Preparation and characterization of paraffin Pickering emulsion without subcooling phenomenon

doi:10.11949/0438-1157.20201053

Abstract

Abstract:

Paraffin wax emulsion is a new functional fluid integrating heat storage and heat transfer, and has broad application prospects. However, when the paraffin emulsion is cooled down, there will be obvious supercooling phenomenon, which reduces its heat storage and heat transfer performance. In the present work, O/W type paraffin Pickering emulsion was prepared via high mechanical shear, using magnesium-aluminum double-layer metal hydroxide (Mg-Al LDHs) instead of chemical surfactant. The microscale morphology, particle size distribution, viscosity, stability, and thermal properties of the as-prepared paraffin Pickering emulsion were characterized by using scanning electron microscope, laser diffraction particle size analyzer, rheometer, multiple light scatterometer and differential scanning calorimeter, respectively. The results show that, with the increase of Mg-Al LDHs content from 1%(mass) and 5%(mass), the mean particle size of paraffin Pickering emulsion decreased, while the viscosity increased significantly, resulting in better long-term stability of the emulsion. The subcooling of paraffin Pickering emulsion was suppressed completely via heterogeneous nucleation of paraffin, which was induced by Mg-Al LDHs nanoparticles absorbed at the water-paraffin interface. Latent heat of as-prepared paraffin Pickering emulsion was around 56.6 J·g^-1, while the mean apparent specific heat capacity was 6.08 J·g^-1·K^-1 in the temperature range concerned (30—70℃), which was about 1.45 times of the value of water.

Key words: paraffin, Pickering emulsion, subcooling phenomenon, magnesium-aluminum double-layer metal hydroxide

摘要：

石蜡乳液是集储热与传热于一体的新型功能流体，具有广阔的应用前景。但是石蜡乳液在降温时会出现明显的过冷现象，降低了其储热与传热的性能。针对这个问题，用镁-铝层状双金属氢氧化物（Mg-Al LDHs）代替化学表面活性剂，采用高速剪切乳化法，制备了石蜡含量为30%（质量）的O/W型Pickering乳液；分别采用扫描电子显微镜、激光粒度分析仪、流变仪、全能稳定性分析仪和差示扫描量热仪对所制得的石蜡Pickering乳液的微观形貌、粒度分布、黏度、稳定性和热力学性质进行了表征。结果表明，当Mg-Al LDHs的含量从1%（质量）增加到5%（质量）时，石蜡Pickering乳液的粒度减小，黏度升高，稳定性得到改善；在石蜡Pickering乳液中，Mg-Al LDHs纳米颗粒吸附在石蜡液滴表面，诱导石蜡在降温时异相成核结晶，从而抑制了其过冷现象；所制备的石蜡Pickering乳液的相变焓值约为56.6 J·g^-1，在测试的温度范围内（30~70℃）的平均表观比热容为6.08 J·g^-1·K^-1，是纯水的1.45倍，具有良好的储热性能。

关键词: 石蜡, Pickering乳液, 过冷现象, 镁-铝层状双金属氢氧化物

CLC Number:

TQ 028.8

RU Shaoqing, WU Yafei, CHE Liming. Preparation and characterization of paraffin Pickering emulsion without subcooling phenomenon[J]. CIESC Journal, 2021, 72(4): 2309-2316.

茹绍青, 武亚飞, 车黎明. 低过冷度石蜡Pickering乳液的制备和表征[J]. 化工学报, 2021, 72(4): 2309-2316.

Figures/Tables 10

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名称	规格	生产厂家
石蜡	熔点58~60℃	上海永华石蜡有限公司
MgCl₂·6H₂O	AR	国药集团化学试剂有限公司
AlCl₃·6H₂O	AR	国药集团化学试剂有限公司
氨水	AR	广东光华科技股份有限公司
NaHCO₃	AR	国药集团化学试剂有限公司
Na₂CO₃	AR	国药集团化学试剂有限公司
NaCl	AR	国药集团化学试剂有限公司
去离子水	电阻率不小于18.2 MΩ·cm^-1	自制

名称	规格	生产厂家
石蜡	熔点58~60℃	上海永华石蜡有限公司
MgCl₂·6H₂O	AR	国药集团化学试剂有限公司
AlCl₃·6H₂O	AR	国药集团化学试剂有限公司
氨水	AR	广东光华科技股份有限公司
NaHCO₃	AR	国药集团化学试剂有限公司
Na₂CO₃	AR	国药集团化学试剂有限公司
NaCl	AR	国药集团化学试剂有限公司
去离子水	电阻率不小于18.2 MΩ·cm^-1	自制

样品	D_3,2平均粒度/μm	D_4,3平均粒度/μm
1% Mg-Al LDHs	17.8	22.0
2% Mg-Al LDHs	26.2	33.5
3% Mg-Al LDHs	20.2	25.1
4% Mg-Al LDHs	19.4	24.5
5% Mg-Al LDHs	16.9	21.7

样品	D_3,2平均粒度/μm	D_4,3平均粒度/μm
1% Mg-Al LDHs	17.8	22.0
2% Mg-Al LDHs	26.2	33.5
3% Mg-Al LDHs	20.2	25.1
4% Mg-Al LDHs	19.4	24.5
5% Mg-Al LDHs	16.9	21.7

样品	熔化温度（起始点）/℃	凝固温度（起始点）/℃	相变焓/(J·g^-1)
石蜡	52.4	55.0	126.6
1% Mg-Al LDHs	53.0	54.1	52.5
2% Mg-Al LDHs	52.5	54.4	52.6
3% Mg-Al LDHs	52.4	54.8	57.3
4% Mg-Al LDHs	51.8	54.6	63.8
5% Mg-Al LDHs	52.8	54.8	56.6