6 Thermally coupled reactors for methanol synthesis - An exergetic approach

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1 6 Thermally coupled reactors for methanol synthesis - An exergetic approach 6.1 Introduction An alternative to the petroleum fuels is today's need due to their impact on global economy and depletion of sources. Crude oil and natural gas reserves are located in politically unstable regions hence becomes a threat to nation s energy security. There are various alternate fuels like ethanol, methanol, hydrogen, coal gas etc. emerged as promising one. Due to high octane number i.e methanol can be mixed in gasoline. Dimethyl ether is produced by dehydration of methanol which can be used as diesel fuel substitute due to high cetane number i.e. 55. Though today methanol is produced by using natural gas, renewable sources are also available which can be transformed into synthesis gas. Biomass, municipal waste, industrial waste and carbon dioxide are the renewable sources for the production of methanol. Apart from fuel, methanol is also used as hydrogen carrier in fuel cell, in production of biodiesel, feedstock for formaldehyde, acetic acid, olefin etc. In the present study exergy analysis of various thermally coupled reactors are carried out. Methanol synthesis is exothermic reaction and dehydrogenation of cyclohexane or methyl cyclohexane is endothermic reaction. Organic chemical hydrides are prominent source of hydrogen because they consisting of 6-8 % (wt) hydrogen. It can also act as hydrogen storage to produce hydrogen without emitting pollutants (Kumar et. al., 2009). 6.2 Production of Methanol Feed for methanol is synthesis gas, which contains carbon monoxide, carbon dioxide and hydrogen. Natural gas is used worldwide for the production of synthesis gas. It is carried out in two steps production of synthesis gas and synthesis of methanol. Natural gas is desulfurized to avoid catalyst poisoning and then fed to the catalytic reformer with steam. Conventional steam reforming is a widely practiced method for synthesis gas production.

2 Synthesis gas is cooled and compressed before sending to methanol synthesis reactor. Following reactions takes place in reformer 1. CH 4 + H 2 O CO + 3 H 2 ΔH R,298 = +206 kj/mol 2. CO + H 2 O CO 2 + H 2 ΔH R,298 = - 41 kj/mol Methanol synthesis is exothermic and accomplished by following reactions Hydrogenation of carbon monoxide 3. CO + 2H 2 CH 3 OH ΔH R,298 = kj/mol Hydrogenation of carbon dioxide 4. CO 2 + 3H 2 CH 3 OH + H 2 O Δ H R,298 = kj/mol Reverse water gas shift reaction 5. CO 2 + H 2 CO + H 2 O Δ H R,298 = kj/mol According to Le Chatelier's principle, higher methanol yield is obtained at higher pressure and lower temperature. A commercial CuO/ZnO/Al 2 O 3 catalyst is used for synthesis reaction. The chemical equilibrium limits the conversions. Methanol synthesis reactor is multi-tubular reactor working like shell and tube heat exchanger. The catalyst is placed in tubes and water is placed in shell. Heat generated in the reaction is taken out by boiling water to produce steam. The temperature in the reactor is controlled by steam pressure (Fundamentals of methanol synthesis, 2015). A temperature rise must be controlled in methanol synthesis reactor to get good equilibrium value as well as to control catalyst activity. Maximum conversion of CO and CO 2 can give maximum methanol yield. Product gases from reactor come out at K which exchange heat with incoming synthesis gas. Further cooling is required before sending product gas into the separator. Crude methanol is separated from the unreacted gas. This gas is compressed and recycled back to the reactor. A small amount of gas is purged to maintain the concentration of inert components in the reactor. The crude methanol is distilled to get pure methanol (Fig.6.1) Chapter-6 Page 143

3 Fig. 6.1 Production process of methanol 6.3 Production of Hydrogen Steam methane reforming (SMR) process is most commercially used process for the hydrogen production. A reformer is used in for synthesis reaction. Methane and steam are used as feed to the reformer and heat is provided to the endothermic reaction by burning extra methane along with recycle gas from the separator (Fig.6.2). Fig. 6.2 Production process of hydrogen Water gas shift reaction takes place in gas shift reactor for further hydrogen yield. Reaction 1 take place in the reformer and reaction 2 takes place in water gas shift reactor. Chapter-6 Page 144

