Prediction of the Thermodynamic Properties of Key Products and

ARTICLE pubs.acs.org/JPCC

Prediction of the Thermodynamic Properties of Key Products and Intermediates from Biomass Monica Vasiliu, Kurt Guynn, and David A. Dixon* Chemistry Department, The University of Alabama, Shelby Hall, Box 870336, Tuscaloosa, Alabama 35487-0336, United States

bS Supporting Information ABSTRACT: The high-level G3MP2 computational chemistry method was used to predict the thermodynamic properties of a wide range of compounds relevant to the conversion of biomass-derived oxygenated feedstocks into fuels or chemical feedstocks. The starting compounds were glucose, 5-hydroxymethyl furfural, sorbitol, levulinic acid, succinic acid, γ-valerolactone, and glycerol. The calculated G3MP2 gas-phase heats of formation were mostly within (2 kcal/mol of the available experimental values. Heats of formation of the liquid were obtained from calculations of the boiling point combined with the rule of Pictet and Trouton using modified values for ΔSvap. The modified values for ΔSvap arise because of the presence of intermolecular hydrogen bonding, ΔSvap = 0.031 cal/(mol K) for carboxylic acids, 0.035 cal/(mol K) for dialcohols, and 0.040 cal/(mol K) for higher polyalcohols. The thermodynamics of a wide range of reactions were predicted. Reaction energies in the aqueous phase at 298 K were estimated from self-consistent reaction field calculations of the solvation energy using the COSMO parametrization. Most of the reactions were exothermic, and the reaction products were stabilized by aqueous solvation. Exceptions include dehydrogenation, decarbonylation, ring-opening, and dehydration reactions when only one mole of water is eliminated.

’ INTRODUCTION Fossil fuel resources are not renewable, and intensive consumption coupled with high demand, especially by the transportation sector, has led to potential decreases in their availability. The combustion of carbon-based fuels releases CO2 into the atmosphere, leading to an increased CO2 concentration that may impact climate change due to the absorption of infrared radiation by the CO2 bending mode. Thus, the development of alternative, preferably renewable, resources is necessary to substitute for existing fuels derived from fossil sources. Biofuels derived from biomass are a promising alternative energy source due to the potential for such fuels to be carbon neutral.14 Readily available biomass under catalytic, thermal, and/or biochemical conversion is broken down into different components that can be used in conventional combustion engines, with some necessary adjustments but without major changes to the existing fuel distribution infrastructure.510 As an example, a key component of biomass or its derivatives is the sugar glucose, which can be written as the hydrate of carbon ((C(H2O))6). The challenge is to develop low-cost processing methods to convert glucose to different chemical compounds that can serve as fuels or as feedstocks to the chemical industry. Accurate thermodynamic properties for these chemicals are important and are needed for the design of new, clean, and more efficient synthetic routes. Computational chemistry using high-level molecular orbital theory methods can be used to predict the thermodynamics of such biomass derivatives. r 2011 American Chemical Society

The energetics for the conversion of glucose to 5-hydroxymethyl furfural (HMF) and then to levulinic acid, including intermediates, have been calculated at the G4 and G4MP2 levels of theory.11,12 The kinetics of glucose decomposition to generate levulinic acid have been reported.13,14 The thermodynamics properties over a range of temperatures chosen according to experimental studies involved in the production of pentenoic/ pentanoic acids and butenes from γ-valerolactone (GVL) have been estimated at the B3LYP/6-311+G(2d,p) level of theory.15 Most of the previous computational studies of biomass conversion have focused on the molecular conformations and on estimating the interaction energies with water or other hydrocarbons.1624 The focus of the current work is the use of high-level computational chemistry methods to predict the thermodynamics of the conversion of biomass-derived oxygenated feedstocks into fuels or chemical feedstocks. In the current study, we consider the following biomass-derived species as starting points and their conversion into a number of valuable biobased chemicals and fuels: glucose, HMF, sorbitol, levulinic acid, succinic acid, GVL, and glycerol. These compounds are among the 12 molecules cited in a recent U.S. Department of Energy report7 as important biomass building blocks. Received: May 6, 2011 Revised: June 20, 2011 Published: July 14, 2011 15686

dx.doi.org/10.1021/jp204243m | J. Phys. Chem. C 2011, 115, 15686–15702

The Journal of Physical Chemistry C

ARTICLE

Figure 1. Conversion of glucose. The complete reactions including the reagents and the byproducts are given in Table 3.

The conversion of biomass to fuels and useful chemical feedstocks involves various types of reaction types, including hydrolysis, dehydration, reforming, CC or CO hydrogenolysis, isomerization, selective oxidation, and hydrogenation/ dehydrogenation. The first step in obtaining the starting material glucose, a monosaccharide, is the hydrolysis of a polysaccharide; the thermodynamic details of these reactions are not considered in the current study. Further dehydration of glucose forms HMF, and hydrogenation of glucose leads to sorbitol. Aldol condensation is a useful synthetic route to increase the number of CC bonds in the biomass-derived molecules from HMF. Rehydration of HMF leads to levulinic acid, another key biofuel building block. CC bonds can be cleaved in the presence of hydrogen, or new CO bonds can be formed, leading to polyalcohols, for example, glycerol. Glycerol has a significant role in the production of high-quality biodiesel and could be one the most important building blocks for biorefineries due to its low cost.8,9,2527 Because glycerol is a byproduct of biodiesel production, increasing the production of biodiesel increases the availability of glycerol, and the cost of biodiesel can be reduced if new uses for glycerin are found. Levulinic acid is a potential building block available from carbohydrates manufactured in a biorefinery.7 Thus, levulinic acid can be used as a starting material for the production of a large number of compounds such as GVL and succinic acid, two important biomass intermediates.7 Glucose can be also used to synthesize a wide range of acids and

ketones with applications in pharmaceuticals and foodstuffs due to its highly functionalized structure.28 As the conversion processes may take place in the gas phase or in solution, we calculated the heats of formation for the pure gas and liquid phases. We also estimated the reaction energies in the aqueous phase.

’ COMPUTATIONAL METHODS The geometries were initially optimized and harmonic vibrational frequencies calculated at the density functional theory (DFT) level with the B3LYP29,30 exchange-correlation functional and the DZVP2 basis set.31 A number of conformations were studied for the compounds to find the lowest-energy conformer in the gas phase. The G3MP2 method32 was then used to predict the heats of formation (ΔHgas) in the gas phase starting from the optimized B3LYP/DZVP2 geometries of the lowest-energy conformer. The G3MP2 method was chosen as it represents a good compromise between cost and accuracy. The use of a single conformer can lead to small errors in the calculated energetics.33 However, given the accuracy of the computational methods, the errors due to conformational changes are probably smaller than errors in the energy calculations, especially for the solution energies using the approach described below. These calculations were done with the Gaussian 09 program system.34 To estimate the heats of formation of the pure liquid phase, we use the fact that the free energy is 0 at a phase change so that 15687

dx.doi.org/10.1021/jp204243m |J. Phys. Chem. C 2011, 115, 15686–15702

15688

C5O2H8 C5O2H8 C5O2H8 C4H6O4 C3H4O5

trans-2-pentenoic acid trans-3-pentenoic acid trans-4-pentenoic acid succinic acid tartronic acid

90.7 89.6 88.1 195.3 222.3

90.2 118.0 77.3

138.5

95.3 101.2

102.4

50.4 26.8

196.7 ( 1.1547 227.5 ( 0.3674

476.4 462.5 460.3 618.3 511.9

375.9 456.2 405.6

512.3

490.8 500.2

439.5

254.1 330.3 366.2 450.3 432.7

537.9

512.3

342.6 589.3 519.7 549.6 535.8

557.8 443.9

45

508.1546

465.15467.1545

373.944 45944 412.15,45 414.7546

554b

487.1545 503.1545

460.15,45 462.1546

345.244 337.8547 370.344 433.744 470.545

460 ( 444

475.1545

477.744 480.15481.1545 518.1545

538.15540.15 388.15,44 389.65,46 391.0555 33945

274.1545

424.15 225.4545 266.8545

45

BP (K) exp

b

b

62.6a, 61.7b

51.8a, 51.7b 96.6 100.1a, 100.0b 112.3a, 110.5b 60.1a, 59.7b

b

36.4 , 36.9 37.9a, 36.6b

a

9.1a, 9.8b

11.9 11.6 11.5 15.5a, 12.7b 12.8

9.4a, 9.3b 11.4a, 11.5b 10.1a, 10.4b

12.8a, 13.8b

12.3a, 12.2b 12.5a, 12.6b

11.0a, 11.5b

102.6 101.2 99.6 210.8a, 208.0b 235.1

99.6a, 99.5b 129.4a, 129.5b 87.4a, 87.7b

151.3a, 152.3b

107.6a, 107.5b 113.7a, 113.8b

113.4a, 113.9b

160.04 ( 0.14,47,67 159.80 ( 0.0568 101.58 ( 0.0761,72 133.7 ( 0.273 91.73 ( 0.2,47,70 90.30 ( 2.2269 106.72 ( 0.547 103.9 ( 0.547 102.9 ( 0.647 224.8 ( 0.1 (cr)47,44 255.35 ( 0.33(cr)74

