بحث:Ø´Û

از ویکی‌پدیا، دانشنامهٔ آزاد.

INTRODUCTIONThe MaxEne process is a new and innovative method ofincreasing the yield of ethylene from naphtha crackersby 30% or more. The increase in ethylene yield isachieved by increasing the concentration of normalparaffin in the naphtha cracker feedstock. The MaxEne process utilizes adsorptive separation torecover C5-C11normal paraffin from naphtha. TheMaxEne process is the newest application of UOP’sSorbex™ technology. More than 100 process units basedon Sorbex technology have been licensed worldwide.APPLICATIONNaphtha is the most common feedstock sent to naphthacracking units for the production of ethylene. A typicalnaphtha feedstock contains a mixture of paraffinic,naphthenic, and aromatic hydrocarbons with varied mol-ecular weight and molecular structure. The compositionof naphtha feedstocks vary considerably, yet the compo-sition has a significant impact on ethylene and byprod-uct yields.If high ethylene yield is desired, for example, then it isdesirable to have a high concentration of normal paraffinin the naphtha. Normal and non-normal paraffin decom-poses to ethylene in a cracker, but the ethylene yieldfrom normal paraffin is much greater. Coincidentally, refiners and aromatics producers desirenaphtha feedstocks that are depleted of normal paraffin.Naphtha that is depleted of normal-paraffin contributesmore octane value to the refiner’s gasoline pool andincreases the aromatics yield in an aromatics complex. Ideally, ethylene producers would utilize naphtha with ahigh normal paraffin concentration, and refiners andaromatics producers would utilize naphtha that isdepleted of normal paraffin. UOP’s MaxEne technologyis now available to cost-effectively separate full rangenaphtha into a stream rich in normal paraffin and astream depleted of normal paraffin. PROCESSDESCRIPTIONThe MaxEne process is a continuous process that sepa-rates normal paraffin from non-normal paraffin in naphtha.The process flow is shown in Figure 1. The separationtakes place in an adsorption chamber that is divided intoa number of beds. Each bed contains proprietary shape-selective adsorbent. There is a specialized grid in eachbed to support the adsorbent. The grids are speciallydesigned to provide highly efficient flow distribution inthe chamber. Each bed in the chamber is connected to a rotary valve.The rotary valve is used along with the shape-selectiveadsorbent to simulate moving bed counter-currentadsorptive separation. There are four major streams distributed by the rotaryvalve to and from the adsorbent chamber. The streamsare as follows:MaxEneTMProcess for Maximum Ethylene ProductionFull Range NaphthaAdsorbentChamberDesorbentRotaryValveExtractRaffinateFeedDesorbentExtractColumnRaffinateColumnNormalParaffinNon-normalHydrocarbon12345678Figure 1MaxEne Process Flow


Page 2 ½ The feed stream is the naphtha feed. It contains amixture of hydrocarbons.½ The extract stream contains normal paraffin anda liquid desorbent. Naphtha rich in normal paraf-fin is recovered from this stream by fractionationand is sent to the naphtha cracker.½ The raffinate stream contains non-normal paraf-fin and a liquid desorbent. Naphtha depleted innormal paraffin is recovered from this stream byfractionation and is sent to a refinery or an aro-matics complex.½ The desorbent stream contains a liquid desorbentthat is recycled from the fractionation section tothe chamber.The rotary valve is used to periodically switch the posi-tion of the liquid feed and withdrawal points in theadsorbent chamber. The process operates in a continuous mode at low tem-peratures in liquid phase. This enables reduced operat-ing costs, low energy requirements and long adsorbentlife compared to past processes. PROCESSPERFORMANCEThe MaxEne Process can be designed and operated toachieve various levels of normal paraffin purity andrecovery.The UOP rotary valve has been engineered for rugged-ness and reliability and has been proven in over 100process units worldwide. Rotary valves typically operatefor several years without the need for maintenance. On-stream availability for a typical Sorbex process unitis very high with minimal maintenance required due tothe mild operating conditions.ECONOMICSCASESTUDYA study was performed for a client who wished toincrease ethylene production from an existing naphthacracking unit. The petrochemical complex in this casewas integrated with a refinery.The effect of the MaxEne process on the yield of prod-ucts from the naphtha cracker is shown in Table 1.Table 1Effect of MaxEne Implementation onCracker YieldsExisting Cracker Cracker Products withProducts,MaxEneKMTAProcess, KMTAHydrogen88Methane139139Ethylene247 330Propylene131130Butylene7359Benzene8250Py Gasoline13887LPG4762It was determined that ethylene production could beincreased from 247 to 330 KMTA with the MaxEneprocess, while maintaining nearly constant propylene pro-duction. The naphtha that is depleted of normal-paraffin would besent to the refinery in this case. The effect of MaxEne onthe refinery balance is shown in Table 2.Table 2 Effect of MaxEne Implementation onRefinery BalanceProducts Without Products withMaxEne Process, MaxEne Process,KMTAKMTALight Gasoline *229713Reformer Gasoline11881246Hydrogen and Tail Gas 13288LPG11988* If there is no need for light gasoline, then this stream can be sentdirectly to the reformer with a limited revamp.The net effect on the refinery gasoline pool is a signifi-cant increase in octane-barrels. The study showed that theMaxEne process increases the octane number of the lightgasoline stream from 71 RONC to 82 RONC, and itincreases the C5+gasoline yield from the reformer by 5%.


Page 3 The most significant economic benefit is due to theincreased ethylene produced from the naphtha cracker.The overall economic benefit of the MaxEne process tothis customer is shown in Table 3.Table 3 Overall MaxEne EconomicsImpact of MaxEne Process Incremental Product Revenue ($MM US/yr) 108.2Incremental Feed Costs ** ($MM US/yr)(70.6)Incremental Utilities ($MM US/yr)(9.0)Margin ($MM US/yr)28.6Investment ($MM US)80Pre-Tax Return on 36%Investment (ROI)** The feed rate to the cracker was held constant for this study. Inorder to accomplish this at the increased normal paraffin concentration,the full-range naphtha feedrate to the MaxEne process unit must behigher than the original full-range naphtha feedrate. This study showed that installation of the MaxEne processyields a significant positive return on investment.EXPERIENCEUOP has licensed more than 100 process units based onSorbex technology. It is well proven and reliable technol-ogy that is currently used in aromatics, refining, and deter-gents applications. FORMOREINFORMATIONMaxEne technological services are available on request. Formore information, contact your local UOP representative or contact our Des Plaines sales office:e-mail: info@uop.comfax:+1-847-391-2253phone: +1-847-391-2000UOP 4217-21 0104PTE0Cu© 2004 UOP LLC. All rights reserved.The information in this document should not be construed as a representation forwhich UOP assumes legal responsibility, or an authorization or recommendation topractice a patented invention without a license.UOP LLC25 East Algonquin RoadDes Plaines, IL 60017-5017, U.S.A.www.uop.com