4 Energy produced by combustion of methane is the source of heat for the reformer. Though water gas shift reaction is exothermic, heat produced cannot be utilized in the process due to low temperature. 6.4 Methanol Synthesis Reactor Synthesis reactor is a core of methanol production process. Conversion of synthesis gas per pass is low due to equilibrium nature of the reaction. The Higher temperature is required at the initial part of the reactor for higher kinetic constant and lower temperature is required at end part to increase thermodynamic equilibrium conversion value. (Fig. 6.3) (Khademi et al., 2009a) Fig. 6.3 Temperature profile in methanol reactor (Kordabadi and Jahanmiri, 2005) Methanol reactor is a multi-tubular reactor having exothermic reaction inside tubes and water heating in the shell as shown in Fig For the better performance of reactor, the entropy generation should be minimized. Various reactor designs have been proposed during last decade. Thermally coupled reactor is used to utilize heat generated by the exothermic reaction by an endothermic reaction. Points to be considered while designing of the reactor is temperature and pressure difference between endothermic and exothermic reaction, phase of both reactions and rate of reaction. When exothermic Chapter-6 Page 145

5 reactions are coupled with endothermic reaction hot spots may be produced due to complete conversion in exothermic reaction which can lead to catalyst deactivation Fig. 6.4 Conventional methanol reactor Following types of reactors are classified by Rahimpour et al. for coupling exothermic and endothermic reactions (Rahimpour et al., 2012). 1. Direct coupled adiabatic reactor: Exothermic and endothermic reactions are taking place in the same reaction zone. Mass and energy is directly exchanged in the reactor. This reactor can be used to couple exothermic reactions with an endothermic reaction like oxidation and reduction, hydrogenation and dehydrogenation, hydration and dehydration, etc. 2. Regenerative coupling: Thermal energy produced by the exothermic reaction is stored in regenerative bed which is utilized by an endothermic reaction. It will lead to efficient heat recovery. This type of reactor is used for producer gas. An exothermic reaction is carried out in blow period while the endothermic reaction is carried out in run period. Direct interchange of energy and mass is possible in this reactor also. Chapter-6 Page 146

6 3. Recuperative coupling: Recuperative reactors are used to conduct exothermic and endothermic reactions simultaneously. Both reaction compartments are separated by a metal wall. Only energy interchange is possible in this scheme. The material can be exchanged by applying membrane system. Recuperative reactors are subdivided into two types Without membrane reactor and a membrane reactor. Without membrane reactors are shell and tube, channels in monolith or micro reactors. Each reactor has its own advantage. In membrane reactor energy is transferred indirectly but mass can be transferred directly. Conversion in membrane reactor can be increased for reversible reaction by removing one on the product. The membrane is popularly used in dehydrogenation reactions for separation of hydrogen from production mass. It is more useful if one side produces hydrogen and another side consumes it. 6.5 Recuperative Reactor for Methanol Synthesis Conventional methanol reactor (CMR) converts the heat of exothermic reaction into steam. Steam is utilized either in a plant or for the production of electricity. Exported power is only 2% of input energy (Rosen and Dincer, 1988). Almost 46% energy is lost through cooling water. Production of methanol can be increased if heat energy available in the reactor is utilized judiciously instead of making steam. CMR product stream contains only 5% methanol due to lower conversion of synthesis gas (Fig.6.5). Energy integration in the reactor can increase production of either methanol or product from the endothermic reaction. Dehydrogenation reaction is chosen as an endothermic reaction. Various reactor schemes are proposed by Rahimpour and his group for methanol synthesis. Chapter-6 Page 147

7 Fig. 6.5 Methanol concentration in the reactor (Kordabadi and Jahanmiri, 2005) Thermally Coupled Reactor (TCR) TCR operates on the same principle as that of a conventional reactor, but instead of boiling water in shell side dehydrogenation of the aromatic compound is carried out as shown in Fig 6.6. Fig. 6.6 Thermally coupled reactor Chapter-6 Page 148

8 Both exothermic and endothermic reactions are carried out in the catalyst bed. Differential Evolution method is used for optimization of the problem and calculates a best fit score for the reactor. Methanol concentration at reactor outlet is objective function and other parameters can be varied within the available limit. Khademi et al. (2009a) optimized methanol and benzene production from cyclohexane in synthesis reactor. Cyclohexane dehydrogenation consumes heat at a higher temperature in the first part and then reducing the temperature at end part favoring thermodynamic equilibrium. It will give similar temperature profile as that of CMR. Dehydrogenation of methyl cyclohexane is another endothermic reaction coupled with methanol synthesis. (Rahimpour et al.,2011a) Thermally Double Coupled Reactor (TDCR) TDCR consist of three concentric tubes wherein the endothermic reaction is carried out in the middle tube and exothermic reaction is in outer and inner tube. A multi-tubular assembly of TDCR is shown in the Fig Fig. 6.7 Thermally double coupled reactor Chapter-6 Page 149

