Method and device for separating and purifying glycolic acid rectification crystallization coupling technology and application
阅读说明：本技术 乙醇酸精馏结晶耦合技术分离提纯的方法、装置及应用 (Method and device for separating and purifying glycolic acid rectification crystallization coupling technology and application ) 是由 金鑫 王元杲 由振超 严文娟 孟可馨 葛会端 张广宇 金有海 杨朝合 杜峰 于 2021-10-21 设计创作，主要内容包括：本发明属于乙醇酸分离提纯技术领域,公开了乙醇酸精馏结晶耦合技术分离提纯的方法、装置及应用。利用生物基平台化合物分子作为原料合成乙醇酸,然后利用精馏结晶耦合技术对获得的粗乙醇酸分离提纯,获得高纯度乙醇酸。本发明开创了乙醇酸新合成路线下的体系分离提纯,本技术的难点在于,乙醇酸在浓缩过程中易聚合,因此对减压精馏的设备设计以及工艺参数的调整有着技术壁垒。同时,在结晶过程中,对结晶釜的设备设计以及工艺参数的调整有着技术壁垒。本发明具有操作工艺简单、方便,分离提纯效果好,工作效率高等优点。且成本低廉,具有较高的市场前景。(The invention belongs to the technical field of glycolic acid separation and purification, and discloses a method and a device for separating and purifying glycolic acid by a rectification crystallization coupling technology, and an application of the method and the device. The glycolic acid is synthesized by using bio-based platform compound molecules as raw materials, and then the obtained crude glycolic acid is separated and purified by using a rectification crystallization coupling technology to obtain the high-purity glycolic acid. The invention creates system separation and purification under a new synthetic route of the glycollic acid, and the technical difficulty is that the glycollic acid is easy to polymerize in the concentration process, so that the invention has technical barriers to the design of equipment for vacuum rectification and the adjustment of process parameters. Meanwhile, in the crystallization process, there is a technical barrier to the equipment design and the adjustment of process parameters of the crystallization kettle. The invention has the advantages of simple and convenient operation process, good separation and purification effect, high working efficiency and the like. And the cost is low, and the market prospect is high.)
1. A method for separating and purifying a bio-based glycolic acid rectification crystallization coupling technology is characterized by comprising the following steps:
the glycolic acid is synthesized by using bio-based platform compound molecules as raw materials, and then the obtained crude glycolic acid is separated and purified by using a rectification crystallization coupling technology to obtain the high-purity glycolic acid.
2. The method for separating and purifying by coupling technology of rectification and crystallization of biobased glycolic acid according to claim 1, characterized in that the method for separating and purifying by coupling technology of rectification and crystallization of biobased glycolic acid specifically comprises the following steps:
step one, preparing crude glycolic acid by using bio-based platform compound molecules as raw materials: converting the platform compound molecules by using a supported catalyst to synthesize crude glycolic acid;
and step two, rectifying and concentrating the obtained crude glycolic acid: concentrating the crude ethanol acid solution in a rectifying tower to more than or equal to 70 wt% by utilizing a vacuum rectification technology;
step three, cooling and crystallizing the concentrated solution, and filtering to obtain high-purity glycolic acid crystals: crystallizing glycolic acid in a crystallization kettle coupled in series with a rectifying device, and filtering and separating to obtain a high-purity glycolic acid product.
3. The method for separating and purifying by coupling technology of rectification and crystallization of biobased glycolic acid according to claim 1, wherein the step one of preparing crude glycolic acid by using a biobased platform compound molecule as a raw material further comprises: the method comprises the steps of reacting ethylene glycol bio-based platform compound molecules serving as raw materials at 80 ℃ for 10 hours by utilizing a Pt/C catalyst to obtain a crude glycolic acid solution.
4. The method for separation and purification by coupling technology of rectification and crystallization of biobased glycolic acid according to claim 1, wherein in the first step, the molecules of the biobased platform compound comprise one or more of ethylene glycol, glyoxal, glyoxylic acid compound, glycerol, butanediol polyuronic acid compound and cellulose.
