Thermodynamics, excess properties, spectra and computational chemistry of 1,2-propanediol + 1,2-propane diamine binary system

Xuan Liu; Jialin Wu; Fu Li; Rumeng Zhang; Xing Qin; Zhaojun Wu; Jianbin Zhang

doi:10.1016/j.arabjc.2022.104130

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Original article

10 2022

:15;

104130

doi:

10.1016/j.arabjc.2022.104130

Thermodynamics, excess properties, spectra and computational chemistry of 1,2-propanediol + 1,2-propane diamine binary system

Xuan Liu^{^a,^b}, Jialin Wu^{^a,^b}, Fu Li^{^a}, Rumeng Zhang^{^a}, Xing Qin^{^a,^b}, Zhaojun Wu^{^a,⁎}, Jianbin Zhang^{^a,^b,⁎}

a Inner Mongolia Engineering Research Center for CO₂ Capture and Utilization, Inner Mongolia University of Technology, Hohhot 010051, China

b Hebei Provincial Key Lab of Green Chemical Technology and High Efficient Energy Saving, School of Chemical Engineering and Technology, Hebei University of Technology, Tianjin, 300130, China

⁎Corresponding authors. nmzhjwu@163.com (Zhaojun Wu), tadzhang@pku.edu.cn (Jianbin Zhang)

Received: 2022-5-5, Accepted: 2022-7-12,

Disclaimer:
This article was originally published by Elsevier and was migrated to Scientific Scholar after the change of Publisher.

Peer review under responsibility of King Saud University.

Abstract

Abstract

The basic density (ρ), kinematic viscosity (v) and surface tension (γ) data of the 1,2-propanediol (1,2-PPD) (1) + 1,2-propane diamine (1,2-PDA) (2) binary system at T = (293.15, 298.15, 303.15, 308.15, 313.15 and 318.15) K were reported under atmospheric pressure (889 hectopascals in Hohhot, China). After that, the absolute viscosity (η), excess volume (V_m^E), viscosity deviation (Δη), surface tension difference (Δ γ), apparent molar volume (V_φ,1 and V_φ,2), partial molar volume ( $\bar{V_{1}}$ and $\bar{V_{2}}$ ), isothermal expansion coefficient (α_p) and excess Gibbs free energy (ΔG^*E) of the binary system were further calculated. Meanwhile, the Redlich-Kister (R-K) equations were fitted to V_m^E, Δ η, and Δ γ values, and the corresponding equation coefficients were obtained to estimate the errors between the experimental and calculated values. Finally, the binary system was characterized by FTIR, UV-vis, FLS, ¹H NMR, Raman spectroscopic techniques, and the bond energy and bond length between molecules were calculated by Gaussian 09 software to discuss the intermolecular interaction between 1,2-PPD and 1,2-PDA. The results show that hydrogen bonding interaction does exist among molecules in the form of -O—H···N-. Herein, the work provides a basis for engineering design and also provides fundamental data for the application of the binary system.

Nomenclature

cal. & exp.: calculated and experimental data
ρ: density, g·cm⁻³
v: kinematic viscosity, mm²/s
η: dynamic viscosity, mPa·s
γ: surface tension, mN·m⁻¹
V_m^E: excess molar volume, cm³·mol⁻¹
Δη: viscosity deviation, mPa·s
Δγ: surface tension deviation, mN·m⁻¹
ΔG^*E: free energy, kJ·mol⁻¹
V_φ,1, V_φ,2: apparent molar volumes, cm³·mol⁻¹
$\bar{V_{1}}$ , $\bar{V_{2}}$: partial molar volumes, cm³·mol⁻¹
α_p: isobaric thermal expansion coefficients, K⁻¹
R: ideal gas constant, 8.314 J·mol⁻¹·K⁻¹
A and B: viscometer constants
AAD%: average deviation from Eq. (9)
x_i: molar fraction from Eq. (10)
M_i: relative molecular mass from Eq. (10)
A_i: polynomial coefficient from Eq. (14)
σ: standard deviation from Eq. (15)
V₁⁰ and V₂⁰: molar volume from Eqs. (18) and (19)

1 Introduction

In recent years, the greenhouse effect becomes more serious due to the rapid development of industry and rapid population growth, which has led to a rapid increase in atmospheric CO₂ concentration and other greenhouse gases far beyond the capacity of natural ecosystems to withstand (Spasojevic et al., 2013). The issue of global warming and climate change caused by the greenhouse effect has become the focus of the international community (Lee et al., 2008; Notz et al., 2007; Stewart and Hessami, 2005 ). Among the gases that contribute to global warming, CO₂ is the dominant factor, so it is imperative to control CO₂ emissions (Ma’mun et al., 2007). The known technologies for capturing CO₂ cover physical, chemical, and physicochemical absorption, variable pressure adsorption, membrane separation, biological methods, injection into coal and deep-sea, etc (Hosseini-Ardali et al., 2020; Dong et al., 1999; Lian et al., 2021; Furtado et al., 2020; Xu et al., 2003; Xu et al., 2002; Figueroa et al., 2008 ). Among them, monoethanolamine (MEA), diethanolamine (DEA), triethanolamine (TEA), and N-methyl diethanolamine (MDEA) are widely used for scrubbing processes with the highest absorption efficiency (Kim et al., 2013; Zoannou et al., 2013; Button and Gubbins, 1999; Vahidi et al., 2013; Aguila-Hernandez et al., 2008; Kim et al., 2004; Mangalapally et al., 2009; Sutar et al., 2012; Elka et al., 2013; Maheswari and Palanivelu, 2014 ). However, this method also presents certain limitations such as the corrosive and strong volatility of amine solution, the larger size of equipment required for application, and the higher regeneration energy, which in turn lead to higher production costs, so the approach is also limited by a certain amount of energy consumption (Zhou et al., 2008; Oexmann et al., 2008). In response to these problems (Klimaszewski et al., 2012; Zhang et al., 2009; Zhang et al., 2010 ), it was proposed that alcohols were added to the amine solution to form a binary system. The hydrogen bonding of alcohol with amine was the dominant factor that can significantly reduce amine loss during CO₂ capture (Gahlyan et al., 2017; Rani and Maken, 2012; Rani et al., 2015 ). Therefore, it is particularly important to study the intermolecular interaction in the alcohol + amine binary system.

In general, to study the intermolecular interaction in the binary system, it is necessary to measure the basic thermodynamic properties, such as density (ρ), absolute viscosity (η), and surface tension (γ) data (Pensado et al., 2005; Singh et al., 1992). The binary systems are closely related to their volume properties, which are not simple solute-solvent, solvent-solvent, or solute-solute, but are determined by the gap structure effect caused by the difference between free volume and molar volume in solutions (Doghaei et al., 2010; Lubowiecka-Kostka and Zorebski, 2009; Tôrres et al., 2006; Verma et al., 2019, Zhao and Zhang, 2022 ). Besides, these properties need to be fully understood in practical engineering design and subsequent operations at various temperatures (Tôrres and Hoga, 2008; Rani et al., 2013). However, the intermolecular interaction has been less studied. Therefore, the intermolecular interaction in alcohol + amine binary systems needs to be deeply discussed.

In this work, the density (ρ), absolute viscosity (η), and surface tension (γ) values of 1,2-PPD (1) + 1,2-PDA (2) were firstly measured at 293.15–318.15 K with 5 K intervals and atmospheric pressure (889 hectopascals in Hohhot, China). These basic data were further used to calculate a series of excess properties of the binary system including excess volume (V_m^E), viscosity deviation (Δ η), surface tension difference (Δ γ), apparent molar volume (V_φ,1 and V_φ,2), partial molar volume ( $\bar{V_{1}}$ and $\bar{V_{2}}$ ). At the same time, FTIR, Raman, UV-vis, FLS, and ¹H NMR techniques were used to measure the shift of characteristic peaks, the shift of absorption peaks, and the change of chemical shifts in the binary system; secondly, the Gaussian 09 software was used to calculate the possible structures of single, double and triple molecules respectively and to derive the most stable structures. And the intermolecular interactions were further discussed in the binary system 1,2-PPD(1) + 1,2-PDA(2). Therefore, this work enriches the database of hybrid binary systems and provides theoretical data for industrial simulation and practical applications.

