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Low-temperature and low-pressure methanol synthesis in liquid-phase catalyzed by a Copper-alkoxide system Bo Li, and Klaus Joachim Jens Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/ie401966w • Publication Date (Web): 20 Sep 2013 Downloaded from http://pubs.acs.org on September 23, 2013

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Industrial & Engineering Chemistry Research

Low-temperature and low-pressure methanol synthesis in liquid-phase catalyzed by Copper-alkoxide systems Bo Li1, Klaus-Joachim Jens1* 1

Faculty of Process, Energy and Environmental Technology, Telemark University College, Kjølnes ring 56, 3901 Porsgrunn, Norway

We report a new very low temperature methanol catalyst system which is produced in-situ by reaction of Cu(CH3COO)2, NaH and methanol. The catalytic reaction is assumed to proceed in two steps: (i) formation of methyl formate from syngas and (ii) hydrogenation of methyl formate to two molecules of methanol. Testing the catalyst system in a batch reactor, syngas conversion of 50-75% is achieved at a temperature of 60-120oC and pressure of 10-20 bar. Syngas generation is a major cost factor in current commercial methanol technology. Very high conversion per pass (low reaction temperature) in the methanol reactor would allow for the use of air for syngas generation (autothermal reforming or partial oxidation reaction) and thereby contribute to potential cost reduction.

1. INTRODUCTION Methanol has been considered as a potential fuel, as a convenient energy-storage molecule or as a feedstock to synthesize hydrocarbons.1 In recent years, it is also attracting growing interest as a source of hydrogen especially for fuel cells in portable use.2 To realize and accelerate the use of methanol, reduction of capital and production cost are important issues for technology improvement. Current CuZnO methanol synthesis technology is highly optimized, however if a catalyst system operating at very low temperature could be identified the syngas recycle step in the current methanol technology could be avoided.3, 4 The conversion of syngas into methanol is temperature dependent due to the exothermic nature and the reversibility of reaction (1). CO + 2H2 CH3OH

∆H = -90.6KJ/mol

(1)

Methanol is conventionally produced in a gas-solid phase process, which is operated at 250 °C and 70-80 bar pressure in the presence of Cu/ZnO-based catalysts. Under these conditions the reaction is seriously limited by thermodynamics. A large part of technology capital cost is associated with syngas generation. Significant cost reduction could be achieved by syngas generation through partial oxidation with air. Due to the nitrogen dilution however, a high syngas conversion per pass would be needed. A concept for very low temperature methanol synthesis opening the possibility of high conversions per pass was proposed in 1919 by Christiansen.5 This concept builds on reaction of CO with an alcohol to give formate (reaction 2) followed by hydrogenation of the formate to methanol (reaction 3). CH3OH + CO HCOOCH3

(2)

HCOOCH3 + 2H2 2CH3OH

(3)

2H2 + CO CH3OH

(4)

Alcohols carbonylation (reaction 2) is catalysed by alkali metals. Kinetic studies suggest a two-step mechanism consisting of reaction between a metal alcoholate and carbon monoxide ________________________________________________________ ∗

Corresponding author. Tel.: +47-35575193; Fax: +47-35575001.

E-mail address: [email protected]

