US20040126292A1

US20040126292A1 - Separation of alkaline salts from industrial byproducts

Info

Publication number: US20040126292A1
Application number: US10/331,044
Authority: US
Inventors: Joel Gutierrez-Antonio; Carlos Fix-Fierro; Armando Garcia-Sanchez
Original assignee: Uniexcel Tech de C V SA
Current assignee: Uniexcel Tech de C V SA
Priority date: 2002-12-28
Filing date: 2002-12-28
Publication date: 2004-07-01
Also published as: MXNL03000053A

Abstract

This invention provides a novel method for separating alkaline salts from industrial byproduct mixtures of solid containing a source of the alkaline salt and a free carbonaceous material. In one embodiment, the industrial byproduct may be a mixture of solid materials that comprises: sodium carbonate, hydrate phases of sodium carbonates, free carbon particulates, water and minor amounts of insoluble materials as impurities. An external source of heat is initially applied to the byproduct mixture to raise the temperature of the free carbon particulates to the ignition point at which time a source of oxygen, introduced into the byproduct mixture, reacts with the heated carbon particulates and combine exothermally to form carbon dioxide gas and autogenously release thermal energy. The autogenously released thermal energy from the carbon-oxygen combustive reaction provides an auto-thermal source heat for the disassociation of the hydrate phases of sodium carbonates into sodium carbonate and water vapor, the evaporation the free water and the volatilization of some of the insoluble materials. The vaporized water and the volatilized materials, together with the carbon dioxide gas, are removed, thereby achieving the separation of the sodium carbonate. As renewed sources of the byproduct mixture are brought in contract with renewed supplies of oxygen, the combustive reaction of the oxygen and carbon particulates is sustained, releasing yet more auto-thermal energy; thereby continuing the separation of the sodium carbonate from the decomposed hydrate phases of sodium carbonate into sodium carbon and vaporized water, the vaporization of the free water, the carbon dioxide gas produced by the combustive reaction and the volatile gases released in the decomposition of insoluble materials.

Description

BACKGROUND OF THE INVENTION

A byproduct mixture obtained from the production of the caprolactam, used in the manufacture of nylon, has been set-aside and confined for a number of years. The byproduct mixture is considered non-toxic, and is, to some extent, water-soluble. However, it may be classified as a pollutant because of the adverse affect the confined bulk stockpile has on the natural surroundings. A vast amount of water and/or land acreage is required to wholly dissolve or suspend all the constituents of the byproduct mixture into benign percentage levels tolerable to both the flora and the fauna.

In one embodiment, the byproduct mixture may contain, on the average, about 41-60 weight-percent of sodium carbonate; the relative corresponding water content is, on the average, about 51-33 weight-percent and it also contains an interesting amount of free carbon particulates, on the average, about 6-9 weight-percent. The remaining constituents consist of traces of other salts and minor amounts of insoluble gangue materials. Sound manufacturing practices necessitate the conversion of this byproduct either into a usable commercial product or the transformation into subcomponents in such a manner that is consistent with acceptable environmental standards and requirements. It is reasonable, therefore, to target the sodium carbonate as a desired recoverable substance because of the relative high percentage presence and the commercial value.

Sodium carbonate, known also as soda ash, is an important chemical compound used extensively in the manufacture of glass, chemicals, soaps and detergents and aluminum, as well as in textile processing, petroleum refining and water softening treatment, among many other uses. Workable processes are known in the art for the separation of the sodium carbonate form the solid byproduct mixture described above. One such process, used extensively in the recovery of chemical substances from their sources, is by the dissolution, filtration, crystallization and evaporation of the source material. Other processes may use spent or unspent activated carbon to concentrate and remove the insoluble gangue materials. These processes are high energy and cost intensive. Therefore, these processes are not considered practical for the separation of the sodium carbonate from the byproduct mixture afore mentioned.

