AU2014101600A4

AU2014101600A4 - Method for separating and purifying p-dichlorobenzene

Info

Publication number: AU2014101600A4
Application number: AU2014101600A
Authority: AU
Inventors: Daocai SHE; Xiaoliang Xu; Jianyu Zhang
Original assignee: Jiangsu Longchang Chemical Co Ltd
Current assignee: Jiangsu Longchang Chemical Co Ltd
Priority date: 2014-07-18
Filing date: 2014-07-30
Publication date: 2017-02-09
Anticipated expiration: 2022-07-30
Also published as: AU2014401238A1; WO2016008175A1; CN104163749A; AU2014101600A6

Abstract

Abstract The present invention provides a para-dichlorobenzene separation and purification method to obtain high-purity, high-yield para-dichlorobenzene which has low energy consumption and 5 pollution-free.The method comprises dissolution, precipitation and fractional crystallization; In the dissolution and precipitation steps, raw para-dichlorobenzene is added in ethanol solution, then distilled water is added in with the temperature controlled in 5'C- 8'C, and a purity of 80% -8 8 % of para-dichlorobenzene is obtained after standing; Then, the crude para-dichlorobenzene is fractional crystallized to obtain para-dichlorobenzene with a purity no less than 99.9% and a 10 yield no less than 90%. In the separation and purification process, ethanol as the primary solvent and water as the precipitation solvent are low-cost, pollution-free solvents and the conditions are mild and are easy to operate;DCS system is used to achieve continuous production, to reduce sublimation and loss of raw material and to increase the processing capacity and product quality in the fractional crystallization process, and the economic benefits are significant. Mther Liquor f-'! TB ittp ICsn Fig. 1

Description

- 1 - 2014101600 30 Jul 2014

Specification A method for separating and purifying para-dichlorobenzene

Technical field 5 The present invention relates to a method for separating and purifying para-dichlorobenzene, which belongs to the organic mixture separation and purification method.

Background technology

Para-dichlorobenzene(abbreviated as p-dichlorobenzene or PDCB) is a white crystalline 10 which has a smell of camphor and is susceptible to sublimate at normal temperature, and has a relative density of 1.4581 g/cm3, boiling point 174°C, melting point 53°C.Para-dichlorobenzene is soluble in ethanol, diethyl ether, benzene, chloroform, or carbon disulfide, but almost insoluble in water. Para-dichlorobenzene is an important organic chemical product as an civilian mothproof and mouldproof product with high-efficiency and hypotoxicity, and the purity of the 15 para-dichlorobenzene is required to be no less than 99.5% in order to ensure usage safety; para-di chlorobenzene is also an important organic synthetic material for synthesizing fuels, pesticides and engineering plastics(e.g. polyphenylene sulfide),etc. But in present industrial production, the content of para-dichlorobenzene is only 77-85wt% which is prepared from dichlorobenzene by catalyzing and chloridizing benzene.Therefore, it is necessary for separating and purifying the 20 para-dichlorobenzene to achieve high purity.

Para-dichlorobenzene is a widely used fine chemical and has nearly a hundred years foreign research history. In China, the development and application of para-dichlorobenzene is still in developing stage due to the limitation of separation technology.Methods commonly used in industry for producing para-dichlorobenzene are as follows:cooling, extraction, washing, 25 distillation, rectification, re-crystallization, fractional crystallization, emulsification and isomerization, etc., wherein cooling is a commonly used method, and all those methods have a ubiquitous problem that the purity of the product is not high enough.Therefore, in order to obtain high-purity para-dichlorobenzene, it’s an urgent need to develop a new separating and refining process for further purifying para-dichlorobenzene product. 30 According to the melting point differences between p-dichlorobenzene and o- dichlorobenzene(PDCB 53°C, ODCB 17°C), multistage melt crystallization and sweating crystallization for separation are commonly used methods in industry. However, it is difficult to -2- 2014101600 30 Jul 2014 achieve high purity because the crystal is easily polluted by mother liquor. To solve this problem, a lot of researches have been done from the perspective of chemical engineering process and a number of new and efficient crystallization equipment and adsorption separation, washing-crystallization and other new separation methods have been developed. 5 Solvent nature is changed to selectively dissolve impurities to maximize target component that crystallized out from the solvents according to differential interactions between a target substance and different solvent molecules in dissolution and precipitation. In order to significantly reduce the solubility of a solute and to achieve the purpose of separation, the process comprises:dissolving a solute in a solvent (called a primary solvent) to form a saturated 10 solution and then dissolving another solvent (called a precipitating solvent) which is miscible with the primary solvent and not immiscible with the solute.In this process, the role of a primary solvent is to selectively dissolve impurities to improve the purity of the target substance, and the role of a precipitating solvent is to reduce the solubility of the target substance and improve the yield thereof. Therefore, high purity and high yield can be achieved by selecting suitable 15 solvent.

