阅读说明：本技术 一种碳酸二甲酯的制备方法及其应用 (Preparation method and application of dimethyl carbonate ) 是由 许可 张新平 尹训娟 吴祥舟 卢健行 刘守国 于 2020-12-28 设计创作，主要内容包括：本发明涉及一种碳酸二甲酯的制备方法及其应用,所述方法包括：(1)在密闭反应装置中加入甲醇和催化剂,然后通入二氧化碳进行吹扫,完成后继续通入二氧化碳使反应装置达到设定的压力,在加热条件下进行反应；所述催化剂的制备方法包括骤：(i)在碳酸钙悬浮液中加入偶联剂,搅拌均匀后再加入CuNiAl类水滑石,得到复合悬浮液。(ii)将棉花浸入复合悬浮液中,然后取出干燥得催化剂前驱体。(iii)将所述催化剂前驱体热分解后烧结,即得。(2)反应结束后给反应装置降温,然后排出反应装置中的气体,放出物料后分离出其中的碳酸二甲酯。本发明方法采用具有特殊结构的催化剂催化二氧化碳和甲醇制备碳酸二甲酯,有效提高了反应效率。(The invention relates to a preparation method and application of dimethyl carbonate, wherein the method comprises the following steps: (1) adding methanol and a catalyst into a closed reaction device, then introducing carbon dioxide for purging, continuously introducing the carbon dioxide after the reaction is finished to enable the reaction device to reach a set pressure, and carrying out reaction under a heating condition; the preparation method of the catalyst comprises the following steps: (i) adding a coupling agent into the calcium carbonate suspension, stirring uniformly, and then adding CuNiAl hydrotalcite to obtain the composite suspension. (ii) And soaking cotton into the composite suspension, taking out and drying to obtain the catalyst precursor. (iii) And thermally decomposing the catalyst precursor and sintering to obtain the catalyst. (2) After the reaction is finished, cooling the reaction device, then discharging the gas in the reaction device, and separating the dimethyl carbonate from the discharged material. The method of the invention adopts the catalyst with special structure to catalyze the carbon dioxide and the methanol to prepare the dimethyl carbonate, thereby effectively improving the reaction efficiency.)

1. The preparation method of the dimethyl carbonate is characterized by comprising the following steps:

(1) adding methanol and a catalyst into a closed reaction device, then introducing carbon dioxide for purging, continuously introducing the carbon dioxide after the reaction is finished to enable the reaction device to reach a set pressure, and carrying out reaction under a heating condition; the preparation method of the catalyst comprises the following steps:

(i) adding a coupling agent into the calcium carbonate suspension, uniformly stirring, then adding CuNiAl hydrotalcite, and uniformly stirring to obtain a composite suspension for later use;

(ii) soaking cotton in the composite suspension, taking out the cotton after soaking, and drying to obtain a catalyst precursor for later use;

(iii) putting the catalyst precursor in a protective atmosphere for thermal decomposition, and then sintering in air to obtain the catalyst with a porous tubular structure;

(2) and (3) cooling the reaction device after the reaction is finished, then discharging the gas in the reaction device, and separating dimethyl carbonate from the discharged material to obtain the product.

2. The method for preparing dimethyl carbonate according to claim 1, wherein in the step (1), the adding ratio of the methanol to the catalyst is 110-140 ml: 0.5 to 1.7 g.

3. The process for producing dimethyl carbonate according to claim 1, wherein in the step (1), the pressure is 1.5 to 5MPa and the heating temperature is 95 to 120 ℃.

4. The method for preparing dimethyl carbonate according to claim 1, wherein in step (i), the calcium carbonate suspension is prepared by ultrasonically stirring calcium carbonate powder and deionized water; preferably, the ratio of the calcium carbonate powder to the deionized water is 1 g: 5-12 ml.

5. The method for preparing dimethyl carbonate according to claim 1, wherein in the step (i), the mass ratio of the calcium carbonate to the CuNiAl hydrotalcite is 55-70: 30-45 parts of; alternatively, in step (i), the coupling agent comprises a silane coupling agent.

6. The method for preparing dimethyl carbonate according to claim 1, wherein in the step (ii), the drying temperature is 60-85 ℃, and the drying time is 2-4 h; alternatively, in step (iii), the protective atmosphere comprises any one of nitrogen and argon.

7. The method as claimed in claim 1, wherein the temperature of the thermal decomposition in step (iii) is 520 ℃ and 650 ℃ for 2-5 h.

