Simulation study of the production of biodiesel using feedstock mixtures of fatty acids in complex reactive distillation columns

Biodiesel can be produced from a number of natural, renewable sources, but vegetable oils are the main feedstocks. The current manufacturing biodiesel processes, however, have several disadvantages: expensive separation of products from the reaction mixture, and high costs due to relatively complex processes involving one to two reactors and several separation units. Therefore, to solve these problems, in recent years several researchers have developed a sustainable biodiesel production process based on reactive distillation. In this paper the production of biodiesel using feedstock mixtures of fatty acids is explored using reactive distillation sequences with thermal coupling. The results indicate that the complex reactive distillation sequences can produce a mixture of esters as bottoms product that can be used as biodiesel. In particular, the thermally coupled distillation sequence involving a side rectifier can handle the reaction and complete separation in accordance with process intensification principles.     

Retrofit of distillation columns in biodiesel production plants

Column grand composite curves and the exergy loss profiles produced by the Column-Targeting Tool of the Aspen Plus simulator are used to assess the performance of the existing distillation columns, and reduce the costs of operation by appropriate retrofits in a biodiesel production plant. Effectiveness of the retrofits is assessed by means of thermodynamics and economic improvements. We have considered a biodiesel plant utilizing three distillation columns to purify biodiesel (fatty acid methyl ester) and byproduct glycerol as well as reduce the waste. The assessments of the base case simulation have indicated the need for modifications for the distillation columns. For column T202, the retrofits consisting of a feed preheating and reflux ratio modification have reduced the total exergy loss by 47%, while T301 and T302 columns exergy losses decreased by 61% and 52%, respectively. After the retrofits, the overall exergy loss for the three columns has decreased from 7491.86 kW to 3627.97 kW. The retrofits required a fixed capital cost of approximately $239,900 and saved approximately $1,900,000/year worth of electricity. The retrofits have reduced the consumption of energy considerably, and leaded to a more environmentally friendly operation for the biodiesel plant considered.     

Synthesis and heat integration of thermally coupled complex distillation system

Based on stochastic optimization strategy and pinch technique, a method is proposed for optimal synthesis and heat integration of thermally coupled complex distillation column systems comprising simple columns, complex columns with side rectifier and/or side stripper as well as partially or fully thermally coupled (Petlyuk) columns with pre‐fractionators. Three example problems for five‐component mixtures separation have been solved and the optimized parameters and economic benefits of different optimal schemes have been analyzed and compared. The results demonstrate that the annual total cost in energy consumption and investment can be effectively reduced by using the heat‐integrated complex distillation configuration. The solutions of example problems also demonstrate that the proposed method is efficient for the heat‐integrated complex distillation synthesis problem. Copyright © 2009 John Wiley & Sons, Ltd.     

Enhancement of simultaneous hydrogen production and methanol synthesis in thermally coupled double-membrane reactor

Coupling the methanol synthesis with the dehydrogenation of cyclohexane to benzene in a co-current flow, catalytic fixed-bed double-membrane reactor configuration in order to simultaneous pure hydrogen and methanol production was considered theoretically. The thermally coupled double-membrane reactor (TCDMR) consists of two Pd/Ag membranes, one for separation of pure hydrogen from endothermic side and another one for permeation of hydrogen from feed synthesis gas side (inner tube) into exothermic side. A steady-state heterogeneous model is developed to analyze the operation of the coupled methanol synthesis. The proposed model has been used to compare the performance of a TCDMR with conventional reactor (CR) and thermally coupled membrane reactor (TCMR) at identical process conditions. This comparison shows that TCDMR in addition to possessing advantages of a TCMR has a more favorable profile of temperature and increased productivity compared with other reactors. The influence of some operating variables is investigated on hydrogen and methanol yields. The results suggest that utilizing of this reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the recuperative reactor.     