2 Experimental

2.1

2.1 Materials

Analytical reagent (AR) 1,2-PPD (CAS: 57-55-6) with purity 99 %, molar mass 76.09 g/mol, and chromatographic grade (GC) 1,2-PDA (CAS: 78-90-0) with purity ≥ 99.5 %, molar mass 74.12 g/mol, were purchased in Shanghai Mac Biochemical Technology Co., ltd. The standard solution required for the experiments was deionized water and chromatographic (HPLC) grade ethanol (CAS: 64-17-5, 99.8 % purity), which was purchased from Tianjin Yong Sheng Technology Development. Before the experiment, 1,2-PPD were dealt with on 4 Å molecular sieve (Tianjin Kermel Chemical Reagent Co., ltd.) for dehydration and ultrasonic degassing. Under atmospheric pressure and (293.15–318.15) K, ultrapure water and HPLC grade ethanol were used to calibrate the gravity bottle and the viscometer. The as-used reagents are summarized in Table 1.

Table 1 Specification of chemical samples at 889 hPa.

Chemicals name	Origin^b	Mass fraction purity	Molecular formula	CAS no	Isolation method
1,2‑Propanediol	Shanghai Macklin Biochemical Technology., Co, ltd., China	≥ 99.0 %	C₃H₈O₂	57-55-6	Desiccation^c and Degasification^d
1,2-Propylenediamine	Shanghai Macklin Biochemical Technology., Co, ltd., China	≥99.5 %(GC)	C₃H₁₀N₂	78-90-0	Desiccation^c and Degasification^d
ethanol^a	Tianjin YongSheng Technology Development., Co, ltd., China	≥ 99.9 %	C₂H₆O	64-17-5	Degasification^d

a Chromatographic grade.

b Declared by the supplier.

c Molecular sieve type 4A.

d Ultrasound.

2.2

2.2 Methods

The mixed solution with a total mass of 80 g was prepared in a volumetric flask with different ratios, in which the mass fraction of 1,2-PPD was in the range of 0 ∼ 100 % with 5 % intervals. The uncertainty between the actual and theoretical masses of 1,2-PDA and 1,2-PPD was calculated at ± 0.0003 g, which were determined by a BSA224S electronic balance (accuracy: ± 0.0001 g). The density was measured using a specific gravity flask with 25 cm³, and all experiments were carried out at (293.15–318.15) K and atmospheric pressure. The solutions with different components were placed in the specific gravity bottle, and each measurement required the bottle to be placed in a smart glass thermostatic water bath (SYP-D type) (Shanghai Yingdi Equipment Co., ltd.) with the accuracy of ± 0.01 K for 20 min to reach constant temperature before weighing. The masses of binary solutions with different solutions were weighed by the electronic balance. Each concentration solution needs to be measured several times until it appears that the uncertainty of three data is less than or equal to ± 0.0003 g. The average value of the three tests was set as the mass of the solution at the corresponding temperature. The volume of the bottle was confirmed by measuring the ultrapure water, and the density values of the binary system were further calculated. Density (ρ) was measured over the entire composition range of the binary mixtures (0–1) mole fraction.

The v values were measured using the ubbelohde viscometer with a specification of 1.2–1.3 mm (British Standards Institution). To measure accurately, the viscometer was firstly calibrated, in which the flow time of ultrapure water and ethanol (HPLC) in the viscometer was carefully measured, η values were obtained by Eq. (2), and then they were compared with literature values. Besides, the temperature of the binary system needs to be controlled, and the temperature measurement is required to reach the uncertainty of ± 0.01 °C. The specific experimental procedure was to invert the configured solution between the viscometer scales, thermostat the water bath for 20 min to obtain thermal stability, and then measure its flow time in the viscometer with a handheld digital stopwatch (accuracy: ± 0.01 s). For different concentrations of experimental samples, 18 groups of data (accuracy: ± 0.03 s) were measured. Then, the average value was taken as the flow time of the component solution in the viscometer to ensure the accuracy of measurement. Absolute viscosity (η) were measured over the entire composition range of the binary mixtures (0–1) mole fraction.

The γ values were measured by the platinum plate method, and the instrument is the BZY-2 automatic surface tension meter (Shanghai Balance Instrument, accuracy: ± 0.01 mN‧m⁻¹). Methods of measurement are as follows: (i) Immersion of platinum plate into liquid was carried out. (ii) Under the immersion condition of the platinum plate, the balance values were measured by the sensor. (iii) The induced equilibrium values were converted into surface tension values and displayed. The surface tension meter was calibrated with standard weights before the test at temperatures from 293.15 − 318.15 K with 5 K intervals and atmospheric pressure. Under the same conditions, the ultrapure water was used to calibrate the automatic surface tension meter, the measured values were compared with the literature values to control the uncertainty of ± 0.03 mN·m⁻¹, each sample was measured three times at least, and the average value was taken as the surface tension value of component solutions. Surface tension (γ) were measured over the entire composition range of the binary mixtures (0–1) mole fraction.

The intermolecular interaction was calculated by Gaussian 09 software, and the density functional form is Becke’s three-parameter mixed exchange functional, namely the correlation functional of Lee, Yang, and Parr (B3LYP) (Becke, 1993). The basis set of all atoms is 6-311G*, all closed-shell layers adopt restrictive methods, all energy information has been zero-point energy correction (ZPE), and the simple harmonic vibration frequency of 1,2-PPD and 1,2-PDA is used to ensure that the optimized structure is locally smallest. Specific calculation information includes bond lengths, bond energies and hydrogen bonds among single, double and triple molecules.

The infrared spectra were measured using an FTIR spectrometer (USA/Nexus 670) from Nikoli Corporation (equipped with two BaF₂ mica flakes), and the scan was in the range of (4000 to 400) cm⁻¹ with a resolution of 1 cm⁻¹. The UV spectra were obtained using a UV-vis spectrophotometer (Shanghai/UV-3200) from Shanghai Meproda Instruments Co., ltd, and the scan was in the range of (190 to 400) nm with a resolution of 1 nm. The fluorescence spectra were obtained using an FLS spectrometer (China Hong Kong/RF-5301P) from Shimadzu with a 500 W Hg-Xe high-pressure lamp. The proton nuclear magnetic resonance spectra were obtained using ¹H NMR spectrometer (USA/500 MHz) from Agilent, and the solvent for the ¹H NMR spectra was CDCl₃. Raman spectra were obtained using a Raman spectrometer (Britain/INVIA REFLEX) from Renishaw, and the scan was in the range of (100 to 4000) cm⁻¹ with the laser wavelength of 532 nm.

3 Results and discussion

3.1

3.1 Density, viscosity, and surface tension

A comparison of ρ, η, and γ values with literature values was shown in Table 2 (Zhang et al., 2020a, 2020b; Islam et al., 2003; Yang et al., 2018; Zhao et al., 2017 ).

Table 2 At six temperatures and 889 hPa, the experimental ρ, η and γ values of 1,2-PPD and 1,2-PDA compared with literature values.

T/(K)	1,2-PDA						1,2-PPD
	ρ/(g·cm⁻³)		η/(mPa·s)		γ/(mN·m⁻¹)		ρ/(g·cm⁻³)		η/(mPa·s)		γ/(mN·m⁻¹)
	Exp.	Lit.	Exp.	Lit.	Exp.	Lit.	Exp.	Lit.	Exp.	Lit.	Exp.	Lit.
293.15	0.8635	0.8633	1.67	1.62	33.93	33.49	1.0366	1.0368 1.0368	59.9	59.2 55.9	36.46	36.40
298.15	0.8589	0.8583 0.8587 0.8584	1.48	1.46 1.47 1.48	33.49	33.30	1.0328	1.0331 1.0329	44.4	43.4 43.4	36.18	36.16
303.15	0.8538	0.8540 0.8528 0.8538	1.34	1.32 1.34 1.31	32.97	32.77	1.0291	1.0291 1.0292	33.8	33.3 33.1	35.69	35.92
308.15	0.8491	0.8496 0.8502 0.8492	1.20	1.20 1.13 1.17	32.52	32.51	1.0257	1.0253 1.0250	25.4	24.9 23.7	35.61	35.68
313.15	0.8441	0.8442 0.8460 0.8445	1.08	1.08 1.06 1.05	32.12	32.16	1.0219	1.0224 1.0225	19.7	19.3 19.4	35.40	35.45
318.15	0.8635	0.8413 0.8428 0.8398	0.99	0.96 0.97 0.95	32.34	31.65	1.0187	1.0173 1.0179	15.7	15.7 15.4	34.96	35.21

The standard uncertainty components u for each variable are u(T) = 0.01 K, u(x₁) = 0.0001, and the combined expanded uncertainty is U(ρ) = 0.0020 g·cm⁻³ at 0.95 confidence level. The un.certainty for t is u(t) = 0.01 s, and the relative expanded uncertainties U_r is U_r(η) = 0.028 mPa·s at 0.95 confidence level. The uncertainty for surface tension is U (γ) = 0.200 mN·m⁻¹ at 0.95 confidence level.

