Intermittent simulated moving bed chromatography: 2. Separation of Tröger’s base enantiomers

The intermittent simulated moving bed (I-SMB) process is a modification of the conventional SMB process that has been recently analyzed theoretically [1]. Here, we present a comparative analysis of the two processes, each operated in a six column 1-2-2-1 configuration (one column in sections 1 and 4 and two columns in sections 2 and 3) and in a four-column 1-1-1-1 configuration. Experiments are carried out on a properly modified laboratory unit to separate racemic mixtures of the enantiomers of Tröger’s base in ethanol on ChiralPak AD at a total feed concentration of 1 g/L. Simulations are carried out for the same system using the equilibrium dispersive model and a bi-Langmuir isotherm, whose parameters have been preliminarily estimated from pulse and breakthrough experiments. Experiments and simulations are fully consistent and demonstrate that the four-column I-SMB process (but not the four-column SMB process) can separate the two enantiomers at very high purity and achieve a productivity twice as large as that of the six-column I-SMB and conventional SMB processes with the same solvent consumption.     

Optimization of simulated moving bed chromatography with fractionation and feedback: Part II. Fractionation of both outlets

A new improvement based on outlet fractionation and feedback has been developed for simulated moving bed (SMB) chromatography. In this contribution, this fractionation and feedback SMB (FF-SMB) concept is extended to the general scenario which integrates a simultaneous fractionation of both outlet streams. A model-based optimization approach, previously adopted to investigate single fractionation, is extended to consider this flexible fractionation policy. Quantitative optimization studies based on a specific separation problem reveal that the double fractionation is the most efficient operating scheme in terms of maximum feed throughput, while the two existing single fractionation modes discussed in our previous study are also significantly superior to the conventional SMB operation. The advantages of the double fractionation extension are further demonstrated in terms of several more detailed performance criteria. In order to evaluate the applicability of the fractionation and feedback modification, the effect of product purity, adsorption selectivity, column efficiency and column number on the relative potential of FF-SMB over SMB is examined.     

Streamlined,two-column,simulated countercurrent chromatography for binary separation

We report on a numerical and experimental study of two-column versions of streamlined, multicolumn, semi-continuous chromatography for binary separation. The systems combine a flexible node design, cyclic flow-rate modulation, and relayed operation of the inlet/outlet ports to extend the mass-transfer zone over the largest possible length, while keeping it inside the system at all times. One advantage of these streamlined designs is the simplicity of their physical realization: regardless of the number of columns, they only require two pumps to supply feed and desorbent into the system, while the flow rates of liquid withdrawn from the system are controlled by material balance using simple two-way valves. In one case, an extra pump is needed to recirculate the fluid in closed-loop. A rigorous model-based optimization approach is employed in the optimal design of the cycles to generate solutions that are physically realizable in the experimental set-ups. The optimized schemes for two-column operation supply fresh feed into the middle of the system where the composition of the circulating fluid is closest to that of the feedstock fluid, and recover the purified products, extract and raffinate, alternately at the downstream end of the unit, while desorbent is continuously supplied into the upstream end of the system. By internally recycling part of the non-pure cut fraction, the scheme with a step of closed-loop recycling significantly reduces its solvent consumption. The feasibility and effectiveness of the reported two-column processes have been verified experimentally on the linear separation of nucleosides by reversed phase subject to 99% purity constraints on both products. It is shown that our processes compare favorably against single-column batch chromatography, steady-state recycling, and four-column, open-loop SMB, for the same amount of adsorbent; they are also better than the four-column, closed-loop SMB at high feed throughputs.     

