Browsing by Author "Chen, Li"

Now showing 1 - 7 of 7
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    Anhydrosugar synthesis
    (2019-07-30) Chen, Li; Wong, Michael S.; Zhang, Zongchao; Rice University; United States Patent and Trademark Office
    Improved methods of making anhydrosugars by pyrolysis of a substrate sugar to remove at least one water molecule thereby producing a desired anhydrosugar and side products, the improvement being either 1) protecting one hydroxyl group of the substrate sugar before pyrolysis; or (2) pretreating the substrate sugar with a metal salt and optional acid before pyrolysis, wherein lower amounts of said side products are produced by said improved method.
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    Ring-locking enables selective anhydrosugar synthesis from carbohydrate pyrolysis
    (Royal Society of Chemistry, 2016) Chen, Li; Zhao, Jinmo; Pradhan, Sivaram; Brinson, Bruce E.; Scuseria, Gustavo E.; Zhang, Z. Conrad; Wong, Michael S.
    The selective production of platform chemicals from thermal conversion of biomass-derived carbohydrates is challenging. As precursors to natural products and drug molecules, anhydrosugars are difficult to synthesize from simple carbohydrates in large quantities without side products, due to various competing pathways during pyrolysis. Here we demonstrate that the nonselective chemistry of carbohydrate pyrolysis is substantially improved by alkoxy or phenoxy substitution at the anomeric carbon of glucose prior to thermal treatment. Through this ring-locking step, we found that the selectivity to 1,6-anhydro-β-D-glucopyranose (levoglucosan, LGA) increased from 2% to greater than 90% after fast pyrolysis of the resulting sugar at 600 °C. DFT analysis indicated that LGA formation becomes the dominant reaction pathway when the substituent group inhibits the pyranose ring from opening and fragmenting into non-anhydrosugar products. LGA forms selectively when the activation barrier for ring-opening is significantly increased over that for 1,6-elimination, with both barriers affected by the substituent type and anomeric position. These findings introduce the ring-locking concept to sugar pyrolysis chemistry and suggest a chemical-thermal treatment approach for upgrading simple and complex carbohydrates.
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    Spin squeezing in a spin-orbit-coupled Bose-Einstein condensate
    (American Physical Society, 2020) Chen, Li; Zhang, Yunbo; Pu, Han; Rice Center for Quantum Materials
    We study the spin squeezing in a spin-1/2 Bose-Einstein condensates (BEC) with Raman-induced spin-orbit coupling (SOC). Under the condition of two-photon resonance and weak Raman coupling strength, the system possesses two degenerate ground states, using which we construct an effective two-mode model. The Hamiltonian of the two-mode model takes the form of the one-axis-twisting Hamiltonian, which is known to generate spin squeezing. More importantly, we show that the SOC provides a convenient control knob to adjust the spin nonlinearity responsible for spin squeezing. Specifically, the spin nonlinearity strength can be tuned to be comparable to the two-body density-density interaction, and hence is much larger than the intrinsic spin-dependent interaction strength in conventional two-component BEC systems such as 87Rb and 23Na in the absence of the SOC. We confirm the spin squeezing by carrying out a fully beyond-mean-field numerical calculation using the truncated Wigner method. Additionally, the experimental implementation is also discussed.
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    Spin-exchange-induced spin-orbit coupling in a superfluid mixture
    (American Physical Society, 2018) Chen, Li; Zhu, Chuanzhou; Zhang, Yunbo; Pu, Han
    We investigate the ground-state properties of a dual-species spin-1/2 Bose-Einstein condensate. One of the species is subjected to a pair of Raman laser beams that induces spin-orbit (SO) coupling, whereas the other species is not coupled to the Raman laser. In certain limits, analytical results can be obtained. It is clearly shown that, through the interspecies spin-exchange interaction, the second species also exhibits SO coupling. This mixture system displays a very rich phase diagram, with many of the phases not present in an SO-coupled single-species condensate. Our work provides a way of creating SO coupling in atomic quantum gases, and opens up an avenue of research in SO-coupled superfluid mixtures. From a practical point of view, the spin-exchange-induced SO coupling may overcome the heating issue for certain atomic species when subjected to Raman beams.
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    Spin-orbit angular momentum coupling in a spin-1 Bose-Einstein condensate
    (American Physical Society, 2016) Chen, Li; Pu, Han; Zhang, Yunbo; Rice Center for Quantum Materials
    We propose a simple model with spin and orbit angular momentum coupling in a spin-1 Bose-Einstein condensate, where three internal atomic states are Raman coupled by a pair of copropagating Laguerre-Gaussian beams. The resulting Raman transition imposes a transfer of orbital angular momentum between photons and the condensate in a spin-dependent way. Focusing on a regime where the single-particle ground state is nearly threefold degenerate, we show that the weak interatomic interaction in the condensate produces a rich phase diagram, and that a many-body Rabi oscillation between two quantum phases can be induced by a sudden quench of the quadratic Zeeman shift. We carried out our calculations using both a variational method and a full numerical method, and found excellent agreement.