9 Endothermic reaction receives heat from both exothermic reactions. Three different reactions are carried out in three tubes, out of which one reaction is endothermic. Catalyst required for these reactions are packed in tubes. Inlet composition of synthesis gas is same as CMR and composition of other reactants are selected according to the kinetics of the reaction. In TDCR heat received by the endothermic reaction is more compared to other thermally coupled reactors. Dehydrogenation reaction is coupled to methanol synthesis to produce hydrogen as one of the product. Dimethyl ether (DME) synthesis is preferred as a second exothermic reaction. In TDCR hydrogen production can be more than TCR due to extra heat available from DMR synthesis (Farniaei et al., 2014) Membrane Coupled Reactor (MCR) Use of membrane for permeation of hydrogen helps to increase the yield of dehydrogenation traction. It will shift the equilibrium of reversible reaction due to the removal of the product during the reaction. A schematic arrangement of MCR is shown in Fig Methanol synthesis reaction is a source of heat in the MCR as like CMR. Dehydrogenation of cyclohexane is the endothermic reaction in the second side. Argon is used as sweep gas in the third side that is separated by a semipermeable membrane to remove hydrogen. Heat is transferred from exothermic side to dehydrogenation reaction and hydrogen is transferred from endothermic side to permeate side. Pure hydrogen is produced from dehydrogenation reaction using a membrane. Two hydrogen perm-selective Pd-Ag membranes are used in thermally coupled double membrane reactor (TCDMR) on the exothermic and endothermic side each (Rahimpour et al., 2011b). Membrane at the exothermic side is used to remove hydrogen from methanol product gas and recycle it to synthesis gas feed increasing the concentration of hydrogen in it. It will shift reversible reaction in the forward direction and enhances the yield of methanol compared to TCR. Chapter-6 Page 150

10 Table.6.1 Various schemes of thermally coupled reactors for methanol synthesis Cyclohexane / Reactor type Exothermic reaction Endothermic reaction Methanol yield (%) Methyl cyclohexane conversion Reference (%) Conventional Methanol reactor Methanol synthesis (tube side) Steam production NA Khademi et al., 2009a Thermally coupled reactor Methanol synthesis (tube side) Dehydrogenation of cyclohexane (shell side) Khademi et al., 2009a Thermally coupled reactor Methanol synthesis (tube side) Dehydrogenation of methylcyclohexane (shell side) Rahimpour et al., 2011a Khademi et al., Thermally coupled membrane reactor Methanol synthesis (tube side) Dehydrogenation of cyclohexane (shell side) b; Khademi et al., 2010; Rahimpour and Pourazadi, 2011 Thermally coupled double membrane reactor Methanol synthesis (tube side) Dehydrogenation of cyclohexane (shell side) Rahimpour et al., 2011b Thermally double coupled two membrane reactor Methanol synthesis (inner tube side) DME synthesis (Outer tube) Dehydrogenation of cyclohexane (middle tube) Farniaei et al.,2014 Thermally double coupled reactor Methanol synthesis (inner tube side) DME synthesis (Outer tube) Dehydrogenation of cyclohexane (middle tube) Farniaei et al., 2014 Thermally double coupled reactor Methanol synthesis (inner tube side) DME synthesis (Outer tube) Dehydrogenation of methyl cyclohexane (middle tube) Samimi et al., 2014 Chapter-6 Page 151

11 Fig. 6.8 Thermally coupled membrane reactor In thermally double coupled two membrane reactor (TDCTMR), double coupled reactor with two membranes is used to separate water from methanol. One membrane placed near the center tube and another hydrogen perm selective membrane is used to remove hydrogen from exothermic reaction (Farniaei et al., 2014). Through this reactor we can achieve production of multiple reactant-product configurations, production of pure hydrogen and energy integration between exothermic and endothermic reaction. (Khademi et al., 2009b) These reactor configurations are yet to be commercialized fully but research is going on to find out the possibilities regarding the commercial implementation of these schemes in methanol process. In many exothermic processes heat is ultimately used to produce steam. If this steam is not required in the plant then it is converted into electricity. Losses in the steam system and turbines reduce useful output and most of the heat is wasted through cooling tower due to its low grade. Thermally coupled reactors can exchange heat instantly at the place by utilizing of heat in a better way than producing steam. Hydrogen is important industrial gas required in many processes and it is also acquiring place as a clean Chapter-6 Page 152

