Rigorous models of staged distillation processes are formulated by setting up material balance eq... more Rigorous models of staged distillation processes are formulated by setting up material balance equations, equilibrium relations, summation equations, and enthalpy balance equations (MESH equations). In these models, the extent of nonlinearity may be very severe, particularly for azeotropic and reactive distillation systems. MESH system based mathematical models can thus yield multiple solutions (multiple steady states), a fact which has been
Abstract Distillation is the most widely used but an energy-intensive separation technology which... more Abstract Distillation is the most widely used but an energy-intensive separation technology which consumes huge amount of thermal energy as a separating agent. Because of low thermal efficiencies of distillation columns, various energy integration methods have been explored in the past in order to reduce the energy requirements for a given separation task. Among them, Internally Heat Integrated Distillation Columns (IHIDiC), in which the rectification zone of the column is at a higher pressure than the stripping zone, are reported to be the best alternative to the conventional columns that give up to 50% energy savings when the rectifying and stripping zones are configured in an annular fashion. However, the structural complexity of IHIDiC draws one’s attention to search for an alternative which involves minimum design effort. In this work, a methodology has been proposed for an IHIDiC with side condensers and side reboilers (SCSR). This configuration introduces minimum structural complexity as the integrated side condensers and side reboilers are external to the columns. The side reboilers of the stripping column are driven by the side condensers of the rectifying column. The problem, however, is to determine the number of such units, their heat loads, and their locations that lead to an optimal design. Thus, a design methodology based on the well known Column Grand Composite Curves (CGCC) has been proposed algorithmically and tested on two separation problems of close-boiling mixtures, namely, Propane-Propylene and Styrene-Ethyl Benzene splitters. A case study of a multi-component mixture has also been analysed. Economic evaluation studies show that the optimized configuration of the IHIDiC with SCSR for the close-boiling mixtures resulted in attractive payback periods and significant savings in operating expenses. The energy savings in the case study of multi-component system, however, is less attractive due to much higher capital investment.
Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageousl... more Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageously used to obtain desired selectivities in case of multi-reaction system. In case of azeotropic systems, the presence of complex vapor liquid equilibrium and distillation boundaries, shrink the feasible stage composition region and thereby increase design complexity for RD systems. Therefore an attempt is made here to develop a conceptual design algorithm based on boundary value method for the synthesis of single feed hybrid reactive distillation (HRD) column to obtain desired selectivities in case of single reactant complex reaction scheme (vande Vusse reaction) involving azeotropic systems. This work is the continuation of our earlier work on ideal multicomponent system ( Hasan et al., 2013 ). We believe that the conceptual design algorithm developed here can be extended to more complex schemes involving multiple reactants.
Industrial & Engineering Chemistry Research, 2003
... Santanu Bandyopadhyay. Energy Systems Engineering, Department of Mechanical Engineering, Indi... more ... Santanu Bandyopadhyay. Energy Systems Engineering, Department of Mechanical Engineering, Indian Institute of Technology, Powai, Bombay 400 076, India. Ranjan K. Malik. Computer Aided Design Centre and Department of Chemical Engineering, Indian Institute of ...
Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageousl... more Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageously used to obtain desired selectivities in case of multi-reaction system. In case of azeotropic systems, the presence of complex vapor liquid equilibrium and distillation boundaries, shrink the feasible stage composition region and thereby increase design complexity for RD systems. Therefore an attempt is made here to develop a conceptual design algorithm based on boundary value method for the synthesis of single feed hybrid reactive distillation (HRD) column to obtain desired selectivities in case of single reactant complex reaction scheme (vande Vusse reaction) involving azeotropic systems. This work is the continuation of our earlier work on ideal multicomponent system ( Hasan et al., 2013 ). We believe that the conceptual design algorithm developed here can be extended to more complex schemes involving multiple reactants.
Kinetic analysis for the acid-catalyzed dimerization of C 4 olefins was performed in a batch reac... more Kinetic analysis for the acid-catalyzed dimerization of C 4 olefins was performed in a batch reactor, and a suitable rate model was developed. It was further used in the rate-based simulation model of a continuous reactive distillation (RD) column. The results obtained were compared with the experimental observations made on a pilot-scale high-pressure RD column. An important outcome of the present work is that RD can be used efficiently to enhance the selectivity of C 8 dimers, thereby avoiding the formation of trimers and tetramers. The use of polar components (such as water or alcohols), as selectivity enhancers, is not necessary.
