Determination of Design parameter of R.D. Column by using etherification reaction system with Ion exchange resin

Determination of Design parameter of R.D. Column by using etherification reaction system with Ion exchange resin

A.M Patare*, D.K. Chandre.**, Dr. R.S Sapkal$

* Principal & Head, Department of Chemical Engineering, A.I.E.T.P, Ashoknagar, Shrirampur, Ahmednagar

**Assistant Professor, Department of Chemical Engineering, S.V.I.T, Chincholi, Sinnar, Nashik , India.

$ Prof & Head. Department of Chemical Engineering, UDCT A mravati , India

Abstract

Nowadays Reactive Distillation is widely used as alternative for conventional distillation. In this work we have to suggest a new technique in Distillation technology rather than ordinary distillation process.

Reactive Distillation technology sounds good for

the system such as synthesis of ETBE, MTBE, and Methyl Acetate where more than one a zeotropes are formed. In this work we have concentrate on all theoretical and basic experimental data which will use ful for some rigorous experimentation and process simulation work

1. Introduction

What is RD? (1)

The co mbination of chemical reaction with distillation in only one unit is called Reactive Distillat ion (R.D) .The performance of reaction with separation in one piece of equipment offers distinct advantages over the conventional, sequential approach. Especially for equilibriu m limited reaction such as esterification, etherification and ester hydrolysis reaction, and conversion can be increased far beyond che mica l equilib riu m conversion due to continuous re mova l o f reaction product from the reactive zone.

Why R.D? (2).

The use of Reactive Distillation has grown in the recent years because it results in less expensive and more efficient processes for some chemical synthesis. There is increase interest in the use of ethyl tert-butyl ether (ETBE) for gasoline blending as a replacement for methyl tert – butyl ether (MTBE) because of the latter's environmental problems. for methyl tert – butyl ether (MTBE) because of the latter's environmental problems.

Fig: Typical R.D.Column. In this new process, of R.D. Column consists of three zones: such as

1. Rectification zone Non reactive Section.

2. Reaction zoneReactive Section.

3. Stripping zoneNon Reactive section.

The top section is called as Rectifying Section. The bottom section is called as Stripping section.

1. Adaptation Technique of Reactive Distillation: – (3)

   React ive Distillat ion has be en successfully applied to react ion h aving a lo w equ ilibriu m constant (K) to realize co mplete conversion independently the value of K. There are two operations Style based on volatility of a product compared with starting material, as shown in fig. If one of the products, C, is most volatile among the components. Operation style – I is adopted. The reaction proceeds completely since a reversible reaction can be driven away by continuously removing the product C fro m the reaction zone and fractionating it away fro m the top of the column. Consequently, one of starting materia l, B, essentially vanishes from the column (in the case of a mole ratio of A / B > 1.) The less volatile product D and an excess of A are realized

   together from the bottom of the column.

   If sta rt ing ma te ria l A is most vo lat ile, ope rat ion style – II is ad opted . In th is case component A dose not vanishes but refluxes to the top of the column without release. The products of the react ion, C & D are re lease fro m the botto m of the colu mn along with the e xcess of B. Component A is essentially absent in the bottom flow.

   Figure 2:-Operation StyleI

   Figurea3:-Operation Style II

   What are Oxygenates? (4)

   Oxyg enates a re hyd roca rbons that conta in one or mo re o xygen ato ms. The prima ry o xyg enates a re a lc oho ls and ethe rs, fo r e.g. fue l ethano l, methy l te rtiary buty l ethe r (MTBE), ethyl tertiary butyl ether (ETBE), and tertiary amyl methyl ether (TAME).

   Introduction of MTBE :- (4, 5)

   Molecular formula of Methyl tertiary-butyl ether: – C5H12O {(CH3OC (CH3)3)} Methyl tertiary-butyl ether is commonly referred to as MTBE.

2. Introduction of ETBE: – (6)

   Molecular formula of Ethyl tertiary-butyl ether: – C6H14O (CH3CH2OC(CH3)3 Ethyl tertiary-butyl ether is commonly referred to as ETBE.

   1. Why ether is used in gasoline blending instead of alcohol and butanes? (5)

      The substitution of ethers (MTBE, ETBE) for alcohols and butanes in gasoline blending would have a positive effect on emissions, in a number of specific areas:

      1. Reduction of carbon monoxide.

      2. Reduction of aromatic content of gasoline and resulting toxics

      3. Reduction of olefin content of gasoline.

      4. Reduction of volatile organic compounds.

      5. Reduction of carbon dioxide.

1. Comparative Properties of MTBE & ETBE:-

   Table 1.

