CN102692357A - Quantitative analysis method for calcium sulphate crystal - Google Patents
Quantitative analysis method for calcium sulphate crystal Download PDFInfo
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- CN102692357A CN102692357A CN2012101840197A CN201210184019A CN102692357A CN 102692357 A CN102692357 A CN 102692357A CN 2012101840197 A CN2012101840197 A CN 2012101840197A CN 201210184019 A CN201210184019 A CN 201210184019A CN 102692357 A CN102692357 A CN 102692357A
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Abstract
The invention discloses a quantitative analysis method for a calcium sulphate crystal, wherein the calcium sulphate crystal contains a calcium sulphate dehydrate crystal, a calcium sulphate hemihydrate crystal and free water. The method comprises the following steps of: contacting the calcium sulphate crystal with absolute methanol and/or absolute ethyl alcohol, and determining the free water content in liquid phase by utilizing a Karl Fischer method, so as to obtain the free water content in the calcium sulphate crystal; and drying the calcium sulphate crystal with the same weight and the same batch to constant weight at the temperature of 230-280 DEG C, calculating the total moisture content in the calcium sulphate crystal according to variation of the total weight of the calcium sulphate crystal before and after drying, and reversely calculating the content of calcium sulphate dehydrate crystal and calcium sulphate hemihydrate in the calcium sulphate crystal according to the total moisture content. By adopting the method disclosed by the invention, the content of calcium sulphate dehydrate crystal and calcium sulphate hemihydrate crystal in the calcium sulphate crystal can be accurately determined through simple operation.
Description
Technical field
The present invention relates to a kind of quantitative analysis method of calcium sulphate crystal, particularly, relate to a kind of calcium sulphate dihydrate crystal and quantivative approach of measuring in the calcium sulphate crystal of half-H 2 O calcium sulphate crystal.
Background technology
Calcium sulphate is of many uses, but residual in the calcium sulphate that calcium citrate salts and sulfuric acid reaction make citric acid and more free water is arranged, and therefore, this has restricted the application of product calcium sulphate, makes to bring into play its due value.
The wet crystal of the calcium sulphate that the hydrolysis procedure of citric acid produces mainly contains calcium sulphate dihydrate and half-H 2 O calcium sulphate, and wherein, calcium sulphate dihydrate is an acicular crystal; Filter and the washing difficulty, need a large amount of water washing solid phases, in order to reduce the residual quantity of citric acid in calcium sulphate; Like this; The free water content of the calcium sulphate that obtains after the Separation of Solid and Liquid is high, and citric acid solution concentration is low, thereby can influence the application of calcium sulphate and increase the concentrated expense of citric acid solution; Half-H 2 O calcium sulphate is a flat crystal, is easy to filter and washing, and the half-H 2 O calcium sulphate free water content that obtains is low.Therefore, the solid slag calcium sulphate that the sulfate dihydrate calcium content is low is easy to rinsing, and the amount of residual citric acid helps improving the yield of acidolysis workshop section with less in the calcium sulphate.But; What reaction obtained is the calcium sulphate of which kind of crystal formation, depends on composite factors such as temperature of reaction, reaction time, reactant concentration, and in the prior art; Citric acid and calcium sulphate are carried out in the process of acidolysis; Therefore the range of choice broad of each condition, can't guarantee the control of the crystalline form in the calcium sulphate crystal that obtains well.If can measure calcium sulphate dihydrate and the content of half-H 2 O calcium sulphate in the calcium sulphate crystal that obtains of reaction; Just can be beneficial in the acidolysis process each reaction conditions is carried out relatively accurate adjusting, thereby can as much as possiblely obtain the higher calcium sulphate crystal of sulfate hemihydrate calcium content.
In the prior art; Usually can lose the amount that weightlessness that water of crystallization causes calculates calcium sulphate dihydrate, half-H 2 O calcium sulphate and dead plaster in the calcium sulphate according to calcium sulphate crystal under different baking temperatures; In theory; Be lower than under 128 ℃ the baking temperature, calcium sulphate crystal loses free water, and calcium sulphate dihydrate is sloughed 1.5 water of crystallization in the time of 128-163 ℃ becomes half-H 2 O calcium sulphate; Half-H 2 O calcium sulphate begins to slough water of crystallization and changes dead plaster into when being higher than 163 ℃, releases the ratio that different hydrated calcium sulfates occupy according to the amount of water of crystallization is counter.But in the actual drying process, this method but can not reflect to entirely accurate calcium sulphate crystal dehydration process and ratio accurately.