119.74 ( 1.0,47,64 115.44 ( 0.7166 114.91 ( 1.2247 120.77 ( 1.36,47,64 120.22 ( 0.566

73.88 ( 1.060 57.17 ( 0.0547 72.32 ( 0.161 71.25 ( 0.254 109.94 ( 0.67,6365 108.89 ( 0.1966

100.6 ( 0.258 110.25 ( 0.2647,59 68.4 ( 0.12,47 63.58 ( 0.1075 62.67 ( 0.12,47 63.51 ( 0.1376 95.17 ( 0.3152

35.47 ( 0.12,47 35.61 ( 0.26 (293 K)54 51.7 ( 0.257

7.96 ( 0.2647

65.65 ( 0.1447,48 0.96 ( 0.6047 4.97 ( 0.2447

66.8 , 66.2 0.9a, 1.3b 6.6a, 7.1b b

ΔHliq exp

a

ΔHliq calc

13.4a, 11.5b, 95.8a, 93.8b, 52 12.74 ( 0.02 95.0 6.4a, 8.6b 71.6a, 73.8b 8.3a, 8.4b 56.1a, 56.2b 9.2a, 9.3b 69.9a, 70.0b 11.3a, 10.8b 67.2a, 66.7b 10.8a, 11.8b 103.5a, 104.5b

12.8a, 11.9b

8.6a, 8.5b 14.7 12.0a, 11.9b 13.7a, 12.0b 13.4a, 13.0b

13.9 , 13.5 11.1a, 9.8b

a

6.2a, 6.9b

11.2 , 10.6 5.2a, 5.6b 6.2a, 6.7b

a

ΔHvap,BP

8.7a, 8.5a, 7.7b, 7.5b 2.0a, 2.1b 4.3a, 4.2b 4.3a, 2.9a, 4.0b, 2.6b 4.1 2.7 3.3

6.3a, 2.0a, 5.8b, 1.5b 7.3a, 7.4b 7.1a, 6.5a, 7.0b, 6.4b

2.3a, 0.1b 1.1a, 1.0b 2.4a, 2.3b 4.1a, 4.6b 6.4a, 5.4a, 5.4b, 4.4b

0.5a, 0.6b 2.0a, 0.2b 8.3a, 3.5a, 8.7b, 3.9b 0.1a, 0.9a, 1.0b, 1.8b 0.6a, 1.4b, 0.2

0.1a, 0.0b

2.4a, 1.2b

1.1a, 1.8b

1.2a, 0.6b 1.9a, 2.3b 1.6a, 2.1b

Δ(ΔHliq) (expcalc) ΔSvap = 0.025

1.0a,f, 0.8a,f, 0.7b,f, 0.9b,f 0.3a,g, 0.2b,g 1.6a,g, 1.5b,g 1.8a,g, 0.4a,g, 1.6b,g, 0.2b,g 1.2g 0.0g 0.5g

1.9a,e, 2.4a,e, 1.2b,e, 3.1b,e 2.4a,e, 2.5b,e 2.1a,e, 1.5a,e, 2.0b,e, 1.4b,e

c c c 0.4a,e, 0.2b,e 2.1a,e, 1.1a,e, 0.7b,e, 0.3b,e

c

c c 1.9a,d, 2.9a,d, 2.5b,d, 2.3b,d c

c

c

c

c c c

Δ(ΔHliq) (expcalc) best ΔSvap

Calculated ΔHvap,BP (ΔHvap = TBPΔSvap) or ΔHliq,298K (ΔHliq = ΔHgas ΔHvap) using the calculated boiling point (BP) value. b Calculated ΔHvap,BP or ΔHliq,298K using the experimental BP value. c Same as previous column. d ΔSvap = 0.037 cal/(mol K) for 2-pyrrolidone as an average between 0.032 and 0.041 cal/(mol K) (see text). e ΔSvap = 0.035 cal/(mol K) for dialcohols. f ΔSvap = 0.040 cal/(mol K) for higher polyalcohols. g ΔSvap = 0.031 cal/(mol K) for acids.

a

C1H2O2 C5H10O2 C3H4O2

C3H8O2

1,2-propanediol

formic acid valeric acid acrylic acid

C3H4O2 CH4O C3H8O C3H6O2 C2H6O2

pyruvaldehyde methanol propanol glycidol ethylene glycol

C3H8O3

C9H18O

5-nonanone

glycerin

65.2 47.8 60.7 55.9 92.7

N-methyl-2-pyrrolidone C5H9NO

C3H8O2 C4H10O2

64.77 ( 1.160 48.16 ( 0.0547 60.97 ( 0.161

82.3

C4H8O C6H6O3 C4H6O2 C5H8O2 C4H7NO

THF HMF δ-butyrolactone GVL 2-pyrrolidone

1,3-propanediol 1,4-butanediol

82.43 ( 0.3152

49.8

C4H4N2 C3H5OCl

succinonitrile epichlorohydrin

93.7 ( 1.0,63,64 94.26 ( 0.67,65 92.73 ( 0.4966 102.72 ( 1,47,64 100.62 ( 0.7166 97.5 ( 1.4347 102.46 ( 1.55,47 101.8 ( 1.36,64 102.55 ( 1.7266 138.12 ( 0.26,47,67 137.8868 90.51 ( 0.1261,72 117.57 ( 0.7273 77.61,69 79.04 ( 1,70 80.52 ( 0.5571

50.39 ( 0.1376

43.2 81.9 88.1 98.5 46.7

C4H8

E-2-butene

2.9

C9H20 C3H6 C4H8 246.5

446.2 207.9 247.7

54.54 ( 0.14, 54.56 4.78 ( 0.17,47 4.8849,50 0.02 ( 0.22,47 0.15 ( 0.1951 2.72 ( 0.24,47 2.58 ( 0.2451 50.12 ( 0.2147,56 25.76 ( 1,47 25.81 ( 154 44.02 ( 0.257 79.9 ( 0.353 87.60 ( 0.258 97.16 ( 0.2647,59 47.17 ( 0.7375

55.6 4.3 0.4 48

BP (K) calc

47

ΔHf(gas) exp

ΔHf(gas) calc

nonane propylene 1-butene

compound

molecular formula

Table 1. Heats of Formation at 298 K in kcal/mol and Boiling Points (BPs) for Compounds in Figures 16 with Known Heats of Formation

The Journal of Physical Chemistry C ARTICLE


C9H12O3 C9H18O3 C9H18O C6H4O3 C6H8O3 C6H12O3 C6H12O6 C6H14O6 C6H12O5 C6H12O5 C6H10O4 C5H8O3

C6H10O6 C6H10O7 C6H8O7 C6H12O7 C6H10O7 C6H10O8 C6H10O7

C4H6O4 C3H6O2 C3H6O2 C3H4O

C3H6O3 C3H6O3 C3H6O4 C3H7O3N C2H4O3 C2H2O3 C2H2O4

C3H4O3 C3H2O2 C3H2O5 C3H6O3 C3H4O4 C6H14O5

C5H10O C5H12O2 C5H9O3N C17H18O4

2-keto-glucose glucuronic acid 2,5-diketo-gluconic acid gluconic acid 5-keto-gluconic acid glucaric acid 2-keto-gluconic acid

glycerin carbonate 3-hydroxy propanal acetol acrolein

glyceraldehyde lactic acid glyceric acid R-amino glyceric acid glycolic acid glyoxalic acid oxalic acid

hydroxymethyl glyoxal triketo mesoxalic acid dihydroxyacetone hydroxypyruvic acid diglyceraldehyde

2-methyl-thf 1,4-pentanediol δ-aminolevulinate diphenolic acid

molecular formula

BH-HMF C9H18O3 C9H18O DFF DHMF DHM-THF glucose sorbitol 1,4-sorbitan 2,5-anhydrosugars isosorbide levulinic acid

compound

466.4 541.1 587.4 536.3 481.0 434.3 536.7 528.4 534.1 550.7 521.8 629.5 810.9 377.8 519.1 612.8 891.5

121.4 141.9 178.8 136.3 134.9 111.3 171.1 95.8 65.1 192.9 118.9 155.8 218.8 53.2 110.7 135.2 153.2

733.0 810.6 838.5 798.0 881.3 840.1 786.1

706.0 660.8 476.4 665.2 671.1 603.2 787.9 709.2 644.7 715.4 625.2 558.1

BP (K) calc

714.1 466.6 458.6 338.4

143.8,12 144.812

90.3,12 90.812 146.4,12 147.612 78.2,12 78.712 64.8,12 65.712 96.0,12 96.812 135.6,12 136.812 266.6,11 268.911

