Elsevier

Journal of Cleaner Production

Volume 57, 15 October 2013, Pages 19-37
Journal of Cleaner Production

Review
A review of cleaner production methods for the manufacture of methanol

https://doi.org/10.1016/j.jclepro.2013.06.017Get rights and content

Highlights

  • Technological advancements of methanol production have been discussed.

  • Recently developed process, kinetic and catalyst deactivation models have been reviewed.

  • Different reactor types and/or configurations used and modelled are described.

  • Environmental impacts of production have been discussed.

Abstract

Growing population and expanding economies are important causes of increasing global energy demand. In wake of the continuous hike in the petroleum prices, depleting world resources and increased constant threat to planet's environment, the need for environment friendly alternative fuels has augmented many times. Methanol has been in the limelight over the past few years. High production cost, catalyst deactivation, economy of scale, huge energy requirements are the leading bottlenecks, which should be resolved to move towards the cleaner production. To address the issues, various reactors and their configurations have been modelled over years and the need to summarise all these efforts seems obligatory. One-dimensional to three-dimensional models for traditional packed bed reactors to processes for direct conversion of natural gas to methanol is available in literature. The presented study is an attempt to compile most of these efforts in order to guide future work in this area for cleaner and healthier environment.

Introduction

World economy relies heavily on energy resources and their abundance. The average rate of global energy use, in terms of power equivalent, was about 1 TW in 1990 and doubled by 1955. It increased to 12 TW by 1999 (Reay et al., 2008) and was projected to attain about 18 TW in 2012 (US Energy Information Administration, 2011). In terms of global annual energy use, the equivalent value projected for 2012 would be about 160,000 TWh or 570 × 106 TJ. Till 2006, 16% growth in primary energy use was recorded worldwide and still growing from that time. The statistics demonstrate heavy reliance of world economy on energy resources and their still considerable availability. Fossil fuels have remained the basic source of energy for centuries, whose demand has increased noticeably during the past decades. More than 80% of global energy demand is still met by fossil fuels due to their abundance, affordability and availability (Kumar et al., 2011). The world fossil fuel resources are depleting and the cautions issued by environmental protection agencies around the globe have stricken energy-famished nations. The oil crisis of 1970s paved way for alternative energy sources and also stressed on the need of effective utilisation of available resources. Even though crude oil prices touched alarming levels at the start of this century, energy supply has been and in all likelihood will continue to be dominated by fossil fuels (Browne et al., 2012).

The increasing dependency and subsequent demand of petroleum and its by-products revolutionized the world but at the same time, this rapid industrialisation caused many environmental problems (Benhelal et al., 2013). They have been various options how to deal with this problem under investigation (Munir et al., 2012). Energy related CO2 emissions around the globe have increased by 38.14% from 21.5 × 109 t to 29.7 × 109 t between 1990 and 2007 (U.S. Energy Information Administration, 2010). The 2012 figure already reached 35.6 × 109 t (Sikdar, 2013). The ever-increasing interest risk of climate change is a stiff challenge for global society. According to Kyoto Protocol, the conference of the parties has agreed that by committed period 2008–2012, developed countries shall be legally committed to reduce their collective greenhouse gas (GHG) emissions by at least 5% compared to 1990 levels (Barranon, 2006). The recent Doha United Nations Climate Change Conference (2012) reached an agreement to extend the life of the Kyoto Protocol, which would expire at the end of 2012, until 2020, and to highlight the Durban Platform for Enhanced Action (2011), meaning that a successor to the Protocol is set to be developed by 2015 and implemented by 2020.

Using renewable resources to substitute fossil fuels is one of the technological options to mitigate GHG emissions. With almost 30% (27% in 2007) of the world's total delivered energy being utilised in the transportation sector only – mostly as liquid fuels (U.S. Energy Information Administration, 2010), increasing energy security and CO2 emissions, both hydrogen and methanol economy may serve as saviours (Olah, 2005). Methanol has edge over hydrogen gas as it is safe liquid. It is easy for storage and distribution; it can be blended with gasoline and can also be used in the direct methanol fuel cells (Masih et al., 2010). There have been some recent developments for sizable proportion of liquid consuming transportation vehicles (cars, trucks, trains, and planes) to use methanol as their energy source (Luyben, 2010).

Methanol can be obtained from multiple sources including biomass and coal but natural gas (NG) is a better choice as a feedstock for methanol. The reason is natural gas is available in high quantities compared to biomass resources and compared to coal; natural gas conversion is environmental friendly process. Production of methanol, dimethyl ether and synthetic fuels from NG has become an important option for exploitation of oil and gas fields, which earlier were not economically viable. This concerns remote gas fields, gas fields without transport infrastructure, and associated gas fields where a total solution for both oil and gas is needed (Kvamsdal et al., 1999). NG, one of the major fossil energy sources has estimated proven gas reserves of 177 × 1012 m3 of which around 40% are too far from market reach (Velasco et al., 2010). Well-established technologies are available for conversion of NG to synthesis gas (SG) and are widely used in chemical process plants. All over the world, methanol production has risen by 42% from 2001 to 2008 (PCI-Ockerbloom & Co. Inc., 2010). Annual production in 2010 was 45 Mt (Aasberg-Petersen et al., 2011).