5. The method for separating and purifying biobased glycolic acid rectification crystallization coupling technology according to claim 1, wherein in the step one, the crude glycolic acid comprises one or more of glycolic acid, glycolaldehyde, ethylene glycol, glyoxal, glyoxylic acid, oxalic acid, formic acid, sorbitol, propylene glycol, butanediol, cellulose, glycerol and lactic acid polyuronic acid compounds.
6. The method for separating and purifying biobased glycolic acid rectification crystallization coupling technology according to claim 1, wherein the step two of rectifying and concentrating the obtained crude glycolic acid further comprises the following steps: carrying out reduced pressure rectification and concentration on the 35 wt% of crude glycolic acid solution until the mass fraction is more than or equal to 70 wt%, wherein the rectification and concentration temperature is 20-250 ℃, and the rectification pressure is 0-10 MPa; wherein the feeding temperature of the rectifying tower is 30 ℃, the number of tower plates is 25, the reflux ratio is 0.32, the temperature of the tower bottom is 60 ℃, and the tower counter pressure is 0.29 MPa;
the rectification concentration method comprises one or more modes of common distillation, normal-pressure rectification, reduced-pressure rectification and molecular rectification which are connected in series.
7. The method for separating and purifying biobased glycolic acid rectification crystallization coupling technology according to claim 1, wherein in the third step, the crystallization method comprises one or more of cooling crystallization, evaporative crystallization, sublimation crystallization and recrystallization in series;
the step of cooling, crystallizing and filtering the concentrated solution to obtain the high-purity glycolic acid crystals further comprises the following steps: crystallizing the obtained glycolic acid concentrated solution in a crystallization kettle, wherein the crystallization temperature of cooling crystallization and recrystallization is-20-40 ℃, the cooling rate is 0.1-20 ℃/min, the stirring rate during cooling is 100-1500r/min, and the amount of glycolic acid seed crystal added accounts for 0.01-20% of the glycolic acid in the concentrated solution; the temperature of evaporative crystallization and sublimation crystallization is-20-200 ℃.
8. Glycolic acid is obtained by the method for separation and purification by the coupling technology of rectification and crystallization of biobased glycolic acid according to any one of claims 1 to 7.
9. A rectification crystallization coupling separation and purification device for realizing the separation and purification method of the bio-based glycolic acid rectification crystallization coupling technology according to any one of claims 1 to 7, wherein the rectification crystallization coupling separation and purification device comprises: a reduced pressure rectifying tower and a crystallization kettle;
the inside of the reduced pressure rectifying tower is welded with a rectifying tower plate, the upper part of the reduced pressure rectifying tower is connected with a condenser through a pipeline, and the lower part of the reduced pressure rectifying tower is connected with a reboiler and a crystallization kettle through pipelines;
the upper part of the crystallization kettle is provided with a crystallization kettle temperature controller and a condensed water circulator; and a mechanical stirring device is arranged in the crystallization kettle.
10. An application of the method for separating and purifying by the coupling technology of rectification and crystallization of biobased glycolic acid as claimed in any one of claims 1 to 7 in the preparation of rust removal and decontamination agents.
Technical Field
The invention belongs to the technical field of glycolic acid separation and purification, and particularly relates to a method, a device and application for separating and purifying glycolic acid by a rectification crystallization coupling technology.
Background
Glycolic acid, also known as glycolic acid, is a colorless, deliquescent crystal. Glycolic acid is readily soluble in water and organic solvents such as methanol, ethanol, ethyl acetate, etc., is slightly soluble in diethyl ether, and is insoluble in hydrocarbons. Glycolic acid has both of alcohol and acid, and decomposes when heated to a boiling point.
At present, glycolic acid is mainly prepared by coal, petroleum and natural gas routes, and the routes require high-temperature and high-pressure operating conditions and consume huge energy. These high CO levels are proposed by carbon peaking, carbon balancing programs2The technical route of discharge does not conform to the current trend of development. While a route for the synthesis of glycolic acid by means of bio-based platform compound molecules through a green, low-energy route has been developed, the impurities in the glycolic acid obtained are different from the traditional route.
The prior glycolic acid separation technology mainly adopts a molecular rectification method, and the method has the defects of complex operation, high equipment investment, low separation efficiency and the like. The technology for the isolation of glycolic acid systems synthesized by the bio-based route has not been proposed so far.