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to form a metal complex which then reacts with another alcohol molecule to give formate and a new metal alcoholate. Substituents increasing the electron density on the oxygen atom of the alkoxide are reported to accelerate the carbonylation reaction.6 Hydrogenation of the formate to methanol is proposed to proceed through a formaldehyde intermediate.7 From a thermodynamic perspective liquid phase hydrogenation of formate can give near complete conversion of formate to methanol at 10 bar hydrogen pressure and temperature of approx. 120 °C.7 A slurry-8, 9 and an intergraded two-stage reactor10 have been reported as very low temperature methanol synthesis reactor technology. Typical catalyst systems for reaction (2) and (3) are a combination of alkali metal reducing agent, alcohol solvent and a transition metal compound. For group 10 metals a Raney nickel/alkoxide system has been shown to be an active catalyst.11 In general, active nickel based catalyst systems can be synthesized starting with various nickel compounds e.g. Ni(CO)4,12-15 nickel(II)acetate,16-18 in combination with an alkali metal alkoxide co-catalyst. It appears that in many cases [HNi(CO)3]- is the active species for methyl formate (MF) hydrogenation to methanol via intermediate formation of HCHO.12-20 The alkoxide co-catalyst seems to be active for methyl formate formation from CO and alcohol. A Raney copper-alkoxide system is reported to be active for methanol synthesis at 80-100 °C and 10 to 20 bar syngas pressure.22 Also other heterogeneous copper systems (copper(II)acetate,23 copper nitrate24 and copper(I)chloride25) are active catalysts, the most prominent of these being copper chromite.26-30 Interestingly, a physical mixture of CuO/Cr2O3 shows catalytic activity which can be related to a long term milling effect based on creation of lattice disorder and increased catalyst surface area.31, 32 In the presence of alkali alkoxide, the catalytic activity of copper chromite is reported to be increased.30 For the CuCl/CH3OK catalyst a reaction mechanism involving carbonylcopper anions as catalytically active species has been proposed.33 Although other transition metals than group 10 have been reported active for the LTMS reaction, the most active catalyst systems are based on nickel and copper; in this case the alkoxide co-catalyst is not only responsible for carbonylation step but also plays an important role to promote the formation of active catalyst species. However, CO2 and water lead to deactivation of the catalyst system although the copper chromite catalyst appears to be somewhat more resistant to such catalyst poisoning.27 The highly active nickel compound/alkoxide LTMS catalyst system may form in-situ toxic and flammable Ni(CO)4. Thus, the focus of our interest is on Cu compound/alkoxide LTMS systems. Our previous work22 has shown that Raney copper works well as the hydrogenation catalyst in LTMS reaction. The current work reports the catalytic behaviour of a copper(II)acetate/NaH/methanol LTMS catalyst system. 2. EXPERIMENTAL SECTION


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Materials and experimental setup. Copper(II) acetate (99.999%), sodium hydride (NaH, 60% dispersion in mineral oil), methanol (anhydrous, 99.8%) and diglyme (1-Methoxy-2-(2-methoxyethoxy)ethane, ≥99%) were purchased from Sigma-Aldrich. The syngas (CO: 33.3 mol% ±2%, H2: 66.7 mol% ±2%) was purchased from Yara Praxair AS. All chemicals and gas were used as received unless otherwise noted. The reaction was carried out in batch operation in a 70 ml (40 mm diameter) stainless steel autoclave

(PREMEX Reactor AG, Switzerland) equipped with a dip tube for sampling,

an internal thermocouple, a stirrer operating at fixed speed of 300, 500 and 700 rpm, a spring operated safety valve set at 25 bar and a pressure transmitter connected to a PC. The maximum practical operating pressure was 20 bar given by the safety valve, gas tank valve and the reactor pressure gauge. The electric stirrer (27 mm diameter) was connected into the reactor by a magnetic coupling and had oblique impeller blades (approx. 30o angle) extending into the reaction liquid reaching near the bottom of the reactor. The reactor was placed into an oil heated block; the temperature of the oil was controlled by a thermostat (Huber, ministat 230). The temperature inside the reactor was independently logged by a PC using the internal thermocouple. Catalyst preparation and reaction procedure. Predetermined amounts of Cu(acetate)2, NaH and 25g diglyme (1-Methoxy-2-(2-methoxyethoxy)ethane) were added into the stainless steel autoclave under N2 blanket gas. The autoclave was heated to 50 °C and stirred for 30 min followed by 15 mmol methanol addition.