Distillation is a separation method carried on in the distillation vessel having a high number of plates and based on boiling point difference between compounds, which means that the more different boiling point, the more easily to separate.The boiling point difference between p-dichlorobenzene and o-dichlorobenzene is just about 5°C. So it’s very difficult to separate them 20 and needs high energy consumption.

Recrystallization method commonly uses two-blade type mould: in a first clean area, crude dichlorobenzene mixture is cooled to 40°C~ 45°C, and pumped to the crystallize, then further cooled to 35°C, and the precipitated p-dichlorobenzene is separated by centrifuge and reheated to melt.Then, the p-dichlorobenzene is sent to a second clean area and cooled to a lower 25 temperature. In order to obtain high-purity p-dichlorobenzene, the crystals can be pulverized and sieved and the fine powder can be melted again and recycled to a second clean zone, and two parts of mother liquors containing o-dichlorobenzene were merged and sent to the vacuum distillation tower and industrial-grade o-dichlorobenzene(87wt%) is obtained at the top of the tower.Redistillation can also be carried out to obtain high-purity p-dichlorobenzene if necessary 30 . The residual liquid in the bottom of the vacuum distillation tower is sent back to crystallizer to recollect trace amount of p-dichlorobenzene.Recrystallization method can get high purity product, but that needs many equipments such as a centrifuge pump and a great energy -3- 2014101600 30 Jul 2014 consumption.

Fractional crystallization method is based on different melting points between components to control the temperatures in process. Since the melting point difference between o-dichlorobenzene and p-dichlorobenzene is 70.6°C, it is easy to separate them by fractional 5 crystallization, and since the latentheat of melting(12.29J/g) is lower than the latentheat of vaporization(271.7J/g) for o-dichlorobenzene, the product decomposition is avoided at a lower temperature and the energy consumption is lower than the distillation method.Therefore, many countries widely use fractional crystallization to separate o-dichlorobenzene and p-dichlorobenzene. At present, crystallization method and emulsification method are generally 10 used home and abroad to refine p-dichlorobenzene. In mulsification method, a surfactant solution and oily o-dichlorobenzene contained in p-dichlorobenzene lattice or lattice surface form a stable emulsion, and 99.5wt% p-dichlorobenzene and less than 0.5wt% o-dichlorobenzene are obtained after cooling, filtration, centrifugation and drying.

The present invention attempts to provide a method that integrates two or more methods 15 with low energy consumption and non-pollution to obtain a high purity and high yield product in accordance with above advantages and disadvantages.