12 fuel. Due to storage issue its use as fuel is limited. Industrial hydrogen requirement is fulfilled by producing synthesis gas form methane. Thermally coupled reactors can produce almost 40-45% hydrogen consumed in methanol synthesis reaction. Cyclohexane and methyl cyclohexane can be used as a hydrogen carrier. Hydrogen produced in the endothermic side can be purified using membrane and used for the methanol production. Make up hydrogen and carbon dioxide are supplied to synthesis reactor along with hydrogen from the endothermic side. As there is market limitation for benzene and toluene production, this hydrogen source cannot fulfill entire requirement for methanol synthesis reaction but will be helpful to reduce consumption of natural gas. Table 6.1 shows various schemes of thermally coupled reactors used for methanol synthesis. 6.6 Exergy Analysis Irreversibility in the chemical reaction is major cause of exergy destruction. In exothermic reaction chemical exergy of reactant is converted into physical exergy in the form of heat. Part of it is lost due to unavoidable irreversibility in the reaction. Most of the exothermic processes utilize this heat in the plant itself in a usable form. As seen in the previous study of mono high pressure nitric acid process, heat is utilized to rise the temperature of expander gas and then to produce high pressure steam which is used in the turbine. Total heat available in the reactor cannot be used at one step hence it is exchanged at later stages in various heat exchangers. Exergy will go on reducing as temperatures reduce though energy is in considerable amount. At each stage of energy conversion process some amount of exergy is lost. Exergy loss in ammonia oxidation reactor is % of total exergy destruction of the plant (Mewada and Nimkar, 2015). In another exothermic process of ethylene oxide production, exergy destruction in reactor is 47% of total exergy destruction (Nimkar and Mewada, 2014) Heat released during methanol synthesis reaction is used for the production of steam. The temperature in the reactor is K and pressure is 7.7 MPa. Synthesis reaction takes place in tubes filled with CuO/ZnO/Al 2 O 3 catalyst and boiling water is circulated in shell side through steam drum as shown in Fig 6.4. If hydrogen from purge gas is separated and recycled back to the reactor, methanol yield can be increased. In TCDMR and TDCTMR hydrogen from the product gas is separated and recycled back to the reactor. In present Chapter-6 Page 153

13 study different types of thermally coupled reactors are analyzed based on exergy. Energy is directly transferred to the endothermic reaction that results in better utilization of exergy. Dehydrogenation reaction is carried at another side of synthesis reactor. The overall efficiency of SMR for hydrogen production is 67.35% (Boyano et al, 2011). Exergy analysis of methanol production process and hydrogen production process is shown in Table 6.2 and 6.3 respectively. Major exergy destruction takes place in the reformer due to combustion of methane in the combustor. Product hydrogen consists of 67% of input exergy mainly in the form of chemical exergy. About 6% exergy is lost in the cooling water and flue gas. Hydrogen produced in the thermally coupled reactor can be mixed with carbon dioxide from the reformer and send to second thermally coupled reactor. Another source of hydrogen is purge gas stream that is also sent to the second reactor. This scheme will increase overall methanol capacity of the plant. New plant layout is shown in Fig Fig.6.9 Proposed plant layout for methanol production Chapter-6 Page 154

14 Table 6.2 Exergy analysis of 100 TPD methanol plant Total Exergy Total Exergy Exergy Exergy Component Exergy Component CH Exergy PH (kw) CH (kw) PH (kw) (kw) (kw) (kw) Natural gas Methanol Steam Hydrogen Compressor Water Reformer Fuel Steam Air Flue Gas Electricity Cooling Water Total Total Exergy Destruction Table 6.3 Exergy analysis of 100 TPD hydrogen plant Exergy Total Exergy Total Exergy Exergy Component CH Exergy Component CH Exergy PH (kw) PH (kw) (kw) (kw) (kw) (kw) Methane Hydrogen Air Flue gas Reformer fuel Cooling water Water Electricity Total Total Exergy Destruction Conventional Methanol Reactor Exergy analysis of CMR is carried out for 100TPD methanol production. Heat given to boiling water during reaction through reactor length is 2420 kw. Steam of 2.9 MPa at K is produced from steam drum. Inlet composition of synthesis gas is kept same for all reactors shown in Table 6.4. Process parameters for reactor operation are shown in Table 6.5. The temperature at the endothermic side is lower to enable transfer of heat from Chapter-6 Page 155