A kind of in addition method then is; Because the calcium sulphate dihydrate crystal is different with the shape of half-H 2 O calcium sulphate crystal; Therefore, can carry out crystal scanning through electron microscope and tell calcium sulphate dihydrate and the general separately proportionate relationship of half-H 2 O calcium sulphate, still; Only can't obtain both definite ratios through microscopic examination; Owing to can only get the calcium sulphate crystal sample of trace and measure, therefore, can't comprehensively react calcium sulphate dihydrate crystal and the relation with contents of half-H 2 O calcium sulphate crystal in the whole calcium sulphate product in addition.
Above-mentioned two kinds of methods all can not obtain calcium sulphate dihydrate and the content accurately of half-H 2 O calcium sulphate in the calcium sulphate crystal.
Summary of the invention
The object of the present invention is to provide a kind of quantitative analysis method of calcium sulphate crystal of the content that can accurately measure calcium sulphate dihydrate crystal and half-H 2 O calcium sulphate crystal in the calcium sulphate crystal.
Inventor of the present invention finds; In the actual drying process; Be lower than under 128 ℃ the temperature; Partially crystallizable water in calcium sulphate dihydrate and the half-H 2 O calcium sulphate also can lose with free water together, and under 128-163 ℃ the temperature, half-H 2 O calcium sulphate also can lose partially crystallizable water; Therefore, losing weightlessness that water of crystallization causes according to calcium sulphate crystal under different baking temperatures calculates the method for the amount of calcium sulphate dihydrate, half-H 2 O calcium sulphate and dead plaster in the calcium sulphate and can not reflect to entirely accurate calcium sulphate crystal dehydration process and ratio accurately.
The inventor is unexpected to be found; Calcium sulphate crystal is insoluble to absolute methanol and/or absolute ethyl alcohol, and calcium sulphate crystal is when contacting with absolute methanol and/or absolute ethyl alcohol, and the water of crystallization of calcium sulphate dihydrate crystal and half-H 2 O calcium sulphate crystal can not dissociate out yet; And contained free water and absolute methanol and/or absolute ethyl alcohol mix in the calcium sulphate crystal; Therefore, after with methyl alcohol and/or ethanol the free water in the calcium sulphate crystal being dissolved out, can utilize the karl Fischer method to measure the content of the water in the liquid phase; Thereby obtain the free water content in the calcium sulphate crystal; In addition, can record the total moisture content that calcium sulphate crystal loses, know that free water and the total moisture content in the calcium sulphate crystal just can be through calculating the content of calcium sulphate dihydrate crystal and half-H 2 O calcium sulphate crystal through drying means.
The objective of the invention is to; A kind of quantitative analysis method of calcium sulphate crystal is provided; Contain calcium sulphate dihydrate crystal, half-H 2 O calcium sulphate crystal and free water in the said calcium sulphate crystal, wherein, this method comprises: said calcium sulphate crystal is contacted with absolute methanol and/or absolute ethyl alcohol; And utilize the karl Fischer method to measure the free water content in the liquid phase, thereby obtain the free water content in the calcium sulphate crystal; Be to be dried to constant weight under 230-280 ℃ the condition with the calcium sulphate crystal temperature of weight same as described above, same batch, and obtain the total moisture content in the said calcium sulphate crystal through the change calculations of calcium sulphate crystal general assembly (TW) before and after dry; Calculate the calcium sulphate dihydrate crystal that contained in the said calcium sulphate crystal and the content of half-H 2 O calcium sulphate crystal according to following formula:
The weight of calcium sulphate crystal to be determined is counted Cg;
Free water content in the calcium sulphate crystal that records is counted Xg;
Total moisture content in the calcium sulphate crystal that records is counted Yg;
The calcium sulphate dihydrate crystalline content that contains in the calcium sulphate crystal to be determined is made as Ag, and the half-H 2 O calcium sulphate crystalline content is made as Bg;
X+A+B=C；
X+36A/172+9B/145=Y。
Method of the present invention just can be measured calcium sulphate dihydrate crystal and the content of half-H 2 O calcium sulphate crystal in the calcium sulphate crystal exactly through shirtsleeve operation.
