522
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 3, 1979
Ethylene Glycol from Formaldehyde Alvin H. Weiss;
Shmuel Trlgerman, Gregory Dunnells, Vladlmlr A. Llkholobov, and Ehud Blron
Chemical Engineering Department, Worcester Polytechnic Institute, Worcester, Massachusetts 0 1609
An aqueous 30 wt % solution of formaldehyde trickled with an equal volume of NaOH solution over NaX, 5A, and Na mordenite at 94 OC, 1 atm, 1.21-2.36 liquid hourly space velocity, catalytically condenses to HOCH,CHO, glycolaldehyde, a fraction of which then converts to HOCH,CH,OH, ethylene glycol, by cross-Cannizzaro side reaction. Zeolite degradation is prevented by maintaining pH near 11. Selectivity can be controlled so that less than 1% byproduct formose sugars are made. Methanol and sodium formate are also byproducts. All of the remaining glycolaldehyde could, in principle, be converted to ethylene glycol in a subsequent hydrogenation step. Thus, the reaction represents a potential nonpetrochemical route for ethylene glycol from CO H, via methanol and formaldehyde.
+
It is believed that the condensation of formaldehyde in the primordial atmosphere to "formose" sugars was the origin of carbohydrates in nature. The reaction is homogeneously catalyzed by organic and inorganic bases, and heterogeneously catalyzed by oxides, carbonates, clays, and resins. Mizuno and Weiss (1974) list catalysts tested. This present work discusses the heterogeneous condensation as a route to glycolaldehyde, which can subsequently be reduced to ethylene glycol. Becker et al. (1974) reacted HCHO vapors over ZnO, ZnCl,, and MgO to yield volatile products such as CH30H, HCOOH, CH300CH, CH,=CHCHO, CH3CH0, and HOCH2CH0. Venuto and Landis (1968) found that these are produced in the gaseous phase over NaX zeolite. Riesz (1968) adsorbed formaldehyde vapor on Type A, NaX and Na- and H-mordenite and then irradiated with y-rays for production of sugar-like products, rather than volatile species. Gabel and Ponnamperuma (1967) refluxed alumina, kaolinite, and illite in formaldehyde and identified sugars in these severely treated products. The catalytic reaction in this present study is confined to the aqueous phase at the low residence time of a trickle bed in order to favor the formation of HOCHzCHO and to avoid the high-temperature regimes where gaseous products are produced. The main reactions that take place in this NaOHHCHO-zeolite system are as follows: (1) formose condensation to glycolaldehyde BHCHO
-+
HOCHzCHO
(2) formose condensation to C3 + formose sugars
(n - 2)HCHO
+ HOCHZCHO
-
-
H(OCHZ),-lCHO
(3) Cannizzaro reaction of formaldehyde BHCHO
+ NaOH
CH30H + NaOOCH
-
cross-Cannizzaro reaction to ethylene glycol HOCHzCHO + HCHO
+ NaOH
HOCHzCH20H+ NaOOCH
Ethylene glycol is currently produced from ethylene, although there is considerable industrial activity to develop a process to produce ethylene glycol directly from CO and Hz at high pressure; see Walker et al. (1976) and Pruett and Walker (1976). The process described here is an atmospheric pressure route to ethylene glycol from synthesis gas, via, of course, prior conversion of CO + Hz to
CH30H and then to HCHO. E x p e r i m e n t a l Section
A 30% aqueous solution of Aldrich Chemical Co. paraformaldehyde and an equal volume of NaOH solution was passed over three types of molecular sieves: 5A, NaX(13X), and Na-mordenite. 5A and 13X beads were received from Linde Division, Union Carbide Corp. Na-mordenite was supplied by the Norton Company as 1/16-in.extrudate. The experimental procedure was described in detail by Trigerman et al. (1977). Briefly, a 1.0 cm i.d. trickle-bed reactor was loaded with 18 g of catalyst positioned between 22-cm inlet, 18-cm outlet beds of 0.6 cm diameter quartz beads, heated to reaction temperature under a stream of nitrogen, and maintained in this condition for 12 h before starting the reaction. The 35 in. long reaction tube was positioned inside a 7 / s in. 0.d. Nichrome wrapped glass tube, which