15 exothermic side to endothermic side. Input exergy in the reactor is mainly chemical exergy of reactant. Chemical exergy of the product is always lower in an exothermic reaction. Data required for analysis is extracted from the respective work of the reactors cited in Table 6.1. Exergy given by exothermic reaction is kw and exergy of steam produced is kw. Exergy taken by steam is lower due to the temperature difference between boiling water and the temperature inside the tubes. Exergy destruction is 45% of the exergy given for steam generation. Table 6.4 Feed compositions for exothermic and endothermic reactions (Khademi et al., 2009a, Rahimpour et al., 2011a, Farniaei et al., 2014) Methanol DME Component Cyclohexane Methylcyclohexane synthesis synthesis (Mole Fraction) feed feed gas gas Methanol Carbon dioxide Carbon monoxide Water Hydrogen Nitrogen Methane Dimethyl ether Cyclohexane Methyl cyclohexane Argon Total Chapter-6 Page 156

16 Table 6.5 Inlet and outlet parameters in reactors (Khademi et al., 2009a, Rahimpour et al., 2011a, Farniaei et al., 2014) Exothermic side Endothermic side Reactor Inlet Outlet Pressure Inlet Outlet Pressure type temp (K) temp (K) (MPa) temp (K) temp (K) (Mpa) CMR TCR-CH TCR-MCH MCR TDCR Thermally Coupled Reactor Energy integration between exothermic reaction (methanol synthesis) and endothermic reaction (dehydrogenation of cyclohexane) are helpful to reduce exergy loss. The short distance between heat source and sink will result in efficient heat transfer. Inlet composition of synthesis gas is same as that of CMR. For comparison only, 100 TPD methanol production is taken as basis like in CMR. Benzene and hydrogen are produced in the dehydrogenation of cyclohexane. 7. C 6 H 12 C 6 H 6 + 3H 2 ΔH R,298 = kj/mol Cyclohexane in the feed at the endothermic side is diluted with argon shown in Table 6.4. The catalyst used for dehydrogenation is Pt/Al 2 O 3. Heat input in the reactor on the both side is available from feed gas heating. Total heat transferred in each section is a combination of heat in feed gas and heat of reaction. Cyclohexane conversion is 100 % in TCR and hydrogen production is 6.30 TPD, which is 41% of hydrogen required for methanol synthesis. Exergy destruction is kw compared to kw in CMR. When dehydrogenation of methyl cyclohexane is used as endothermic reaction synthesis gas feed must be increased by 27% to get 100 TPD of methanol. It increases chemical and physical exergy input in the reactor. Exergy destruction is 68.42% of exergy received from the exothermic reactor. Hydrogen production has come down to 4.87 TPD for this combination. Chapter-6 Page 157

17 6.6.3 Thermally Double Coupled Reactor TDCR provide more heat compared to TCR due to two exothermic reactions taking place in it. The endothermic side will receive heat from inside as well as from outside also because it is placed in between two concentric tubes (Fig.6.7). Heat given by DME reaction is more than methanol synthesis. DME production involves methanol synthesis reactions and dehydration of methanol. Inlet composition in DME synthesis side is shown in Table CH 3 OH CH 3 OCH 3 + H 2 O ΔH R,298 = kj/mol Physical exergy inlet into the reactor has heat and pressure component. Exergy destruction is 68% of the exergy provided by both exothermic reactions. Higher exergy destruction is due to the exchange of heat at different temperature regimes in the reactor at various sections. Inlet molar flow rate for both exothermic reactions are almost same. Hydrogen production is 20 TPD, which is almost 3.2 times more than TCR due to the availability of more heat Membrane Coupled Reactor Hydrogen gas is separated using perm-selective membrane in MCR. The reaction is favored by removing one the product i.e. hydrogen in dehydrogenation section. Total hydrogen production is 5.06 TPD, and almost 95% is recovered by using a membrane. Physical and chemical exergy is transferred to permeation side while transferring hydrogen. Exergy given by exothermic reaction is kw and exergy taken by the endothermic reaction is kw. 6.7 Conclusion Irreversibility in exothermic reactions is the major sources of exergy loss in the process. Irreversibility in the combustion of methane to provide heat for reforming is unavoidable in the present combustion system. Almost 18% of input exergy is lost in the reformer in SMR process. Exergy efficiency of the reformer is 87.3% and exergy destruction in reformer per Chapter-6 Page 158

