A Project report on
Master of Engineering
Charuhas Yogesh Patil L20447965
Ashwin Kumar Jajala L20455802
Meghana Faltane L20431327
Jamil Jabr L20457743
Under the Guidance of
Dr. James Henry
DEPARTMENT OF CHEMICAL ENGINEERING
Georgius Agricola explained a process on retrieving gold from gold ores in one of his book in 16th century. The process was completely related to stirrers. The vision for process of and for chemical industry was then understand by the world. This process was not really intensification. The intensification was followed later as the modification of previous process and newer process is developed. The PI got recognition in 1995 at first International Conference on Process Intensification in the Chemical Industry.
Process intensification (PI) is a chemical and process design to approach a generously smaller, cleaner, secure and more vitally productive process innovation. The idea of PI includes moving away from large scale reactions towards stream reactors in which the genuine volume is very small. PI is a change made to the procedure to influence in a smaller volume for a similar execution.
According to Cross and Ramshaw (1986) “PI is a strategy of reducing the size of a chemical plant needed to achieve a given production objective”.
In recent years PI has made a massive academic interest as a potential for technical/ process improvement, to meet the increasing needs for sustainable manufacturing. A range of enhanced operations developed in industrial and academic field, creates a massive number of options to probably improve the procedure but to look in to the set of feasible options for PI in which the most effective way can be located which takes wide spread resources. Hence, a process synthesis device to obtain PI, would potentially assist in the assessment and generation of PI options. Presently, many processes design tools which focuses on a particular PI task exists.
According to Stankiewicz and Moulijn (2000), PI can be divided into two areas:
Process Intensifying equipment, which are special designs that optimize critical parameters (e.g., heat transfer, mass transfer), and
Process Intensifying methods, where multiple processing steps are integrated into a single unit operation or alternative energy sources are used.
Figure 1: Process intensification and its components
Process intensification is broadly classified in to:
Process intensifying equipment:
Process intensifying tools offer many advantages to a chemical process industry where mass and heat transfer are highly significant. Chemical reactions are also dependent on temperature in many process industries.
Examples: Noval reactors, intensive mixing, heat and mass transfer devices.
Process intensifying methods:
Process intensifying methods fall in to three categories:
Integration of reaction into multifunctional reactors, development of new hybrid separation and use of different source of energy for processing.
Figure 2: Process intensification: Utilization of process integration
In chemical process industry, enhancement in environmental and economic sector are required for new as well as present process. PI plays a very important role in attaining the desired enhancement in processing options through the strategies that contains extra sustainable alternatives that is hybrid unit equipment.
Barriers for PI:
The primary focus of the R&D in chemical companies is on the new product rather than that on new methods to synthesize. Processing techniques and developing equipment was ignored by chemical manufacturers. Hence chemical companies are not keen on PI.
On industrial scale mini equipment’s and method are yet proven. No companies are keen to take risk in the application of the equipment or methods that have not been tested on full scale.
The industrial chemical engineers are also not yet familiar with PI. They are not aware of developing types of equipment and processing methods. It is because PI is not a part of chemical engineering curricula.
The methodology for modern process development from the laboratory to commercial scale are often missing. Any new developing chemical processes will only stick to standard available methods.
Advantages of PI:
In Petroleum refining area, sulfur naturally exists as an impurity in fossil fuels. Sulfur dioxide is released from sulfur when fuels are burned which causes air pollutant as a result it is responsible for several respiratory problems in humans and acid rain. Several environmental policies have increased to restrain sulfur dioxide emissions, forcing the removal of sulfur from fuels and gases in the refineries. The cost of removal of sulfur from petroleum and gases is very high. Sulfur is present as hydrogen sulfide and sulfur containing organic compounds in natural gas and petroleum respectively. This sulfur is converted in to hydrocarbons and h2s during the removal process called hydrodesulfurization. This process uses catalytic oxidation and partial combustion to convert 97% of H2S to sulfur. This process is widely used and well established.
Hydrodesulfurization (HDS) is a catalytic technique which is used in Petroleum and Refining industries to remove sulfur from natural gas and its derivative products which includes gasoline, jet fuel, diesel fuel, gas oil and naphtha. Sulfur removal is important in order to decrease the sulfur dioxide emissions from the combustion of those fuels in industries, aircrafts, energy plants, automobiles etc. Another essential reason for eliminating sulfur from the intermediate product naphtha streams inside a refinery is that sulfur, even in an extremely low concentrations, in the catalytic reforming gadgets that are used to upgrade the naphtha stream, poisons the noble metal catalyst platinum and rhenium.