was in a 2 in. 0.d. glass tube. The annulus inside the outer tube served as an insulating space; that outside the inner tube prevented localized overheating by the Nichrome wires. A Harvard Instrument Co. syringe pump fed the NaOH and HCHO solutions at equal rates from separate 50-mL Hamilton gas-tight syringes into the top of the reactor. The combined feed HCHO concentration was 16 wt 70. The product was collected at the bottom, after passing through a condenser for cooling. No gas production was found. HCHO conversion and the extent of methanol formation by the Cannizzaro reaction were determined using a Perkin-Elmer 900 thermal conductivity gas chromatograph with a 6 ft X 1 / 8 in. Carbosieve B column at 200 "C. Detector temperature was 200 "C and detector current was 150 mA. Ethylene glycol, glycolaldehyde, and higher polyols and sugars were analyzed as trimethylsilyl (TMS) ethers, using an adaptation of Sweeley's procedure (1963). TMS derivatives were injected into a Perkin-Elmer 880 FID gas chromatograph equipped with a 3 ft X in. OV 17 packed column operated at 4 cm3/min Nz and programmed from 100 to 250 "C at 4 "C/min. Injector and detector temperatures were 250 "C. It has been shown by Weiss et al. (1970) that peak area is proportional to weight percent of each carbohydrate. Table I lists the retention times of authentic TMS derivatives and retention time groupings that were used to establish carbon-number distributions. Liquid product from the reactor was quickly neutralized and then evaporated over steam. The more or less water-free product was exposed to vacuum for about 10
0019-7882/79/1118-0522$01.00/00 1979 American Chemical Society
(7;::-
Ind. Eng. Chem. Process Des. Dev., Vol. Table I. Retention Times for Authentic TMS Carbohydrates and Retention Time Intervals for Carbon-Number GrouDinns ethylene glycol glycoaldehyde dihydroxyacetone hydroxymethylglyceraldehyde erythrose arabinose D-xylose mannose sorbose fructose a-glucose b-glucose sucrose D -galactose
80 90-120 231 28 1 310 398 480 508-556 500,538,602 549 562 618 969 568
c 2
100-120
C6
C" EFFECT 14
OF
\
A
No Mordenite
A
O A
2 0 .
- o
Cannizzoro S e l e c t i v i t y
80
d,
1.21 L H S V 0.85 N o O H / H C H O 94'C
# 60; 40
-
20
c-=
0
A
100 -OA--~~-A-OA-O~-A-OA-~-D
200-250 250-380 400-500 500-630 630-800
c5
r t
l4
retention time, s
c 4
523
COMPARISON OF Z E O L I T E S
TMS ether of carbohydrate
c 3
18, No. 3, 1979
80 -
Total HCHO Conversion
-
60
"..i
LHSV
20
-0->-8=fj=fj=8= /
0
2
I
3
Time On Streom (Hours)
Figure 2. Zeolites 5A, NaX, and Na-mordenite are practically equivalent in activity and Cannizzaro selectivitywhen operated near 100% total HCHO conversion. The higher NaOH/HCHO ratio of 0.85 resulted in about 25% Cannizzaro selectivity.
t
2:
Connizzoro
E F F E C T OF N o O H / HCHO R A T I O
Selectivity
SA A T 9 4 . C NOOH/ H C H O = 0.2\ 40
80
c
0
J
0.21
I-
t
Connizzoro Select iVI t y
5 A AT 94.G
60
20 0
Total HCHO Conversion I
1
seriously in the NaOH/HCHO reaction over 5A Zeolite at 94 "C, 0.fl NaOH/HCHO.
min to remove residual water and to form a solid product with a large surface area. The reaction mixture used to form the derivative was a solution of 10 parts of pyridine, 4 parts of hexamethyldisilazane, and 2 parts of trimethylchlorosilane; 1 mL of this mixture was added to 10 mg of dried product in a 10-dram vial and the reaction was carried out at room temperature and for a period of about 1 2 h. Before injection into the GC, the TMS-ether derivatives were extracted into hexane in order to eliminate pyridine solvent tailing. The extraction procedure of Partridge and Weiss (1970) was followed. The zeolites at the end of each run were dissolved in HF. After the used catalysts were intensively washed with water
c
2o
Conversion
t
0
0 0
I
2
3
Time On S t r e a m ( H o u r s )
Figure 3. There is an optimal NaOH/HCHO ratio to minimize undesired Cannizzaro selectivity and to maintain operation near 100% total HCHO conversion over 5A at 94 "C, 1.21 LHSV.
