An improved standing-wave design method is developed for nonlinear simulated moving bed (SMB) systems with significant mass-transfer effects and an operating pressure limit. The design method was verified with rate model simulations and then tested for enantioseparation of phenylpropanolamine. High purity (>99%) and high yield (>99%) were achieved experimentally using a SMB with a pressure limit of 350 psi. The verified design method was used to find the optimal column length that gives the maximum throughput per bed volume. For a given particle size and a pressure limit, the optimal column length falls on the boundary between the masstransfer-limiting region and the pressure-limiting region. If a characteristic dispersion velocity is more than 0.2% of an interstitial velocity, mass-transfer effects must be considered in the design in order to guarantee 99% purity and yield.

A simulated moving bed (SMB) process has been developed for the resolution of racemic mixtures of cis-(()-FTC-ester, a precursor of a potential anti-HIV drug. Chiralpak AD was chosen as the stationary phase and methanol as the mobile phase for this study. The nonlinear standing wave design method was used to determine the zone flow rates and step times of the SMB process. Computer simulations and several laboratory-scale SMB experiments were conducted to test the proposed SMB processes. Extracolumn dead volume (DV) had significant effects on the performance of the laboratory-scale SMB with small columns (10 × 1 cm). Nonuniformly distributed DV was considered in the design and simulations. Different pump arrangements were investigated to reduce the DV effects. High purity (99.8%, or 99.6% e.e.) and high yield (98.9%) were achieved in the SMB experiments. If mass-transfer effects were ignored in the design, the yield would have been lower than 93%.

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A continuous biomass fractionation process for producing ethanol and low-molecular-weight lignin was developed, and its economic feasibility was evaluated. The two-stage process fractionates biomass into three streams: a solid cellulose stream and two liquid streams containing mostly hemicellulosic sugars and lignin, respectively. Process optimization was conducted using corn stover as feedstock in a continuous pilot-scale unit, with the goals of efficient hemicellulose and lignin hydrolysis for the countercurrent first and cocurrent second stage, respectively. Countercurrent prehydrolysis in an extruder is a novel feature of the process. Autohydrolysis at 2108C followed by NaOH (0.06 g/g biomass) catalyzed delignification at 2208C was determined to be optimal. Economic feasibility of the process for ethanol production was compared to that of the National Renewable Energy Laboratory (NREL; Golden, CO) process. Major differences between the two scenarios are that the PureVision process generates lignin as a sellable output but needs to replace the lost fuel value of the lignin with additional stover. The minimum ethanol selling price, calculated following the NREL protocol, is projected to be lower for the PureVision process ($0.94/gal) than that for the NREL process ($1.07/gal)-the differential depending on lignin selling price-indicating a process with commercial potential.