Valorization of Biodiesel Derived Glycerol to Acetins by Continuous

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Valorization of biodiesel derived glycerol to acetins by continuous esterification in acetic acid: focusing on high selectivity to diacetin and triacetin with no by-products Hajar Rastegari, Hassan S. Ghaziaskar, and Mohammad Yalpani Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b00234 • Publication Date (Web): 24 Mar 2015 Downloaded from http://pubs.acs.org on March 31, 2015

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Industrial & Engineering Chemistry Research

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Valorization of biodiesel derived glycerol to acetins by continuous esterification in acetic

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acid: focusing on high selectivity to diacetin and triacetin with no by-products

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Hajar Rastegari1, Hassan S. Ghaziaskar*1 and Mohammad Yalpani2

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1

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Email: [email protected], Tel: 0098-31-33913260, Fax: 0098-31-33912350

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2

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Isfahan, 85131-14461, I.R. Iran. Email:[email protected]. Tel: 0098-31-42290748, Fax: 0098-

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31-42290746

Department of Chemistry, Isfahan University of Technology, Isfahan, 84156-83111, I.R. Iran

R & D Department, Farzin Chemicals Sepahan Co., Montazerie Industrial Complex, Villashahr,

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1 ACS Paragon Plus Environment


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Abstract

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This work represents a continuous, easy to scale up esterification system with 100% conversion

3

of glycerol in acetic acid with the high selectivity to DA and TA with no by-products at

4

industrially applicable reaction conditions. The main emphasize is to obtain TA from glycerol

5

esterification in acetic acid without using any acetic anhydride and harsh conditions. The effect

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of reaction parameters including acetic acid to glycerol mole ratios (1-9), temperatures (66-

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134) oC, pressures (1-199) bar with 0.5 mL.min-1 feed flow rate, on the glycerol conversion and

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selectivity to monoacetin, diacetin, triacetin and by-products were investigated. Under the

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optimum conditions of acetic acid to glycerol mole ratio of 7, temperature of 100oC and

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pressure of 1 bar, over 3g Amberlyst®36, glycerol conversion, monoacetin, diacetin and

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triacetin selectivity obtained 100%, 43%, 44% and 13%, respectively. The formation of by-

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products was not detected at these optimum conditions. Amberlyst®36 remained stable after 25

13

h being on-stream. The recovered catalyst was reused with no significant deactivation after 3

14

cycles. This continuous system, also can be used for monoacetin synthesis with 85% selectivity

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and glycerol conversion of 95% with acetic acid to glycerol mole ratio of 1, temperature of 100

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o

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Keywords: Continuous glycerol esterification, Monoacetin, Diacetin, Triacetin, Acetic acid,

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By-products.

C and pressure of 100 bar.

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1

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Biodiesel has attracted considerable attention all over the world, as a substitute fuel for diesel

3

engines because of its similar characteristics to petroleum-derived diesel1. One of the major

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problems in the production of biodiesel is glycerol formation (~10 wt %) as a by-product2. It

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is expected that by 2016 the global production of glycerol will reach 37 billion gallons per

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year3. Since glycerol production is increasing faster than its consumption, a sharp price drop

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has been observed. So it is highly desirable to convert this huge amount of low cost glycerol

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to some value-added products. In this regard, production of valuable chemicals such as fuel

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additives seems to be a suitable large market where a high volume of glycerol could be

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absorbed for value-added applications. Ketals, ethers and esters have demonstrated the

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potential to be used as oxygenated fuel additives4-6. Glycerol acetates (acetins) have great

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industrial applications. Glycerol monoacetate named monoactin (MA), is used as food

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additive, in the manufacturing of explosives and smokeless powder7. Glycerol diacetate or

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diacetin (DA) has been utilized as a cocoa butter blooming or as an intermediate in the

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synthesis of structural lipids8, also it is used for plasticizer coating and foodstuffs9-10. The

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mixtures of MA and DA have applications in cryogenics and biodegradable polyesters11,

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chemical products in the food12 and cosmetic industries13. Glycerol triacetate or triacetin (TA),

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is used in cigarette filters and as gelatinizing agent7, also as fuel additive for increasing the

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octane number in gasoline14. Mixtures of MA, DA and TA have many other applications

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including solvents for printing inks and dyestuffs, as plasticizers and softening agents7. In

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addition blends of DA and TA with diesel fuel, serve as valuable additives improving the

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viscosity and cold properties15.