Catalyst conditioning was finalized by stirring for

another 60 min at 50°C. All gas produced during this step was then vented to the ventilation system and typically a 1.5 ml reaction mixture sample was taken through a dip tube connect to a syringe body. Thereafter the autoclave was purged with syngas (H2: CO = 2:1), pure CO or pure H2, pressurized to the designated pressure and then heated to the desired reaction temperature level. Reaction product sampling (typically 1.5 ml) was performed at room temperature. A typical example of the recorded temperature and pressure curves during the course of a catalytic run is shown in Figure 1. The ranges of operating conditions are given in Table 1. For analysis the syringe was disconnected from the dip tube, connected to a needle and 1 g of liquid sample was injected into the sample vial. 0.05g heptane was added into each sample vial as internal GC standard. The samples were manually (not using an auto-sampler) injected into a gas chromatograph (Thermo Electron S.p. A, GC Focus Series) equipped with a FID detector at 250℃. A 60m, 0.32mm I.D., 1.2μ. film thickness, 007 series CARBOWAX 20M column and a programmed temperature profile were employed for product analysis. The initial temperature of the oven was 40 °C with a hold time of 0.5 min, thereafter the oven was ramped 10 °C /min up to the final temperature of 200 °C. Trace amounts of CH3OCH3 are detected in the liquid phase sample after the reaction.



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The catalytic formation of methanol/methyl formate was calculated by subtracting the quantity of methanol/methyl formate present (GC analysis) in the initial reaction mixture (point b in Figure 1.) from the quantity of methanol/methyl formate measured (point d in Figure 1.) at the end of the catalytic reaction. A negative value for methanol formation can be expected for the case of methanol consumption in the carbonylation step only. Syngas conversion is determined as the pressure difference before (point b, Figure 1.) and after (point d, Figure 1.) the catalytic reaction. 3. RESULTS AND DISCUSSION Effect of agitation speed. At constant reaction condition the agitation speed was changed from 300 rpm to 700 rpm. The results are shown in Figure 2. An increase of methanol formation is observed with syngas as reaction gas; methyl formate formation is independent of stirring speed. These results indicate that syngas conversion to methanol, e.g. methyl formate hydrogenation, is mass transfer limited in contrast to MF formation which is not. Our in-situ catalyst formation chemistry could lead to NaOCH3 as a solvent soluble catalyst function and Cu containing material as an insoluble catalyst part. This could be one possible reason for the observed mass transfer limitation of H2 since in this case more phase boundaries would have to be crossed than for the case of CO. I. Wender et al. reported for a related catalyst system tested at somewhat higher pressure and temperature that the carbonylation and its reverse rate are more rapid than the hydrogenation rate.26 It was also reported that the concentration of methyl formate in the liquid phase is close to equilibrium after an initial transient period, indicating that hydrogenation of methyl formate is the rate-limiting step.27 Also in our case the hydrogenation step rather than the CO carbonylation seems to be the bottle neck of the reaction. Effect of reaction temperature. The dependence of the catalytic productivities on temperature is shown in Figure 3. As the temperature increases from 60 to 80 °C, methanol formation and gas conversion increase while methyl formate formation decreases. A maximum of 6.6 mmol methanol was obtained at 100 °C. Further temperature increase does not influence the catalytic reaction. The high productivity of methyl formate obtained at low temperature is noteworthy and indicates the methanol carbonylation reaction to be more active than the methylformate hydrogenation reaction. Thermodynamic equilibrium (100% methyl formate conversion to methanol) is not attained by the hydrogenation function of the catalyst since methyl formate is still observed in the reaction mixture.7 Effect of reaction pressure. The effect of the initial reaction pressure on the catalyst activity was then investigated (Figure 4). The experiment was carried out in the range of 10 bar to 20 bar. Methanol formation is constant up to 15 bar pressure and is highest at 20 bar syngas pressure. Methyl formate formation is by and large constant as the reaction pressure increases