The ρ, η, and γ data are listed in Tables 3–5 and shown in Figs. 1–3 .

Table 3 Experimental ρ values of 1,2-PPD (1) + 1,2-PDA (2) at T = (293.15 to 318.15) K with the step of 5 K and 889 hPa.

x₁	ρ/(g·cm⁻³)
x₁	T = 293.15 K	T = 298.15 K	T = 303.15 K	T = 308.15 K	T = 313.15 K	T = 318.15 K
0.0000	0.8635	0.8589	0.8538	0.8491	0.8441	0.8404
0.0488	0.8736	0.8689	0.8645	0.8596	0.8548	0.8503
0.0977	0.8846	0.8795	0.8753	0.8705	0.8657	0.8612
0.1467	0.8950	0.8902	0.8858	0.8812	0.8764	0.8722
0.1958	0.9055	0.9006	0.8962	0.8916	0.8869	0.8826
0.2451	0.9164	0.9116	0.9070	0.9026	0.8975	0.8933
0.2945	0.9267	0.9218	0.9176	0.9130	0.9083	0.9040
0.3441	0.9374	0.9324	0.9281	0.9238	0.9191	0.9147
0.3937	0.9476	0.9427	0.9384	0.9339	0.9293	0.9251
0.4435	0.9572	0.9523	0.9482	0.9436	0.9389	0.9349
0.4934	0.9668	0.9620	0.9582	0.9539	0.9491	0.9449
0.5435	0.9754	0.9709	0.9667	0.9622	0.9576	0.9535
0.5937	0.9841	0.9795	0.9755	0.9711	0.9666	0.9627
0.6440	0.9923	0.9876	0.9838	0.9794	0.9750	0.9710
0.6945	0.9996	0.9953	0.9913	0.9872	0.9826	0.9791
0.7451	1.0066	1.0024	0.9986	0.9944	0.9902	0.9864
0.7958	1.0131	1.0091	1.0054	1.0013	0.9973	0.9934
0.8466	1.0194	1.0156	1.0118	1.0077	1.0037	1.0001
0.8976	1.0256	1.0216	1.0180	1.0139	1.0100	1.0065
0.9487	1.0308	1.0274	1.0238	1.0199	1.0158	1.0124
1.0000	1.0366	1.0328	1.0291	1.0257	1.0219	1.0187

The standard uncertainty components u for each variable are u(T) = 0.01 K, u(x₁) = 0.0001, and the combined expanded uncertainty is U(ρ) = 0.0020 g·cm⁻³ at 0.95 confidence level.

Table 4 η values of 1,2-PPD (1) + 1,2-PDA (2) at T = (293.15 to 318.15) K with the step of 5 K and 889 hPa.

x₁	η/(mPa·s)
x₁	T = 293.15 K	T = 298.15 K	T = 303.15 K	T = 308.15 K	T = 313.15 K	T = 318.15 K
0.0000	1.67	1.48	1.34	1.20	1.08	0.99
0.0488	2.05	1.81	1.60	1.43	1.27	1.16
0.0977	2.68	2.32	2.02	1.78	1.55	1.42
0.1467	3.53	2.98	2.58	2.24	1.93	1.74
0.1958	4.70	3.92	3.36	2.84	2.42	2.17
0.2451	6.52	5.29	4.42	3.71	3.10	2.70
0.2945	8.96	7.15	5.87	4.83	3.98	3.44
0.3441	12.60	9.82	7.94	6.41	5.18	4.39
0.3937	17.54	13.39	10.61	8.40	6.69	5.57
0.4435	24.26	18.16	14.05	10.93	8.56	7.04
0.4934	32.98	24.17	18.39	14.12	10.86	8.81
0.5435	42.85	30.93	23.22	17.55	13.37	10.75
0.5937	53.70	38.41	28.53	21.42	16.16	12.84
0.6440	63.69	45.11	33.32	24.81	18.68	14.80
0.6945	71.47	50.91	37.58	27.97	21.00	16.62
0.7451	76.55	54.57	40.40	30.14	22.65	17.90
0.7958	77.87	55.61	41.49	31.10	23.43	18.58
0.8466	76.03	55.02	41.23	31.00	23.48	18.72
0.8976	72.03	52.47	39.59	29.96	22.84	18.32
0.9487	66.03	48.76	36.96	28.25	21.69	17.47
1.0000	59.88	44.36	33.77	25.40	19.67	15.67

The uncertainty for t is u(t) = 0.01 s, and the relative expanded uncertainties U_r is U_r(η) = 0.028 mPa·s at 0.95 confidence level.

Table 5 Experimental γ values of 1,2-PPD (1) + 1,2-PDA (2) at T = (293.15 to 318.15) K with the step of 5 K and 889 hPa.

x₁	γ/(mN·m⁻¹)
x₁	T = 293.15 K	T = 298.15 K	T = 303.15 K	T = 308.15 K	T = 313.15 K	T = 318.15 K
0.0000	33.93	33.49	32.97	32.52	32.12	31.34
0.0488	34.22	33.80	33.23	32.64	32.38	31.75
0.0977	34.53	34.14	33.65	32.92	32.74	32.55
0.1467	34.88	34.56	33.89	33.41	33.29	32.48
0.1958	35.25	34.87	34.31	33.89	33.68	33.15
0.2451	35.68	35.27	34.65	34.36	33.95	33.61
0.2945	36.15	35.81	35.06	34.94	34.50	33.96
0.3441	36.38	36.01	35.50	35.04	34.95	34.32
0.3937	36.60	36.31	35.72	35.46	35.14	34.81
0.4435	36.97	36.61	36.01	35.90	35.53	34.99
0.4934	36.98	36.91	36.40	36.10	35.97	35.38
0.5435	37.33	37.04	36.50	36.23	36.10	35.71
0.5937	37.35	37.20	36.58	36.36	36.28	35.78
0.6440	37.47	37.29	36.78	36.69	36.43	35.87
0.6945	37.50	37.25	36.85	36.64	36.31	35.66
0.7451	37.40	37.05	36.76	36.49	36.23	35.58
0.7958	37.29	36.90	36.75	36.34	36.16	35.54
0.8466	37.02	36.66	36.52	36.17	35.95	35.52
0.8976	36.95	36.43	36.13	36.05	35.76	35.31
0.9487	36.68	36.33	36.03	35.79	35.64	35.18
1.0000	36.46	36.18	35.69	35.61	35.40	34.96

The uncertainty for surface tension is U (γ) = 0.200 mN·m⁻¹ at 0.95 confidence level.

Experimental ρ values with mole fraction for the binary system of 1,2-PPD (1) + 1,2-PDA (2).

η values with mole fraction for the binary system of 1,2-PPD (1) + 1,2-PDA (2).

Experimental γ values with mole fraction for the binary system of 1,2-PPD (1) + 1,2-PDA (2).

From Fig. 1, the ρ values of the binary system at the same temperature increase nonlinearly with the increase of 1,2-PPD concentration, and the ρ values decrease regularly with the increase of temperature at the same concentration.

From Fig. 2, with the increase of 1,2-PPD concentration, the η values increases to a maximum value and then decreases at the same temperature, and reach the maximum at x₁ ≈ 0.80 (4PPD:1PDA). At x₁ < 0.80, with the increase of 1,2-PPD concentration, the η values of the binary system increase. At x₁ > 0.80, with the increase of 1,2-PPD concentration, the η values of the binary system decrease. This is because when x₁ < 0.80, the self-association fracture is less than the intermolecular interaction between different fractions; and when x₁ > 0.80, the intermolecular interaction between different fractions is less than the self-association fracture, so the maximum viscosity values are obtained at x₁ ≈ 0.80. At the same component concentration, the η values decrease with the increase of temperature, which is due to the acceleration of molecular thermal motion and the increase of intermolecular spacing, resulting in the weakening intermolecular interaction. Therefore, the η values decrease with the increase of temperature.

