Introduction

Cyclopentanol is an important fine chemical intermediate, which has been used in the production of perfumes, medicines and dyes, and as a solvent for medicines and perfumes [1]. The main production process for cyclopentanol was cyclopentanone hydro-conversion, and the cyclopentanone was produced by decarboxylation of adipic acid at high temperature; however, the development of this process was limited due to the formation of a great deal of pollutant [2, 3]. Cyclopentanol can also be produced from furfural using the Noble-metal catalysts (such as Pt/C and Ru/C); however, the selectivity of cyclopentanol is quite low, and future development of high efficient, stable and economical catalysts will be highly desired [4, 5].

The dicyclopentadiene could be separated from the cracked C5 fraction available as a by-product of ethylene production, and the cyclopentadiene was produced by dicyclopentadiene cracking; cyclopentene was the hydrogenation product of cyclopentadiene, and the cyclopentanol could be produced from the direct hydration or indirect hydration of cyclopentene. Theoretically, cyclopentanol could be synthesized using a two-step process from cyclopentene, e.g., the addition-esterification reaction of cyclopentene with acetic acid, the transesterification of cyclopentyl acetate and methanol, the process of hydration of cyclopentene was one environment friendly technology with less pollution [6]. The flow charts of the main production process for cyclopentanol and indirect synthesis of cyclopentanol from cyclopentene are shown in Fig. 1. However, so far, no literatures have been published for this indirect process either from the theoretical or experimental study. In this work, the thermodynamic analysis of the two reaction steps was carried out in the paper, which could provide theoretical principle for the experimental research and industrial production, and preliminary experimental work has been carried out and the results are in good agreement with the thermodynamic calculation results.

Fig. 1
figure 1

Flow chart of the main production process for cyclopentanol and indirect sythesis of cyclopentanol from cyclopentene

Full size image

Thermodynamic calculation

Reaction equations

The two reactions have been considered in the system, the addition-esterification reaction of cyclopentene and acetic acid:

(1)

The transesterification of cyclopentyl acetate and methanol:

(2)

Physical properties data of thermodynamic analysis

The standard enthalpy of formation and standard entropy of liquid cyclopentene, acetic acid, methanol, methyl acetate and cyclopentanol were adopted from the data handbooks [7, 8], the results are shown in the Table 4. The liquid heat capacities of cyclopentene, acetic acid, methanol and methyl acetate at the temperature range from 273.15 to 373.15 K were taken from the data handbook [9, 10], and the expression of liquid heat capacities was fitted as multinomial; the results are shown in Table 2.

However, not all the physical properties of the chemicals could be obtained from handbook, the group contribution methods were investigated to estimate the physico–chemical properties of organic compounds, such as Joback method [11], Constantinou–Gani method [12], Benson method [13] and so on [14, 15]. In this paper, the liquid heat capacities of cyclopentanol and cyclopentyl acetate, the standard enthalpy of formation and standard entropy of gaseous cyclopentyl acetate at the temperature of 298.15 K, and the standard vaporization enthalpy of cyclopentyl acetate were estimated by Ruzicka–Domalski method [16], Yoneda method (ABWY) [17] and Ducros method [18, 19], respectively [20].

The liquid heat capacities of cyclopentanol and cyclopentyl acetate were estimated by Ruzicka–Domalski group contribution method [16, 20], the calculation formula was:

$$ C_{\text{p,t}} \, = \,R\left[ {A\, + \,B\frac{T}{100}\, + \,D\left( \frac{T}{100} \right)^{2} } \right] $$
(3)

In the Eq. 3 \( A\, = {\kern 1pt} \sum {n_{i} a_{i} } \), \( B\, = \,\sum {n_{i} b_{i} } \), \( D = \sum {n_{i} d_{i} } \), the contribution values of group are shown in Table 1 and the calculation results in Table 2.The standard enthalpy of formation and standard entropy of gaseous cyclopentyl acetate at the temperature of 298.15 K were estimated using Yoneda method (ABWY) [17, 20], and the effect of substitutions was covered with data from Ref. [20], and the calculation formula being

$$ \Delta_{f} H_{{{\text{g}},298.15}}^{\theta } = \sum {n_{i} \Delta H_{i} } $$
(4)
$$ S_{\text{m,g}}^{\theta } = \sum {n_{i} } \Delta S_{i} $$
(5)