and wetted with a solution of 3:l HC1 to "OB, HF was added, and the vessel was cooled in an ice bath. The solution was neutralized, evaporated to dryness, exposed to vacuum for 10 min, the TMS-ether derivative prepared,
524
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 3, 1979 E F F E C T OF C O N V E R S I O N ON P R O D U C T F R O M 5 A AT 9 4 O C
PRODUCTS F R O M 5 A , N a X , A N D No-MORDENITE AT 1 0 0 % CONV., 9 4 O C , 1.21LHSV,AND 0.85 N a O H I H C H O
loo^-^[^
PRODUCT C A R B O H Y D R A T E D I S T R I B U T I O N
PRODUCT C A R B O H Y D R A T E D I S T R I B U T I O N
75 LHSV
ap
2.36
8
I
IT
I
G L Y C O L A L D E Y Y D E / E T H Y L E N E GLYCOL R A T I O
I
O
l
3
50
I 2
O
Time IO0
l
2
0
1
2
I
I
n C 2
75
20 5
illn,
Carbon
.
0
On S t r e a m ( H o u r s )
CARBOHYDRATES INSIDE ZEOLITE
1
No- M O R O E N I T E
5A
G L Y C O L A L D E H Y D E / E T H Y L E N E GLYCOL R A T I O
l
2
and the derivatived sugars from the cavities of the zeolites were then analyzed. Results and Discussion Experimental data are given in Figures 1-5 as a function of time on stream, to show both transient initial and steady-state activities. Figure 1 illustrates the effect of liquid hourly space velocity (LHSV). The higher the LHSV, the lower the total conversion. The selectivity to Cannizzaro reaction (and the consequent reduced product pH) are little affected by LHSV. Choice of NaOH/HCHO ratio is the key technique to minimize Cannizzaro selectivity. It will be shown later that product distribution is a function of the extent of the total HCHO conversion, and hence, a function of LHSV at fixed NaOH/HCHO ratio. It is probably that 5A exchanged to the sodium form in the course of the experiments using it. Figure 2 compares 5A, NaX, and Na mordenite at a fixed reaction condition of 94 "C, 1.21 LHSV, and 0.85 NaOH/HCHO ratio. Total HCHO conversion at this condition approximated 100% for all of the zeolites. Because of the high NaOH/HCHO ratio of 0.85,Cannizzaro selectivity is high (-25%). Figure 3 shows that for 5A at 94 "C, 1.21 LHSV, NaOH/HCHO ratio is the key variable to maintain the total conversion of HCHO near 100% and, at the same time, minimize Cannizzaro selectivity to less than 10%. Table I lists the product carbohydrate carbon number distributions as a function of time on-stream and the operating conditions and catalysts that correspond to the analyses. Table I1 shows that, at least initially, only Cz species are produced. These Cz species are actually a mixture of ethylene glycol and glycolaldehyde, due to the favorable alkaline environment for cross-Cannizzaro reaction to proceed. The ratio of glycolaldehyde/ethylene glycol is a measure of cross-Cannizzaro reaction extent. It is desirable to
1
2
0
1
2
3
On S t r e a m ( H o u r s )
CARBOHYDRATES INSIDE ZEOLITE
Number
Figure 4. Product distributions from reaction of NaOH/HCHO solutions at 94 "C over 5A zeolite. The effect of increasing conversion is shown.
0
Time
c
i n
Carbon
Number
Figure 5. Comparison of product distributions from reaction of 0.85 NaOH/HCHO solution at 94 "C, 1.21 LHSV, and 100% total HCHO conversion over 5A, NaX, and Na-mordenite.
