Control and implementation of DCS system ofMTBE device

I. Profile

With the development of high-performancegasoline motor, the high-octane petrol is required for refineries. To improvethe octane value of gasoline, firstly, the octane value of basic componentgasoline shall be increased; secondly, appropriate amounts of components withhigh octane value shall be added. The components of high octane value aremainly alkylate, congruent oil, isomerized oil and methyl tertiary butyl ether(refers to MTBE for short). The boiling point of MTBE is about 55℃, the relativedensity is 0.746 and the molecular weight is 88. The property of MTBE issimilar to gasoline and can be mutually dissolved completely in hydrocarbon. Ithas no negative impact on the physical property of gasoline. It has high octanevalue with sound antiknock property.

II. Process introduction

The methyl tertiary butyl ether (refers to MTBEfor short) is obtained from synthetic reaction of isobutene in methanol and C4fraction under the function of acid catalyst. This reaction is a reversibleexothermic reaction. The lower the reaction temperature is, the bigger theequilibrium constant is and the higher the conversion rate is. This reaction iscompleted in liquid phase conditions with rapid speed.

The production process is divided into threetypes, two phases of deepening conversion process flow (THC), one phase ofgeneral conversion process flow (OGC) and general deepening conversion processflow (OHC).

The raw material (C4 fraction) is mixed withmethanol during the THC flow and enters into the first stage reactor withreaction product entering into the azeotropic fractional column. The MTBEdischarged from the bottom of the column will be discharged from the device asproducts, and the methanol and C4 fraction azeotrope from the top of the columnwill enter into the second stage reactor for continuous reaction aftersupplemented with methanol. The product of second reaction enters into the C4fractional column, and the C4 fraction and methanol azeotrope are dischargedfrom the top of the column and enter into the methanol water extraction column.The products (MTBE+ methanol) of the second stage reaction from the bottom ofthe column will be discharged from the device with MTBE from the bottom ofazeotropic fractional column, or returned to the first stage reactor forfurther reaction. The C4 fraction and methanol compound will be separated inthe methanol water extraction column with C4 fraction discharged from thedevice and water solutions of methanol into methanol distillation column. Theseparated methanol will be returned to reactor for recycling.