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Module 1: Introduction to Natural Gas

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Syngas to Liquid Fuel Production

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Hi friends, now we will discuss on the topic syngas to liquid fuel production.So in the previous class, we have discussed how the syngas can be produced from the naturalgas and now we are going to discuss how this syngas will be converted to liquid fuels.(Refer Slide time: 00:45)So the contents of this class is why syngas to liquid fuel and then some important routesfor liquid fuel production from syngas.So, why syngas to liquid fuel?Already we have discussed that if we convert syngas to liquid fuel, then we will be gettingmore market, we will be getting the value-added products, different types of chemicals orsome liquid fuels.So that is the major features of this liquid fuel conversion.Now we see natural gas which is available in nature, so from this reserve, it can gothrough the pipeline and then it can be used in different application, particularly forheat application, say it go to conventional market or it can be liquefied.So liquefied natural gas, then also we have some supply chain arrangement already existingand then it will go into conventional market.So these are the 2 conventional routes, but if you go through this third one route thatis the GTL route, then this is a new technology.Here we get some large existing transport fuels, market, we have good market and canget chemicals also.So that is the advantage and that is why people are trying to convert it into liquid fuels.Another is natural gas has low energy density, but if it is converted to liquid fuels, energydensity will be increased, so application of these in transport fuel will be easierthan the natural gas.Now we will see different methods which are used for this syngas to liquid fuel conversion.So, one is Fischer-Tropsch synthesis.So in Fischer-Tropsch synthesis, syngas is converted to liquid fuels that is called saydiesel, petrol, kerosene, etc.So what happens in this case?At first, we get wax, then wax is hydrocracked to get different products of it after fractionation.So the basic reaction so you can see here CO+H2 we have in the syngas so that will producethe hydrocarbon chain as mentioned here CH2n.So this hydrocarbon chain we can get or nCO+(2n+1)H2, this reaction can take place CnH2n+2+nH2O.So we are getting paraffin type of compounds.Again same other reaction can take place nCO+2nH2, so CnH2n+nH2O, olefin type of compounds youmay get.Again CO+H2O, CO2+H2, water-gas shift reaction can also take place.So overall reaction is strongly exothermic, -180 kilojoule/mol in these reactions.So we are getting basically hydrocarbons or paraffin and olefins basically.So once the paraffins are produced and carbon number is, if this n number, higher, thenwe will be getting wax.So that wax is the major product by this fast type of this FT synthesis, then that willbe converted to different liquid.So if you see the flow sheet, then we are having the syngas, so 2:1 hydrogen is to COratio, then it is coming to FT reactor, then FT reactor will basically give us olefinsand paraffin type of compounds, so higher carbon paraffins means wax.So we will be having wax here or we may get some oil, light oil, and light wax will alsoget.So it will be gas phase, it is coming here, so it is going out as a vapor, and then itis coming as gas and vapor.So gas is recycled and the condensed part is coming out that is we are talking aboutlight oil and light wax and this is wax from the bottom of the reactor we are getting.So this light wax and heavy wax, these 2 wax will be hydrocracked here.So after hydrocracking, there will be the conversions of the high molecular weight paraffinsto low molecular weight paraffins and then we will get the distillation and we will getdifferent fractions.So, we will get off gas that can be combustion as shown and then naphtha, we can get kerosene,we can get distillate, diesel FT fuel, other FT products.So that way, we can get the liquid fuels from the natural gas.Now these reactions at what part we are taking the reactions and what type of catalyst wecan use that will influence the distributions of these different products and that partwill go to discuss now.So here we see the process conditions and catalyst.So H2/CO ratio is 2-2.2 and then pressure is 15-30 bar and temperature as we mentionedthere are 2 temperature range has been reported, that is 325-370 degrees centigrade high temperatureand low temperature 220-270 degree centigrade.Obviously, we will see the variations in the product quality by the application of differenttemperature range and GHSV, gas hourly space velocity, is 700 per hour.The catalyst basically has been used is iron based, cobalt based, and ZSM-5 supported bimetallicFT catalyst for gasoline synthesis.So this Fe based, iron based, catalyst are fuel flexible, but Co based catalyst suitablefor high hydrogen/CO ratio and preferable for natural gas based syngas.So we are talking about natural gas, so CO will be preferred