From Fig. 3, with the increase of 1,2-PPD concentration, the γ values increases to a maximum value and then decreases at the same temperature, and reach the maximum values when x₁ is at around 0.65 (2PPD:1PDA). The reason for the surface tension is that the liquid surface is subjected to unbalanced forces in different directions from the air and the body in contact with it, and the former force is always smaller than the latter, so there is a resultant force directed to the body phase, which will make the liquid surface contraction produces surface tension (Du, 2014). When x₁ < 0.65, as the alcohol concentration increases, the intermolecular interaction of alcohols with amines strengthens, which leads to an increase in the ability of the liquid surface to contract inward, so the surface tension values increase. When x₁ > 0.65, as the concentration of alcohol continues to increase, the intermolecular forces of alcohols with amines weaken, resulting in a weakened ability to shrink the surface of the liquid, so the surface tension values decrease. At the same concentration, as the temperature increases, the thermal motion of molecules in the solution intensifies, and the energy required for the liquid molecules to move from the inside to the surface decreases, so the surface tension values decrease (Yu et al., 2020).

The η values were calculated by using Eqs. (1) and (2) (Bagheri et al., 2016; Sha et al., 2015):

(1)

v = A t - \frac{B}{t}

(2)

η = ρ v

In the formula, t is the time when the binary system passes through the viscometer, A and B are the constants of the viscometer, which is obtained by measuring the time when the ultrapure water and HPLC grade ethanol pass through the viscometer, and ρ is the density of the binary system.

The relationship between experimental ρ, η, and γ values and binary system composition was fitted by Eqs. (3–5) (Ku and Tu, 2000; Li et al., 2020):

(3)

ρ_{cal, 1} = \sum_{i = 0}^{4} a_{i} x_{1}^{i}

(4)

η_{cal, 1} = \sum_{j = 0}^{6} b_{j} x_{1}^{j}

(5)

γ_{cal, 1} = \sum_{k = 0}^{4} c_{k} x_{1}^{k}

The relationship between experimental ρ, η, and γ values and experimental temperature was fitted by Eqs. (6–8) (Esteve et al., 2003; Zhang et al., 2018):

(6)

ρ_{cal, 2} = c_{0} + c_{1} T + c_{2} T^{2}

(7)

η_{cal, 2} = η_{0} \exp (\frac{E_{a}}{RT})

(8)

v = A t - \frac{B}{t}

where, a_i, b_j_, c_k, c₀, c₁, c₂, η₀, k₀, and k₁ are undetermined coefficients; R is the ideal gas constant of 8.314 J·mol⁻¹·K⁻¹; T is the absolute temperature of the mixed solution; and Ea is the viscous flow activation energy. ρ_cal.1, ρ_cal.2, η_cal.1, η_cal.2_, γ_{cal. 1}, and γ_{cal. 2} are obtained by Eqs. (3–8).

Besides, the average deviation is obtained by Eq (9) (Yang et al., 2008):

(9)

AAD % = \frac{\sum |100 \times (Y_{\exp . 1} - Y_{cal . 1}) / Y_{\exp . 1}|}{n}

In the formula, Y_exp represents the experimental ρ, η, and γ values, Y_cal represents the calculated ρ, η, and γ values, and n represents the number of experimental points. All the parameters calculated by the above formula are listed in Tables S1-6. The deviations between the calculated and experimental values (ρ_cal.-ρ_exp), (η_cal.-η_exp), and (γ_cal.-γ_exp) are also plotted in Fig. S1-6. It can be seen that there are certain differences between the experimental and calculated values, but they are acceptable, indicating that the experimental data is reliable and accurate.

Excess molar volumes (VmE) with mole fraction for the binary system of 1,2-PPD (1) + 1,2-PDA (2).

Viscosity deviations (Δη) with mole fraction for the binary system of 1,2-PPD (1) + 1,2-PDA (2).

Surface tension deviation (Δγ) with mole fraction for the binary system of 1,2-PPD (1) + 1,2-PDA (2).

3.2

3.2 Excess property

The excess molar volume (V_m^E) was calculated by the formula (10) based on measured density (Guo et al., 2012):

(10)

V_{M}^{E} = \frac{x_{1} M_{1} + x_{2} M_{2}}{ρ_{m}} - \frac{x_{1} M_{1}}{ρ_{1}} - \frac{x_{2} M_{2}}{ρ_{2}}

In the formula, x_i, M_i, and ρ_i are the molar fraction, molar mass (g·mol⁻¹), and density (g·cm⁻³) of pure components, and ρ_m are the density (g·cm⁻³) of the binary system. The calculated data are listed in Table S7, and the curves are plotted in Fig. 4.

From Fig. 4, the V_m^E values of 1,2-PPD (1) + 1,2-PDA (2) binary systems are less than zero in the whole range of molar fractions, indicating that there is volume contraction after mixing the two solutions and the real solution molar volume is less than the ideal solution molar volume. The V_m^E values for the alcohol-amine binary system are mainly influenced by the synergistic effect of three factors: (i) physical, (ii) chemical, and (iii) molecular structure (Henni et al., 2003). Physical factors disrupt the volume expansion due to the intermolecular polymerization of alcohol-amine homologs. Chemical structures are complex between alcohol and amine molecules causing volume contraction, including dipole-dipole interactions, competition between cohesion and dispersion forces, and hydrogen bonding (Hamid Reza and Farshid, 2015). Molecular structure refers to the wrapping effect caused by the shape and size of molecules, so that smaller molecules can easily enter the gap of larger molecular structures and further cause volume shrinkage. Since its V_m^E values are negative, chemical and molecular structure factors dominate, and it is presumed that there is an intermolecular interaction between alcohol and amine molecules. The V_m^E values decrease and then increase with the addition of 1,2-PPD at the same temperature, and the minimum values are obtained at x₁ ≈ 0.5, which is close to the content of the components corresponding to the minimum values of V_m^E of the existing alcohol-amine solution (Prakash and Krishan, 2011).

The viscosity deviation (Δη) is obtained by formula (11) (Ma et al., 2016):

(11)

Δ η = η - (x_{1} η_{1} + x_{2} η_{2})

In the formula, η₁ and η₂ denote the absolute viscosity of 1,2-PPD and 1,2-PDA. The calculated data are listed in Table S8, and the curves are drawn in Fig. 5.

From Table S8 and Fig. 5, the variation trend of Δη values at all experimental temperatures are consistent. When the mole fraction is x₁ ≈ 0.3, the Δη values are the smallest; and when the mole fraction x₁ ≈ 0.75, the Δη values are the largest, which is found at x₁ ≈ 0.45. According to reference (Dominguez et al., 2000), the viscosity of the mixed solution is mainly related to the structure of liquid molecules and the interaction between mixed molecules. Therefore, the Δη values of the binary system can reflect the intermolecular interaction and molecular structure, and the positive or negative Δη values depend on the self-binding fracture between the same molecules (Δη < 0) and the strong interaction between different molecules (Δη > 0) (Dominguez et al., 2000). When x₁ < 0.45, the effect of self-bonding fracture on viscosity with more 1,2-PDA content is greater than that of interaction between alcohol and amine, so the Δη values are negative. When x₁ > 0.45, as the alcohol concentration continues to increase, the binding capacity of alcohol with amine molecules strengthens, and a new intermolecular interaction is formed. This force has a greater impact on viscosity than the self-association and fracture of amine molecules on viscosity, so Δη was positive. From Fig. 5, the change of Δη value is less with the increase of temperature at the same component concentration, which shows that temperature increase will accelerate the movement of molecules, weaken the ability of molecules to bind to each other, and further lead to a decrease in the viscosity of the binary system, and the Δη values decrease.

The surface tension deviation (Δγ) values are obtained by formula (12) (Carvalho et al., 2015):

(12)

Δ γ = γ - (x_{1} γ_{1} + x_{2} γ_{2})

In the formula, γ₁ and γ₂ are the surface tension of pure 1,2-PPD and pure 1,2-PDA. The calculated data are listed in Table S9, and the curves are drawn in Fig. 6.

From Table S9 and Fig. 6, the change trends of Δγ values at each temperature were consistent, and the Δγ value of the binary system is constantly greater than zero. The Δγ values increase and then decrease with the increase of temperature at the same temperature, and the maximum values of surface tension deviation are obtained at x₁ ≈ 0.5. This is because when the alcohol concentration is low, the contact between the alcohol and amine molecules is less and the amine molecules themselves can be fully contacted, resulting in the fact that the force between the alcohol and amine molecules is less than the self-association of amine molecules. Therefore, the inward shrinkage capacity of the binary system is weakened, and the reduction of surface tension further leads to a smaller deviation of surface tension. As the alcohol concentration continues to increase, the interaction between alcohol and amine molecules is greater than the self-association of amine molecules, and the surface tension deviation increases. When x₁ ≈ 0.5, the interaction between alcohol and amine molecules is the strongest, so the surface tension deviation to reach maximum. However, with the continuous increase of alcohol concentration, the binding capacity of alcohol with amine molecules decreases, and the binding capacity among alcohol molecules increases, and the inward shrinkage of the mixed solution is weakened, and the surface tension decreases, which in turn leads to a decrease in surface tension deviation. Under the same concentration, as the temperature increases, the surface tension deviation values increase. This is because as the temperature increases, the molecular thermal motion accelerates, which weakens the interaction between the molecules, and the inward shrinkage of the molecules weakens the surface tension, which in turn leads to an increase in surface tension deviation.