ΔHf(gas) other calcb

165.6 78.3 85.1 16.2

231.4 296.4 272.5 317.7 297.5 361.0 293.9

89.4 153.8 78.4 63.0 94.0 133.6 264.3 277.8 212.1 212.6 154.6 144.9

ΔHf(gas) calc

15689 Figure 4 35244

34844

430.1546

418.744 330 ( 3044 325.15 329.1546

Figure 3

Figure 2

519.1545

569.1546

Figure 1

BP (K) exp

Table 2. Calculated Heats of Formation at 298 K in kcal/mola for Compounds in Figures 16

0.025 0.035 0.031 0.035

0.025 0.025 0.031 0.035 0.031 0.040

0.035 0.031 0.035 0.031 0.031 0.031 0.031

0.025 0.025 0.025 0.025

0.040 0.040 0.040 0.040 0.040 0.040 0.040

0.035 0.035 0.025 0.025 0.035 0.035 0.040 0.040 0.040 0.040 0.035 0.031

ΔSvap

9.4c, 8.8d 18.2 19.0 31.2

13.2 13.4 17.1 18.3 19.5 32.4

16.3 16.8 20.6 16.6 14.9 13.5 16.6c 13.3d

17.9 11.7 11.5c, 10.5d 8.5c, 8.39.0d, 8.18.2d

29.3 32.4 33.5 31.9 35.3 33.6 31.4

24.7 23.1 11.9 16.6 23.5 21.1 31.5 28.4c 22.8d 25.8 28.6 21.9 17.3c, 16.1d

ΔHvap,BP

62.6c, 62.0d 128.9 154.2 184.4

109.1 78.4 210.0 137.2 175.3 251.2

183.5 90.0 96.6c, 95.6d 24.7c, 24.5 to 25.2d, 24.3 to 24.4d 137.7 158.7 199.4 152.9 149.8 124.8 187.7c, 184.4d

260.7 328.8 306.0 349.6 332.8 394.6 325.3

114.1 176.9 90.3 79.6 117.5 154.7 295.8 306.2c 300.6d 237.9 241.2 176.5 162.2c, 161.0d

ΔHliq calc

198.12 ( 0.11(cr),78 198.36 ( 0.36(cr)79

175.13 ( 0.067(cr)77

161.6 (cr)44

304.3 (cr)47

ΔHliq exp

The Journal of Physical Chemistry C ARTICLE



C4H8N2O2 C6H10O4 C4H12N2 C3H6O3

C9H20 C9H20

succindiamide dimethyl succinate 1,4-diaminobutane 3-hydroxypropanoic acid

4-methyl-octane 3.4-dimethylseptane

ΔSvap = 0.025 cal/(mol K), with the exception of the carboxylic acids, dialcohols, and polyalcohols, where ΔSvap = 0.031, 0.035, and 0.040 cal/(mol K), respectively. b Other calculated ΔHf,298K values at G4MP2 and G4 levels. c Calculated ΔHvap,BP or ΔHliq,298K using the calculated boiling point (BP) value. d Calculated ΔHvap,BP or ΔHliq,298K using the experimental BP value.

67.3c, 66.8d 66.1c, 66.0d 10.8c, 10.4d 10.5c, 10.3d 0.025 0.025 Figure 6 415 ( 144 413.846 433.9 418.0 56.4 55.7

469.15473.15 431.15433.1545

119.6 200.4c, 198.4d 22.3c, 22.5d 158.9 18.1 13.8c, 11.8d 10.6c, 10.8d 15.9 0.025 0.025 0.025 0.031 46

722.7 553.4 422.2 513.1 101.5 186.6 11.7 143.0

Figure 5

BP (K) exp 512.6 447.9 534.9

BP (K) calc

72.1 72.3 114.8 C5H6O2 C5H6O2 C5H6O3 angelilactones I angelilactones II β-acethylacrylic acid

ΔHf(gas) other calcb ΔHf(gas) calc molecular formula compound

Table 2. Continued

a

138.91 ( 0.5(cr)63,80

ΔHliq exp ΔHliq calc 84.9 83.5 135.7 ΔHvap,BP 12.8 11.2 20.9 0.025 0.025 0.031

ΔSvap

ARTICLE

ΔHvap = TBPΔSvap where ΔHvap is the enthalpy of vaporization, ΔSvap is the entropy of vaporization, and TBP is the boiling point in Kelvin. ΔSvap is approximately constant for many compounds, as noted by Pictet and Trouton;35 therefore, given TBP, one can estimate ΔHvap and obtain ΔHliq = ΔHgas ΔHvap. The COSMO-RS36,37 approach as implemented in the ADF38 program was used to estimate TBP from DFT results at the B88P86/ TZ2P level.39 For small molecules, a value of ΔSvap = 0.022 cal/(mol K) is appropriate, but we have shown40 for larger molecules that a value of ΔSvap = 0.025 cal/(mol K) provides better agreement with experiment. The application of this approach is discussed in more detail below. Continuum solvation models, COSMO models37,41 as implemented in the Gaussian 03,42 and ADF38 programs were used to calculate solvation free energies in water at 298 K using the gasphase geometries. For the COSMO (B3LYP/DZVP2) calculations in Gaussian 03, the radii developed by Klamt and coworkers were used to define the cavity.41 For the COSMO calculations at the B88P86/TZ2P level39 in ADF, the default MM3 radii from Allinger and co-workers43 were used to define the cavity. The aqueous Gibbs free energy (free energy in aqueous solution) (ΔGaq) was calculated from eq 1 ΔGaq ¼ ΔGgas þ ΔΔGsolv

ð1Þ

where ΔGgas is the gas-phase free energy and ΔΔGsolv is the aqueous solvation free energy. A dielectric constant of 78.39 corresponding to that of bulk water was used in the COSMO calculations. The solvation energy is calculated as the sum of the electrostatic energies (polarized solute solvent) and the nonelectrostatic energies. The calculations were performed on the Xeon-based Dell Linux cluster at the University of Alabama and a local AMD Opteron-based and Intel Xeon-based Linux cluster from Penguin Computing.

’ RESULTS AND DISCUSSION The computational studies were performed for the reaction schemes shown in Figures 16. DFT-optimized Cartesian coordinates for all of the compounds reported in this work are listed in the Supporting Information together with the appropriate total energies in au. For each scheme, the computational thermodynamic predictions are divided into two parts, (1) the heats of formation (gas and liquid phases) and (2) the reaction energies and solvation effects. Heats of Formation: Benchmarks. The heats of formation of all compounds are given in Tables 1 and 2 at the G3MP2 level of theory for the gas-phase values and in the liquid phase using the methods described above. A comparison with experiment is possible only for some of the studied compounds, and these values can serve as benchmarks of our approach (Table 1). A comparison with G4MP2 and G4 values11,12 is provided for some of the compounds as well in Table 2. Where the experimental boiling points were available, we calculated the heats of vaporization and the heats of formation for the liquid phase, respectively, using both the calculated and the experimental4446 values of the boiling points. Our calculated gas-phase heats of formation are usually within (2 kcal/mol of the experimental data. The overall good agreement with experiment for the gas-phase values suggests that our use of the lowest-energy conformer for the prediction of the gas-phase heats of formation is a reasonable approximation. 15690



ARTICLE

Table 3. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 1 ΔGsolaqueous no.

a

reaction

ΔHgas

ΔGgas

ΔHliq

G03a

G03b

ADFa

ADFb 36.7

1

glucose f HMF + 3H2O

9.0

25.1

5.7

43.3

38.9

41.2

2

HMF + acetone + H2 f BH-HMF + H2O

13.4

2.9

25.2

5.2

7.0

6.1

7.6

3

BH-HMF + 3H2 f C9H18O3

64.4

34.1

62.8

32.9

37.1

31.1

35.5

4

C9H18O3 + 2H2 f C9H18O + 2H2O

40.2

42.5

50.0

49.4

50.0

47.7

47.6

5

C9H18O + 2H2 f nonane + H2O

35.0

27.7

44.2

31.9

32.7

31.2

32.5

6

HMF + H2 f DHMF

12.1

3.1

20.9

7.0

8.7

8.1

9.5

7

DHMF + 2H2 f DHM-THF

39.6

19.5

37.2

14.9

16.3

13.7

15.2

8 9

HMF + 1/2O2 f DFF + H2O HMF + 2H2O f levulinic acid + HCOOH

38.9 37.6

44.6 31.2

51.3 27.3

57.4 23.0

56.9 23.7

56.5 24.3

55.8 25.7 4.8

10

glucose + H2 f sorbitol

13.5

6.0

4.8

2.1

4.0

3.4

11

glucose + 6H2O f 6CO2 + 12H2

46.8

64.2

141.0

6.5

13.6

12.5

3.6

12

sorbitol + 2H2 f 3(ethylene glycol)

0.3

7.0

12.9

18.9

19.1

16.5

16.3

13

sorbitol + H2 f 2(glycerol)

0.8

2.9

4.0

11.1

10.7

9.0

8.9

14

sorbitol f isosorbide + 2H2O

7.6

10.7

12.5

27.7

25.6

24.7

21.8

15

sorbitol f 1,4-sorbitan + H2O

7.9

1.3

5.6

9.4

8.1

7.3

5.9

16

sorbitol f 2,5-anhydrosugars + H2O

7.4

2.1

8.9

12.6

11.0

10.4

9.0

Electrostatic value of the solvation free energies (ΔGsol). b Total (electrostatic and nonelectrostatic) value of the solvation free energies.