   Oxygenates	MTBE	ETBE
   Chemical Formula	CH3OC( CH3)3	CH3CH2O C(CH3)3
   Molecular Weight	88	102
   Boiling Point ( 0C )	55.2	71.3
   Oxygen Content, (Percent by weight )	18.15	15.66
   Octane Number, (R+M)/2*	110	111
   Blending Vapor pressure, RVP	8	4
   Source:- National Petrochemical Council, U.S Petroleum Refin ing :Meeting requirements for Cleaner fuels and Refineries (Washington, Dc, August 1993) appendix L

   * R = Research Octane Number. M = Motor Octane Number.

2. Amberlyst 15 Wet: – (7)

   AM BERLYST 15 W ET is a ma cro reticular, strong ly a cid ic , po ly me ric c atalyst. It is continuous open pore structure make it an excellent heterogeneous acid catalyst for a wide variety of organic reactions. AMBERLYST 15 WET catalyst polymeric structure is extremely resistance to breakdown by osmotic, mechanical &

   thermal shock. It also possesses greater

   resistance to oxidants such as chloride, oxygen and chromates than most other polymeric catalyst.

   AMBERLYST 15 W ET can use directly in the aqueous system or in organic medium after conditioning with a water miscib le solvent. AMBERLYST 15 W ET has the optimal balanceaof surface area, acid capacity & pore diameter, thus it makes a bestaachoiceaforaetherificationa(MTBE,a ETBE,aT AME) esterification and hydration reactions. AMBERLYST 15 WET can also be used for chemical process applications to remove the impurities (metal ions) and basic organic compounds (amines, etc) from aqueous and non aqueous environments (appropriate pretreatment required).

   Properties:-

   Physical forms Opaque beads Ionic form as shipped Hydrogen Total e xchange capacity 1.7 eq / L Moistureaholdingacapacity ..52 to 57 % Particle size

   Harmonic mean size 600 to 850 m. Average pore diameter. 24 n m Surface area … 45 m2/g m Shrin kage Water to methanol: 4.0%

   Suggested Operating Condition:- Maximu m operating condition .. 1200C Minimu m bed depth …1000mm Operation flow rate … 1 to 5 LHSV* Pressure drop limitation .. bar across the bed.

   * LHSV: – Liquid Hourly Space Velocity for liquid

   density at 250C.

3. Experimental Procedre:-

   1. Catalyst Treatment:-

      A strong cation exchange resin, Amberlyst 15 in the H+ form, was used as the catalyst. The average sizes 0.78 mm were chosen. This ion exchange resin was a sulfonated styrene diviniyl benzene copolymer with a mac ro-reticu lar structure. A new fresh catalyst was kept at 368 K in a vacuum oven, overnight to get rid of any moisture contents.

      The used resin was washed with d istilled wat er and then soa ked ove r n ight at roo m

      te mpe ratu re . Th ere fore, it was ke pt at 368 K in a va cuu m ove n fo r 24 h fo r re using . It was confirmed fro m pre limina ry e xperiments that the regenerated resin had the same activ ity as the fresh resin.

   2. Procedure for MTBE:-

      The equilmolar TBA and MeOH were taken in the batch reactor and 7-8 sa mples were taken and cooled rapidly to 277 K to avoid any further reaction. Measurements were preferred between the temperatures 313 K to 323 K. The samples are analyzed by using the gas chromatograph.

   3. Analysis for MTBE:-

      Analysis was carried out in the gas chromatograph with 2.5 m column of Gaskuropack 54, 60, 80 mesh as packing material. The colu mn temperature was set at 4630K=1900K and carrier gas was helium at 0.12 MPa. Good separations had been achieved for all components. Norma l he xane was used as an internal standard for the analysis.

   4. Procedure for ETBE:-

      The equimolar TBA and EtOH were taken in the batch reactor and 7-8 samples were taken and cooled rapidly to 277 K to avoid any further reaction. Measurements were preferred bet ween the te mp erature 323 K to 338 K. Th e sa mples are ana ly zed by us ing the gas chromatography .

   5. Analysis ETBE:-

Analysis was ca rried out in the gas chro matography with 2.5 m colu mn of Gaskuropac k 54, 60, 80 mesh as packing materia l. The column te mperature was set at 4430 K= 1700C and carrier gas was helium at 0.12 MPa. Separations had been achieved for all components.

Experimental Set Up. :-

RD processes for very large flow rates because of liquid distribution problems in packed Rd column.

1. Process conditions mismatch. In some processes the optimu m conditions of temperature and pressure for distillation may be far from optimal for reaction and vice versa.

2. Advantages and Disadvantages of Reactive Distillation (1)

   1. Advantages of Reactive Distillation:-

      1. Simplification or elimination of the separation process can lead to significant capital saving.

      2. Improved conversion of reactant approaching 100%. This increase in conversion gives a benefit in reduced recycle cost.