Thermodynamic analysis of syngas production from biodiesel via chemical looping reforming

In this study, thermodynamic analysis of the syngas production using biodiesel derived from waste cooking oil is studied based on the chemical looping reforming (CLR) process. The NiO is used as the oxygen carrier to carry out the thermodynamic analysis. Syngas with various H₂/CO ratios can be obtained by chemical looping dry reforming (CL-DR) or steam reforming (CL-SR). It is found that the syngas obtained from CL-DR is suitable for long-chain carbon fuel synthesis while syngas obtained from CL-SR is suitable for methanol synthesis. The carbon-free syngas production can be obtained when reforming temperature is higher than 700 °C for all processes. To convert the carbon resulted from biodiesel coking and operate the CLR with a lower oxygen carrier flow rate, a carbon reactor is introduced between the air and fuel reactors for removing the carbon using H₂O or CO₂ as the oxidizing agent. Because of the endothermic nature of both Boudouard and water-gas reactions, the carbon conversion in the carbon reactor increases with increased reaction temperature. High purity H₂ or CO yield can be obtained when the carbon reactor is operated with high reaction temperature and oxidizing agent flow.     

Hydrogen looping approach in optimized methanol thermally coupled membrane reactor

In this study, cyclohexane and hydrogen loop approach is proposed in optimized thermally coupled dual reactors in methanol production via Differential Evolution (DE) method. This new generation of thermally coupled membrane reactors uses simultaneously the advantages of hydrogen carrier characteristic and multifunctional reactors. This configuration is named thermally coupled dual methanol reactor (TCDMR). In the first reactor, cyclohexane dehydrogenation reaction is coupled with methanol production reactions. Cyclohexane is produced in the second reactor due to carrying all produced hydrogen from the first reactor to the second reactor for benzene hydrogenation reaction. The operating conditions of TCDMR are optimized via DE method and six decision variables are considered to investigate its performance. Since cyclohexane is produced continuously in the second reactor and enters the first reactor as the endothermic feed, the external cyclohexane injection rate is minimized, too. A comparison is made between the optimized TCDMR (OTCDMR), TCDMR and Thermally coupled methanol reactor (TCMR) and conventional methanol reactor (CMR). The modeling results demonstrate the superiority of OTCDMR to all previously proposed configurations. A continuous system is achieved and slight amount of exterior cyclohexane injection rate (3.6 mol h⁻¹) is required in this configuration. Furthermore, the hydrogen storage problem is solved by this configuration owing to simultaneous hydrogen production and utilization. In addition, produced benzene in OTCDMR is about 10% of the one in TCMR which can be appealing from the environmental viewpoint.     

Mathematical simulation and optimization of methanol dehydration and cyclohexane dehydrogenation in a thermally coupled dual-membrane reactor

Thermally coupling of endothermic and exothermic reactions in a membrane reactor improves thermal efficiency and production rate in the processes, reduces the size of reactors and decreases purification cost. This paper focuses on modeling and optimization of a thermally coupled dual-membrane reactor for simultaneous production of hydrogen, dimethyl ether (DME) and benzene. A steady state heterogeneous mathematical model is developed to predict the performance of this novel configuration. The catalytic methanol dehydration reaction takes place in the exothermic side that supplies the necessary heat for the catalytic dehydrogenation of cyclohexane to benzene in the endothermic side. Selective permeation of hydrogen and water vapor through the Pd/Ag and composite membranes are achieved by co-current flow of sweep gas through the membrane wall. The differential evolution method is applied to optimize the thermally coupled dual-membrane reactor considering the summation of DME and benzene mole fractions from reaction sides and hydrogen mole fraction in the permeation side as the main objectives. The optimization results are compared with corresponding predictions for an industrial methanol dehydration adiabatic reactor operated at the same feed conditions. Methanol conversion enhances about 5.5% in the optimized thermally coupled dual-membrane reactor relative to the conventional DME reactor. The results suggest that coupling of these reactions in the proposed configuration could be feasible and beneficial.     

Simulation analysis of methanol flash distillation circulation process in biodiesel production with supercritical method

High methanol-to-oil ratio is required to obtain a high conversion of oil for the production of biodiesel with supercritical methanol. Recovering the methanol of a stream issuing from a transesterification supercritical reactor by flash distillation instead of evaporation was analyzed. The one-stage and two-stage flash distillation processes were presented and compared. The difference of the recovery percentage of methanol of the above two flash processes is less than 0.5% and the methanol concentration in the vapor for the one-stage process decreases rapidly when feed temperature increases. The process in which the product of transesterification of soybean oil with supercritical methanol is cooled to an appropriate temperature (about 240°C) first and then flashed was put forward. The effect of cooling temperature, feed pressure and flash pressure on methanol concentration and recovery percentage was investigated. According to this study, when the feed pressure range is 15–30 MPa, the flash pressure equals 0.4 MPa, and cooling temperature range is 240°C–250°C, the recovery percentage of methanol is not less than 85%, and the concentration of the vapor in mass fraction of methanol is approximately 99%. Thus, the vapor leaving the flash tank can be directly circulated to the transesterification reactor.     