Embodiment
Following specific embodiments of the invention is elaborated.Should be understood that embodiment described herein only is used for explanation and explains the present invention, is not limited to the present invention.
According to the present invention; In order to measure the free water content in the calcium sulphate crystal; To calcium sulphate crystal to be measured be contacted with absolute methanol and/or absolute ethyl alcohol earlier, because calcium sulphate is insoluble to absolute methanol and/or absolute ethyl alcohol, therefore; Free water in the calcium sulphate crystal of contact back can enter into absolute methanol and/or absolute ethyl alcohol mutually, thereby can utilize the free water content in the karl Fischer volumetric determination liquid phase.The mode of said contact can be directly said calcium sulphate crystal to be joined in absolute methanol and/or the absolute ethyl alcohol to mix, and preferred, said mixing is under agitation carried out.
The concrete analyzing step of said formula is following:
X+A+B=C；
X+36A/172+9B/145=Y。
B=（145×36C-145×172Y+136×145X）/3672；
A=C-B-X。
According to the present invention; Amount ratio for said calcium sulphate crystal and absolute methanol and/or absolute ethyl alcohol has no particular limits; As long as the amount of used absolute methanol or absolute ethyl alcohol can fully be dissolved out the free water in the calcium sulphate crystal; Preferably, be as the criterion with the said calcium sulphate crystal of every gram, the consumption of absolute methanol and/or absolute ethyl alcohol is 35-45ml.
According to the present invention, for said calcium sulphate crystal is had no particular limits with the condition that absolute methanol and/or absolute ethyl alcohol contact, the contact temperature is not so long as influence the temperature of stability of the water of crystallization of calcium sulphate dihydrate and half-H 2 O calcium sulphate in the calcium sulphate crystal and get final product; As long as duration of contact and stirring rate can guarantee to make the free water in the said calcium sulphate crystal fully to be dissolved out: preferred; Contact conditions comprises: the contact temperature is 10-30 ℃, and in order fully to make the free water stripping, said contact is under agitation carried out; Preferably; Said stirring rate is 20-40rpm, and the method for said contact is not special to be limited, as long as guarantee the abundant stripping of water; Preferably, the way of contact is for mixing.
According to the present invention, have no particular limits for said drying means, can be this area various drying means commonly used, as long as guarantee to be dried constant weight.For example; Can be selected from methods such as high temperature furnace drying, air dry, vacuum drying, forced air drying; The preferred high temperature furnace that uses is dry, has no particular limits for said drying condition, but in order to make the calcium sulphate crystal drying more complete more fast; Preferably, the temperature of said drying is 230-280 ℃; More preferably, wherein, said baking temperature is 245-255 ℃.
According to the present invention, said calcium sulphate crystal can be various calcium sulphate crystals, and is preferred, produced the wet crystal of calcium sulphate of the hydrolysis procedure generation of citric acid by calcium salt method.Contain calcium sulphate dihydrate crystal, half-H 2 O calcium sulphate crystal and free water in this calcium sulphate crystal.
According to the present invention, adopting the liquid water content in the karl Fischer method working sample is according to the amount of the Ka Shi reagent that consumes in the titration process, calculates the liquid water content in the sample, and its principle is shown in following chemical formula.
I
2+ SO
2+ H
2O+3 pyridine+CH
3OH → 2 hydroiodic acids pyridine+methylsulfuric acid pyridine
Under the situation that pyridine and methyl alcohol exist, the redox reaction of the moisture in the working sample and iodine and sulphuric dioxide generates hydroiodic acid pyridine and methylsulfuric acid pyridine, and when moisture all exhausted, iodine can show that oneself is own brown, is judged as reaction end with this.Directly utilize the karl Fischer moisture teller to measure in the present invention, used karl Fischer moisture teller can be the karl Fischer moisture teller of DL55 for the model that Mettler Toledo Inc. produces.