Gasification characteristics of woody biomass in the packed bed reactor

Gasification technology is recognized as one of the possibilities for utilizing biomass effectively. This study focused on woody biomass gasification fundamentals, using a bench-scale packed-bed reactor. In this experiment, pellets of black pine were gasified, using air as the oxidizing agent. Gasification tests were carried out under both updraft and downdraft conditions. Temperature distributions and compositions of syngas inside the gasifier were continuously monitored during gasification experiments at several ports on the wall of the reactor. The syngas at the exit of the gasifier was also sampled to estimate the amount of tar. Lower heating values of the syngas under updraft and downdraft conditions were 4.8 and 3.8 MJ/m³N, respectively. It was easier to control the height of the packed bed under the downdraft condition than under the updraft condition. Under the updraft condition, a bridging phenomenon occurred. Tar generation under the downdraft condition was lower than that under the updraft condition. This is because tar passes through a partial combustion zone or higher temperature zone in the downdraft gasifier.     

超临界水流化床流动阻力特性的实验研究

本文在压力23～27 MPa,温度360～420℃的参数范围内,研究了固定床与流化床的流动阻力特性。实验结果表明：传统的计算固定床压降的Ergun公式在超临界水条件下仍可适用,实验值与Ergun公式计算值的平均误差为13.3%。基于固定床及流化床流动阻力特性实验结果拟合了一个适用于超临界水条件下计算流化床最小流化速度的...     

Bubbling and bistability in two parameter discrete systems

We present a graphical analysis of the mechanisms underlying the occurrences of bubbling sequences and bistability regions in the bifurcation scenario of a special class of one dimensional two parameter maps. The main result of the analysis is that whether it is bubbling or bistability is decided by the sign of the third derivative at the inflection point of the map function.     

An overview of advances in understanding electrostatic charge buildup in gas-solid fluidized beds

Electrostatic charging of particles in gas-solid fluidized beds often results in operational complications in commercial processes. This paper provides a comprehensive review of the advances from the last decade in three key areas, namely the fundamental understanding of triboelectric charging, methods to measure particle charge, and experiments to elucidate particle charging processes in fluidized beds. This review underscores the need for better understanding the mechanisms of triboelectric charging in granular systems, effective online charge monitoring techniques, and experiments under industrially relevant conditions to better comprehend the problems in commercial reactors that can enable strategies to mitigate charging.     

ADSORPTION OF GOLD ON TBP EXTRACTING RESIN FROM HCI SOLUTION

Solventextractionandadsorption,asordinarymethodsofretrievinggoldfromwasteliquid,havetheshortcomingsofthedifficultyofsolventrecoveryandlimitingadsorptioncapacityrespectively.Fixingtheextractionsolventinthesmallopeningsoftheadsorptionresintoformtheextractingresin,thentoadsorbsoluteinsolution,partakesofcharacteristicsofbothsolventextractionandad.sorption,remedyingthedefectsoftheabovementionedtwo..th.d.[IJ.Extractingresincontaining50%tributylphosphate(TBP)hasbeenusedinextractionchromatographyfor…     

EFFECT OF NOZZLE FAN ANGLE ON SPRAYS IN GAS-SOLID RISER FLOW

A three-dimensional simulation study is performed for investigating the hydrodynamic behaviors of a cross-flow liquid nitrogen spray injected into an air-fluidized catalytic cracking （FCC） riser of rectangular cross-section. Rectangular nozzles with a fixed aspect ratio but different fan angles are used for the spray feeding. While our numerical simulation reveals a generic three-phase flow structure with strong three-phase interactions under rapid vaporization of sprays, this paper tends to focus on the study of the effect of nozzle fan angle on the spray coverage as well as vapor flux distribution by spray vaporization inside the riser flow. The gas-solid （air-FCC） flow is simulated using the multi-fluid method while the evaporating sprays （liquid nitrogen） are calculated using the Lagrangian trajectory method, with a strong two-way coupling between the Eulerian gas-solid flow and the Lagrangian trajectories of spray. Our simulation shows that the spray coverage is basically dominated by the spray fan angle. The spray fan angle has a very minor effect on spray penetration. The spray vaporization flux per unit area of spray coverage is highly non-linearly distributed along the spray penetration. The convection of gas-solid flow in a riser leads to a significant downward deviation of vapor generated by droplet vaporization, causing a strong recirculating wake region in the immediate downstream area of the spray.