New Production Processes of Dichlorohydrins from Glycerol Using

Jan 26, 2016 - A new class of catalysts promoting the hydrochlorination of glycerol to obtain selectively 1,3-dichlorohydrin has recently been discove...
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New Production Processes of Dichlorohydrins from Glycerol Using Acyl Chlorides as Catalysts or Reactants R. Vitiello,†,‡ R. Tesser,*,†,‡ E. Santacesaria,§ and M. Di Serio†,‡ †

Department of Chemical Sciences, University of Naples “Federico II”, Via Cinthia 80126, Naples, Italy Consorzio Interuniversitario di Reattività Chimica e Catalisi (CIRCC), Via Celso Ulpiani 70126, Bari, Italy § Eurochem Engineering srl, Via Codogno 5 20139, Milan, Italy ‡

S Supporting Information *

ABSTRACT: A new class of catalysts promoting the hydrochlorination of glycerol to obtain selectively 1,3-dichlorohydrin has recently been discovered. These catalysts are acyl chlorides and prove to be much more active and sometimes more selective than the corresponding carboxylic acids, usually employed to promote this reaction. Many different kinetic runs have been performed to compare the performances of acetyl chloride and acetic acid, propanoyl chloride and propionic acid, adipoyl dichloride and adipic acid, succinyl dichloride and succinic acid, and malonyl dichloride and malonic acid, respectively. In all cases, the activity of the acyl chloride proved to be much higher. This behavior has been discussed and explained on the basis of a possible reaction mechanism. The reaction occurs rapidly even if glycerol is contaminated with NaCl. By adding a stoichiometric amount of an acyl chloride to glycerol, the hydrochlorination occurs in a short time, with a high selectivity, without any external supply of HCl, because acyl chlorides react promptly and quantitatively with glycerol forming HCl in situ. To avoid an excessive increase of the HCl pressure, acyl chlorides must be fed into a reactor containing glycerol with an opportune flow rate. The flow rate employed affects both the activity and the selectivity as has been demonstrated in two kinetic runs performed at two different flow rate levels of acetyl chloride.

1. INTRODUCTION It is well-known that in biodiesel production, starting from triglycerides, glycerol (GLY) is obtained as a byproduct in an amount corresponding to about 10% by weight.1 Therefore, by increasing the production of biodiesel, the production of the byproducts increases too. Glycerol has found, in the past, profitable applications in many fields such as foods, cosmetics, pharmaceuticals, personal care, drugs, polyethers/polyols, explosives, alkyd resins, and detergents, etc. These markets are already saturated and cannot absorb the glycerol glut deriving from the growing production of biodiesel. As a consequence, glycerol is often burned by the biodiesel producers themselves to satisfy the energy demands of their plants. A recently proposed alternative use of a large amount of this glycerol could be the production, by chlorination, of dichlorohydrins (DCHs), which are used for the synthesis of epoxy resins.2−13 In fact, it has been well-known,14−16 for a long time, that glycerol can be converted into dichlorohydrins by hydrochlorination with aqueous HCl, using acetic acid as a catalyst.17−20 In some cases, an inert solvent has been used dissolving selectively 1,3-dichlorohydrin.21 However, all of the traditional processes for producing dichlorohydrins from glycerol have different important drawbacks, such as (i) the loss of the catalyst during the reaction due to the low boiling point of acetic acid (117 °C); (ii) the reaction rate decreasing caused by the accumulation of water in the reaction mixture occurring either when aqueous hydrochloric acid is added as a reagent or when water is formed as a consequence of the reaction; and (iii) the difficulty in separating the desired product 1,3-dichlorohydrin from the reaction mixture at the end of the reaction. On account of these drawbacks, in all related recently © 2016 American Chemical Society

