Method and apparatus for the enhanced separation of calcium eggshell from organic membrane

Abstract

A method and system is provided to separate calcium carbonate inorganic eggshell from the inner lining of organic protein-based membrane in eggshell by-product. The method involves three phases: mechanical agitation/separation, functional chemical digestion and refining chemical digestion. In the mechanical stage, agitation and sieving are used to remove large pieces, and the majority of, membrane material. In the functional chemical digestion stage, the by-product is processed through at least one basic solution to remove additional organic membrane and impurities. In the refining chemical digestion stage, the remaining organic membrane and impurities are removed. The purified calcium carbonate is then rinsed and dried, in preparation for further refinement and processing to finished goods specifications.

Claims

1. A method for the separation of calcium carbonate from an eggshell by-product comprising the steps of: a. Agitating the eggshell by-product; b. Sieving the eggshell by-product resulting from step a; c. Subjecting the eggshell by-product resulting from step b to a functional digestion with a first base solution at a temperature of at least 30 degrees Celsius and a residence time of at least 15 minutes, wherein the first base solution is primarily sodium hydroxide mixed with water; d. Subjecting the eggshell by-product resulting from step c to a refining digestion with a second base solution; wherein the refining digestion with a second base solution comprises a solids loading between 15-45% solids by volume, ambient temperature, 6%-12% sodium hypochlorite mixed in water by weight with less than 1% sodium hydroxide, with fluidization and a residence time of between 10 and 40 minutes; and e. Running the eggshell by-product resulting from step d through a washing stage using water to obtain calcium carbonate.

2. The method of claim 1 where the step of subjecting the eggshell by-product to the functional digestion comprises digestion with between 15-45% solids loading, a temperature between 30 to 90 degrees Celsius, and 0.5 to 5% sodium hydroxide solution mixed in water by weight, with fluidization and a residence time between 15 min to 60 min.

3. The method of claim 1 where the step of subjecting the eggshell by-product to the functional digestion comprises digestion with 15% solids loading by volume, a temperature of 60 degrees Celsius, a 2.5% sodium hydroxide solution mixed in water by weight, with fluidization, and a residence time of 30 minutes.

4. The method of claim 1 where the step of subjecting the eggshell by-product to the refining digestion comprises a 30% solids loading by volume, with an 8% sodium hypochlorite solution mixed in water by weight, at ambient temperature, with fluidization, with a residence time of between 10 to 15 minutes.

5. The method of claim 1 wherein the obtained calcium carbonate has a purity of greater than 98%.

6. The method of claim 1 wherein the obtained calcium carbonate has less than 2% impurities excluding water.

7. A method for the separation of calcium carbonate from an eggshell by-product comprising the steps of: a. Agitating the eggshell by-product using a ball mill for between 5 and 40 minutes; b. Sieving the eggshell by-product with a sieve with a mesh size between of an inch and of an inch; c. Subjecting the eggshell by-product to a functional digestion with a NaOH solution comprising digestion with between 15-45% solids loading, a temperature between 30 to 90 degrees Celsius, and 0.5 to 5% NaOH in water, with fluidization, and a residence time between 15 min to 60 min. d. Subjecting the eggshell by-product to a refining digestion with a NaClO solution comprising digestion with a solids loading between 15-45% solids by volume, ambient temperature, 6%-10% NaClO mixed in water by weight with less than 1% NaOH, with fluidization, and a residence time of between 10 and 40 minutes; and e. Running the eggshell by-product through a washing stage using water to obtain calcium carbonate.

8. The method of claim 7 wherein the obtained calcium carbonate has a purity of greater than 98%.

9. The method of claim 7 wherein the obtained calcium carbonate has less than 2% impurities excluding water.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic illustrating the steps of the process for separating eggshell from membrane.

(2) FIG. 2 is an elevation view of one embodiment of a system to implement the process;

(3) FIG. 3 is an aerial view of the embodiment illustrated in FIG. 2.

DETAILED DESCRIPTION

(4) The process that is the subject of this patent works with a wide variety of liquid egg discharged by-product products. It can process both shell material that has or has not passed through a centrifuge, and material that has small amounts of liquid egg remaining. The method will also operate when there is little to no liquid egg remaining in the by-product feedstock.