Other methods for the production of desired chemical substances, from either natural source or other industrial byproducts, in either a solid or in a liquid state, rely on the addition of an external source of carbonaceous material that, when ignited, releases thermal energy to drive the production processes. A wide variety of sources exist for carbonaceous material, such as coke, pitch coke, semi-coke, petroleum coke, charcoal, and carbon particulates. Although these processes are looked upon as containing an internal exothermic material, they are strictly speaking non auto-thermal since an external source of thermal energy is added to drive the process, and therein lies the disadvantage in that additional process costs are incurred by the inclusion of external carbonaceous sources. Herein lies the novelty of the present invention

The novel feature of the present invention uses the autogenously free carbon particulates, proper to the source material for providing the thermal energy to drive the separation process. This can be viewed as either an advantage or as a disadvantage. On one side, the method of the present invention can be viewed with a possible disadvantage; wherein it is limited only to those compositions that already contain an ample amount of a carbonaceous source to provide the auto-thermal energy required by the production process. On the other side, there are sources for desired chemical substances, which do contain, therein, suitable amounts of a carbonaceous material to adequately provide the auto-thermal energy necessary to drive the production process. In these cases, the application of the present invention has a distinct and unique advantage not only in the reduction of production costs but also in the effective positive use of resources.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is disclosed an embodiment of the invention that comprises a method for the separation of sodium carbonate from a solid mixture source of sodium carbonate, hydrate phases of sodium carbonate, insoluble impurities, a carbonaceous material, and water; wherein the temperature necessary to drive the separation is provided autogenously. Further, the method of the present invention allows for the efficient utilization of the carbonaceous material, intrinsic to the substance source, to provide the autogenously thermal energy. In this embodiment of the invention, oxygen in atmospheric air is used to react with the carbonaceous material in a confined temperature-controlled environment. The exothermic reaction of the oxygen and the carbonaceous material, contained within the sodium carbonate source, provides the required auto-thermal energy to disassociate the hydrate phases of sodium carbonate, decompose the insoluble impurities into volatile components, evaporate the water and drive off the evaporated water together with the volatilized impurities. By careful controlling of the sodium carbonate source and the oxygen and other operating conditions, the reaction temperature is confined in favor of separating the sodium carbonate without affecting its chemical composition.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 contains a plot of the byproduct sample weight percent loss and the temperature difference versus the temperature rise of an unprocessed byproduct source sample, contained in a muffle furnace in an ambient air environment, with a temperature range between 20-1400° C. [0007]

DETAILED DESCRIPTION OF THE INVENTION

Interestingly, a method for separating the sodium carbonate from the byproduct mixture has been discovered that provides for efficient and economical use of the free carbon particulates, within the byproduct mixture itself, for the calcining of the byproduct mixture and thereby decomposing some of the insoluble materials into volatile components, and vaporizing the water. [0008]
Further and even more interestingly, is has been discovered that the separation of the sodium carbonate can be enhanced by controlling the calcining temperature of the byproduct mixture by regulating the combusting of the free carbon which heretofore would have been discarded for the removal volatile gases and water vapors and by carefully controlling the exothermic reaction of the carbon within the decomposition of the sodium carbonate, the chemical integrity of the sodium carbonate is unaffected. [0009]

EXAMPLE 1

This example illustrates the composition of samples taken from the byproduct mixture source material in the preferred embodiment of the invention. The samples where obtained from various regions in the stockpile of the byproduct source material. The primary constituents in eight samples of the source material were measured applying well-known methods in the art of chemical and physical procedures for the identification of substances, such as ion precipitation, titration of a weak base with a strong acid, atomic absorption among others.

Composition Percentages of Unprocessed Source Samples

Sample Number

	1	2	3	4	5	6	7	8

Na₂CO₃	66.37%	45.11%	54.42%	54.46%	40.05%	43.54%	44.47%	47.79%
H₂O	21.36%	43.77%	38.68%	39.33%	50.00%	46.07%	47.68%	44.90%
Carbon	6.40%	9.49%	5.69%	5.50%	8.92%	9.30%	6.59%	6.63%
Insoluble*	5.87%	1.72%	1.27%	0.65%	0.94%	1.07%	0.94%	0.63%
Total	100.00%	100.09%	100.06%	99.94%	99.91%	99.98%	99.68%	99.94%