Central European Journal of Energetic Materials, 2016
The main hurdle for the estimation of the purity of 1,3,5-triamino-2,4,6trinitrobenzene (TATB) is... more The main hurdle for the estimation of the purity of 1,3,5-triamino-2,4,6trinitrobenzene (TATB) is its insolubility in most of the known organic solvents. In the conventional method, TATB is digested with steam in a modified Kjeldahl digester and the ammonia evolved is estimated quantitatively. To do away with this cumbersome method, a simple, rapid HPLC technique using a reverse phase C-18 column has been established for quantitative determination of the purity of TATB. A sharp and symmetrical peak with a retention time of 2.92 min at 355 nm is obtained for pure TATB when the flow rate is 2.0 mL/min. The linearity of the detector response has been studied with sample concentrations ranging from 10 to 50 mg/L. The method addresses two important issues of sample preparation and the precision of measurement. Unlike the previously reported HPLC techniques which mainly aimed at the detection of TATB, the present work is a validated account of a quantitative estimation of purity. Regular production batch samples have been assayed by this method and the results are compared with those obtained from the conventional analysis. The HPLC method is convenient and reliable for quality control of the product at the plant level.
ABSTRACT The solubility of ammonia in toluene has been measured at 398 K and at pressures up to 3... more ABSTRACT The solubility of ammonia in toluene has been measured at 398 K and at pressures up to 340 kPa using a static, synthetic and isochoric technique. The goal of the present study is to determine the equilibrium solubility of ammonia in toluene at a pressure and temperature regime that is relevant to the reaction conditions of amination of 1,3,5-trichloro-2,4,6-trinitrobenzene leading to the formation of 1,3,5-triamino-2,4,6-trinitro benzene. The ammonia solubility data in toluene were hitherto unavailable under these experimental conditions. The solubility data have also been compared with the result obtained from a direct sampling method. The results are in agreement with Krichevsky–Kasarnovsky equation. The Henry’s law constant at the reaction temperature has been determined.
The complexity and difficulty of determination of Multiple Steady States (MSS) in azeotropic and ... more The complexity and difficulty of determination of Multiple Steady States (MSS) in azeotropic and reactive distillation have remained a matter of concern for the development of a systematic and easily verifiable criterion for the detection and characterization of MSS. This has resulted in a plethora of methods that are either experimental or model-based in nature adapting different solution strategies. However, no single methodology is solely suitable for all systems. A sensible approach would be to apply together several solution methodologies for consistent and accurate solutions. It is then obviously desirable to have a framework that enables such a bouquet of tools to be used in an easy and efficient manner. In this paper, one such framework is proposed that relies on model based methodologies, and uses the process models and the property equations already present in the commercial simulators such as Aspen Plus and Aspen Hysys. A developed tool has also been demonstrated to study the sensitivity of the parameters incorporated together with the solution strategy while solving the system of equations representing the distillation column.
Industrial & Engineering Chemistry Research, 2014
A new synthesis and design method is developed for simple and complex hybrid reactive distillatio... more A new synthesis and design method is developed for simple and complex hybrid reactive distillation columns, to achieve desired selectivity in case of multireaction schemes involving multicomponent mixtures wherein, reactant is a saddle in the corresponding residue curve map. The developed methodology makes use of attainable region approach as well as combined graphical-simulation approach. We determine the surface of reactive stage compositions (SRSC) such that if the reaction takes place at any of the compositions that belongs to SRSC then the desired selectivity is ensured. Design guidelines have been formulated based on the number of compositions of the reactive species that appear in the equation of the SRSC, to identify appropriate hybrid RD configurations for the reaction scheme of interest. The method is illustrated using an industrially relevant example of intramolecular aldol condensation of cyclohexanone to achieve the desired selectivity toward 2-cyclohexylidene cyclohexanone. The results provide good initialization for rigorous simulation. The algorithm presented here can be applied to any number of components and can be directly applied to even multiazeotropic systems as well but is restricted to single reactant (i.e., single feed configurations) multireaction schemes with multiple products undergoing side reactions.
Thermal condition of the feed may be altered to reduce the reboiler duty. However, only a portion... more Thermal condition of the feed may be altered to reduce the reboiler duty. However, only a portion of the thermal energy given to the feed reduces the reboiler duty. By splitting the feed and altering the thermal condition of a part of the feed, it is possible to achieve reduction only in the reboiler duty (100% preheat efficiency). Based on the thermodynamic analysis of a distillation column, a methodology is developed to target split fraction of the feed for preheating to obtain reduction only in the reboiler duty.
h i g h l i g h t s Conceptual design of multi-side draw hybrid reactive distillation columns. Th... more h i g h l i g h t s Conceptual design of multi-side draw hybrid reactive distillation columns. The design procedure is a combination of graphical method and simulations. The algorithm typically generates multiple designs of desired selectivity. The developed algorithm can be applied directly to multi azeotropic systems. Methodology is illustrated for transesterification of dimethyl carbonate with ethanol.