published papers and patents, hydrochlorination has instead been made by using gaseous HCl and carboxylic acids less volatile than acetic acid. The use of less volatile catalysts allows you to operate at temperatures higher than 100 °C, thus increasing the reaction rate and converting all of the glycerol to the desired product in less time. In a patent published by Solvay,22 for example, the use of adipic acid is proposed. In another patent published by Eurochem Engineering23 the use of the following carboxylic acids is proposed: propionic acid, malonic acid, levulinic acid, citric acid, and succinic acid. The possibility of recovering 1,3-dichlorohydrin by stripping is also suggested. In another patent, published by DOW Global Technologies,11 an exhaustive list of possible catalysts is reported with their corresponding performances, but, in particular, the advantage of operating under pressure is stressed, the reaction rate and yields being strongly affected by the partial pressure of HCl. In a patent of CONSER SpA,24 the opportunity of operating by using two different catalysts in sequence is suggested, adding initially malic acid at a low pressure (1−2 bar) and adding then succinic acid at a higher pressure (8−10 bar). The performances of different carboxylic acids as catalysts have been intensively studied as reported in a recent review,13 and a rough correlation has been found between the pKa of the acid12 (it must be included within the range 4−5) and the catalytic activity. Some carboxylic acids have proved to be selective in producing monochlorohydrins, in particular 1-monochlorohydrin (1-MCH), with lower amounts of Received: Revised: Accepted: Published: 1484

October 8, 2015 January 14, 2016 January 26, 2016 January 26, 2016 DOI: 10.1021/acs.iecr.5b03765 Ind. Eng. Chem. Res. 2016, 55, 1484−1490

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Industrial & Engineering Chemistry Research Scheme 1. General Reaction Scheme for Chlorohydrin Production

2-monochlorohydrin (2-MCH).25 In this case, the reaction is stopped after the first step as in Scheme 1. This reaction scheme, suggested by Tesser et al.,10 explains also the good selectivity of the glycerol hydrochlorination to 1,3-dichlorohydrin, with reactions 2 and 4 being very slow. In this Article, we suggest the use of a completely new class of catalysts, to promote the glycerol hydrochlorination reaction, catalysts that are more active and selective as compared to those previously reported in the literature. In two recently published patents,26,27 it has been reported that some acyl chlorides are much more active and selective in converting glycerol to 1,3-dichlorohydrin than the corresponding carboxylic acid. Moreover, as HCl is formed as a byproduct in the reaction with acyl chlorides, it is also possible to use these compounds in stoichiometric amounts to obtain dichlorohydrins directly without feeding gaseous HCl, this reagent being formed in situ. This opens the possibility for the producers of biodiesel of producing dichlorohydrin, even if they have difficulties in obtaining the HCl supply. As will be seen, another advantage of using acyl chlorides as catalysts or reactants is the possibility of promoting the reaction also by using crude glycerol, which is glycerol that is not refined or contaminated by a mineral salt as it arises from the industrial biodiesel plant. In this Article, a comparison will be made between the performances respectively obtained by using different carboxylic acids and the corresponding acyl chlorides by using the same molar concentration, the same temperature, and the same reaction time. In particular, kinetic runs have been performed by using acetic acid, propionic acid, adipic acid, succinic acid, and malonic acid, and, for comparison, acetyl chloride, propanoyl chloride, adipoyl dichloride, succinyl dichloride, and malonyl dichloride. On the basis of the reaction mechanism, an explanation will be given for the observed behaviors of these new catalysts. Finally, the possibility of using acyl chlorides also as reactants to obtain directly 1,3-dichlorohydrin from glycerol, thanks to the HCl formed in situ as a consequence of the acyl chloride reaction with the hydroxyls of glycerol, will be described in detail. In particular, the effect of the acyl chloride feeding rate into a reactor containing glycerol will be described, insofar as it concerns both the increase of the pressure and the observed reaction rate.

Figure 1. Scheme of the plant used in the tests where 1 is a Hastelloy reactor with a capacity of 300 mL; 2 is a HCl cylinder; 3 is a valve for drawing off the samples to be analyzed; 4 is a magnetic stirrer; 5 is a temperature control and reader; 6 is a pressure reader; and 7 is a system for neutralizing the nonreacted HCl (two Drechsel bubblers in a series containing a solution of sodium hydroxide).

