Catalytic properties study of mixed MFI-mord type zeolite in bioethanol transformation

Бюллетень науки и практики / Bulletin of Science and Practice

Decreasing of fossil fuel production and annual growth of energy demand needs to develop sustainable methods of synthetic hydrocarbons production from renewable materials [1-4]. Bioethanol can be considered as sustainable material widely acceptable and easy producing through biofermentation of agriculture and wood processing residuals [4-6]. However direct application of bioethanol is problematic due to technical issues and in some countries because of social problems of bioethanol applications for beverage production. Therefor bioethanol needs to be transferred do some valuable product prior to its direct application. Catalytic bioethanol transformation is a process of special interest due to it industrial value for synthetic hydrocarbons synthesis for energy and transport demand. Bioethanol can be easily transferred to synthetic hydrocarbons applicable for transport application [7-11].

Typically, different zeolites and zeotypes are used as catalysts for bioethanol transformation. The main problem of zeolites application for bioethanol transformation is rapid deactivation of synthesized zeolites due to active sites carbonization. One possible solution to solve this problem can be application of mixed zeolite systems with mixed structure for better hydrocarbons diffusion and catalytic transformation [12-14].

MFI type zeolites are characterized by three-dimensional structure of straight channels connected to one another via the sinusoidal channels with diameter 5.1-5.6 Å. Mordenite is characterized by two-dimensional channels structure with six ring pores opening acceptable for molecules diffusion with following dimensional parameters a: 1.57 Å, b: 2.95 Å, c: 6.45 Å. The article is devoted to MFI-mordenite catalytic properties study.

Materials and Methods

For obtaining mixed structure material consecutive MFI-mordenite synthesis was provided. For obtaining initial MFI zeolite chemical grade sodium hydroxide, sodium aluminate, silica gel and MFI zeolite seeds with purity not less than 99% were purchased from local supplier. Distillate water was purified using DE-25 aqua distillation system. Prior to synthesis silica gel was crashed in laboratory milling machine to obtained 10-100 μm particles fraction. In initial zeolite synthesis 9.54 g of sodium hydroxide 0.6 g of sodium aluminate 21.8 g of silica powder were dissolved in 250 ml of water in autoclave at 600 rpm and 70°C for one hour. Then temperature was set to 240°C for 72 hours. Reaction mixture was placed in IEC HN-SII centrifuge and initial zeolite was separated from reaction solution. Zeolite was washed with distillate water three times and dried in laboratory drier at 140°C. For mordenite synthesis ten grams of dried MFI zeolite samples were placed in autoclave and treated with two hundred milliliters of 0.1M solution of sodium hydroxide for one hour at 50℃ for desoldering initial zeolite surface structure. Then suspension was placed on shell for sedimentation for two hours and solution was decantated and twenty milliliters of n-butylamine was added and stirred for three hours. Then mixture of reagents was added to gel consist of 1.6 g of sodium hydroxide, 1 g of sodium aluminate and 9.1 g of silica dissolved in 150 ml of distillated water. Then suspension was sealed in autoclave equipped with impeller and heated to 240°C for 72 hours. Then reaction mixture was placed in IEC HN-SII centrifuge and mixed zeolite was separated from reaction solution. Zeolite was washed with distillate water three times and dried in laboratory drier at 140°C. Synthesized MFI mordenite samples were designated according to synthesis procedure MFI-MORD. Mixed MFI mordenite sample was tested in ethanol catalytic process in tube reactor systems. Quantity of formed liquid hydrocarbons was calculated due to gravimetric data.

Results and Discussions

Reaction temperature is of great importance for catalytic performance in ethanol to hydrocarbons transformation process. Increasing of reaction temperature (Figure 1) from 350°C to 370°C results in appropriate increase of liquid hydrocarbons transformation rate from 0.52 g(HC)/(g(Cat)*h) up to 0.64 g(HC)/(g(Cat)*h), that can be explained by increase of hydrocarbons formation reactions rate.

