Comparison between Ethanol and Diethyl Carbonate as Ethylating

Research Note pubs.acs.org/IECR

Comparison between Ethanol and Diethyl Carbonate as Ethylating Agents for Ethyl Octyl Ether Synthesis over Acidic Ion-Exchange Resins Jordi Guilera, Roger Bringué, Eliana Ramírez, Montserrat Iborra, and Javier Tejero* Chemical Engineering Department, Faculty of Chemistry, University of Barcelona, c/Martí i Franquès 1, 08028 Barcelona, Spain S Supporting Information *

ABSTRACT: Direct addition of bioethanol to diesel reduces the quality of commercial blends. An alternative way to introduce bioethanol into diesel is as linear ether such as ethyl octyl ether (EOE). EOE synthesis by 1-octanol (OcOH) reaction with ethanol (EtOH) or diethyl carbonate (DEC) over acidic ion-exchange resins has been studied in a 100-mL batch reactor (130− 150 °C, 25 bar). The main drawback for ethylating OcOH in both reaction systems is the loss of ethyl groups by diethyl ether formation. In OcOH excess, selectivity to EOE with respect to EtOH and to DEC was found to be similar (58−59%) when the ethylating agent was entirely consumed. However, the initial reaction rate of EOE formation from DEC is lower, due to the formation of ethyl octyl carbonate as reaction intermediate. Accordingly, EtOH showed to be more interesting ethylating agent to produce a synthetic biofuel such as EOE over acidic ion-exchange resins.

1. INTRODUCTION The introduction of biofuels to the European energy market is currently ruled by the renewable energy (2009/28/EC) and the fuel quality (2009/30/EC) directives. The European Union settled as mandatory a 10% minimum target for the share of biofuels in transport fuels by 2020. As a means of reducing oildependency, interest in using bioethanol in commercial diesel fuels has currently increased. However, bioethanol−diesel blends are not satisfying. The main drawbacks are that direct addition of ethanol (EtOH) decreases the cetane number, fuel viscosity, and mixture stability of commercial blends in comparison with the diesel base.1,2 An alternative way to introduce EtOH into the diesel pool is as an ethylating agent to give oxygenated compounds for diesel such as linear long-chain ethers:3 for instance ethyl octyl ether (EOE). It has suitable fuel properties, specially its high cetane number 97−100 and its boiling point of 187 °C compatible with the lower part of diesel distillation curve.4,5 EOE can be synthesized successfully either by the dehydration reaction of 1-octanol (OcOH) and EtOH6 or by the transesterification reaction between OcOH and diethyl carbonate (DEC) to ethyl octyl carbonate (EOC) and its subsequent decomposition to EOE.7 However, to the best of our knowledge, comparison between EtOH and DEC as ethylating agents to give linear asymmetrical ethers is not found in the open literature. Ethanol and DEC are considered as environmentally friendly reactants. Still, since DEC is produced from EtOH,8,9 DEC use as ethylating agent would be justified only if higher selectivity and yield were obtained at the same working conditions. Thus, the aim of this work is to compare the efficiency of EtOH and DEC as ethylating agents to produce EOE by the reaction with OcOH. EOE synthesis has been carried out in the liquid phase over commercial acidic low cross-linked ion-exchange resins. The influence of the initial molar ratio and temperature on © 2012 American Chemical Society

selectivity and yield to EOE are discussed; apparent activation energies are also estimated.

2. EXPERIMENTAL SECTION 2.1. Materials. OcOH (≥99.5%, Fluka), DEC (≥98%, Fluka), and EtOH (≥99.8%, Panreac) were used as reactants. Distilled water, diethyl ether (DEE) (≥99%, Panreac), 1-octene (≥97%, Fluka), and di-n-octyl ether (DNOE) (≥97%, Fluka) were used for analysis purposes. EOE was synthesized and purified in our lab by rectification to 99%. A series of acidic polystyrene−DVB ion-exchange resins were used as catalysts: the macroreticular Amberlyst 39 (Rohm and Haas) and geltype Dowex 50Wx8 and Dowex 50Wx2 (Dow), CT124 and CT224 (Purolite), and Amberlyst 121 (Rohm and Haas). The main properties of tested catalyst are shown in Table 1. 2.2. Procedure. Experiments were performed in a 100-mL batch reactor. Resins were used with the commercial Table 1. Main Properties of Tested Acidic Resins catalyst