(5) Turning to FIG. 1, the first stage of this process begins with newly discarded eggshell by-product 10, which is waste to egg breaking companies, containing shell and organic membrane. As a general matter, the shell may or may not be ground, and the organic membrane may or may not have been subject to some sort of separation process at the supplier (i.e. before it enters the present system). The present method can process by-product with wide variations without the need to recalibrate or vary the process.

(6) In step 12, the by-product 10 is agitated to loosen the membrane from the shell aiding the effectiveness of the subsequent sieving step(s) via this initial mechanical separation of membrane and shell.

(7) This agitation may be accomplished by numerous types of equipment. The agitation may be accomplished by milling the incoming by-product. In a preferred embodiment, the mill is a ball mill that produces material with a diameter of no greater than 5 mm. Testing shows that with such a ball mill, sufficient separation can be achieved by between 5 and 60 minutes of milling. In a preferred embodiment, the separation is achieved by milling for 20 minutes.

(8) Although the primary goal of stage 12 is agitation and the resulting separation of the membrane and shell, some size reduction of the shell will take place as a by-product of this stage. This reduction can assist in the efficient sieving in the next step 14.

(9) In step 14, the discharged material from step 12 is sieved to separate larger pieces of organic membrane from smaller pieces of membrane and shell. Generally, as more organic membrane is removed at this stage, the subsequent digestion stage can become more efficient, proficient and cost-effective.

(10) Generally, the sieving is best done through one or more screens or sieves. Flowing water may be added to aid in the screening/sieving of preliminarily separated membrane material and shell.

(11) In a preferred embodiment, the sieving will use one or more mesh screens with each having a mesh size of of an inch to of an inch, with flowing water. In another preferred embodiment, the sieves are tiered with decreasing mesh sizes, culminating in a sieve with a mesh size of of an inch to of an inch.

(12) The discharge of membrane and shell that has successfully passed through the sieving step will then pass on to the chemical phase of the process, step 18. The membrane material that is removed by the sieving and is discharged from this process, indicated by 15 in FIG. 1, will account for approximately 3%-7% of the by-product 10, by weight. This membrane material 15 can be dried, preserved and further processed into a value-added saleable product.

(13) Steps 12 and 14 comprise the mechanical portion of the process, indicated by 16 on FIG. 1.

(14) In step 18, the sieved material is put through a digestion process comprised of at least two digestion steps using base solutions to remove remaining organic membrane and other impurities from the calcium carbonate (or shell). Many variations of which bases to employ, how many digestion steps to use, and the processing conditions are possible. The processing conditions include the solids content (as a percent of volume), the temperature of the base solution, the concentration of the base solution, the residence time, and the presence of agitation or fluidization.

(15) A preferred embodiment has a functional digestion step 20, intended to remove the bulk of organic membrane (left after the sieving step 14) from the shells, and a refining digestion step 22, which is intended to remove the remaining traces of organic membrane as well as any other (non-membrane) organic impurities. The functional digestion step 20 could be performed with sodium hydroxide, ammonium hydroxide, potassium hydroxide, or an organic base. The functional digestion step could also be performed with a combination of bases. In a preferred embodiment, the functional digestion step 20 uses sodium hydroxide and the refining digestion step 22 uses sodium hypochlorite.

(16) In a preferred embodiment of step 20, after being screened through the screener/sifter in step 14, the remaining sieved pieces of shell and membrane will be conveyed via mechanical and/or pneumatic conveyance to a steel tank fitted with an agitation apparatus containing a solution between 0.5 and 5% sodium hydroxide (NaOH) mixed in water, by weight. In a preferred embodiment, the solution is 2.5% sodium hydroxide (NaOH) mixed in water, by weight. The sodium hydroxide solution should be slightly warmer than ambient room temperature, and testing shows that the process works well at between 30 and 90 degrees Celsius. In a preferred embodiment, the temperature of the NaOH solution is 60 degrees Celsius.

(17) The amount of solids loading (solids to liquid ratio) in step 20 will vary depending on desired operation time and volume required, but tests have shown that it should remain within a basic range of 15%-60% solids loading by volume. The desirable and effective residence time in the solution will also depend on application needs, and the temperature of the solution.