Fischer-Tropsch synthesis can be advantageously carried out in reactive distillation (RD) mode. P... more Fischer-Tropsch synthesis can be advantageously carried out in reactive distillation (RD) mode. Parametric studies like the effect of reflux ratio, pressure, etc. have been reported in our earlier work [Srinivas et al. Ind. Eng. Chem. Res. 2009, 48, 4719-4730] using Aspen Plus. As an extension of this work, multiparameter sensitivity analysis is performed on a simple RD configuration without side-draws or side-coolers in Aspen Plus, retaining the kinetic and thermodynamic models used previously. A feasible solution space in terms of reflux ratio, pressure, and total catalyst loading is identified and possible reasons for the bounds observed are provided. Changes in the column configuration toward various objectives like maximum conversion, maximum gasoline yield, or selectivity, etc. are also investigated. Regions of interest corresponding to different objectives are represented on a Da-reflux ratio plot.
While Fischer-Tropsch synthesis (FTS) using coal and natural gas in conventional reactors is an a... more While Fischer-Tropsch synthesis (FTS) using coal and natural gas in conventional reactors is an almost well-established technology, the production of liquid hydrocarbons from syngas obtained from biomass is in its preliminary stages of commercialization in countries like Germany. With concerns about global warming and ways of disposing of CO2 being searched for, CO2 hydrogenation using FTS to liquid hydrocarbons can act as a CO2 sink. A brief review of FTS using CO2-rich syngas is given in this paper, looking at FTS as a technology that can help reduce global warming and as a process integration alternative. The reverse water gas shift (r-WGS) reaction is vital for CO2 hydrogenation. We have studied the effect of this using an FT kinetic model and have proposed a new flow sheet alternative for FTS using CO2-rich syngas. Simulations suggested that this new process gives better conversion of CO2. The product selectivity and yields from an FT plant are vital to make the process viable economically.
Rigorous models of staged distillation processes are formulated by setting up material balance eq... more Rigorous models of staged distillation processes are formulated by setting up material balance equations, equilibrium relations, summation equations, and enthalpy balance equations (MESH equations). In these models, the extent of nonlinearity may be very severe, particularly for azeotropic and reactive distillation systems. MESH system based mathematical models can thus yield multiple solutions (multiple steady states), a fact which has been
Abstract Distillation is the most widely used but an energy-intensive separation technology which... more Abstract Distillation is the most widely used but an energy-intensive separation technology which consumes huge amount of thermal energy as a separating agent. Because of low thermal efficiencies of distillation columns, various energy integration methods have been explored in the past in order to reduce the energy requirements for a given separation task. Among them, Internally Heat Integrated Distillation Columns (IHIDiC), in which the rectification zone of the column is at a higher pressure than the stripping zone, are reported to be the best alternative to the conventional columns that give up to 50% energy savings when the rectifying and stripping zones are configured in an annular fashion. However, the structural complexity of IHIDiC draws one’s attention to search for an alternative which involves minimum design effort. In this work, a methodology has been proposed for an IHIDiC with side condensers and side reboilers (SCSR). This configuration introduces minimum structural complexity as the integrated side condensers and side reboilers are external to the columns. The side reboilers of the stripping column are driven by the side condensers of the rectifying column. The problem, however, is to determine the number of such units, their heat loads, and their locations that lead to an optimal design. Thus, a design methodology based on the well known Column Grand Composite Curves (CGCC) has been proposed algorithmically and tested on two separation problems of close-boiling mixtures, namely, Propane-Propylene and Styrene-Ethyl Benzene splitters. A case study of a multi-component mixture has also been analysed. Economic evaluation studies show that the optimized configuration of the IHIDiC with SCSR for the close-boiling mixtures resulted in attractive payback periods and significant savings in operating expenses. The energy savings in the case study of multi-component system, however, is less attractive due to much higher capital investment.
Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageousl... more Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageously used to obtain desired selectivities in case of multi-reaction system. In case of azeotropic systems, the presence of complex vapor liquid equilibrium and distillation boundaries, shrink the feasible stage composition region and thereby increase design complexity for RD systems. Therefore an attempt is made here to develop a conceptual design algorithm based on boundary value method for the synthesis of single feed hybrid reactive distillation (HRD) column to obtain desired selectivities in case of single reactant complex reaction scheme (vande Vusse reaction) involving azeotropic systems. This work is the continuation of our earlier work on ideal multicomponent system ( Hasan et al., 2013 ). We believe that the conceptual design algorithm developed here can be extended to more complex schemes involving multiple reactants.
Industrial & Engineering Chemistry Research, 2003
... Santanu Bandyopadhyay. Energy Systems Engineering, Department of Mechanical Engineering, Indi... more ... Santanu Bandyopadhyay. Energy Systems Engineering, Department of Mechanical Engineering, Indian Institute of Technology, Powai, Bombay 400 076, India. Ranjan K. Malik. Computer Aided Design Centre and Department of Chemical Engineering, Indian Institute of ...
Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageousl... more Abstract Reactive Distillation (RD) which combines reaction and distillation can be advantageously used to obtain desired selectivities in case of multi-reaction system. In case of azeotropic systems, the presence of complex vapor liquid equilibrium and distillation boundaries, shrink the feasible stage composition region and thereby increase design complexity for RD systems. Therefore an attempt is made here to develop a conceptual design algorithm based on boundary value method for the synthesis of single feed hybrid reactive distillation (HRD) column to obtain desired selectivities in case of single reactant complex reaction scheme (vande Vusse reaction) involving azeotropic systems. This work is the continuation of our earlier work on ideal multicomponent system ( Hasan et al., 2013 ). We believe that the conceptual design algorithm developed here can be extended to more complex schemes involving multiple reactants.
Kinetic analysis for the acid-catalyzed dimerization of C 4 olefins was performed in a batch reac... more Kinetic analysis for the acid-catalyzed dimerization of C 4 olefins was performed in a batch reactor, and a suitable rate model was developed. It was further used in the rate-based simulation model of a continuous reactive distillation (RD) column. The results obtained were compared with the experimental observations made on a pilot-scale high-pressure RD column. An important outcome of the present work is that RD can be used efficiently to enhance the selectivity of C 8 dimers, thereby avoiding the formation of trimers and tetramers. The use of polar components (such as water or alcohols), as selectivity enhancers, is not necessary.
Central European Journal of Energetic Materials, 2016
The main hurdle for the estimation of the purity of 1,3,5-triamino-2,4,6trinitrobenzene (TATB) is... more The main hurdle for the estimation of the purity of 1,3,5-triamino-2,4,6trinitrobenzene (TATB) is its insolubility in most of the known organic solvents. In the conventional method, TATB is digested with steam in a modified Kjeldahl digester and the ammonia evolved is estimated quantitatively. To do away with this cumbersome method, a simple, rapid HPLC technique using a reverse phase C-18 column has been established for quantitative determination of the purity of TATB. A sharp and symmetrical peak with a retention time of 2.92 min at 355 nm is obtained for pure TATB when the flow rate is 2.0 mL/min. The linearity of the detector response has been studied with sample concentrations ranging from 10 to 50 mg/L. The method addresses two important issues of sample preparation and the precision of measurement. Unlike the previously reported HPLC techniques which mainly aimed at the detection of TATB, the present work is a validated account of a quantitative estimation of purity. Regular production batch samples have been assayed by this method and the results are compared with those obtained from the conventional analysis. The HPLC method is convenient and reliable for quality control of the product at the plant level.
ABSTRACT The solubility of ammonia in toluene has been measured at 398 K and at pressures up to 3... more ABSTRACT The solubility of ammonia in toluene has been measured at 398 K and at pressures up to 340 kPa using a static, synthetic and isochoric technique. The goal of the present study is to determine the equilibrium solubility of ammonia in toluene at a pressure and temperature regime that is relevant to the reaction conditions of amination of 1,3,5-trichloro-2,4,6-trinitrobenzene leading to the formation of 1,3,5-triamino-2,4,6-trinitro benzene. The ammonia solubility data in toluene were hitherto unavailable under these experimental conditions. The solubility data have also been compared with the result obtained from a direct sampling method. The results are in agreement with Krichevsky–Kasarnovsky equation. The Henry’s law constant at the reaction temperature has been determined.
