Methanol, production efficiency

For the methanol route the solar-to-biomass efficiency of 0.2% is followed by a methanol production efficiency (50%), a DMFC or reformer-PEMFC efficiency of 40%, an electric motor efficiency of 93% and the same power train and driving efficiencies as for the fossil fuel car. 

The rate-based model gave a distillate with 0.023 mol % ethylbenzene and 0.0003 mol % styrene, and a bottoms product with essentially no methanol and 0.008 mol % toluene. Miirphree tray efficiencies for toluene, styrene, and ethylbenzene varied somewhat from tray to tray, but were confined mainly between 86 and 93 percent. Methanol tray efficiencies varied widely, mainly from 19 to 105 percent, with high values in the rectifying section and low values in the stripping section. Temperature differences between vapor and liquid phases leaving a tray were not larger than 5 F. 

However, there are several issues with widespread methanol usage. Methanol production from natural gas is relatively inefficient ( 67%), and this largely offsets the vehicular improvement in efficiency and carbon dioxide reduction (since gasoline can be made with "85% efficiency from oil). Additionally, the PEM fuel cell demands very pure methanol, which is difficult to deliver using existing oil pipelines and may require a new fuel distribution infrastructure. 

Both new catalysts and new processes need to be developed for a complete exploitation of the potential of CO2 use [41]. The key motivation to producing chemicals from CO2 is that CO2 can lead to totally new polymeric materials and also new routes to existing chemical intermediates and products could be more efficient and economical than current methods. As a case in point, the conventional method for methanol production is based on fossil feedstock and the production of dimethyl carbonate (DMC) involves the use of toxic phosgene or CO. A proposed alternative production process involves the use of CO2 as a raw material (Figure 7.1)... 

Onboard gasoline reforming could serve as an interim step and accelerate the commercialization of PEM fuel cells. It does not require a hydrogen infrastructure. Onboard methanol reformers are likely to be even less efficient than gasoline reformers. For the immediate future, increases in methanol production are likely to come from overseas natural gas. 

Methanol can be produced from biomass, essentially any primary energy somce. Thus, the choice of fuel in the transportation sector is to some extent determined by the availability of biomass. As regards to the difference between hydrogen and methanol production costs, conversion of natural gas, biomass and coal into hydrogen is generally more energy efficient and less expensive than the conversion into methanol. 

Further examples of recent attempts to reduce the consumption of electrical energy are the electrolysis of aqueous solutions of methanol (but CO2 is still produced at the anode) [78, 79] and water electrolysis using ionic liquids as electrolytes [80]. In the latter case, the authors claimed the possibility of obtaining high hydrogen production efficiencies using an inexpensive material such as low-carbon steel. 

Larger methanol production plants are more efficient than smaller ones. The size of a large (called world-scale) methanol plant is in the range of2000-2500 metric tons per day. If methanol were to become a widely used alternative fuel, many more methanol production plants would be required. Plants as large as 10,000 metric tons per day have been postulated to serve the demand created by transportation vehicles. 

In an aqueous C02-saturated Na2S04 electrolyte, using electroplated Ru electrodes, Frese and Leach observed faradaic efficiencies of up to 42% for methanol production at a temperature of 333 K at a potential of only -0.55 V (versus SCE) [54]. Faradaic yields of up to 30% were likewise obtained for methane. When Popic et al. examined Ru02 electrodes, either alone or with Cu and Cd adatoms [64], in 0.5 M NaHC03 at a potential of-0.8 V (versus SCE), they were able to reduce C02 to methanol with faradaic efficiencies of 17%, 41%, and 38% after 480 min of electrolysis for Ru02, Ru02/Cu, and Ru02/Cd electrodes, respectively. 

More recently, the use of a pyridinium mediator in an aqueous p-GaP photo-electrochemical system illuminated with 365 nm and 465 nm light has been reported [125], In this case, a near-100% faradaic efficiency was obtained for methanol production at underpotentials of 300-500 mV from the thermodynamic C02/methanol couple. Moreover, quantum efficiencies of up to 44% were obtained. The most important point here, however, was that this was the first report of C02 reduction in a photoelectrochemical system that required no input of external electrical energy, with the reduction of C02 being effected solely by incident fight energy. 

Methanol production today is not a sustainable process but is part of a petrochemical route for conversion of fossil carbon into chemicals and fuels (see Section 5.3.3). It has to be emphasized that a one-to-one upscaling of existing industrial methanol synthesis capacities for fuel production is not useful. This is mainly because the current industrial process has not been developed and optimized under the boundary conditions of conversion of anthropogenic C02, but rather for synthesis gas feeds derived from fossil sources such as natural gas or coal. The switch to an efficient large-scale methanol synthesis with a neutral C02 footprint is still a major scientific and engineering challenge, and further research and catalyst and process optimization is urgently needed to realize the idea of a sustainable methanol economy. ... 

Most of the efficiency loss in methanol production occurs in the reformer (]). This is because high grade fuel must be burned to supply the reforming heat load and combustion is a thermodynamically inefficient process. 

So, therefore, in all respects the two reactions are incompitable. Even if new and more highly active catalysts can be developed, it will be difficult to match them such that a significant reduction can be achieved in the efficiency of methanol production via reforming. 

It is obvious that the production efficiency of the methanol vectors is lower than gasoline production efficiency, due to the conversion of the primary energy (hydro)electric power to a completely different energy carrier. As shown in Fig.l the primary energy demand for the production of methanol is 9.5 (conc.-C02) and 11.4 kWh/1 methanol (air-C02). This is corresponding to an efficiency for the fuel generation of 45.8 and 38.1%, respectively... 

The ultimate goal in methanol production will be achieved if satisfactory catalysts and reactor technologies can be developed for efficient direct catalytic oxidation of methane or natural gas. 

In methanol the efficiency of formation of elimination product 39 is higher than in TFE. In the cation-molecule pair formed upon photolysis of 37 in methanol (Scheme 53), the methanol not only acts as a nucleophile but also as a base. In TFE the proton has to be abstracted by the less basic agents iodobenzene, the leaving group, or external TFE. 

Summarising what has been discussed in section 4, we present the global production of some alternatives in Table V. The scale of demand for gasoline calls for huge investment to replace gasoline by, e.g., methanol. Economic factors as well as the low efficiency of methanol production (Tkble IV) indicate that careful consideration is required before vigorously pursuing alternatives like these. 

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