8. The method as claimed in claim 1, wherein the sintering temperature in step (iii) is 600-780 ℃ for 1.5-3 h.

9. The method for preparing dimethyl carbonate according to any one of claims 1 to 8, wherein in the step (2), the dimethyl carbonate product in the reaction product is separated by distillation or the like.

10. Use of the process for the preparation of dimethyl carbonate according to any one of claims 1 to 9 in the chemical sector.

Technical Field

The invention relates to the technical field of dimethyl carbonate preparation, in particular to a preparation method and application of dimethyl carbonate.

Background

Dimethyl carbonate of the formula C₃H₆O₃And is colorless transparent liquid at normal temperature. Dimethyl carbonate is a good methylating agent, carbonylating agent, hydroxymethylating agent and methoxylating agent, and has very active chemical characteristics. Can be used for preparing polycarbonate and water treatment agent in industry; in medicine and pesticide, the compound can be used as an organic synthesis intermediate to prepare ciprofloxacin, carba oxygen and the like; in addition, the method is also one of the necessary raw materials for preparing the electrolyte of the high-energy battery. Because of its excellent chemical properties and environmental protection efficacy, recently, it can be used to replace benzene, toluene, xylene, ethyl acetate, butyl acetate and other solvents in paint, ink and adhesive. Dimethyl carbonate is also an ideal substitute for phosgene, dimethyl sulfate, methyl chloroformate and other highly toxic products, and is known as a green chemical product in the 21 st century.

Disclosure of Invention

The invention aims to provide a preparation method of dimethyl carbonate and application thereof, and the preparation method adopts a catalyst with a special structure to catalyze carbon dioxide and methanol to prepare the dimethyl carbonate, thereby effectively improving the reaction efficiency. In order to achieve the purpose, the invention discloses the following technical scheme:

firstly, the invention discloses a preparation method of dimethyl carbonate, which comprises the following steps:

(1) adding methanol and a catalyst into a closed reaction device, then introducing carbon dioxide for purging, continuously introducing the carbon dioxide after the reaction is finished to enable the reaction device to reach a set pressure, and carrying out reaction under a heating condition; the preparation method of the catalyst comprises the following steps:

(i) adding a coupling agent into the calcium carbonate suspension, uniformly stirring, then adding CuNiAl hydrotalcite, and uniformly stirring to obtain a composite suspension for later use;

(ii) soaking cotton in the composite suspension, taking out the cotton after soaking, and drying to obtain a catalyst precursor for later use;

(iii) putting the catalyst precursor in a protective atmosphere for thermal decomposition, and then sintering in air to obtain the catalyst with a porous tubular structure;

(2) and (3) cooling the reaction device after the reaction is finished, then discharging the gas in the reaction device, and separating dimethyl carbonate from the discharged material to obtain the product.

Further, in the step (1), the adding ratio of the methanol to the catalyst is 110-140 ml: 0.5 to 1.7 g.

Further, in the step (1), the pressure is 1.5-5MPa, the heating temperature is 95-120 ℃, and the heating and pressurizing are helpful for promoting the reaction of the carbon dioxide and the methanol.

Further, in the step (i), the calcium carbonate suspension is prepared by ultrasonically stirring calcium carbonate powder and deionized water, so that the calcium carbonate can be uniformly dispersed in the water to form the suspension.

Preferably, the ratio of the calcium carbonate powder to the deionized water is 1 g: 5-12 ml.

Further, in step (i), the coupling agent includes a silane coupling agent or the like, which mainly functions as a "molecular bridge" to allow better contact between reactants.

Further, in the step (i), the mass ratio of the calcium carbonate to the CuNiAl hydrotalcite is 55-70: 30-45. The CuNiAl hydrotalcite has abundant Cu and Ni, and can be used for synergistically catalyzing carbon dioxide and methanol to react, so that the reaction efficiency is improved. Calcium carbonate and aluminum element in CuNiAl hydrotalcite are subjected to subsequent reaction to generate calcium aluminum oxide which has good mechanical property and high temperature resistance.

Further, in the step (ii), the drying temperature is 60-85 ℃, and the drying time is 2-4 hours.

Further, in the step (iii), the protective atmosphere includes any one of nitrogen, argon, and the like.

Further, in step (iii), the temperature of the thermal decomposition is 520-650 ℃ and the time is 2-5 h. Through thermal decomposition, firstly, cotton in a catalyst precursor is removed, secondly, calcium carbonate is decomposed into calcium oxide, and CuNiAl hydrotalcite is decomposed into aluminum oxide, so that aluminum oxide can be conveniently obtained by the two in subsequent reactions.

Further, in step (iii), the sintering temperature is 600-780 ℃ and the sintering time is 1.5-3 h. The catalyst with the porous tubular structure containing the copper oxide, the nickel oxide and the calcium-aluminum oxide components in a sintered state is obtained by sintering.