Summary of the invention

The invention is to provide a low energy consumption and non-pollution method for separating and purifying para-dichlorobenzene and obtain a high purity and high yield product. 20 In order to achieve these purposes, the invention is mainly implemented through the following technical solution. A method for separating and purifying para-dichlorobenzene, which comprises: dissolution, precipitation and fractional crystallization, wherein the dissolution and precipitation comprise: 25 al.a raw material containing 40~78wt% para-dichlorobenzene is added in 70~95wt% ethanol solution and are thoroughly mixed to homogeneous solution, wherein the mass ratio of para-dichlorobenzene and ethanol solution is 1 : 2.5 ~ 7.1, bl .then distilled water is gradually added in the homogeneous solution when the temperature is controlled in 5~8°C, and para-dichlorobenzene with a purity of 80-88wt% and a yield no less 30 than 77% is obtained after standing 20 ~ 40min, wherein the weight of distilled water is 0.35 to 0.45 times the weight of ethanol solution, wherein melting crystallization is used in fractional crystallization to refine the 80-88 wt% -4- 2014101600 30 Jul 2014 para-dichlorobenzene, and the process comprises: a2. para-dichlorobenzene with a purity of 80-88% is then refined by cooling and crystallizing in 1A stage, and 95-97 wt% para-dichlorobenzene product and a mother liquor are obtained, then the mother liquid is sent to a ortho-dichlorobenzene refining process, 5 b2. the obtained para-dichlorobenzene product in 1A stage is sent to IB melting crystallization stage to obtain 98-99wt% refined para-dichlorobenzene product and a mother liquor, the mother liquor is introduced to the feed tank and 1A stage crystallization process is repeated, c2. the obtained para-dichlorobenzene product in IB stage is thawed in 1C stage for further 10 refining process, d2. the thawed para-dichlorobenzene product in 1C stage is sent to 2A stage, and no less than 99.5wt% para-dichlorobenzene and a mother liquor are obtained after cooling and crystallizing process, then the mother liquor is introduced to the feed tank and 1A stage crystallization process is repeated , 15 e2.the obtained para-dichlorobenzene product in 2A stage is sent to the 2B melting crystallization stage, and no less than 99.9wt% refined para-dichlorobenzene product and a mother liquor are obtained, then the mother liquor is introduced to 2A stage for cooling and crystallization. f2.finally, the obtained para-dichlorobenzene product in 2B stage is sent to 2C stage to 20 thaw, and then sliced and packed.

Wherein the original material mixture comprises impurities such as o-dichlorobenzene and low boiling point materials, wherein the low boiling point materials further comprise monochlorobenzene and meta-dichlorobenzene. wherein the concentration of ethanol solution in dissolution and precipitation is 90wt%. 25 wherein the mass ratio of para-dichlorobenzene and ethanol solution in dissolution and precipitation is 1 ' 3-5. wherein the weight of distilled water is 0.4 times the weight of ethanol solution. wherein the temperature is gradually increased from 5°C to 8°C in bl step with the heating rate 0.075-0.15°C/min. 30 As the solubilities of o-dichlorobenzene and p-dichlorobenzene are sensitive to composition and mass changes of solvent, p-dichlorobenzene gradually precipitates when water is gradually added in.It is mainly because the hydrogen bonds between water molecules and -5- 2014101600 30 Jul 2014 ethanol molecules and the water molecules gradually surrounding the alcohol molecules weaken the molecular force between ethanol and p-dichlorobenzene.At the same time p-dichlorobenzene precipitated from the mixed solvent by gradually lowering the temperature. The method which integrates extraction, crystallization and washing, uses the selectivity of the main solvent 5 ethanol to impurities (ODCB) and the water precipitation to the target product (PDCB) and uses the mixed solvent to wash crystal effectively solves the problems that the impurities are adhered to and included in product and ensures the yield and purity of the product. wherein the cooling temperature in 1A stage in fractional crystallization a2~c2 steps is from 50°C to 10°C with the cooling rate 0.15°C/min, the melting temperature in IB stage is from 10 10°C to 48°Cwith the heating rate 0.1 °C/min, the melting temperature in 1C stage is 48°C to 80°C with the heating rate l°C/min. wherein the cooling temperature of 2A stage in fractional crystallization d2~f2 steps is from 15°C to 70°Cwith the cooling rate 0.2°C/min, the melting temperature in 2B stage is from 15°C to 50°C with the heating rate 0.08°C/min, and the melting temperature in 2C stage is from 15 50°C to 80°C with the heating rate l°C/min.

Wherein DCS system which is used in bl and A2 ~ f2 steps to achieve continuous operation and precisely control the p-dichlorobenzene separation and purification steps ensures the purity and the yield of the product and reduces energy consumption .

Wherein the yield of completed p-dichlorobenzene production in the fractional 20 crystallization is no less than 90%.

The advantageous effects of the invention are as follows: (1) In dissolution and precipitation, ethanol is used as a primary solvent and water as a precipitation solvent to easily and effectively separate p-dichlorobenzene from a mixture of o-dichlorobenzene and p-dichlorobenzenein, and 25 the solvents are low-cost and pollution-free.(2) In dissolution and precipitation,the equipment is simple, the conditions are mild and the operation is flexible.(3) The fractional melt crystallization process ensures precise control of temperature and materials, thereby improves the yield. (4) DCS system is used to achieve continuous production, automated control and loss reduction of raw material sublimation which ensure the continuity and stability of 30 dichlorobenzene refining process to improve the capacity and quality of product and achieve greater economic benefits. (5)the content of p-dichlorobenzene in raw material is in the range of 40%-78% in dissolution and precipitation steps that widens the purified scope of the p- -6- 2014101600 30 Μ 2014 dichlorobenzene, and the product prepared by the invention has a high purity and a high yield.