maximize this ratio, which is plotted in Figures 4 and 5 because, even if reduction of glycolaldehyde to ethylene glycol is desired, it will most probably be more economically advantageous to do this in an external hydrogenation process HOCHzCHO
+ H2
catalyst
HOCHzCH2OH
Experimental data or conditions are not available for glycolaldehyde hydrogenation. The procedures reported by Wisniak et al. (1974)for xylose hydrogenation over Raney nickel or by Brahme and Doraiswamy (1976)for glucose hydrogenation over Raney nickel may be applicable here, but experimental demonstration for glycolaldehyde is required. Figures 4 and 5 show that increasing conversion at 94 "C from 46% over 5A to 100% over 5A, NaX, and Namordenite increased the ratio from 0.3 to 3.0. Higher severities, i.e., lower LHSV in connection with optimal NaOH/HCHO ratio, are more favorable in minimizing cross-Cannizzaro reactions. HCHO usage in cross-Cannizzaro reaction is one mole per mole of glycol formed and is an undersirable nonselective loss of HCHO, unless the conversion of glycolaldehyde to ethylene glycol is done intentionally by cross-Cannizzaro reaction. If such is the case, it is recommended that a separate noncatalytic reaction be pursued in the range of pH 12-13. Table I1 and Figures 1 and 4 show that, within analytical accuracy, 5A catalyst can be operated to produce only Cz species at 94 "C, 0.21 NaOH/HCHO, and 1.21 to 1.36 LHSV (46-62% total HCHO conversion) in a manner in which HCHO converted by Cannizzaro is only 5-lo%, but cross-Cannizzaro reactions are high: 0.5-1 HOCH2CHO/HOCHzCHz0Hratio. Figures 3, 4, and 5 show that if conditions are forced to 100% conversion over 5A at 94 "C, these nonselective reactions decrease (-5%
Ind. Eng. Chern. Process Des. Dev., Vol. 18,
No. 3,
1979
525
Table 11. Carbohydrate Analyses a t Various Times On-Stream, Trickle Bed Reaction at 9 4 " C
type of zeolite
NaOH/ HCHO mole ratio
Na-mordenite
0.85
NaX
5A
5A
5A
5A
0.85
0.85
0.42
0.21
0.21
time o n LHSV stream, h 1.21
1.21
1.21
1.21
1.21
2.36
0.5 1.0 1.50 2.25 2.50 3.00 0.25 0.50 1.00 1.50 2.25 0.50 0.75 1.00 1.50 0.25 0.50 1.00 1.50 2.00 2.50 0.25 0.50 1.00 1.50 2.00 2.50 2.75 0.5 1.0 1.5 2.0 2.5 2.8
product distribution, wt % C,
c 3
c 4
c5
C6
C,
ratio inside zeolite HOCH,CHO/ HOCH,CH,OH
100 100 100 100 100 100
100 38.56 61.30 89.50 80.20 100 90.63 63.8 76.38 100 53.29 25.29 30.05 48.20 41.70 100 100 100 100 90.0 93.9
100 100 100 100 100 100 100
Cannizzaro and a glycolaldehyde/ethylene glycol ratio of 4), but about 20% carbohydrates of higher molecular weight are also formed as the 5A catalyst approaches steady state. The formation of higher carbohydrates (formose sugars) reduces the overall selectivity of HCHO to Cz species. Figure 5 compares products from 5A, NaX, and Na mordenite a t a high severity operation-0.85 NaOH/ HCHO, 1.21 LHSV, and 94 "C. One hundred percent conversion is had in all cases. NaX behaves similarly to 5A, in that about 80% of the carbohydrates are selectively C2. However, Na-mordenite is unique in that Cz carbohydrates are produced at 100% HCHO conversion in the absence of other carbohydrates. There are no product losses to higher molecular weight species, cross-Cannizzaro reaction is minimal (HOCHzCHO/HOCH2CH20H= 6), but HCHO lost to Cannizzaro reaction is -25%. Note that in all of the plots of HOCH,CHO/ HOCHzCHzOHratio shown in Figures 4 and 5, the ratio appears to be increasing with time and does not appear to be a t steady state. Perhaps, in longer periods of time, the ratio will be so high that the cross-Cannizzaro reaction will become unimportant. Experiments of longer duration than those given here are, of course, required to demonstrate this point as well as to document catalyst deactivation. Figures 4 and 5 also show bar graphs of the formose sugar distributions found inside the catalysts a t the end of the experiments. The significant amounts of C3, C4, C5, and C6 sugars detected after dissolution of the washed 5A
0.150 0.41 0.59 1.11 2.17
13.81 13.52 4.24 6.36
21.30 5.12 1.70 5.26
25.47 14.13 1.62 5.54
2.5 8.58 9.74
5.12 10.11 8.42
0.63 7.42 3.78
1.12 10.10 1.67
1.35 3.53 1.97 2.79 1.89
12.55 11.90 23.04 16.10 17.91
5.96 8.40 13.26 9.97 9.35
26.84 50.23 24.50 10.32 24.77
0.63 7.17 2.61 4.38
0.270
0.00 0.00
5.29 2.71
0.71 0.59
0.71 0.59
4.0 2.74
0.300
0.45 4.34 1.37 0.00
0.071
0.301
0.290