For nonane, both the gas and liquid calculated heats of formation are in agreement with experiment, within about 1 kcal/mol.47,48 Our G3MP2 calculated value is less than 0.5 kcal/ mol more negative than the previously reported G4 and G4MP2 calculated heat of formation values of 55.1 and 55.3 kcal/mol, respectively.12 The calculated gas heat of formation of propylene is in good agreement with the experiment,47,49,50 and the liquid heat of formation is within 2 kcal/mol of the experimental value.47 For 1-butene and E-2-butene, the calculated gas-phase heats of formation are in good agreement with the reported experimental data,47,51 and the calculated liquid phase heats of formation are less than 2 kcal/mol lower that the experimental ones.47 The calculated gas- and liquid-phase heats of formation for 5-nonanone are in very good agreement with experiment.52 The experimental gas heat of formation of HMF was recently reported by Verevkin et al.53 Our G3MP2 value is 2 kcal/mol more negative than the experimental value and in good agreement with the previously reported G4 and G4MP2 calculated heat of formation values of 81.2 and 82.1 kcal/mol, respectively.11 The calculated gas heat of formation of epichorohydrin is in good agreement with experiment including the error bars.47,54 The calculated liquid heat of formation of epichorohydrin is within 12 kcal/mol of the experiment using either the experimental or calculated boiling points.44,46,55 The calculated gas-phase heat of formation of succinonitrile is in very good agreement with the experiment.47,56 For the heats of formation of THF57 and δ-butyrolactone,58 there is a very good agreement with the experiment for both gas and liquid phases. The calculated gas-phase heat of formation of GVL is in good agreement with the experiment47,59 within 1 kcal/mol. The calculated liquid heat of formation of GVL is in good agreement with the experimental value47,59 within 2 kcal/mol. The calculated gas-phase heat of formation of pyruvaldehyde is in very good agreement with experiment.60 The calculated liquid-phase heats of formation of pyruvaldehyde are also in agreement with the experiment using a value of ΔS vap = 0.025 cal/(mol K). 60

The calculated and experimental gas heats of formation of propanol61,62 and methanol47 are in good agreement. For propanol and methanol, the calculated heats of formation of the liquid are 261,62 and 147 kcal/mol, respectively, too positive as compared to experiment. For ethylene glycol, there is good agreement between the calculated and experimental6366 gas-phase values, but a value of ΔSvap of 0.035 cal/(mol K) is needed to obtain good agreement with the liquid heat of formation. Use of ΔSvap = 0.025 cal/(mol K) leads to liquid heats of formation that are 46 kcal/mol too positive as compared to the experimental values.6366 The calculated and experimental gas heats of formation of 1,2propandiol47,64,66 and 1,3-propandiol47 are in good agreement. A value of ΔSvap of 0.036 cal/(mol K) is found for 1,3-propandiol; use of ΔSvap = 0.025 cal/(mol K) leads to a liquid heat of formation that is 7 kcal/mol too positive as compared to experiment.47 The use of ΔSvap = 0.025 cal/(mol K) in calculating the liquid heat of formation of 1,2-propandiol leads to agreement within 2 kcal/mol with some experiments66 and about a 6 kcal/mol difference when compared to other reported experimental values.47,64 Thus, a value of ΔSvap = 0.035 cal/ (mol K) for 1,2-propandiol gives a better agreement with experiment.47,64 Glycidol, a dialcohol obtained by decarboxylation of glycerin carbonate or from glycerin via epichorohydrin, has a value of ΔSvap = 0.035 cal/(mol K); use of ΔSvap = 0.025 cal/(mol K) leads to a calculated heat of formation of the liquid about 4 kcal/mol more positive than the experiment. The calculated gas-phase heat of formation of 1,4-butanediol is in very good agreement with the experimental heats of formation47,64,66 within the experimental uncertainties. The value of ΔSvap for 1,4-butanediol is 0.037 cal/(mol K); use of ΔSvap= 0.025 cal/(mol K) gives an error of ∼7 kcal/mol.47,64,66 The calculated glycerin heat of formation for the gas phase is in very good agreement with experiment.47,67,68 Use of the experimental boiling point and experimental heat of formation of the liquid shows that ΔSvap = 0.040 cal/(mol K) rather than a value of 0.025 cal/(mol K). Use of the latter value for ΔSvap leads to 15691


The Journal of Physical Chemistry C calculated heats of formation for the liquid phase that are too positive by 89 kcal/mol as compared to experiment.47,67,68 The gas-phase heat of formation of acrylic acid is in very good agreement with one experimental69 value but 2 to 3 kcal/mol lower as compared to other experimental data.70,71 The calculated value for ΔSvap is 0.031 cal/(mol K). Use of ΔSvap = 0.025 cal/(mol K) yields a liquid heat of formation that is 34 kcal/mol too positive as compared to experiment.47,69,70 The calculated heat of formation of formic acid in the gas phase is in good agreement with the experimental value.61,72 The calculated value for ΔSvap is 0.030 cal/(mol K). Use of ΔSvap = 0.025 cal/(mol K) yields a liquid heat of formation that is 2 kcal/mol too positive as compared to experiment.61,72 The calculated gas-phase heat of formation of succinic acid is in good agreement with the experiment to within 1 kcal/mol.47,59 For the trans-n-pentenoic acids, estimated values of ΔSvap are 0.034, 0.031, and 0.032 cal/(mol K) for n = 2, 3, and 4, respectively.47 For valeric acid, the calculated gas-phase value is in excellent agreement with experiment.73 A value of ΔSvap = 0.035 cal/(mol K) is found from the experimental data; use of ΔSvap = 0.025 cal/(mol K) gives a liquid heat of formation that is 4 kcal/mol more positive than experiment.73 There is a larger difference than expected between the calculated and experimental gas-phase heats of formation of tartronic acid, with the calculated heat of formation being 5 kcal/mol more positive than the experimental value.60,74 For 2-pyrrolidone, the calculated gas-phase heat of formation is in very good agreement with the experimental heat of formation. The value of ΔSvap using the most positive experimental heat of formation of the liquid75 is 0.032 cal/(mol K); use of the more negative experimental liquid heat of formation47 gives a value of ΔSvap = 0.041 cal/(mol K), which seems to be far too large. For N-methyl-2-pyrrolidone, there is again good agreement for the calculated gas-phase heat of formation with experiment. The calculated and experimental heats of formation of the liquid are within 2 kcal/mol using ΔSvap = 0.025 cal/ (mol K).47,76 This is consistent with the lack of intermolecular hydrogen bonding with the substitution of the methyl group on the N blocks. The above results show that the presence of substantial intermolecular hydrogen bonding in the liquid gives values of ΔSvap that are substantially higher than 0.025 cal/(mol K). To provide more insight into the ΔSvap values for different functional groups, we set ΔSvap= 0.025 cal/(mol K) for the compounds from Table 1 for which experimental data is available and found variations from experiment with errors of up to 9 kcal/mol for the heats of formation of the liquid, which suggested that ΔSvap could be as high as 0.041 cal/(mol K). We then modified ΔSvap to improve the agreement with the known experimental values for different classes of compounds and obtained ΔSvap = 0.031 cal/(mol K) for acids, 0.035 cal/(mol K) for dialcohols, and 0.040 cal/(mol K) for higher polyalcohols based on the glycerin result. The results for the liquid heats of formation at 298 K using the new values for ΔSvap (Table 1) are, for the most part, within 2 kcal/mol of the experimental values. The new values of ΔSvap were used to predict the heats of formation of compounds where experimental values are not available (Table 2). The heats of formation of a number of crystalline materials are given for completeness when there is no other data.47,7780 Reaction Energies and Solvation Effects. We used the calculated heats of formation to predict the reaction enthalpies of the gas and liquid phases (Tables 38). The gas-phase free