for this case.As we mentioned, we have 2 temperature range, one is 300-350 and another is 220-270 degreescentigrade and under these 2 different operations, we will see the distributions of the product.So here high temperature range is 300-350 degrees centigrade, we are getting C5+ isequal to 50-80% and here we are getting C5+ 20-30%.So low wax we are getting, high temperature, lower percentage of low wax, and here we aregetting 50% of wax.So wax we are getting higher when the temperature is less.Gasoline to diesel ratio at high temperature we are getting more gasoline, at low temperaturewe are getting more diesel.At high temperature, we are getting cetane number 50-60, low temperature we are gettingcetane number 80.So at low temperature, we are getting more diesel with more cetane number.So depending upon the need in the market, we can choose what type of FT synthesis reactionwe will prefer, at low temperature or high temperature.Now we will show some commercial plant available in the world for this liquid fuel productionfrom the natural gas.So one is Australia here, then Qatar, Italy, South Africa and then Malaysia.So here some plants are already available on the basis of natural gas and these arethe capacity.So we see here these are very big capacity also and with it, they have used proprietarycatalyst and some iron based and proprietary catalyst not shown here.The technology licensers are Shell and Axens with Eni and ISP and Gasel TM technology isalso used some cases.So these are the technology licensers and we also see that the plants are not very old,it is started in 90s and 2006 one like thisNow we are coming to methanol synthesis.So methanol can be produced from syngas.So how we will do it, so this is our biomass waste to syngas, but in our case, this ismethane, reforming, then it will give us syngas.So then that syngas which we are getting that will be converted to methanol.So what is the condition, we need one catalyst, that is copper based catalyst has been usedwidely and copper zinc oxide alumina and then H2:CO ratio 2:1 and this is the reactions.So that way, we can produce methanol.Overall reactions very simple we have mentioned here, but this is not very simple becauseit is gas phase, gas and solid phase reaction.So I will discuss more.Then for this conversion, 2 technology licensers are capturing the market basically.So one is ICI technology and other is Lurgi technology.So this ICI process was first commercialized in 1970 and currently accounts for more than70% of undergoing projects.So, this ICI process is having more application.Now we will see what are the reactions which take place during this methanol synthesis?So actually we have seen that CO and H2 we have, so it is giving CH3OH and we need somecarbon dioxide for the initiation of the methanol reactions and so that CO2+H2,CO+H2O and itis believed that CO is first converted to CO2 and then CO2 reacts with CO and H2 andthen it gives methanol.So the CO2+ this H2, this is the major reactions for methanol synthesis.So from these different reactions, we have different del H value as mentioned here, somewherewe are getting exothermic, somewhere we are getting endothermic.So the one important condition or pre-requirement to get required conversion syngas to methanol,the R-value that is described as H2:CO ratio that is around equal to 2, it is used forthis application, but here later another factor has been developed because of this complexreaction scenario, that is what is R is equal to it is given here, H2-CO2/CO+CO2.So this what is the concentration of these 3 gases that will give the R-value as perthis expression.So R-value is basically around 2, when we maintain it at around 2, we get suitable conversationsof the syngas to methanol.As it is a solid-gas phase reaction in the conventional reactors, so one pass conversionsof CO is around 25%, so that is why we need a very big reactor for the conversion of syngasto methanol.The process operates at 220-250 degrees centigrade and 5 to 8 megapascal pressure and uses aseries of catalytic adiabatic reactor beds.So this is the important features of the methanol synthesis reactions.So apart from those major reactions, there are some other reactions that take place.As you see here, methanol is converted to CH3OCH3, dimethyl ether, and then dimethylether to hydrocarbons and +H2O and you methanol +CO+2H2O that can also give us CH3CH2OH.So what we are getting, some side reactions are going on in this reactor that produceshydrocarbons, higher alcohols, even some amount of ether.So these are the other reactions which can take place.So we can get syngas R-value around 2, so methanol reactors, we can get the unconvertedsyngas recycling and then methanol purifications.So this is the concept of methanol production and the catalyst basically copper and zincoxide based catalyst and other catalysts have been used of chromium zinc oxide, zirconiumpotassium, zirconium manganese potassium, and zirconium zinc oxide on high pressure240-300 bar, so this is not that efficient one because high pressure and high temperatureis required.So once we