EXAMPLE 2

This example illustrates the thermal analyses of a sample of the byproduct source material preformed in a muffle furnace. The method of the thermal analyses is adapted to determine the constituent percent weight loss of the source material and the occurrences of exothermic and endothermic reactions as the source material is heated from room temperature to a predetermined elevated final temperature. Whereas the final temperature is above the thermal decomposition of the primary constituents of the source material; the method of the thermal analyses is also adapted to demonstrate the effect of the calcining the free carbon particulates on the two primary constituents: the sodium carbonate and the water. Two types of tests were performed using the muffle furnace: Thermo Gravimetric Analysis (TGA) and Differential Temperature Analysis (DTA). The operation of muffle furnaces, in the performances of Thermo Gravimetric Analysis and Differential Temperature Analysis, is well known to those well versed and skilled in the art of pyroprocessing systems. The results are obtained from the two graphs in FIG. 1; the percent weight loss curve, [0011] 110, and the difference temperature curve, 120. The test conditions for the operation of the muffle furnace are summarized below.

Muffle Furnace Test Conditions

Final Temperature 1350° C.

Sample Size 7.645 mg

Sample Preparation None

Temperature Ramp

10° C./min

Ambient Environment Static

Atmospheric Air

According to FIG. 1, the weight loss curve, 110, contains three principal regions with significant amounts of weight loss. The first, at 112, a weight loss of about 15 percent at a temperature of about 100° C. is attributed to the vaporization of the water in the source sample. At this same temperature, the difference temperature curve, 120, indicates two thermal reactions: an endothermic reaction, a peak at 122 and endothermic reaction, a valley at 124. The endothermic reaction, at 122, is attributed to the reaction minor impurities in the source material. The exothermic reaction, at 124, is identified with the liquid-vapor phase transition of the water. The second weight loss, between 4 and 5 percent at 114, occurs at a temperature of about 400° C., and is associated with the calcining of the free carbon particulates. The corresponding peak in the difference temperature curve, 120, clearly identifies this region as the exothermic reaction of the free carbon reaction with the ambient air. Finally, at a temperature of about 800° C., a loss in the material source weight begins to take place and terminates roughly at about 1250° C. This weight loss, identified by 118, is attributed to the decomposition of the sodium carbonate. The endothermic reaction, corresponding to the decomposition of the sodium carbonate, is given by the valley, at 128, on the difference temperature curve 120. The results of the thermal analyses are summarized below.

Thermo Gravimetric Analysis & Differential

Temperature Analysis

TGA

DTA

Source	Weight	Item	Temperature	Item
Constituent	Loss	Number	Difference	Number

Water	15%	112	Endothermic	122
Carbon	4%	114	Exothermic	124
Soda	62%	118	Endothermic	128

Accordingly, an object of the invention is to provide a source of oxygen for calcining of the heated free carbon thereby providing the auto-thermal energy to vaporize the water content in the source material and drive of the combustion gases and water vapors. [0013]

EXAMPLE 3

This example illustrate the amount of excess thermal energy released the auto-calcining of the material source by developing the balance of thermal energy provided by the auto-thermal reaction for releasing autogenously energy from the combustion of the free carbon particulates in the source material in an outside source of oxygen, wherein the source of oxygen is ambient air. The development of the energy balance treats the composition weight loss percentages previously identified in Example 2.



Temperature	Source	kcal

Thermal Energy Balance

Tstart

Tend

Constituent

per kg

Constituent	Activity	° C.	° C.	Percentage	Source

Na₂CO₃	Heating	20	100	62%	15.18
H₂O	Heating	20	100	15%	5.76
C	Heating		20	100	4%	0.51
H₂O	Transition	100	100	15%	81.06
Na₂CO₃	Heating	100	400	62%	56.92
H₂O	Heating	100	400	15%	22.5
C	Heating		100	400	4%	1.92
Endothermic Energy					183.85
C	Oxidation		400	400	4%	−313.24
Exothermic Energy					−313.24
Net Thermal Energy					−129.39