Through the above analysis, the problems and defects of the prior art are as follows:
(1) because glycolic acid is easy to polymerize in the concentration process, the prior art can not effectively adjust the equipment and process parameters of the vacuum rectification, so that the glycolic acid separation and purification effect is poor.
(2) The glycolic acid is poor in separation and purification effect because the equipment of a crystallization kettle and process parameters are not adjusted in the crystallization process of the glycolic acid.
(3) The prior art has complex glycolic acid preparation process, low working efficiency and high cost.
The difficulty in solving the above problems and defects is: the need of providing a new process for separating and purifying bio-based glycolic acid is mainly reflected in the design of a coupling device and the adjustment of process parameters, and the process is simulated and optimized. The significance of solving the problems and the defects is as follows: can improve the separation and purification effect of the bio-based glycolic acid and provide process guidance for the purification of other bio-based glycolic acids.
Disclosure of Invention
In order to overcome the problems in the related art, the disclosed embodiment of the invention provides a method, a device and an application for separating and purifying a glycolic acid rectification crystallization coupling technology, and particularly relates to a method for separating and purifying a bio-based glycolic acid rectification crystallization coupling technology.
The technical scheme is as follows: a method for separating and purifying bio-based glycolic acid by rectification crystallization coupling technology comprises the following steps:
step one, preparing crude glycolic acid by using bio-based platform compound molecules as raw materials. The method comprises the specific steps of carrying out green conversion on platform compound molecules by using a supported catalyst to synthesize crude glycolic acid, for example, reacting the ethylene glycol bio-based platform compound molecules serving as a raw material for 10 hours at 80 ℃ by using a Pt/C catalyst to obtain a crude glycolic acid solution.
And step two, rectifying and concentrating the obtained crude glycolic acid to 70 wt% or more. The method comprises the specific steps of concentrating the crude ethanol acid solution in a rectifying tower by using a vacuum rectification technology, wherein the crude ethanol acid solution with the mass fraction of 35 wt% is subjected to vacuum rectification, the feeding temperature of the rectifying tower is 30 ℃, the number of tower plates is 25, the reflux ratio is 0.32, the tower bottom temperature is 60 ℃, and the tower counter pressure is 0.29 MPa.
And step three, cooling and crystallizing the concentrated solution, and filtering to obtain high-purity glycolic acid crystals. Crystallizing glycolic acid in a crystallization kettle coupled with a rectifying device in series, filtering and separating to obtain a high-purity glycolic acid product, for example, crystallizing the obtained glycolic acid concentrated solution in the crystallization kettle at the crystallization temperature of-15 ℃, the cooling rate of 0.5 ℃/min, the stirring speed of 400r/min, and the addition amount of glycolic acid seed crystals of 1 wt%.
In one embodiment, the bio-based platform compound molecules of step one include one or more of glycol acid compounds such as ethylene glycol, glyoxal, and oxalic acid, polyol acid compounds such as glycerol and butanediol, and cellulose.
In one embodiment, the crude glycolic acid in step one comprises one or more of glycolic acid, glycolaldehyde, ethylene glycol, glyoxal, glyoxylic acid, oxalic acid, formic acid, sorbitol, propylene glycol, butylene glycol, cellulose, glycerol, lactic acid and other polyaluronic acid compounds.
In one embodiment, the crude glycolic acid concentration of step one is from 0.5 to 99 wt%.
In one embodiment, the rectification concentration method in the second step includes one or more modes of common distillation, atmospheric rectification, vacuum rectification, molecular rectification and the like in series. The rectification concentration temperature is 20-250 ℃, and the rectification pressure (absolute pressure) is 0-10 MPa.
In one embodiment, the crystallization method in the second step includes one or more of temperature reduction crystallization, evaporative crystallization, sublimation crystallization, recrystallization and the like in series.
In one embodiment, the crystallization temperature of the temperature reduction crystallization and the recrystallization is-20-40 ℃, the temperature reduction rate is 0.1-20 ℃/min, the stirring rate during temperature reduction is 100-1500r/min, and the content of the glycolic acid seed crystal added accounts for 0.01-20% of the glycolic acid in the concentrated solution.
The temperature of the evaporative crystallization and the sublimation crystallization is-20 to 200 ℃.