The methanol market is in a state of change with some derivatives declining, such as methyl tertiary-butyl ether (MTBE), whilst others are increasing strongly such as biodiesel, gasoline blending, dimethyl ether (DME), Methanol to Olefins and Methanol to Propylene. Demand potential into these new outlets is highly dependent on the cost competitiveness of methanol against traditional alternatives such as liquefied petroleum gas. This in turn is determined by future developments in feedstock prices and the structure of the methanol production base (Chem Systems, 2009/10). Overall world demand for methanol is projected to grow at an average annual rate of 9.8% from 2010 to 2015, with lower growth expected in the industrialised areas of the world where the markets are mature. But none of these facilities suffice to produce and supply the quantities required if SG/methanol were to play an increasing role as a new energy source for road traffic Swain et al. (2011). China has been the largest methanol consuming country, and will increase its share of world consumption from almost 41% in 2010 to about 54% in 2015 (Saade, 2011). With increased demand, it is essential to economise the various available processing technologies. Since the industrial implementation of methanol manufacturing process in 1923, there have been constant efforts to upgrade the technology and to incorporate latest research developments (Lange, 2001).

Methanol is a key chemical intermediate and numerous applications transform it into vital products and commodities that span and drive modern life. Fig. 1 gives an overview of methanol demand by end use. Worldwide, formaldehyde production is the largest consumer of methanol, accounting for almost 32% of world methanol demand in 2011. This is anticipated to fall to 25% by 2016 with Gasoline/Fuel applications becoming the largest demand sector, totalling 31%. The consumption of methanol into direct fuel applications surpassed MTBE as the second largest market for methanol, with almost 11% of global methanol demand; by 2016, it is expected to account for 16%, increasing at an average annual rate of nearly 20%. Acetic acid/anhydride and MTBE each share 10% of methanol market volume (Saade, 2011). Methanol to Olefins (MTO) and methanol to propylene (MTP) demand is anticipated to become a high growth sector, rising from 6% of end use demand in 2011 to 22% by 2016, the vast majority of which is forecast to take place in China (Johnson, 2012). Other uses of methanol include wastewater de-nitrification, hydrogen carrier for fuel cells, transesterification of vegetable oils for biodiesel production and electricity generation (Biedermann et al., 2006). There are thousands more products that also touch our daily lives in which methanol is a key component.

Methanol production is today a mature technology and literature covers almost every aspect of its process. High-energy inputs, subsequent installation and maintenance cost render further investment in the field of methanol unless new, improved and efficient processes are not developed. Additionally the process has cleaner production problems associated with deactivation of the catalyst. Existing models only address individual steps or consider localised problems and the need to model the broader canvass is obligatory or imperative.

The main objective of this paper is to highlight the problems associated with mass production of methanol and compile the efforts put in by scientists and researchers to overcome them all in the field of modelling and optimisation. The environmental benefits of utilising methanol for CO2 reduction shall also be discussed. Hereafter, methanol production process and its challenges are detailed briefly, followed by description of various kinetic, catalyst deactivation and process models. Next is discussion on the application of different reactor types and their models to methanol synthesis for process improvement. This is followed by details of solved optimisation problems and finally the conclusion is presented.

Section snippets

Methanol synthesis technologies

One of the most difficult problems in designing methanol synthesis reactor is removal of reaction heat. Precise temperature control is an additional constraint in the solution of this problem, as excessive temperatures largely affect catalyst life. Tijm et al. (2001) reviewed the development of methanol process and reactor technologies, and broadly classified them into two categories, namely, the gas phase and liquid phase processes. Table 1 shows main technology suppliers and the operating

Modelling as solution

Environmentally benign technical solutions, sustainability, efficient plant design, optimisation of process schemes and development of new technologies are only few of the methods that may be adopted to hold decrease in the capital cost of any process (Velasco et al., 2010). The application of modelling and simulation to chemical reactors is handy for design, development, operation and improvement of chemical reactors in their online performance. Theoretical and experimental studies for packed

Optimisation

Optimisation strategies for avoiding the reactor catalyst deactivation have been discussed by many authors. Ogunye and Ray (1971) studied optimal control of adiabatic and isothermal reactors, optimal catalyst distribution along the reactor and feed distribution between multiple reactor beds. Elnashaie and Abdel-Hakim (1988) used a heterogeneous model to calculate optimal feed temperature of an adiabatic reactor based on both interphase and intra-particle mass and heat transfer resistances. The

Life cycle assessment

Life cycle analysis (LCA) of a product refers to the impacts made by the product(s) on environment at each and every stage of the production cycle, from extraction of raw materials to waste disposal. LCA is carried out in four steps (Varanda et al., 2011):

  • Purpose and Scope

  • Inventory

  • Impact Assessment

  • Analysis and Improvement

Referring to Fig. 1, the share of methanol as blending component in gasoline is projected to increase from current value of 11 to 16%. Now this has dual impact as there will be

Conclusion

Competition with the existing and far established energy sources is imperative and inevitable for all alternative energy sources. Over the years, improvements in the practical efficiencies have been achieved by a combination of chemical engineering and catalyst development. Further development of methanol synthesis technology has the potential of reducing overall plant cost. SG routes are highly efficient, but capital intensive because they involve exchange of energy in the reformers and heat

Acknowledgements

The first two authors would like to acknowledge financial support of Universiti Teknologi Malaysia under project #Q.J130000.2525.00H81. The third author gratefully acknowledges the financial support from the Hungarian State and the European Union under project TAMOP-4.2.2.A-11/1/KONV-2012-0072 has been significantly contributing to the completion of this analysis.

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