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Qi L.,City University of Hong Kong | Qi L.,University of California at Santa Barbara | Mui Y.F.,City University of Hong Kong | Lo S.W.,City University of Hong Kong | And 4 more authors.
ACS Catalysis | Year: 2014

The conversion of fructose, glucose, and sucrose to 5-(hydroxymethyl) furfural (HMF) and levulinic acid (LA)/formic acid (FA) was investigated in detail using sulfuric acid as the catalyst and γ-valerolactone (GVL) as a green solvent. The H2SO4/GVL/H2O system can be tuned to produce either HMF or LA/FA by changing the acid concentration and thus allowing selective switching between the products. Although the best yields of HMF were around 75%, the LA/FA yields ranged from 50% to 70%, depending on the structure of the carbohydrates and the reaction parameters, including temperature, acid, and carbohydrate concentrations. While the conversion of fructose is much faster than glucose, sucrose behaves like a 1:1 mixture of fructose and glucose, indicating facile hydrolysis of the glycosidic bond in sucrose. The mechanism of the conversion of glucose to HMF or LA/FA in GVL involves three intermediates: 1,6-anhydro-β-d-glucofuranose, 1,6-anhydro-β-d-glucopyranose, and levoglucosenone. © 2014 American Chemical Society.

Csefalvay E.,City University of Hong Kong | Csefalvay E.,Budapest University of Technology and Economics | Akien G.R.,City University of Hong Kong | Akien G.R.,Center for Environmentally Beneficial Catalysis | And 3 more authors.
Catalysis Today | Year: 2014

Ethanol equivalent (EE) is defined as the mass of ethanol needed to deliver the equivalent amount ofenergy from a given feedstock using energy equivalency or produce the equivalent amount of mass of acarbon-based chemical using molar equivalency. The production of ethanol from biomass requires energy,which in a sustainable world could be produced from biomass. Therefore, we also define a real ethanolequivalent (EEx) indicating that the ethanol equivalent also includes the use of 1 unit of bioethanol toproduce x units of bioethanol. Thus, the abbreviation EE2.3used in this paper shows a 2.3 output/inputbioethanol ratio or efficiency. Calculations of the corresponding mass of corn and size of landwere basedon the first generation corn-based bioethanol technology as commercially practiced in the US in 2008.Since the total energy and essential materials requirements of a given process can be calculated, theEE2.3of a production process or even a total technology can be estimated. We show that the EE2.3couldbe used as a translational tool between fossil- and biomass-based feedstocks, products, processes, andtechnologies. Since the EE2.3can be readily determined for any given biomass-based technology, therequired mass of biomass feedstock, the size of land, and even the volume of water can be calculated.Scenario analyses based on EE2.3could better visualize the demands of competing technologies on theenvironment both for the experts and to the general public. While differentiating between 1, 1000, and100,000 BTUs for different options is rather difficult for most people, comparing the amount of the landneeded to produce the same amount of energy or mass via different technologies is more straightforward. © 2014 Elsevier B.V.

Akien G.R.,City University of Hong Kong | Akien G.R.,Center for Environmentally Beneficial Catalysis | Qi L.,City University of Hong Kong | Horvath I.T.,City University of Hong Kong
Chemical Communications | Year: 2012

Several intermediates and different reaction paths were identified for the acid catalysed conversion of fructose to 5-(hydroxymethyl)-2-furaldehyde (HMF) in different solvents. The structural information combined with results of isotopic-labelling experiments allowed the determination of the irreversibility of the three steps from the fructofuranosyl oxocarbenium ion to HMF as well as the analogous pyranose route. © 2012 The Royal Society of Chemistry.

Kumar M.,Center for Environmentally Beneficial Catalysis | Chaudhari R.V.,Center for Environmentally Beneficial Catalysis | Subramaniam B.,Center for Environmentally Beneficial Catalysis | Jackson T.A.,Center for Environmentally Beneficial Catalysis | Jackson T.A.,University of Kansas
Organometallics | Year: 2015

M06-L-based quantum chemical calculations were performed to examine two key elementary steps in rhodium (Rh)-xantphos-catalyzed hydroformylation: carbonyl ligand (CO) dissociation and the olefin insertion into the Rh-H bond. For the resting state of the Rh-xantphos catalyst, HRh(xantphos)(CO)2, our M06-L calculations were able to qualitatively reproduce the correct ordering of the equatorial-equatorial (ee) and equatorial-axial (ea) conformers of the phosphorus ligands for 16 derivatives of the xantphos ligand, implying that the method is sufficiently accurate for capturing the subtle energy differences associated with various conformers involved in Rh-catalyzed hydroformylation. The calculated CO dissociation energy from the ea conformer (ΔE = 21-25 kcal/mol) was 10-12 kcal/mol lower than that from the ee conformer (ΔE = 31-34 kcal/mol), which is consistent with prior experimental and theoretical studies. The calculated regioselectivities for propene insertion into the Rh-H bond of the ee-HRh(xantphos)(propene)(CO) complexes were in good agreement with the experimental l:b ratios. The comparative analysis of the regioselectivities for the pathways originating from the ee-HRh(xantphos)(propene)(CO) complexes with and without diphenyl substituents yielded useful mechanistic insight into the interactions that play a key role in regioselectivity. Complementary computations featuring xantphos ligands lacking diphenyl substituents implied that the long-range noncovalent ligand-ligand and ligand-substrate interactions, but not the bite angles per se, control the regioselectivity of Rh-diphosphine-catalyzed hydroformylation of simple terminal olefins for the ee isomer. Additional calculations with longer chain olefins and the simplified structural models, in which the phenyl rings of the xantphos ligands were selectively removed to eliminate either substrate-ligand or ligand-ligand noncovalent interactions, suggested that ligand-substrate π-HC interactions play a more dominant role in the regioselectivity of Rh-catalyzed hydroformylation than ligand-ligand π-π interactions. The present calculations may provide foundational knowledge for the rational design of ligands aimed at optimizing hydroformylation regioselectivity. © 2015 American Chemical Society.

Subramaniam B.,University of Kansas | Subramaniam B.,Center for Environmentally Beneficial Catalysis | Akien G.R.,Center for Environmentally Beneficial Catalysis
Current Opinion in Chemical Engineering | Year: 2012

Gas-expanded liquids (GXLs) are a continuum of tunable solvents generated by mixing liquid solvents and compressed near-critical gases such as CO 2 and light olefins. The compressed gas provides tunability of the physical and transport properties of GXLs making them ideal for performing sustainable catalysis characterized by process intensification at mild conditions, high product selectivity and facile separation of catalyst and products. Sustainable technology alternatives to industrial hydroformylations and epoxidations that employ GXLs as enabling solvents are provided. In these examples, the GXLs involve conventional organic as well as non-traditional solvents such as ionic liquids (ILs) and compressible gases such as CO 2 (as inert) or light olefins (as substrates). Such technologies are essential for facilitating sustainable growth of the fledgling biorefining industry. © 2012 Elsevier Ltd. All rights reserved.

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