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Acetins can be synthesized via direct esterification of glycerol with acetic acid and acetic

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anhydride or transesterification of glycerol with methyl acetate. Morales et al. reported

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glycerol transesterification with methyl acetate using sulfonic acid-functionalized catalysts in

Introduction



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a 100 mL stainless steel autoclave under autogenously pressure16. Transesterification runs

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were performed at temperatures ranging from 120 oC to 195 oC and the reaction duration were

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4 h. Optimization of the reaction conditions showed that it is necessary to use a high methyl

4

acetate to glycerol mole ratio of 50 and a high catalyst loading (7.5 wt % based on glycerol)

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in order to obtain simultaneously very high glycerol conversion (99.5%) and high selectivity

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toward DA and TA (74.2%)16.

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Direct esterifications had better yields compared with transesterification ones. Many

8

researchers have focused on the synthesis of acetins via direct esterification of glycerol with

9

acetic acid or acetic anhydride in batch or continuous processes using different catalysts.

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Traditionally esterification of glycerol is performed by means of homogeneous mineral acids.

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These catalysts are non-reusable, toxic, and also hard to remove from the products17. Solid

12

acids significantly differ in acidity, surface area, and cost of production compared to

13

homogeneous ones. But using them is a feasible economic way due to the reusability of

14

catalyst for both processes e.g. batch and continuous18. Mota et al. reported esterification of

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glycerol with acetic acid catalyzed by different solid acid catalysts including Amberlyst® 15,

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K-10 montmorillonite, niobic acid, HZSM-5 and HUSY in a round bottom flask under reflux

17

conditions (temperature of around 110 oC)19. The reactions were performed at room

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temperature with acetic acid to glycerol mole ratio of 3. According to their report the acid

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exchange resin, Amberlyst® 15 was the most active catalyst, achieving 97% conversion for

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glycerol and 31%, 54% and 13% selectivity to MA, DA and TA, respectively after 30 min of

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reaction time. At these conditions 2% selectivity was obtained for acetol as the by-product.

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Acetol formation was reported as a result of glycerol dehydration in many works19-21. Glycerol

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dehydration products causes a change in acetins color and odor and hence acetins purification

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must be performed that is difficult and costly.


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Liao et al investigated TA production from glycerol in 2 steps, esterification and acetylation22.

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They used Amberlyst® 15, Amberlyst® 35, HZSM-5 and HY zeolite as catalyst for the

3

esterification reaction. The catalytic runs were performed in a 100mL round bottom glass flask.

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Amberlyst® 35 was the best catalyst. By using 0.5 g Amberlyst® 35, at temperature of 105oC,

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acetic acid to glycerol mole ratio of 6, after 4h of reaction, 26% selectivity to TA with 99%

6

conversion for glycerol was obtained. Also recycling experiments was performed over

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Amberlyst® 35. The glycerol conversion had not dropped significantly during the five one hour

8

repetitions of reaction. Moreover, the reaction time was extended to as long as 12 h, and the

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catalyst remained stable.

10

Recently promoted metal oxides have been used to investigate glycerol esterification with

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acetic acid because of various attractive features such as facile synthesis procedure, remarkable

12

thermal stability and improved catalytic performance23. A series of zirconia-based mixed

13

oxides were investigated for the esterification of glycerol with acetic acid by Reddy et al24.

14

Experiments were undertaken at atmospheric pressure and a Dean-Stark trap was attached to

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the flask to remove water from the reaction mixture. With acetic acid to glycerol mole ratio of

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6, temperature of 120 oC, 5wt % of SO42-/CeO2-ZrO2 loading with respect to glycerol and after

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1h of reaction time, 100% glycerol conversion and 25%, 59% and 16% selectivity was obtained

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to MA, DA and TA, respectively. The reusability of this catalyst studied for five one hour

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catalytic runs and the conversion of glycerol was only 5% at fifth catalytic run with 100%

20

selectivity of MA and no DA and TA was formed. This low reusability was a drawback of the

21

process and it is not economically viable. Moreover, the leaching of the sulfate ion from the

22

catalyst usually occurs and reduces the catalyst activity.