cylinder and kept at the desired pressure. All tests were carried out, for 4 h of reaction, in the same conditions of temperature, stirring rate, and catalyst concentration (T = 100 °C, stirring speed = 1000 rpm, catalyst concentration = 8 mol %). During the runs, some small samples were withdrawn respectively after 30 min, and 1, 2, 3, and 4 h. These samples, after neutralization with an excess of sodium bicarbonate, were analyzed on a gas chromatograph to evaluate both the glycerol conversion and the chlorinated product distribution. At the end of the run, that is, after 4 h of the reaction, the unreacted HCl was discharged from the system by bubbling it into a series of neutralizing traps containing NaOH. The stirring was then stopped, and the system was cooled to room temperature. The GC column used for the analysis was a CHROMPACK CPWax, with a stationary phase of 100% polyethylene-glycol, a length of 30 m, an I.D. of 0.25 mm, and a film thickness of 0.25 μm. The GC was equipped with an FID detector, and helium was used as the carrier gas. The other parameters were: injector temperature = 250 °C, detector temperature = 280 °C, temperature program = 1 min at 40 °C, heating rate = 20 °C/min up to 100 °C then 40 °C/min up to 200 °C, and finally held for 10 min. The withdrawn samples were first diluted with methanol in a volumetric ratio of 1:30, and then 1 μL of the resulting solution was injected into the GC. The quantitative analysis was expressed as a mole percent normalized with respect to the sum of the known components. The catalysts studied in this work were certain carboxylic acids and their corresponding acyl chlorides with the aim of showing the comparison between them in terms of both activity and selectivity. The catalysts studied were acetic acid/acetyl chloride, propionic acid/propanoyl chloride, adipic acid/adipoyl dichloride, succinic acid/succinyl dichloride, and malonic acid/malonyl dichloride.

2. EXPERIMENTAL SECTION The reagents used for the experimental runs were all purchased from Sigma-Aldrich at the highest purity level available (glycerol anhydrous >99.0% and catalyst >99.0%) and were used as received without any further purification. The hydrochloric acid was purchased from Sol spa (>99.8 vol %). All of the experimental runs were carried out in a 300 cm3 hastelloy steel reactor. The reactor and the laboratory plant are reported in the scheme of Figure 1. The glycerol and the catalyst were both loaded into the reactor, and this was rapidly closed. After the reactor was closed and the reaction mixture was heated to the reaction temperature, HCl was fed into the reactor from an external

3. RESULTS AND DISCUSSION 3.1. Comparison of the Performances, as Catalysts of Glycerol Hydrochlorination, of Some Carboxylic Acids, and Their Corresponding Acyl Chlorides. As before 1485

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Industrial & Engineering Chemistry Research mentioned, all tests were carried out with the use of the acyl chlorides in comparison with their corresponding carboxylic acids. Comparing the results obtained, in the same operating conditions, the measured reaction rates are much higher in every case when acyl chlorides are used as catalysts except for runs 5 and 6 in which 100% of conversion has been obtained in all cases, and this prevents any possible comparison (see Table 1).

Table 3. Effect of HCl Partial Pressure in the Presence of Acetyl Chloridea

Table 1. Conversion of Glycerol in the Presence of Acyl Chlorides after 30 and 60 mina run

catalyst

1 2 3 4

acetic acid acetyl chloride propionic acid propanoyl chloride adipic acid adypoyl dichloride succinic acid succinyl dichloride malonic acid malonyl dichloride

5 6 7 8 9 10

glycerol conversion after 0.5 h of reaction (% mol)

