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The simulation of block or random ethylene oxide (EO) and propylene oxide (PO) copolymerization with a deterministic model requires the solution of many thousands of differential and algebraic equations. This approach, therefore, is not practicable, requiring too long computer calculation time. The use of a stochastic model allows overcoming this drawback. In this work, a Monte Carlo based model has been developed considering, for a given substrate such as ethylene glycol, only the reaction of the overall consumption of the alkoxides. The addition of new units of EO or PO, respectively, to the hydroxyls of the substrate or the terminal hydroxyls of the growing chains is ruled by the stochastic probability of the two mentioned events. The developed model considers also the effect of the side reaction of PO conversion to allyl alcohol with the formation of new growing polymeric chains. To do the calculations a microscopic volume, assumed to be a well-mixed system, is considered containing about 5000 or a few more molecules, which is a number significant for statistical validity. Kinetic laws and related parameters have been estimated from data published in the literature. Examples of simulations of high-molecular-weight EO and PO homopolymers, of an EO-PO random copolymer, and a triblocks copolymer of the type (EO)a-(PO)b-(EO)a will be presented.

Propylene oxide (PO) homopolymer and PO/ethylene oxide (EO) copolymers, initiated by the starter glycerol (GLY), are the most popular polyols employed in the production of elastic polyurethanes. Th...

Catalytic glycerol dehydration provides a sustainable route to produce acrolein because glycerol is a bioavailable platform chemical. However, in this process catalysts are rapidly deactivated due to coking. This paper examines and discusses recent insights into coking of catalysts during catalytic glycerol dehydration. The nature and location of coke and the rate of coking depend on feedstock, operating conditions, and the acidity and pore structure of the solid catalysts. Several methods have been suggested for inhibiting the coking and slowing the deactivation of catalyst, including (1) cofeeding of oxygen, (2) tuning of the pore size of the solid acid catalysts, (3) doping noble metals (Ru, Pt, Pd) into the solid acid catalysts, and (4) designing new reactors. The present methods for inhibiting coking are still unsatisfactory. The deactivated catalysts can be regenerated by removing coke. Nevertheless, the rapid deactivation of the regenerated catalyst remains problematic. The literature survey indicates that the exact chemical compositions of the coke on the catalyst during glycerol dehydration remain elusive. The thermodynamics, kinetics, and mechanism of coking need to be probed so as to advance the development of a catalyst with high activity, selectivity, and resistance to coking to put the catalytic glycerol dehydration into practice.

The reactions of soluble and reactive solids with components in the liquid phase are of high relevance in the field of chemical engineering. A mathematical model was recently developed applying an extended film theory, where the reactive solid material dissolves in the liquid phase and diffuses through a dynamic liquid film surrounding the particle. In the present work, this Extended Shrinking Film Model (E.S.F.M.) was applied to a very challenging reaction, the limestone dissolution in an acid environment. The model was applied to experimental data collected under a wide range of operation conditions, i.e., varying temperature, particle size, stirring rate, and type of limestone. A very good fit of the model to experimental data was obtained, and the chemical and physical phenomena were clearly identified, significantly contributing to understanding of the reaction kinetics. The work clearly demonstrates that the data interpretation can be considerably enhanced by rigorously taking into account the physi...

The epoxidation of soybean oil is a hot topic for biorefinery. The process is nowadays performed in the presence of a strong mineral acid (H2SO4, H3PO4) that catalyzes both the epoxidation and the oxirane ring opening reactions, leading to high conversions and low selectivity. Moreover, the separation of such a catalyst needs neutralization steps, thus operation units. Previous studies revealed that Amberlyst-16, an acid exchange resin, is a stable and active catalyst in the epoxidation of soybean oil, showing high selectivity. In the present paper, a rigorous liquid–liquid–solid kinetic model has been proposed to interpret the kinetics of the soybean oil epoxidation reaction catalyzed by Amberlyst-16. The intrinsic kinetics of the overall reaction network has been investigated by taking into account all the occurring chemical and physical phenomena, overall dealing with the intraparticle diffusion limitations. From the data elaboration, it has been demonstrated that the unique role of the resin is to catalyze the formic to performic acid step. Formic acid showed a higher rate in decomposing the oxirane ring with respect to performic; this was justified by its higher acidity. The high selectivity is due to the fact that the resin has no action in catalyzing the ring opening reactions because of its high hydrophilicity. The obtained results are a good starting point for designing a continuous reactor.

