline CA and a peak at low intensity corresponding to the two-theta range of the strongest peak of crystalline ~A.
Therefore, from a review of its X-ray diffraction pattern, it would appear that while this sample contains CMA double salt, it also contains moderate amounts oE crystalline CA and some crystalline MA, and thus is not substantially pure C~ double salt.
FIG. 7F depicts the X-ray diffraction pattern of a CMA sample not of the present invention having a calcium to magnesium ratio of 3 to 7, but which was prepared at low temperature according to Example 11. The diffraction pat-tern of this sample exhibits the double peak characteristic of CMA
double salt, but also shows peaks of moderate intensity which correspond to the two-theta range of the two strongest peaks of crystalline CA~ Accordingly, it would appear that this sample contained moderate amounts of crystalline CA, and is not sub-stantially pure CMA double salt.

~L302~

FIG. 7G depicts the X-ray diffraction pattern of a CMA sample of the present invention without the superimposed lines corresponding to the peak positions of crystalline CA.
This pattern clearly shows the absence of crystalline CA and MA
in this sample. As noted above, Table XIII summarizes these peak positions and intensities.
In addition, we have found that heating the C~
slurry to relatively high temperatures during the process of preparing the deicing compositions results in deicing composi-tions having a higher proportion of crystalline CMA double saltas compared with CA and/or MA. See FIGS. 7C, 7D, 7F, and 7G.
FIG. 8 shows the TGA-GC-MSD spectra for the CMA
sample prepared according to Example 10. FIG. 9 shows the TGA-GC-MSD spectra for the CMA sample prepared according to Example lOA. FIG. 10 shows the TGA-GC-MSD spectra for a commercial CMA sample prepared by Verdugt. The calcium to magnesium ratio was about 3:7. FIG. 11 shows a CMA sample prepared by the method of Gancy, U.S. Patent No. 4,699,725, Example III containing a calcium to magnesium ratio of about 2 to 8. FIG. 11 shows a CMA sample prepared by the method of Gancy, U.S. Patent No. 4,699,725, Example IIB containing a calcium to magnesium ratio of about 1 to 2.
The A portion of each of these figures shows the total ion count. The B portion of the figures shows the evol~
ved CO2 as a function of time, and therefore temperature. The C portion of the figures shows the evolved water as a function of time, and therefore temperature. The D portions of the figure shows the evolved acetone as a function of time, and therefore tempera-ture.
As can be seen by comparing FIGS. 8 through 11, the samples prepared by the method of the present invention as shown in FIGS. 8D and 9D are substantially free of peaks in the evolved acetone spectrum below 35 minutes (about 350), and therefore are substantially free of magnesium acetate. The commercial sample and samples prepared by methods disclosed by ~1 ~Q

~3~Z~73 others, as shown in FIGS. lOD, llD, and 12D respectively all show significant MA peaks.
Table 16 summarizes the X-ray diffraction and TGA-GC-MSD data for several samples of CMA. The data shown include the X-ray peak intensities for the CMA double salt at 9.1 and 9.~ two-theta, and the peak intensities for the crystalline CA impurity (peaks located at ~.2 and 7.4 two-theta) in these samples. Also shown on this Table is the amount of water in the samples, as determined by TGA, and the amount of MA, as determined by the ratio of the evolved ace-tone peaks in the TGA-GC-MSD. The M~ acetone evolution is calculated as a percent of total acetone evolution. None of -these samples has unreacted magnesium base, so this data is not shown.
Samples A00636, B00796, B00~01, and K-10-11-87 are samples of substantially pure crystalline CM~ double salt. The other samples show signi~icant amounts oE crystalline CA :in the X-ray diffraction data, or MA in evolved acetone data from the TGA-GC-MSD; these samples are clearly not substantially pure crystalline double salt.
EXAMPLES
The following non-limiting examples are typical of deicing compositions prepared according to the process of the present invention. The preparations of Examples 1 to 7 and 10 were performed using apparatus having combined distributing and drying means substantially as shown in FIGS. 2 to 4.
Unless stated otherwise, measurement of slurry pH was performed after diluting the slurry one part slurry to two parts water and then measuring the pH of the thusly diluted slurry.

~?

~L302~73 -- 61936-1~48 Ex~
Batchwise Preparation of Calcium Magnesium Acetate on Sand A calcium magnesium acetate (CMA) slurry was prepared batchwise by the following procedure. Seventy-two (72) gallons of water was charged to an agitated, ventilated reaction tank.
One hundred fifty ~150) pounds of Type S hydrated dolomitic lime was added gradually. A uniform suspension of lime in water resulted. Glacial acetic acid, Technical Grade, was pumped into the tank at a rate of about 1.0 lb/minute. The heat of reaction of the acid and lime resulted in an increase in the temperature of -the mixture as the acid was added. When 186.5 lbs of acid had been added, the slurry became excessively -thick. The slurry temperature was 130. An additional ~
gallons of water was added to thin the slurry. Acid addition was resumed until a total of 239 lbs of acid had been added.
The slurry p~l was 8.2 initially and rose to 8.8 after standing overnight. The slurry moisture was 68%. This molsture was a little less than calculated by a mass balance and indicated that a small amount of evaporation had occurred. Sub~equent batches of slurry were made in a similar way except that a larger quantity of water was added at the start to avoid thick-ening during the reaction stage.
The CMA slurry was then converted into a particulate deicing composition comprising CMA coated onto sand by the following methods. A pilot plant rotary drum, 3 feet diameter by 12 feet long was used. The drum was equipped with internal lifters, an internal dam and an extarnal solids recycle system.
Also included was an air system consisting of a fan, an inlet air heater and a baghouse dust collector on the outlet airO
Five Hundred (5Q0) pounds of No. 2 Sandblasting Grade sand was charged into the rotary drum. The system was prehe~t-ed to about 150F. The CMA slurry at a temperature of about 112F was pumped to an atomizing nozzle positioned to spray onto the falling curtain of sand particles inside the rotating X ')~