Embodiments

In order to enable the public to fully understand the technical essence and the advantageous effects of the present invention, the applicant reveals the embodiments of the present invention 5 with reference to the drawings, but the embodiments are not to limit the scope of the invention and any form change rather than substance change according to the invention should be regarded as the scope of the present invention.

Example 1

First, 10kg mixture of 48wt% p-dichlorobenzene was added 25kg of 90wt% ethanol 10 solution and mixed thoroughly. Then, 8.75kg distilled water was gradually added in with the heating rate of 0.075°C/ min to increase temperature from 5°Cto 8°C, and 8.6 kg p-dichlorobenzene with a purity of 88% was obtained after standing 20min. In general, fractional melting crystallization is used in the invention, the raw material is added to tank A and pumped into the fractional crystallizer C for 1A-1C crystallization process and the material is cooled and 15 partially melted at different temperature, then non-condensed liquid is discharged and semifinished product is sent to 2A-2C to obtain the final product.The specific processing steps in this embodiment were as follows: (1) The para-dichlorobenzene was then refined by cooling and crystallizing in 1A stage,and a 97 wt% para-dichlorobenzene product and a mother liquor were obtained, then the mother liquid was sent to a ortho-dichlorobenzene refining process, wherein 20 the cooling temperature range was from 50°C to 10°C with the cooling rate 0.15°C/min. (2) The obtained 97wt% para-dichlorobenzene product in 1A stage was sent to IB melting crystallization stage, then a 98.1wt% refined para-dichlorobenzene product and a mother liquor were obtained, the mother liquor was introduced to the feed tank and 1A stage process was repeated, wherein the melting temperature range was from 10°C to 48°C with the heating rate 0.1 25 °C/min.(3) The obtained 98. lwt% para-dichlorobenzene product in IB stage was sent to 1C stage to thaw for next further refining, wherein the melting temperature range was from 48°C to 80°C with the heating rate 1 °C/min.(4)The thawed product in 1C stage was sent to 2A stage to cool and crystallize, then a 99.2wt% refined para-dichlorobenzene product and a mother liquor were obtained, the mother liquor was introduced to the feed tank and 1A stage process was 30 repeated, wherein the cooling temperature range was from 70°C to 15°C with the cooling rate 0.2°C/min.(5) The obtained product in 2A stage was sent to 2B stage and then a 99.9wt% refined para-dichlorobenzene product and a mother liquor were obtained, the mother liquor was sent -7- 2014101600 30 Jul 2014 back to 2A stage, wherein the melting temperature range was from 15°C to 50°C with the heating rate 0.08°C/min.(6)Finally, the obtained para-dichlorobenzene product in 2B stage was sent to 2C stage to thaw, then sliced and packed, wherein the melting temperature range was from 50°Cto 80°C with the heating rate l°C/min and the purity of completed para-dichlorobenzene 5 product was 99.96%.

Example 2 12kg mixture containing 40wt% p-dichlorobenzene was added 85.2kg of 70wt% ethanol solution and mixed thoroughly. Then, 38.4kg distilled water was gradually added in with the 10 heating rate of 0.12°C/ min to increase temperature from 5°Cto 8°C, and 9.5 kg p- dichlorobenzene with a purity of 80% was obtained after standing 30min. Then the para-di chlorobenzene was refined by cooling and crystallizing in 1A stage,and a 97 wt% para-di chlorobenzene product and a mother liquor were obtained, then the mother liquid was sent to a ortho-dichlorobenzene refining process, wherein the cooling temperature range was from 50°C 15 to 10°C with the cooling rate 0.15°C/min. Then a 98. lwt% refined para-dichlorobenzene product and a mother liquor were obtained after IB melting crystallization stage, and the mother liquor was introduced to the feed tank and 1A stage process was repeated, wherein the melting temperature range was from 10°C to 48°C with the heating rate 0.1°C/min.The obtained para-di chlorobenzene product was then sent to 1C stage to thaw for next further refining, wherein the 20 melting temperature range was from 48°C to 80°C with the heating rate l°C/min.The thawed product was sent to 2A stage to cool and crystallize, and then a 99.2wt% refined para-di chlorobenzene product and a mother liquor were obtained, the mother liquor was introduced to the feed tank and 1A stage process was repeated, wherein the cooling temperature range was from 70°C to 15°C with the cooling rate 0.2°C/min.The obtained product was sent to 2B stage 25 and then a 99.9wt% refined para-dichlorobenzene product and a mother liquor were obtained, the mother liquor was sent back to 2A stage, wherein the melting temperature range was from 15°C to 50°C with the heating rate 0.08°C/min.Finally, the obtained para-dichlorobenzene product in 2B stage was sent to 2C stage to thaw, then sliced and packed, wherein the melting temperature range was from 50°Cto 80°C with the heating rate l°C/min and the purity of 30 completed para-dichlorobenzene product was 99.94%.

