Manufacturing Dimethyl Ether From Methanol

Abstract

One of the sources of dimethyl ether is methanol. This report analyzes the viability of manufacturing dimethyl ether from methanol by heating it and converting it to dimethyl ether and water. The report considers different costs of operation to calculate the profitability of a plant producing 100,000 tonnes annually. Calculations reveal it is a viable project and the report offers recommendations for making the project safer and more efficient.

Introduction

Dimethyl ether (DME) also known as Prozone or blue fuel is made by converting hydrocarbons which are first converted to methanol and then to DME (Aresta 13). It can be made from other sources such as wood byproducts, household and crop waste, or algae biomass. It has a chemical formula CH₃OCH₃ and is considered a more clean fuel than methanol. It is also used for making dimethyl sulfate, a methylating agent, and for making acetic acid. The process of converting methanol to DME basically involves methanol dehydration. Dimethyl Ether is only useful in very low temperatures, limiting its usefulness.

Process description

The raw material in this experiment is pure methanol. The feed, which is at 1 atm pressure and 25⁰c, together with the recycling from the last distillation column or a methanol recycle separator is pumped to a feed preheater. The pump increases the pressure to15 bar or 14.80 atm. Here it is superheated to vaporization at 250⁰c and a pressure of 14.80 atm. The source of energy must be above 25⁰0c to be able to deliver that much energy. It is then sent to a dimethyl ether reactor where methanol converts to DME and water. The reaction is as follows:

From here, the already formed crude dimethyl ether or effluent is sent to a crude DME product cooler where it is cooled and partially condensed and then sent to a separating column. Its pressure is reduced by passing it through control valves before the product cooler. This is because the exit pressure must be below 14.80 atm but must equal that of the DME separator. The distillation column then separates DME from water and methanol, resulting in three output streams.

One is pure dimethyl ether or the distillate, which is sent to a condenser. At the condenser, pure dimethyl ether is condensed from saturated vapor to saturated liquid and then sent to storage. The second stream which is recycled delivers unconverted methanol to a reboiler where it is vaporized from saturated liquid to saturated vapor and send back to the distillation column. The third stream carries water and unconverted methanol to a methanol recycle separator. In this separator, effluent water is sent to a wastewater treatment plant while the unconverted methanol or recycle is sent back to the feed stream.

Assumptions

• Methanol used is in its pure form.
• The DME to the storage tank is pure assuming 100% efficiency of the distillation column.
• The methanol recycle separator has 100% efficiency meaning the cost of wastewater is zero.
• 330 days per year to allow shutdowns and maintenance

Results

Figures to be used in this experiment are: Q = 26,574 MJ/h

Pressure of saturated steam P_sat= 42.37 bar

Temperature of saturated steam = 253.72⁰c

Dimethyl ether production rate= 15670.19 kg/h

Cost of steam = $ 135.55/hr or $ 1, 084,377.35/year

Cost of fuel = $ 79.72’hr or $ 637,776/year

Using these figures for cost calculations, the cost of production amounts to $ 8.65/ 1000kgs of DME produced.

Cost of dimethyl ether = $0.43/lb

cost of methanol = $ 0.60/gal

Analysis

From this experiment, the costs of operation are steam production, fuel gas for heating, electricity, and cooling water.

From the calculations, the cost of production is $ 8.65/ 1000kgs pf DME produced. The cost of dimethyl ether in the market is $ 0.43/lb or $ 0.43/0.45359237kgs since

1 pound=0.45359237kgs.

Therefore 1000kgs of DME are worth $ 1055

This translates to a profit of $ 1046.35 for every 1,000 kgs of DME produced.

In this experiment, the desired production rate at an optimum level is 100,000 tonnes/year.

The project then translates to a profitability of $104,635/year.

Conclusion

Dimethyl ether can be made from many other sources such as wood byproducts, household, and crop waste, or from algae biomass. These sources although more affordable than methanol may not have reliable sources. Producing DME from methanol proves viable from the figures, with a profit of $ 104,635/year, assuming a production of 100,000 tonnes/ year. Methanol is easily available considering it can now be produced easily from natural gases. It can also be made from H₂ and CO₂, increasing its availability. This makes it a reliable source for the manufacture of DME.

Using methanol in its pure form minimizes the cost of purifying it. It also reduces the amount of energy used to heat it as it evaporates easily in its pure form. Purity minimizes the chances of contamination of the final product eliminating the need for purification. Undoubtedly, many commercial plants would be able to manufacture much more than the quantity in this experiment, making it a very viable project. Since DME is easily explosive, high safety measures required for manufacturing it add up to its cost of production.

Recommendations

Dimethyl ether has more hazardous fires as a result of its low flashpoints. It has a flashpoint of -41⁰c causing it to form explosive mixtures easily (Frederick 13). Any experiment involving DME should be done under professional supervision and uncompromising safety measures. The process requires a lot of water for cooling and condensation. DME manufacturing plants should be located in places where water is easily accessible. Since the biggest cost of production is that of energy, the project can be made cheaper by using renewable energy such as solar where applicable.

Works cited

Aresta, Molar. Carbon Dioxide Recovery and Utilization. New York: Kluwer Publishers. Print.

Frederick, Albright. Chemical Engineering Handbook. Boca Raton: CRC press, 2009. Print.