~3~2~73 drum. The in]et air was heated to 575F. The slurry spray rate was adjusted to 0.3 gpm as indicated by a magnetic flow-meter. A Spraying Systems Company nozzle, body number 60150 and cap number 120, was used to atomize the slurry with an atomizing air pressure of 50 psig. Solids which discharged from the outlet of the rotary drum were recycled back to the inlet of the drum. The atomized slurry coated the sand parti-cles and was simultaneousl~ dried. As this process continuea, a uniform off-white coating of CMA was formed on the sand particles. There was no sign of particle agglomeration.
Inspection of the baghouse showed that a large amount of very fine lightweight dust was collecting in the baghouse hopper.
Spraying was continued and the amount of CMA coating on the sand increased steadily with time. As spraying was continued, samples were withdrawn over time that consisted of particles with 16%, 27~, 36~ and 56~ CMA coating. Calculations showed that the spray yield (weight percent of the CMA sprayed that goes to a coating on the sand rather than to dust) was only 42~. (This meant that there would be a very high dust recycle required in a commercial process and the production rate would be substantially lowered and the drying costs would be substan-tially increased because of the low spray yield.) The composite particles consisted of individual sand particles coated substantially evenly with an outer shell of CMA. The crushing strength of the CMA shell was measured and found to decrease as the percent CMA increased. With the high-est percent CMA, and the soEtest shell, the shell was suffic~
iently hard to withstand normal storage and handling without appreciable breakage. The crushing strength of the outlet shell of the 56~ CMA pellets was 2.8 lbs force as measured with a force gauge.
The pH of a solution of the product was 10.2 for 1 part 27% CMA product mixed with 3 parts water. Tests of the final product containing 56% CMA showed a bulk density of 60.8 lbs/cu.ft.

~ ~ ?~

~L302~73 - 61g36-1848 The ice melting tendency of the 36~ CMA product was tested at 27F. The pellets stuck to the ice immediately.
Visible liquid formed in 5 minutes and visible melting continued for 90 minutes. A liquid run-off of 129 milliliters was measured for 100 grams of 36% CMA pellets after 90 minutes melting -time.
Example 2 Production of CMA on Sand Deicing Composition with Increased Yield The basic procedure outlined in Example 1 was followed. Since it was apparent that a large part of the CMA
in the slurry spray was going to dust rather than to a coating on the particles, tests were run to measure the spray coating efficiency (percentage of CMA in the spray which coated substrate particles) at different slurry temperatures. This was done by analyzing the slurry for percent water combined with reading the slurry tank level to determine the amount of CM~ input, and measuring of the initial weight of sand placed in the rotary drum, then analyzing the CMA coated sand for the percent CMA present as a coating on the sand particles. We discovered that the spray yield was primarily dependent on the slurry temperature. Other variables such as slurry moisture, excess unreacted lime, particle temperature and spray atomization had much smaller effects on the coating efficiency.
The results for runs with CMA slurry prepared by the reaction of dolomitic lime and acetic acid are shown in Table I. The data show that spray coating yields were much higher when the slurry was heated above 155F.
For a practical process the CM~ dust that was formed must be collected and recycled to the slurry tank along with additional water. Tests were run in which all of the slurry was made from reslurried dust. The coating yields for that case were also very dependent on slurry temperature as shown in Table II.
The data in Table II showed that the spray coating yield was again much higher for heated slurry, however, it was not as high for the reslurried dust as for slurry made by ~ ,f5~

~L3~2~)~3 reacting lime and acid. The ability to control dust formation by small changes in slurry temperature was surprising. The slurry appearance was not changed greatly by heating and such a dramatic effect on coating yield would not be expected from solubility data or from previous experience with slurry granulation.
We have discovered that another beneficial effeck of operation with high slurry temperature was that the hardness of the CMA coating increased by 50% for high slurry temperature operation compared to low slurry temperature operation. This increase in the hardness of the CMA coating provided a product that can better withstand degradation to form dust and fines during shipping and storage of the product.

TABLE I
Effect of Slurry Temperature on -the Spray Coating Yield in the Slurry Process for Making Calcium Magnesium Acetate Coated Sand Slurry Conditions:
Temperature, F 135-150 155-165 Moisture, ~ 62-70 62-70 Spray Coating Yield, % 52-61 73-90 TABLE II
Effect of Slurry Temperature on Spray Yield in the Slurry Process for Coating Sand With CMA Using Reslurried Baghouse Dust Slurry Conditions:
Te~perature, F 79 170 Moisture, ~ 65 66-67 Spray Coating Yield, % 0 62 ...~.~i ~S ~

~3020~3 xample 3 Continuous Production of CMA-coated Sand CMA coated sand was prepared by a continuous process using the same pelletizing apparatus that was described in Example 1.
Sand was fed continuously to the inlet end of the rotary drum. Slurry was sprayed onto the moving solids in the front portion of the drum. Conditions used in initial runs gave a high rate of discharge of solids from the exit end of the drum; these solids were continuously returned to the inlet end of the drum. A portion of the exit solids was removed at frequent intervals to maintain a consistent quantity of solids in the drum. With the condition of a high solids recycle rate it was readily seen that the coated sand particles had a wide range of coating thicknesses. A portion oE the fres~ sand feed was traveling through the drum rapidly and did nok receive much CMA coating~ Other portions Oe the sand feed had longer resi~
dence time in the drum and received higher coating levels. The product had a salt-and-pepper appearance, since it was compris-ed of a mixture of lesser coated sand and higher coated sandparticles.
The rotary drum was equipped with an intermediate dam which comprised an annular member of a depth that was about 15 of the drum diameter. This dam ensured a hold-up of granular material in the drum so that a large quantity of it will be available in the bed in the spray impingement zone of the drum.
The dam was equipped with a gate which could be opened to allow emptying of the bed at the end of a run.
After the above tests, it was found that the gate in the dam was not sealing properly which caused a low hold-up and a high solids recycle rate. The dam was sealed and new runs were made with continuous sand feed and continuous product withdrawal. It was found possible to operate with no recycle.
We discovered that this resulted in product with an even level of CMA coating. Operating conditions for this run are shown in Table III.