In the present work, a new laboratory device specifically developed to obtain microchannels to test the process intensification effects on a suitable test reaction will be described. Ideally, this device represents a connection between a traditional tubular packed-bed reactor and the recently appeared microreactors that are very efficient, as it is well-known, in mass- and energy-transfer operations. To test the performance of this microreactor, the decomposition of hydrogen peroxide (H2O2) has been chosen as a test reaction. This reaction is of great industrial interest, because many processes use H2O2 as an oxidizing agent and the decomposition of the excess is normally performed under batch conditions by creating an alkaline medium. We observed that the H2O2 decomposition can also be promoted by stainless steel acting as a catalyst. Therefore, the decomposition of H2O2 is particularly enhanced in our device that is characterized by a relatively high surface area of stainless steel per unit of packing volume. Consequently, its result is particularly efficient in the chosen reaction. Experimental runs for H2O2 decomposition have been performed preliminarily under batch conditions, both in the homogeneous phase and in the presence of a known amount of metallic surface area as a catalyst, in the temperature range of 65−85 °C, to collect kinetic data. Successively, continuous runs at different temperatures (50−65 °C) and pH have been performed in the microchannel device, obtaining good performances and maintaining safety conditions. The obtained results have been interpreted and successfully simulated in a simplified way.

In the synthesis of biodiesel via the transesterification of vegetable oils, 10 wt % of glycerol is obtained as byproduct. This means that, by increasing the biodiesel production, the glycerol availability also increases and its cost goes down more and more. In order to consume the large amount of glycerol derived from biodiesel production in a profitable way, only two strategies are possible: (i) use glycerol as raw material to produce fuel additives and (ii) use glycerol as raw material to produce commodities. In the present work, we have briefly considered the first aspect while focusing, in particular, on the second opportunity by reviewing the production of chlorohydrins by glycerol hydrochlorination with HCl. Chlorohydrins are important intermediates in the production of epichlorohydrin used to produce epoxy–resins. The advantages of producing chlorohydrins by starting from glycerol instead of propene—that is, the classical route—will be discussed. The glycerol hydrochlorination reaction is catalyzed by carboxylic acids, and in this work, we describe (i) the reaction conditions normally adopted; (ii) the behavior of different catalysts proposed in the literature (concerning activity and selectivity); (iii) the reaction mechanism; (iv) the kinetic laws, reported by different authors, along with the related parameters; and (v) the role of mass transfer. A brief discussion on the best reactors for performing the reaction and some information about the different processes used to produce epichlorohydrin starting from glycerol will also be reported. Some catalysts, other than carboxylic acids, have also been briefly reviewed, although they have not been used in industrial plants until recently.

Propene oxide is a very important chemical whose production technology has changed a lot during the last 30 years. Nowadays, the most promising technology is the HPPO process in which the propene oxide is produced by oxidizing propene with hydrogen peroxide, via titanium silicalite-1 (TS-1) catalysis. Even if this technology has been patented in the early 1980s and some chemical plants are already in production, only few papers have been published until now dealing with the catalytic and kinetic aspects of the process. In this paper, the state of the art of the scientific knowledge and technical aspects related to propene oxide synthesis in the presence of TS-1 catalyst have been reviewed.

Biodiesel is usually produced by reacting triglycerides, contained in vegetable oils, with methanol in the presence of KOH, NaOH, or related alkoxides as catalysts. In industry, the reaction is performed in stirred tank reactors and requires 1–2 h of reaction time being the reaction rate strongly affected by mass transfer limitation. We have recently shown, by using a Corrugated Plates Heat Exchanger Reactor, that a very high productivity (about 2 tons/day L) can be obtained by working at 60–100 °C thanks to the presence of an intense local “micromixing”. Moreover, we have recently tested the performances obtained in a tubular reactor filled with stainless steel spheres of different diameters. By opportunely changing the spheres diameters it is possible to obtain microchannels in a range of 300–1000 μm with an intense local micromixing. Again, thanks to micromixing we obtained very high productivities. However, in these last reactors the void portion of the reactor is low and the productivity per overall ...

Epoxidized soybean oil (ESBO) is produced in industry by reacting soybean oil, at 60-70 degrees C, with hydrogen peroxide in the presence of formic or acetic acid. A small amount of sulphuric or phosphoric acid is necessary to catalyze the oxidation of the carboxylic acid to the corresponding per-carboxylic acid. Per-carboxylic acid, formed in situ, migrates from the aqueous phase to the oil phase where it spontaneously reacts with the double bonds to give an oxirane ring. This reaction is extremely exothermic (Delta H = -55 kcal/mol) and must be kept under thermal control. Two undesired side reactions can occur: the oxirane ring-opening and the hydrogen peroxide decomposition. In a previous work, a biphasic kinetic model for describing the epoxidation of soybean oil in fed or pulse-fed-batch reactors has been developed and the parameters of the model have been determined by mathematical regression analysis. In the present paper, the model has been adapted to simulate also kinetic runs performed in two continuous tubular reactors of different sizes, filled with spheres of stainless steel (AISI 316) used as static mixer. The agreement found, in simulating the continuous runs, validates the developed biphasic kinetic model. This model constitutes a valid base for the design of a continuous process and for promoting the process intensification.