The Gibbs free energy of binary system (ΔG^*E) values are obtained by formula (13) (Dubey et al., 2008):

(13)

Δ G^{* E} = R T [l n (η V) - x_{1} l n (η_{1} V_{1}) - x_{2} l n (η_{2} V_{2})]

where V is the molar volumes. The data are listed in Table S10, and the curves are drawn in Fig. 7.

Excess free energies of activation (ΔG* E) for viscous flow with mole fraction for the binary system of 1,2-PPD (1) + 1,2-PDA (2).

According to Table S10 and Fig. 7, the ΔG^*E values of the 1,2-PPD (1) + 1,2-PDA (2) binary system are positive. The values of ΔG^*E increase and then decrease with the addition of 1,2-PPD at the same temperature and reaches a maximum at x₁ ≈ 0.6.

The V_m^E, Δη, Δγ, and ΔG^*E values were fitted according to the Redlich-Kister polynomial Eq. (14) (Shi et al., 2018; Gao et al., 2013):

(14)

Z = x_{1} (1 - x_{1}) \sum_{i = 0}^{n} A_{i} {(2 x_{1} - 1)}^{i}

In the formula: Z denotes V^E_{m cal}, Δη_cal, Δγ_cal, and ΔG^*E_cal, n is a polynomial parameter, and A_i is a parameter obtained by fitting the equation (using the least square method).

The standard deviations for V_m^E, Δη, Δγ and ΔG^*E values are calculated by the formula (15) (Li et al., 2014):

(15)

σ = {[\sum_{i = 1}^{N} {(Y_{\exp . i}^{E} - Y_{cal . i}^{E})}^{2} / (N - m)]}^{\frac{1}{2}}

In the formula: Y is V_m^E, Δη, Δγ, or ΔG^*E, and N and m are the numbers of test points and the number of parameters retained in each equation as Table S11. From the data, it can be seen that the R² of the fitting curve of V_m^E, Δη, Δγ, or ΔG^*E is close to 1, indicating that the experimental values and the calculated values are better fitted.

3.3

3.3 Apparent molar volume and partial molar volume

The apparent molar volumes, V_φ,1, and V_φ,2, of 1,2-PPD (1) + 1,2-PDA (2) binary system were obtained by the formula (16) and (17) (Zheng et al., 2020; Zhang et al., 2004):

(16)

V_{φ, 1} = \frac{x_{2} M_{2}}{x_{1}} \times \frac{ρ_{2} - ρ_{m}}{ρ_{2} ρ_{m}} + \frac{M_{1}}{ρ_{m}}

(17)

V_{ϕ, 2} = \frac{x_{1} M_{1}}{x_{2}} \times \frac{ρ_{1} - ρ_{m}}{ρ_{1} ρ_{m}} + \frac{M_{2}}{p_{m}}

Table S12 and Fig. S8 shows the values of V_φ,1 and V_φ,2 at atmospheric pressure and T = (293.15–318.15) K. It can be concluded from Table S12 and Fig. S8 that the V_φ,1 value presented an irregular change in the interval of 0.05 < x₁ < 0.15 at different temperatures. When x₁ > 0.15, as the concentration of 1,2-PPD increases, and V_φ,1 steadily increases to V₁⁰. The V_φ,2 value presented an irregular change in the interval of 0.85 < x₁ < 0.95 at different temperatures. As the concentration of 1,2-PDA increases at x₁ < 0.85, and the V_φ,2 value steadily increases to V₂⁰. In addition, it can be concluded that the values of V_φ,1 and V_φ,2 at different temperatures are less than the molar volume values of the pure substance at the corresponding temperature. Therefore, it is speculated that there is an interaction between the alcohol and amine molecules, and the intermolecular bond is tighter, so that the apparent molar volume is smaller than the molar volume of a pure substance. At the same component concentration, as the temperature increases, the V_φ,1 and V_φ,2 values also increase, but because the temperature rises, the molecular thermal motion intensifies, and the molecular density in a certain mass of binary solution decreases, and the volume increase.

Partial molar volumes of 1,2-PPD (1) + 1,2-PDA (2) binary system, in which V₁⁰ and V₂⁰ are pure molar volumes, were obtained by formula (18) and (19) (Tôrres et al., 2006; Kinart et al., 2006):

(18)

\bar{V_{1}} = V_{m}^{E} + V_{1}^{0} + (1 - x_{1}) {(\partial V_{m}^{E} / \partial x_{1})}_{P, T}

(19)

\bar{V_{2}} = V_{m}^{E} + V_{2}^{0} - x_{1} {(\partial V_{m}^{E} / \partial x_{1})}_{P, T}

Table S13 and Fig. S9 represents the values of $\bar{V_{1}}$ and $\bar{V_{2}}$ at T = (293.15–318.15) K and atmospheric pressure. From Table S13 and Fig. S9, as the concentration of 1,2-PPD increases, the $\bar{V_{1}}$ value steadily increases to V₁⁰; and as the concentration of 1,2-PDA increases, the $\bar{V_{2}}$ first increases and then decreases in the entire concentration range, at 0 < x₁ < 0.30, $\bar{V_{2}}$ > V₂⁰, this may be due to the fact that when the alcohol concentration is low, the electrostatic force between amine molecules is stronger than the interaction between different molecules, which makes $\bar{V_{2}}$ slightly larger than V₂⁰.At 0.35 < x₁ < 1, $\bar{V_{2}}$ < V₂⁰. this may be due to the fact that when the alcohol concentration is high, the electrostatic force between the amine molecules is weaker than the interaction between different molecules, so that $\bar{V_{2}}$ is less than V₂⁰.The degree of increase in both ends is slower, and in the middle is faster. In addition, it can be concluded that the values of $\bar{V_{1}}$ and $\bar{V_{2}}$ (at 0.35 < x₁ < 1) at different temperatures are less than the molar volume values of the pure substance at the corresponding temperature, which further proves that there is intermolecular interaction between the alcohol and amine molecules (Maham et al., 1994).

3.4

3.4 Computational chemistry

To further prove the intermolecular interaction between 1,2-PPD and 1,2-PDA molecules, Gaussian 09 software was used to simulate the structure of single-molecule, double-molecule, and triple-molecule in the binary system. Because 1,2-PPD and 1,2-PDA molecules own various isomers, it is necessary to find the minimum energy for calculation, and then calculate the bi-molecular and tri-molecular structure. The calculation results are shown in Fig. 8.

1,2-PDA Single-molecule computational structures.

From Fig. 8, the Hartree energy (HF) values of the three different 1,2-PDA structures were calculated as HF_a, HF_b, and HF_c. The HF_c value of the most stable structure (Fig. 8c) was −229.7573 kcal/mol, and the HF values of the other two structures were HF_a = -229.7546 kcal/mol and HF_b = -229.7552 kcal/mol. The N—H bond length of the amine group in 1,2-PDA is 1.105 Å, and the C—N bond length of amine carbon is 1.470 Å. The bond lengths of three C—H bonds on the carbon without the amine group attached are all equal at 1.094 Å, while the C atom with the amine group attached has three C—H bonds of unequal bond lengths, and the length of the C—H bond on the C atom attached to the amine group is longer than the length of the C—H bond on the C atom not attached to the amine group.

From Fig. 9, the HF values of three different structures of 1,2-PPD were calculated as HF_a, HF_b, and HF_c. The most stable structure after comparison was confirmed as Fig. 9c, whose HF_c value was −269.5315 kcal/mol, and the HF values of the other two structures were HF_a = -269.5269 kcal/mol and HF_b = -269.5309 kcal/mol. The O—H bond length of the hydroxyl group on 1,2-PPD is 0.967 Å, while its C—O bond length on the C atom to which the hydroxyl group is attached is 1.433 Å. The C atom without a hydroxyl group has three C—H bonds with bond lengths of 1.093 Å, 1.092 Å, and 1.094 Å, in contrast, the C atom to which the hydroxyl group is attached has bond lengths of 1.097 Å, 1.098 Å and 1.101 Å for the three C—H bonds. Obviously, the length of the C—H bond on the C atom connected to the hydroxyl group is greater than the bond length of the C—H bond on the C atom of the unconnected hydroxyl group.

