Sustainable and Efficient CO2 Utilization: Production of Dimethyl Carbonate By an Indirect Route Using Ethylene Oxide and Methanol

Abstract

Global warming is one of the most challenging phenomena to be faced by humankind in recent history. Anthropogenic greenhouse gases (GHG) are a major culprit in the phenomena. Around 60% of the anthropogenic GHG emissions between 1970 and 2010 are CO2 from fossil fuel and industrial process[1]. However, the increasing demand for chemicals will consequently increase the amount of CO2 emitted. This calls for additional means for CO2 reduction. Such means could bethe capture of CO2 and using it as a new carbon source to produce a variety of chemicals. However, such process are few and not widespread. The process considered consist of two parts: CO2 capture plant and a CO2 utilization plant that converts CO2 to DiMethyl Carbonate (DMC). DMC is a versatile, non-volatile chemical compound used as reactive intermediate for methylation and carboxylation reactions, as fuel additive, as solvent for coating as well as inpolymerization reactions [2, 3]. The market value for this green agent is rapidlyon the rise; valued at US$ 390 mn in 2014 and projected to reach US$ 690 mnby 2023 [4]. The high demand for DMC represents the perfect platform for this sustainable design problem. The problem is mainly concerned with the sustainable design and optimization of the utilization plant. The design is preformed based on a 12-step hierarchical decomposition strategy. Starting from collecting information about the raw materials and the possible reaction pathways to generation of a preliminary flow-sheet based on which the process parameters are set. This is followed by mass and energy balance, which are then verified by performing a process simulation with a commercial simulator like PRO/II. Sizing and costing are then performed on all equipment used to enable a full economic evaluation of the process. A brief description of the proposed process is as follows: CO2 is reacted inexcess with ethylene oxide (EO) to produce ethylene carbonate (EC), eventual impurities are removed by means of a distillation. EC is then reacted with excess methanol (MeOH) to produce ethylene glycol (EG) alongside the product of interest DMC. The recovery of the DMC and EG is done by: separating {DMC+MeOH}from {EG+EC} by regular distillation. The unreacted EC is hydrothermally converted into EG. The system {DMC+MeOH} form a pressure sensitive azeotrope and are therefore separated by pressurized distillation. The proposed process de-sign is able to supply 100,000 metric tons DMC and similar quantity of EG, utiliz-ing around around 53,000 metric tons of CO2 and consuming around 75,000 metrictons EO and 74 metric tons MeOH on a yearly basis. The base case is then subjected to environmental impact analysis as well as an investigation into further improvements and optimization e.g. mass and heat integration, enabling the setting of design targets for further improvement so that a more sustainable process design can be obtained. The original design is thus further developed to incorporate a more thorough sustainability analysis and a life-cycle assessment (LCA) to determine process bottlenecks that when removed through, for example, process intensification or alternative hybrid operations, leads to a more sustainable process design.