The standard enthalpy of formation and standard entropy of liquid cyclopentyl acetate at the temperature of 298.15 K were estimated by Eqs. 6 and 7:

$$ \Delta_{f} H_{{{\text{l,298}} . 1 5}}^{\theta } = \Delta_{f} H_{{{\text{g,298}} . 1 5}}^{\theta } - \Delta_{v} H_{ 2 9 8. 1 5}^{\theta } $$
(6)
$$ S_{\text{m,l}}^{\theta } \, = \,S_{\text{m,g}}^{\theta } \, - \,\frac{{\Delta_{v} H_{ 2 9 8. 1 5}^{\theta } }}{298.15} $$
(7)

The standard vaporization enthalpy of cyclopentyl acetate was estimated by the Ducros method [18–20], and the contribution values of group are shown in Table 3. The standard enthalpy of formation and standard entropy of liquid cyclopentyl acetate appear in Table 4.

Table 1 Contribution values of group of Ruzicka–Domalski and the group numbers in the each substance
Full size table
Table 2 The functional correlations between C p,t of materials and temperature
Full size table
Table 3 Contribution values of group of Ducros
Full size table
Table 4 The \( \Delta_{f} H_{l,298.15}^{\theta } \) and \( S_{m,l}^{\theta } \) of each substance at 298.15 K
Full size table

Calculation results and discussion

The enthalpy changes, free energy changes of each reaction were calculated by Eqs. 8–12 [21]:

$$ \Delta_{r} H_{ 2 9 8. 1 5}^{\theta } = \sum {\left( {\Delta_{f} H_{{{\text{l,298}} . 1 5}}^{\theta } } \right)}_{p} - \sum {\left( {\Delta_{f} H_{{{\text{l,298}} . 1 5}}^{\theta } } \right)}_{R} $$
(8)
$$ \Delta_{r} H_{\text{m}}^{\theta } = \Delta_{r} H_{ 2 9 8. 1 5}^{\theta } + \int_{298.15}^{T} {\left( {\sum {\left( {C_{\text{p}} } \right)_{P} - \sum {\left( {C_{\text{p}} } \right)_{R} } } } \right){\text{dT}}} $$
(9)
$$ \Delta_{r} S_{{{\text{m,298}} . 1 5}}^{\theta } = \sum {\left( {S_{\text{m}}^{\theta } } \right)}_{p} - \sum {\left( {S_{\text{m}}^{\theta } } \right)}_{R} $$
(10)
$$ \Delta_{r} S_{\text{m}}^{\theta } = \Delta_{r} S_{{{\text{m,298}} . 1 5}}^{\theta } + \int_{298.15}^{T} {\left( {\frac{{C_{\text{p}} }}{T}} \right)} {\text{d}}T $$
(11)
$$ \Delta_{r} G_{\text{m}}^{\theta } \, = \,\Delta_{r} H_{\text{m}}^{\theta } \, - \,T\Delta_{r} S_{\text{m}}^{\theta } $$
(12)

The equilibrium constant of each reactions was calculated by Eq. 13 [21, 22]:

$$ K^{\theta } \, = \,\,\exp ( - \Delta_{r} G_{m}^{\theta } /{\text{RT}}) $$
(13)

Addition-esterification reaction of cyclopentene and acetic acid

The enthalpy changes and free energy changes of the addition-esterification reaction

The enthalpy changes (\( \Delta_{{r_{1} }} H_{\text{m}}^{\theta } \)) and free energy changes (\( \Delta_{{r_{1} }} G_{\text{m}}^{\theta } \)) of addition-esterification reaction were calculated at different temperature, the results are shown in Fig. 2.