      3..Improved selectivity. Removing one of the products from the reaction mixture or maintaining a low concentration of one of the reagent can lead to reduction of the rates of side reactions and hence improved selectivity for the desired products.

      1. Significantly reduced catalyst requirement for the same degree of conversion.

      2. Avoidance of the azeotropes. RD is particularly advantageous when the reactor product is a mixture of species that can form several azeotropes with each other.

      3. Reduced by- product formation.

      4. Heat integration benefits. If the reaction is exothermic, the heat of reaction can be used to provide the heat of vaporization and reduced the reboiler duty.

   2. Disadvantages of Reactive Distillation:-

1. Volatility constraints. The reagent and product must have suitable volatility to ma intain high concentration of reactant and low concentration of products in the reaction zone.

2. Residence time require ment. If the residence time for the reaction is long, a large colu mn size (For packed column) and large tray hold – ups (for tray column) will be needed and it may more economic to use a reactor – separator arrangement.

3. Scales up to large flows. It is difficult to design

Figure :- Composition V/s Height from Top. For MTBE system

1. Parameter condition for Reactive Distillation:-

   1. For MTBE System:-

      1. Colu mn pressure: – 1 atm.

      2. Flow rate TBA: – 0.5 mole / hr = 105 ml / 2hr

      3. Feed to Bottom MeOH: – 1 mole = 43 ml 4FeedmolarRatio:-1:1

      1. Catalyst loading: – 50gm.

      2. Te mperature of Re -boiler: – 3410K

   2. For ETBE System:-

1. Colu mn pressure: – 1 atm.

2. Flow rate TBA: – 0.5 mole / hr = 105ml / 2 hr.

3. Feed to Bottom EtOH: – 1 mole = 60 ml

4. Feed molar Ratio: – 1: 1

5. Catalyst loading: – 50gm. ,

6. Te mperature of Re -boiler: – 3550K

   Figure: – Temperature V/s Height from Top for MTBE system

   Fig: – Reflux Ratio V/sMole frication of for MTBEsystem

   Fig: – Composition V/s Height from Top. For ETBE system

   Fig: – Temperature Frofile for ETBE system

   Fig: – Reflux ratio V/s mole fraction, for ETBE system

7. Conclusion:-

   Direct synthesis of MTBE fro m MeOH and TBA and also ETBE fro m Et OH and TBA ,in the liquid phase was studied by using Amberlyst 15 in the H+ form in Reactive distillation Process under atmospheric pressure. Dehydration of TBA not be neglected and three reactions took place simultaneously.

   The react ive d istillat ion co mb ined with pervaporation would be suitable way fo r the d irect production of MTBE & ETBE fro m Me OH, EtOH

   and TBA. respectively

   Abbreviations:-

   k = Forward rate constant k= Backward Rate constant. r = Rate of reaction

   C = concentration

   TBA = Tertiary Butyl Alcohol. IB= Iso-Butene

   MeOH = Methanol EtOH = Ethanol.

   MTBE = Methyl tert. Butyl Ether ETBE = Ethyl tert. Butyl Ether Cc = catalyst concentration

   Q = Ion e xchange capacity W = Weight of catalyst.

   V = volume of Reactant. T = Temperature.

   CEtOH,0 = Initial Concentration of EtOH. A-15 = Amberlyst – 15 WET catalyst.

   E = Activation Energy

   R = Gas constant.

8. Reference:

   1. S.Steingeweg, T. Popken, J. Gmehling, Chemical Engg. Tech. 66, 1994, Pg- 1372-1375

   2. M uhammad A. Al-Arfaj, King Fahd, Ind. Engg.

      Chem. Res. 2002, 41, Pg. 3784-3796

   3. M c. Graw Hill Publications, Perrys Chemical Engg. Handbook, Pg. 22-67 to. 22-699.

   4. ''MTBE, Oxygenates and M otor Gasoline, Energy Information Administration. Washington, DC, Aug.1993, Appendix-L.

   5. Vasant B.Shah, Richard Yu, Refining LNG & Petrochemasia, 94, Dec. 7- 8 – 1994. Pg.02-03.

1. ''AMBERLYST 15 WET'' Industrial Grade Strong acid catalyst. PDS – 0373A- April- 97-112.

2. Robert E. Trybal, Mass Transfer Operation M c

   Graw Hill Publications 3rd edition, Pg. 185-195

3. Xiaodong Yin, Bolun Yang, and Shigeo Gotot, International Journal of Chemical Kinetics Vol.25, (1993), Pg. 825-831.

International Journal of Chemical Kinetics Vol.27, (1995), Pg. 1065- 074.