~1 3~

13~ 073 After 3.5 hours of operation, produc-t that was rernov-ed was sieved into different size fractions and each fraction was analyzed for percent CMA coating. The results are shown in Table IV.
The results showed that the majority of the product was in the size range -5 to +20 mesh and that the coating level was reasonably uniform in this size range.
Continuous reactor operation was demonstrated in other test runs. No unusual operation problems wexe encountered. Operating conditions are summarized in Table V.
As the data in Table Y showed, there was an increase in pM between the reactor and the slurry tank, due to addition-al reaction with lime.
TABLE III
Continuous Operation of the Slurry Process ~or Coating Sand with CMA
Feed Rates:
No. 2 Sand, lb/hr 105 CMA Slurry, gpm 0.33 Slurry Conditions:
Moisture, ~ 68 Temperature, F 170 Drum Operating Conditions:
DamGate closed and sealed Inlet Air Temp. F 550-570 Outlet Air Temp. F164-175 Spray atomization air, psig 50 Product Removal Rate, lb/hr 140 Product Analysis:
Hours of Operation ~CMA
0 (starting bed) 26 1.5 25 2.5 31.5 3.5 27.
4.5 36.5 ~;1 3~

~30~

- 6.l936-1848 TABLE IV
_ Size Distri ution Versus Coating with CMA
Mesh Size Weight % %CMA
Tyler Sieve NoO
+6 1.9 63.0 -6~10 8.8 47.5 -10+12 21.~ 35.3 -12+14 30.2 26.9 -14+20 34.0 18.7 -20+28 3.0 24.5 -2~ 0.8 42.2 TABLE V
Continuous Reactor Operating Results FEED RATES
Mix Tank:
Water, lb/hr 146 Lime, lb/hr 37.5 Reactor:
Acetic Acid, lb/hr 60.0 OPERATING CONDITIONS
Reactor:
pH (undiluted) 6.6-7.4 Temperature, F 155 Moisture, ~ 60 Residence Time, minutes 7.8 Surge Tank:
pH (undiluted) 8.3 Example 4 Relationship Between Slurry pH and Product pH
i During the course of making CMA coated sand composi-tions by procedures described in the above examples, we dis-covered that the product pH was significantly higher than the pH of the slurry from which it was made. Tests were run to see 131[~21D73 what the product pH would be for operation with slurry that was slightly acidic. The slightly acidic slurry would be expected to give complete reaction of the lime leaving a minimum of insolu~le material. It was discovered that slurry with a pH of 6.3 to 6.8 resulted in product with pH of 9.8 to 10Ø The results for operation with slurry pH from 6.3 to 6.8 are shown in Table VI.
Exit gas from the rotary drum was tested at the bag-house exit for acetic acid to determine if there was volatili-zation of acid. The results showed from 30 to 80 ppm aceticacid by volume, depending on slurry pH. With slurry pH levels of 6.6 or above, the exit gas acetic acid concentration was 30 ppm. With slurry pH levels of 6.3, the exit gas acid concen-tration was 80 ppm. Thus, apparently excess acid in the slurry was volatilized; however, there was some acid loss, even when there was no excess of acid in the slurry. These acid losses were quite small, however, based on the measured exit gas flow-rate and measured concentrations of acetic acid in the exit gas of 30-50 ppm. It was calculated that the loss was less than 1 percentage of the total acetic acid in the product CMA. These acid losses were not a significant economic factor.
The pH increase during the coating operation was, nonetheless, not fully explained by the acid vapor losses des-cribed above and is thus surprising. ~It is possible that a small amount of basic magnesium acetate was formed due to this acid loss but this did not appear to be a full explanation for the pH increases that were observed.) This pH increase was very beneficial and desirable, however, since a minimum of insoluble, unreacted lime was obtained due to neutralization to a neutral or slightly acidic final slurry pEI but at the same time a product pEI was obtained that had a pH high enough to avoid concrete scaling which may occur below pH 8 according to studies by R. W. Schenk "Ice-Melting Characteristics of Calcium Magnesium Acetate, Final Report, E~ecutive Summary", February, 1985.

~1 ~' ~3~2~)73 TA~LE VI
Ca:Mg Run No Mole Ratio ~ubstrate Slurrv ~H* Product pH
~.
46 5:5 sand 6.3 9.8 48 4:6 sand 6.7 10.0 3:7 sand 6.5 10.0 5:5 CMA 6.8 9.8 47 4:6 CMA 6.5 9.9 44 3:7 CMA 6.~ 9.8 * 1 part slurry and 2 parts water.

Example 5 Preparation of Calcium Acetate Coated on Sand The procedure outlined in Example 1 was followed using a high calcium containing lime to produce calcium acetate that did not contain a high level of magnesium. Slurry was made according to the procedure described in Example 1.
Seventy (70) gallons of water were charged into the reaction tank and 150 pounds of ~igh Calcium Hydrated Lime (Genstar Lime Co., San Mateo, California, 85~ Ca(0~1)2 min.), were added. Two hundred (200) pounds of G]acial Acetic Acid were added gradual-ly. Toward the end of the acid addition, the slurry became very thick. Two gallons of water was added to thin the slurry.
The procedure outlined in Example 1 was followed to convert the slurry to calcium acetate coated sand. The test run conditions and results are summarized in Table VII. No operating problems occurred. Forty-four pounds of dust were recycled to the slurry during the run. The results shown in Table VII show that the slurry process for coating sand~ with acetate salts gave results for caIcium acetate that were simi-lar to the results for calcium magnesium acetate. The slurry temperature was low, 82 to 94F, and, therefore, the spray coating yield was low, 34 percent. This finding was consistent with the results for calcium magnesium acetate which gave low yields with low slurry temperatures.

~L3al2~73 - 61936-1~48 TA~ VlI
Production of Sand Coated With Calcium Acetate Operating Conditions:
Slurry Moisture, % 66~8 Slurry I`emperature, F 82 to 94 Inlet Air Temp., F 550 to 600 Outlet Air Temp., F 175 to 210 Slurry Feedrate, gpm 0.3 to 0.4 Results:
% Ca Acetate at end of run 21.4%
Total Baghouse Dust, % of Feed 66 Example 6 Preparation of High Magnesium Content CMA-Coated Sand Referring to Table VIII, runs numbers 46, 48 and 45, procedures similar to those described in Example 1 were used to produce CMA-coated sand, however, a mixture oE dolomitic lime and magnesium oxide was used to give a higher magnesium con-tent. The magnesium oxide used was Grade 20, Type 325, (National Magnesia Corporation, Moss Landing, California). In addition, slurry was made slightly acidic to obtain complete lime reaction. The slurry was heated prior to spraying to increase the spray yield.
As shown in Table VIII, the pH of the final product was Erom 9.8 to 10.0, thus the residual base level in the product was very low. The product also had a high crushing strength for the CMA coating and high product bulk densities.
Example 7 Preparation_of "Neat-CMA"
Run numbers 35, 40, 47 and 44 of Table VIII, were made using procedures similar to Example 1 except that essen-tially no sand was used. The initial material was used to establish a bed of solid CMA particles in the rotary drum was obtained by crushing 56% CMA coated sand, and screening the ~30ZC)73 crushed material on a 24 mesh screen to separate the CMA parti-cles from the sand. The 24 mesh CMA partieles were used as the starting bed. In commercial operation oversize produet or a portion of the on size product eould be crushed and recycled of the drum to provide small particles that eould be eoated by the slurry feed. Undersize partieles eould also be removed from the material that discharged from the drum by screening and then reeycled with the crushed material.
As the data in Table VIII show, the bulk density of the product was from 3~.4 to 44 lbs per eubic foot, lower than for the sand coated products, but high enough for good handling characteristics. In runs 35 and 40, a 24 mesh product screen was used whieh gave a small size product. In runs 47 and 44, a 10 mesh produet sereen was used whieh gave a much larger pro-duct~ Even larger size produet eould be produeed by using a produet screen with larger openings. The erushing strength of the straight CMA pellets improved w;th higher slurry tempera-ture operation (run ~0) and with lower ealeium to magnesium ratios (runs 47 and 44). The pellet attrition tests showed very good resistanee to attrition whieh showed that dust forma-tion during handling of the product would not be a problem.