DVB %

acid capacity (meq H+/g)a

Vsp (cm3/g)b

SBET (m2/g)c

Tmax (°C)

Amberlyst 39 Dowex 50Wx8 CT124 CT224 Dowex 50Wx2 Amberlyst 121

8 8 4 4 2 2

5.0 4.83 5.0 5.34 4.83 4.8

1.451 1.627 1.994 1.811 2.655 3.263

0.09 0.23 0.07 0.95 1.32 0.02

130 150 130 150 150 130

a

Determined by titration against standar base. bSpecific volume of swollen polymer from analysis of ISEC data in aqueous phase.7 cBET surface area in dry state (Kr adsorption−desorption). Received: Revised: Accepted: Published: 16525

February 24, 2012 October 4, 2012 November 26, 2012 November 26, 2012 dx.doi.org/10.1021/ie3004978 | Ind. Eng. Chem. Res. 2012, 51, 16525−16530

Industrial & Engineering Chemistry Research

Research Note

Figure 1. Reaction scheme of EOE synthesis from OcOH and EtOH (A) and from OcOH and DEC (B).

distribution of particle sizes, and dried first at 110 °C at 1 bar and later at 110 °C under vacuum overnight. Then, the reactor was loaded with 70 mL of OcOH/DEC or OcOH/EtOH mixture, heated up to the reaction temperature (130−150 °C) and stirred at 500 rpm. Pressure was set at 25 bar with N2 to maintain the liquid phase. When the liquid reached the working temperature, dried catalyst (2 g) was injected into the reactor by shifting with N2 from an external cylinder; this time was taken as zero time. Typical runs lasted 8 h but 48 h experiments were also performed. Setup and analysis procedure are described in detail elsewhere.7 Experiments were replicated twice to ensure the reproducibility of experimental data. Initial reaction rates to form EOE were computed analogously to previous works.10,11 Conversion of ethylating agent (EA), selectivity, and yield to EOE with respect to EA were computed conventionally by means of eqs 1, 2, and 3, respectively. XEA = EOE SEA =

mole of EA reacted 100 mole of EA initially

(1)

mole of EA reacted to form EOE 100 mole of EA reacted

[%, mol/mol] EOE YEA =

[%, mol/mol]

3.1. Reaction Scheme. Figure 1 shows the reaction pathways for obtaining EOE as a function of the ethylating agent, EtOH or DEC. In the OcOH/EtOH system, the network involves three parallel reactions (Figure 1A): the dehydration reaction between EtOH and OcOH forming EOE and water (1) which is the reaction of interest, the dehydration of two EtOH molecules to give DEE (2), and that of two OcOH molecules forming DNOE (3). As for the OcOH/DEC system the reaction network is a series-parallel one (Figure 1B). EOE synthesis takes place in two steps in series: carboxylation of DEC with OcOH to form EOC (4), and EOC decomposition to EOE (5). Undesirably, some DEC decomposes to DEE (6). Likewise, some EOC may be carboxyocthylated to dioctyl carbonate (DOC) (7), and later decomposed to DNOE (8). As a consequence of EtOH release in step (4), the reaction between EtOH and OcOH also takes place in OcOH/DEC runs. The presence of water in the reaction mixture confirmed the direct reaction between alcohols when DEC was the ethylating agent (Figure 1A, steps 1,2,3). 7 In both reaction systems intramolecular dehydration of OcOH and EtOH to octenes and ethylene (plus water), respectively, is possible over less swollen resins of high cross-linking degree as a consequence of diffusion restrictions.6 The fact that octenes and ethylene were not detected confirms that diffusion of bulky substances is improved on highly swollen low cross-linked resins. 3.2. Initial Molar Ratio Influence. Experiments were carried out by varying the initial OcOH to ethylating agent molar ratio (ROcOH/EA = 0.5−2) at 150 °C over Dowex50Wx2. As seen in Table 2, XEtOH or XDEC increases on increasing ROcOH/EA, whereas XOcOH decreases. Product distribution at 8 h for OcOH/EtOH and OcOH/DEC systems is shown in Figure 2A,B, respectively. It is to be noted that EtOH formed in OcOH/DEC runs was not plotted for the sake of clarity since it can be further dehydrated to DEE or else to EOE. As expected,

(2)

X ·S EOE moles of EA reacted to form EOE 100 = EA EA moles of EA initially 100

[%, mol/mol]