Total moisture content in the calcium sulphate can be with reference to National Standard GB 1892-2007 food additives calcium sulphate " in the loss on drying method measure.
Ka Shi reagent is available from Chemical Reagent Co., Ltd., Sinopharm Group, and the trade mark is 31000962.
Employed all ingredients all is to analyze pure rank among the present invention.
Below specify the quantitative analysis method of calcium sulphate crystal of the present invention through embodiment.
Embodiment 1
Present embodiment is used to explain the quantitative analysis method of calcium sulphate crystal of the present invention.
In the titration bottle of karl Fischer moisture teller, add the 40mL absolute methanol; Taking by weighing calcium sulphate crystal C=1.0000g with the decrement method joins in the absolute methanol; Under 20 ℃; Stirred 10 minutes with the speed of magnetic stirring apparatus with 25rpm, the speed with 0.2mL/min drips Ka Shi reagent in the above-mentioned titration bottle that calcium sulphate crystal and absolute ethyl alcohol are housed while stirring, and the content that question response is accomplished measured free water is X=0.3150g.
Total liquid water content is measured: the calcium sulphate crystal sample (being accurate to 0.0001g) of getting same batch, identical weight; Place the porcelain crucible that under 250 ℃ ± 5 ℃, is dried to constant mass in advance, in 250 ℃ ± 5 ℃ high temperature furnace, dry by the fire, take out to be placed in the exsiccator and cool off to constant mass; Weighing; The amount of total moisture is the weight that the weight of calcium sulphate crystal sample deducts the dead plaster that drying obtains, that is, and and Y=0.4200g.
The content of calcium sulphate dihydrate crystal, half-H 2 O calcium sulphate crystal and the dead plaster crystal that is contained in the said calcium sulphate crystal that calculates according to following formula:
The weight of calcium sulphate crystal to be determined is counted C;
Free water content in the calcium sulphate crystal that records is counted Xg;
Total moisture content in the calcium sulphate crystal that records is counted Yg;
The calcium sulphate dihydrate crystalline content that contains in the calcium sulphate crystal to be determined is made as Ag, and the half-H 2 O calcium sulphate crystalline content is made as Bg;
X+A+B=C；
X+36A/172+9B/145=Y。
Calculated the calcium sulphate crystal sample in the content of calcium sulphate dihydrate crystal and half-H 2 O calcium sulphate crystal shown in the table 1.
Embodiment 2
Present embodiment is used to explain the quantitative analysis method of calcium sulphate crystal of the present invention.
Adopt and analyze with embodiment 1 identical method; Calcium sulphate crystal also is same batch a sample; Different is: add the 35ml absolute methanol; Under 10 ℃, stirred 5 minutes, carry out titration with the speed of 0.1mL/min while stirring, the X=0.3180g that records, Y=0.4229g, C=1.022g with the speed of 40rpm.
Calcium sulphate dihydrate crystal and half-H 2 O calcium sulphate crystalline content are shown in the table 1 in the calcium sulphate crystal sample that is calculated.
Embodiment 3
Present embodiment is used to explain the quantitative analysis method of calcium sulphate crystal of the present invention.
Adopt and analyze with embodiment 1 identical method; Calcium sulphate crystal also is same batch a sample; Different is: add the 45ml absolute ethyl alcohol; Under 30 ℃, stirred 5 minutes, carry out titration with the speed of 0.1mL/min while stirring, the X=0.3503g that records, Y=0.4664g, C=1.1066g with the speed of 30rpm.
Calcium sulphate dihydrate crystal and half-H 2 O calcium sulphate crystalline content are shown in the table 1 in the calcium sulphate crystal sample that is calculated.
Comparative Examples 1
This Comparative Examples is the reference method of the quantitative analysis method of calcium sulphate crystal, and what measure with embodiment 1 is with a collection of calcium sulphate crystal.
1, double dish is placed in the baking oven, dry to constant weight, accurately weighing on analytical balance, and recording quality 20.5025g at 128 ℃.