~, P~) ~3~2~3 ;~ N Q) 0 r` Q ~ ~ ~ 1~ ~ o ~ 7 ~ O

r~ O ~o o ~ u~
; N ~ O
N .~: la '~
0~ 1 O ~ ~1~ ~ ~ ~ r- ~ o u~
~ U~ C
:~
O
.,.1 N
V ~ ~ .~:: O ''I -O
V f~
J~
tq tl) r4 J U) O
u~ ~ o ~O
_1 O ~¢ ~ 1 ~ D O
J~ . N

n~ ~ l t~ N 1 U~ ~ l ~
: t~ 1 ~ ~ O
C5~ ~ ~ 1~
a J~ ~ ~ 7 o ~0 ~ U~
P~ ~ A O ~ ~-ri .~
V ~ U~ ~ 1~ O ~ ~ C:~ I
.C ~ ~ r ~ . ~ ~ o ~p ~0 ~ u~
a ~, 3 ~ O
~ U~
g . o h ~1 ~
v Cl~ O ~.q ~ Cl' v o o ~ ~ ~ .~ Q, ~ U, ~ ~ ~ a~
E-t a) o ~ h--~ h Z ~ ~ O
~, O ~ N ~J ~~ ~ '~ ~rl C

o ~ ~

~0'ci 035 ddO~ NOd~3i~ 02:0Z ~8, E~ 'Ntl~

~L3020~73 ~' ~! N ~1 ~ 1-- 0 CO
~ ~ ~ ~ ,~ " ~ O ~ 8 ~:J N ~ 1~ Ll ~

o ~ ~, . I I O cn c~ U ' q,J N S 1~ '~ ~ ~ h ~
.rl ~ ~0 I O ~o ~ o ~ r' r~ o o r~ o t`

:~ .
~t N

u~ v I I ~ oo o o ~ r~ oo c:
~co~r ~-a~

s o ., u ~ ~3 a ~ , o U~ ~ ~no oou~ 8 ~-~ N O ~ (a O ~ r` ~ O ~
q~ ~, ~ ~e;, ~ ~, ~ tl'l ~, Lt) U N
~ J
~ o~ I r ~ ~ g o U~ o u~
tn ~ x; o ~ ~ I ~ o ~ o ~ ~ N ~ ~

~ OD U~ ~ V ~ U t ~

JJ C~
~ O (~ t ~ O

~ h a) ~i h O ~ C ~ r~

o U~ ~ U
O O ~

,.
,~
Z~0'~ 0~5 c~O~ N~3H0 ~Z:0Z 88~ ~:I'Ntl~ ~

~3~2~3 - - 6193~-l8~8 Example ~
Preparation of Deicing Composition By Simultaneous Reaction and Coating Process_Using a Cement Mixer Calcium magnesium acetate-coated sand was prepared by the direct reaction process using a cement mixer according to the following procedure.
Into the cement mixer, twenty-five (25~ pounds of sand (No. 2 sandblasting grade) were placed. The internal lifters of the mixer created a dense curtain of sand. Water, one pound, was sprayed on the sand using an atomizing nozzle.
Powdered lime, 1.79 pounds of Type S hydrated dolomitic lime was added to the wet sand. Using an atomizing nozzle, 2.47 pounds glacial acetic acid were sprayed on the sand-lime mix-ture. After the acid addition was complete, mixing was contin-ued for about one-half hour.
Compositions prepared in accordance with the above procedure are disclosed as sample numbers l and 2 oE Table X.

Exam~e 9 Preparation of Calcium Magnesium Acetate-Coated Sand Usin~ a Rotary Drum Pelletizer-Dryer Calcium magnesium acetate-coated sand was prepared by the direct reaction process using a rotary drum pelletizer-; dryer according to the following procedure:
A rotary drum pelletizer-dryer was charged with 500 pounds of sand (No. 2 Sandblasting grade), so that sand was recirculated from the drum outlet to the drum inlet. Water was continuously sprayed on the sand in the front section of the drum, before the sand reached the lifters. Lime (Type S
hydrated dolomitic), was continuously fed into -the front section continuously ~up to 48 pounds~. After the wetted sand and dry lime mixture passed to the lifter section, acetic acid (up to 67 pounds) was sprayed on the mixture using an air atom-izing spray nozzle. A Elowable mass of discrete particles was obtained which had some acid odor.

~3020~7~

A composition prepared in accordance with the above procedure is disclosed as Sample No. 3 in Table X.