0,8 0,6 Q ^ Св g Д U 0,4 "d § О 'В £ Я 0,2	• •••••    •    •    •    •        • ::::::   i   :   •   •        : ••••••   •   •   •   •        •
0 0	• t=350 %  *1=370 %   *t=400 %   *t=430 % 5             10            15            20            25 Time on stream, h

Figure 1. Influence of reaction temperature on liquid hydrocarbons formation rate (reaction temperature 350-430%, ethanol liquid hourly space velocity 1 g(EtOH)/(g(Cat)*h))

Further increase of reaction temperature up to 430°C results in decrease of liquid hydrocarbons formation rate down to 0.32 g(HC)/(g(Cat)*h) that can be explained by increasing of liquid hydrocarbons destruction rate to gaseous hydrocarbons.

Increase of ethanol weight hourly space velocity (Figure 2) from 0.5 g(EtOH)/(g(Cat)*h) to 2 g(EtOH)/(g(Cat)*h) results in in appropriate decrease of liquid ethanol formation rate that can be explained by decreasing of hydrocarbons chain growth rate.

0,8	• •••••	•	•	•      •
0,6	• •••••	•	•	•      •
	• •••••	•	•
0,4
0,2	• •••••   • • WHSV=0.5 g(EtOH)/(g(Cat)*h)		•	•      • • WHSV=1 g(EtOH)/(g(Cat)*h)
0	___•WHSV=1.5 g(EtOH)/(g(Cat)*h)			• WHSV=2 g(EtOH)/(g(Cat)*h)
05		10 Time	on	15              20 stream, h

Figure 2. Influence of ethanol weight hourly space velocity on liquid hydrocarbons formation rate (reaction temperature 370°C, ethanol liquid hourly space velocity 0.5-2 g(EtOH)/(g(Cat)*h))

Pressure influence is of great importance on ethanol to hydrocarbons transformation rate (Figure 3). Increasing of system pressure from 1 to 15 Bars results in appropriate increase of hydrocarbons formation rate from 0.34 to0.83 g(HC)/(g(Cat)*h).

	0,85
.2 -О S и Л o'	0,8 0,75  ••••••    •    •    •    •         • 0,7 0,65  ••••••    •    •    •    •         • 0,6 0,55 0,5          • P=1,15 Bar     • P=5 Bar     • P=10 Bar     • P=15 Bar 0,45 0,4 0               5              10              15              20              25

Time on stream, h

Figure 3. Influence of system pressure on liquid hydrocarbons formation rate (reaction temperature 370 ° C, ethanol liquid hourly space velocity 1 g(EtOH)/(g(Cat)*h))

However, increase of system pressure results in shift of formed hydrocarbons to heavy products due to enhanced hydrocarbons chain grows under high pressure.

Conclusions

Ethanol to hydrocarbons transformation rate strongly influenced by process conditions. Increasing of reaction temperature from 350°C to 370°C results in appropriate increase of liquid hydrocarbons transformation rate from 0.52 g(HC)/(g(Cat)*h) up to 0.64 g(HC)/(g(Cat)*h), that can be explained by increase of hydrocarbons formation reactions rate. Further increase of reaction temperature up to 430°C results in decrease of liquid hydrocarbons formation rate down to 0.32 g(HC)/(g(Cat)*h) that can be explained by increasing of liquid hydrocarbons destruction rate to gaseous hydrocarbons. Increase of ethanol weight hourly space velocity from 0.5 g(EtOH)/(g(Cat)*h) to 2 g(EtOH)/(g(Cat)*h) results in in appropriate decrease of liquid ethanol formation rate that can be explained by decreasing of hydrocarbons chain growth rate. Increase of system pressure from 1 to 15 Bars results in appropriate increase of hydrocarbons formation rate from 0.34 to 0.83 g(HC)/(g(Cat)*h).

Acknowledgments: The reported study was funded by Russian Foundation for Basic Research (RFBR), project number 20-08-00191.