and NaX suggest that the formose condensation reaction proceeded inside the cavity and that the sugars formed were too large to exit. An X-ray diffraction pattern showed a slight loss of crystallinity in the 13X, which could be due to bulky molecules blocking the pores. Cross-Cannizzaro reaction also occurs extensively inside the zeolite cavities. Table I1 shows that HOCH2CHO/HOCHzCHzOHratios were quite low inside the catalyst specimens that were analyzed, 0.07 to 0.3. Only C2 and C3 species were found inside the Na mordenite cavity, but it would seem that formose sugars must form if precursors such as these are inside the mordenite pore. It may be possible, as suggested by Bierenbaum et al. (1973) in separate studies on cumene cracking over H-mordenite, that the activity of Na mordenite is at the pore mouth and HCHO is really not inside. Alternatively, since the pores were not filled with terminal products, one could also conclude that entry of HCHO and egress of Cz's from mordenite are very rapid processes. However, the HOCH2CHO/HOCH2CHz0Hratio inside the mordenite of 0.150 did not differ greatly from that measured for the other catalysts, 0.07-0.30 (see Table 11), suggesting just as intense a cross-Cannizzaro activity for molecules of glycolaldehyde inside mordenite as for molecules of glycolaldehyde inside 5A or NaX.
Process Concept Glycolaldehyde is a very reactive species, not currently commercially available. If a commercial process for it were developed, byproduct ethylene glycol, methanol, sodium
526
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 3, 1979
* - .
LB
..
-
Y
co 1.0
-
' & -l . & q-
Figure 6. Process flow sheet to convert HCHO to ethylene glycol. NaOOCH is decomposed to NaOH for recycle and C3 and heavier byproduct sugars are carbonized.
formate, and carbohydrates could either be sold or methanol recycled to the formaldehyde plant and sodium formate converted to NaOH for recycle. Ethylene glycol could be the major product by reacting the mixture with HCHO and NaOH for cross-Cannizzaro conversion of the glycolaldehyde to ethylene glycol. Possibly more preferable for economic reasons would be catalytic hydrogenation of the product glycolaldehyde to ethylene glycol. The net effect is that ethylene glycol can be produced selectively from formaldehyde in this system. Such a process has not been developed, but we shall now described what it may be and the type of problems that will occur. Figure 6 is a conceptual process flow sheet for ethylene glycol manufacture. Formalin solution from a formaldehyde plant is mixed with NaOH solution and heated to process temperature, 94 "C. This solution is then pumped at 1.21 LHSV into parallel trickle bed condensation reactors at atmospheric pressure. The formaldehyde reacts to 100% conversion over zeolite catalyst. The condensation reaction 2HCHO HOCH2CH0 is 75% selective and competes with the Cannizzaro reaction 2HCHO
+ NaOH
-
that the stream will flow as a liquid. This mixture is evaporated and melted. Upon melting, the sodium formate (mp 253 "C) decomposes spontaneously to sodium hydroxide (mp 318.4 "C) and carbon monoxide. NaOOCH NaOH + CO
-
CH30H + HCOONa
The Cannizzaro selectivity is 24% and it should be assumed that there is at least 1% selectivity to sugars. Both reactions are liquid phase in a trickle bed reactor, using sodium mordenite as a catalyst. Sodium hydroxide is necessary to prevent formic acid from destroying the zeolite catalyst. The output of the condensation reactors is then used as feed for the hydrogenation step, where the glycolaldehyde/ethylene glycol mixture is hydrogenated a t 125 OC, 400 psig over nickel catalyst to ethylene glycol. Three reactors in series, with interstage cooling, are suggested for hydrogenation, and we caution again that this reaction is not demonstrated. The product from the hydrogenation reactors is separated, e.g., by extraction, and ethylene glycol and lighter are recovered. Inorganics and sugars are combined in water solution. Methanol is recycled back to the formaldehyde process. The liquid product from the separation step is sodium hydroxide solution, with sodium formate and nonselectively formed C3 and higher sugars and enough water so
Thus, all of the reacted sodium hydroxide is recovered for recycle. This reaction is spontaneous upon melting, and is also quite exothermic. The carbon monoxide and steam given off during operation can either be appropriately disposed of as waste gas or dried and sent back "over the fence" to a methanol plant where it can be used as raw material. Formose sugars will thermally decompose in the melter to carbonaceous materials. For example, a simplification of glucose decomposition is CJH20)b
A 6C + 5H20
This carbon will be in the NaOH from the melter. The NaOH which is flaked and reconstituted into a recycle stream can then be filtered before recycle to separate and reject not only the carbon but also solution wetting it, thereby preventing accumulation of impurities in the system. The only experimentation pursued at this point is the reaction over zeolites. The separation and thermal decomposition steps require experimental demonstration in a development program.