Example 3 -8- 2014101600 30 Jul 2014 20kg mixture containing 70wt% p-dichlorobenzene was added 55kg of 80wt% ethanol solution and mixed thoroughly. Then, 22kg distilled water was gradually added in with the heating rate of 0.10°C/ min to increase temperature from 5°Cto 8°C, and 46.3 kg p-dichlorobenzene with a purity of 86.5% was obtained after standing 30min. Then the para-5 dichlorobenzene was refined by cooling and crystallizing in 1A stage,and a 96.5 wt% para- dichlorobenzene product and a mother liquor were obtained, then the mother liquid was sent to a ortho-dichlorobenzene refining process, wherein the cooling temperature range was from 50°C to 10°C with the cooling rate 0.15°C/min. Then a 98.0wt% refined para-dichlorobenzene product and a mother liquor were obtained after IB melting crystallization stage, and the mother liquor 10 was introduced to the feed tank and 1A stage process was repeated, wherein the melting temperature range was from 10°C to 48°C with the heating rate 0.1°C/min.The obtained para-dichlorobenzene product was then sent to 1C stage to thaw for next further refining, wherein the melting temperature range was from 48°C to 80°C with the heating rate l°C/min.The thawed product was sent to 2A stage to cool and crystallize, and then a 99.2wt% refined para-15 di chlorobenzene product and a mother liquor were obtained, the mother liquor was introduced to the feed tank and 1A stage process was repeated, wherein the cooling temperature range was from 70°C to 15°C with the cooling rate 0.2°C/min.The obtained product was sent to 2B stage and then refined a 99.91wt% para-dichlorobenzene product and a mother liquor were obtained, and the mother liquor was sent back to 2A stage, wherein the melting temperature range was 20 from 15°C to 50°C with the heating rate 0.08°C/min.Finally, the obtained para-dichlorobenzene product in 2B stage was sent to 2C stage to thaw, then sliced and packed, wherein the melting temperature range was from 50°Cto 80°C with the heating rate l°C/min and the purity of completed para-dichlorobenzene product was 99.91%. 25 Example 4 8kg mixture containing 65wt% p-dichlorobenzene was added 40kg of 95wt% ethanol solution and mixed thoroughly. Then, 16kg distilled water was gradually added in with the heating rate of 0.15°C/ min to increase temperature from 5°Cto 8°C, and 6.5 kg p-dichlorobenzene with a purity of 85% was obtained after standing 40min. Then the para-30 di chlorobenzene was refined by cooling and crystallizing in 1A stage,and a 96wt% para-

dichlorobenzene product and a mother liquor were obtained, then the mother liquid was sent to a ortho-di chlorobenzene refining process, wherein the cooling temperature range was from 50°C 2014101600 30 Jul 2014 -9- to 10°C with the cooling rate 0.15°C/min. Then a 98.0wt% refined para-dichlorobenzene product and a mother liquor were obtained after IB melting crystallization stage, and the mother liquor was introduced to the feed tank and 1A stage process was repeated, wherein the melting temperature range was from 10°C to 48°C with the heating rate 0.1°C/min.The obtained para-5 dichlorobenzene product was then sent to 1C stage to thaw for next further refining, wherein the melting temperature range was from 48°C to 80°C with the heating rate l°C/min.The thawed product was sent to 2A stage to cool and crystallize, and then a 99.1 wt% refined para-dichlorobenzene product and a mother liquor were obtained, the mother liquor was introduced to the feed tank and 1A stage process was repeated, wherein the cooling temperature range was 10 from 70°C to 15°C with the cooling rate 0.2°C/min.The obtained product was sent to 2B stage and then refined a 99.9wt% para-dichlorobenzene product and a mother liquor were obtained, and the mother liquor was sent back to 2A stage, wherein the melting temperature range was from 15°C to 50°C with the heating rate 0.08°C/min.Finally, the obtained para-dichlorobenzene product in 2B stage was sent to 2C stage to thaw, then sliced and packed, wherein the melting 15 temperature range was from 50°Cto 80°C with the heating rate l°C/min and the purity of completed para-dichlorobenzene product was 99.92%.