(18) Tests have shown that an NaOH digestion step with between 15-45% solids loading, a temperature between 30 to 90 degrees Celsius, and 0.5 to 5% NaOH in H.sub.2O and a residence time between 15 min to 60 min will work. In a particularly preferred embodiment, tests have shown that at 15% solids loading by volume and a temperature of 60 degrees Celsius and a 2.5% sodium hydroxide (NaOH) solution mixed in water (by weight), a residence time of 30 minutes will be effective for this stage of separation.

(19) All remaining eggshell material at the end of functional digestion step 20 will be discharged and conveyed to the refining digestion step 22.

(20) In a preferred embodiment of refining digestion step 22, the remaining shell product will be conveyed via mechanical and/or pneumatic conveyance to a steel tank fitted with an agitation apparatus containing a base solution. In a preferred embodiment, the solution is a sodium hypochlorite solution. The sodium hypochlorite solution will work to remove any remaining membrane via digestion, as well as any other (non-membrane) organic impurities. Residence time and solids loading by weight can vary, however tests have shown that a high level of purity can be achieved with a solids loading between 15-45% solids by volume, ambient temperature, 6%-12% sodium hypochlorite (NaClO) mixed in water (by weight) with trace elements (less than 1%) of sodium hydroxide (alkaline solution) and an residence time of between 10 and 40 minutes.

(21) In a particularly preferred embodiment (based on tests), step 22 has a 30% solids loading (by volume), with an 8% NaClO solution (mixed in water by weight), at ambient temperature, with fluidization/agitation, for a residence time of 10-15 minutes.

(22) It is also possible for the solution in the refining digestion step to contain a mixture of bases, including mixtures of sodium hypochlorite with sodium hydroxide, ammonium hydroxide, potassium hydroxide, or an organic base.

(23) The sodium hydroxide and sodium hypochlorite digestion stages 20 and 22 discussed above, working in tandem as a functional digestion followed by a refining digestion, act to achieve a high level of calcium carbonate purity via the digestion of organic membrane and purification of the shell. However, these stages 20 and 22 may be used independently of one another, and can each achieve a high level of purity in isolation, albeit lower than the purity achieved by the two steps together.

(24) A re-circulation and/or drainage system may be built-in to the system used in steps 20 and 22 (or more broadly step 18) to accommodate the drainage and refilling of the digestion solutions upon the liquid becoming saturated and/or diluted from excessive batch use.

(25) After digestion in step 18, the remaining shell material will be conveyed via mechanical and/or pneumatic conveyance to a water rinsing stage 24 where it will pass through a water bath or spray to remove any remaining surface sodium hypochlorite or related salts (sodium chloride) (and surface NaOH, if any) from the shell.

(26) At this stage, a high purity calcium carbonate has been achieved, albeit in the presence of water (for many purposes, the water will need to be removed as seen in the next stage).

(27) From the water-rinsing phase, the material will typically be passed through a drying device in step 26 to remove any excess moisture. Equipment that could be used in this stage includes a range of different drying technologies. In a preferred embodiment, a rotary dryer is used. In a preferred embodiment, the dryer operates within a temperature range of 50 Degrees to 350 Degrees. It is important to not perform the drying stage in such a way as to calcine the calcium carbonate; generally, the temperature should be kept below 800 degrees Celsius.

(28) The method described herein can produce a calcium carbonate product 28 in flake form with a purity between 99% and 100% calcium carbonate. The shell product can be packaged as is into various forms of sanitary packaging, or further passed through a mill capable of fine grinding to wide-ranging particle size distributions, followed by finished goods packaging, depending upon the target market(s) and/or application(s).

(29) An analysis of a representative final product from this process is given in Table 1. In some specific experimental runs, this method has resulted in calcium carbonate purity (measured using thermographic metric analysis) of 100%, with all impurities being below detectable limits.

(30) In principle, the functional and refining digestion stages 20 and 22 can be used without the initial agitation and/or sieving steps to achieve a high purity calcium carbonate product. However, this approach would be more costly than an approach that incorporates the agitation and sieving steps, since the agitation and sieving steps will remove membrane that otherwise would need to be removed through more aggressive and costly digestion.