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Reddy et al reported glycerol esterification with acetic acid over promoted SnO2 solid acids23.

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The catalytic experiments were performed in a 10mL round-bottom flask with acetic acid to

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glycerol mole ratio of 6, 100 oC of reaction temperature, 5 wt % of catalyst loading with 5 ACS Paragon Plus Environment


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respect to glycerol and 2h of reaction time. Among the studied solid acid catalysts, SO42-/SnO2

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showed better catalytic activity. The obtained glycerol conversion was 89% and the selectivity

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of DA and TA was 21% and 6%, respectively. Moreover the achieved glycerol conversion

4

were 89%, 78%, 66% and 51% for the 1st, 2nd, 3rd and 4th cycle, respectively which is not

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favorable at industrial scale.

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An ideal process is a continuous process25 which operates at industrially applicable reaction

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conditions and short reaction times also minimum formation of undesirable by-products to

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eliminate the need for multitudinous downstream separation and purification steps26. Also the

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solid catalyst can be reused multiple times without significant loss of activity and selectivity23.

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A continuous process for the production of TA from glycerol, acetic acid and acetic anhydride

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is reported by Bremus et al27. This process consists of a tray column reactor wherein, glycerol

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and excess acetic acid flow in a countercurrent mode. They also use some amounts of acetic

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anhydride as water scavenger. The maximum conversion obtained for glycerol was 96% at

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7.5 bar and 160oC using 32 plates in the column. Although the use of acetic anhydride

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improved the reaction yield to TA as the only product, but this procedure is not convenient

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due to the high amounts of waste and also acetic anhydride price that is higher than acetic

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acid.

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Continuous esterification of glycerol with acetic acid had been performed previously in our

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research group with 100% selectivity for TA and 41% yield, with acetic acid to glycerol mole

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ratio of 24 at temperature of 110 oC and pressure of 200 bar in supercritical carbon dioxide

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using Amberlyst® 15 as catalyst 28.

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This work represents a continuous, easy to scale up esterification system with 100%

23

conversion of glycerol in acetic acid with the high selectivity to DA and TA with no by-

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products at industrially applicable reaction conditions. The main emphasize is to obtain TA

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from glycerol esterification in acetic acid without using any acetic anhydride and harsh


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conditions. For the catalytic esterification, it is well known that sulfonated resins (e.g.

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Amberlyst® 1529-30, Amberlyst® 3530) are the most widespread and selective acidic catalysts

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to carry out either gas or liquid phase esterification reactions at industrial scale. Since

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Amberlyst® 36 has higher acidity (5.4 eq.g-1) 25and higher thermal stability (140 oC) it was

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used in this study.

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2

7

2.1

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Acetic acid (purity > 99.85%), glycerol (purity > 99.9%), TA (purity > 99%) and DA (purity

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=50%), wet Amberlyst® 36, Amberlyst® 15, p-TSA) purity > 95%), absolute ethanol (purity >

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99.9%) and 2-ethylhexanol (purity > 99%), were supplied from Fanavaran Petrochemical Co.

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(Iran), USP (Malaysia), Fluka (Germany), Fluka (Germany), Sigma-Aldrich (Germany),

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Sigma-Aldrich (Germany), Farzin Chemicals Co. (Iran), Bidestan Co. (Iran) and Tat Chemicals

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Co. (Iran), respectively. MA (purity > 95%) was synthesized via described method in our

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previous study31 and its concentration verified by GC-FID.