In one embodiment, the present invention preferably converts bio-based platform compound molecules to glycolic acid in a mild green manner. The obtained crude glycolic acid was concentrated by rectification under reduced pressure at 50 ℃ under an absolute pressure of 0.5MPa to 70% by weight. And cooling and crystallizing the obtained concentrated solution, wherein the cooling rate is 0.5 ℃/min, the crystallization temperature is-20 ℃, the stirring speed is 800r/min, and the amount of the glycolic acid seed crystal added accounts for 2% of the amount of glycolic acid in the concentrated solution.
The invention also aims to provide glycolic acid which is obtained by a method for separating and purifying the bio-based glycolic acid by rectification crystallization coupling technology.
Another object of the present invention is to provide a rectification crystallization coupling separation purification apparatus, which includes: a reduced pressure rectifying tower and a crystallization kettle;
the inside of the reduced pressure rectifying tower is welded with a rectifying tower plate, and the upper part of the reduced pressure rectifying tower is connected with a condenser through a pipeline; the lower part is connected with a reboiler and a crystallization kettle through pipelines; a crystallization kettle temperature controller and a condensed water circulator are arranged at the upper part of the crystallization kettle; and a mechanical stirring device is arranged in the crystallization kettle.
The invention also aims to provide the application of the separation and purification method of the bio-based glycolic acid rectification crystallization coupling technology in preparation of rust removal and detergents.
By combining all the technical schemes, the invention has the advantages and positive effects that:
the glycolic acid of the invention is synthesized by using bio-based platform compound molecules as raw materials, and then the obtained crude glycolic acid is separated and purified by using a rectification crystallization coupling technology to obtain the high-purity glycolic acid.
The invention creates system separation and purification under a new synthetic route of the glycollic acid, and the technical difficulty is that the glycollic acid is easy to polymerize in the concentration process, so that the invention has technical barriers to the design of equipment for vacuum rectification and the adjustment of process parameters. Meanwhile, in the crystallization process, there is a technical barrier to the equipment design and the adjustment of process parameters of the crystallization kettle. The raw materials for purifying and separating the bio-based glycolic acid are derived from a special synthetic route, a difficult-to-overcome catalyst design barrier exists, and for a purification and separation section, the easy polymerization property of the glycolic acid causes a technical barrier to the selection of separation and purification process parameters and the device coupling mode.
The invention has the advantages of simple and convenient operation process, good separation and purification effect, high working efficiency and the like. And the cost is low, and the market prospect is high.
Experiments show that: the purity of the glycolic acid obtained by the invention is about 91.5-99.1%, and is greatly improved compared with the prior art.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the present disclosure and together with the description, serve to explain the principles of the disclosure.
FIG. 1 is a flow chart of a method for separation and purification by a coupling technology of rectification and crystallization of biobased glycolic acid provided by an embodiment of the invention.
Fig. 2 is a schematic structural diagram of a rectification crystallization coupling separation and purification device provided by an embodiment of the invention.
In the figure: a is a decompression rectifying tower; b is a crystallization kettle; 1. a rectifying tower plate; 2. a condenser; 3. a reboiler; 4. a temperature controller of the crystallization kettle; 5. a condensate circulator; 6. a mechanical stirring device.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather should be construed as broadly as the present invention is capable of modification in various respects, all without departing from the spirit and scope of the present invention.
All technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
As shown in figure 1, the invention provides a method for separating and purifying bio-based glycolic acid by rectification crystallization coupling technology, which comprises the following steps:
s101, preparing crude glycolic acid by using bio-based platform compound molecules as raw materials. The method comprises the specific steps of carrying out green conversion on platform compound molecules by using a supported catalyst to synthesize crude glycolic acid, for example, reacting the ethylene glycol bio-based platform compound molecules serving as a raw material for 10 hours at 80 ℃ by using a Pt/C catalyst to obtain a crude glycolic acid solution.
S102, rectifying and concentrating the obtained crude glycolic acid to 70 wt% or more. The method comprises the specific steps of concentrating the crude ethanol acid solution in a rectifying tower by using a vacuum rectification technology, wherein the crude ethanol acid solution with the mass fraction of 35 wt% is subjected to vacuum rectification, the feeding temperature of the rectifying tower is 30 ℃, the number of tower plates is 25, the reflux ratio is 0.32, the tower bottom temperature is 60 ℃, and the tower counter pressure is 0.29 MPa.