(3)

3. RESULTS AND DISCUSSION Tested resins were selected because they proved to be effective in the synthesis of C10 and C12 linear ethers.6,7,10,11 They have 2−8% of DVB, and highly swell in polar media (aqueous, alcoholic) giving rise to wide spaces between polymer chains. In this way they allow most of active sites to be accessible and, at the same time, offer a proper environment for relatively bulky reactants such as OcOH or DEC to react. Detailed swelling data are given in the Supporting Information, and an extensive morphological description of the swollen catalysts gel-phase in aqueous phase can be found elsewhere.7 EOE synthesis from the ethylating agents EtOH and DEC are compared over the six resins.

Table 2. EtOH and DEC Conversion on Dowex 50Wx2, T = 150 °C, W = 2 g at 8 h Reaction Time OcOH/EtOH system

16526

OcOH/DEC system

REtOH/EA

XOcOH

XEtOH

XOcOH

XDEC

2 1 0.5

28.8 ± 0.7 20.7 ± 0.2 17.5 ± 0.5

84.0 ± 2.0 60.6 ± 0.4 51.0 ± 0.8

55.6 ± 0.4 69.0 ± 0.8 79.2 ± 1.9

96.7 ± 0.4 93.2 ± 1.1 83.5 ± 1.9

dx.doi.org/10.1021/ie3004978 | Ind. Eng. Chem. Res. 2012, 51, 16525−16530


Research Note

Figure 2. Influence of ROcOH/EtOH (A) and ROcOH/DEC (B) on product distribution: (dark black) EOE; (light black) EOC; (white) DNOE; (light gray) DOC; (dark gray) DEE. Dowex 50Wx2, T = 150 °C, W = 2 g, t = 8 h.

Figure 3. Conversion (A), selectivity (B), and yield (C) to EOE with respect to the ethylating agent (○ EtOH; ● DEC). Dowex 50Wx2, T = 150 °C, ROcOH/EA = 2, W = 2 g. The error bars indicate the confidence interval at a 95% probability level.

Figure 4. Product distribution on tested catalysts from OcOH/EtOH (A) and from OcOH/DEC (B) feeds: (dark black) EOE; (light black) EOC; (white) DNOE; (light gray) DOC; (dark gray) DEE. T = 150 °C, ROcOH/EA = 2, W = 2 g, t = 8 h.

reaction product in the two systems, particularly in the OcOH/ EtOH system. As a result, the loss of ethyl groups to form EOE is minimized when the limiting reactant is the ethylating agent, EtOH or DEC. Accordingly, further experiments were performed in OcOH initial excess (ROcOH/EA = 2). Long time experiments were performed at ROcOH/EA = 2 to study the evolution versus time of DEC and EtOH conversion,

EOE formation is highly influenced by the initial molar ratio OcOH/ethylating agent, and the production of the lower molecular weight ether was favored (DEE > EOE > DNOE) for ROcOH/EA ≤ 1, DEE being the product formed in higher amount. As seen the efficiency of EtOH or DEC as ethylating agents to synthesize EOE is mainly limited by the loss of ethyl groups giving place to DEE. At ROcOH/EA = 2, EOE is the main 16527



Research Note

EOC and DOC appeared in significant amounts particularly the first one. In the OcOH/EtOH system, EOE selectivity was about 50%, DEE selectivity was a bit higher than 25%, and that of DNOE was about 20%, but on Dowex 50Wx8, whose selectivity to DNOE was only about 15%, while selectivity to DEE rose to 35%. As the Vsp values of Table 1 show, tested resins clearly swell in aqueous media. Morphological analysis of ISEC data reveals that in the swollen gel phase of Dowex 50Wx8 predominates a zone of very high dense polymer (2 mm−2); spaces between chains being equivalent to pores of diameter ≤ 1 nm).7 Amberlyst 39, CT124, CT224, Dowex 50Wx2, and Amberlyst 121 have zones of polymer density ≤ 1.5 mm−2 (spaces between chains are equivalent to pores of diameter > 1 nm).7 From swelling data it is seen that OcOH and EtOH are present inside the resin from the start of the reaction, however some diffusion restriction could be advanced for OcOH. Moreover, steric restrictions would be higher for the long ethers EOE and DNOE than for shorter ether DEE. In the case of Dowex 50Wx8, this zone of higher polymer density probably causes more significant steric restrictions for bulky ether DNOE than the other resins and would explain the distinct selectivity of this resin in the OcOH/EtOH system. As for the OcOH/DEC system, swelling data point out that probably at short reaction times OcOH predominates inside the catalyst, however gelphase morphology is flexible enough to allow OcOH and DEC to access more or less easily to acidic centers. As for reaction intermediates, EOC and DOC probable have similar steric restrictions than EOE and DNOE, respectively. Nevertheless, in the OcOH/DEC reaction system, morphology of the resins hardly influences their selectivity because, as seen in Figure 4, products distribution is very similar over all these catalysts although selectivity to EOE over Dowex 50Wx8 is something lower. As a consequence, to favor EOE production, ionexchangers with pores wider than 1 nm diameter in the swollen state showed to be flexible enough to synthesize EOE in the two systems. Figure 4 also shows that selectivity of Dowex 50Wx2 to EOE is slightly higher in both of them. Finally, Dowex 50Wx2 gives the better EOE yield after 8 h reaction time. It is to be noted that the EOE yield is much higher when EtOH is used as the ethylating agent.