Further, in the step (2), a dimethyl carbonate product in the reaction product is separated by adopting a method such as rectification and the like.

Secondly, the invention discloses the application of the preparation method of the dimethyl carbonate in the chemical field.

Compared with the prior art, the invention has the following beneficial effects:

(1) the invention synthesizes the multi-component catalyst with special structure by using calcium carbonate and CuNiAl hydrotalcite as raw materials. First, the catalyst not only contains rich copper and nickel for catalyzing the reaction of methanol and carbon dioxide, but also the two elements have synergistic effect in catalyzing the reaction of methanol and carbon dioxide, so that the catalyst shows better catalytic activity. Secondly, the catalyst has a porous tubular structure formed by taking a calcium-aluminum oxide component as a framework, and the structure has higher specific surface area and specific pore volume and stronger carbon dioxide capture capacity, thereby being beneficial to improving the activity of the catalyst and promoting the conversion rate of methanol. Thirdly, the sintered calcium-aluminum oxide in the catalyst has better temperature resistance and pressure resistance, so that the catalyst has better stability in the reaction, is not easy to collapse and is convenient to recycle.

(2) According to the invention, calcium carbonate and CuNiAl hydrotalcite are used as raw materials, firstly, the calcium carbonate is pyrolyzed into calcium oxide, the CuNiAl hydrotalcite is pyrolyzed into copper oxide, nickel oxide and aluminum oxide, and the aluminum oxide and the calcium oxide can further react to form a sintered calcium-aluminum oxide in the subsequent sintering process. The CuNiAl hydrotalcite not only provides active components required by catalytic reaction, but also provides components required by generating a sintered skeleton.

Detailed Description

It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. The invention will now be further illustrated by means of specific embodiments.

Example 1

1. Preparation of a porous tubular structure catalyst, comprising the steps of:

(i) calcium carbonate powder and deionized water were mixed in a ratio of 1 g: mixing 8ml of the calcium carbonate suspension, and then ultrasonically stirring for 15min to uniformly disperse the calcium carbonate in water to obtain a calcium carbonate suspension; then adding 4ml of silane coupling agent into the suspension, mechanically stirring uniformly, adding CuNiAl hydrotalcite-like powder (the mass ratio of calcium carbonate to CuNiAl hydrotalcite-like powder is 58: 42), and continuously stirring for 10min to obtain composite suspension for later use.

(ii) And completely soaking cotton into the composite suspension prepared in the embodiment, taking out the cotton after soaking, placing the cotton in a drying furnace, and drying at 70 ℃ for 2 hours to obtain a catalyst precursor for later use.

(iii) The catalyst precursor is placed in a nitrogen atmosphere, is subjected to thermal decomposition for 3 hours at 550 ℃, and is sintered for 2 hours at 700 ℃ in the air, so that the catalyst with the porous tubular structure is obtained.

2. The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 120 ml: 1.2g of methanol and the catalyst with the porous tubular structure prepared in the embodiment are added into a high-pressure reaction kettle, then carbon dioxide is introduced to purge for 10min, after the purging, the carbon dioxide is continuously introduced to enable the pressure of the high-pressure reaction kettle to reach 3MPa, and then the high-pressure reaction kettle is heated to 110 ℃ to perform reaction.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Example 2

1. Preparation of a porous tubular structure catalyst, comprising the steps of:

(i) calcium carbonate powder and deionized water were mixed in a ratio of 1 g: mixing 10ml of the calcium carbonate suspension, and then ultrasonically stirring for 15min to uniformly disperse the calcium carbonate in water to obtain a calcium carbonate suspension; then adding 5ml of silane coupling agent into the suspension, mechanically stirring uniformly, adding CuNiAl hydrotalcite-like powder (the mass ratio of calcium carbonate to CuNiAl hydrotalcite-like powder is 55: 45), and continuously stirring for 10min to obtain composite suspension for later use.

(ii) And completely soaking cotton into the composite suspension prepared in the embodiment, taking out the cotton after soaking, placing the cotton in a drying furnace, and drying at 60 ℃ for 4 hours to obtain a catalyst precursor for later use.

(iii) The catalyst precursor is placed in a nitrogen atmosphere, is subjected to thermal decomposition for 2 hours at 650 ℃, and is sintered for 1.5 hours at 750 ℃ in the air, so that the catalyst with the porous tubular structure is obtained.