S103, cooling and crystallizing the concentrated solution, and filtering to obtain high-purity glycolic acid crystals. Crystallizing glycolic acid in a crystallization kettle B coupled with a rectifying device in series, filtering and separating to obtain a high-purity glycolic acid product, for example, crystallizing the obtained glycolic acid concentrated solution in the crystallization kettle B at the crystallization temperature of-15 ℃, the cooling rate of 0.5 ℃/min, the stirring speed of 400r/min and the addition amount of glycolic acid seed crystals of 1 wt%.
In an embodiment of the present invention, as shown in fig. 2, a rectification crystallization coupling separation and purification apparatus is further provided, which is composed of a vacuum rectification tower a and a crystallization kettle B, and specifically includes: a rectifying tower plate 1, a condenser 2, a reboiler 3, a crystallization kettle temperature controller 4, a condensed water circulator 5 and a mechanical stirring device 6. Feeding crude glycolic acid from a tower plate 1 of a rectifying tower; and (4) taking out the glycolic acid crystals from the bottom of the crystallization kettle B. A rectifying tower plate 1 is welded inside the reduced pressure rectifying tower A, and the upper part of the reduced pressure rectifying tower A is connected with a condenser 2 through a pipeline; the lower part of the decompression rectifying tower A is connected with a reboiler 3 and a crystallization kettle B through pipelines; the upper part of the crystallization kettle B is provided with a crystallization kettle temperature controller 4 and a condensed water circulator 5; and a mechanical stirring device 6 is arranged in the crystallization kettle B.
The technical solution of the present invention will be further described with reference to the following specific examples.
Example 1:
a method for separating and purifying by coupling technology of rectification and crystallization of biobased glycolic acid comprises the following steps
Performing one-step hydrothermal conversion on cellulose by adopting a tungsten/nickel catalyst at the temperature of 200 ℃ and under the initial hydrogen pressure of 6MPa to obtain ethylene glycol, and performing one-step hydrothermal conversion on the ethylene glycol by adopting a Pt/AC catalyst at the temperature of 80 ℃ and under the initial oxygen pressure of 2MPa to obtain crude glycolic acid;
rectifying and concentrating the obtained crude glycolic acid under reduced pressure, wherein the reduced pressure temperature is 50 ℃, the absolute pressure is 0.5MPa under reduced pressure, and the crude glycolic acid is concentrated to 70 wt%;
cooling and crystallizing the obtained concentrated solution, wherein the cooling rate is 0.5 ℃/min, the crystallization temperature is-20 ℃, the stirring speed is 800r/min, and the amount of the glycolic acid seed crystal is 2% of the amount of glycolic acid in the concentrated solution;
obtaining the high-purity glycolic acid crystal.
Examples 2 to 10:
according to the method for separating and purifying glycolic acid of example 1, the temperature and pressure of the vacuum rectification used were adjusted, and the other parameters were the same, glycolic acid was separated and purified, and the yield and purity of glycolic acid were recorded as shown in table 1.
TABLE 1
T，℃
P，MPa
Yield and content of
Purity%
Example 1
40
0.05
56.7
91.5
Example 2
40
0.1
70.5
93.9
Example 3
40
0.2
81.4
92.7
Example 4
40
0.5
60.6
95.8
Example 5
40
1.0
66.9
96.8
Example 6
30
0.1
59.9
93.4
Example 7
50
0.1
72.3
95.8
Example 8
60
0.1
76.9
96.5
Example 9
70
0.1
78.5
98.7
Example 10
80
0.1
89.4
99.1
Examples 11 to 20:
according to the method for separating and purifying glycolic acid of example 1, the cooling rate, the crystallization temperature and the rotation speed of the cooling crystallization used were adjusted, and the same parameters were used, and glycolic acid was separated and purified, and the yield and purity of glycolic acid were recorded as shown in table 2.