84.2 100 81.9 100

92.7 82.1

2-MCH

1,3 DCH

1,2 DCH

GLY

0 15 30 45 60

0 22.9 0.0 0.0 0.0

0 9.1 10.2 11.6 8.8

0 65.0 85.4 82.4 86.1

0 3.0 4.4 6.0 5.1

100 0.0 0.0 0.0 0.0

dissolved in the glycerol. In Table 5, the evolution is reported with the duration of the product distribution for a run performed always in the same conditions previously adopted, but containing also a molar concentration of NaCl of 8%. In the presence of NaCl, the reaction remained fast, and the selectivity surprisingly increased considerably. This behavior opens the possibility of the direct use of crude glycerol as a reactant, that is, glycerol recovered from the production plant of biodiesel without any expensive purification steps. In Table S1, the performances obtained by using as catalysts propionic acid and propanoyl chloride, respectively, are compared. As can be seen, in the presence of propanoyl chloride, the reaction rate was much higher, confirming the behavior observed for the couple acetic acid/acetyl chloride, while the selectivity was only moderately higher. However, the reaction could be considered completed in about 3 h instead of 4 h. In Tables S2−S4, similar comparisons are reported for, respectively, the couples of catalysts characterized by the presence of two functionalities in the molecules, that is, adipic acid/adipoyl dichloride, succinic acid/succinyl dichloride, and malonic acid/ malonyl dichloride. Considering all of the results reported in the Supporting Information, it can be confirmed that the acyl chlorides were much more active as catalysts than the corresponding carboxylic acids, while the selectivities were comparable over a long reaction time. On the contrary, considering a shorter reaction time, the differences in selectivity between a carboxylic acid and the corresponding acyl chloride were more pronounced, as reported in the diagram in Figure 2. To explain the reaction observed, we can start from the threestep mechanism suggested by Santacesaria et al.10,25 based on the observed kinetic behavior in the presence of carboxylic acids as catalysts. The first step is a nucleophilic addition reaction followed by a water elimination in which glycerol attacks the protonated carbonyl group of the carboxylic acid. This step corresponds to the universally accepted mechanism of

100 100 86.3 100 81.9 95.0

100

1-MCH

a Operating conditions: temperature, 100 °C; HCl partial pressure, 10 bar; stirring rate, 1000 rpm; and molar catalyst concentration, 8%.

glycerol conversion after 1 h of reaction (% mol)

100

time (min)

a

The conversions achieved by using carboxylic acids after 60 min are also reported for the purposes of comparison. Operating conditions: temperature, 100 °C; HCl partial pressure, 4.5 bar; stirring rate, 1000 rpm; and molar catalyst concentration, 8%.

As can be seen, in the presence of acyl chlorides, the glycerol conversion was very high or complete after just 30 min. Let us consider now in Table 2 the product distributions over time obtained in the presence of acetic acid and acetyl chloride, respectively. It is clear that, in the presence of acetyl chloride, the reaction was faster even if the final selectivity toward the formation of 1,3-dichlorohydrin was almost the same. In Table 3, it is interesting to observe the effect of the pressure of HCl in the presence of acetyl chloride as catalyst. As is evident, in this case the time for a complete conversion of glycerol was less than 15 min, although the final selectivity to 1,3-dichlorohydrin proved to be somewhat lower if compared to the final value of Table 2. In Table 4, still using acetyl chloride, it is possible to compare the effect of the catalyst concentration. Runs were made at molar concentrations of respectively 2%, 4%, and 8%. As can be seen, the catalyst concentration showed a great effect on the reaction rate that significantly increased with the increasing catalyst concentration. However, the selectivity to 1,3 DCH seemed poorly affected. It is interesting then to observe that the acetyl chloride catalyst was positively affected by the presence of a mineral salt like NaCl

Table 2. Comparison of the Evolution over Time of the Product Distributions in the Presence of Acetic Acid and Acetyl Chloride, Respectivelya

a

time (min)

1-MCH RCOOH/RCOCl

2-MCH RCOOH/RCOCl

1,3 DCH RCOOH/RCOCl

1,2 DCH RCOOH/RCOCl

GLY RCOOH/RCOCl

0 60 180 240

0 23.6/18.8 2.6/1.6 0.7/0.5

0 7.0/4.9 9.9/9.6 7.7/4.8

0 52.6/74.0 85.1/85.0 89.4/91.7

0 1.6/2.3 2.8/3.8 2.8/3

100 15.8/0.0 0.3/0.0 0.0/0.0

Operating conditions: temperature, 100 °C; HCl gauge pressure, 4.5 bar; stirring rate, 1000 rpm; and molar catalyst concentration, 8%. 1486

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Industrial & Engineering Chemistry Research Table 4. Effect of Acetyl Chloride Concentration on Reaction Rate and Selectivitya time (min)