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2.2

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Experiments were carried out in a continuous fixed-bed tubular reactor (i.d.=0.84 cm,

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length=23 cm) placed vertically in an air oven with a temperature control of ± 1oC, given as

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Fig. S1 in supporting information. The stream was depressurized after passing through the back

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pressure regulator (model BP 1580-81, JASCO Co.). An HPLC pump (model PU-980, JASCO

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Co.) was used to enter feed into the reactor with a flow rate of 0.5 mL.min-1 over 3.0 g of solid

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acid catalyst throughout the work.

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In this study acetic acid was used in excess both as reactant and solvent. This solvent has the

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ability to induce swelling of Amberlyst® 36. The swelling of the resin as a function of different

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acetic acid mole ratios, could give access to new acidic sites. So before performing

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experiments, the catalyst (3g) was moved to a beaker containing acetic acid and after 20 min

Experimental Materials

Procedure



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the swelled polymer was separated by using filter paper and then transferred to the reactor.

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Before the reaction, the feed was sonicated for 15 min in ultrasonic bath at room temperature

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to remove any dissolved gas. The feed was pumped in to the system after temperature

4

stabilization, and the pressure was adjusted via the back pressure regulator. At each experiment

5

samples were collected at different time intervals with collection efficiency of higher than 95%

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verified experimentally.

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2.3

8

Analysis of the samples was carried out using a GC-FID (model 3420, BEIFEN, China). The

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carrier gas was nitrogen and the capillary column of HP-5 (i.d. = 0.25 mm, length = 30 m, film

10

thickness = 0.25 µm) was used. All injections were made in the split mode (split ratio of 1:30)

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and temperature program was used for the analysis. The initial column temperature was set at

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80 oC ramped to 90 oC at the rate of 3 oC.min-1 and from 90 oC to 280 oC at the rate of 30

13

o

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set at 280 oC and 300 oC, respectively. Some standard solutions containing 2-ethylhexanol as

15

an internal standard was injected and integration of the peak areas was done to establish the

16

calibration curves. Identification of the products was carried out by GC-MS (model 6890N,

17

Agilent technologies). The glycerol conversion and each product selectivity were calculated as

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is reported by Morales et al.16. It must be mentioned that when glycerol concentration was

19

lower than the detection limit of the analysis method, the conversion was assumed 100%.

20

3

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3.1

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The experimental design was carried out by Central Composite Design (CCD) leading to a

23

study for investigating the influences of the acetic acid to glycerol mole ratio (X), temperature

24

(T) and pressure (P) on the responses. These variables were selected responds to Le Chatelier’s

25

principle. In our previous study31, increasing feed flow rate lead to decrease in conversion. But

Analytical method

C.min-1 where it was held for 5 min. The GC injection port and the detector temperature were

Results and discussions Design of experiments


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later studies showed that at feed flow rates lower than 0.5 mL.min-1, a high selectivity for by-

2

products obtained after passing the feed over the catalyst bed. So all experiments were

3

performed at feed flow rate of 0.5 mL.min-1.

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As can be seen from Fig. 1, TA selectivity was about 16% at first 20 min of sampling time and

5

after that it decreased to about 11% and afterward there was no significant change in the TA

6

selectivity. The reason is that at initial times of the reaction, the catalyst surface is dry so the

7

reaction shifts forward to produce TA with higher selectivity. But producing 1 mole TA leads

8

to production of 3 moles water which are adsorbed on the catalyst surface and hydrolyze TA

9

to DA and MA. So TA selectivity decreases. Because of these changes the selectivity of MA,

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DA and TA after 2h of passing the feed over the catalyst bed, were chosen as the responses.

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Design matrix of carried experiments and the experimental values of the responses are

12

incorporated in Table S1 given as Supporting Information (SI). The central point experiment

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(acetic acid to glycerol mole ratio of 5, temperature of 100 oC, and pressure of 100 bar), was

14

repeated 6 times in order to check the experimental reproducibility. Response Surface

15

Methodology (RSM) was used to analyze the obtained responses as mentioned in our previous

16

work31. The influences of the variables on the values of the responses through the coefficients

17

are shown in Table S2 (SI). The most influential variables have larger coefficients while

18

negative coefficients are related to a detrimental effect.