The complexity and difficulty of determination of Multiple Steady States (MSS) in azeotropic and ... more The complexity and difficulty of determination of Multiple Steady States (MSS) in azeotropic and reactive distillation have remained a matter of concern for the development of a systematic and easily verifiable criterion for the detection and characterization of MSS. This has resulted in a plethora of methods that are either experimental or model-based in nature adapting different solution strategies. However, no single methodology is solely suitable for all systems. A sensible approach would be to apply together several solution methodologies for consistent and accurate solutions. It is then obviously desirable to have a framework that enables such a bouquet of tools to be used in an easy and efficient manner. In this paper, one such framework is proposed that relies on model based methodologies, and uses the process models and the property equations already present in the commercial simulators such as Aspen Plus and Aspen Hysys. A developed tool has also been demonstrated to study the sensitivity of the parameters incorporated together with the solution strategy while solving the system of equations representing the distillation column.
Industrial & Engineering Chemistry Research, 2014
A new synthesis and design method is developed for simple and complex hybrid reactive distillatio... more A new synthesis and design method is developed for simple and complex hybrid reactive distillation columns, to achieve desired selectivity in case of multireaction schemes involving multicomponent mixtures wherein, reactant is a saddle in the corresponding residue curve map. The developed methodology makes use of attainable region approach as well as combined graphical-simulation approach. We determine the surface of reactive stage compositions (SRSC) such that if the reaction takes place at any of the compositions that belongs to SRSC then the desired selectivity is ensured. Design guidelines have been formulated based on the number of compositions of the reactive species that appear in the equation of the SRSC, to identify appropriate hybrid RD configurations for the reaction scheme of interest. The method is illustrated using an industrially relevant example of intramolecular aldol condensation of cyclohexanone to achieve the desired selectivity toward 2-cyclohexylidene cyclohexanone. The results provide good initialization for rigorous simulation. The algorithm presented here can be applied to any number of components and can be directly applied to even multiazeotropic systems as well but is restricted to single reactant (i.e., single feed configurations) multireaction schemes with multiple products undergoing side reactions.
Thermal condition of the feed may be altered to reduce the reboiler duty. However, only a portion... more Thermal condition of the feed may be altered to reduce the reboiler duty. However, only a portion of the thermal energy given to the feed reduces the reboiler duty. By splitting the feed and altering the thermal condition of a part of the feed, it is possible to achieve reduction only in the reboiler duty (100% preheat efficiency). Based on the thermodynamic analysis of a distillation column, a methodology is developed to target split fraction of the feed for preheating to obtain reduction only in the reboiler duty.
h i g h l i g h t s Conceptual design of multi-side draw hybrid reactive distillation columns. Th... more h i g h l i g h t s Conceptual design of multi-side draw hybrid reactive distillation columns. The design procedure is a combination of graphical method and simulations. The algorithm typically generates multiple designs of desired selectivity. The developed algorithm can be applied directly to multi azeotropic systems. Methodology is illustrated for transesterification of dimethyl carbonate with ethanol.
Fischer-Tropsch synthesis can be advantageously carried out in reactive distillation (RD) mode. P... more Fischer-Tropsch synthesis can be advantageously carried out in reactive distillation (RD) mode. Parametric studies like the effect of reflux ratio, pressure, etc. have been reported in our earlier work [Srinivas et al. Ind. Eng. Chem. Res. 2009, 48, 4719-4730] using Aspen Plus. As an extension of this work, multiparameter sensitivity analysis is performed on a simple RD configuration without side-draws or side-coolers in Aspen Plus, retaining the kinetic and thermodynamic models used previously. A feasible solution space in terms of reflux ratio, pressure, and total catalyst loading is identified and possible reasons for the bounds observed are provided. Changes in the column configuration toward various objectives like maximum conversion, maximum gasoline yield, or selectivity, etc. are also investigated. Regions of interest corresponding to different objectives are represented on a Da-reflux ratio plot.
While Fischer-Tropsch synthesis (FTS) using coal and natural gas in conventional reactors is an a... more While Fischer-Tropsch synthesis (FTS) using coal and natural gas in conventional reactors is an almost well-established technology, the production of liquid hydrocarbons from syngas obtained from biomass is in its preliminary stages of commercialization in countries like Germany. With concerns about global warming and ways of disposing of CO2 being searched for, CO2 hydrogenation using FTS to liquid hydrocarbons can act as a CO2 sink. A brief review of FTS using CO2-rich syngas is given in this paper, looking at FTS as a technology that can help reduce global warming and as a process integration alternative. The reverse water gas shift (r-WGS) reaction is vital for CO2 hydrogenation. We have studied the effect of this using an FT kinetic model and have proposed a new flow sheet alternative for FTS using CO2-rich syngas. Simulations suggested that this new process gives better conversion of CO2. The product selectivity and yields from an FT plant are vital to make the process viable economically.
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Papers by Ranjan Malik