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 production has increased greatly in recent years, because of the less-detrimental effects of this fuel on the environment, compared to a conventional diesel obtained from petroleum. This ...work investigates the possibility of using MgO and calcined hydrotalcites as catalysts for the transesterification of soybean oil with methanol. The achieved experimental data show a correlation not only with the catalysts basicity, but also with its structural texture. However, the structural texture of the examined catalysts is dependent on both the precursor and the preparation method. At least four different types of basic sites have been individuated on the surface of MgO and calcined hydrotalcite catalysts. The strongest basic sites (super-basic) promote the transesterification reaction also at very low temperature (100 °C), while the basic sites of medium strength require higher temperatures to promote the same reaction. Ultimately, all the tested catalysts are resistant to the presence of moisture in the reaction environment.
► Some commercial copper chromite catalysts have been tested in ethanol dehydrogenation. ► A satisfactory activity and very high selectivity and good stability to sintering has been obtained for one ...of the proven catalysts. ► The best catalyst is a dispersed Cu catalyst, supported on alumina containing Cu chromite and BaCrO
4. ► Optimal conditions for high selectivities are:
T
=
240
°C,
P
=
20 bars and ethanol contact time (100
g
h
mol
−1). ► Pure hydrogen (exempt of CO) is obtained as by-product.
In the recent years, the interest in the ethanol production from renewable natural sources, as a possible alternative energy vector, has strongly grown in the world. The low-cost ethanol availability has also favored the study of the production of different chemicals such as ethylene, ethyl ether, acetaldehyde and ethyl acetate starting from ethanol as raw material. In this paper, ethanol dehydrogenation to ethyl acetate, in one step reaction, has been studied by using three different commercial copper based catalysts. The reaction has been conducted in a conventional packed bed tubular reactor, by exploring a temperature range of 200–260
°C and a pressure range of 10–30 bars. The best results have been found by using a commercial copper/copper chromite catalyst, supported on alumina and containing barium chromite as promoter, operating at 220–240
°C, 20 bars and 98
g
h
mol
−1 of ethanol contact time. In these conditions, a conversion of 65% with a selectivity to ethyl acetate of 98–99% has been obtained. However, the effect of temperature, pressure and ethanol contact time on both conversion and selectivity to ethyl acetate has been investigated. Moreover, the best catalyst has also shown a good stability to deactivation. For these reasons, the behavior of this catalyst has been subjected to a deeper investigation. The obtained results have been discussed on the basis of a reliable reaction scheme and mechanism. At last, a simplified scheme of a possible process is reported.
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► A review of the main technologies studied for producing biodiesel at lower cost is reported. ► The possibility of using new feedstock cheaper and not competing with food is ...mentioned. ► The possibility of intensify the traditional process catalyzed by homogeneous alkaline catalyst is reviewed. ► The main heterogeneous basic and acid catalysts studied in the literature are discussed and compared. ► New uses for the by-product glycerol reported in the literature are examined and discussed.
Biodiesel is a fuel safe, renewable, non-toxic, biodegradable and much less contaminant for the environment than conventional diesel. Moreover, it represents a strategic source of energy especially for the countries that have not oilfields. For these reasons, even if the cost of biodiesel is still greater than diesel from petroleum, many governments sustain this production. The cost of biodiesel is mainly affected by the cost of the feedstock but also an improvement of the adopted technology can contribute in reducing the costs. Therefore, it is imperative: to employ less expensive feedstock, that is, unrefined or waste oils; to use not edible oil coming from alternative sources as, for example, algae or Jathropa Curcas; to improve the actual technology based on the use of homogeneous alkaline catalysts through a better understanding of the reaction mechanism, to develop new biphasic kinetic models; to adopt techniques of process intensification; to introduce the use of heterogeneous catalysts, possibly finding a catalyst promoting in one step both esterification of free fatty acids and transesterification of tri-glycerides; to find new remunerative uses for the by-product glycerol. In this paper, all the mentioned aspects will be considered by reporting some of the most relevant results obtained in the last years.
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► A kinetic study of the ethanol dehydrogenation to ethyl acetate. ► Cu/CuCr2O4 as catalyst supported on Al2O3 promoted with BaO–Cr2O3. ► A Langmuir–Hinshelwood–Hougen–Watson kinetic ...model resulted the best to interpret all the performed kinetic runs. ► A reliable mechanism is suggested and discussed.
A kinetic study of the ethanol dehydrogenation to ethyl acetate on a copper/copper-chromite catalyst has been performed. The used catalyst, in cylindrical pellets, contained also alumina as a support and barium chromate as a promoter. Support and promoter have the effect of increasing the activity, the selectivity and the stability of the catalyst, as shown in a previous work. The kinetic runs were carried out in a packed bed tubular reactor, alternatively filled with 2 or 50g of catalyst, approximately isothermal, by feeding pure ethanol together with a mixture of nitrogen and hydrogen as carrier gas. Kinetic runs have been made by changing the temperature, in the range of 200–260°C, the pressure between 10 and 30bar and the space time from 1 to 100ghmol−1. We have verified, at first, that inter-phase and intra-phase mass transfer limitations were negligible in the adopted conditions. Then, a Langmuir–Hinshelwood–Hougen–Watson kinetic model has been used for interpreting all the experimental data collected. This model corresponds to a mechanism in which the first step is the dissociative adsorption of ethanol on the surface, giving an adsorbed ethoxy group. Then, two other consecutive steps give place to respectively acetaldehyde as intermediate and ethyl acetate. This kinetic model allows a satisfactory fitting of all the performed experimental runs with a standard error below 15% for the runs performed with 2g of catalyst and less than 12% for the runs made with 50g of catalyst.