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energies at 298 K and the free energies including the aqueous solvation effects at 298 K are also reported in Tables 38. The free energies of solvation are reported in the Supporting Information for each compound using the approaches in the Gaussian 03 and ADF programs. The electrostatic component to the free energies of solvation in water from both Gaussian 03 and ADF are calculated to be negative, as would be expected. The electrostatic energies differ by less than 2 kcal/mol for the two software implementations. However, the nonelectrostatic energies can vary significantly between Gaussian 03 and ADF. The ADF nonelectrostatic energies are approximately constant between 2 and 3 kcal/mol for essentially all of the molecules. The Gaussian 03 nonelectrostatic energies show a much broader range. Thus, the total value of the aqueous free energy of solvation determined as the sum of the electrostatic energies (polarized solute solvent) and the nonelectrostatic energies using ADF are, in general, more negative (or less positive) as compared to the Gaussian 03 values due to the positive nonelectrostatic energy component being smaller. Because of the nonelectrostatic energy term, there are a few molecules for which the total aqueous free energy of solvation is a positive value, notably, the alkanes nonane, 4-methyl-octane, and 3,4-dimethyl-septane and 5-nonanone (see Supporting Information). These compounds are insoluble in water, consistent with the positive solvation energy. The alkenes propylene, 1-butene, and E-2-butene are predicted to be insoluble in water from the Gaussian 03 results and barely soluble with ADF. These olefins are weakly or barely soluble in water at 298 K, consistent with the accuracy of the predictions.81 The R-D-glucose is transformed to HMF by removal of three molecules of water (1). Levulinic acid and formic acid are formed by rehydrating the HMF (9). These steps and the corresponding intermediates have been studied experimentally8286 and theoretically.11 The enthalpies for reaction 1 are calculated to be endothermic in the gas phase (9.0 kcal/mol) and exothermic in the liquid (5.7 kcal/mol) (Table 3). From the free-energy perspective, reaction 1 is thermodynamically favorable. Inclusion of solvation effects leads to the products being stabilized in water by more than 11 kcal/mol, although the actual value depends on whether the nonelectrostatic values are included and which program was used to calculate the continuum solvation effects. The stabilization in water for the formation of HMF could be due to the formation of three water molecules as noted by Assary et al.11,12 Reaction 9 is calculated to be exothermic for both the gas and liquid phases, and the calculated value of the free energy of the reaction is thermodynamically favorable. However, the free energy of solvation shows a destabilization of the products as reaction 9 consumes two molecules of water. Our calculated gas and solvation values at the G3MP2 level are very similar to what Assary et al.11 previously reported at the G3MP2B3 and G4 levels. Aldol condensation is a useful synthetic organic chemistry reaction to form new CC bonds between biomass derivatives. Thus, 3-hydroxybutenyl-hydroxymethylfuran (BH-HMF) is obtained in an aldol condensation of HMF with acetone (Table 3).10,87,88 Reaction 2 is exothermic in the gas and liquid phases and is thermodynamically favorable in terms of the free energy as well. Nonane can be synthesized from BH-HMF by a series of hydrogenations and dehydrogenationhydrogenation reactions, as shown in reactions 3, 4, and 5. These reactions are highly exothermic, especially reaction 3. The hydrogenation of HMF to 2,5-di(hydroxymethyl)furan (DHMF) and further to 2,5-di(hydroxymethyl)tetrahydrofuran (DHM-THF) (reactions 6 and 7) and the hydrogenation of glucose to sorbitol (Reaction 10) are exothermic processes 15692



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Figure 2. Conversion of linear glucose. The complete reactions including the reagents and the byproducts are given in Table 4.


a

reaction

ΔHgas

ΔGgas

ΔHliq

G03a

G03b

ADFa

ADFb

17 18

glucose (linear) f 2-keto-glucose + H2 glucose (linear) + 1/2O2 f glucuronic acid + H2

29.0 36.0

18.4 41.9

25.2 42.9

13.7 49.4

16.2 47.6

13.9 49.7

18.1 46.4

19

glucose (linear) + 1/2O2 f 2-5-diketo-gluconic acid +2 H2

12.1

28.0

20.1

38.2

34.8

38.5

33.6

20

glucose (linear) + 1/2O2 f gluconic acid

57.3

52.9

63.7

59.1

59.3

59.7

57.8

21

glucose (linear) + 1/2O2 f 5-keto-gluconic acid + H2

37.1

42.9

46.7

53.6

52.1

53.8

50.4

22

glucose (linear) + O2 f glucaric acid + H2

100.6

100.6

108.7

109.1

109.0

110.0

107.4

23

glucose (linear) + 1/2O2 f 2-keto-gluconic acid + H2

33.5

39.0

39.4

45.1

43.3

25.2

24.5


(Table 3). In terms of the free energies, the hydrogenation of a CdC bond as in reaction 7 with DHMF is thermodynamically more favorable as compared to the hydrogenation of a CdO bond as in reaction 6 with HMF or the hydrogenation of a carbohydrate to its corresponding alcohol (reaction 10) as previously observed.10 The oxidation reactions are highly exothermic processes, as seen in reaction 8, where the alcohol group in HMF is oxidized to the aldehyde diformylfuran (DFF). The free energy of solvation shows that the products are stabilized in aqueous solution (Table 3). This oxidation reaction was studied experimentally with a wide range of oxidation agents, and it has been shown that the oxidation of HMF to DFF is feasible and can be implemented as an industrial process.89,90

The formations of CO2 and H2 when water is added to glucose are highly endothermic processes (reaction 11). The calculated gas free energy for this reaction is thermodynamically favorable, but the free energy of solvation shows a destabilization of the products (Table 3) due to the poor solvation of the H2. The CC hydrogenolyses of sorbitol in the presence of hydrogen with the formation of ethylene glycol (reaction 12) or glycerol (reaction 13) are nearly energetically neutral in the gas phase and are exothermic processes in the liquid phase (Table 3). From the gasphase free energies, reactions 12 and 13 are thermodynamically favorable, and solvation in aqueous solution is predicted to stabilize the products, resulting in ethylene glycol and glycerol. A mixture of the cyclic ethers91 isosobide, 1,4-sorbitan, and 2,5-anhydrosugars (reactions 14, 15, and 16) is obtained from 15693



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a

reaction

ΔHgas

ΔGgas

ΔHliq

G03a

G03b

ADFa

ADFb

24

glycerol + H2 f 1,2-propanediol + H2O

21.7

22.7

29.9

28.1

28.2

27.3

27.2

25

glycerol + H2 f 1,3-propanediol + H2O

14.6

15.9

23.5

7.4

7.8

8.7

8.8

26

glycerol + H2 f ethylene glycol + CH3OH

2.0

4.7

8.4

8.0

8.3

7.6

7.5

27

glycerol + 2H2 f propanol + 2H2O

37.8

40.2

54.3

50.6

50.8

49.0

48.9

4.9

10.1

16.3

16.2

6.8

11.6

4.9

9.2

11.1

5.4

1.9

2.8

0.9

0.9

18.2

7.9

1.2

1.4

0.1

0.3

1.2

24.8 30.6

14.4 43.4

16.8 53.5

6.5 58.0

7.9 56.6

7.5 55.9

8.9 54.3

59.3

3.0

73.1

7.2

19.8

5.7

14.6

2.4

9.3

6.0

17.4

15.7

16.2

14.7

4.4

16.3

11.6

23.2

21.6

22.6

21.1

4.3

5.4

3.0

10.0

8.5

9.6

8.1

28

glycerol + 2H2 f 3CH3OH

29

glycerol + CO2 f glycerin carbonate + H2O

30

glycerol + HCl f epichlorhydin +2 H2O

31 32

glycerol f glycidol + H2O gycerol + 2H2 f propylene + 3H2O

33

glycerol f 3CO + 4H2

34

glycerol f 3-hydroxy propanal + H2O

35

glycerol f acetol + H2O

36

3-hydroxy propanal f acrolein + H2O

37

acrolein + 1/2O2 f acrylic acid

61.1

56.0

63.0

56.4

57.1

57.0

57.7

38

glycerol + 1/2O2 f acrylic acid + 2H2O

54.4

70.8

72.0

83.5

81.4

82.9

80.7

39 40

glycerol f glyceraldehyde + H2 glyceraldehyde f lactic acid

17.1 20.4

7.5 21.2

14.6 21.0

7.8 22.8

9.4 22.5

8.1 23.5

9.5 23.5

41

glyceraldehyde + 1/2O2 f glyceric acid

42

glyceric acid + O2 f tartronic acid + H2O

57.4

53.1

61.7

56.5

57.5

57.1

57.8

101.3

102.1

104.0

110.7

111.4

110.4

110.5

43

glyceric acid + NH3 f R-amino glyceric acid + H2O

4.3

4.3

4.8

4.7

4.7

4.7

4.7

44

tartronic acid f glycolic acid + CO2

6.7

18.6

8.8

15.3

13.3

15.6

14.1

45

tartronic acid + 1/2O2 f glyoxalic acid + CO2 + H2O

46

tartronic acid + O2 f oxalic acid + CO2 + H2O

47 48

tartronic acid + 1/2O2 f mesoxalic acid + H2O glyceraldehyde + 1/2O2 f hydroxymethyl glyoxal + H2O