2. The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 110 ml: adding 0.5g of methanol and the catalyst with the porous tubular structure prepared in the embodiment into a high-pressure reaction kettle, then introducing carbon dioxide to purge for 10min, continuing introducing the carbon dioxide to enable the pressure of the high-pressure reaction kettle to reach 5MPa, and then heating to 100 ℃ to perform reaction.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Example 3

1. Preparation of a porous tubular structure catalyst, comprising the steps of:

(i) calcium carbonate powder and deionized water were mixed in a ratio of 1 g: mixing 12ml of the calcium carbonate suspension, and then ultrasonically stirring for 15min to uniformly disperse the calcium carbonate in water to obtain a calcium carbonate suspension; then adding 5ml of silane coupling agent into the suspension, mechanically stirring uniformly, adding CuNiAl hydrotalcite-like powder (the mass ratio of calcium carbonate to CuNiAl hydrotalcite-like powder is 65: 35), and continuously stirring for 10min to obtain composite suspension for later use.

(ii) And completely soaking cotton into the composite suspension prepared in the embodiment, taking out the cotton after soaking, placing the cotton in a drying furnace, and drying at 80 ℃ for 2 hours to obtain a catalyst precursor for later use.

(iii) The catalyst precursor is placed in a nitrogen atmosphere, is subjected to thermal decomposition for 4 hours at 550 ℃, and is sintered for 1.5 hours at 780 ℃ in the air, so that the catalyst with the porous tubular structure is obtained.

2. The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 130 ml: 1.5g of methanol and the catalyst with the porous tubular structure prepared in the embodiment are added into a high-pressure reaction kettle, then carbon dioxide is introduced to purge for 10min, after the purging, the carbon dioxide is continuously introduced to enable the pressure of the high-pressure reaction kettle to reach 1.5MPa, and then the high-pressure reaction kettle is heated to 120 ℃ to react.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Example 4

1. Preparation of a porous tubular structure catalyst, comprising the steps of:

(i) calcium carbonate powder and deionized water were mixed in a ratio of 1 g: 5ml of the calcium carbonate suspension is obtained by mixing the components in proportion and then ultrasonically stirring the mixture for 20min to uniformly disperse the calcium carbonate in water; then adding 5ml of silane coupling agent into the suspension, mechanically stirring uniformly, adding CuNiAl hydrotalcite-like powder (the mass ratio of calcium carbonate to CuNiAl hydrotalcite-like powder is 70: 30), and continuously stirring for 20min to obtain a composite suspension for later use.

(ii) And completely soaking cotton into the composite suspension prepared in the embodiment, taking out the cotton after soaking, placing the cotton in a drying furnace, and drying at 85 ℃ for 2 hours to obtain a catalyst precursor for later use.

(iii) The catalyst precursor is placed in a nitrogen atmosphere, is subjected to thermal decomposition for 5 hours at the temperature of 520 ℃, and is sintered for 3 hours at the temperature of 600 ℃ in the air, so that the catalyst with the porous tubular structure is obtained.

2. The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 140 ml: 1.7g of methanol and the catalyst with the porous tubular structure prepared in the embodiment are added into a high-pressure reaction kettle, then carbon dioxide is introduced to purge for 10min, after the purging, the carbon dioxide is continuously introduced to enable the pressure of the high-pressure reaction kettle to reach 3.5MPa, and then the high-pressure reaction kettle is heated to 95 ℃ to carry out reaction.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Test example 1

The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 120 ml: adding methanol and a catalyst (copper chloride solid) into a high-pressure reaction kettle according to the proportion of 1.2g, then introducing carbon dioxide to purge for 10min, continuing introducing the carbon dioxide to enable the pressure of the high-pressure reaction kettle to reach 3MPa after the purging is finished, and then heating to 110 ℃ to carry out reaction.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Test example 2

1. Preparation of a porous tubular structure catalyst, comprising the steps of:

(i) mixing CuNiAl hydrotalcite-like powder and deionized water according to the weight ratio of 1 g: mixing the components in a proportion of 8ml, and then ultrasonically stirring for 15min to uniformly disperse the CuNiAl hydrotalcite-like compound in water to obtain a CuNiAl hydrotalcite-like compound suspension; then 4ml of silane coupling agent is added into the suspension, and the mechanical stirring is carried out for 10min, thus obtaining CuNiAl hydrotalcite-like suspension for later use.

(ii) And completely soaking cotton into the CuNiAl hydrotalcite-like compound suspension prepared in the embodiment, taking out the cotton after soaking, placing the cotton in a drying furnace, and drying at 70 ℃ for 2 hours to obtain a catalyst precursor for later use.