1-MCH cat. 2%/4%/8%

2-MCH cat. 2%/4%/8%

1,3 DCH cat. 2%/4%/8%

1,2 DCH cat. 2%/4%/8%

GLY cat. 2%/4%/8%

0 60 180 240

0 78.7/43.1/18.8 18.1/2.9/1.6 7.4/0.0/0.5

0 9.2/4.9/4.9 8.8/5.4/9.6 5.3/6.7/4.8

0 0.0/50.8/74.0 71.8/91.0/85.0 86.8/89.5/91.7

0 0.0/1.2/2.3 1.3/0.7/3.8 0.5/3.8/3.0

100 12.1/0.0/0.0 0.0/0.0/0.0 0.0/0.0/0.0

Operating conditions: temperature, 100 °C; HCl partial pressure, 4.5 bar; stirring rate, 1000 rpm; and molar catalyst concentration, 2%, 4%, and 8%. a

Table 5. Effect of NaCl (8 mol %) on Reaction Rate and Selectivity Using Acetyl Chloride as the Catalysta time (min)

1-MCH

2-MCH

1,3 DCH

1,2 DCH

GLY

0 60 180 240

0 15.0 0.0 0.0

0 4.1 2.4 1.8

0 78.7 96.4 95.7

0 2.2 1.2 2.5

100 0.0 0.0 0.0

The second step of the reaction mechanism, that is, the ratedetermining step, corresponds to the formation of a threemembered oxonium group and the recovery of the catalyst:

Operating conditions: temperature, 100 °C; HCl partial pressure, 4.5 bar; stirring rate, 1000 rpm; and molar catalyst concentration, 8%.

a

The third and last step is a nucleophilic substitution SN2 involving the attack of a chlorine anion on the less substituted carbon atom (α position) of the oxonium intermediate:

With a similar mechanism, another chlorine group enters preferably in the γ position but with a different rate.25 This mechanism well explains the high selectivity to 1,3-dichlorohydrin obtained in the hydrochlorination of glycerol. Another two mechanisms have been proposed in the literature,28,29 but in both cases the first reaction step is always the ester formation. When acyl chlorides are used instead of carboxylic acids, the first step of the described mechanism does not occur, because the ester of glycerol is directly and quantitatively formed in a short time as a consequence of the reaction:

Figure 2. Comparison of the selectivity to 1,3-DCH of the catalysts studied: acetic acid (AcA), acetyl chloride (AcC), propionic acid (PA), propanoyl chloride (PC), adipic acid (AdA), adypoyl dichloride (AdC), succinic acid (SA), succinyl dichloride (SC), malonic acid (MA), and malonyl dichloride (MC).

esterification catalyzed by the acid environment:

R′COCl + GLY−OH → R′COO−GLY + HCl

(5)

The formation of the ester, which is necessary to start the catalytic cycle, occurs in this case without the formation of water, and this reaction is completely shifted toward the right. The ester concentration is then much higher than in the case of the carboxylic acids for which an equilibrium reaction is involved, which is limited by the presence of water. In this case, also the second step is largely favored for the higher ester concentration, the initial absence of water, and the acid environment generated by reaction 5. Subsequently, the reaction probably proceeds with the same mechanism seen for the carboxylic acids catalysts, that is, the formation of the oxonium intermediate (the second step) and a molecule of carboxylic acid, then giving way to the third step of nucleophilic substitution SN2. This hypothesis follows directly from the observation that, when using carboxylic acids, we have always found10,12 that 2-MCH reaches a low and constant concentration also at a high reaction time. On the contrary, when acyl chlorides are used as the catalyst or chlorinating agent, 1487

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pressure increases considerably when the stoichiometric amount of the acyl chloride is all added in one step. To overcome this problem, by working at a reasonable pressure of HCl, acyl chloride can be added to glycerol with an opportune flow rate giving the optimal rate and selectivity. For this purpose, we performed two different runs by changing the flow rate of acetyl chloride from 1 to 2 cm3/min (measured at room temperature). The amount of glycerol in both cases was 100 g, and the reaction temperature was 100 °C. In the first case, acetyl chloride was fed for 154 min, while in the second case it was for 80 min. The runs were then continued for an overall time of 4 h. In Figure 3, the