18 ton of hydrogen is kw as shown in Table 6.6. This value will further increase to 557 kw when pure hydrogen is coming out as a product. Efficiency can be increased if losses in the reformer are reduced. Due to high temperature in the reformer it is difficult to integrate directly it with another reactor. Change in the hydrogen production route will give better results. Coupling of hydrogen production with exothermic methanol synthesis reaction reduces exergy losses. These two products have practical aspects for implementation in the existing plant or future plants. Table 6.6 Exergy analysis of various reactor of 100 TPD methanol production Reactor Type Conventional Methanol Reactor Thermally coupled reactor (Cyclohexane dehydrogenation) Thermally coupled reactor (methylcyclohexane dehydrogenation) Thermally Double coupled Reactor Membrane Coupled Reactor Reactor Exergy Efficiency (%) H 2 Production in Reactor (TPD) Exergy Exergy Exergy Destruction Destruction Destruction (kw) Per ton (kw) Per (kw) of CH 3 OH ton of H NA NA Steam Methane Reformer NA The heat required for the production of hydrogen is GJ/t in the reformer. It is far more than heat produced in methanol synthesis 2.21 GJ/t. Heat requirement for hydrogen production can be brought down up to GJ/t if dehydrogenation reaction is used. The temperature required for dehydrogenation is less than methanol synthesis that enables coupling of both reactions. As heat requirement for hydrogen production is 16 times higher than heat produced by synthesis reaction, dedicated hydrogen production facility is economically not feasible. Chapter-6 Page 159

19 25 Hydrogen production (TPD) TCR-CH TCR-MCH TDCR MCR Reactor type Fig Hydrogen production in 100 TPD methanol thermally coupled reactors Exergy efficiency (%) CMR TCR-CH TCR-MCH TDCR MCR SMR Reactor type Fig Exergy efficiency of various reactors Chapter-6 Page 160

20 Exergy destruction (kw/t of CH 3 OH) CMR TCR-CH TCR-MCH TDCR MCR Reactor type Fig Exergy destruction per ton of methanol in various reactors 1200 Exergy destruction (kw/t of H 2 ) TCR-CH TCR-MCH TDCR MCR SMR Reactor type Fig Exergy destruction per ton of hydrogen in various reactors Chapter-6 Page 161

21 Though methanol itself is emerging as a fuel for future its scope is totally dependent upon the availability of feedstock. Large capacity plants are using natural gas as feed stock; hence hydrogen production in thermally coupled reactor is limited by methanol production capacity of the plant. MCR with 100 TPD methanol production can produce 5 TPD of hydrogen. If more heat is added by another exothermic reaction keeping same methanol production capacity, hydrogen production can be increased by 4 times. TDCR can produce 20 TPD of hydrogen by using DME synthesis as another source of heat as shown in Fig Exergy destruction is more in TDCR due to the coupling of extra exothermic reaction. Exergy efficiency will reduce due to this loss as shown in Fig TCR-C6H12 is having highest exergy efficiency among all reactors followed by MCR. TDCR and TCR-MCH are having less efficiency because chemical exergy values are playing an important role in the reaction. In exothermic process chemical exergy of the product is always lower than reactants. In the case of MCH, reaction kinetics limits the conversion of methyl cyclohexane compared to cyclohexane. Exergy destruction per ton of methanol is 1.48 kw in MCR and 1.73 kw in TCR-CH (Fig.6.12) but for hydrogen production TCR-CH is a better candidate than MCR (Fig.6.13). Finally, it is concluded that TCR-CH and MCR are the best thermally coupled reactors on the basis of exergy analysis. These reactors can get the advantage of the heat generated by exothermic reaction in exergy efficient way than other reactors. Use of this reactor will reduce the number of equipments for the production of methanol and hydrogen, results saving in capital cost. Equilibrium conversion can be enhanced by keeping lower output temperature. Along with methanol it produces hydrogen that is valuable industrial gas and future fuel. Though hydrogen production capacity cannot be matched as per SMR, it can be advantages to use produced hydrogen as make up quantity. Chapter-6 Page 162