49

hydroxymethyl glyoxal + 1/2O2 f triketo + H2O

50

triketo + O2 f mesoxalic acid

51

mesoxalic acid + 2H2 + 1/2O2 f 3(formic acid)

52

glycerol f dihydroxyacetone + H2

53

40.9

58.8

52.1

54.6

53.1

54.3

52.3

100.7

111.7

111.7

119.1

117.3

118.8

117.3

28.4 32.2

35.8 39.2

43.2 39.7

42.1 53.5

40.8 52.4

42.4 49.2

41.7 48.4

27.1

33.4

37.6

39.0

38.7

41.7

41.0

127.8

118.4

131.6

116.8

118.6

119.0

120.5

77.7

76.6

88.5

85.9

87.5

85.0

85.6

19.6

9.5

15.1

4.0

6.2

4.3

5.9

dihydroxyacetone + 1/2O2 f hydroxymethyl glyoxal + H2O

34.7

41.2

28.1

54.3

53.0

49.3

48.6

54

dihydroxyacetone + O2 f hydroxypyruvic acid + H2O

94.7

96.3

106.4

109.0

109.0

108.0

108.0

55 56

hydroxypyruvic acid + O2 f mesoxalic acid + H2O dihydroxyacetone f pyruvaldehyde + H2O

94.9 4.1

96.7 15.2

103.0 4.9

101.2 18.0

101.3 16.0

102.1 17.1

102.1 15.6

57

2(glycerol) f diglyceraldehyde + H2O

0.4

1.1

14.9

6.9

6.0

5.6

5.6


cyclodehydration processes of sorbitol. These reactions are calculated to be slightly endothermic in the gas phase and slightly exothermic in the liquid phase (Table 3). The calculated values for the Gibbs free energies show that reactions 1416 are thermodynamically possible, and we predict a stabilization of the cyclic alcohols over sorbitol in aqueous solution. Nonane is expected to be formed from glucose on the basis of the negative free energy of the addition of reactions 16. In a similar way, the addition of reactions 1 + 7 + 8, which yield DHM-THF from glucose, shows that the free energy is negative for this overall reaction, and thus, DHM-THF could be formed. The addition of the reactions 10 + 12, 10 + 13, 10 + 14, 10 + 15, and 10 + 16 with the formation of ethylene glycol, glycerol, and cyclic ethers from glucose with sorbitol as an intermediate show, from the calculated negative free energy, that the sorbitol derived products are expected to be generated. The oxidation of glucose can be a useful technique to synthesize acids/aldehydes/ketones, as shown in Figure 2. These oxidation

reactions (reactions 1823) are calculated to be highly exothermic and also have negative free energies (Table 4). The dehydrogenation of glucose to 2-keto-glucose (17) is an endothermic process in both gas and liquid phases; the gas-phase free energy shows that this is not a thermodynamically favorable reaction. A large number of valuable chemicals can be prepared from glycerol (glycerin), as shown in Figure 3.8,9,25,26 In 2005, a number of companies including Dow, ADM (Archer Daniels Midland), Cargill, and Ashland revealed plans to produce propylene glycol from glycerol, while BioMCN opened a methanol production plant from glycerol.92 A series of mono- and dialcohols can be prepared from glycerol (reactions 2428) by CO hydrogenolysis, CC bond breaking, and dehydration/hydrogenation reactions. The synthesis of 1,2-propanediol, 1,3-propanediol, and propanol are calculated to be exothermic processes where only CO hydrogenolysis of glycerol takes place. The CO hydrogenolysis is actually a 15694



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Figure 3. Conversion of glycerin. The complete reactions including the reagents and the byproducts are given in Table 5.

dehydration followed by a hydrogenation.93 As the dehydration reactions are close to thermoneutral and the hydrogenations are exothermic or highly exothermic, the overall CO hydrogenolysis reactions are exothermic. When there is CC bond breaking, for example, leading to the formation of ethylene glycol or methanol, these processes are still exothermic but are closer to thermoneutral (Table 5). The Huntsman Corporation is the world’s largest producer of alkylene carbonates; the reactive intermediate glycerin carbonate is prepared by a carboxylation reaction of glycerin.92 Glycerin carbonate is an environmentally friendly solvent and can replace volatile and hazardous solvents currently in use.7,8 Glycerin carbonate has unique reactive possibilities due to the presence of hydroxyl and carbonate reactive sites. However, the heat of formation of glycerin carbonate is not known from experiment; therefore, our calculated values provide the first reasonable estimates of these values. Glycerin carbonate can be prepared directly from glycerol and carbon dioxide (as seen in reaction 29) under supercritical conditions.94,95 This reaction is calculated to be an endothermic process in the gas phase and slightly exothermic in the liquid phase. Glycerin can be used in the production of epichlorohydrin, a commodity chemical used in the production of epoxy resins.7 The production of epichlorohydrin involves reacting propylene and chlorine in a multistep process,96 but several companies

including Dow and Solvay have developed a cheap two-step synthesis of epichlorohydrin from glycerol.97,98 The chlorination of glycerol with the formation of epichlorohydrin (30) and the synthesis of glycidol (31) are endothermic in terms of the gasphase reaction enthalpies, and the formation of epichlorohydrin in the liquid phase is predicted to be very close to thermoneutral. The calculated free energies for the formation of glycerin carbonate, epichlorohydrin, and glycidol are positive; therefore, their formation is not thermodynamically favored in the gas phase. However, reaction 30 is predicted to be essentially thermoneutral in the liquid and in aqueous solution. Propylene made from glycerin is under study by Quattor as a feedstock for “green” polypropylene.92 The synthesis of propylene from glycerol (32) in a series of dehydration/hydrogenation reactions is calculated to be highly exothermic. Propylene synthesis is stabilized by solvation (Table 5). CO/H2 (syngas) gas mixtures are obtained from glycerol (33) in a highly endothermic re-forming reaction in terms of the enthalpy. The calculated gas free energy is 3.0 kcal/mol due to the formation of seven molecules. The products of this re-forming reaction are destabilized by solvation, as would be expected due to the solubilities of CO and H2. Thus, it is necessary to minimize the concentration of water in the glycerol feedstock if syngas is to be produced. 15695



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Figure 4. Conversion of levulinic acid. The complete reactions including the reagents and the byproducts are given in Table 6.

Table 6. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 4 ΔGsolaqueous

a

no.

reaction

ΔHgas

ΔGgas

ΔHliq

G03a

G03b

ADFa

ADFb

58

levulinic acid + 3/2O2 f succinic acid + HCOOH

140.6

137.8

146.5

145.9

147.4

146.9

147.6

59 60

levulinic acid + 3H2 f 1,4-pentanediol + H2O levulinic acid + NH3 f δ-aminolevulinate + H2

23.9 20.7

4.3 21.5

36.2 23.8

10.6 24.6

13.9 24.6

9.5 23.7

12.4 23.7 4.1

61

levulinic acid + 2(phenol) f diphenolic acid + H2O

19.5

3.3

18.9

3.1

3.0

2.4

62

levulinic acid f angelilactones I + H2O

15.0

7.8

7.8

0.1

0.4

1.0

1.0

63

levulinic acid f angelilactones II + H2O

14.9

7.4

9.2

3.0

3.2

3.6

5.0

64

levulinic acid + 3H2 f 2-Me-THF + 2H2O

23.9

13.3

37.6

20.8

24.1

19.1

20.5

65

levulinic acid + H2 f GVL + H2O

11.4

8.9

17.8

15.4

16.8

14.1

14.1

66

levulinic acid f β-acethylacrylic acid + H2

30.1

21.3

25.3

22.0

23.6

21.6

23.1


Similarly, Arkema has proposed the synthesis of acrolein and acrylic acid from glycerin.92 Acrolein is used not only for the acrylic acid synthesis but also in the production of a series of polymers and detergents.99 3-Hydroxypropanal generated by reaction 34 or acetol generated by reaction 35 can be prepared by dehydration of glycerol depending on the nature of the catalyst used.100 In the gas phase, the enthalpies for reactions 34 and 35 are close to thermoneutral, slightly endothermic for 3-hydroxypropanal formation, and slightly exothermic for acetol formation. In the liquid phase, the enthalpies of reaction for the formation of both 3-hydroxypropanal and acetol are calculated to be exothermic. The gas free energies for the synthesis of 3-hydroxypropanal and acetol from glycerol are calculated to be negative (Table 5). These dehydration reaction products are stabilized by solvation, and a water molecule is formed as a byproduct. The dehydration of 3-hydroxypropanal with the formation of acrolein (reaction 36) is calculated to be close to thermoneutral, slightly endothermic in the gas phase and slightly exothermic in the liquid.

