PEP Review METHYL TERTIARY BUTYL ETHER PRODUCTION FROM STEAM CRACKER C 4 STREAM By Syed N. Naqvi (December 2012)

Transcription

1 PEP Review METHYL TERTIARY BUTYL ETHER PRODUCTION FROM STEAM CRACKER C 4 STREAM By Syed N. Naqvi (December 2012) ABSTRACT This Review presents a technoeconomic evaluation of a methyl tertiary butyl ether (MTBE) production process from raffinate-1, a C 4 -hydrocarbon stream coming after butadiene extraction from a steam-cracking-based olefins plant. MTBE production in this Review is targeted as an intermediate product that would subsequently be converted to high-purity (polymer-grade) isobutylene in an integrated MTBE cracking plant (analyzed in PEP Review ). This twostep (commercialized) route for production of high-purity isobutylene from C 4 streams is an important commercial step/option among others, aimed at enhancing the value of C 4 streams produced in refineries, olefins plants, and natural gas liquids plants. Other commercial options used needed involve chemical conversions of C 4 components (1-butene, 2-butenes, butanes, and butadiene) employing processes such as metathesis, selective hydrogenation, total hydrogenation, dehydrogenation, extraction, isomerization, skeletal isomerization, etc. Products from C 4 feeds can include propylene (via metathesis of butenes with ethylene), 1-hexene (via self-metathesis of butenes), MTBE, isobutane, isobutylene, butadiene, C 4 -based liquefied petroleum gas, maleic anhydride, etc. In the conventional type of MTBE plants, two catalytic fixed-bed reactors are generally used with attached external coolers that remove heat of reaction from the reactors. Because the etherification reaction is equilibrium-controlled and a low reaction temperature favors isobutylene conversion, the presence of MTBE in the reaction system and potential temperature gradients in the catalyst beds tend to limit the conversion rate of reactants. Therefore, despite the fact that a two-reactor system provides a higher catalytic area for reaction, the overall conversion rate is generally limited within a range of 90 95%. More recent etherification systems are comprised of a primary reactor followed by a reactive distillation column in which MTBE product is removed from the reaction system as soon as it is formed. As a result, overall isobutylene conversion of up to 99% is possible. This Review is based on that design. The catalyst consists of a strongly acidic ion-exchange resin having sulfonic acid groups (preferably of styrene-divinylbenzene type). Details about the catalyst are given in the description section. Another feature of the new system (used in our design) is that the cooling system for the reactor is not external, but rather, the reaction is carried out at or close to the boiling temperature of the reactants mixture, allowing a portion of the liquid to vaporize, and thus, removing the heat of reaction from the reactor. This partially vaporized reactor stream then goes to the reactive distillation column for additional reaction in addition to providing an advantage of reduced reboiler duty. Separation of MTBE product, unreacted methanol, and non-reactive C 4 components is done in a conventional way by means of extraction and distillation columns. Based on our cost analysis, the economics of a standalone MTBE plant with an installed capacity of approximately 284 thousand metric t/yr of MTBE (designed to operate at a stream factor of 0.9) are provided in this Review. In addition, the economics of an integrated MTBEisobutylene plant producing 150 thousand metric t/yr of isobutylene (the installed capacity of the plant being 167 thousand metric t/yr) are also given (see Tables 9, 10, and 11) IHS PEP Review

2 A private report by the Process Economics Program Review No METHYL TERTIARY BUTYL ETHER PRODUCTION FROM STEAM CRACKER C 4 STREAM by Syed N. Naqvi December 2012 Santa Clara, California 95054

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4 CONTENTS REVIEW SUMMARY... 1 INTRODUCTION... 5 PROCESS DESCRIPTION... 6 PROCESS DISCUSSION Raw Material Catalyst Reactors System Product Separation/Recovery Materials of Construction Process Design Optimization COST ESTIMATES Fixed-Capital Costs Production Costs CITED REFERENCES IHS iii PEP Review

5 FIGURES 1 Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Process Flow Diagram Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Net Production Cost and Product Value of MTBE as a Function of C 4 Stream (Raffinate-1) Price (for Base-Capacity Plant) High-Purity Isobutylene Production from Steam Cracker C 4 Stream Net Production Cost and Product Value of Isobutylene as a Function of C 4 Stream (Raffinate-1) Price (for Base-Capacity Plant) Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Net Production Cost and Product Value of MTBE as a Function of C 4 Stream (Raffinate-1) Price (for Base-Capacity Plant) High-Purity Isobutylene Production from Steam Cracker C 4 Stream Net Production Cost and Product Value of Isobutylene as a Function of C 4 Stream (Raffinate-1) Price (for Base-Capacity Plant) Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Product Value of Mtbe as a Function of Plant Operating Level and Plant Capacity High-Purity Isobutylene Production from Steam Cracker C 4 Stream Product Value of Isobutylene as a Function of Plant Operating Level and Plant Capacity IHS iv PEP Review

6 TABLES 1 Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 -Stream Total Capital Investment and Production Costs High-Purity Isobutylene Production from Steam Cracker C 4 -Stream Total Capital Investment and Production Costs Methyl Tertiary Butyl Ether from Steam Cracker C 4 Stream Design Bases Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Stream Flows Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Major Equipment Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Utilities Summary Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Total Capital Investment Methyl Tertiary Butyl Ether Production from Steam Cracker C 4 Stream Production Costs High-Purity Isobutylene Production from Steam Cracker C 4 Stream Total Capital Investment High-Purity Isobutylene Production from Steam Cracker C 4 Stream Total Capital Investment High-Purity Isobutylene Production from Steam Cracker C 4 Stream Production Costs IHS v PEP Review