Fig. 2
figure 2

The \( \Delta_{{r_{1} }} H_{m}^{\theta } \) and \( \Delta_{{r_{1} }} G_{m}^{\theta } \) for the addition-esterification reaction as functions of temperature

Full size image

As seen from Fig. 2, the \( \Delta_{{r_{1} }} H_{\text{m}}^{\theta } \) was less than 0 in the temperature range from 273.15 to 373.15 K, the addition-esterification reaction was exothermic, and the \( \Delta_{{r_{1} }} H_{m}^{\theta } \) decreased with increasing temperature in the range 273.15 to 373.15 K.

The \( \Delta_{{r_{1} }} G_{\text{m}}^{\theta } \) value was less than 0 in the 273.15 to 373.15 K, which showed that the addition-esterification reaction could occur spontaneously. \( \Delta_{{r_{1} }} G_{\text{m}}^{\theta } \) increased with the temperature rise, which indicated that lower temperatures were more favorable for the reactions in the temperature range from 273.15 to 373.15 K.

Equilibrium constant and equilibrium conversion of the addition-esterification reaction

The molar ratio of acetic acid to cyclopentene was set as r 1, the conversion of cyclopentene was set as x 1,so:

$$ K^{\theta }_{1} = \frac{{x_{1} }}{{(1 - x_{1} )(r_{1} - x_{1} )}} $$
(14)

The equilibrium constant (\( K^{\theta }_{1} \)) of the addition-esterification reaction at different temperature was calculated from Eq. 13, and the conversion of cyclopentene as x 1 at different temperature with different r 1 was calculated from Eq. 14 and the results appear in Figs. 3 and 4.

Fig. 3
figure 3

Changes of the addition-esterification reaction equilibrium constant (\( K^{\theta }_{1} \)) with temperature

Full size image
Fig. 4
figure 4

Changes of the cyclopentene equilibrium conversion (x 1) with temperature

Full size image

Figures 3 and 4 show that \( K^{\theta }_{1} \) and x 1 decreased at higher temperature and that the x 1 increased at higher values, r 1, at the same temperature. The conversion of cyclopentene was higher at lower temperature and a greater molar ratio of acetic acid to cyclopentene. However, very low temperatures reduced the reaction rate, and the acetic acid spent increased with increasing of r 1, and the cost of separation of acetic acid and cyclopentyl acetate increased. The most suitable reaction conditions were temperature in the range from 333.15 to 353.15 K with an r 1 value between 2:1 and 3:1.

Transesterification reaction of cyclopentyl acetate and methanol

The enthalpy changes and free energy changes of transesterification reaction

The enthalpy changes (\( \Delta_{{r_{1} }} H_{\text{m}}^{\theta } \)) and free energy changes (\( \Delta_{{r_{1} }} G_{\text{m}}^{\theta } \)) of transesterification reaction were calculated at different temperature and the results are plotted in Fig. 5.

Fig. 5
figure 5

The \( \Delta_{{r_{2} }} H_{m}^{\theta } \) and \( \Delta_{{r_{2} }} G_{m}^{\theta } \) of transesterification reaction as functions of the temperature

Full size image

Figure 5 shows that \( \Delta_{{r_{2} }} H_{\text{m}}^{\theta } \) was negative in the temperature range from 273.15 to 373.15 K, the addition-esterification reaction was exothermic, and the \( \Delta_{{r_{2} }} H_{\text{m}}^{\theta } \) decreased at higher temperatures from 273.15 to 373.15 K.

The \( \Delta_{{r_{2} }} G_{\text{m}}^{\theta } \) was greater than 0 in the temperature range from 273.15 to 373.15 K, which showed that the addition-esterification reaction couldn’t carry through spontaneously. And the\( \Delta_{{r_{2} }} G_{\text{m}}^{\theta } \) increased with the raising of the temperature, which indicated that temperature increased was unfavorable for the reactions at the temperature range from 273.15 to 373.15 K.

Equilibrium constant and equilibrium conversion of the transesterification reaction

The molar ratio of methanol to cyclopentyl acetate was set as r 2, the conversion of cyclopentyl acetate was set as x 2, so:

$$ K^{\theta }_{2} = \frac{{x_{2}^{2} }}{{(1 - x_{2} )(r_{2} - x_{2} )}} $$
(15)

In the same way, the equilibrium constant (\( K^{\theta }_{2} \)) of the transesterification reaction at different temperature was calculated from Eq. 13, and the conversion of cyclopentene as x 1 at different temperature with different r 1 was calculated from Eq. 15, and the results are shown in Figs. 6 and 7.