1,2-PPD Single-molecule computational structures.

From Fig. 10, the HF values of three different structures of 1,2-PDA + 1,2-PDA were calculated as HF_α, HF_b, and HF_c. After comparison, the most stable structure was confirmed as Fig. 10c with an HF_c value of −459.5185 kcal/mol, and the HF values of the other two structures were calculated at HF_a = -459.5174 kcal/mol and HF_b = -459.5183 kcal/mol. The distance between the N atom and the adjacent H atom in 1,2-PDA belongs to the hydrogen bonding range (1.2 Å-3.0 Å), and the dissociation energy between 1,2-PDA (2) + 1,2-PDA (2) is 2.3875 kcal/mol. The dissociation energy after mixing the two molecules has increased in different degrees compared to twice the dissociation energy, which also proves that there is an intermolecular interaction between the two molecules that makes them more stable.

1,2-PDA (2) + 1,2-PDA (2) Bimolecular calculation structure diagram.

From Fig. 11, the HF values of three different structures of 1,2-PPD (1) + 1,2-PPD (1) were calculated as HF_α, HF_b, and HF_c. The most stable structure was confirmed as Fig. 11c with an HF_c value of −539.0730 kcal/mol, and the HF values of the other two structures were HF_a = -539.0704 kcal/mol and HF_b = -539.0686 kcal/mol. The distance between the O atom and the adjacent H atom in 1,2-PPD belongs to the hydrogen bonding range (1.2 Å-3.0 Å), and the dissociation energy between 1,2-PPD molecules is 6.0872 kcal/mol greater than zero. The dissociation energy after mixing the two molecules has increased in different degrees compared to twice the dissociation energy, which also proves that there is a more stable intermolecular interaction.

1,2-PPD (1) + 1,2-PPD (1) Bimolecular calculation structure diagram.

From Fig. 12, the HF values of eight different structures of 1,2-PPD (1) + 1,2-PDA (2) were calculated as HF_a, HF_b, HF_c, HF_d, HF_e, HF_f, HF_g, and HF_h. The most stable structure was confirmed as Fig. 12f, whose HF_f value was −499.3021 kcal/mol, and the HF values of the other seven structures were HF_a = −499.2915 kcal/mol, HF_b = −499.2925 kcal/mol, HF_c = −499.2989 kcal/mol, HF_d = −499.2917 kcal/mol, HF_e = −499.2994 kcal/mol, HF_g = −499.2975 kcal /mol and HF_h = −499.2989 kcal/mol. The O—H bond length of the hydroxyl group on 1,2-PPD was 0.986 Å compared with the previous 0.963 Å, and the N—H bond length of the amine group on 1,2-PDA was 1.018 Å compared with the previous 1.015 Å. Secondly, the distances between the N atom in 1,2-PDA and the hydroxyl H atom in 1,2-PPD both fall within the hydrogen bonding range (1.2 Å–3.0 Å), and the -O—H···N- formed is a strong hydrogen bond, in agreement with the literature (1.5 Å–2.2 Å) (Yu et al., 1994). In addition, the dissociation energy between 1,2-PPD and 1,2-PDA molecules is 8.0736 kcal/mol. The dissociation energy after mixing the two molecules has increased in different degrees compared to twice the dissociation energy, which also proves that there is a more stable intermolecular interaction between two molecules.

1,2-PPD (1) + 1,2-PDA (2) Bimolecular calculation structure diagram.

From Fig. 13, the O—H bond length and C—O bond length of the hydroxyl group in 1,2-PPD increased from (0.963 and 1.425) Å to (0.997 and 1.427) Å, and the C—N bond length in 1,2-PDA increased from 1.475 Å to 1.482 Å. The distance between the hydroxyl H atom in 1,2-PPD and the N atom in 1,2-PDA belonged to the hydrogen bonding range of (1.2–3.0) Å. The calculations show that there is a hydrogen bond between 1,2-PDA and 1,2-PPD.

Calculation of single-molecule 1,2-PDA and bimolecular 1,2-PPD.

The dissociation energy of Fig. 13 is 18.4753 kcal/mol greater than zero. The dissociation energies of two 1,2-PPD (1) + one 1,2-PDA (2) are much larger than the sum of their respective dissociation energies, which also proves that there is an interaction among three molecules.

From Fig. 14, the O—H bond length and C—O bond length of hydroxyl in 1,2-PPD increased from (0.963 and 1.425) Å to (0.982 and 1.426) Å, and the C—N bond length in 1,2-PDA increased from 1.475 Å to 1.476 Å. The distance between the hydroxyl H atom in 1,2-PPD and the N atom in 1,2-PDA belongs to the hydrogen bonding range of (1.2–3.0) Å. The calculations show that there is a hydrogen bond between 1,2-PDA and 1,2-PPD.

Calculation of single-molecule 1,2-PPD and bimolecular 1,2-PDA.

The dissociation energy of Fig. 14 is 15.8862 kcal/mol greater than zero. The dissociation energies of two 1,2-PDA molecules and one 1,2-PPD molecule are much larger than the sum of their respective dissociation energies, which also proves that there is a hydrogen bond between the three molecules.

The optimal structures of (1,2-PDA, 1,2-PPD, 1,2-PDA + 1,2-PDA, 1,2-PPD + 1,2-PPD and 1,2-PDA + 1,2-PPD) were obtained from the previous calculations. On this basis, the weak interactions existing between the individual subsets were investigated using Multiwfn, VMD software, and Reduced Density Gradient (RDG) (Lu and Chen, 2012), and the specific results are shown in Fig. 15.

RDG isosurface plot and scatter plot of (A and B) 1,2-PDA, (C and D) 1,2-PPD, (E and F) 1,2-PDA + 1,2-PDA, (H and I) 1,2-PPD + 1,2-PPD and (J and K) 1,2-PDA + 1,2-PPD interaction.

From Fig. 15 it is obvious that closed equivalence surfaces are formed in both single molecules (A, C) and bimolecules (E, H, J), which is good evidence that some kind of force is formed within the single-molecule as well as between the bimolecules (Bader et al., 1984). Secondly, according to AIM theory, the closed equivalence surface of RDG should generally include the corresponding critical point ρ(BCP), which is one of the important indicators of the strength of weak interactions. Therefore, the strength of the interaction can be understood at a glance by mapping the numerical magnitude of ρ(BCP) to the RDG equivalent surface in different colors, but ρ(BCP) can only reflect the strength and its type need to be reacted by the sin(λ₂) function, which is the sign of the second eigenvalue of the electron density Hessian matrix λ₂, multiplying ρ(BCP) with sin(λ₂) to obtain the function sin(λ₂)ρ(BCP), which is projected onto the RDG equivalent surface, and the position, strength and type of the weak interaction becomes clearly visible (Johnson et al., 2010). The color scale is usually set at [−0.035,0.020] in the order blue->green->red (blue: strong attractive interactions (hydrogen bonding, strong halogen bonding, etc.); green: van der Waals force interactions; red: strong mutually exclusive interactions (position blocking effects in rings, cages)) (Emamian et al., 2019). Based on the RDG isosurface plot and the scatter plot it is clear that the strongest hydrogen bonding interaction is formed between 1,2-PDA + 1,2-PPD with a value of −0.04323 specifically in the form of -O—H···N-.

Based on the above calculations, it is assumed that hydrogen bonds are formed between 1,2-PPD and 1,2-PDA, so that the molecules can keep at more stable states.

3.5

3.5 Spectral characterization and discussion

To further study the intermolecular interaction of binary system, various spectra were carried out.

Fig. 16 shows the FTIR spectral change of pure 1,2-PDA, pure 1,2-PPD, and binary system with different concentrations. The peak at 3372 cm⁻¹ shown in Fig. 16 is due to the stretching vibration of the hydroxyl group in 1,2-PPD (Yang et al., 2018; Yang et al., 2003). With the increase of 1,2-PDA concentration, the stretching vibration peak of the hydroxyl group in 1,2-PPD shifted from 3372 cm⁻¹ to 3352 cm⁻¹. The phenomenon was explained as the following three aspects: (i) With the increase of 1,2-PDA concentration, the original hydrogen bonds among 1,2-PPD molecules are destroyed, and new hydrogen bonds are formed between 1,2-PDA and 1,2-PPD molecules. (ii) Due to the formation of new hydrogen bonds, the -O—H bond is elongated, the dipole moment increases, the stretching vibration frequency moves to the low-frequency direction, and the corresponding wave number decreases. (iii) The inducing effect of N atoms is stronger than that of C atoms, and the bond energy of -O—H···N- is greater than that of -O—H···O-, so the -O—H···N- hydrogen bond is more stable (Sada et al., 1985; Mahapatra and Dey, 2015). Therefore, the stretching vibration of the -O—H bond moves to lower frequency; and with the addition of 1,2-PDA, the stretching vibration peak of the -O—H bond gradually changes from wide peak to sharp peak.