2-MCH shows a low but not null conversion into 1,2-DCH, resulting in a decrease of its concentration at a high reaction time. This aspect could be explained by taking into account the alternative mechanisms proposed in the literature,28,30 involving the intervention of five- and six-membered rings as reaction intermediates, which are more compatible with the experimental profile of the 2-MCH concentration found. A deeper mechanistic investigation would be necessary to interpret the different behavior of carboxylic acids and acyl chlorides, also from the energetic point of view. For example, in our previous work,10 for the catalyst malonic acid, values of activation energies in the range 8−10 kcal/mol were estimated. Even if these values could be considered too low for a ring strain, we must take into account that they are related to lumped pseudo kinetic constants containing both equilibrium and kinetics contributions. The initial elevated ester concentration, the initial absence of water, and the local formation of HCl explain the greater activities registered by using as catalysts acyl chlorides instead of carboxylic acids. 3.2. Use of Acyl Chlorides as Reactants of Glycerol Hydrochlorination, a New Process Not Requiring the Supply of Gaseous HCl. As has been observed, acyl chlorides react promptly and quantitatively with glycerol according to the type of the reaction:

Figure 3. Evolution of the HCl pressure as a function of time by adding 100 g of glycerol acetyl chloride with a flow rate of 1 and 2 cm3/min, respectively.

forming gaseous HCl and creating, therefore, the acid environment necessary to prosecute the reaction toward the glycerol hydrochlorination. If glycerol is put in contact with a stoichiometric amount of an acyl chloride, the hydrochlorination reaction occurs also without the addition of HCl, because the HCl formed in situ is sufficient to complete the reaction as follows:

evolution over time of the pressure measured on the reactor for a flow rate of 1 and 2 cm3/min, respectively, is reported. This pressure corresponds to the difference between the HCl produced by the reaction of acetyl chloride with glycerol and the HCl disappearing as a consequence of the hydrochlorination reaction. From this figure (Figure 3), it is evident that the run in which the acyl chloride was fed a higher flow rate shows a steeper increase in HCl pressure involving a higher acyl chloride consumption and consequently a higher overall reaction rate. For the run performed with an acetyl chloride flow rate of 1 cm3/min, a constant value of pressure obtained after about 170 min indicated that the reaction was terminated, and the final pressure corresponds to few unreacted HCl that remained in the reactor. In Table 6 is reported the composition of the reacting mixture after 3 and 4 h of reaction.

In practice, we can write the following overall reaction:

Table 6. Product Distribution Evaluated after 3 and 4 h of the Reaction between Acetyl Chloride and Glycerol in the Run with an Acetyl Chloride Flow Rate of 1 cm3/min for 154 min As can be seen, a carboxylic acid is formed as a reaction byproduct. It can be separated, purified, and sent back to the acyl chloride supplier to synthesize again the corresponding acyl chloride according to the reaction: CH3COOH + SOCl 2 → CH3COCl + SO2 + HCl

time (min)

1-MCH

2-MCH

1,3 DCH

1,2 DCH

GLY

0 180 240

0 1.8 0.5

0 8.2 5.9

0 81.4 82.3

0 8.6 11.3

100 0.0 0.0

(9)

As it can be seen, in less than 180 min, the reaction can be considered complete, and the selectivity is satisfactory. For the run performed with an acetyl chloride flow rate of 2 cm3/min, the reaction is completed in less time (less than 2 h),

In this way, the producer of acyl chlorides can receive a reduction of costs related to carboxylic acids. The only problem arising in performing the stoichiometric reaction between glycerol and an acyl chloride is that the HCl 1488

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this case much higher, and this strongly affects the reaction rate. The hydrochlorination occurs with a high rate and with a better selectivity even if the glycerol is contaminated with a consistent amount of sodium chloride. This opens the possibility of using crude glycerol as it arises from the plant without submitting it to an expensive process of purification. As acyl chlorides react with glycerol giving the corresponding ester and HCl, by using a stoichiometric amount of the two reactants, it is possible to complete the hydrochlorination reaction directly thanks to the HCl formed in situ without any external supply of this component. To avoid an excessive increase of the HCl pressure, the acyl chloride must be added to the glycerol with an opportune flow rate. We have observed by comparing two experimental runs that the acyl chloride addition modality has an influence on both the activity and the selectivity. This procedure opens the possibility of producing 1,3-dichlorohydrin also in industrial sites where HCl is not available.