The strong growth of biodiesel production occurring in the last years has determined the availability of a great amount of the byproduct glycerol. Many researches in the world are therefore oriented to find new possible uses for glycerol also with the aim of reducing the cost of biodiesel. In this paper the chlorination of glycerol with gaseous hydrochloric acid to obtain 1,3-dichlorohydrin and then epichlorohydrin will be described. All the advantages of this process will be examined and discussed. The behavior of the different proposed catalysts (normally compounds containing carboxylic acid groups), the reaction kinetics, the effect of the catalyst concentration, the effect of HCl pressure, the vapor−liquid phase equilibria of the reaction products in the reaction environment, and the most convenient operative conditions have been studied, concluding with useful suggestions for the design of the industrial plants.

The growing availability of glycerol, as a consequence of the increase in biodiesel production (for which glycerol is a byproduct), is rapidly saturating the market, and consequently, a great interest is now addressed to the development of new process routes for alternative uses of glycerol. Among the various possibilities, our attention has been focused on the glycerol chlorination reaction, with the aim to produce dichlorohydrin. This compound can then subsequently be converted into epichlorohydrin, which is an important intermediate in the production of epoxy resins. dicholorhydrin, together with R,â-dichlorohydrin, is currently synthesized starting from propylene via allyl chloride. In the present paper, the kinetics of glycerol chlorination with gaseous hydrochloric acid, for the production of dichlorohydrin, has been investigated by means of a jacketed glass reactor operated in batch conditions for the substrate (glycerol) and continuously for the hydrochloric acid. Different organic acids have been tested as catalysts with good performances in terms of both activity and, in particular, selectivity toward the desired 1,3-dichlorinated product. A reaction mechanism has been proposed and a consequent kinetic model has been developed in order to quantitatively describe the experimental data collected at various temperatures (80-120 °C), and the kinetic parameters have been evaluated. A generally good agreement between the experimental data and the theoretical model has been found.

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.

Catalysts that are very active and selective in the oxidative dehydrogenation of ethanol to acetaldehyde have been prepared by grafting vanadyl triisopropoxide onto a silica support whose surface was coated with TiO2. Together with acetaldehyde, small amounts of byproducts were obtained, including acetic acid, acetals, and CO2. The kinetic behaviors of the catalysts were studied in the temperature range 100−180 °C, by changing the ethanol residence time, the molar ratio between the reagents, and the vanadium load. A four-step mechanism was adopted, consisting of the following steps: (i) dissociative adsorption of ethanol onto vanadium, (ii) α-hydrogen withdrawal by the metal to form acetaldehyde and a hydride group, (iii) oxidation of the formed hydride, and (iv) dehydration of the vanadium site to restore the original active site. This mechanism can be simplified, and the resulting kinetic expression is similar to a Mars and van Krevelen kinetic expression. The reaction is well-described by this kinetic...

The kinetics of the alkylation of p-cresol with isobutene has been studied, first of all, in a well-stirred slurry reactor. Preliminary runs of CO2 absorption in water and of isobutene absorption in p-cresol, in the same reactor, have been made for estimating the gas−liquid mass-transfer coefficient in an independent way. The kinetic model, developed in a previous work, has been improved and the related parameters have been determined by mathematical regression analysis of many kinetic runs. Different kinetic runs have then been performed also by using a spray tower loop reactor (STLR) in similar physical conditions. These runs have been simulated in a satisfactory way by using the same kinetic model and parameters, changing only mass-transfer parameters for taking into account the different fluid dynamic conditions. The performances obtained by the two different reactors are in some conditions comparable. This work has demonstrated, therefore, the possibility and the convenience of extending the use of S...

The behavior of spray tower loop reactors has been examined in details, also by reviewing previous works, with the aim of suggesting useful criteria for the design and simulation of these devices. Different possible situations have been considered and quantitatively interpreted. For gas−liquid systems, for example, physical absorption in the absence of a reaction, absorption with a moderately fast reaction, and absorption with an extremely fast reaction have been studied. Moreover, an attempt to extend the use of spray tower loop reactors to a gas−liquid−solid system has been made with satisfactory results.

Laboratory membrane reactors have been studied with the main aim of using such types of devices in kinetic studies of gas−liquid and gas−liquid−solid reactions. As a matter of fact, these reactors allow a better control of the gas−liquid mass transfer phenomena thanks to the absence of emulsions and foams, the interfacial area being constant and stable with different flow rates, and the modular design and ease of scale-up.Four different reactors have been tested to determine what impacts gas absorption from the internal part of the membrane-tube toward the liquid, both in the absence and in the presence of a chemical reaction. In particular, two different agitated reactors have been used: one well-stirred without membranes and the other moderately stirred and containing a coiled bundle of membranes. These two reactors had exactly the same size and stirrer, with the presence of the membrane being the unique difference. The performances of these reactors have been compared for both the physical absorption ...