Research On The Purification Process Of The Crude Methanol With Rich Ethanol

Methanol is an important industrial raw material and can be widely used in everyfield of C1chemistry.With the development of downstream industries and expansionof the usable range, there is an increasing demand for the high quality of methanol.The question that the quality level of methanol product was influenced by ethanol isubiquity in the domestic coal-based methanol installation.Research on the way toreduce ethanol content in the methanol product, on the one hand, improve the productquality and raise market competition, on the other hand, provide qualified material forthe downstream products that are sensitive to ethanol content, such as acetic acid.A coal-based methanol installation with the annual output of60thousand tons,the product level should achieve double A grade in the design process (the massfraction of ethanol should less than or equal to10ppm), but the ethanol content is upto1200ppm in the site process. In this paper, based on the background of the fourtower distillation process of the methanol plant, three kinds of retrofit schemes wereproposed, in order to reduce the ethanol content and make the products achievedouble A grade. The main works are shown as follows:(1)By collecting the production data of the field, a simulation model that basedon the real process was built. The influence of the extraction water of thepre-distillation column, feed stage, side product stage and reflux ratio on the ethanolcontent in the products were discussed. The reason why there is a high ethanol contentin the products were analyzed in two aspects, and decided that under currentconditions, to get double A grade methanol should control the content of ethanol inthe crude methanol lower than77ppm.(2)A modified process was put forward, in which a de-ethanol column was addedbefore the original four tower distillation process, for the sake of separating theethanol from the crude methanol. By using the heat pump distillation method, energyconsumption of the device was effectively reduced. Then do the simulation of themodified process and optimization of the designed parameters. Simulation resultsindicated that in the modified process, products can achieve double A grade. (3)There are still some drawbacks of the modified process, the flowsheet was toolong and a high energy consumption. So that a new energy-saving process wasestablished, which was made up of four columns, de-ethanol column, pre-distillationcolumn, main column and recovery column, both the de-ethanol column and maincolumn were adopted with heat pump distillation, methanol of double A grade wasdistillated from the top of the main column, compared with the original process, thenew process not only reduces the investment of the equipment but also have anobvious effect of energy saving.(4) The simulation of the energy-saving distillation process and optimization ofthe designed parameters were taken, then an economic analysis for the three schemeswere finished from the point of energy consumption, advantages and disadvantages ofthe three schemes were compared.For the de-ethanol column, in order to separate micro amount of ethanol, amethod that vaporized almost all the liquids in the bottom of the column was adopted.The details for the design of the two columns that using heap pump distillation werepresented, which were useful for the design of some other process with heat pumpsystem.