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    Synthetic U(1) gauge invariance in a spin-1 Bose gas
    (American Physical Society, 2022) Gao, Chunping; Liu, Jinghu; Chang, Maolin; Pu, Han; Chen, Li
    Recent experimental realizations of the U(1) gauge invariance [Nature (London) 587, 392 (2020); Science 367, 1128 (2020)] open a door for quantum simulation of elementary particles and their interactions using ultracold atoms. Stimulated by such exciting progress, we propose a platform—a spin-1 Bose-Einstein condensate—to simulate the deconfined lattice Schwinger model. Unlike previous platforms, it is shown that the atomic interactions in the spin-1 condensate naturally lead to a matter-field interaction term which respects the U(1) gauge symmetry. As a result, a new Z3-ordered phase with threefold ground-state degeneracy emerges in the phase diagram. The Z3 phase connects to the disordered phase by a three-state Potts criticality, which is in contrast to the conventional Coleman's transition with Ising criticality. Furthermore, the ordered state is constructed by a set of weak quantum scars, which is responsible for the anomalously slow dynamics as it is quenched to a special point in the phase diagram. Our proposal provides a platform for extracting emergent physics in synthetic gauge systems with matter-field interactions.
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    Understanding Pyrolysis Chemistry to Improve Biomass to Chemicals Transformation
    (2018-04-19) Chen, Li; Wong, Michael S.
    Biomass pyrolysis is a promising technology for the production of renewable fuels, due to fast conversion rates, simplicity of operation, and feedstock flexibility. However, the decrease of crude oil prices due to the overproduction makes biofuel economically unattractive, which motivates the formation of a wider product portfolio (especially the production of valuable chemicals) than only fuels for biomass pyrolysis. Anhydrosugars are valuable chemicals primarily prepared from biomass-derived carbohydrate pyrolysis. These molecules are highly desirable precursors used in the synthesis of drugs, surfactants, polymers, and others. However, anhydrosugars are difficult to synthesize in large quantities with high selectivity and yield due to various competing pathways during pyrolysis, making this approach economically unfeasible. A lack of understanding of the fundamental pyrolysis chemistry hinders the development of this field. A simple, cheap, and reliable method to produce anhydrosugars with high selectivity and yield would be a game-changing breakthrough in biomass pyrolysis field. In this work, we developed a two-step ex-situ “ring-locking” strategy to alter the nonselective condense-phase chemistry of carbohydrate pyrolysis. In this method, an alkoxy or phenoxy substitution was introduced at the anomeric carbon of glucose prior to thermal treatment. Through this ring-locking step, we found that the selectivity to 1,6- anhydro-β-D-glucopyranose (levoglucosan, LGA) increased from 2% to greater than 90%. DFT analysis indicated that LGA formation becomes the dominant reaction pathway when the substituent group inhibits the pyranose ring from opening and fragmenting into non-anhydrosugar products. To ease scale-up issues, we further developed a one-step in-situ “ring-locking” method for LGA production. We demonstrated that co-mixing an alkali/alkaline earth salt (e.g., Na2SO4) with an acid (e.g., H2SO4) selectively passivated the sugar ring and significantly enhanced the yield of LGA from 6% to as high as 40% during glucose pyrolysis. Compared with other Group I and Group II metal salts, the co-addition of Na2SO4 was found to give the best LGA yield due to the moderate electronegativity of sodium cation, which led to the preferred binding at ring oxygen site and hindered H+ initiated ring-opening reactions. Additionally, sulfate anions were found to protect LGA from further reactions likely through the complexation with the hydroxyl oxygen of glucose. As an extension of the in-situ “ring-locking” method, I provided a general approach to mediate the condense-phase chemistry by co-mixing the metal salt with glucose. We found that the product spectrum (primarily the yields of LGA and LGO) can be tuned by adding Fe2(SO4)3 at different loadings. The co-addition of Na2SO4 with Fe2(SO4)3 can selectively stabilize the sugar ring and enhance the yields of LGA and LGO, likely through the competition between Na+ and Fe3+ for the oxygen sites. These works first introduced the ring-locking concept to alter the non-selective chemistry of sugar pyrolysis and suggest an economical and simple thermo-chemical approach for upgrading simple and complex carbohydrates. To scale-up our lab discovery into a prototype, we studied the interplay between reaction kinetics and heat and mass transport phenomena during fast pyrolysis. Through characteristic times analysis, we categorized the operating conditions (particle size and temperature) into different regimes based on the dominant phenomenon, and identified mass transfer is the key descriptor for LGA yields. Furthermore, we explored the commercialization potential of our LGA product. We received $50K grant from NSF Innovation Corps (I-Corps) program and interviewed 100+ customers across three industries: pharmaceutical, biochemical and the oil field chemical industry. The outcomes from the I-Corps are: (1) we validated our product and market fit; (2) we found a $300milion market opportunity in generic SGLT2 antidiabetic drug industry; (3) we identified that we need to produce 1-5g LGA as customer sample (MVP: minimum viable product).