Example 10 Continuous Production of "Neat CMA"
A calcium-magnesium acetate ~CMA) deicer was produced on a com~ercial scale by the ~ollowing continuous process.
Water was continuously added to a covered, agitated mix tank (at a rate sufficient to maintain about a 32 wt % CMA slurry on exiting the reaction chain) with approximately 1~40 lb/hr of Type S hydrated dolomitic lime, and approximately 750 lb/hr of magnesium oxide. The magnesium oxide was added as a slurry with water prepared by drawing solid magnesium oxide into the throat of an eductor using water as the educting medium. The resultant mixture flowed by gravity through a series of four additional mixing vessels. One overflowing throùgh a trough into the next.
Upon overElowing the ~ieth mix tank, glacial acetic acid was added at a rate of approximately 9.6 yal/min. to a reactor with thorough, high shear mixing, resùlting in an exit pH of approximately 5.6. The reactor was vented through a high-energy wet scrubber to reduce acetic acid emissions to the environment. The water from this scrubber was continuously blown down and used as feed water to the first mix tank. As the slurry overflowed into the second reactor, a slight flow of additional acetic acid was added to maintain a slurry pH of approximately 6.0 in the slurry tank.
The overall average recipe for CMA slurry was:

Acetic acid 0.80 lbs/lb dried CMA
Type S lime 0.23 lbs/lb dried CMA
Magnesium oxide 0.11 lbs/lb dried C~A

The resultant slurry was maintained at a temperature of approxima~ely 186F and pumped through an atomizing nozzle 4-~

~31~)Z0~3 and sprayed on a falling bed of CMA pellets in the front of a rolling drum. The drum was equipped with internal lifters, an internal dam and an external solids recycle system. Also included was an air system consisting of a fan, an inlet air heater and a baghouse dust collector on -the outlet air. Air was introduced at a temperature of approxi~ately 700F, and a flow rate of approximately 29,000 standard cubic feet per minute (SCFM). The air exited the drum at approximately 151F
and entered a baghouse for dust removal before entering the environment. The dust collected from the baghouse, approxi~ately 1500 lb/hr, was recycled to -the slurry tank and additional water added to maintain approximately a 68 wt %
moisture slurry.
CMA pellets formed or enlarged in the drum were classified with a screening system. Pellets which did not pass a 3/8-inch screen were crushed and recycled to the ~ront oE ~he drum~ Pellets which passed through a 30-mesh screen were also recycled. Approximately 5% of the pellets which were in the product range of 3/8 inch ~30 mesh were withdrawn as product and moved to the warehouse, with the remaining 95% being recycled to the front o~ the drum.
Product produced from this run had a calcium/magnesium mol ratio of approximately 0.45 (i.e., 3.1 to 6.9 [about 1 to 2.2]), had a pH of about 9.5, and contained about 1.86 wt ~ water insoluble material.

Example lOA
Continuous Production of "Neat CMA"
A calcium magnesium acetate (CMA) deicer was produced on a commercial scale by the following continuous process.
Water was continuously added to an agitated mixing vessel at a rate sufficient to maintain about 42 weight percent CMA slurry on exiting the reactor train with approximately 2120 pounds/hour of Type S hydrated dolomitic lime and approximately 990 pounds/hour of magnesium oxide. The resulting mixture ~1 r ~30Z07~
- - 61936-18~8 flowed by gravity through an additional mixing vessel, over-flowing one through a trough into the next.
Upon overflowing the second mixing vessel, glacial acetic acid was added at a rate of approximately 11.3 gallons/-minute to a reactor with thorough mixing, resulting in an exit pH of approximately 9. As the slurry overflowed into the second reactor, a slight flow of additional acetic acid was added to maintain a slurry of approximately 7.5 in the slurry tank. The reactors were vented through a high-energy wet scrubber to reduce acetic acid emissions to the environment.
The water from this scrubber was continuously used as feed water to the first mixing vessel.
The overall formula for the CMA slurry was:
Acetic acid 0.79 poundslpound dried CMA
Type S lime 0.26 pounds/pound dried CMA
Magnesium oxide 0.12 pounds/pound dried CMA

The resultant slurry was ~laintained at a temperature of approximately 190F (88C) and pumped through an atomizing nozzle and sprayed on a falling bed of CMA pellets in the front of a rolling drum. The drum was equipped with internal lifters, an internal dam and an external solids recycle system.
Also included was an air system consisting of a fan, an inlet air heater and a baghouse dust collector on the outlet air~
Air was introduced at a temperature of approximately 800F
(427C), and a flow rate of approximately 32,000 standard cubic feet per minute (SCFM). The air exited the drum at approxima-tely 200F (93C) and entered a baghouse for dust removal before entering the environment. The dust collected from the baghouse, approximately 500 pounds/hour, was recycled to the slurry tank and additional water added to maintain approximate-ly a 58 weight percent moisture slurry.
After exiting the drum, CMA pellets formed or employ-ed in the drum were classified with a screening system. Pellets ~30Z1~73 - 61936-1~48 which were larger than a 6-mesh screen were crushed and recycl-ed to the front of the drum. Pellets which were smaller than an 8-mesh screen were also recycled. Approximately 5 percent of the pellets from the drum were in the product range of minus 6 mesh to plus 8 mesh and were withdrawn as product and moved tG the warehouse, with the remaining 95 percen-t being recycled to the front of the drum.
Product produced from this run had a calcium/-magnesium mol ratio of approximately 0.46 (about 1 to 2.2), had a pH o~ about 9.5, and contained about 2.1 weight percent water insoluble material.

Example 11 CMA Preparation at Low Temperature Lime ~Type S dolomitic), magnesium oxide and water were combined in a beaker to give a slurry. Glacial acetic acid was added to the slurry. The resulting slurry was heated with stirring for 1/2 hr to give a Einal slurry temperature of about 130 to 140F. The pH of the slurry was measured; if necessary, additional acetic acid was added to give a pH in the range of about 5.0 to 7Ø The slurry was fil-tered through filter paper to remove insolubles. The filtrate was dried overnight in a vacuum oven at about 95 to 100C to give the low temperature CMA samples.
Samples prepared in accordance with the above proce-dure are disclosed in Table IX.

TABLE IX
Sam~les Prepared Accordinq to Example 11 Amount Ca:Mg Ratio Sample ~o. Reagent(g) in Sample B5669-23-1 Lime 10.0 5:5 MgO 0.4 Water108.04 Acetic Acid 18.56 B5669-23-~ Lime 5.00 3.3:6.7 (X-ray diffraction MgO 1.90 pattern shown Water100.68 in FIG. 7F) Acetic Acid 14.36 ~1 ~

~L3~2C173 The X-diffraction pattern in FIG. 7F showed incom-plete reaction to CMA double salt at this lower temperature.

Example 12 Measurement of Crush Strength Crush strength of the CMA layer of deicing composi-tions was measured using a Chatilon DPP 1 force gauge ~duro-meter). One revolution around the gauge equaled a force of 10 lbf (divisions were in 0~1 lbf increments). The particle to be tested was placed on a lab jack immediately below the plungerldisc assembly of the force gauge. The lab jack was raised using the height adjustment screw until the particle to be tested was held in place. The force gauge was zeroed.
Pressure was applied to the particle until the CMA layers broke; the force reading at that point was taken. Results are tabulated in Table X.

