Jordi Bonet

From residual to useful oil: Revalorization of glycerine from the biodiesel synthesis

The reaction kinetics for the synthesis of glycerol triacetate (triacetin) from glycerol and acetic acid has been studied in the frame of revalorization of residual glycerol in biodiesel production. The reaction has taken place in a stirred reactor at a pressure of 1070 kPa. No external catalyst has been added because the reaction performs better by using as catalyst an excess of acetic acid. Kinetic parameters were obtained at 120 and 160 degrees C and a model of three reactions with monoacetin, diacetin and triacetin formation was proposed with a good agreement with the experimental results. Arrhenius constants were determined for the involved reactions.

Simple Equation for Suitability of Heat Pump Use in Distillation

Abstract A distillation column can be considered as a heat engine that produces separation instead of work. The heat is provided in the reboiler and collected degraded at a lower temperature at the condenser. The energy collected at low temperature at the top of the column can be upgraded back to higher temperatures by means of a heat pump and reused to heat a lower column stage.This can bring saving in terms of the overall amount of energy required. However, the energy required to increase the pressure is of higher quality and price than hot services. The aim of the present paper is to provide an easy way to check, in the early stages of design, when the use of a heat pump can provide a more sustainable distillation process decreasing its energy requirements. After several simplifications, it can be stated that it depends mainly on the efficiency of Carnot. When the efficiency of Carnot is evaluated for the industrial systems where the heat pumps are used, it is concluded that all have Carnot efficiency around 0.1 or lower. Therefore, in the early design of a new distillation column, this criterion is useful to decide when a heat pump is worth to be included in the more rigorous simulations.

Infinite/infinite analysis as a tool for an early oriented synthesis of a reactive pressure swing distillation

The study contributes to the characterization of an original reactive pressure swing distillation system. The methyl acetate (MeAc) transesterification with ethanol (EtOH) to produce methanol (MeOH) and ethyl acetate (EtAc) is shown as illustrative example. The streams outside the units are evaluated by the ∞/∞ analysis to provide insights on the process behavior. Two simpler systems with recycling stream are also presented. The ∞/∞ analysis allows checking the interrelation of the system streams without any column design consideration. Unfeasible regions, low limit values, multiplicity regions, discontinuities, control difficulties, recommendable operation conditions and column profile combinations are predicted and discussed. All these information are useful to establish an early and suitable system design strategy.

Fast solvent screening for counter-current liquid–liquid extraction columns

Liquid–liquid extraction (LLEx) provides the separation of a certain solute present in a stream when adding a solvent that produces a phase split. Then the raffinate is collected free of solute, which in turn is to be found in the extract. The solute is separated from one phase and mixed in another phase from which it is recovered, in most cases, by distillation. The main difficulty of the process is to find a suitable solvent. When an immiscible solvent is not found, in some cases, the extractive distillation is an alternative. The present work compares the LLEx process with extractive distillation process. Furthermore, two parameters are provided to rank the solvents useful for LLEx, one related to the solvent aqueous toxicity impact, and another related to the energy required for solvent recovery. Both parameters for a counter-current LLEx column are calculated using a simple decanter, i.e. a single liquid–liquid equilibrium stage. The first parameter depends on the solvent lost in the raffinate, and its aqueous toxicity is represented by LC50 (lethal concentration required to kill half the members of a tested population). The second parameter depends on the minimum solvent flow rate and its boiling point. Hence, the proposed parameters are suitable to easily check when new proposed solvents are more environmental friendly.

Shortcut assessment of alternative distillation sequence schemes for process intensification

Abstract Finding good process schemes is a difficult task due to its search among multiple alternatives. In literature, several methods are successfully implemented as computer tools, but their use is limited to their developers. There are several useful rules of thumb and heuristics providing useful guidelines, but sometimes these are contradictory. Some authors tried to rank the various alternatives, defining heuristic equations to provide a quantitative parameter to choose among possible solutions. In this paper, mathematical model of distillation columns is simplified, assuming infinite number of stages. The resulting proposed equation has a great similarity to one of the previous heuristic ones. A simple equation not relying on heuristics and easy to use in calculation is provided to evaluate the distillation sequence energy efficiency (DSE) for each alternative. This allows to quantify the advantages derived from process intensification for a given feed composition. The proposed equation is dimensionless, as the Carnot efficiency is used instead of the temperature difference between distillate and bottoms. On the other hand, intermediate results provide also useful information. For instance, the Carnot efficiency of each column indicates when a heat pump or enhanced distillation would be useful. The recovery efficiency for each particular compound allows an easy comparison between alternatives, considering variations on the feed composition. The new equation is verified comparing its results with cases already solved in literature using different methods. The results show that all the methods in literature are able to provide the best sequence, except the heuristics-based ones that are not providing an overall sequence evaluation. The novelty of the proposed DSE method resides in its ease of application, compared to nowadays available methods, and requires only the feed composition and products boiling points.