EOE selectivity, and EOE yield with respect to ethylating agent of both reaction systems. DEC reacts faster than EtOH and DEC (Figure 3A) in such a way that XDEC is about 97% at about 8 h, whereas XEtOH is nearly 84%. However, at 48 h both DEC and EtOH are almost depleted. In the OcOH/EtOH system, SEOE EtOH increased quickly to 55% at 20 h; it further rises to 59% but very slowly (Figure 3B). As for the OcOH/DEC system, probably because the EOC decomposition to EOE is EOE slow, SEOE DEC values lower than SEtOH ones were initially observed. Nevertheless, when the intermediate EOC was almost entirely depleted (48 h), similar selectivity and yield to EOE values were achieved in both reaction systems (Figure 3B,C). Summarizing, similar potential selectivity and yields to EOE were obtained by using DEC or else by using EtOH in excess of OcOH at very large reaction times, but at a reaction time of a few hours the OcOH/EtOH system gave a higher EOE yield (Figure 3C). 3.3. Screening over Low Cross-Linked PolystyreneDVB Resins. The six resins were tested in OcOH molar excess (ROcOH/EA = 2) at 150 °C. The products distribution at 8 h is shown in Figure 4A for the OcOH/EtOH system and in Figure 4B for OcOH/DEC one. In line with what seen in Figure 3 for Dowex 50Wx2, EOE yield was higher on each resin in the OcOH/EtOH system (Table 3) because the selectivity to EOE Table 3. EOE Yield with Respect to the Ethylating Agent (Dowex 50Wx2, T = 150 °C, ROcOH/EA = 2, W = 2 g, t = 8 h) catalyst Amberlyst 39 Dowex 50Wx8 CT124 CT224 Dowex 50Wx2 Amberlyst 121

YEOE EtOH (%) 37.4 33.7 37.0 39.6 43.4 42.9

± ± ± ± ± ±

0.8 0.2 0.5 1.4 0.4 0.9

YEOE DEC (%) 30.5 30.2 29.5 33.1 33.2 33.2

± ± ± ± ± ±

1.2 0.8 1.3 0.2 0.9 1.2

on all catalysts was always clearly higher in the OcOH/EtOH system than in the OcOH/DEC one. On the other hand, it is to be noted that for each reacting system selectivity to EOE was similar on the different catalysts. In this way, in the OcOH/ DEC system EOE selectivity was a bit less than 40%, that of DNOE about 10%, and the DEE selectivity was close to 30%.

Figure 5. Temperature influence on product distribution from OcOH/EtOH (A) and OcOH/DEC (B) feeds: (dark black) EOE; (light black) EOC; (white) DNOE; (light gray) DOC; (dark gray) DEE. Dowex 50Wx2, ROcOH/EA = 2, W = 2 g, t = 8 h. 16528



Research Note

1-hexanol to di-n-hexyl ether.11 As the later reactions were carried out free from the influence of internal and external mass transfer, it can be assumed a negligible effect of external and internal mass transfer influences the two EOE formation reactions.