Example 13 Measurement of Atrition Resistance The attrition resistance of CMA deicing compositions were measured using ASTM method D 4058-81.
The results or various CMA compositions, reported in percent loss on attrition are tabulated in Table X.

36~ 3 .. ~

o o ~C
oC ~ I` O
J~
C~ CO U~
., ,¢
,o r~ ~ o ~ ~ c~ o h c: ~ ~ ~ ~ ~/ ~ o r~l V _~
I
I
U~ C ~
h Ll V
U~
3 ~ JJ
o ~ E~
K
O

I
e ~ c U~
o .,., h . . " , .. , . "
C~ CO ~ O U~ ~
~ ~1 ~1 ~ Lf') O . O
_ ~-1~1 N ~ ~1 ~) ~ In ~ U~
o N co ~ a~ l CO N
C~O O O O C~ O O
~D i I I I I I I I I I ~ I I I I I I
C~ OO O O o O ~ Cl O ~ O

~q fr~ cq m ~ h _I ~

U~
- ~ ~ o ~ o ~
o o ~

6~0'd O~S dl:!O~ NO~1~3H~) ~Z:0Z ~8. ~I'N~r ., L3(~2~3 o C ,.
. . . ~ ~ ~ .
J ~
~,) O~ ~P

~::
.0 0 U~
P
V
h ., I
S I
V ~
~q ~ ~ I I

~ .

_~ . ~
v a h ~ ~ o Q
(q ~ h .r~

l ~
n~
r~ ~ ~
_ ~ ~ .
~P ~ U~ U~ 'v ~ ' ~ .. ~ ~
;~ 1~
U ~ Lr ~ C
_ ~ ~ æ

_ ~c .
~1 Yl c~ o ~ h r~

~n m ~ h C~
_I a Q..~l O ,~
~ ~ ,~
U~ Z ~1 Q u~ o u~
O r~l .

030'd OIS d;~lO3 NO~3H~) 3Z:02 88. ~'N~

~311:12~73 - - ~1936-1848 Example 14 Evolved Gas Anal~sis by TGA-GC-MSD
CMA samples produced by both the direct reaction and slurry process (Examples 1 to 9) were compared using Evolved Gas Analysis by TGA-GC-MSD. This technique took the evolved gases from a standard thermogravimetric analyzer (TGA) as they were produced over time and subjected the gases to capillary tube gas chromatography (GC). The gases at the end of the GC
column were analyzed using a mass selective detector (MSD).
The total ion count at several preset masses was monitored over time. Typical analyses ran about 50 minutes.
The TGA used was a DuPont 951 T~A which was set up so it was controlled by a Northstar microcomputer. The GC-MSD was a Hewlett Packard 5890A GC equipped with a 5970 quadruple MSD.
The GC used either a 15- or a 50-meter SC-32 capillary column (cross-linked methyl silicone, 0.33 micron Eilm thickness, 0.30 micron internal diameter). The TGA outlet was connected to the GC injector. The GC inlet system was se-t at a 100:1 split ratio. All transfer lines between the TGA and the GC injector were wrapped with heating tape.
The GC-MSD continuously monitored the TGA evolved gases.
To detect unreacted magnesium base, gas evolution at mass 18 (water) was monitored. At a temperature of about 300C, or after about 14 to 16 minutes in the TGA, heating at a rate of 20C/minute, the reaction of magnesium hydroxide (or hydrated magnesium oxide) to magnesium oxide was observable.
The lower limit for detection of unreacted magnesium base by the above method was about 1%.
Samples of CMA prepared according to the direct reaction process method (of Examples 8 and 9) showed approxima-tely 5% (of the CMA) as unreacted magnesium base.
Samples of CMA prepared according to the slurry pro-cess method ~of Examples 1 to 7) showed essentially no detect-able magnesium base.

~L31D2~'73 Example 15 Analysis of CA, MA, and CMA
Samples By TGA-GC-MSD Analysis CA and MA standards and CMA samples produced by both the direct reac-tion process and the slurry process as described in Examples 1 to 10A were compared using Evolved Gas Analysis by TGA-GC-MSD. This technique took the evolved gases from a standard thermogravimetric analyzer (TGA) as they were produced over time and subjected the gases to low resolution gas chroma-tography (GC). The gases at the end of the GC column were recorded using a mass selective detector (MSD). The total ion coun-t at a preset mass can be monitored over time.
The TGA-GC-MSD apparatus used was described in Example 14.
The TGA-GC-MSD analyses were carried out at a heating rate of 10~C/min, unless otherwise indicated and using a helium carrier gas. The helium flow rate was set at 80 cc/min. The GC-MSD chromatograms were plotted as a function of time. The TGA starting temperature was kept at 25C.
The relative ion abundance at the molecular weights of acetone, carbon dioxide, and water were monitored and plot-ted over time. In addition, a spectrum showing the Total Ion Count (TIC) versus -time was also plotted. In some of the plots, the carbon dioxide abundance was scaled down by a factor oE 2.5 to 3 in order to match the scale of the acetone abun-dance so the two plots could be overlaid on the same figure.
The CA hemihydrate and MA tetrahydrate standards were purchased from J. T. Baker. A CA-MA mixture was prepared by mixing CA and M~ in a ratio of l lo Other CMA preparations were prepared according to processes such as these described in Examples 1 to 10A. Samples used for TGA-GC-MSD analysis were set forth in Table XI.
Gas evolution at the masses corresponding to acetone and carbon dioxide were monitored and plotted as a function of time.

~i ~t ~L3~2~3 The TGA-GC-MSD chromatograms are shown in FIGS. 5A to 5C and 6A to 6C plot the gas evolution at the masses corres-ponding to acetone and carbon dioxide as a function of time.
The TGA-GC-MSD chromatograms shown in FIGS. 8A to 8D, 9A to 9D, lOA to lOD, llA to llD, and 12A to 12D plot the gas evolution at the masses corresponding to wa-ter, acetone, and carbon dioxide as well as total ion content, as a function of time.