Advantages of Process Integration Evaluated by Gibbs Energy: Biodiesel Synthesis Case

Abstract The present study shows that the potential for process integration is easily evaluated by the Gibbs energy change between input and output streams assuming isotherm and isobaric units. The minimum energy requirements to get the streams to the desired temperature at the entrance and output of the units for the overall process can be later evaluated by the second thermodynamic principle, i.e. Pinch Analysis. In the case study of biodiesel synthesis from oils, a single hybrid reactive extraction unit substitutes a reactor, one extractive column and three distillation columns and therefore avoids the residual streams.

Use of computer dynamic simulation for indoor exposure assessment based on chronogram incident as air pollution source characterization

Abstract Determination of the level of exposure due to a chemical incident is crucial for the assessment of public health risks and environmental impact. This kind of information is also useful for the subsequent legal responsibilities. If the air contaminant concentrations are not quantified during the incident, then its air concentration may fall below detectable levels shortly after the incident has passed. In case of smelly compounds, usually the incident chronogram indicates the time when the smell was detected and when the smell was gone. Unfortunately, an objective and analytical measure of odour is impossible. The present study shows that it is possible to computer simulate the concentration evolution in time for a defined indoor scenario. Comparing the odour detection in the chronogram with the computer simulations, it is feasible to determine the maximum gas contaminant exposure during the incident and its evolution in time. Once the pollution source indoor concentration is characterized, considering the overall air renewal time and a plume model, the effects on the environment around the building can be estimated.

Infinite/infinite analysis as a tool for an early oriented synthesis of a reactive pressure swing process

Abstract The study deals with the methyl acetate (MeAc) transesterification with ethanol (EtOH) to produce methanol (MeOH) and ethyl acetate (EtAc). A first screening has shown that a reactive pressure swing process would have the best performance regarding this reaction. This study provides insights on this process behaviour and control via the infinite/infinite analysis. The infinite/infinite analysis allows checking the interrelation of the system streams without any column design consideration. Unfeasible regions, low limit values, multiplicity regions, discontinuities, control difficulties, recommendable operation conditions and column profiles combination are predicted and discussed. All this information is useful to establish an early and suitable system design strategy.

Software Tool for Computing and Visualization of Enhanced Residue Curve Maps

Residue curve maps (RCM) are readily implemented on most chemical engineering commercial simulation software because they are very useful to check the distillation columns feasibility. A section of a residue curve corresponds to a column composition profile of a packed column operated at infinite reflux flow rate between a distillate and bottoms compositions corresponding to the initial and final point of the curve section. The existence of the residue curve between distillate and bottoms assures that the separation is feasible when the mass balances are fulfilled with a high enough reflux. It is also well known that an infinite reflux requires a minimum number of transfer units between distillate and bottoms composition. Unfortunately, no information about the minimum number of transfer units is included in the RCM. This study implements for first time a Visual Basic® program able to generate RCM including the information about the minimum number of transfer units required. In this way, the enhanced RCM provides a valuable information about the difficulty of the separation. Some case studies are provided as examples.

Distillation Sequence Efficiency (DSE) for Suitable Liquid-Liquid Extraction Solvents: Acetic Acid Extraction with TOA

Abstract The use of renewable sources to produce chemical compounds is a hot issue, and takes more importance when considering the valorisation of a waste stream. Acetic acid is a useful chemical commodity that can be produced by biotechnological treatment of waste streams. Unfortunately, is rather diluted and its recovery by distillation is quite energy demanding. There are many experimental studies about the capabilities of the basic trioctylamine mixed with organic non-polar compounds to extract acetic acid. Usually the literature studies focus on finding a solvent that requires a low solvent flow rate during the extraction. In this paper, a suitable and simple solvent screening method for reactive extraction is proposed. The overall separation process including also the solvent recovery is considered, at the contrary of available studies that focus only on the extraction operation. For the first time, the DSE concept is applied to a process including other types of separations units besides distillation columns. The obtained results show that the best solvent is 1-octanol, which is in agreement to literature data in which it is the reference solvent.