FTIR spectra change of 1,2-PPD (1) + 1,2-PDA (2) binary system.

Fig. 17 shows the UV spectral change of 1,2-PPD with different concentrations of 1,2-PDA. Because the O atom in the hydroxyl group of 1,2-PPD contains lone pair electrons, it is easy to occur n → σ* transition under UV irradiation, and the absorption wavelength is<200 nm (Yang et al., 2018). With the increase of 1,2-PDA concentration, the orbitals of N atom in amine molecule and O atom in alcohol molecule overlap partially, which increases the activity range of O atom lone pair electrons and reduces the binding effect of H atom in alcohol hydroxyl on O atom, making the n → σ* transition of O atom be easier, so the characteristic peak shifts from 201 nm to 208 nm. Therefore, it is inferred that the association of 1,2-PPD molecules is destroyed due to the addition of 1,2-PDA, a new hydrogen bond is formed with 1,2-PDA molecules, and -O—H···N- is the specific bond form.

UV-vis spectral change of 1,2-PPD (1) + 1,2-PDA (2) binary system.

Fig. 18 showed the fluorescence spectral change of binary mixtures with various 1,2-PPD concentrations. Pure 1,2-PPD molecules easily form molecular clusters by hydrogen bonding, and this structure has certain rigidity, which provides the necessary geometric structure for fluorescence generation (Sada et al., 1985). Besides, the O atom in the 1,2-PPD molecule contains two pairs of solitary electron pairs (n electrons), and the absorbed photons undergo n → σ* transition. After vibration relaxation to the lowest vibration level of the excited state, σ*→n transition occurs, and then fluorescence is generated. It can be seen from the diagram that the transition wavelength is 335 nm. With the addition of 1,2-PDA, the characteristic peak shifts from 335 nm to 344 nm, and the relative intensity of the peak increases. This indicates that the electron cloud of the N atom in 1,2-PDA overlaps with that of the O atom in 1,2-PPD, which results in the breaking of association and the formation of conjugated electron cloud by new association clusters, which further increases the electronic activity range of O atom and makes σ*→n easier. The bond energy of -O—H···N- is stronger than that of -O—H···O-, so -O—H···N- is more stable, and its energy is lower (Sada et al., 1985), in which it is easier to transition to a low level. Secondly, the fluorescence intensity is proportional to the solution concentration and conjugation degree, so the relative fluorescence intensity increases with the increase of 1,2-PDA concentration and conjugation degree.

Fluorescence spectral change of 1,2-PPD (1) + 1,2-PDA (2) binary system.

Fig. 19 shows ¹H NMR spectra of 1,2-PPD (1) + 1,2-PDA (2) binary mixtures at 0 % (pure PDA), 50 % and 100 % (pure PPD). For pure 1,2-PPD, the chemical shifts of the H atom in the hydroxyl group were 4.20 ppm (2H), that of the H atom in –CH- was 3.87 ppm (1H), that of –CH₂ was 3.56 ppm (1H) and 3.39 ppm (1H), and that of H atom in –CH₃ was 1.13 ppm (3H) (Zhao et al., 2017). For pure 1,2-PDA, the chemical shifts of the H atom in the amine group are 1.05 ppm (2H) and 1.19 ppm (2H), the chemical shift of the H atom in –CH- is 2.84 ppm (1H), the chemical shift of the H atom in –CH₂ is 2.66 ppm (2H), and the H atom in –CH₃ is 2.44 ppm (3H) (Zhang et al., 2020a, 2020b). For the ¹H NMR spectra of 50 % binary mixtures, the chemical shift of H atom in –OH in 1,2-PPD shifted from 4.20 ppm to 3.86 ppm, and the chemical shift of H atom in –NH₂ in 1,2-PDA shifted from 1.19 ppm to 2.23 ppm. For 1,2-PPD, the decrease in the chemical shift of the hydroxyl H atom is due to the addition of 1,2-PDA, the H-atom in the hydroxyl group exerts a certain attraction to the N-atom in the amine group, which makes the electron cloud density around the hydroxyl H-atom increase, then the shielding effect also increases, and the chemical shift decreases, and the position of the peak appears at a relatively high magnetic field. Conversely. For 1,2-PDA, the chemical shift of the amine H atom increases because, with the addition of 1,2-PPD, the N atom in the amine group is subject to a certain attraction of the hydroxyl H atom, which makes the electron cloud density around the amine H atom decrease, then the shielding effect also decreases, the de-shielding effect increases, the chemical shift value increases, and the position of the peak appears at a relatively low magnetic field. Therefore, it can be presumed that hydrogen bonds are formed at 1,2-PPD and 1,2-PDA, and the specific form of -O—H···N- (Wu, 2011).

1H NMR spectral change of 1,2-PPD (1) + 1,2-PDA (2) binary system.

Fig. 20 showed the Raman spectral change of pure 1,2-PDA, 1,2-PPD, and binary mixtures with different concentrations. The N—H symmetric stretching vibration peak of –NH₂ in pure 1,2-PDA was found at 3299 cm⁻¹. With the addition of 1,2-PPD, the characteristic peak of stretching vibration peak of –NH₂ shifts towards 3293 cm⁻¹. This is because with the addition of 1,2-PPD, the H atom of the hydroxyl group has a certain fixation effect on the N atom of the amine group, which makes the symmetric stretching vibration of N—H easier and the energy required for the vibration is correspondingly less, so the vibration moves toward the lower frequency. Secondly, with the addition of 1,2-PPD, the electron cloud of the N atom in the amine group is biased toward the side of the O atom with a larger nucleus mass, at which time the N—H bond is elongated, the dipole moment increases, the bond force constant decreases, the characteristic peak moves to the low frequency direction, and the wave number decreases. Therefore, it is presumed that hydrogen bonding is formed between 1,2-PPD and 1,2-PDA, and the specific form is -O—H···N-.

Raman spectral change of 1,2-PPD (1) + 1,2-PDA (2) binary system.

Combining the results of Gaussian calculations and various spectral characterizations, it can be concluded that hydrogen bonding exists in the binary system of 1,2-PPD (1) + 1,2-PDA (2), and the specific hydrogen bonding form is -O—H···N-.

3.6

3.6 1,2-PPD + 1,2-PDA captures CO₂

CO₂ gas was passed into the 1,2-PPD (1) + 1,2-PDA (2) solution (molar ratio 1:1) at a flow rate of 250 mL/min and 3–5 % of secondary water was added to the whole system with the aim of reducing the viscosity of the system and making the mass transfer rate faster. The solution became viscous at t = 20 min and gave off a lot of heat, and a white viscous solid appeared after t = 24 h. The white solid CO₂-storage material (CO₂SM) was formed after continuing to pass CO₂ gas for 2 h. After washing with ethanol three times, the solid CO₂SM was dried under vacuum at 60 °C for 12 h. After characterization, it was proved that CO₂SM is an alkyl carbonate salt (Fig. 22), and under the heating condition CO₂SM can be decomposed to 1,2-PPD (1) + 1,2-PDA (2) and CO₂, and the specific synthesis process and reaction equation are shown in Fig. 21 and Scheme 1.

Reaction process of 1,2-PDA + 1,2-PPD with CO2 at different times.

(a) XRD patterns of CO2SM, NH4HCO3 and Na2CO3; (b) FTIR spectra of CO2SM.

1,2-PDA + 1,2-PPD and CO2 reaction equation.