19

The obtained F-values from Analysis of Variance (ANOVA) of the models for MA, DA and

20

TA were 4.70, 3.30 and 2.88 respectively. These values were lower than the critical F-value

21

(5.05) and confirmed the validity of the models at confidence level of 95% (calculated F-lack

22

of fit are less than the critical values). The P-values demonstrate the significance in predicting

23

the response values. Low probability values, close to 0, indicates the high significance of the

24

fitted models. The P-values for MA, DA and TA models were 0.028, 0.038, and 0.037

25

respectively, describing that the regressions at the confidence level of 95% (P < 0.05) are



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significant. The adjusted R2 values for MA, DA and TA selectivity were 0.979, 0.934, and

2

0.967 respectively, which indicate good performance of the models in predicting the data

3

trends.

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3.2

5

According to Table S1 given in SI, at all the acetic acid to glycerol mole ratios, 100% glycerol

6

conversion are obtained except at ratio of 1 in run no. 6. At this experiment, the obtained

7

glycerol conversion and MA selectivity are 95% and 85%, respectively which is the highest

8

selectivity to MA. Considering the influence of variables through their coefficients, shown in

9

Table S2 (SI), it is noteworthy that the acetic acid to glycerol mole ratio is the most effective

10

variable on the MA selectivity. This fact can be explained by Le Chatelier’s principle. Due to

11

the reversibility of esterification, the higher mole ratio of acetic acid to glycerol shifts the

12

reversible reactions forward, to the 2nd and 3rd steps, so MA selectivity decreases while

13

glycerol conversion increases. Temperature and pressure have lower detrimental effect on MA

14

selectivity (Table S2). It can be explained by thermodynamics. As esterification reactions are

15

endothermic, it is expected that high reaction temperatures favor the formation of the other

16

products, so MA selectivity decreases while DA and TA selectivity increases. Coefficients

17

presented in Table S2 indicate that acetic acid to glycerol mole ratio and temperature have

18

positive effect on DA and TA selectivity, and mole ratio is more effective than temperature in

19

the formation of DA and TA.

20

ANOVA was used to assess the effect of different variables on the by-products selectivity.

21

Results are shown in Table S3 given in SI. Acetic acid to glycerol mole ratio has no significant

22

effect at confidence level of 95% because calculated F-values are less than the critical values

23

shown in runs no. 3, 8, 7, and 16 in Table S3 (SI). Comparison of run no. 3 with 16 indicates

24

that pressure has no significant effect too. The only effective variable is temperature as the

Effects of process parameters


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calculated F-value is lower than the critical one (comparison of run no. 16 with 17 in Table S3

2

given in SI).

3

Fig. 2 shows the effect of process variables on the selectivities of different acetins. The adverse

4

effect of increasing temperature (Fig. 2a) and pressure (Fig. 2b) on MA selectivity are more

5

pronounced when acetic acid to glycerol mole ratios higher than 5 are used, but the effect of

6

pressure is lower than that of temperature. As it can be seen from Fig. 2c, increasing pressure

7

from 1 bar to 199 bar at temperatures higher than 90 oC, causes only about 10% decrease in

8

MA selectivity. Since high pressure is practically and economically not favorable, the optimal

9

values for lowest MA selectivity, were chosen as acetic acid to glycerol mole ratios higher than

10

5, temperatures higher than 80 oC, and pressures of 1 bar at feed flow rate of 0.5 mL.min-1.

11

The optimal conditions for DA production are achieved when both acetic acid to glycerol mole

12

ratios and temperatures were at moderate levels (Fig. 2d, 2e, 2f). At the temperature of 100 oC,

13

increasing acetic acid to glycerol mole ratio from 3 to 5 causes a 15% increase in DA

14

selectivity. Subsequently the DA selectivity rises from 30% to about 45% as shown in Fig. 2d

15

while increasing mole ratio from 5 to 9 (Fig. 2e) and also temperature from 100 oC to 134 oC

16

(Fig. 2f), decreases DA selectivity due to the transformation to TA. Fig. 2g and Fig. 2h display

17

an adequate combination of temperature and acetic acid to glycerol mole ratio favor the

18

formation of the most desirable acetylated derivative of glycerol (TA), but the only effective

19

variable on the by-products formation is temperature. Since by-products production is wasting

20

the starting material and their separation from products are time consuming, therefore, high

21

temperatures are not desirable.