(31) TABLE-US-00001 TABLE 1 Chemical Composition Breakdown - Calcium Carbonate Test Method Compound Symbol Compound Name Results Thermographic Metric Analysis (TGA) CaCO3 Calcium Carbonate 98.3% MgCO3 Magnesium Carbonate 0.23% Infrared Spectroscopy TOC Total Organic Carbon 0.0052% XRF & ICP LOI @1000 C. Loss on Ignition (Weight) 43.99% X-Ray Fluorescence CaO Calcium Oxide 54.4% Inductively Coupled Plasma MgO Magnesium Oxide 0.49% SiO2 Silicon Dioxide (Silica) 0.33% Al203 Aluminum Oxide <0.1% Fe2O3 Iron Oxide <0.01% Na2O Sodium Oxide 0.01% K2O Potassium Oxide <0.01% TiO2 Titanium Dioxide <0.01% MnO Manganese <0.001% SrO Strontium Oxide (Strontia) 0.019% P2O5 Phosphorous Pentoxide 0.31% S Sulfur 0.021% Instrumental Neutron Activation Analysis Cl Chlorine NMT 0.01% AMS Fe Iron <0.001% Accelerator Mass Spectrometry As Arsenic 1.9 ppm Ba Barium 10.7 ppm Cd Cadmium 0.02 ppm Cr Chromium <1 ppm Pb Lead 0.07 ppm F Fluorine Not Detected Cold Vapor Hg Mercury Not Detected Hunter Brightness L Scale 94.3 a Scale 0.02 b Scale 3.73

(32) Optionally, after the sieving stage but before the digestion stage, further membrane may be removed from the feedstock by burning. There are several devices known to persons skilled in the art that could be used for this step, including flash dryers. However, this step is disfavored, since such burning is necessarily an expensive process, and tends to produce a calcium carbonate product that is greyish in colour and thus unacceptable in many markets. It is also unnecessary, since a high purity calcium carbonate product can be achieved using the method described above without this step. If this step was to be used, care needs to be taken to avoid calcining the calcium carbonate, which occurs at temperatures approaching 800 degrees Celsius, and also occurs at a slower rate at lower temperatures.

(33) FIGS. 2 and 3 illustrate a system implementation of the invention. Turning to FIG. 2, the newly discarded eggshell by-product, containing inorganic shell and organic membrane, is introduced into an agitator 50. Numerous types of equipment known to those skilled in the art may be used as an agitator 50. One type of equipment that may be used is a milling machine. In a preferred embodiment, the agitator 50 is a ball mill that produces material with a diameter of no greater than 5 mm. Testing shows that with such a ball mill, sufficient separation can be achieved after between 5 and 60 minutes. In a preferred embodiment, the separation is achieved by agitating for 20 minutes.

(34) The discharged material from agitator 50 is passed to a sieving device 52. Optionally (and not illustrated), the discharged material may rest in a holding tank before being passed to a sieving device 52. In a preferred embodiment, the sieving device has a single sieve with a mesh size of of an inch to of an inch, optionally with flowing water to assist in moving the material. In another preferred embodiment, the sieving will use a multi-layer mesh screen with multiple sieves each having a mesh size of of an inch to of an inch, optionally with flowing water to assist in moving the material. In another preferred embodiment, the sieves are tiered with decreasing mesh sizes, culminating in a sieve with a mesh size of of an inch to of an inch, optionally with flowing water.

(35) The organic membrane material that is removed by sieving device 52 is discharged into device 54. Device 54 may be any desirable device for the further processing, holding, or disposal of the organic membrane material that is removed by sieving device 52.

(36) The shell and remaining organic membrane that has passed through sieving machine 52 is passed to a functional digester 56 which uses a base mixed with water. Optionally (and not illustrated), the discharged material may rest in a holding tank before being passed to the functional digester 56. In a preferred embodiment, the shell and remaining organic membrane that has passed through sieving machine 52 are conveyed via mechanical and/or pneumatic conveyance to functional digester 56. In a preferred embodiment, functional digester 56 is a steel tank fitted with an agitation apparatus containing a solution of sodium hydroxide (NaOH) mixed in water. In other embodiments, the solution may be ammonium hydroxide mixed in water, potassium hydroxide mixed in water, an organic base mixed in water, or a mixture of these possible bases (sodium hydroxide, ammonium hydroxide, potassium hydroxide, an organic base) mixed in water.

