The practical application of liquids and solid bases in industrial and environmental processes is reviewed. Liquid bases include water solutions of metal hydroxides such as caustics and potash, amines, phosphorus compounds and other molecular bases, solutions and slurries of alkali and alkaline-earth carbonates, organic solutions of organometallics, and superbases. Solid bases include basic clays, alkaline-earth oxides, alkali metals containing oxides and zeolites, synthetic hydrotalcites, rare-earth oxides and mixed oxides, impregnated carbons, and supported alkali metals. Some health and safety considerations are discussed, together with process features. Conclusions about the future use of bases and the perspective of a more massive application of solid bases are offered.

Bases and Basic Materials in Industrial and Environmental Chemistry: A Review of Commercial Processes

In the last 5 years, reductive catalytic fractionation of lignocellulose biomass has emerged as a promising biorefinery concept that combines biomass fractionation with the preservation of chemical functionality in its products. Although significant efforts have been made in optimizing this technology on lab scale, the implementation on a larger (pilot) scale is still in its infancy. In our own search for the scale-up potential of this technology, we faced several fundamental and technical research questions that, to this day, remain unanswered. These fundamental questions are related to four main aspects of RCF, the lignocellulose feedstock, the operating pressure, the redox catalyst, and the solvent. In order to inspire future multidisciplinary research in the RCF community, these scale-up challenges are presented and discussed via multiple angles combining chemical process hurdles with more technical aspects, such as reactor design and process consequences.

Perspective on overcoming scale-up hurdles for the reductive catalytic fractionation of lignocellulose biomass

The reactor modeling and recipe optimization of conventional semibatch polyether polyol processes, in particular for the polymerization of propylene oxide to make polypropylene glycol, is addressed. A rigorous mathematical reactor model is first developed to describe the dynamic behavior of the polymerization process based on first-principles including the mass and population balances, reaction kinetics, and vapor-liquid equilibria. Next, the obtained differential algebraic model is reformulated by applying a nullspace projection method that results in an equivalent dynamic system with better computational performance. The reactor model is validated against plant data by adjusting model parameters. A dynamic optimization problem is then formulated to optimize the process recipe, where the batch processing time is minimized, given a target product molecular weight as well as other requirements on product quality and process safety. The dynamic optimization problem is translated into a nonlinear program using the simultaneous collocation strategy and further solved with the interior point method to obtain the optimal control profiles. The case study result shows a good match between the model prediction and real plant data, and the optimization approach is able to significantly reduce the batch time by 47%, which indicates great potential for industrial applications. © 2013 American Institute of Chemical Engineers AIChE J, 59: 2515–2529, 2013

Reactor modeling and recipe optimization of polyether polyol processes: Polypropylene glycol

Waste oils used in biodiesel production contain high concentrations of free fatty acids. We studied the esterification of oleic acid, dissolved in soybean oil, with methanol in order to simulate its behavior. We used sulfonic exchange acid resin as the catalyst in two different reactors: a well-stirred slurry reactor (WSSR) and a spray tower loop reactor (STLR) both working at atmospheric pressure. Methanol was fed continuously to both the reactors with very low feed rates in order to minimize the amount of methanol emerging from the reactor outlet. This methanol removed the water produced in the reaction thereby favoring esterification. The WSSR and STLR had very similar performance in that were both better than that of a plug flow reactor (PFR) working in the same conditions of atmospheric pressure and low methanol feed rate. Both the WSSR and STLR showed liquid-solid phase mass transfer limitations. All the kinetic runs have been interpreted with a mathematical model adopting the kinetics previously developed by the authors using a well-stirred batch reactor. For both the reactors, the feasibility of a pseudocontinuous operation has also been successfully tested.

Comparison of Different Reactor Configurations for the Reduction of Free Acidity in Raw Materials for Biodiesel Production

A novel approach to removing water from near-azeotropic ethanol–water mixtures is proposed based on the hydration of ethylene oxide (EO) to produce ethylene glycol (EG) in a reactive distillation (RD) column. Steady-state simulations using the Aspen Plus software package were carried out to investigate the feasibility of the suggested approach, and a sensitivity analysis was carried out to obtain the optimal design parameters. The results showed that, using the optimal operating conditions, a reactive distillation column is capable of circumventing the azeotropic limitation to obtain anhydrous ethanol. Compared with traditional approaches, the proposed approach is promising because of its great potential for reducing energy consumption and capital costs.

Simulation and Analysis of a Reactive Distillation Column for Removal of Water from Ethanol–Water Mixtures

Ethoxylation and/or propoxylation are performed in industry to produce surfactants and polyglycols. The reaction is normally promoted by an alkaline catalyst (such as NaOH or KOH) and is performed in gas−liquid stirred reactors, Venturi loop reactors, and spray tower loop reactors. In the first two types of reactors, the gas phase is dispersed into the liquid phase; on the contrary, in the latter case, the liquid phase is dispersed into the gaseous one. In this paper, the key factors in ethoxylation/propoxylation technology will be examined:  (i) the types of reactors employed and their performances; (ii) the role of kinetics and mass transfer in the process; and (iii) safety.

and Riccardo Tesser

Papers

Comparison of Different Reactor Types Used in the Manufacture of Ethoxylated, Propoxylated Products