Hydrogen rich gas production by the autothermal reforming of biodiesel (FAME) for utilization in the solid-oxide fuel cells: A thermodynamic analysis

The thermodynamics of the autothermal reforming (ATR) of biodiesel (FAME) for production of hydrogen is simulated and evaluated using Gibbs free minimization method. Simulations are performed with water-biodiesel molar feed ratios (WBFR) between 3 and 12, and oxygen-biodiesel molar feed ratio (O_XBFR) from 0 to 4.8 at reaction temperature between 300 and 800 °C at 1 atm. Yields of H₂ and CO are calculated as functions of WBFR, O_XBFR and temperature at 1 atm. Hydrogen rich gas can be produced by the ATR of biodiesel for utilization in solid-oxide fuel cells (SOFCs). The best operating conditions for the ATR reformer are WBFR≥9 and O_XBFR = 4.8 at 800 °C by optimization of the operating parameters. Yields of hydrogen and carbon monoxide are 68.80% and 91.66% with 54.14% and 39.2% selectivities respectively at the above conditions. The hydrogen yield from biodiesel is higher than from unmodified oils i.e., transesterification increases hydrogen yield. Increase in saturation of the esters, results in increase in methane selectivity, while an increase in unsaturation results in a decrease in methane selectivity. Increase in degree of both saturation and unsaturation of esters, increases coke selectivity. Similarly an increase in the linoleic content of esters, increases coke selectivity.     

Techno-economic comparison of three biodiesel production scenarios enhanced by glycerol supercritical water reforming process

In this study, techno-economic comparison of three different biodiesel production scenarios integrated with glycerol supercritical water reforming (SCWR) process to produce electricity is conducted. In the first scenario, biodiesel is synthesized from acid-pretreated waste cooking oil (WCO) in the presence of alkali catalyst. In the second scenario, biodiesel is obtained from WCO by acid catalyst. In the third scenario, biodiesel is derived from WCO using acid catalyst, followed by hexane extraction of the produced methyl esters. The glycerol evolved from all the above-mentioned pathways is then subjected to the SCWR process in order to produce hydrogen. The produced hydrogen is then combusted to provide thermal energy required by biodiesel production and purification processes as well as to generate electricity. All the developed scenarios are modeled and simulated in Aspen HYSYS software environment. In order to simplify the simulation process, canola-based WCO is considered as triolein with 6 wt% oleic acid (free fatty acid) and, accordingly, the prepared biodiesel is taken into account as methyl oleate. In order to compare the economic profitability of the developed approaches, several economic indicators including net present value (NPV), internal rate of return (IRR), payback period (PBP), discounted payback period (DPBP), and return on investment (ROI) are used. A sensitivity analysis is also carried out to show how variations in feedstock, biodiesel, and electricity prices can affect the NPV of the developed scenarios. According to the results obtained, the highest IRR and ROI values as decision-making parameters are obtained for the first scenario, manifesting its suitability from the techno-economic viewpoint. The economic indicators of the second scenario are also acceptable and very close to the first approach. Overall, upgrading glycerol into hydrogen using SCWR process appears to be an attractive strategy for enhancing the economic viability of biodiesel production plants.     

Modeling and parameters fitting of chemical and phase equilibria in reactive systems for biodiesel production

Biodiesel, a non-toxic biodegradable fuel from renewable sources such as vegetable oils, has been developed in order to reduce dependence on crude oil and enable sustainable development. The knowledge of phase equilibrium in systems containing compounds for biodiesel production is valuable, especially in the purification stage of the biodiesel. Nonetheless, the refining process of biodiesel and by-products can be difficult and can elevate the production costs considerably unless it has an appropriate knowledge about the phase separation behavior. In addition, the transesterification reaction yield for producing biodiesel depends upon several operation parameters e.g. the feed molar ratio oil-to-alcohol and the temperature. These parameters were analyzed through a thermodynamic analysis by direct Gibbs energy minimization method in this paper, with the purpose of calculating the chemical and phase equilibrium of some mixtures containing compounds found in biodiesel production. For this, optimization techniques associated with the GAMS^® 2.5 software were utilized and the UNIQUAC and NRTL models were applied to represent the non-idealities of the liquid phases. Also, binary interaction parameters of studied compounds were correlated for NRTL and UNIQUAC models by using the least squares principle. The results showed that the use of optimization techniques associated with the GAMS software are useful and efficient tools to calculate the chemical and phase equilibrium by minimizing the Gibbs energy. Moreover, a good agreement was observed in cases in which calculated data were compared with experimental data.     

