Article pubs.acs.org/jced
Cite This: J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Measurement and Thermodynamic Models for Ternary Liquid− Liquid Equilibrium Systems {Water + Polyoxymethylene Dimethyl Ethers +4-Methyl-2-pentanol} at Different Temperatures Liping Wang, Saisai Zhou, Pan Li, Pengzhou Li, Qingsong Li,* and Yingmin Yu
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State Key Laboratory of Heavy Oil Processing, College of Chemical Engineering, China University of Petroleum - East China, Qingdao, Shandong 266580, China ABSTRACT: Polyoxymethylene dimethyl ethers (DMMn) have attracted particular attention in industry as excellent oxygenated fuel additives. This study aims to reveal the liquid−liquid equilibrium (LLE) values regarding ternary mixtures {water + methylal (DMM1) + 4-methyl-2-pentanol (MIBC)}, {water + DMM2 + MIBC}, {water + DMM3 + MIBC}, and {water + DMM4 + MIBC} at 298.2 and 308.2 K under 101.3 kPa. Distribution factor and selectivity were utilized to assess the extracting capabilities of the selected extractant. The well known Hand equation and Othmer− Tobias equation were utilized to test the consistency of the LLE values. In addition, the experimental results were correlated by the UNIQUAC and NRTL thermodynamic models with all of the root-mean-square deviation values less than 0.0127,which indicated that both models agree well with the experimental tieline data. hemiformal (CH3−O−(CH2O)n−CH2OH, HFn) as follows in eq 3.5,10 It can be seen that obtaining the high-purity DMMn products is very difficult, and thus it is necessary to separate the DMM1−4 compounds from the aqueous solution.
1. INTRODUCTION Diesel engines have excellent dynamic performance, economy, and durability, which are widely used in various power devices.1 However, the main emission pollutants NOx and PM (particles with sizes between 0.1 and 10 μm) of diesel engines are harmful to the environment and human health.1−3 As green and environmental diesel additives, polyoxymethylene dimethyl ethers (DMMn or PODEn, n > 1, CH3−O−(CH2O)n−CH3) have a promising application prospect due to their high cetane numbers, high oxygen contents, and ability to easily blend with diesel.5,6 Among all DMMn compounds, DMM2 does not meet safety standards due to its low flash point, and DMMn > 5 will precipitate at low temperature due to high melting point, and thus DMM3−4 are considered to be the optimal components as diesel additives.4,7 In general, the synthesis of DMMn can make full use of a large amount of excess C1 chemicals (methanol and formaldehyde) to ease the crisis in the supply of diesel fuel and bring huge environmental and economic benefits.8,9 The chemical reaction equation is listed as follows FA + 2ME F DMM1 + H 2O
(1)
FA + DMM n − 1 F DMM n
(2)
H 2O + DMM n F HFn + ME
At present, the unreacted raw materials and water contained in the products composition are usually separated by ordinary distillation and solvent extraction in the engineering industry.9,10 However, the self-polymerization of formaldehyde can likely lead to blocking the pipeline by distillation. In contrast, solvent extraction plays a significant part in separating DMMn products due to its higher efficiency and smaller energy consumption. Zhuang et al.11,12 investigated the LLE data of the ternary mixtures {water + PODE1−4 + p-xylene} at 293.15 and 313.15 K, while the ternary data of {water + PODE1−4 + n-hexane} systems were also studied at 293.15 K. Shi et al.13,14 reported the LLE values of {water + DMM3 + (p-xylene toluene or n-heptane)} and {water + methylal + (cyclohexane n-heptane)} systems at the temperatures from 303.15 to 313.15 K, respectively. Given the relative lack of available data, it is still imperative to find more and new extractants to separate DMMn products. According to the work by Liu et al.,15,16 4-methyl-2-pentanol (MIBC) can exhibit good extraction ability in aqueous solution. Therefore, MIBC was chosen as a new solvent for extracting PODE1−4 from water in this study.
where ME and FA refer to methanol and formaldehyde, respectively. In this synthetic route, water enters the chemical reaction system through raw materials and is produced as a byproduct. In an acid-catalyzed reaction at a certain temperature, water causes the hydrolysis of DMMn compounds to form methanol and poly © XXXX American Chemical Society
(3)
Received: April 21, 2018 Accepted: July 9, 2018
A
DOI: 10.1021/acs.jced.8b00323 J. Chem. Eng. Data XXXX, XXX, XXX−XXX
Journal of Chemical & Engineering Data
Article
Table 1. Properties of the Materials component
source
chemical formula
mass fraction puritya
purification method
analysis method
CAS
4-methyl-2-pentanol methylal DMM2 DMM3 DMM4 waterc
Aladdin Aladdin self-made self-made self-made self-made
C6H14O C3H8O2 C4H10O3 C5H12O4 C6H14O5 H2O
≥99.00% ≥99.50% ≥98.00% ≥98.00% ≥98.00%
none none distillation distillation distillation distillation
GCb GCb GCb GCb GCb
108-11-2 109-87-5
7732-18-5
Mass fraction purity is stated by the gas chromatograph with peak area. Gas chromatograph. Electrical conductivity of water is 8.35 μs/cm.22
a
b
c
more than 8 h to ensure that liquid−liquid phase equilibrium was established. The evaporated compound was completely condensed by the condenser during the experimental operation to ensure mass balance. 2.3. Analysis. When the ternary mixture reached phase equilibrium, the samples were taken out from the water-rich layer and the MIBC-rich layer by a syringe, respectively. Agilent GC6820 gas chromatography, equipped with a 3 m × 3 mm Porapak N column and a thermal conductivity detector (TCD), was utilized to analyze those samples. A standard analytical method was implemented to convert the peak area ratio into a mass composition, and tetrahydrofuran and isopropyl alcohol were selected as the internal standard materials. Good peak detection was achieved according to the following designed operating procedure. The detector and injector port temperature were fixed at 523.2 K, the initial temperature was maintained at 388.2 K for 3 min, the column temperature was increased to 423.2 K at a rate of 5 K/min, and then the temperature was increased by 15 K/min to a final temperature of 523.2 K for 2 min. Hydrogen was used as the carrier gas with a flow rate of 1 mL/s. The final composition of each sample was repeated three times to ensure data reliability, and a series of experimental values were achieved by changing the feed composition. Additionally, the GUM standard25 was utilized to determine the uncertainty of the mass compositions for the two enriched phases, which has been used elsewhere.26,27 The estimated uncertainty of the equilibrium mixture (in mass fraction) was