22 References Boyano, A., Blanco-Marigorta, A.M., Morosuk, T. and Tsatsaronis, G (2011). Exergoenvironmental analysis of a steam methane reforming process for hydrogen production, Energy, Vol. 36, pp Farniaei, M., Abbasi, M., Rasoolzadeh, A. and Rahimpour, M.R. (2014) Performance enhancement of thermally coupling of methanol synthesis, DME synthesis and cyclohexane dehydrogenation processes: Employment of water and hydrogen permselective membranes via different recycle streams, Chemical Engineering and Processing, Vol, 85, pp Farniaei, M., Abbasi, M., Rahnama, H. and Rahimpour, M.R. (2014) Simultaneous production of methanol, DME and hydrogen in a thermally double coupled reactor with different endothermic reactions: Application of cyclohexane, methylcyclohexane and decalin dehydrogenation reactions, Journal of Natural Gas Science and Engineering, Vol 19, pp Fundamentals of methanol synthesis available at PSESSID=c9ngo2ijq0pbon5n1jgd2d2tr2 (accessed on 12/03/2015) Khademi, M. H., Setoodeh, P., Rahimpour, M.R. and Jahanmiri, A. (2009a) Optimization of methanol synthesis and cyclohexane dehydrogenation in a thermally coupled reactor using differential evolution (DE) method, International Journal of Hydrogen Energy, Vol. 34, No. 16, pp Khademi, M.H., Jahanmiri, A. and Rahimpour, M.R. (2009b) A novel configuration for hydrogen production from coupling of methanol and benzene synthesis in a hydrogen-permselective membrane reactor. International Journal of Hydrogen Energy, Vol. 34, pp Khademi, M.H., Rahimpour, M.R. and Jahanmiri, A. (2010) Differential evolution (DE) strategy for optimization of hydrogen production, cyclohexane dehydrogenation and methanol synthesis in a hydrogen-permselective membrane thermally coupled reactor, International Journal of Hydrogen Energy, Vol. 35, pp Kordabadi, K., and Jahanmiri A.(2005) Optimization of methanol synthesis reactor using genetic algorithms, Chemical Engineering Journal, Vol. 108, No. 3, pp Kumar, S., Gaba, T. and Kumar, S. (2009) Simulation of Catalytic Dehydrogenation of Cyclohexane in Zeolite Membrane Reactor, International Journal of Chemical Reactor Engineering, 7(Article A13): DOI: / Mewada, R.K. and Nimkar, S.C. (2015). Minimization of exergy losses in mono high pressure nitric acid process, International Journal of Exergy, Vol. 17, No.2, pp Chapter-6 Page 163

23 Nian, W.C. and You, F. (2013). Design of methanol plant, available at (accessed on 01/04/2015) Nimkar, S.C. and Mewada, R.K.(2014) An overview of exergy analysis for chemical process Industries,.International Journal of Exergy, Vol. 15, No.4, pp Rahimpour, M.R., Dehnavi, M.R., Allahgholipour, F., Iranshahi, D. and Joker, S.M. (2012) Assessment and comparison of different catalytic coupling exothermic and endothermic reactions: A review, Applied energy, Vol. 99, pp Rahimpour, M.R. and Pourazadi, E. (2011) A comparison of hydrogen and methanol production in a thermally coupled membrane reactor for co-current and countercurrent lows, International Journal of Energy Research, Vol. 35, No. 10, pp Rahimpour, M.R., Rahmani, F., Bayat, M. and Pourazadi, E. (2011b) Enhancement of simultaneous hydrogen production and methanol synthesis in thermally coupled double-membrane reactor, International Journal of Hydrogen Energy, Vol. 36, pp Rahimpour, M.R., Vakili, R., Pourazadi, E., Bahmanpour, A.M. and Iranshahi, D. (2011a) Enhancement of hydrogen production via coupling of MCH dehydrogenation reaction and methanol synthesis process by using thermally coupled heat exchanger reactor, International Journal of Hydrogen Energy, Vol. 36, pp Rosen, M.A. and Scott, D.S. (1988). Energy and exergy analyses of a production process for methanol from natural gas, International Journal of Hydrogen Energy, Vol. 13, No. 10, pp Chapter-6 Page 164