Final Report: Micro Channel Electrochemical Production of Dimethyl Carbonate
EPA Contract Number:
Micro Channel Electrochemical Production of Dimethyl Carbonate
C. Kimble, Dr. Michael
Reactive Innovations, LLC
May 1, 2014 through
May 1, 2015
Small Business Innovation Research (SBIR) - Phase I (2014)
Small Business Innovation Research (SBIR)
SBIR - Innovation in Manufacturing
Presently, there are no U.S. manufacturers for producing dimethyl carbonate (DMC), an environmentally benign solvent used in the manufacturing of numerous products. These products range from lithium ion batteries to the production of polycarbonates, lubricants, polyurethanes, cleaning and degreasing solvents, construction materials such as paints and adhesives, fuel additives and biodiesel production. Surprisingly, this strategically important solvent is produced almost exclusively in China and South Korea, which adds additional shipping costs and transportation delays to U.S. manufacturers.
DMC is usually manufactured from one of three methods. The first method is the phosgene route, where it reacts with methanol, yielding DMC and hydrogen chloride. The second method is the epoxide route, where epoxides such as ethylene oxide react with carbon dioxide, yielding cyclic carbonates. These carbonates are then transesterificated with methanol, producing DMC and glycols. One major issue with the production of glycols is the health effects: it can be fatal. The final traditional method is the oxidative carbonilation route, where carbon monoxide and methanol react with an oxidant compound such as nitric acid yielding DMC. If nitric acid is used, an ammonia oxidation unit is necessary for producing large capacities. In addition, the synthesis of DMC takes place through methyl nitrite as an intermediate that can cause safety issues as well.
Although DMC is a green solvent itself, the traditional dimethyl carbonate production methods involve toxic and hazardous phosgene and carbon monoxide reagents while producing harmful byproducts. It would be better if a green manufacturing method could be used to produce this green DMC solvent. And with this green DMC solvent, U.S. manufacturers could produce a myriad of products using green manufacturing technology.
Toward this goal, Reactive Innovations, LLC, worked on developing a green manufacturing technology to produce DMC using an electrochemical synthesis method that reacts carbon dioxide and methanol feedstocks in an ionic liquid electrolyte medium. A microchannel electrochemical synthesis reactor was examined to enable the continuous production of DMC using these benign chemical feedstocks.
Several university research groups in China have reported the electrochemical production of DMC via bubbling carbon dioxide gas in an ionic liquid electrolyte while applying upwards of 5 volts for 48 hours. Subsequently, methanol would be added, which would produce a low yield of dimethyl carbonate. Reactive Innovations examined this prior published work by using the recommended ionic liquids that include Bmim-Br and Bmim-Cl using platinum based electrodes. After calibrating a gas chromatograph for DMC detection, the company did not observe any DMC produced using these published methods. Variations of the methods were conducted that examined different molar ratios of ionic liquid to methanol, CO2 reduction voltages, time and different ionic liquids. In all cases, no DMC was produced.
Reactive Innovations’ initial proposed method aimed to speed up the production of dimethyl carbonate by imbibing the ionic liquids into a Nafion ion-exchange membrane that is catalyzed on both membrane surfaces. Methanol is fed to the anode side of the reactor where MeOH permeates through the ionic-liquid imbibed membrane to the cathode side. On the cathode side, carbon dioxide gas flows where it is reduced to a carbon oxide radical on the catalyzed surface and where it subsequently reacts with the methanol molecules permeating from the anode side to produce DMC. The company has shown previously higher reduction rates for CO2 reduction on platinized membrane surfaces rather than via dissolving CO2 into ionic liquid electrolytes. Consequently, Reactive Innovations developed electrochemical reactors accordingly and found no evidence of DMC being produced by this method.
Reactive Innovations examined other methanol and ionic liquid mixtures that include Bmim-BF4 and Emim-TFMS using similar methods to introduce carbon dioxide to the cathode over time while reducing it to produce DMC. Measurements included cyclic voltammetry, and gas chromatograph analysis did not show any evidence of DMC being produced.
Another research group in China demonstrated DMC production using via bubbling CO2 in an ionic liquid electrolyte while reducing it for 6 hours. This was followed by adding methanol, and then by adding methyl iodide to produce DMC. Reactive Innovations examined variations of this approach and were able to produce DMC electrochemically although in low yields on the order of 0.2 percent. The company conducted a cost assessment of this approach and found that the use of methyl iodide is cost prohibitive, culminating in a cost of $4,500 per ml of DMC. Thus, although a safer method for producing DMC is possible, the cost is too excessive to commercialize using a methyl-halide compound.
This Phase I program examined numerous ionic liquid, methanol and catalytic variations via applying a reductive potential over time to produce dimethyl carbonate using carbon dioxide and methanol feedstocks. Only via using a methyl-halide compound was Reactive Innovations able to produce DMC electrochemically. This compound is cost prohibitive. However, it does show that other reaction pathways are possible for electrochemical production of DMC using CO2 and methanol.
The importance of producing DMC using benign and low-cost carbon dioxide and methanol feedstocks is still present. The reduction process for reducing carbon dioxide to a carbon oxide radical is too long, being more than 48–60 hours in a small batch process. This is the main reason a catalytic ion-exchange membrane surface is deemed essential to speed up this process since it overcomes the low solubility and diffusion rates of CO2 in ionic liquid electrolytes. Continued work should focus on this approach, examining other catalysts to speed up the reaction process. It also is suggested that the presence of a halide compound may help synthesize the formation of DMC from methanol and the carbon oxide radical. To this end, the halide catalyst should be integrated into the ion-exchange functional membrane groups so that it facilitates the DMC reaction while not being consumed.
Commercialization: Toward commercializing this DMC production process, there are no firms in the United States producing this solvent, with the bulk of production occurring in China, South Korea and Russia. There are a few firms in the U.S. that might have an interest in producing DMC once a low-cost and environmentally acceptable process is defined. This compound is listed on the Toxic Substances Control Act (TSCA) inventory, where a Bona Fide Intent to Manufacture should be filed during the Phase II program that will help identify any restrictions toward manufacturing DMC.
There are two drivers that affect DMC production: (1) regulation issues associated with the hazardous/toxic chemicals used to produce DMC, and (2) thin margins in the United States. This appears to be why there is little to no U.S. manufacturing of this solvent, with most being produced overseas. The company’s nonhazardous synthesis method should ease the first issue, and being a U.S. manufacturer should minimize shipping costs and speed up delivery times, addressing the second issue.
The market size for solvents continues to grow in the United States at a continuous aggregate growth rate of 5 percent. For DMC, the market size is growing faster at a compound annual growth rate of 8.8 percent, which bodes well for its continued product demand. With the continued adoption of DMC as a solvent by manufacturers, and with incentives to manufacture products using green manufacturing methods, DMC demand will continue to grow. The initial goal for this program still holds true in that a low-cost, safe and environmentally safe process is needed to produce DMC using inexpensive CO2 and methanol feedstocks.
green manufacturing, dimethyl carbonate, DMC, energy consumption