Conclusions The reaction of HCHO to Cz's proceeds selectively and to complete conversion over NaX, 5A, and Na-mordenite at 94 OC and 1.21-2.36 LHSV in a trickle bed. The technique of maintaining and optimizing catalyst activity, selectivity, and structure is to use mixtures of NaOH and HCHO as feed to the system. If not, acid is formed by Cannizzaro reaction and the catalyst destroyed. The overall process might be regarded as a route from synthesis gas CO + H2 to ethylene glycol via methanol and formaldehyde. The purpose of the present paper is to present experiments that show the feasibility of controlling the formose condensation to produce glycolaldehyde and to show the process conceptualization and attendant problems. Economic analysis, process development, and catalyst life studies have not yet been made. Acknowledgment The experimental work in this report was done by Shmuel Trigerman in partial fulfillment of the requirements for the degree of Master of Science in Chemical Engineering at Worcester Polytechnic Institute. Financial support was provided by WPI for Mr. Trigerman to work on this study, experimental assistance given him by Dr. Ehud Biron, and advice with the analyses given by Dr. Vladimir A. Likholobov. Mr. Gregory Dunnels did process studies. Professor Leonard Sand provided the catalysts used. Dr. Likholobov was supported at WPI as an exchange fellow in the US/USSR Research Collaboration on Catalysis, Topic IV, Applications of Catalysis. Literature Cited Becker, R . S., Bercovlci, T., Hong, K., J . Mol. Evol., 4, 173 (1974). Bierenbaum. H. S.. Partridae. R. D.. Weiss. A. H.. Adv. Chem. Ser.. NO. 121. 605-617 (1973). Brahme, P. H., Doraiswamy, L. K., Ind. Eng. Chem. Process Des. Dev., 15, 130 11976). > - -, Gabel: N. W., Ponnamperuma, C.. Nature (London), 218, 453 (1967). Mizuno, T., Weiss, A. H., Adv. Carbohydr. Chem. Biochem., 29, 173 (1974). Partridge, R. D., Weiss, A. H., J . Chromatogr. Sci., 8 , 553 (1970). Pruett, R. L., Walker, W. E., U S . Patent 3957857 (May 18, 1976). Riesz. C. H., Report No. IITFU U6062-9, "Study of Conversion of Formaldehyde into Sugar-llke Products",Final Repat, NASA Ames Research Center, Moffatl
-
Ind. Eng. Chem. Process Des. Dev., Vol. 18, No. 3, 1979 527 Field, Calif., Contract Nas 2-4184, Jan 23, 1968. Sweeley, C. C., Bentley, R., Makita, M., Wells, W. W., J . Am. Chem. SOC., 85, 2497 (1963). Trigerman, Sh., Biron, E., Weiss, A. H., React. Kinet. Catal. Lett.,8 (3), 269 (1977). Venuto, P. B., Landis, P. S., Adv. Catal., 18, 340 (1968). Walker, W. E., Bryant, D.R., Brown, E. S., Jr., U.S. Patent 3 952 039 (Apr 20, 1976). Weiss, A. H.,Lapierre, R. B., Shapira, J., J . Catal., 18, 332 (1970). Wisniak, J., Hershkowitz, M., Leibowitz, R., Stein, S., Ind. Eng. Chern. Prod.
Res. Dev., 13, 75 (1974).