2, take by weighing the quality of the sample that mixes, and recording quality 5.3678g.
3, above-mentioned calcium sulphate crystal sample is placed above-mentioned double dish, put in the baking oven, dry 4 hours to constant weight at 128 ℃; Sample taken out to be placed on be cooled to room temperature (25 ℃) in the exsiccator; To double dish and samples weighing, quality 23.8305g is according to the method described above successively after drying under 163 ℃, 250 ℃; To double dish and samples weighing, quality is respectively 23.7200g and 23.6080g respectively.
Lose free water at 128 ℃ of calcium sulphate crystals, the weight change of institute's weighing is the weight of free water; Lose water of crystallization at 163 ℃ of calcium sulphate dihydrate crystal and all be converted into the half-H 2 O calcium sulphate crystal, the weight change of institute's weighing is the weight of the water of crystallization that calcium sulphate dihydrate lost; Lose water of crystallization at 250 ℃ of half water H 2 O calcium sulphate crystal and all be converted into the dead plaster crystal, the weight change of institute's weighing is the weight of the water of crystallization that half-H 2 O calcium sulphate lost.
Calcium sulphate dihydrate crystal and half-H 2 O calcium sulphate crystalline content are shown in the table 1 in the calcium sulphate crystal sample that is calculated.
Table 1
Data by table 1 can know, result's repeatability of utilizing method of the present invention to measure is high, and it is accurately reliable more to compare the method for ratio.
More than describe the preferred embodiments of the present invention in detail; But the present invention is not limited to the detail in the foregoing description, in technical conceive scope of the present invention; Can carry out multiple simple variant to technical scheme of the present invention, these simple variant all belong to protection scope of the present invention.
Claims (5)
1. the quantitative analysis method of a calcium sulphate crystal; Contain calcium sulphate dihydrate crystal, half-H 2 O calcium sulphate crystal and free water in the said calcium sulphate crystal; It is characterized in that; This method comprises: said calcium sulphate crystal is contacted with absolute methanol and/or absolute ethyl alcohol, and utilize the karl Fischer method to measure the free water content in the liquid phase, thereby obtain the free water content in the calcium sulphate crystal; Be to be dried to constant weight under 230-280 ℃ the condition with the calcium sulphate crystal of weight same as described above, same batch, and obtain the total moisture content in the said calcium sulphate crystal through the change calculations of calcium sulphate crystal general assembly (TW) before and after dry in temperature; Calculate the calcium sulphate dihydrate crystal that contained in the said calcium sulphate crystal and the content of half-H 2 O calcium sulphate crystal according to following formula:
The weight of calcium sulphate crystal to be determined is counted Cg;
Free water content in the calcium sulphate crystal that records is counted Xg;
Total moisture content in the calcium sulphate crystal that records is counted Yg;
The calcium sulphate dihydrate crystalline content that contains in the calcium sulphate crystal to be determined is made as Ag, and the half-H 2 O calcium sulphate crystalline content is made as Bg;
X+A+B=C；
X+36A/172+9B/145=Y。
2. method according to claim 1 wherein, is as the criterion with the said calcium sulphate crystal of every gram, and the consumption of said absolute methanol and/or absolute ethyl alcohol is 35-45ml.
3. method according to claim 1 wherein, comprises said calcium sulphate crystal with the condition that absolute methanol and/or absolute ethyl alcohol contact: the contact temperature is 10-30 ℃, and said contact is under agitation carried out, and the mode of said contact is for mixing.
4. method according to claim 1, wherein, dry temperature is 245-255 ℃.
5. method according to claim 1, wherein, said calcium sulphate crystal is the wet crystal of calcium sulphate of being produced the hydrolysis procedure generation of citric acid by calcium salt method.
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103245586A (en) * | 2013-04-15 | 2013-08-14 | 广州天赐高新材料股份有限公司 | Method for measuring trace moisture content in borate compound |
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2012
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| CN103245586B (en) * | 2013-04-15 | 2016-04-27 | 广州天赐高新材料股份有限公司 | The assay method of trace moisture content in a kind of boric acid ester compound |
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