get the methanol, so that can be used as a building block for different typesof chemicals.Some of the chemicals which you can get as mentioned here we can get dimethyl ether,we can get ethylene, we can get propylene, we can get polyolefin, we can get oxo-chemicals,methyl acetate, acetic anhydride, acetic acid, acetate ester, keten, diketens, etc. and manymore.So conventionally, methanol is produced in a gas-solid phase reactor and heterogeneouscatalysts are used and we have already seen that 25% conversion is possible and the catalystrequires high purity of the syngas.If small amount of sulphur is present, then the catalyst life reduces and it harms thewhole process.So to eliminate those limitations, the low temperature low pressure methanol synthesismethods are being developed and in this case, we use some homogeneous phase reactions andhomogenous catalysts are used.Some examples are Brookhaven National Laboratory, BNL, method.So they have a homogeneous nickel catalyst and alkoxide in an organic solvent that istriethylene glycol dimethyl ether, triglyme, so this organic solvent is used where nickelcatalyst and alkoxides are mixed.Then in this liquid phase, syngas is passed through it and reaction takes place.Another is methyl formate formation method.So this employs a mixture of copper-based oxide and alkoxide as a catalyst.So one is nickel-based catalyst, another is copper-based catalyst, and then alkoxide andthis triglyme media solvent that people have used and studied the conversion of syngasto methanol.Basic reaction has been reported as CH3OH+CO, HCOOCH3 particularly for methyl formate process,so we are getting methyl formate, and then methyl formate is further converted to methanolokay.So both these processes we see here, this requires around 100 degrees centigrade andit requires 20-25 bar, unlike say 60-80 or 90 bar or somewhere 200 bar, we are gettinghere with 20-25 bar and temperature is also less 100 degree centigrade.So, now it has been reported that if we can use some nano-material based catalyst, thenthis performance will can be further increased, but this is under development stage and notin commercial scale.Now we will see how we will select the reactor type, what will be the type of reactor forthe methanol synthesis?So this is the thumb rule we can say that the reactor selection for methanol synthesiswe have given here say we have liquid-liquid reactions may take place, liquid-solid reactionmay take place, liquid gas solid reaction may take place, gas liquid solid reactioncan take place.So different types of phases may be available during the reactor and depending upon that,we can select a particular type of reactor for that too far from that specific reaction.In our case, we have syngas that is CO+H2 in gas phase and then solid catalyst.So we need gas and solid, so this is our domain, we have to choose, so for this applicationyou get multi bed reactor, multi tubular reactor, fluidized bed reactor, and monolithic reactor.So these reactors are more suitable for the conversions of syngas to methanol.What we have discussed, there is a multi tubular reactor that is used commercially in mostof the technology available in market.We see the typical plant operation, the catalyst lifetime is about 2 years, but if sulphuris present, then it reduces.So sulphur condition, sulphur in the syngas should be less than 0.5 ppm.Catalyst deactivation also occurs due to thermal sintering of catalyst.Above 300 degree centigrade, copper oxide starts to crystallize which reduces the activityof catalyst.Then plant economy is the function of operating temperature, pressure, and recycle ratio.As we have discussed, the carbon dioxide is required for the reactions and 5-8% of carbondioxide in syngas feed is required to initiate the methanol synthesis reactions.The temperature of the reactor is controlled by controlling steam pressure through shellside.We see the reaction mechanism.So overall the reactions although we have CO+H2O, it is giving up CO2+H2 and then CH3OH.So carbon monoxide is converted to CO2 and then it is giving us methanol, this is theoverall reaction, but how it happens, this is not very so simple.Then Froment proposed a redox type of mechanism.So here carbon dioxide, so what happens in this case?So you are using your syngas and it is going through the catalyst bed, so diffusion ofthe gas molecules to the pores is the first step, then the active sites are there in thecatalyst, so reactions of the active site takes place.So when carbon dioxide it is coming with this reactor site say solid s+ so that is it isgiving us O2+Os solid and then CO or it can also give this Os, one Os and another s, carbondioxide can also mix with these and gives us CO3 2s, two sides commonly it gives CO3.2s.Then CO3.2s some ages may combine and give this one, further this can combine with anothers and then it can give this one.So that way, different types of products, intermediate products are formed.Here also, we can get Os which we are getting that can react with Hs another site containinghydrogen so that can give us this one, similarly this, this one, so