Received for review July 20, 1978 Accepted January 8, 1979
This paper was presented both at the Fifth Soviet-American ~~~~~i~~ on catalysis,~ ~USSR, k M~~ ~ 18,, 1978, at the 71st National AIChE Meeting, Session 44, Miami Beach, Fla., Nov 14, 1978.
Process Aging Studies in the Conversion of Methanol to Gasoline in a Fixed Bed Reactor Serge1 Yurchak,' Sterling E. Volts, and John P. Warner Mobil Research and Development Corporation, Paulsboro, New Jersey 08066
Catalyst aging studies of the methanol-to-gasoline process were conducted in an adiabatic fixed bed unit. An aging test of over 200 days on stream was achieved during which 8000 Ib of methanol/lb of conversion catalyst was processed. Catalyst activii was still satisfactory at the end of the aging test. Some changes in product selectivities were observed during individual cycles and from cycle to cycle. The properties of the methanol-derived gasoline are generally comparable to those of commercially marketed gasolines. Combination of this process with the commercially available coal-to-methanol technology provides an alternate route for the conversion of coal to high octane gasoline.
Introduction Coal is expected to become a more important source of gaseous and liquid fuels during the next several decades. Coal gasification technology is used commercially, and improved gasifiers are under development. Several coal liquefaction processes have been developed, and large pilot plants and demonstration plants are being built and operated. Methanol can be obtained from coal (via synthesis gas) with commercially available technology. Studies have shown that methanol can be used directly as an automotive fuel or blended with petroleum-derivedgasoline. However, there are some serious problems associated with these uses. A novel process is being developed for the conversion of methanol to high octane gasoline (Meisel et al., 1976, 1977; Wise and Silvestri, 1976; Daviduk et al., 1976; Yurchak et al., 1977; Chang et al., 1978; Liederman et al., 1978). Combination of this process with the commercial technology for the production of methanol from coal provides another route to obtain gasoline from coal. This methanol-to-gasoline process uses a new type of zeolite catalyst. The conversion of methanol to hydrocarbons and water is virtually stoichiometric. Only small quantities of CO, COz, coke, and H2are formed as byproducts. The yield of gasoline is typically greater than 75 wt % of the total hydrocarbons, and additional gasoline can be obtained by alkylating propene and butenes with isobutane. The ultimate gasoline yield is about 90 wt %. Small amounts of LPG and high Btu fuel gas are the other hydrocarbon products. In contrast to the Fischer-Tropsch process, no significant amounts of oxygenated products are formed, except water. The conversion of methanol to gasoline is highly exothermic, and the heat of reaction is 650-750 Btullb of methanol depending on the particular product distribution. 0019-7882/79/1118-0527$01.00/0
In the fixed bed process, two reactors are used. Methanol is partially dehydrated to an equilibrium mixture of methanol, dimethyl ether, and water in the first reactor. The methanol and dimethyl ether are converted to hydrocarbons and water over a zeolite catalyst in the second reactor. Light gases are recycled to the second reactor to reduce the adiabatic temperature rise to 100-200 O F under typical operating conditions. About 20 and 80% of the total heat of reaction is released in the first and second reactors, respectively. Some further details of the fixed bed process were presented in the earlier publications. As part of the process studies, long-term aging tests were made to establish catalyst stability and regenerability. The results of an aging test in the fixed bed unit are described in this paper. Some effects of coke formation and steam on catalyst performance and changes in product distribution during individual cycles and from cycle to cycle are presented. Experimental Section The experimental studies of the conversion of methanol to gasoline were conducted in an adiabatic fixed bed unit which is shown schematically in Figure 1. It consisted of two fixed bed reactors in series. The first reactor had an inside diameter of 5/s in. and contained an axial thermowell along its entire length. It had a capacity of about 60 cm3 of catalyst. The products from the first reactor were mixed with recycle gas, and the mixture was passed over the conversion catalyst in the second reactor, where the formation of hydrocarbons occurred. The conversion reactor had an inside diameter of 1.30 in. and contained a thermowell along its axis for the entire length. A catalyst bed length of 9.25 in. was generally used, giving an L I D ratio of 7.2. To minimize entrance effects and to establish the inlet temperature, the catalyst was preceded by a bed of quartz 0 1979 American Chemical Society