3.4. Temperature Influence. Temperature influence on both reaction systems was checked in the range 130−150 °C over Dowex 50Wx2, as it showed to be the most active catalyst. The products distribution shown in Figure 5 suggests that selectivity to EOE in OcOH/EtOH reaction system was not significantly affected by the temperature (Figure 5A), which indicates that the reaction rate of DEE, EOE, and DNOE formation has a similar dependence on the temperature. On the contrary, in OcOH/DEC runs the products distribution changed drastically with temperature (Figure 5B). Decomposition of carbonates (DEC, EOC, and DOC) to ethers (DEE, EOE, and DNOE, respectively) was more noticeable than the carboxylation of DEC to EOC on increasing temperature. As a result, DEC decomposition to DEE was more hindered at 130 °C. However, a drawback to operate industrially at this relatively low temperature is that the reaction rate to form EOE would be around 5-fold lower than that at 150 °C, as shown in Table 4.

4. CONCLUSIONS EOE synthesis from OcOH/EtOH and OcOH/DEC mixtures over acidic ion-exchange resins is compared. The main secondary reaction in the two reaction schemes (and therefore the main drawback in industrial practice) is the loss of ethyl groups to produce DEE. As a consequence, selectivity to EOE with respect to ethylating agent (DEC or EtOH) is relatively low (40 −50% at 8 h reaction time). The loss of ethyl groups by DEE formation is a serious problem since this ether cannot be blended straightforwardly in commercial diesel fuels. Similar selectivities and yields to EOE were obtained at long reaction time (48 h). Nevertheless, initial reaction rates to form EOE are slightly higher in the OcOH/EtOH system than in the OcOH/DEC one. Accordingly, EtOH was shown to be a more suitable ethylating agent to produce synthetic ethers biofuels such as EOE over acidic resins of low cross-linking degree. Otherwise, the EOE synthesis from OcOH and DEC is only competitive at long reaction times or, in continuous units, if oversized reactors are used. Furthermore, the reaction between OcOH and EtOH gives water as a byproduct, a nontoxic substance. It would be an environmentally friendly process, like the one based on the OcOH/DEC system (there is no net CO2 production). In summary, the current availability of EtOH and the production of water as byproduct suggest EtOH to be a suitable ethylating agent to produce long-chained ethers such as EOE.

Table 4. Initial Reaction Rates to Form EOE Depending on the Ethylating Agent at Different Temperatures (Dowex 50Wx2, ROcOH/EA = 2, W = 2 g) r0EOE (mol/(h·kgcat)) T (°C)

EtOH

DEC

130 140 150

1.91 ± 0.11 4.74 ± 0.30 9.94 ± 0.19

1.79 ± 0.10 4.08 ± 0.15 9.42 ± 0.61

By comparing the behavior of both ethylating agents, initial EOE reaction rates were always lower for OcOH/DEC system than for OcOH/EtOH one. This is probably due to the fact that synthesis of EOE from DEC requires the formation and subsequently decomposition of EOC, whereas in the OcOH/ EtOH system EOE synthesis is straightforward from the two alcohols. Table 5 shows the apparent activation energies for EOE synthesis and it is compared to that of some linear ethers

■

Analysis of swelling data in water and reactants (Table S2 and Figure S1) and morphology of swollen resins (Figure S2). This material is available free of charge via the Internet at http:// pubs.acs.org.

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Table 5. Comparison of Apparent Activation Energy Values for Several Ethers Syntheses ether

reactant

catalyst

ethyl octyl ether

OcOH and EtOH OcOH and DEC

1-pentanol

Dowex 50Wx2 Dowex 50Wx2 Dowex 50Wx4 Amberlyst 70

1-hexanol

Amberlyst 70

ethyl octyl ether di-n-pentyl ether di-n-pentyl ether di-n-hexyl ether

1-pentanol

ASSOCIATED CONTENT

S Supporting Information *

AUTHOR INFORMATION

Corresponding Author

Ea [kJ/mol]

ref

117 ± 5

this work

126 ± 2

this work

115 ± 2

10

115 ± 5

10

108 ± 7

11

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS Financial support was provided by the State Education, Universities, Research & Development Office of Spain (Project CTQ2010-16047). The authors thank Rohm and Haas and Purolite for providing ion exchange resins.