Fig. 6
figure 6

Changes of the transesterification reaction equilibrium constant (\( K^{\theta }_{2} \)) with temperature

Full size image
Fig. 7
figure 7

Change of the cyclopentyl acetate equilibrium conversion (x 2) with temperature

Full size image

Similarly, as seen from Figs. 6 and 7, the \( K^{\theta }_{2} \) and x 2 decreased with the raising of the temperature, the x 2 increased with the raising of the r 2 at the same temperature. The conversion of cyclopentyl acetate was higher with lower temperature and greater molar ratio of methanol to cyclopentyl acetate. However, the extremely lower temperature reduced the reaction rate which was unfavorable for the transesterification reaction, and the methanol spent increased with increasing of r 2, and the cost of separation increased. The suitable reaction conditions were temperature of range from 323.15 to 343.15 K, r 2 of range from 3:1 to 4:1.

Experimental validation, results and discussion

Chemical and catalysts

Cyclopentene [AR  > 98.0 % (wt)] was purchased from Changzhou Sinly Pharmchem Co., Ltd. Acetic acid [AR > 99.5 % (wt)] was purchased from Reagent No. 1 Factory of Shanghai Chemical Reagent Co., Ltd. Methanol [CP > 99.9 % (wt)] was purchased from Shanghai Coking Co., Ltd. Amberlyst-35 strong acidic cation-exchange resin catalysts were obtained from Rohm and Haas Shanghai Chemical Industry Co., Ltd. QRE-01 strong acidic cation-exchange resin catalysts were obtained from Research Institute of Qilu Petrochemical Co., SINOPEC.

Analysis and calculations

Chemical composition of products was analyzed using a gas chromatography (Agilent GC-6890) with a HP-FFAP silica capillary column (30 m × 0.32 mm × 0.25 μm). Nitrogen was used as the carrier gas at a flow rate of 0.7 mL/min. The temperature of column oven was programmed from 60 °C increased at 5 °C/min to 80 °C, and held with an isothermal for 4 min, then increased at 10 °C/min to 220 °C, and held with an isothermal for 15 min. The temperature of injector and detector was set at 220 and 250 °C, respectively. The split ratio was 1:100; the sample injection volume was 0.4 μL. Calibration normalization method was performed on the GC to ensure accuracy of the measurements.

The conversions of cyclopentene and cyclopentyl acetate, the selectivity of cyclopentyl acetate and cyclopentanol can be determined with the Eqs. (16–20).

$$ {\text{Conversion of cyclopentene }}\left( \% \right)\, = \,{\text{ Con}}_{\text{Cyclopentene}} \,{ = }\,\frac{{m_{\text{Cyclopentene,\,raw materials}} \, - \,m_{\text{Cyclopentene,\,products}} }}{{m_{\text{Cyclopentene,\,raw materials}} }}\, \times \, 1 0 0 $$
(16)
$$ {\text{ Selectivity of cyclopentyl acetate }}\left( \% \right) = \,{\text{Sel}}_{\text{Cyclopentyl\, acetate}} = \frac{{m_{\text{Cyclopentyl\,acetate}} }}{{m_{\text{Cyclopentene,\, raw materials}} - m_{\text{Cyclopentene,\, products}} }} \times 100 $$
(17)
$$ {\text{Conversion of cyclopentyl\,acetate }}\left( \% \right) = {\text{ Con}}_{\text{ cyclopentyl\,acetate}} \,{ = }\,\frac{{m_{\text{ cyclopentyl acetate, raw\,materials}} \, - \,m_{\text{ cyclopentyl acetate,\,products}} }}{{m_{\text{ cyclopentyl\,acetate, raw\,materials}} }}\, \times \, 1 0 0 $$
(18)
$$ {\text{Selectivity of cyclopentanol }}\left( \% \right) = {\text{ Sel}}_{\text{cyclopentanol}} = \,\frac{{m_{\text{cyclopentanol}} }}{{m_{\text{ cyclopentyl\,acetate,\,raw materials}} {\kern 1pt} - \,m_{\text{ cyclopentyl\, acetate,\,products}} }}\, \times \,100 $$
(19)
$$ {\text{Yield of cyclopentanol }}\left( \% \right) = \,{\text{Yie}}_{\text{Cyclopentene}} = \frac{{{\text{Con}}_{\text{ cyclopentyl\,acetate}} \times {\text{Sel}}_{\text{cyclopentanol}} }}{100} $$
(20)