Hydrogenation of sulfur elements affects in the formation of undesirable, poisonous gaseous hydrogen sulfide. The industrial hydrodesulfurization process encompass services further capture and removal of hydrogen sulfide gas. In refineries, the hydrogen sulfide gas is then consequently changed in to byproduct elemental sulfur.
Desulfurization of the crude oil is required to convert it to refined final product. Fuel specification that regulate transportation fuels have over the years become more and more demanding with respect to sulfur content. Presently, many products produced in the refinery are almost sulfur free. The elimination of sulfur from oil is as a result of one of the central conversion necessities in most refineries and the price which also include the processing cost of crude oil is changed by using its sulfur content.
The concentration and nature of the compounds that contains sulfur changes over the range of boiling. With increase in the boiling range, the amount of sulfur in the distillation column increases.
Addition of hydrogen is a result of hydrogenation of chemical reactions. Hydrogenolysis is a type of hydrogenation which is a result of a chemical bond C-X, where C is A carbon atom and X is an oxygen, sulfur or nitrogen atom. Therefore, the result of the hydrogenation reaction is the generation of C-H and H-X chemical bonds. The Hydrodesulfurization reaction can be expressed using Ethanethiol(C2H5SH), sulfur compound present in refinery stream.
Ethanethiol + Hydrogen ? Ethane + Hydrogen Sulfide
C2H5SH + H2 ? C2H6 + H2S
Figure 3: Hydrodesulfurization Reaction
The widely used catalyst for hydrodesulphurization consists of an Alumina base impregnated with Cobalt and Molybdenum (Co-Mo catalyst). It contains molybdenum as the active catalyst and cobalt as a promoter. To provide high dispersion for the metals Al2O3 is used as a support to the catalyst. The dispersion of the molybdenum on the support is very high and it probably involves mono-layer type coverage. Metal concentration and calcination temperature affects the geometry of the Mo ions with respect to the support. Increasing the Molybdenum concentration up to monolayer coverage (~15-20% MoO3) favors octahedral coordination whereas an increase in calcination temperature favors tetrahedral coordination. The addition of cobalt as a promoter complicates structural analysis of the catalyst. While considering Co/Al2O3 as a system, the interaction between the metals and support is strong as a result of this a portion of cobalt gets chemically inert. If the catalyst contains more than 1.5% of Co on alumina then it forms Co3O4. However the formation of CoMoO4 is also detected independently. For some specific difficult to treat feed stocks which contains high level of chemically bound Nitrogen, the combination of Nickel and Molybdenum (Ni-Mo) is used in addition to the Co-Mo catalyst.
Activated carbon has received attention as a carrier for hydrodesulphurization catalysts for several reasons such as variable amount of surface functional groups, large specific surface area with an easily controlled pore volume and relatively lower coking activity. Also to increase the active cites (active mass) of the catalyst, the unsupported catalyst Co-Mo-Carbide is been used which is not bound to Al2O3. The catalyst is found to be 3 times more active than that of Co-Mo with Al2O3.
Preparation of Co-Mo-Carbide:
The Co-Mo carbides were prepared by the co-precipitation of a mixture of aqueous solutions of 8.5 mmol cobalt nitrate 6-hydrate (Co(NO3)2·6H2O, Kishida Chemical Co., 99%) and 2.8 mmol ammonium heptamolybdate 4-hydrate ((NH4)6Mo7O24·4H2O, Kishida Chemical Co., 99%). The solid hydroxide products were dissolved in water at 353 K while being stirred, dried overnight at 373 K, and then heated at 773 K for 5 h to obtain CoMoO4. A 0.2 g sample of the CoMoO4 was placed on a porous quartz plate in a microreactor (10 mm i.d.), calcinated in dry air, oxidized at 773 K for 1 h, and then cooled to 573 K. The oxidized catalyst was carburized from 723–973 K at the rate of 1 K min?1 with 20% CH4/H2 (99.999%), and maintained at its final temperature for 2 h. The carburizing product was then cooled to room temperature and passivated overnight in a stream of 1% O2/He. Ketjen carbon (Cabot Co.) was then mixed with the Co-Mo carbides in methanol so that the concentration of the catalyst was 30 wt% followed by drying overnight in air. These KC supported Co-Mo catalysts were placed in the anode and a 20 wt% Pt/C (EC-20-PTC, ElectroChem, Inc.) was used in the cathode of all the fuel cells. The 20 wt% Pt/C was also used as the anode catalyst for comparison of the Co-Mo carbide activity. For the sake of simplicity, CoMoC-873/KC was denoted as the Co-Mo catalyst carburized at 873 K and supported on KC.