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up to 15 bar. This finding indicates once more that the methanol formation function of the catalyst appears less active than the methyl formate formation function. Effect of Cu(acetate)2 on alcohol carbonylation. To investigate the carbonylation step, experiments with and without Cu(acetate)2 were performed (Figure 5). There is little difference in methyl formate formation between the experiments with and without Cu(acetate)2. This implies that Cu(acetate)2 may not be involved in the carbonylation reaction. Effect of Cu(acetate)2 dosage and NaH dosage. Figure 6 and 7 illustrate the effect of Cu(acetate)2 and NaH dosage on the catalytic performance of the catalyst system. Both compounds give a relatively strong positive effect on methanol formation and a small negative effect on methyl formate formation. During the catalyst preparation step, we expect NaH to first reduce Cu(acetate)2; subsequently the rest may react with methanol to give CH3ONa acting as carbonylation catalyst to form methyl formate. With only 2.5 mmol NaH in the system, apparently CH3ONa only was present to perform the carbonylation step to make methyl formate. Effect of catalyst concentration. Comparing the low- and the high catalyst concentration case in Figure 8 we note that the ratio of Cu: NaH is 1:2.5 in both cases. However, no methanol is formed for the low concentration case while methanol formation is observed for the high concentration case. This implies that two different catalyst types could have been formed in these two cases. It is known that a compound consisting of NaH-NaOR-Metal salt can form in polar aprotic solvents.34 Something similar may happen in our case since our solvent diglyme is of such solvent type. Therefore we suspect that for the low concentration case insufficient NaH (or NaOCH3 through reaction with methanol co-solvent) is available to participate in the formation of the hydrogenation function of the catalyst system. The opposite may be true for the high concentration case. This speculation is in accordance to our earlier observation22 of a synergistic effect between CH3OK and Raney copper for the hydrogenation step of the LTMS reaction. Single step- vs. dual-step reaction. The effect on the catalytic performance by conducting the reaction as a concurrent- or as a dual-reaction was then investigated. The reactions were performed at 100 °C (Figure 9).

The one step reaction produced higher

methanol formation. A similar result was reported by I. Wender et al.27. We speculate that there could be some synergistic effect between carbonylation and hydrogenation step. Catalyst deactivation. The deactivation of the catalyst system was then tested (Figure 10). In each reaction run, at the end of the catalytic reaction (2 hours), the reactor was charged with syngas up to the original starting pressure and a new catalytic reaction was started. After 4 reactions the gas phase of the reactor was vented (from point a to point b in Figure 10) and the total gas phase substituted with syngas at appropriate pressure. ACS Paragon Plus5Environment


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The carbonylation of methanol is much faster than the hydrogenation of methyl formate, a speculation can be made that there is much more H2 than CO left in the system before each re-pressurization. Therefore, the CO content gradually decreased after each pressurization in each run. The decrease of gas conversion in each run could be due to the CO content reduction and catalyst deactivation. As the second run was conducted with the same batch, the faster decrease of gas conversion indicates the permanent catalyst deactivation. In this experiment the reactor was re-pressurized 8 times leading to a total pressure drop of 82.6 bar (107 mmol gas consumption). Based on Equation (1), this translates into 36 mmol methanol formation. Hence 7 times more methanol (36 mmol) has been formed than the starting amount of NaH (5 mmol). This result confirms that this methanol formation is a catalytic reaction rather than stoichiometric reaction at our experimental conditions. 4. CONCLUSION We report a new very low temperature methanol synthesis catalyst system which is produced in-situ by reaction of Cu(CH3COO)2, NaH and methanol. The catalytic reaction is assumed to proceed in two steps: (i) formation of methyl formate from syngas and (ii) hydrogenation of methyl formate to two molecules of methanol. Testing the catalyst system in a batch reactor, syngas conversion of 50-75% is achieved at a temperature of 60-120°C and pressure of 10-20 bar. The reaction is mass transfer limited for the hydrogenation step (ii); both reaction steps are accelerated by pressure and temperature increase. A single step methanol synthesis (concurrent reaction step (i) and (ii)) gives higher methanol product formation than a corresponding two step (separation of reaction step (i) and (ii)) methanol synthesis. Hence it appears that synergistic effects may be realized in a single step reaction. Considering catalyst chemistry, the known issue of catalyst tolerance towards poisons (e.g. CO2, H2O) remains to be addressed. Focus is also needed on catalyst activity in future work as thermodynamics would allow the high gas conversion needed for the potential substitution of O2 by air in syngas generation.