13(12(173 TABLE XI
Samples Used for TGA-GC-MSD Analysis _ FIG. No. Sample Preparation Ca:M~ Ratio .
5A CA Commercial Ca only (J. T. Baker) 5B MA Commercial Mg only ~J. T. Baker) 5C CA-MA physical Commercial 1:1 mixture (J. T. Baker) 6A B8105~02-6 According to Approx.
Example 10 3.5:6.5 6B B8105-40-3 According to 1:1 USP 4,606,836 6C B8105-40-5 According to 3:7 USP 4,606,836 8A to 8DCMA double saltAccording to 3.3:6.7 Example 10 9A to 9DCMA double saltAccording to 3.1:6.9 Example lOA
lOA to lOD CMA Commercil (Verdugt) llA to llD CMA According to 2:8 USP 4,699,725 12A to 12D CMA According to 1:2 USP 4,699,725 Example 16 X-Ray Diffraction Analysis X-ray diffraction analysis was performed on crystal-line calcium acetate hemihydrate, crystalline magnesium acetate tetrahydrate and various CMA samples.
The X-ray diffraction peaks of crystalline CA was superimposed on FIGS. 7A, 7C, 7D, 7E, and 7F, to help locate the position of any crystalline CA impurities.
The X-ray diffraction pattern of CMA double salt is summarized in Table XIII. The peak position in degrees ~3~2~73 two theta; the d-spacings and the relative intensity are shown.
The analyses were done using a Siemens D50Q diffrac-tometer equipped with a copper tube (so that the two-theta values shown in FIGS. 7A to 7F are for Cu K radiation). The Siemens DIFFRAC 11 software package was used for peak location.
Samples used -Eor X-ray diffraction studies are shown in Table XII.
FIGS. 7A to 7F show X-ray diffrac-tion patterns for the samples shown in Table XII.
TABLE XII
Samples for X-Ra~ Diffraction FIG. No. Sample Preparation Ca:Ma Ratio 7A CA Commercial Ca only (J. 1'. Baker) 7B MA Commercial Mg only (J. T. Baker) 7C B8105-02-5 According to 3:7 Example 7 7D B8105-02-6 According to 3.5:6.5 Example 10 7E B8105-02-4 According to 1:1 Example 7 7F B5669-23-3 According to 3.3:6.7 Example 11 7G CMA double According to 3:7 salt Example 10 ~Z

~2~7~1 TABLE XIII
X-Ray Powder Diffraction Data for Crystalline CMA Double Salt (Cu K~tRadiation) ~ . .
Spacing Relative 20 Degrees d,A Intensit ~ ) 9.1 9.7 V5 9.8 9.0 m Ca-13.9 6.4 vvw 16.2 5.5 vvw 17.2 5.2 vvw 18.2 4.9 vvw 18-5-Mg 4.8 vvw 19.8 4.5 vvw 20.9 4.3 vvw 21.7 4.1 vvw 22.4 4.0 vvw 23.6 3.8 vvw 23.8 3.7 vvw 24.1 3.7 vvw 25.2 3.6 vvw ~5 7 3.5 vvw Ca-26.1 3.4 vvw Ca-26.9 3.3 vvw Ca-27.6-Mg 3.2 vvw 28.1 3.2 vvw 28.9 3.1 vvw 30.6-Mg 2.9 vvw Ca-31.5 2.8 vvw :
Ca-There is overlap with a peak from Ca(C2H302)2.1/2H20.
Mg-There is overlap with a peak from ~-Mg~C2H302)2.4H20.
vs = 100-80; s = 80-60; m = 60-40; w = 40-20;
vw = 20-10; vvw = 10-0 r, c~
~.

~3~2~3 ., ~7~

~ r r c~ ~o r .. ~I ~ I I .. .. .. . . ..

~ ~ .-~ ~ ~P ~ o r- ~ ~
,~ ~ u~ ,~ r ~ ~ N t`~
!~i ~
~ ~ o,~,l , , o ~ o ~ 51 ~ ~ ~ t~ N 0 3 ~. ~
~ .~ ~ ~ N r~ U'l O
Ul ~_ J- ~ 1~
i~i ~ ~ c~
~ ~i ~D ¦ ~) ~ ~
~ ;~ ~ 0~ r-l u~ N U~ 1 u~ ~ ul )~
.u~ ~ O~ ~o ~ O o c ~ æ o ~ ~
~ ~ N ~ ~ ~ ~ O ~ ~
~n ~ o ~ O
, .~ 0~ ~ w æ ~
~ ~ ~ r~ u~ 0 N ~ ~2 N æ ~

- ~ v N C ~ C

-- `~ -- O -- ~ r~
a~ L ~ O
1 N 1~ U t~ CO O
~ ~ 0~

O o ~ _~ O ~

,~~C

O~S ~10~) NO;~ IH~ ZE :0Z 88, E~ 'Ntl~
~30 d

Claims (39)

1. A composition comprising less than about 8 percent by weight crystalline calcium acetate, less than about 8 percent by weight magnesium acetate, about 1 percent to about 3 percent by weight unreacted base, less than about 5 % by weight water and the remainder being calcium magnesium acetate double salt.

2. A composition according to Claim 1 containing less than about 5 percent by weight crystalline calcium acetate, less than about 5 percent by weight magnesium acetate, and about 1 percent by weight unreacted magnesium base.

3. A composition according to Claim 1 which is substan-tially anhydrous.

4. A composition according to Claim 1 containing less than about 2.5 percent by weight water.

5. A composition according to Claim 1 which exhibits TGA-GC-MSD spectra substantially the same as Figures 6A, 8A to 8D
or 9A to 9D and an X-ray diffraction pattern substantially the same as Figures 7C, 7D or 7G.

6. A composition according to Claim 1 having a calcium:
magnesium ratio of about 4:6 to about 3:7.

7. A composition according to Claim 6 having a calcium:
magnesium ratio of about 3:6 to about 3:7.

8. A composition according to Claim 7 which exhibits TGA-GC-MSD spectra substantially the same as Figures 8A to 8D
or 9A to 9D and an X-ray diffraction pattern substantially the same as Figures 7C, 7D or 7G.

9. A composition according to Claim 1 having the empirical formula:
CaxMgy(C2H3O2)2(x+y) wherein x is 3 to 4 and y is 7 to 6.

10. A composition according to Claim 9 which exhibits TGA-GC-MSD spectra substantially the same as Figures 6A, 8A to 8D or 9A to 9D and an X-ray diffraction pattern substantially the same as Figures 7C, 7D or 7F.

11. A composition according to Claim 9 containing less than about 2.5 weight percent water.

12. A composition according to Claim 11 containing less than about 5 percent by weight crystalline calcium acetate, less than about 5 percent by weight magnesium acetate and about 1 percent by weight unreacted magnesium base.