(iii) The catalyst precursor is placed in a nitrogen atmosphere, is subjected to thermal decomposition for 3 hours at 550 ℃, and is sintered for 2 hours at 700 ℃ in the air, so that the catalyst with the porous tubular structure is obtained.

2. The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 120 ml: 1.2g of methanol and the catalyst with the porous tubular structure prepared in the embodiment are added into a high-pressure reaction kettle, then carbon dioxide is introduced to purge for 10min, after the purging, the carbon dioxide is continuously introduced to enable the pressure of the high-pressure reaction kettle to reach 3MPa, and then the high-pressure reaction kettle is heated to 110 ℃ to perform reaction.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Test example 3

1. Preparation of a porous tubular structure catalyst, comprising the steps of:

(i) calcium carbonate powder and deionized water were mixed in a ratio of 1 g: mixing 8ml of the calcium carbonate suspension, and then ultrasonically stirring for 15min to uniformly disperse the calcium carbonate in water to obtain a calcium carbonate suspension; then adding 4ml of silane coupling agent into the suspension, mechanically stirring uniformly, adding CuNiAl hydrotalcite-like powder (the mass ratio of calcium carbonate to CuNiAl hydrotalcite-like powder is 58: 42), and continuously stirring for 10min to obtain composite suspension for later use.

(ii) And (3) placing the composite suspension in a drying furnace to be dried into a solid to obtain a catalyst precursor for later use.

(iii) The catalyst precursor is placed in a nitrogen atmosphere, is subjected to thermal decomposition for 3 hours at 550 ℃, and is sintered for 2 hours at 700 ℃ in the air, so that the catalyst with the porous tubular structure is obtained.

2. The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 120 ml: 1.2g of methanol and the catalyst with the porous tubular structure prepared in the embodiment are added into a high-pressure reaction kettle, then carbon dioxide is introduced to purge for 10min, after the purging, the carbon dioxide is continuously introduced to enable the pressure of the high-pressure reaction kettle to reach 3MPa, and then the high-pressure reaction kettle is heated to 110 ℃ to perform reaction.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Test example 4

The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 120 ml: 1.2g of methanol and a catalyst (the catalyst used in the preparation of dimethyl carbonate in example 1) were added to a high-pressure reactor, then purged with carbon dioxide for 10min, and then heated to 110 ℃ to effect reaction, after the purging with carbon dioxide was continued to bring the pressure in the high-pressure reactor to 3 MPa.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

Test example 5

The preparation of dimethyl carbonate includes the following steps:

(1) according to the ratio of methanol to catalyst of 120 ml: 1.2g of methanol and a catalyst (the catalyst used in the preparation of dimethyl carbonate in test example 2) were added into a high-pressure reaction kettle, then carbon dioxide was introduced to purge for 10min, after completion, carbon dioxide was continuously introduced to make the pressure of the high-pressure reaction kettle reach 3MPa, and then the reaction kettle was heated to 110 ℃ to perform a reaction.

(2) And after the reaction is finished, cooling the high-pressure reaction kettle to room temperature, then discharging gas in the reaction device, discharging the material, and rectifying and separating dimethyl carbonate in the material to obtain the dimethyl carbonate.

The conversion of methanol, the selectivity to dimethyl carbonate and the yield of dimethyl carbonate separated in the above examples and experimental examples were calculated and the results are shown in tables 1 and 2, respectively.

TABLE 1

	Example 1	Example 2	Example 3	Example 4
					Conversion of methanol/%)	19.7	21.6	18.3	19.4
Selectivity of dimethyl carbonate/%)	99.2	99.5	98.8	99.3
					Dimethyl carbonate yield/%	71.3	73.6	67.1	69.7

TABLE 2

	Test example 1	Test example 2	Test example 3	Test example 4	Test example 5
						Conversion of methanol/%)	4.9	13.7	7.7	19.1	11.3
Selectivity of dimethyl carbonate/%)	82.3	92.1	96.4	98.7	94.4
						Dimethyl carbonate yield/%	33.6	56.8	38.6	70.4	60.6

From the results in table 1, it can be seen that the catalyst with a porous tubular structure synthesized by using calcium carbonate and cunai hydrotalcite as raw materials has excellent catalytic performance for the reaction of methanol and carbon dioxide, and particularly, the conversion rate of methanol and the yield of dimethyl carbonate are obviously improved. The catalytic performance of the catalysts prepared in test examples 1-3 is significantly lower than that of the examples. It can be seen from the calculation results of test examples 4 and 5 that when the catalyst does not contain a calcium aluminum oxide skeleton, the catalyst has a large influence on the catalytic performance for reuse because the microstructure of the catalyst may be damaged by high temperature and high pressure during the reaction.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.