22

The TA selectivity increases while DA and MA selectivity decreases. This observation explains

23

that TA and other acetins are formed through consecutive esterification reactions. The

24

maximum selectivity to TA of 17% was obtained at the mole ratio of 7, temperature of 120 oC,

25

and pressure of 159 bar with 3% selectivity to by-products. As mentioned before the reason for



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this low selectivity is that the reaction is equilibrium limited and water production makes it

2

necessary to use very high acetic acid to glycerol mole ratios or water removal from medium

3

to increase TA selectivity.

4

3.3

5

The optimal values of responses were calculated using response optimizer tool of the

6

MINITAB 14 software. The optimization was conducted in such a way that more focus was

7

placed on the higher selectivity to DA and TA while minimizing by-products. Among the

8

acetylated derivatives, DA and TA are the most interesting for fuel-applications. MA has

9

relatively high water solubility and hence it is not suitable as a diesel component. The minimum

10

selectivity to by-products is desirable because it is economically unfavorable to separate many

11

by-products from reaction post-mixture. Thus the predicted optimum conditions were an acetic

12

acid to glycerol mole ratio of 7, a temperature of 100 oC and pressure of 1 bar. To confirm the

13

models predictions, an experiment was carried out under predicted optimum conditions and

14

only the differences shown in Table 1 were observed. t-Test was used to verify that there is no

15

significant difference between real values and predicted values. Since the calculated t were

16

lower than the critical values (t-test) real values verify the model predictions.

17

The remarkable difference between control reaction and catalytic reaction results, show that

18

catalyst is effective to push this reaction forward. The standard reaction Gibbs free energies of

19

the three steps are all positive. These values are relatively small for the first and second steps,

20

(19.15 and 17.80 kJ/mole), while that of the third step is large to 55.58 kJ/mole. This shows

21

quantitatively the reason for low selectivity of TA32.

22

3.4

23

The effect of other sulfonic acid catalysts including Amberlyst®15 and pTSA on the glycerol

24

esterification with acetic acid was also investigated at the optimum conditions. The results are shown

25

in Table 2. It was observed that all the catalysts displayed similar activities. For all three catalysts the

Process optimization

Catalyst study


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1

glycerol conversion was 100% while the total selectivity to the most desirable acetins, DA and TA, was

2

about 57%. This selectivity to DA and TA can be explained due to consecutive formation of DA and

3

TA through esterification reaction.

4

3.5

5

The stability of the catalyst for glycerol conversion and the products selectivity were monitored

6

for 25 h over 3g of Amberlyst® 36 on stream at acetic acid to glycerol mole ratio of 7,

7

temperature of 100 oC, feed flow rate of 0.5 mL.min-1 and pressure of 1 bar. It could be inferred

8

from the results shown in Fig. 1, that the catalyst maintains its activity up to 25h on stream

9

with almost constant glycerol conversion and selectivity. Therefore, the Amberlyst® 36 as

Stability and reusability of the catalyst

10

catalyst demonstrated good stability, remaining active for 25h on stream.

11

The reusability of the catalyst was also investigated. Three consecutive catalytic runs were

12

performed at the optimum reaction conditions. Each cycle was continued up to 25h. After each

13

cycle a Soxhlet extraction apparatus was used for removal of the unreacted substrates and

14

products from the catalyst surface. Absolute ethanol was used as extraction solvent because of

15

its good solubility for unreacted substrates 28 and products. Then the washed catalyst was dried

16

before being used again in the next cycle. The results showed that the recycled catalyst has

17

retained its activity after three cycles. However, at the 3rd cycle the selectivity of MA increased

18

from 43% to 55%, while DA and TA total selectivity decreased from 57% to 45%, respectively

19

after 17h on stream.