Table 7. Product Distribution Evaluated after 3 and 4 h of the Reaction between Acetyl Chloride and Glycerol in the Run with an Acetyl Chloride Flow Rate of 2 cm3/min for 80 min time (min)

1-MCH

2-MCH

1,3 DCH

1,2 DCH

GLY

0 180 240

0 0.0 0.0

0 4.0 3.7

0 91.9 92.3

0 4.1 4.0

100 0.0 0.0

and it is possible to evidence the HCl consumption as a consequence of the hydrochlorination reaction. In Table 7 is reported the composition of the reacting mixture after 3 and 4 h of reaction. As can be observed, in this case, not only did the reaction rate prove to be higher as compared to the previous run, but also the selectivity was much improved. In conclusion, the flow rate modality is important to obtain the best result in terms of both reaction rate and selectivity to 1,3-dichlorohydrin. The stoichiometric process is attractive in the perspective of its integration with the process of biodiesel production as depicted in Figure 4.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.5b03765. Table S1, comparison of the kinetic runs performed in the presence of propionic acid and propanoyl chloride as catalysts; Table S2, comparison of the performances obtained with adipic acid and adipoyl dichloride; Table S3, comparison of the performances obtained with succinic acid and succinyl dichloride; and Table S4, comparison of the performances obtained with malonic acid and malonyl dichloride (PDF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We are grateful to CONSER SpA and to Eurochem Engineering srl for the collaboration in undertaking this work and for the financial support.

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Figure 4. An integrated process for producing biodiesel and dichlorohydrins without the supply of gaseous HCl.

REFERENCES

(1) Santacesaria, E.; Martinez Vicente, G.; Di Serio, M.; Tesser, R. Main technologies in biodiesel production: State of the art and future challenges. Catal. Today 2012, 195, 2. (2) Behr, A.; Obendorf, L. Development of a Process for the AcidCatalyzed Etherification of Glycerine and Isobutene Forming Glycerine Tertiary Butyl Ethers. Eng. Life Sci. 2002, 2, 185. (3) Jaecker-Voirol, A.; Durand, I.; Hillion, G.; Delfort, B.; Montagne, X. Glycerin for New Biodiesel Formulation. Oil Gas Sci. Technol. 2008, 63, 395. (4) Di Serio, M.; Casale, L.; Tesser, R.; Santacesaria, E. Development of a Process for the Acid-Catalyzed Etherification of Glycerine and Isobutene Forming Glycerine Tertiary Butyl Ethers. Energy Fuels 2010, 24, 4668. (5) Atia, H.; Armbruster, U.; Martin, A. Dehydration of glycerol in gas phase using heteropolyacid catalysts as active compounds. J. Catal. 2008, 258, 71. (6) Katryniok, B.; Paul, S.; Bellière-Baca, V.; Rey, P.; Dumeignil, F. Glycerol dehydration to acrolein in the context of new uses of glycerol. Green Chem. 2010, 12, 2079.

4. CONCLUSIONS From all of the reported results, it is possible to conclude that acyl chlorides are significantly more active as catalysts than the corresponding carboxylic acids. The use of acyl chlorides in place of the corresponding acids leads to the overall conversion of glycerol in a short time, maintaining and sometimes improving the selectivity toward the formation of the desired product 1,3-dichlorohydrin. We attribute the better performance to the high reactivity of acyl chlorides that, on contacting the glycerol, react promptly and quantitatively, giving the corresponding ester and HCl, which is not forming water in the initial part of the reaction and increasing the acidity of the reaction environment. Moreover, the concentration of the ester as the intermediate is in 1489

DOI: 10.1021/acs.iecr.5b03765 Ind. Eng. Chem. Res. 2016, 55, 1484−1490

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DOI: 10.1021/acs.iecr.5b03765 Ind. Eng. Chem. Res. 2016, 55, 1484−1490