COMPARATIVE ANALYSIS OF THE MAIN COMMERCIALLY AVAILABLE ALCOHOL DEHYDRATION PROCESSES―AZEOTROPIC, EXTRACTIVE AND MOLECULAR SIEVE―A TECHNICAL AND ECONOMICAL APPROACH

摘要

The main commercially available processes for dehydration of alcohol, say, azeotropic, extractive and molecular sieve, present a number of characteristics such as plant sizes and quality of water or steam availability, which make them especially suitable for different situations. Besides, an important and differentiating characteristic of the process nowadays is its capacity of energetic interactions with other parts of the sugar and alcohol plant. Historically, in Brazil, extractive distillation using glycerine as dehydrating agent was largely used up to the 1970s, but faced process limitations mainly due to glycerine viscosity. Then the process was successfully substituted by azeotropic distillation, based on benzene as dehydrating agent. The latter process had obvious hazards, and was adjusted to the use of cyclohexane in the 1980s. Worldwide, the application of the molecular sieve solution occurred at the same time. Recently, extractive distillation became a third commercial option, using a process with ethylene glycol as dehydrating agent. The present study has been developed with the intention to show, in a technical and economical approach, both the positive and negative points involving each of the referred processes. To do this, Dedini, as manufacturer of the three processes, collected data from plants worldwide, and submitted the data to a rigorous analysis of the following points: 1 - Steam consumption, considering source, price and availability. 2 - Water consumption and refrigeration, based on inlet and outlet temperature, and necessity of treatment. 3 ― Possible undesired residues and recycles. 4 - Safety, health and environment. 5 - Capacity of energetic interactions with other parts of the sugar and alcohol plant. 6 - Plant size and initial investment. 7 - Automation required. The study concluded that each process has its optima in performance for different situations, as expected. As a general rule, the cyclohexane process is very suitable for small to middle plants of alcohol for fuel purposes and represents minimum investment. The extractive process based on ethylene glycol represents a good option as a middle-investment for anhydrous alcohol production containing a trace of the agent present in the product. Finally, the molecular sieve, whose anhydrous alcohol does not show any trace of the dehydrating agent, has the lowest steam consumption, but with a higher investment. The final choice will require more evaluation.