20

4

21

A continuous process developed for the synthesis of acetins from esterification of glycerol with

22

acetic acid with no by-products at mild reaction conditions to obtain 100% glycerol conversion

23

and high selectivity (57%) to the most desirable acetins, DA and TA in one step. Glycerol

24

esterification was carried out over Amberlyst® 36 as catalyst. CCD and RSM were used for

25

experimental design and optimization, respectively. The experiments were carried out for

Conclusions



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Page 14 of 22

1

different levels of acetic acid to glycerol mole ratio, temperature and pressure. The results

2

showed that it is necessary to use excess acetic acid in order to push the equilibrium towards

3

the simultaneous enhancement of glycerol conversion and selectivity for the most valuable

4

acetins, DA and TA. This One-step transformation obtained high selectivity to MA and DA,

5

because esterification reaction is comprised of three consecutive steps and each step is

6

equilibrium limited due to the formation of water as an unavoidable by-product. Also it is

7

advantageous to work at moderate temperatures because at high temperatures by-products will

8

be produced. Within the studied range, the optimal conditions have been found to be an acetic

9

acid to glycerol mole ratio of 7, temperature of 100 oC and pressure of 1 bar with almost 100%

10

conversion for glycerol and 43%, 44% and 13% selectivity to MA, DA and TA respectively.

11

Amberlyst® 36 as catalyst remained stable with no significant deactivation after 25 h being on

12

stream. Recycling experiments indicated that no significant deactivation for Amberlyst® 36

13

occurred after 3 consecutive cycles. However, the selectivity of MA increased from 43% to

14

55%, while DA and TA total selectivity decreased from 57% to 45% respectively after 17h on

15

stream at the 3rd cycle.

16 17

AUTHOR INFORMATION

18

Corresponding Author

19

*E-mail: [email protected]. Tel.: +98 31 33913260/+98 913 111 8276. Fax: +98 31 33912350.

20 21

Acknowledgement

22

The partial financial support by Isfahan University of Technology is acknowledged. H.R.

23

would like to thank Amin Shafiei for his assistance in doing part of the experimental works.

24 14 ACS Paragon Plus Environment

Page 15 of 22

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1

Supporting Information

2

The schematic diagram of the setup used for the esterification reaction is given in supporting

3

information. The Tables S1, S2, and S3 are also available as Supporting Information.

4

Supporting Information is available free of charge via the Internet at http://pubs.acs.org/.

5

References

6

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3

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4

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5

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6

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8


Page 19 of 22

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1

Table 1. The predicted optimal and real values and results obtained from the control experiment at

2

acetic acid to glycerol mole ratio of 7, temperature of 100 oC and pressure of 1 bar. Selectivity (%) Conversion (%) MA

DA

TA

By-products

Predicted optimal values

100

42

46

12

0

Real optimal values

100

43

44

13

0

Control experiment values

95

75

23

2

0

3 4



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Page 20 of 22

1

Table 2. Glycerol conversion and products selectivity of glycerol esterification with acetic acid over

2

sulfonic acid catalysts at optimum reaction conditions of acetic acid to glycerol mole ratio of 7,

3

temperature of 100 oC and pressure of 1 bar. Selectivity (%) Conversion (%) MA

DA

TA

By-products

p-TSA

100

44

44

12

0

Amberlyst®36

100

43

44

13

0

Amberlyst®15

100

42

44

14

0

4 5 6


Page 21 of 22

60 55 50 45 40

Selectivity (%)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


35

MA

30

DA TA

25 20 15 10 5 0 0

120

240

360

480

600

720

840

960

1080 1200 1320 1440 1560

Time (min)

1 2

Fig. 1. Products selectivities versus time at acetic acid to glycerol mole ratio of 7, temperature of 100oC,

3

feed flow rate of 0.5 mL.min-1 and pressure of 1 bar over 3g Amberlyst® 36. In all samples the glycerol

4

conversion was 100%.

5 6



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

2 3

Fig. 2. Response surface plots for MA, DA and TA selectivities in the continuous esterification of

4

glycerol with acetic acid.


Page 22 of 22

Valorization of Biodiesel Derived Glycerol to Acetins by Continuous

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