TABLE 2
t，℃/min
T，℃
R，r/min
Yield and content of
Purity%
Example 11
0.5
-5
500
56.8
93.5
Example 12
0.5
-5
500
69.4
96.7
Example 13
0.5
-5
500
68.9
94.9
Example 14
1
-5
500
75.9
95.6
Example 15
1
-5
500
78.4
97.2
Example 16
1
-20
800
84.2
98.3
Example 17
5
-20
800
85.5
96.1
Example 18
5
-20
800
87.3
93.6
Example 19
5
-20
800
89.1
94.7
Example 20
10
-20
800
88.4
95.2
Example 21:
a method for separating and purifying by coupling technology of rectification and crystallization of biobased glycolic acid comprises the following steps
Glycerol is Pt-Fe/CeO2Carrying out one-step hydrothermal conversion on the catalyst at the temperature of 100 ℃ and under the initial oxygen pressure of 1MPa to obtain crude glycolic acid;
rectifying and concentrating the obtained crude glycolic acid under reduced pressure, wherein the reduced pressure temperature is 50 ℃, the absolute pressure is 0.5MPa under reduced pressure, and the crude glycolic acid is concentrated to 70 wt%;
cooling and crystallizing the obtained concentrated solution, wherein the cooling rate is 0.5 ℃/min, the crystallization temperature is-20 ℃, the stirring speed is 800r/min, and the amount of the glycolic acid seed crystal is 2% of the amount of glycolic acid in the concentrated solution;
obtaining the high-purity glycolic acid crystal.
Example 22:
a method for separating and purifying bio-based glycolic acid by rectification crystallization coupling technology comprises the following steps of obtaining crude glycolic acid by hydrolyzing methyl glycolate in one step;
rectifying and concentrating the obtained crude glycolic acid under reduced pressure, wherein the reduced pressure temperature is 50 ℃, the absolute pressure is 0.5MPa under reduced pressure, and the crude glycolic acid is concentrated to 70 wt%;
cooling and crystallizing the obtained concentrated solution, wherein the cooling rate is 0.5 ℃/min, the crystallization temperature is-20 ℃, the stirring speed is 800r/min, and the amount of the glycolic acid seed crystal is 2% of the amount of glycolic acid in the concentrated solution;
obtaining the high-purity glycolic acid crystal.
Example 23:
a method for separating and purifying by coupling technology of rectification and crystallization of biobased glycolic acid comprises the following steps
Carrying out one-step hydrothermal conversion on ethylene glycol by adopting an Au/NaY catalyst at the temperature of 95 ℃ and under the initial oxygen pressure of 1MPa to obtain crude glycolic acid;
rectifying and concentrating the obtained crude glycolic acid under reduced pressure, wherein the reduced pressure temperature is 50 ℃, the absolute pressure is 0.5MPa under reduced pressure, and the crude glycolic acid is concentrated to 70 wt%;
cooling and crystallizing the obtained concentrated solution, wherein the cooling rate is 0.5 ℃/min, the crystallization temperature is-20 ℃, the stirring speed is 800r/min, and the amount of the glycolic acid seed crystal is 2% of the amount of glycolic acid in the concentrated solution;
obtaining the high-purity glycolic acid crystal.
The temperature and pressure of the vacuum distillation were adjusted according to the different synthetic sources of glycolic acid of examples 24-31, the remaining parameters were the same, glycolic acid was isolated and purified, and the yield and purity of glycolic acid was recorded as shown in table 3.
TABLE 3
The temperature and pressure of the vacuum distillation were adjusted according to the glycolic acid of the different synthetic sources of examples 32-39, the remaining parameters were the same, the glycolic acid was isolated and purified, and the yield and purity of glycolic acid were recorded as shown in table 4.
TABLE 4
Other embodiments of the disclosure will be apparent to those skilled in the art from consideration of the specification and practice of the disclosure disclosed herein. This application is intended to cover any variations, uses, or adaptations of the disclosure following, in general, the principles of the disclosure and including such departures from the present disclosure as come within known or customary practice within the art to which the disclosure pertains. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the disclosure being indicated by the following claims.
It will be understood that the present disclosure is not limited to the precise arrangements described above and shown in the drawings and that various modifications and changes may be made without departing from the scope thereof. The scope of the present disclosure should be limited only by the attached claims.
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