Experiment

The addition-esterification reaction of cyclopentene with acetic acid was operated in a glass tube fixed bed reactor (φ25 mm × 500 mm) over Amberlyst-35 strong acidic cation-exchange resin catalysts, the reaction temperature was adjusted by the temperature control system, the reactants mass flow rate was controlled by the feeding pump. The addition-esterification reaction of cyclopentene and acetic acid with different reaction conditions was carried out under normal pressure, the mass space velocity of 2.0 h−1. The analysis results showed that the selectivity of cyclopentyl acetate was around 98 %. The cyclopentyl acetate product (mass fraction of 99 %) was obtained by distillation, the unreacted cyclopentene and superfluous acetic acid could be reused by distillation recovery. The conversion of cyclopentene from experimental results and the equilibrium conversion of cyclopentene from thermodynamics calculation in the addition-esterification reaction are compared in Table 5.

Table 5 Comparisons between experiments results and calculation data of the addition-esterification reaction
Full size table

From Table 5, we can see that, the cyclopentene conversion relative errors of experiment nos. 6 and 7 were more than 10 %. Since the reaction rate I was slower in the lower temperature, it was difficult to achieve equilibrium at a lower reaction temperature during a short reaction time, the relative errors in the lower reaction temperature were larger than that in higher reaction temperature. The relative error of other experiments was lower than 7.0 %, and the average relative error was 2.98 % (experiment nos. 6 and 7 are not included); the thermodynamic calculation was in good agreement with the experiment results.

The transesterification of cyclopentyl acetate and methanol was operated in a glass tube fixed bed reactor (φ25 mm × 500 mm) over QRE-01 strong acidic cation-exchange resin catalysts, the reaction temperature was adjusted by the temperature control system, the reactants’ mass flow rate was controlled by the feeding pump. The transesterification of cyclopentyl acetate and methanol was carried out under normal pressure, the reaction temperature of 50 °C, the molar ratio of methanol to cyclopentyl acetate of 3:1, the mass space velocity of 2.0 h−1, the conversion of cyclopentyl acetate was 55.3 %, the selectivity of cyclopentanol was 99.5 %, the yield of cyclopentanol was 55.0 %. The cyclopentanol product was obtained by distillation, the unreacted cyclopentyl acetate and superfluous methanol could be reused by distillation recovery.

Conclusions

Thermodynamic analysis for reactions of indirect synthesis of cyclopentanol from cyclopentene has been carried out based on partial physical properties data of cyclopentyl acetate and cyclopentanol estimated by group contribution methods. The enthalpy changes, free energy changes, equilibrium constant and equilibrium conversion of the addition-esterification reaction and transesterification reaction were calculated.

The addition-esterification reaction of cyclopentene and acetic acid was exothermic reaction at the temperature range from 273.15 to 373.15 K, the optimal reaction condition was temperature of range from 333.15 to 353.15 K, molar ratio of acetic acid to cyclopentene of 2:1–3:1.

The transesterification reaction of cyclopentyl acetate and methanol is exothermic reaction at the temperature range from 273.15 to 373.15 K, the optimal reaction condition was temperature of range from 323.15 to 343.15 K, molar ratio of methanol to cyclopentyl acetate of 3:1 to 4:1.

The addition-esterification of cyclopentene and acetic acid experiments were carried out in a glass tube fixed bed reactor, and the experiments results showed that the thermodynamic calculation was in good agreement with the experiment results.