this ultimately we aregetting H2O, we are ultimately getting CH3OH and here hydrogen is added, CO2 and hydrogenthat we are talking about CO2 and hydrogen.So this hydrogen is converted to 2Hs, so this is the source for Hs and this is the sourceof Hs.So this is the scheme through which the methanol and water is formed.This is proposed by Froment and they have modeled the reaction.Now coming to DME synthesis.So DME synthesis, we can get here as we have seen that methanol to DME, just dehydrationreaction is required, so we can get the methanol first from the syngas, then dehydration, willbe using some special catalyst, and after dehydration, we will get the DME or directfrom syngas to DME is also possible using another type of catalyst, bi-functional catalystwe can do it, but here basics will be we are having a biomass waste at this zone, but wecan use methane also.Then gasification will be replaced by reforming and then we will get syngas and this willbe the reactions, already we have discussed this one and this is methanol, this is dehydrationand DME or this is direct route also, but here we see H2/CO requirement is 1:1, buthere we need 2:1 for methanol, then further dehydration.So, this is the difference between the H2/CO requirements for these two routes.This is your flow sheet say natural gas, it will go to reformer, so if it is steam useof reforming, then we can get more hydrogen, hydrogen can be separated and 1:1 H2/CO requirementfor direct method and 2:1 for methanol synthesis route, so that is 2 to 2.5 is maintained here,rest hydrogen is recovered, then it is going to methanol, then methanol unconverted syngas,then it is dehydrated.For dehydration, it is going to DME reactor and after dehydration, we will get DME, DMEwill be separated, and again if unconverted methanol that will be recycled back here forthe further DME conversion and here we will be getting the water.So this is the flow sheet through which the DME can be produced from the natural gas.So DME synthesis, we see reactions and catalyst.So using dehydration catalyst like alumina along with copper, zinc, and aluminum basedcatalyst we can get DME from the methanol.If we get DME, then it has low ignition temperature, very high cetane number, high oxygen content,very low particulate emissions, that is the advantage of DME.It is suitable as source of hydrogen for fuel cells.It can also be used as additive to bio fuels to improve their ignition characteristics,LPG substitutes, and diesel engine, it has versatile application.Then these are the technology licensers for DME that is Chevron, Haldor Topsoe, TOTAL,NKK, Itochu, Mitsubishi etc.Now we will see some example of DME plants.So China is the leader of the DME synthesis and China’s current annual output of DMEis 120,000 tons.It plans to produce 20 million tons of DME based on coal feedstock by 2020 and alreadyon the roll is 200,000 tons coal to DME plant at Shanghai, so coal to syngas and like this,so natural gas can also be processed like this to syngas, natural gas to syngas andthen syngas to DME.Other countries which are taking strides in setting up DME plants are Japan, Iran, Russia,and Qatar.Note there are some issues with syngas utilization from stranded natural gas.So natural gas may be available in some remote area in less amount, in that case the technologyshould be different.So small scale reactors are basically needed for that application and it has been reportedthat the gas to liquid conversion processes can be economically feasible when the plantcapacity is very high, that is 30,000 barrels per day or more, but these stranded naturalgases will be having less reserve and it is in remote area, so we need to convert it atlesser amount, so that is why it requires some development in the reactor side.So small scale plants for fuel production from syngas is required and recently smallerscale GTL plants are designed to be economic at 1500 barrels per day to 15,000 barrelsper day.So initially, it was reported 30,000 barrels per day will be economic, but due to the developmentin the reactor side, now it is possible to 1500 barrels per day to 15,000 barrels perday.The Velocys have reported it.Then the Velocys’ first commercial plant is now under constructions and the plant isjointly ventured between Velocys, Waste Management.Another plant in planning stage is Ashtabula, Ohio near Lake Erie using natural gas fromthe Marcellus Shale.So, initial productions will be 2,800 barrels per day.Then Oberon fuel has developed small scale methanol plant which can utilize syngas fromnatural gas as well as biogas containing 50% of carbon dioxide.Typical capacity of the plant using syngas derived from natural gas as well as biogasis 10,000 gallons for day DME or 11,300 gallons per day methanol.Footprint of the plant is 40,000 square feet.Feedstock required is 12,40,000 standard cubic feet natural gas per day, 15,40,000 standardcubic feet biogas per day.So we have discussed on the processes how to convert liquid fuel from the syngas whichcan be derived from the natural gas, so up to this in this class.Thank you very much for your patience.