LITERATURE CITED (1) Olah, G. A. Beyond Oil and Gas: The Methanol Economy. Angew. Chem. Int. Ed. 2005, 44, 2636. (2) St-Pierre, J.; Wilkinson, D. P. Fuel Cells: a New, Efficient and Cleaner Power Source. AlChE J. 2001, 47(7), 1482. (3) Hansen, J. B.; Højlund, N. PE In: Ertl G, Knozinger H, Schuth F, Weitkamp J (eds) Handbook of Heterogeneous Catalysis, Vol 6. Wiley, Weinheim, 2008, p 2920. (4) Marchionna, M.; Massimo, Lami, Massimo.; Raspolli Galletti, A. M. Synthesizing methanol at lower temperature. Chem. Tech. 1997, 27(4), 27. (5) Christiansen, J. A. Method of producing methyl alcohol from alkyl formates. US Patent 1,302,011, 1919.


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(6) Tonner, S. P.; Trimm, D. L.; Wainwright, M. S. The base-catalysed carbonylation of higher alcohols. J. Mol. Catal. 1983, 18, 215. (7) Sørum, P. A.; Onsager, O. T. Hydrogenolysis of Methyl formate to Methanol. 8th International Congress on Catalysis. DECHEMA and Verlag Chemie, Weinheim, 1984, p II-233. (8) Zhao, Y.; Huang, Z.; Zhang, K.; Li, S. Investigation of low-temperature methanol synthesis in a bubble column slurry reactor with a flash column. Fuel Process. Technol. 2007, 88, 137. (9) Zhang, K.; Song, H. S.; Sun, D. K.; Li, S. F.; Yang, X. G.; Zhao, Y. L.; Huang, Z.; Wu, Y. T. Low-temperature methanol synthesis in a circulating slurry bubble reactor. Fuel 2003, 82, 233. (10) Linghu, W. S.; Liu, Z. Y.; Zhu, Z. P.; Yang, J. L.; Zhong, B. Methanol synthesis in an integrated two-stage reactor. Chem. Eng. Sci. 1999, 54, 3671. (11) Lee, E. S.; Aika, K. I. Low-temperature methanol synthesis in liquid-phase with a Raney nickel–alkoxide system: effect of Raney nickel pretreatment and reaction conditions. J. Mol. Catal. A: Chem. 1999, 141, 241. (12) Mahajan, D.; Sapienza, R. S.; Slegeir, W. A.; O’Hare, T. E. Homogeneous Catalyst Formulation for Methanol Production. US Patent 4,935,395, 1990. (13) Marchionna, M.; Basini, L.; Aragno, A.; Lami, M.; Ancillotti, F. Mechanistic studies on the homogeneous nickel-catalyzed low temperature methanol synthesis. J. Mol. Catal. 1992, 75, 147. (14) Li, K. L.; Jiang, D. Z. Methanol synthesis from syngas in the homogeneous system. J. Mol. Catal. A: Chem. 1999, 147, 125. (15) Mahajan, D.; Krisdhasima, V.; Sproull, R. D. Kinetic modelling of homogeneous methanol synthesis catalyzed by base-promoted nickel complexes. Can. J. Chem. 2001, 79, 848. (16) Ohyama, S. Low-temperature methanol synthesis in catalytic systems composed of nickel compounds and alkali alkoxides in liquid phases. Appl. Catal., A-Gen. 1999, 180, 217. (17) Ohyama, S. Transformation of the nickel precursor in catalytic systems for low-temperature methanol synthesis in liquid phase. Appl. Catal., A-Gen. 1999, 181, 87. (18) Ohyama, S. A comparison of the catalytic performance for low-temperature methanol synthesis in a liquid medium. Stud. Surf. Sci. Catal. 2000, 130, 3753. (19) Ohyama, S. Catalytically active species in Ni-based catalytic systems for low-temperature methanol synthesis probed by in situ ATR/FTIR in combination with reaction kinetics. Appl. Catal., A-Gen. 2006, 313, 58. (20) Ohyama, S. In situ FTIR study on reaction pathways in Ni(CO)4/CH3OK catalytic system for low-temperature methanol synthesis in a liquid medium. Appl. Catal., A-Gen. 2001, 220, 235.