Again, similar to dehydration of 3-hydroxypropanal, the formation of acrolein is thermodynamically allowed, and solvation stabilizes the formation of the products including acrolein by up to 5 kcal/mol. Experimentally, catalytic dehydration of glycerol to acrolein has been observed in the presence of water.101103 Oxidation of acrolein to acrylic acid (reaction 37) is a highly exothermic process that is not affected by solvation. The direct oxidation of glycerin to acrylic acid (38) is a highly exothermic reaction in the gas and liquid phases. Glycerol can be used also as a feedstock for the production of useful oxygenated compounds. Gycerol can be relatively easily oxidized in the presence of air, oxygen, or hydrogen peroxide to a large number or ketones/aldehydes and carboxylic acids,9,104 as shown in Figure 3; the usual routes to these compounds involve oxidative methods that are costly or involve highly toxic compounds. Thus, a large number of products (acids, ketones/ aldehydes) for use as new chemical intermediates for the further synthesis of fine chemicals and new polymers can be obtained from the oxidation of glycerol (reactions 3955). All of the 15696



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Figure 5. Conversion of succinic acid. The complete reactions including the reagents and the byproducts are given in Table 7.

Table 7. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 5 ΔGsolaqueous no. 67 68

a

ΔHgas

ΔGgas

ΔHliq

G03

G03b

ADFa

ADFb

succinic acid + 4H2 f 1,4-butanediol + 2H2O succinic acid + 2NH3 f succinamide + 2H2O

21.5 0.2

4.3 3.5

42.4 14.2

17.9 14.7

21.4 14.6

15.3 14.7

18.1 14.7

25.6

9.0

53.7

25.2

28.5

22.3

25.2

36.5

14.3

5.7

8.1

4.4

5.5

2.5

reaction

a

69

succinic acid + 2NH3 + 4H2 f 1,4-diamonibutane + 4H2O

70

succinic acid + 2NH3 f succinonitrile + 4H2O

71

succinic acid + 2CH3OH f dimethyl succinate + 2H2O

11.3

8.7

14.6

13.0

14.6

12.2

12.6

72

succinic acid + CH3OH + NH3 + 2H2 f N-methyl-2-pyrrolidone + 4H2O

26.9

26.0

54.6

43.5

44.8

40.6

40.7

73

succinic acid + NH3 + 2H2 f 2-pyrrolidone + 3H2O

13.8

14.0

40.0

30.8

32.4

28.5

28.5

74

succinic acid f 3-hydroxypropanoic acid + CO

25.9

14.2

22.7

15.8

18.2

15.6

17.1

75 76

succinic acid + 4H2 f thf + 3H2O succinic acid + 2H2 f thf-2-one + 2H2O

21.3 8.4

12.7 7.9

48.6 28.6

27.9 21.7

31.4 23.3

24.5 19.0

28.0 19.0


reactions in this complex pathway are calculated to be exothermic or highly exothermic (reactions 42 and 46), with the exception of reactions 39 and 52, which are calculated to be endothermic. Even though the free energy of reaction 39 is calculated to be positive, the addition of reactions 39 and 40 with the formation of lactic acid yields a negative free energy. Thus, lactic acid is expected to form by increasing the reaction temperature to overcome any activation energies and to avoid the high-energy intermediate, glyceraldehyde. Similarly, the other oxidation products of glycerol could be formed because the sums of the free energies of the appropriate reactions are negative.

The dimerization of glycerol (reaction 57) leading to the formation of diglyceraldehyde is calculated to be close to thermoneutral in the gas phase. The gas free energy is calculated to be ∼1 kcal/mol, and solvation in water stabilizes the products by up to 8 kcal/mol; therefore, the dimerization process is expected to be more favorable in aqueous solution. Levulinic acid is a nontoxic precursor for cleaner burning fuels and has been used in food, fragrance, and other chemical applications.7 Succinic acid can be synthesized from levulinic acid instead of using hydrocarbon-based processes. Succinic acid is used in food additives, soldering fluxes, and plarmaceutical 15697



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Figure 6. Conversion of GVL. The complete reactions including the reagents and the byproducts are given in Table 8.

Table 8. Reaction Energies in the Gas, Liquid, and Water Solution in kcal/mol at 298 K for Figure 6 ΔGsolaqueous

a

no.

reaction

ΔHgas

ΔGgas

ΔHliq

77 78

GVL f trans-2-pentenoic acid GVL f trans-3-pentenoic acid

7.8 8.9

5.6 6.1

7.9 9.3

79

GVL f trans-4-pentenoic acid

10.4

7.8

10.9

10.4

11.7

9.7

9.7

80

trans-2-pentenoic acid f 1-butene + CO2

3.8

15.1

1.9

9.7

8.0

9.4

7.8

81


7.4

17.9

2.0

12.4

10.9

12.1

10.6

82


6.4

17.3

1.1

11.9

10.4

11.9

10.4

83

GVL + H2 f valeric acid

19.5

12.4

19.0

8.7

9.1

9.5

10.9

84

2(valeric acid) f 5-nonanone + H2O + CO2

1.8

8.5

1.6

10.1

8.0

8.6

7.1

85 86

5-nonanone + 2H2 f nonane + H2O 5-nonanone + 2H2 f 4-methyl-octane + H2O

31.1 31.9

21.0 22.1

39.5 40.1

22.4 23.5

24.1 25.3

21.8 23.0

23.2 24.4

87

5-nonanone + 2 H2 f 3,4-dimethyl-heptane + H2O

31.2

20.4

39.3

21.8

23.9

21.2

22.7

a

G03

8.2 8.8

G03b

ADFa

ADFb

9.2 10.0

7.1 7.6

7.2 7.6


products.7 In addition, GVL can be prepared from levulinic acid and is a possible substitute for blending with ethanol in gasoline. Levulinic acid can be oxidized to succinic acid and formic acid in a highly exothermic reaction (58), and the products of this oxidation reaction are stabilized in water (Table 6). The hydrogenation and cyclization/hydrogenation reactions leading to the formation of 1,4-pentanediol (59), 2-methyltetrahydrofuran (64), and GVL (65) are exothermic. From the calculated gas free energies, reactions 59, 64, and 65 are thermodynamically

allowed, and the products are further stabilized by solvation. The condensation reaction of levulinic acid with 2 mol of phenol, which leads to a diphenolic acid (reaction 61), is calculated to be exothermic in both the gas and liquid phases. Thermodynamically, reaction 61 is allowed, and solvation does not significantly affect the stability of the products. The cyclodehydration reactions with the formation of angelilactones I and II (62 and 63) are endothermic reactions, as are the reactions of levulinic acid with ammonia to generate 15698


The Journal of Physical Chemistry C Δ-aminolevulinate (60) and the dehydrogenation reaction with the formation of β-acethylacrylic acid (66). From the calculated free energies, these reactions are not favorable thermodynamically, and reactions 60 and 66 are not strongly affected by solvation. Succinic acid is a potential intermediate for the production of a wide range of chemicals, as shown in Figure 5. The hydrogenation reaction of succinic acid to 1,4-butanediol (67) is calculated to be substantially exothermic in the gas and the liquid phases (Table 7). The gas-phase free energy is ∼4.3 kcal/mol, and the products of reaction 67 are stabilized by solvation by more than 10 kcal/mol. The synthesis of 1,4-butanediol from succinic acid has been explored experimentally using different transition-metal catalysts at elevated temperatures and pressures.105 Reaction 69 to form 1,4-diaminobutane from succinic acid is also highly exothermic, and the products are stabilized by aqueous solvation (Table 7). The reduction/cyclization reactions to form N-methyl-2-pyrrolidone (72) and 2-pyrrolidone (73) are calculated to be exothermic for both the gas and liquid phases; because they are dehydration processes, water solvation stabilizes the products. The amide synthesis of succinamide from succinic acid (reaction 68) is calculated to be almost thermoneutral in the gas phase and exothermic in the liquid phase. This acylation reaction (68) is thermodynamically allowed in the gas phase, with ΔGgas = 3.5 kcal/mol; the reaction products are stabilized by aqueous solvation by more than 10 kcal/mol. The reaction for dinitrile formation (70) is calculated to be endothermic. The decarbonylation reaction 74, which produces 3-hydroxypropanoic acid, is also calculated to be an endothermic process. The syntheses of THF (reaction 75) and Δ-butyrolactone (reaction 76) are calculated to be exothermic reactions, and the products of both reactions 75 and 76 are stabilized by water solvation (Table 7). GVL is a potential feedstock in the production of energy and fine chemicals.106109 In ring-opening reactions, GVL is converted to alkenes and alkanes, as shown in Figure 6, and these products can be directly used as gasoline, jet, and/or diesel fuels. Experimentally, it has been demonstrated that butenes can be synthesized from GVL over a solid acid catalyst SiO2/Al2O3 in the presence of water.106 The first step for the synthesis of the targeted butenes from GVL is the ring-opening of GVL (reactions 7779), leading to a mixture of three unsaturated pentenoic acids. Ring-opening is calculated to be a slightly endothermic process with values in the gas enthalpy of reaction varying from 7.8 to 10.4 kcal/mol for trans-2-pentenoic acid to trans-4-pentenoic acid and 7.9 to 10.9 for the liquid enthalpy of reaction (Table 8). The free energy changes during the GVL ring-opening are also positive values and not very different from the enthalpy changes. The second step in the synthesis of butenes is the decarboxylation of pentenoic acids (reactions 8082). These reactions are exothermic in the gas phase, and the free energies are negative. The decarboxylation reaction products are destabilized by aqueous solvation (Table 8), but the reactions still have negative free energies. The addition of reactions 77 + 80, 78 + 81, and 79 + 82, which yield the formation of a butene + CO2 from GVL, shows that the free energies are all negative for the compound reaction; therefore, butene could be formed. Higher temperatures could be required to go over any activation energy barriers and to avoid high-energy intermediates. Previous computational studies15 at the B3LYP/6-311+G(2d,p) level are consistent with our higher-level calculations. Liquid hydrocarbon fuels (nonane, 4-methyloctane, or 3,4dimethylheptane) can be prepared from GVL, and the literature provides experimental strategies for these processes.110 In the