Residue curves map analysis for tert-amyl methyl ether synthesis by reactive distillation in kinetically controlled conditions with energy-saving evaluation

Distillation is a largely used separation operation, but at the same time it is intensively energy consuming. Distillation columns need huge amount of energy due to evaporation steps involved; more than half of the process heat distributed to plant operations ends up in the reboilers of distillation columns. ∞/∞ analysis is a framework that allows studying distillation systems, checking the feasibility, detecting multiple steady states and getting the influence of the distillate flow rate and recycle streams on purities in early stage of process design. Also, ∞/∞ analysis is useful to evaluate new alternatives for existing processes and to propose energy-efficient alternatives by process integration. Process intensification is an issue of constant interest, providing strategies to develop more effective and cheaper technologies with lower environmental impact. The originality of this paper lies in the applicability of this framework to kinetically controlled reactive distillation including hybrid systems. TAME synthesis is used as an illustrative example. Energy savings obtained by using reactive distillation are evaluated comparing with the traditional system consisting of reactor and distillation columns. The solution proposed, subsequent to the validation by rigorous simulation, offers a 20% decrease in the number of stages and a reboiler energy saving of 10%.     

Hydrogen as an energy carrier: A comparative study between decalin and cyclohexane in thermally coupled membrane reactors in gas-to-liquid technology

Due to proposing hydrogen as the main energy carrier, technologies including production, storage and utilization of hydrogen have attracted increasing attention recently. Regarding this, the feasibility of decalin as a promising hydrogen carrier is investigated in this study. The performance of decalin thermally coupled membrane reactor (DCTCMR) is compared with cyclohexane thermally coupled membrane reactor (CTCMR) for Fischer-Tropsch synthesis (FTS) in gas-to-liquid (GTL) technology. Some important parameters such as hydrogen production rate, H₂ recovery yield, exothermic and endothermic temperature profiles and etc. are considered as criteria to recognize the most appropriate configuration. A comparison between the modeling results of two coupled configurations shows that DCTCMR is superior to CTCMR owing to achieving remarkably higher hydrogen production (seventeen times) compared with CTCMR. Furthermore, considerably higher H₂ recovery yield (about twelve times) and faster dehydrogenation reaction rate in DCTCMR than CTCMR proposes decalin as one of the best hydrogen carriers. This study demonstrates the superiority of DCTCMR to CTCMR owing to achieving remarkably higher hydrogen production rate, H₂ recovery yield and recognizing decalin as an appropriate hydrogen carrier.     

A novel integrated, thermally coupled fluidized bed configuration for catalytic naphtha reforming to enhance aromatic and hydrogen productions in refineries

In the recent years, refineries have focused on developing new ways to gain more from their asset utilization owing to increasing demand for high octane gasoline. In this regard, a thermally coupled fluidized bed naphtha reactor (TCFBNR) is proposed in this study. The first and the second reactors of a conventional catalytic naphtha reactor configuration (CR) are substituted by thermally coupled fluidized bed reactors. In this novel configuration, naphtha reforming reactions which are highly endothermic are coupled with the exothermic hydrogenation of nitrobenzene to aniline. Some drawbacks of CR such as pressure drop, internal mass transfer limitation and radial gradient of concentration and temperature are successfully solved in this novel configuration. In addition to some mentioned advantages of this novel configuration, TCFBNR configuration enhances the aromatic production rate about 20.54% and 7.13% higher than CR and TCNR, respectively. Also, the TCFBNR is capable to enhance hydrogen production rate in the shell side, the aniline flow rate in the tube section and simultaneously improves the thermal behavior of endothermic side and reduces the undesirable temperature drop. The modeling results of TCFBNR is compared with the results of CR and thermally coupled fixed-bed naphtha reactor (TCNR). These studies provide a good initial insight for some modifications and revamping of the old facilities with more efficient ones.     