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(21) Ohyama, S. In situ ATR/FTIR observation of transformation of the nickel species in low temperature methanol synthesis. Prepr. Pap. -Am. Chem. Soc., Div. Fuel Chem. 2003, 48(2), 833. (22) Li, B.; Jens, K. J. Liquid-Phase Low-Temperature and Low-Pressure Methanol Synthesis Catalyzed by a Raney Copper-Alkoxide System. Top. Catal. 2013, 56, 725. (23) Dijk, A. V.; Drent, E. Process and catalyst for reducing carbon monoxide to methanol. UK Patent GB 2 240 052, 1991. (24) Chen, Y. Z.; Liao, B. J.; Chen, B. J. One-step synthesis of methanol from CO/H2 at low temperature over ultrafine CuB catalysts. Appl. Catal., A-Gen. 2002, 236, 121 (25) Marchionna, M.; Lami, M. Catalyst system and process for the liquid-phase production of methanol from synthesis gas. US. Patent 5,610,202, 1997. (26) Liu, Z.; Tierney, J. W.; Shah, Y. T.; Wender, I. Kinetics of Two-Step Methanol Synthesis in The Slurry Phase. Fuel Process. Technol. 1988, 18, 185. (27) Liu, Z.; Tierney, J. W.; Shah, Y. T.; Wender, I. Methanol Synthesis via Methyl formate in a Slurry Reactor. Fuel Process. Technol. 1989, 23, 149. (28) Palekar, V. M.; Jung, H.; Tierney, J. W.; Wender, I. Slurry phase synthesis of methanol with a potassium methoxide/copper chromite catalytic system. Appl. Catal., A-Gen. 1993, 102, 13. (29) Chu, W.; Zhang, T.; He, C. H.; Wu, Y. T. Low-temperature methanol synthesis (LTMS) in liquid phase on novel copper-based catalysts. Catal. Lett. April 2002, 79(1-4), 129. (30) Ohyama, S. Low-temperature methanol synthesis in catalytic systems composed of copper-based oxides and alkali alkoxides in liquid media: effects of reaction variables on catalytic performance. Top. Catal. April 2003, 22(3-4), 337. (31) Ohyama, S.; Kishida, H. Physical mixture of CuO and Cr2O3 as an active catalyst component for low-temperature methanol synthesis via methyl formate. Appl. Catal., A-Gen. 1998, 172, 241. (32) Ohyama, S.; Kishida, H. XRD, HRTEM and XAFS studies on structural transformation by milling in a mixture of CuO and Cr2O3 as an active catalyst component for low-temperature methanol synthesis. Appl. Catal., A-Gen. 1999, 184, 239. (33) Marchionna, M.; Girolamo, M. D.; Tagliabue, L.; Spangler, M. J.; Fleisch, T. H. A review of low temperature methanol synthesis. Stud. Surf. Sci. Catal. 1998, 119, 539. (34) Caubere, P. Complex reducing agents: their applications and their outcome in the field of carbonylation. Pure & Appl. Chem. 1985, 57, 1875.