ARTICLE

presence of H2, GVL forms petanoic acid (valeric acid) (reaction 83). Reaction 83 is calculated to be exothermic in the gas phase, and the products are destabilized slightly by aqueous solvation (Table 8). Ketonization,111 involving CC coupling and deoxygenation of valeric acid, leads to the formation of 5-nonanone (reaction 84). Reaction 84 is predicted to have a slightly positive ΔHgas and a more negative ΔGgas; the reaction free energy is not strongly affected by aqueous solvation. Then, by hydrogenation, dehydration, and/or isomerization reactions, nonane, 4-methyloctane, and 3,4-dimethylheptane can be obtained from 5-nonanone (reactions 8587). Reactions 8587 are calculated to be exothermic, and solvation does not affect the free energies as there are no hydrogen bonds with the alkanes in aqueous solution.

’ CONCLUSIONS We present a detailed computational study of the thermodynamics for the conversion of glucose, HMF, sorbitol, levulinic acid, succinic acid, GVL, and glycerol as biomass-derived starting materials to a number of biobased fuels and chemicals using the high-level G3MP2 method. The heats of formation for a large number of compounds in the gas and liquid phases were calculated. Our calculated gas heats of formation are mostly within (2 kcal/mol of the experimental values. The presence of substantial intermolecular hydrogen bonding in the pure liquid phase requires values of ΔSvap that are substantially higher than the usual range of 0.0220.025 cal/(mol K) typically used based on the rule of Pictet and Trouton. Comparison with the available experimental heats of formation of the liquid leads to the use of the following values for ΔSvap: 0.031 cal/(mol K) for carboxylic acids, 0.035 cal/(mol K) for dialcohols, and 0.040 cal/(mol K) for higher polyalcohols. We estimated the reaction energies in the aqueous phase using a self-consistent reaction field approach with the COSMO parametrization. Overall, most of the reactions that were studied are exothermic; therefore, they are favorable thermodynamically, and the products are stabilized by aqueous solvation. In some cases, higher temperatures will be needed to overcome activation energies and to avoid high-energy intermediates. Processes that are endothermic in both the gas and liquid phases include the dehydrogenation reactions 17, 39, 52, 60, and 66, the decarbonylation reaction 74, the ring-opening reactions 7779, and the dehydration reactions 31, 62, and 63 where only 1 mol of water is eliminated. Aqueous solvation has almost no effect on these reactions. Reaction 29 is endothermic in the gas phase but exothermic in the liquid and in aqueous solution. Reaction 70 is endothermic in the gas and liquid phases but exothermic in aqueous solution. These results can be used in designing new catalytic approaches for these reactions to improve our ability to convert biomass into useful fuels and chemical feedstocks. This paper represents a first step in tackling the problem of the conversion of biomass. The measurement and prediction of the kinetics for these processes represents a true grand challenge as a large number of reaction intermediates and pathways are possible, and these processes need to be studied in aqueous solution or organic solvents or at the interfaces of liquids. ’ ASSOCIATED CONTENT

bS

Supporting Information. Thermochemical values at the G3MP2 level of theory in au. Aqueous solvation energy contributions in kcal/mol. Optimized B3LYP/DZVP2 Cartesian coordinates in Angstroms for the various structures. This

15699


The Journal of Physical Chemistry C material is available free of charge via the Internet at http://pubs. acs.org.

’ AUTHOR INFORMATION Corresponding Author

*E-mail: [email protected].

’ ACKNOWLEDGMENT This work was supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, U.S. Department of Energy (DOE) under Grant No. DE-FG0203ER15481 (catalysis center program). D.A.D. also thanks the Robert Ramsay Chair Fund of The University of Alabama for support. ’ REFERENCES (1) Petrus, L.; Noordermeer, M. Green Chem. 2006, 8, 861–867. (2) Ragauskas, A. J; Williams, C. K.; Davison, B. H.; Britovsek, G.; Cairney, J.; Eckert, C. A.; Frederick, W. J., Jr.; Hallett, J. P.; Leak, D. J.; Liotta, C. L.; Mielenz, J. R.; Murphy, R.; Templer, R.; Tschaplinski, T. Science 2006, 311, 484–489. (3) Inderwildi, O. R.; King, D. A. Energy Environ. Sci. 2009, 2, 343–346. (4) Manzer, L. E. Top. Catal. 2010, 53, 1193–1196. (5) Corma, A.; Iborra, S.; Velty, A. Chem. Rev. 2007, 107, 2411– 2502. (6) Hubar, G. H.; Iborra, S.; Corma, A. Chem. Rev. 2006, 106, 4044–4098. (7) Werpy, T.; Petersen, G. Top Value Added Chemicals from Biomass: Vol. 1, Results of Screening for Potential Candidates from Sugars and Synthesis Gas, Report No. NREL/TP-510-35523; National Renewable Energy Laboratory: Golden, CO, 2004; available electronically at http://www.osti.gov/bridge. (8) Bozell, J. L.; Peterson, G. R. Green Chem. 2010, 12, 539–554. (9) Zhou, C.-H.; Beltramini, J. N.; Fan, Y.-X.; Lu, G. Q. Chem. Soc. Rev. 2008, 37, 527–549. (10) Chheda, J. N.; Huber, G. H.; Dumesic, J. A. Angew. Chem., Int. Ed. 2007, 46, 7164–7183. (11) Assary, R. S.; Redfern, P. C.; Hammond, J. R.; Greeley, J.; Curtiss, L. A. J. Phys. Chem. B 2010, 114, 9002–9009. (12) Assary, R. S.; Redfern, P. C.; Hammond, J. R.; Greeley, J.; Curtiss, L. A. Chem. Phys. Lett. 2010, 497, 123–128. (13) Chang, C.; Ma, X. J.; Cen, P. L. Chin. J. Chem. Eng. 2006, 14, 708–712. (14) Xiang, Q.; Lee, Y. Y.; Torget, R. W. Appl. Biochem. Biotechnol. 2004, 115, 1127–1138. (15) Bond, J. Q.; Alonso, D. M.; West, R. M.; Dumesic, J. A. Langmuir 2010, 26, 16291–16298. (16) Csonka, G. I.; French, A. D.; Johnson, G. P.; Stortz, C. A. J. Chem. Theory Comput. 2009, 5, 679–692. (17) Raju, R. K.; Ramraj, A.; Hillier, I. H.; Vincent, M. A.; Burton, N. A. Phys. Chem. Chem. Phys. 2009, 11, 3411–3416. (18) Appell, M.; Strati, G.; Willett, J. L.; Momany, F. A. Carbohydr. Res. 2004, 339, 537–551. (19) Momany, F. A.; Appell, M.; Strati, G.; Willett, J. L. Carbohydr. Res. 2004, 339, 553–567. (20) Appell, M.; Willett, J. L.; Momany, F. A. Carbohydr. Res. 2005, 340, 459–468. (21) Momany, F. A.; Appell, M.; Willett, J. L.; Bosma, W. B. Carbohydr. Res. 2005, 340, 1638–1655. (22) Momany, F. A.; Appell, M.; Willett, J. L.; Schnupf, U.; Bosma, W. B. Carbohydr. Res. 2006, 341, 525–537. (23) Ma, B. Y.; Schaefer, H. F.; Allinger, N. L. J. Am. Chem. Soc. 1998, 120, 3411–3422.

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