(37) In a preferred embodiment, the functional digester 56 is implemented with a solids loading of between 15-45% (by volume), a temperature between 30 to 90 degrees Celsius, a 0.5 to 5.0% NaOH mixed in water solution (by weight) and a residence time between 15 minutes to 60 minutes. In a particularly preferred embodiment, the functional digester 56 is implemented at 15% solids loading by volume and a temperature of 60 degrees Celsius and a 2.5% sodium hydroxide (NaOH) solution mixed in water (by weight) and a residence time of 30 minutes.

(38) All shell and remaining membrane material after processing through functional digester 56 is then conveyed to refining digester 58 which uses a second base (not the same as the base used in the functional digester) mixed with water. Optionally (and not illustrated), the discharged material may rest in a holding tank before being passed to the refining digester 58. In a preferred embodiment, the shell and remaining organic membrane that has passed through functional digester 56 is conveyed via mechanical and/or pneumatic conveyance to refining digester 58. In a preferred embodiment, refining digester 58 is a steel tank fitted with an agitation apparatus containing a solution of sodium hypochlorite (NaClO) mixed in water.

(39) In a preferred solution, the refining digester 58 is configured so the incoming material has a residence time of between 10 and 40 minutes, solids loading between 15-45% solids by volume, ambient temperature, and a 6%-12% sodium hypochlorite (NaClO) mixed in water (by weight) with trace elements (less than 1%) of sodium hydroxide (alkaline solution).

(40) In a particularly preferred embodiment, refining digester 58 is configured to operate at a 30% solids loading (by volume), with an 8% NaClO solution (mixed in water by weight), at ambient temperature, with fluidization, for a residence time of 10-15 minutes.

(41) In another embodiment, the solution used in refining digester 58 is sodium hypochlorite plus one or more additional bases mixed with water. The additional bases may include sodium hydroxide, ammonia hydroxide, potassium hydroxide, or organic bases.

(42) A re-circulation and/or drainage system (not illustrated) may be built-in to digesters 56 and 58 to accommodate the drainage and refilling of the digestion solutions upon the liquid becoming saturated and/or diluted from excessive use.

(43) After digestion in the refining digester 58, the remaining shell material will be conveyed to a water rinse 60. Optionally (and not illustrated), the shell material may rest in a holding tank before being passed to the water rinse 60. The water rinse may be any water bath or spray known in the art that will remove any remaining surface sodium hypochlorite or related salts (sodium chloride) (and surface NaOH, if any) from the shell. In a preferred embodiment, the shells pass via mechanical and/or pneumatic conveyance through water rinse 60.

(44) At this stage, a high purity calcium carbonate has been achieved, albeit in the presence of water (for many purposes, the water will need to be removed as seen in the next stage).

(45) From water rinse 60, the shell material is passed through a drying device 62 to remove any excess moisture. Optionally (and not illustrated), the shell material may rest in a holding tank before being passed to the drying device 62. Many types of drying equipment are known to a person skilled in the art and could be used as drying device 62. In a preferred embodiment, drying device 62 is a rotary dryer. In a preferred embodiment, the drying device 62 operates within a temperature range between 50 degrees to 350 degrees Celsius. It is important to not perform the drying stage at a temperature that would calcine the calcium carbonate; generally, the temperature should be kept well below 800 degrees Celsius.

(46) The system and apparatus described above can produce a calcium carbonate product in flake form with a purity between 98% and 100% calcium carbonate.

(47) The calcium carbonate can then be subject to further processing as desired for the end-market. The calcium carbonate product can be packaged as is into various forms of sanitary packaging, or further passed through a mill capable of super-fine grinding to a smaller/finer particle sizes, followed by finished goods packaging, depending upon the target market and/or application.

(48) Although the foregoing description and accompanying drawings relate to specific preferred embodiments of the present invention as presently contemplated by the inventor, it will be understood that various changes, modifications and adaptations may be made without departing from the spirit of the invention.