Simultaneous production of ultrapure hydrogen and gasoline in a novel thermally coupled double‐membrane reactor

In this study, simultaneous production of ultrapure hydrogen and gasoline via a novel catalytic fixed‐bed double‐membrane reactor with co‐current flow was investigated, mathematically. The thermally coupled double‐membrane reactor (TCDMR) consists of two Pd/Ag membranes, one for separation of pure hydrogen from endothermic side and another one for permeation of hydrogen from endothermic into exothermic side. Ammonia decomposition reaction is coupled with the Fischer–Tropsch Synthesis (FTS) reaction to improve the heat transfer between endothermic and exothermic sides. Some of the produced hydrogen via ammonia decomposition reaction is utilized in FTS reaction, and the other is extracted and stored. A steady‐state heterogeneous model of the two fixed beds predicts the performance of this novel configuration. The achieved results of this simulation have been compared with the results of the conventional fixed‐bed reactor (CR) at identical process conditions. The simulation results show 67.34% hydrogen production in the permeation side and 32.66% hydrogen utilization in the exothermic side for compensates of hydrogen lack in the FTS reaction through the TCDMR configuration. Moreover, the gasoline yield in TCDMR increases about 18.42% because of a favorable profile of temperature along the TCDMR in comparison with the one in CR. Therefore, this approach utilizes and produces large amounts of pure hydrogen and decreases environmental impacts owing to ammonia emission. Copyright © 2011 John Wiley & Sons, Ltd.     

Performance evaluation of artificial neural network coupled with generic algorithm and response surface methodology in modeling and optimization of biodiesel production process parameters from shea tree (Vitellaria paradoxa) nut butter

This work investigated the potential of shea butter oil (SBO) as feedstock for synthesis of biodiesel. Due to high free fatty acid (FFA) of SBO used, response surface methodology (RSM) was employed to model and optimize the pretreatment step while its conversion to biodiesel was modeled and optimized using RSM and artificial neural network (ANN). The acid value of the SBO was reduced to 1.19 mg KOH/g with oil/methanol molar ratio of 3.3, H₂SO₄ of 0.15 v/v, time of 60 min and temperature of 45 °C. Optimum values predicted for the transesterification reaction by RSM were temperature of 90 °C, KOH of 0.6 w/v, oil/methanol molar ratio of 3.5, and time of 30 min with actual shea butter oil biodiesel (SBOB) yield of 99.65% (w/w). ANN combined with generic algorithm gave the optimal condition as temperature of 82 °C, KOH of 0.40 w/v, oil/methanol molar ratio of 2.62 and time of 30 min with actual SBOB yield of 99.94% (w/w). Coefficient of determination (R²) and absolute average deviation (AAD) of the models were 0.9923, 0.83% (RSM) and 0.9991, 0.15% (ANN), which demonstrated that ANN model was more efficient than RSM model. Properties of SBOB produced were within biodiesel standard specifications.     

Investigation of green hydrogen production and development of waste heat recovery system in biogas power plant for sustainable energy applications

In this study, biogas power production and green hydrogen potential as an energy carrier are evaluated from biomass. Integrating an Organic Rankine Cycle (ORC) to benefit from the waste exhaust gases is considered. The power obtained from the ORC is used to produce hydrogen by water electrolysis, eliminate the H₂S generated during the biogas production process and store the excess electricity. Thermodynamic and thermoeconomic analyses and optimization of the designed Combined Heat and Power (CHP) system for this purpose have been performed. The proposed study contains originality about the sustainability and efficiency of renewable energy resources. System design and analysis are performed with Engineering Equation Solver (EES) and Aspen Plus software. According to the results of thermodynamic analysis, the energy and exergy efficiency of the existing power plant is 28.69% and 25.15%. The new integrated system's energy, exergy efficiencies, and power capacity are calculated as 41.55%, 36.42%, and 5792 kW. The total hydrogen production from the system is 0.12412 kg/s. According to the results of the thermoeconomic analysis, the unit cost of the electricity produced in the existing power plant is 0.04323 $/kWh. The cost of electricity and hydrogen produced in the new proposed system is determined as 0.03922 $/kWh and 0.181 $/kg H₂, respectively.