Chemistry: physical processes – Physical processes – Crystallization
Reexamination Certificate
1996-10-31
2003-12-09
Langel, Wayne A. (Department: 1754)
Chemistry: physical processes
Physical processes
Crystallization
C023S30200R, C023S30200R, C023S304000, C423S422000
Reexamination Certificate
active
06660049
ABSTRACT:
TECHNICAL FIELD
The invention relates to processes for control of crystallization of inorganics, such as Na, Li, K, Ca and Mg bicarbonates, phosphates, borates, hydroxides, nitrates and sulfates from aqueous solutions containing the respective ions thereof. More particularly, the invention relates to the use of lecithin as a generally regarded as safe (GRAS) food grade and Kosher crystal growth promoter and crystal size classifier (size control agent) for the crystallization of sodium bicarbonate from solution mined Nahcolite pregnant liquor.
BACKGROUND
Global sodium bicarbonate demand in 1996 is projected at one million tons per year, with U.S. capacity at about two thirds that amount. There are four major processes for production of sodium bicarbonate, all of which involve crystallization from aqueous solution. The most commonly currently used process involves mining impure Trona mineral which is purified by recrystallization from a hot aqueous solution via intermediate steps of production of sodium carbonate or sesquicarbonate and recarbonation with CO
2
. A second method involves carbonation of brines rich in sodium, borate, carbonate and bicarbonate ions, such as lake brines, e.g. brines of Owens Lake, Lake Natrona and from Searles Lake, Calif., and Lake Magabi, Tanzania. Still another method involves the production of sodium bicarbonate in the ammonia soda process. Finally, one of the lowest cost processes is solution mining Nahcolite mineral from the evaporate deposits of the Green River Formation in the Piceance Creek Basin, Colo. according to the Nahcolite Solution Mining Process of the: Rosar and Day. U.S. Pat. No. 4,815,790. The pregnant liquor is pumped above ground where it is crystallized at atmospheric pressure and ambient temperature in a series of crystallizers staged in parallel or series.
Crystal nucleation and growth rate from a solution is expressed in terms of crystallization kinetics. Crystal habit is the shape which results from the different rates of growth of the various crystal faces. Both crystallization kinetics and crystal habit influence production costs, product purity, caking, bulk density, dusting, flowability and the like. Both brine concentration, natural and/or induced solution impurities even in low concentrations, impact crystallization kinetics and crystal habit in commercial crystallization operations. Ordinarily, the nature and extent of the impact of such impurities is both adverse and unpredictable.
Impurities in brine or solution mined Nahcolite pregnant liquor change from time to time. These impurities are both inorganic and organic. For example, in Nahcolite solution mining, the Nahcolite beds are typically some 2,000 feet below the surface. Nahcolite beds typically include inter-bedded stringers, lenses or rosettes of kerogen-containing shale, salt or Dawsonite mineralization, among others. Thus, commercial operations often experience “drift” in which, due to subtle variations in impurity content over time even while maintaining the same mining and crystallizer conditions of temperature, agitation, heat exchange and throughput rate, there can be vast differences in the end product. For example, there can be relatively wide swings in the quantities of “oversized” or “undersized” product, and in the bulk density, caking and friability of the product. That is, the percentage of crystals which are too large and percentage of very fine crystals (called “fines”), may vary over time, in some instances as quickly as within a few days. Where the product crystals are too large, the product becomes unsuitable or uneconomic to use, particularly in food products, or as an SO
x
sorbent in pollution control processes, one of the significant uses of sodium bicarbonate. Likewise where the product is too fine, it is difficult to dewater during processing, increases process energy costs, and the resulting product cakes easily, creates dust when handled and is difficult for the customers to use.
As pointed out in the Bauer et al. U.S. Pat. No. 3,072,466, bicarbonate crystals obtained by various commercial crystallization processes in many cases are of inferior quality considering such factors as crystal shape, purity, settling rate, size, uniformity, dewaterability, bulk density and resistance to breakage during handling. The Bauer et al. patent is directed to the use of anionic-active surfactants of the organic sulfate or sulfonate-type derivatives, and most preferred are the alkyl benzene or alkyl naphthalene sulfonates. The Bauer et al. patent also teaches that cationic and nonionic surfactants are “totally ineffective as additives in improving the crystallization of sodium bicarbonate.” It states that “various theories have been considered in an effort to explain the clearly established, unique effectiveness of the anionic-active surfactants” and “the complete lack of effectiveness of the cationic and nonionic classes,” but those theories “have all failed to fully explain” the “unexpected result” of anionic surfactant activity.
Crystal growth modifiers can impart positive and/or negative influences, with the goal being to enhance the positive and reduce or eliminate the negative. In inorganic solution crystallization, the manner in which modifiers function on the molecular level is unpredictable and speculative.
There is another factor involving such modifiers. Sodium bicarbonate is used in many food products and processes. Thus, crystallization agents such as the alkyl benzene or naphthalene sulfonates do not have GRAS classification, and at best may only be sparingly used in food grade sodium bicarbonate production. The field is replete with attempts to use commercial dishwasher detergents such as DBSA, Petro AG (DeSoto Chemical Company) with diesel fuel, kerosene or styrene. All of these have serious food grade and GRAS non-approval issues, and are not very efficient modifiers. Other additives have been tried, such as hexametaphosphate, but such additives result in an extremely high loss in yield and extremely dendritic crystal habit which makes them unsuitable for use.
DISCLOSURE OF THE INVENTION
It is among the objects and advantages of the invention to provide a GRAS crystal growth modifier for crystallization of inorganics from aqueous solutions containing Na, Li, K, Ca and Mg cations, and carbonate, bicarbonate, borate, hydroxide, nitrate and sulfate anions, which modifier is a selective crystal size classifier and limiter. It is another object and advantage of the invention to employ lecithin full strength, or in solutions, suspensions, mixtures and emulsions in minor (parts per million) quantities, as an extremely good crystal growth promoter, size classifier, dewatering agent and supersaturation reducing agent. It is still another object and advantage of the invention to provide a process employing adding lecithin in parts per million quantities to aqueous inorganic solutions, for example, of sodium bicarbonate from a variety of sources, including Nahcolite solution mining and brine mining pregnant liquor, as an improved crystal growth promoter and which reduces both heat exchanger and crystallizer scaling. It is another object and advantage of the invention to provide a method for introduction of lecithin in controllable parts per million quantity to aqueous solutions of inorganic ions in a simple, reproducible and effective manner without the need for additional emulsification, detergent, saponification or Ph control agents. These and other objects and advantages are evident from the description of the invention herein.
The invention comprises the use of parts per million quantities of lecithin, particularly lecithin extracted from soybean oil, in the range of from about 2 to about 200 ppm, and more particularly in the range of from about 5 to about 60 ppm as a crystal growth promoter and size classifier for crystallization of inorganics from solutions containing the above-listed cations and anions. By “size classifier” is meant the property of narrowing the range of crystal sizes, especially to within the useful product range of
Langel Wayne A.
Natural Soda AALA, Inc.
Scully Scott Murphy & Presser
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