As can be observed, the auto-thermal energy provided by the combustion of the free carbon particulates, −313.24 kilocalories per kilogram, far exceeds the amount of thermal energy, 183.85 kilocalories per kilogram, required to raise the temperature of the source material from the base temperature of 20° C. to the combustion temperature of carbon at 400° C. The melting temperature of sodium carbonate being about 856° C., the method of the invention is adapted to provide for the dissipation of the excess thermal heat from the reaction so as to avoid heating the sodium carbonate near its decomposition temperature. The method of the invention is further adapted to select of the granularity of the source material and the regulation of the flow of oxygen so as to control the rate of reaction of the free carbon particulates and thus contain the temperature of the reaction below the decomposition temperature of the sodium carbonate. It is understood that the control of flow of oxygen includes, but is not limited, to the metering of both the volume and the velocity of the oxygen. Although there exists an art for calcining materials: such as fluidize beds, incline or vertical reactors and others, the method of the invention is yet further adapted to extend this art and thereby control the air source; drive the free carbon oxygen exothermic reaction; and maintain the reaction temperature below the critical decomposition temperature of the sodium carbonate. [0015]
The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood to those well versed and skilled in the art that variations and modifications can be effected without departing from the scope and spirit of the invention. The applicants intend that the clams shall not invoke the application of 35 U. S. C. §112, ¶ 6 unless the claim is explicitly written in means-plus-function or step-plus-function format. [0016]

Claims

We claim:

1. A method for separating an alkaline salt from a solid mixture industrial byproduct that at least comprises: a source of the alkaline salt, hydrate phases of the alkaline salt, a source of a free carbonaceous material, insoluble impurities and water, whereby the carbonaceous material in the mixture is used autogenously to provided auto-thermal energy for the separation; said method comprising the steps of:

a) applying an external heat source to the mixture, thus raising the temperature of the mixture to the ignition point the free carbonaceous material; and

b) infusing the mixture with oxygen; and

c) combusting or oxidizing the free carbonaceous material in the mixture; and

d) converting the free carbonaceous material and oxygen into carbon dioxide gas and thermal energy; and

e) heating the mixture by the autogenously thermal energy provided by the combustion of the free carbonaceous material; and

f) regulating the rate of the thermal reaction of the free carbonaceous material by adjusting the amount of infused oxygen; and thereby

g) controlling the temperature of the mixture to levels below the decomposition point of the alkaline salt; and thus

h) converting the hydrates of the alkaline salt to free alkaline salt and water vapor; and

i) converting the free water into water vapor; and

j) decomposing some of the insoluble materials; and

k) volatilizing the decomposed insoluble materials; and

l) removing the carbon dioxide gas, water vapor, and volatilized material; and thereby.

m) recovering the free alkaline salt.

2. The method wherein the preferred embodiment of the invention, the alkaline salt is sodium carbonate.

3. The method of claim 2, wherein the temperature of the mixture is raised to ignite the free carbonaceous material.

4. The method of claim 2, wherein the ignited free carbonaceous material enters a sustained combustion state.

5. The method wherein a source of oxygen is infused into the ignited free carbonaceous material.

6. The method of claim 5, wherein the reaction of the free carbonaceous material with the oxygen converts the free carbonaceous material into carbon dioxide gas.

7. The method of claim 5, wherein the combustion of the free carbonaceous material provides autogenously thermal energy to the mixture.

8. The method of claim 5, wherein the amount of oxygen infused into the mixture is adjusted to control the temperature of the mixture.

9. A method, wherein the temperature of the mixture is regulated to supports the continuous and efficient recovery of the sodium carbonate.

10. The method of claim 9, wherein the regulated temperature of mixture supports the transition of the hydrate phases of the sodium carbonate into sodium carbonate and water.

11. The method of claim 9, wherein further the regulated temperature of the mixture is below the softening point of sodium carbonate.

12. The method wherein maintaining the temperature of the sodium carbonate below the softening point prevents the formation of agglomerates of sodium carbonate.

13. The method of claim 12, wherein the separation of the sodium carbonate is efficient and continuous by the prevention of formation of agglomerates of sodium carbonate.

14. A method, wherein the carbon dioxide gas is driven off the mixture.

15. A method, wherein the water in the mixture is vaporized and driven off the mixture.

16. A method, wherein some of the insoluble material is decomposed.

17. A method, wherein the decomposed insoluble material is volatilized and driven off the mixture.