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.
Biodiesel, a renewable fuel of vegetal origin, has been an object of a rapidly growing interest, in the latest years, both as a pure fuel and as blending component to reduce exhaust pollutants of ...traditional diesel fuel. Biodiesel is conventionally produced through a well-established technology that involves the use of alkaline catalysts and is, therefore, not compatible with the presence of free fatty acids (FFAs) in the feedstock due to the formation of soaps. Also the presence of FFA in small amounts is detrimental, because, formed soaps strongly affect the successive glycerol separation giving place to a long settling time. Normally, highly refined vegetable oils are used as raw materials for biodiesel production. A preliminary stage of acidity reduction is necessary, when the starting material is characterized by a high free acidity (higher than 0.5% by weight). This pre-treatment can be pursued, as example, by means of an esterification reaction of the FFAs with methanol, catalyzed by sulphonic ionic exchange resins. In the present work, a batch reactor has been used for the study of the above-mentioned reaction and different acid ionic exchange resins have been tested as heterogeneous catalysts. Two kinds of substrates have been submitted for esterification with methanol: a model mixture of soybean oil artificially acidified with oleic acid and a commercial high-acidity mixture of waste fatty acids (oleins). A detailed kinetic model has been developed and tested in which the following key phenomena, characterizing the system, have been introduced: (i) the physical phase equilibrium (partitioning equilibrium) of the components between the resin-absorbed phase and the external liquid phase; (ii) the ionic exchange equilibria; (iii) an Eley–Rideal surface reaction mechanism. The developed kinetic model was able to correctly interpret all the experimental data collected, both as a function of the temperature and of the catalyst concentration.
In the present work, the kinetics, mass transfer and heat transfer of soybean oil epoxidation with H₂O₂ have been studied in a fed and pulse-fed-batch reactor. The reaction has been performed with ...peroxyformic acid (PFA), generated in situ, by reacting concentrated hydrogen peroxide (60wt.%) with formic acid (FA), in the presence of sulphuric or phosphoric acid as catalysts. The kinetic study also considers two important aspects occurring simultaneously with the epoxidation reaction, namely: the degradation resulting from the opening of the oxirane rings, and the hydrogen peroxide decomposition. Epoxidation is a highly exothermic reaction and the evolution of the temperature in the reactor over a period of time is strongly dependent on the amounts and way in which a mixture of H₂O₂ and formic acid is added to the mixture of oil and catalyst. In this paper, a biphasic kinetic model has been developed considering all of the occurring reactions in each phase, the partition of reagents and products between the phases and the evolution of any involved chemical specie along the time. Different kinetic runs have been successfully simulated after the evaluation, by mathematical regression analysis or by independent means, of all the kinetic and thermodynamic parameters of the model. The heat transfer properties of the used reactor have been determined following different approaches. In addition, the evolution of the temperature of the reacting mixture during the time has also been simulated with the developed mathematical model.
A continuous hydrogen peroxide propene oxide (HPPO) lab-scale pilot plant was designed and tested for the production of propene oxide via HPPO process. The plant was equipped with a continuous ...stirred tank reactor, able to work under nitrogen pressure with liquid propene. Attention was paid to the feed system and the plant control, the lab-scale pilot plant being completely automated. Hydraulic tests were performed to check the performance of the plant; a fluid-dynamic characterization was conducted to evaluate the residence time distribution. Propene oxide synthesis experiments were performed to evaluate both hydrogen peroxide conversion and propene oxide selectivity. The collected data were interpreted with a recently published kinetics, validating the developed model, obtaining satisfactory results, also in simulating the start-up transient state of the reactor. The model can be considered of high utility in designing and optimizing HPPO process, to achieve high reactant conversions and propene oxide yields.
The production of biodiesel as a fuel in diesel engines greatly increased in recent years and is expected to grow more and more in the near future. Increasing biodiesel consumption requires optimized ...production processes allowing high production capacities, simplified operations, high yields, and the use of more economic feedstocks such as waste oils and fats. However, the latter often contain large amounts of free fatty acids and cannot be processed with the commonly practiced technology based on the use of alkaline catalysts in the homogeneous phase that requires the use of highly refined oil as raw materials. Therefore, the development of processes for low-cost biodiesel production requires the individuation of heterogeneous catalysts that are very efficient in promoting the transesterification reaction also in the presence of free fatty acids and water, allowing the prompt separation of pure glycerol and not requiring expensive purification of this byproduct. In the present contribution, the performances of different heterogeneous catalysts are compared both in the absence and in the presence of free fatty acids. In some cases, the resistance of the catalysts to the presence of water and the eventual deactivating effects after the first use have also been tested. The catalysts considered are both basic and acidic in nature, such as hydrotalcite, MgO, TiO2 grafted on silica, vanadyl phosphate, and different metals-substituted vanadyl phosphate of the type Me(H2O) x VO1- x PO4·2H2O, where Me is a trivalent cation such as Al, Ga, Fe, and Cr and where x = 0.18−0.20. Finally, the understanding of the kinetic behavior of the most stable catalyst TiO2/SiO2 has been deepened.