13. A composition according to Claim 12 which exhibits TGA-GC-MSD spectra substantially the same as Figures 6A, 8A to 8D or 9A to 9D and an X-ray diffraction pattern substantially the same as Figures 7C, 7D or 7G.

14. A deicing composition which comprises a plurality of layers of a composition according to Claim 9 on discrete sub-strate particles.

15. A deicing composition according to Claim 14 wherein said substrate particles comprise a traction aid.

16. A deicing composition according to Claim 14 wherein said substrate particles comprise particles of a calcium magnesium acetate double salt.

17. A deicing composition comprising a composition according to Claim 1 which has a bulk density of at least about 40 pounds per cubic foot, a particle specific gravity greater than about 1.2 and attrition of less than about 3 percent.

18. A pelletized deicing composition comprising a com-position according to Claim 9 which has a bulk density of at least about 40 pounds per cubic foot, a particle specific gravity greater than about 1.2 and attrition of less than about 3 percent.

19. A process for preparing a calcium magnesium acetate double salt which is substantially free from crystalline calcium acetate, magnesium acetate and unreacted magnesium base which comprises:
(a) preparing an aqueous mixture of CM base having a calcium:magnesium ratio of from about 4:6 to about 3:7 which contains at least about 40 percent by weight water;
(b) admixing the mixture of step (a) with from about 70 percent to about 110 percent of the stoichiometric amount of acetic acid necessary to convert said CM base to said double salt, the resulting mixture containing at least about 50 percent by weight water to give a CMA slurry;
(c) if required, adding sufficient additional acetic acid to said slurry so that the total amount of acetic acid is approximately the stoichiometric amount of acetic acid necessary to convert said CM base to said double salt; and (d) aging the CMA slurry to allow substantially complete reaction of the CM base with acetic acid.

20. A process according to Claim 19 further comprising:
(e) drying and pelletizing the slurry of step (d) to give a dry, free-flowing product.

21. A process according to Claim 20 wherein said drying and pelletizing of step (e) comprises distributing the slurry of step (d) in a thin layer on discrete substrate particles and drying the substrate particles.

22. A process according to Claim 21 wherein in step (e) the slurry of step (d) is distributed in a thin layer on a falling curtain of discrete substrate particles in the presence of heated gas to give layered particles.

23. A process according to Claim 22 further comprising:
(f) repeating step (e) to give layered particles having a plurality of layers on said particles.

24. A process according to Claim 19 wherein step (b) further comprises simultaneous admixing the mixture of step (a) and said amount of acetic acid.

25. A process according to Claim 24 wherein step (c) further comprises measuring the pH of the slurry of step (b) and, if necessary, adding sufficient acetic acid to give a pH
of about 7 to about 8.5.

26. A process according to Claim 19 wherein step (d) is conducted at a temperature of at least about 150°F.

27. A process according to Claim 19 wherein step (d) is conducted at a temperature of about 170°F to about 200°F.

28. A process according to Claim 27 wherein the CMA
slurry contains from about 55 percent by weight to about 68 percent by weight water.

29. A process according to Claim 27 wherein step (b) further comprises admixing about 90 percent by weight of the stoichiometric amount of acetic acid.

30. A process according to Claim 29 wherein step (d) comprises aging said slurry for at least about 3.5 hours.

31. A process for preparing a calcium magnesium acetate double salt which is substantially free from crystalline calcium acetate, magnesium acetate and unreacted magnesium base and which is substantially anhydrous comprising:
(a) preparing an aqueous mixture of CM base having a calcium:magnesium ratio of about 4:6 to about 3:7 which contains at least about 40 percent by weight water;
(b) simultaneously admixing the mixture of step (a) with about 90 percent of the stoichiometric amount of acetic acid necessary to convert said CM base to said double salt; the resulting mixture containing at least about 50 percent by weight water, to give a CMA slurry;
(c) if necessary, adding additional acetic acid to give a pH of about 7 to about 8.5;
(d) aging the CMA slurry to allow substantially complete reaction of the CM base with acetic acid; and (e) drying and pelletizing the slurry of step (d) to give a dry, free-flowing product.

32. A process according to Claim 31 wherein step (d) is conducted at a temperature of at least about 150°F.

33. A process according to Claim 31 wherein step (d) is conducted at a temperature of about 170°F to about 200°F.

34. A process according to Claim 32 wherein said drying and pelletizing of step (e) comprises distributing the slurry of step (d) in a thin layer on discrete substrate particles and drying the substrate particles.

35. A process according to Claim 34 wherein said dis-tributing of step (e) is done without additional atomizing air.

36. A process for preparing a calcium magnesium acetate double salt having the empirical formula:
CaxMgy(C2H3O2)2(x+y) wherein x is 3 to 4 and y is 7 to 6 which is substantially free of crystalline calcium acetate, magnesium acetate and un-reacted magnesium base comprising:
(a) preparing an aqueous, flowable mixture of CM base having a calcium:mangnesium ratio of about 4:6 to about 3:7;
(b) admixing the mixture of step (a) with from about 70 percent to about 110 percent of the stoichiometric amount of acetic acid necessary to convert said CM base to said double salt to give a CMA slurry, said slurry containing sufficient water to be fluid and pumpable;
(c) if required, adding sufficient additional acetic acid to said slurry so that the total amount of added acetic acid is approximately the stoichiometric amount of acetic acid necessary to convert said CM base to said double salt; and (d) aging the CMA slurry to allow substantially complete reaction of the CM base with acetic acid.

37. A process according to Claim 36 further comprising:
(e) drying and pelletizing the slurry of step (d) to give a dry, free-flowing product which is substantially anhydrous.

38. A process for preparing a calcium magnesium acetate double salt which is substantially free from crystalline calcium acetate magnesium acetate and unreacted magnesium base which comprises:
(a) preparing an aqueous mixture of CM base having a calcium:magnesium ratio of from about 4:6 to about 3:7 which contains at least about 40 percent by weight water;
(b) admixing the mixture of step (a) with from about 70 percent to about 110 percent of the stoichiometric amount of acetic acid necessary to convert said CM base to said double salt and, if necessary, adding sufficient additional acetic acid to said slurry so that the total amount of acetic acid is approximately the stoichiometric amount necessary to convert said CM base to said double salt, so that substantially complete reaction occurs.

39. A process according to Claim 38 further comprising:
(a) drying and pelletizing the slurry of step (b) to give a dry, free-flowing product which is substantially anhydrous.