As shown in Fig. 22(a), CO₂SM, NH₄HCO₃ and Na₂CO₃ have an identical diffraction peak (29.71°), which indicates that CO₂SM, NH₄HCO₃ and Na₂CO₃ may exist with similar CO₃^2– structures. Meanwhile, the XRD results of CO₂SM are similar to the characteristic peak of the carbamate (–NH-COO^-) (JCPDS 34–1993). Secondly, it can be seen from Fig. 22(b) that the absorption peak located at 3342 cm⁻¹ is attributed to the stretching vibration of –OH, which may be attributed to the presence of incomplete 1,2-PPD of CO₂SM, while the absorption peaks located at 3302 cm⁻¹ and 2216 cm⁻¹ are attributed to the stretching vibration of N—H and the characteristic vibration of –NH₃⁺, respectively (Zhao et al., 2016). 1576 cm⁻¹ and 1480 cm⁻¹ are attributed to the –COO- asymmetric stretching vibration and symmetric stretching vibration, respectively (Sha et al., 2016). The characteristic peak at 1326 cm⁻¹ is attributed to the characteristic vibration of CO₃^2–. Therefore, it is presumed that 1,2-PPD (1) + 1,2-PDA (2) reacts with CO₂ to form alkyl carbonate amine salts.

4 Conclusion

The present work systematically reports the basic ρ, v, and γ data for the binary system of 1,2-PPD (1) + 1,2-PDA (2) at different concentrations at T = 293.15 K, 298.15 K, 303.15 K, 308.15 K, 313.15 K and 318.15 K and atmospheric pressure (889 hectopascals in Hohhot, China). Based on these basic experimental data, η, V_m^E, Δη, Δγ, ΔG^*E, V_φ,1, V_φ,2, $\bar{V_{1}}$ , $\bar{V_{2}}$ and α_p were calculated. At different concentrations, the ρ values keeps increasing, the η values first increase and then decrease, and reach the maximum at x₁ ≈ 0.80, the γ values first increase and then decrease, and reach the maximum at x₁ ≈ 0.65. The values of V_m^E were negative, the values of Δη were negative at first and then positive, and the values of Δγ were positive, which indicates that there is an intermolecular interaction in the binary system. Additionally, there is a hydrogen bond between the H atom of the hydroxyl group in the 1,2-PPD molecule and the amino N atom in the 1,2-PDA molecule, and the specific form is -O—H···N-.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (21666027), the Program for Grassland Excellent Talents of Inner Mongolia Autonomous Region, and the Inner Mongolia Science and Technology Key Projects.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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Appendix A

Supplementary data

Supplementary data to this article can be found online at https://doi.org/10.1016/j.arabjc.2022.104130.

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Density, viscosity, and surface tension
Excess property
Apparent molar volume and partial molar volume
Computational chemistry
Spectral characterization and discussion
1,2-PPD + 1,2-PDA captures CO2

Conclusion

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[1] Aguila-Hernandez J., Trejo A., Gracia-Flores B.E., Molnar R., . Fluid. Phase. Equilib.. 2008;267:172-180.

[2] Bader R.F.W., Essén, H.,, . J. Chem. Phys.. 1984;80:1943-1960.

[3] Bagheri A., Fazli M., Bakhshaei M., . J. Mol. Liq.. 2016;224:442-451.

[4] Becke A.D., . J. Chem. Phys.. 1993;98:5648-6565.

[5] Button J.K., Gubbins K.E., . Fluid. Phase. Equilib.. 1999;158–160:175-181.

[6] Carvalho P.J., Fonseca C.H.G., Moita M.L.C.J., Santos Â.F.S., Coutinho J.A.P., . J. Chem. Eng. Data. 2015;60:3721-3737.

[7] Doghaei A.V., Omrani A., Rostami A.A., . J. Chem. Eng. Data. 2010;55:2894-2899.

[8] Dominguez M., Pardo J.I., Gascon I., Royo F.M., Urieta J.S., . Fluid. Phase. Equilibria. 2000;169:277-292.

[9] Dong F., Lou H., Kodama A., Goto M., Hirose T., . Sep. Purif. Technol.. 1999;16:159-166.

[10] Du, L., 2014. North China Electric Power University.

[11] Dubey G.P., Sharma M., Dubey N., . J. Chem. Thermodyn.. 2008;40:309-320.

[12] Elka N.J.M.C.P., Hamborg E.S., Huttenhuisa P.J.G., Fradetteb S., Carley J.A., Versteeg G.F., . Int. J. Greenh. Gas. Con.. 2013;12:259-268.

[13] Emamian S., Lu T., Kruse H., Emamian H., . J. Comput. Chem.. 2019;40:2868-2881.

[14] Esteve X., Conesa A., Coronas A., . J. Chem. Eng. Data. 2003;48:392-397.

[15] Figueroa J.D., Fout T., Plasynski S., McIlvried H., Srivastava R.D., . Int. J. Greenh. Gas. Con.. 2008;2:9-20.

[16] Furtado I.O., Dos Santos T.C., Vasconcelos L.F., Costa L.T., iorot, F.R.G., Ronconia, C.M., Carneiro, J.W.M.,, . Chem. Eng. J.. 2020;408:128002

[17] Gahlyan S., Verma S., Rani M., Maken S., . J. Mol. Liq.. 2017;244:233-240.

[18] Gao F., Niu Y., Zhang J., Sun S., Wei X., . J. Chem. Thermodyn.. 2013;62:8-16.

[19] Guo Z.H., Zhang J.B., Zhang T., Li C.P., Zhang Y.F., Bai J., . J. Mol. Liq.. 2012;165:27-31.

[20] Hamid Reza R., Farshid F., . Thermochim. Acta. 2015;611:36-46.

[21] Henni A., Hromek J.J., Tontiwachwuthikul P., Chakma A., . J. Chem. Eng. Data. 2003;48:1062-1067.

[22] Hosseini-Ardali S.M., Hazrati-Kalbibaki M., Fattahi M., Lezsovits F., . Energy. 2020;211:119035

[23] Islam M.N., Ali M.A., Monirul Islam M., Nahar M.K., . Phys. Chem. Liq.. 2003;41:271-282.

[24] Johnson E.R., Keinan S., Mori-Sánchez P., Contreras-García J., Cohen A.J., Yang W., . J. Am. Chem. Soc.. 2010;132(18):6498-6506.

[25] Kim S., Kim H.T., Choi B.C., . Stud. Surf. Sci. Catal.. 2004;153:429-434.

[26] Kim Y.E., Lim J.A., Jeong S.K., Yoon Y.I., Bae S.T., Nam S.C., . Chem. Soc.. 2013;34:783-787.

[27] Kinart C.M., Bald A., Kinart W.J., Kolasinski A., . Phy. Chem. Liq.. 2006;36:245-256.

[28] Klimaszewski K., Boruń, A., Bald, A., Sengw, R.J.,, . J. Chem. Eng. Data. 2012;57:3164-3170.

[29] Ku H.C., Tu C.H., . J. Chem. Eng. Data. 2000;45:391-394.

[30] Lee S., Song H.J., Maken S., Yoo S.K., Park J.W., Kim S., Shim J.G., Jang K.R., . J. Chem. Eng.. 2008;25(1):1-6.

[31] Li F., Li B., Zhang Y., Wang Y., Jia X., Li Q., Zhang J., . J. Mol. Liq.. 2020;303:112677

[32] Li L.H., Zhang J.B., Li Q., Guo B., Zhao T.X., Sha F., . Thermochim. Acta. 2014;590:91-99.

[33] Lian S., Song C., Liu Q., Duan E., Ren H., Kitamura Y., . J. Environ. Sci-China.. 2021;99:281-295.

[34] Lu T., Chen F., . J. Comput. Chem.. 2012;33:580-592.

[35] Lubowiecka-Kostka B., Zorebski E., . J. Chem. Thermodyn.. 2009;41:197-204.

[36] Ma L., Sha F., Qiao X., Zhao T., Li Q., Zhang J., . J. Mol. Liq.. 2016;219:149-157.

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[60] Verma S., Gahlyan S., Kaur J., Maken S., . J. Mol. Liq.. 2019;292:111359.

[61] Wu, B., 2011. Nanjing University of Science and Technology.

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Thermodynamics, excess properties, spectra and computational chemistry of 1,2-propanediol + 1,2-propane diamine binary system

Abstract

Abstract

Nomenclature

1 Introduction

2 Experimental

2.1 Materials

2.2 Methods

3 Results and discussion

3.1 Density, viscosity, and surface tension

3.2 Excess property

3.3 Apparent molar volume and partial molar volume

3.4 Computational chemistry

3.5 Spectral characterization and discussion

3.6 1,2-PPD + 1,2-PDA captures CO2

4 Conclusion

Acknowledgments

Declaration of Competing Interest

References

Appendix A

Supplementary data

Appendix A

Supplementary data

Supplementary data 1

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3.6 1,2-PPD + 1,2-PDA captures CO₂