MoO3 MoO2 + MoCyOz and CoMoO4 CoMoCyOzStep-2
and CoMoCyOz CoMoCy + Co metal.Catalytic Hydrodesulphurization Activity:
The carbide particles may basically fill in as a template on which a stressed or exceptionally scattered sulfide phases are formed. Based on the theory, carbon could be considered as a textural promoter, acting to increase the active sites rather than the activity. While hydrotreating of the catalyst, it forms a new active site (MoSxCy) which improves the activity of hydrodesulphurization.
Ethanethiol hydrodesulphurization activities are reported as pseudo first order constant for ethanethiol disappearance in units of moles of ethanethiol converted to products per gram of catalyst per minute after ?3 hr of reaction time. During the reaction it is possible that Co-Mo-Carbide reacts with H2S gas and get sulphided. As a result of sulfidation, Co-Mo-S is formed on the surface of the catalyst. The Co-Mo-S is the most active species in catalyst for hydrodesulphurization reaction. The “Co-Mo-S” phases formed on the carbide surface are beneficial for hydrotreating and would enhance the HDS activities of carbide catalysts.
The structure of Cobalt-Molybdenum-Carbide is shown below
Figure 4: Hydrodesulphurization process in a petroleum refinery
The liquid feed which is olefin free is combined with stream of hydrogen rich recycle gas after pumping to the desired elevated operating pressure. The mixed feedstock needs to reach the operating temperature of the reactor, hence it is preheated through heat exchanger and then again heated in fired heater until the feed mixture is vaporized and achieves the operating temperature of reactor. The feed mixture is then passed through fixed bed reactor, where hydrodesulphurization reaction takes place. The reaction occurs in the presence of an CoMo-Carbide catalyst. This reaction takes place at temperature ranging from 300 to 400 °C and elevated pressure ranging from 30 to 130 atmosphere.
The hot products from fixed bed reactor are then partially cooled by passing through the heat exchanger where the reactor feed was preheated and further cooled in a water-cooled heat exchanger. The product then enters a gas separator at 35 °C and 3 to 5 atmosphere of absolute pressure. Before entering the gas separator the product passes through a pressure controller to reduce the pressure.
Most of the gas from the separator vessel is either hydrogen or hydrogen sulfide. These are the recycle gases which are routed to the amine contactor for the removal of hydrogen sulfide. After removal of Hydrogen sulfide the remaining gas is then returned back to reactor section for reuse. Any extra gas from the gas separator vessel joins the sour gas from the stripping of the reaction product liquid.
The liquid separated from the gas separator, go to the reboiler stripper distillation column. The bottom product of this distillation column is the final desulfurized liquid product.
The sour gas from the overhead of distillation column contains many gases like hydrogen, methane, ethane, hydrogen sulfide, propane and perhaps some butane and heavier components. To remove hydrogen sulfide from other gases, sour gas is sent to the refinery’s central gas processing plant a then passed through a series of distillation tower for recovery of butane, pentane, propane and other heavier compounds. The hydrogen sulfide which recovered in central gas processing unit is converted to elemental sulfur. Other residual hydrogen, methane, ethane and some propane are used as a refinery fuel gas.
The thermodynamics equation used in the simulation of hydrodesulphurization reaction is modified Peng-Robinson equation of state. Since the feed contains liquid and gas, Peng-Robinson can model both phases. Also after preheating the feed the resulting feed is complete gaseous, Peng-Robinson can describe the state of the gas under given conditions, relating pressure, temperature and volume of the constituent matter. V2
The Peng-Robinson equation of state is as follows
? is the acentric factor of the species.
R is the Universal gas constant
Z=PV/nRT is the compressibility factor.
In polynomial form
A=a?pR2T2B=bpRTZ3-1-BZ2+A-2B-3B2Z-AB-B2-B3=0This equation is useful to calculate the fluid properties in natural gas processes.
The modified Peng-Robinson equation of state used in the reaction is Peng-Robinson-Stryjek-Vera (PRSV). The modified Peng-Robinson equation of state was published by Stryjek and Vera in 1986. It improves the accuracy of the model with the help of pure component parameter adjustments and by the modification of the polynomial fit of the acentric factor.
The modification is as follows
K1 is an adjustable pure component parameter.
The further modification improves the accuracy of model with the help of two additional pure component parameter adjustment to the previous modification.
The modification is as follows
K1,K2 and K3 are adjustable pure component parameters.
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