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Table 1. Ranges of operating conditions. Temperature

80-120 °C

Total pressure

10-20 bar

Reactant gas ratio (H2/CO)

2.0

Stirrer speed

300, 500, 700 rpm

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Figure 1. Temperature and pressure curve of a typical catalytic run. Catalyst system: 1 mmol Cu(acetate)2, 5 mmol NaH, 25 g diglyme and 15 mmol methanol. Reaction conditions: 100 °C, 20 bar syngas (H2: CO = 2:1), 2 h reaction time. a: methanol addition (catalyst preparation); b: syngas pressurization (reaction start); c: heating stop; d: reaction end.

Figure 2. Effect of agitation speed. Catalyst system: 1 mmol Cu(acetate)2, 5 mmol NaH, 25 g diglyme and 15 mmol methanol. Reaction conditions: 120 °C, 20 bar syngas (H2: CO = 2:1) and 6.5 bar CO for CO only tests, 2 h reaction time.


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Figure 3. Effect of reaction temperature. Catalyst system: 1 mmol Cu(acetate)2, 5 mmol NaH, 25 g diglyme and 15 mmol methanol. Reaction conditions: 20 bar syngas (H2: CO = 2:1), 2 h reaction time, 700 rpm agitation speed. Gas conversion= syngas pressure drop/ initial syngas pressure.

Figure 4. Effect of initial reaction pressure. Catalyst system: 1 mmol Cu(acetate)2, 5 mmol NaH, 25 g diglyme and 15 mmol methanol. Reaction conditions: 100 °C, syngas (H2: CO = 2:1), 2 h reaction time, 700 rpm agitation speed.



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Figure 5. Effect of Cu acetate on carbonylation. Catalyst system: 1 mmol Cu(acetate)2 or no Cu(acetate)2,5 mmol NaH, 25 g diglyme and 15 mmol methanol. Reaction conditions: 100 °C, 6.5 bar CO, 2 h reaction time, and 700 rpm agitation speed.

Figure 6. Effect of Cu(acetate)2 dosage. Catalyst system: 5 mmol NaH, 25 g diglyme and 15 mmol methanol. Reaction conditions: 100 °C, 20 bar syngas (H2: CO = 2:1), 2 h reaction time, 700 rpm agitation speed.


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Figure 7. Effect of NaH dosage. Catalyst system: 1 mmol Cu(acetate)2, 25 g diglyme and 15 mmol methanol. Reaction conditions: 100 °C, 20 bar syngas (H2: CO = 2:1), 2 h reaction time, 700 rpm agitation speed.

Figure 8. Effect of catalyst concentration. Catalysts system: Low concentration: Cu(acetate)2 1 mmol, NaH 2.5 mmol, 25 g diglyme and 15 mmol methanol; Medium concentration: Cu(acetate)2 1 mmol, NaH 5 mmol, 25 g diglyme and 15 mmol methanol; High concentration: Cu(acetate)2 2 mmol, NaH 5 mmol, 25 g diglyme and 15 mmol methanol; Reaction conditions: 100 °C, 20 bar syngas (H2: CO = 2:1), 2 h reaction time, 700 rpm agitation speed.



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Figure 9. Results from one step and two step reaction. Catalyst system: 1 mmol Cu(acetate)2, 5 mmol NaH, 25 g diglyme and 15 mmol methanol. One step reaction conditions: 100 °C, 20 bar syngas (H2: CO = 2:1), 2 h reaction time, 700 rpm agitation speed. Two step reaction conditions: first step: 100 °C, 6.5 bar CO, 2 h, agitation speed 700 rpm; second step: 100 °C, 14 bar H2, 2 h, and 700 rpm agitation speed.

Figure 10. Results of multiple charging experiments. Catalyst system: 1 mmol Cu(acetate)2, 5 mmol NaH, 25 g diglyme and 15 mmol methanol. Reaction conditions: 100 °C, 20 bar syngas(H2:CO = 2:1), 2 h reaction time, 700 rpm agitation speed.


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