■

syntheses. Apparent activation energies were computed by an Arrhenius fit of initial reaction rates. In fact, the apparent activation energy estimated for OcOH/DEC system corresponds to the decomposition reaction of EOC to produce EOE and CO2. The EOC decomposition rate to EOE shows a slightly higher dependence with the temperature than the dehydration reaction of EtOH and OcOH to EOE. Finally, it is to be noted that the apparent activation energy of the reaction between OcOH and EtOH to give EOE is in the range of the dehydration reactions of 1-pentanol to di-n-pentyl ether10 and 16529

NOMENCLATURE DEC = diethyl carbonate DEE = diethyl ether DNOE = di-n-octyl ether DOC = dioctyl carbonate DVB = divinylbenzene EA = ethylating agent (EtOH or DEC) Ea = apparent activation energy (kJ/mol) EOC = ethyl octyl carbonate EOE = ethyl octyl ether dx.doi.org/10.1021/ie3004978 | Ind. Eng. Chem. Res. 2012, 51, 16525−16530


Research Note

EtOH = ethanol OcOH = 1-octanol r0EOE = initial rate of EOE formation (mol/(h·kg cat)) ROcOH/EA = initial 1-octanol to ethylating agent molar ratio (mol/mol) SBET = BET surface area (m2/g) SEOE EA = selectivity to EOE with respect to EA (%, mol/mol) T = temperature (°C) Tmax = maximum operating temperature of resins (°C) Vsp = specific volume of swollen polymer (gel-phase) (cm3/ g) XEA = conversion of ethylating agent (%, mol/mol) YEOE EA = yield to EOE with respect to i (%, mol/mol)

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REFERENCES

(1) Hansen, A. C.; Zhanga, Q.; Lyne, P. W. L. Ethanol-Diesel Fuel BlendsA Review. Bioresour. Technol. 2005, 96, 277. (2) Kwanchareon, P.; Luengnaruemitchai, A.; Jai-In, S. Solubility of a Diesel−Biodiesel−Ethanol Blend, Its Fuel Properties, and Its Emission Characteristics from Diesel Engine. Fuel 2007, 86, 1053. (3) Olah, G. A. Cleaner Burning and Cetane Enhancing Diesel Fuel Supplements. U.S. Patent 5,520,710, May 18, 1996. (4) Pecci, G. C.; Clerici, M. G; Giavazzi, F.; Ancillotti, F.; Marchionna, M.; Patrini, R. Oxygenated Diesel Fuels 1: Structure and Properties Correlation. IX Int. Symp. Alcohol Fuels 1991, 321. (5) Nel, R. J. J.; de Klerk, A. Dehydration of C5−C12 Linear 1Alcohols over η-Alumina to Fuel Ethers. Ind. Eng. Chem. Res. 2009, 48, 5230. (6) Pros, S. Ethyl Octyl Ether Formation over Acidic Ion-Exchange Resins. M.S. Chem. Eng. Thesis, University of Barcelona, 2009 (7) Guilera, J.; Bringué, R.; Ramírez, E.; Iborra, M.; Tejero, J. Synthesis of Ethyl Octyl Ether from Diethyl Carbonate and 1-Octanol over Solid Catalysts. A Catalyst Screening. Appl. Catal. A. Gen. 2012, 413−14, 21. (8) Dunn, B. C.; Guenneau, C.; Hilton, S. A.; Pahnke, J.; Eyring, E. M.; Dworzanski, J.; Meuzelaar, H. L. C.; Hu, J. Z.; Solum, M. S.; Pugmi, R. J. Production of Diethyl Carbonate from Ethanol and Carbon Monoxide over a Heterogeneous Catalyst. Energy Fuels 2002, 16, 177. (9) Zhu, D.; Mei, F.; Chen, L.; Mo, W.; Li, T.; Li, G. An Efficient Catalyst Co(salophen) for Synthesis of Diethyl Carbonate by Oxidative Carbonylation of Ethanol. Fuel 2011, 90, 2098. (10) Bringué, R.; Iborra, M.; Tejero, J.; Izquierdo, J.; Cunill, F.; Fité, C.; Cruz, V. Thermally Stable Ion-Exchange Resins as Catalysts for the Liquid-Phase Dehydration of 1-Pentanol to Di-n-pentyl Ether (DNPE). J. Catal. 2006, 244, 33. (11) Medina, E.; Bringue, R.; Tejero, J.; Iborra, M.; Fite, C. Conversion of 1-Hexanol to Di-n-hexyl Ether on Acidic Catalysts. Appl. Catal., A Gen. 2010, 374, 41.

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Comparison between Ethanol and Diethyl Carbonate as Ethylating

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