Item Result Purity of completed product >99.9wt% The freezing point 52.9-53.0°C Production capacity 8400t/a Yield eluted precipitation: >77%; fractional crystallization: >90% Steam consumption 0.8kg steam / 1kg completed product Power consumption 0.22kW h / 1kg completed product 20

Claims

Claims l.A method for separating and purifying para-dichlorobenzene, which comprises: dissolution, precipitation and fractional crystallization, wherein the dissolution and precipitation comprise: al.a raw material containing 40-78wt% para-dichlorobenzene is added in 70-95wt% ethanol solution and are thoroughly mixed to homogeneous solution, wherein the mass ratio of para-dichlorobenzene and ethanol solution is 1 : 2.5-7.1, bl.then distilled water is gradually added in the homogeneous solution when the temperature is controlled in 5-8°C, and para-dichlorobenzene with a purity of 80-88wt% and a yield no less than 77% is obtained after standing 20-40min, wherein the weight of distilled water is 0.35-0.45 times the weight of ethanol solution, wherein melting crystallization is used in fractional crystallization to refine the 80-88 wt% para-dichlorobenzene, and the process comprises: a2. para-dichlorobenzene with a purity of 80-88% is then refined by cooling and crystallizing in 1A stage, and 95-97 wt% para-dichlorobenzene product and a mother liquor are obtained, then the mother liquid is sent to a ortho-dichlorobenzene refining process, b2. the obtained para-dichlorobenzene product in 1A stage is sent to IB melting crystallization stage to obtain 98-99wt% refined para-dichlorobenzene product and a mother liquor, the mother liquor is introduced to the feed tank and 1A stage crystallization process is repeated, c2. the obtained para-dichlorobenzene product in IB stage is thawed in 1C stage for further refining process, d2. the thawed para-dichlorobenzene product in 1C stage is sent to 2A stage, and no less than 99.5wt% para-dichlorobenzene and a mother liquor are obtained after cooling and crystallizing process, then the mother liquor is introduced to the feed tank and 1A stage crystallization process is repeated , e2.the obtained para-dichlorobenzene product in 2A stage is sent to the 2B melting crystallization stage, and no less than 99.9wt% refined para-dichlorobenzene product and a mother liquor are obtained, then the mother liquor is introduced to 2A stage for cooling and crystallization. f2.finally, the obtained para-dichlorobenzene product in 2B stage is sent to 2C stage to thaw, and then sliced and packed.
2. A method according to claim 1, wherein the concentration of ethanol solution in dissolution and precipitation is 90wt%.
3. A method according to claim 1, wherein the mass ratio of para-dichlorobenzene and ethanol solution is 1 : 3-5
4. A method according to claim 1, wherein the weight of distilled water is 0.4 times the weight of ethanol solution.
5. A method according to claim 1, wherein the temperature is gradually increasing from 5°C to 8°C in b2 step with the heating rate 0.075-0.15°C/min.
6. A method according to claim 1, wherein the cooling temperature in 1A stage in fractional crystallization a2~c2 steps is from 50°C to 10°C with the cooling rate 0.15°C/min, the melting temperature in IB stage is from 10°C to 48°Cwith the heating rate 0.1 °C/min, the melting temperature in 1C stage is 48°C to 80°C with the heating rate l°C/min.
7. A method according to claim 1, whereinthe cooling temperature of 2A stage in fractional crystallization d2~f2 steps is from 15°C to 70°Cwith the cooling rate 0.2°C/min, the melting temperature in 2B stage is from 15°C to 50°C with the heating rate 0.08°C/min, and the melting temperature in 2C stage is from 50°C to 80°C with the heating rate l°C/min.