New Process for Production of Tetrahydrofuran JUNlCHl KANEPAKA TAISUKE ASANO SHINOBU M A S A M U N E
A n e w one-stage, high-selectivity process f o r manufacture of tetrahydrofuran directly from maleic anhydride
etrahydrofuran (THF) is used mainly as a raw
Tmaterial for spandex fibers and polyurethan elastomers, but also finds application as a solvent since T H F is a strong dissolving agent of both synthetic and natural resins especially polyvinylchloride and vinylidenechloride copolymers. Recently, the demand of T H F has grown rapidly with a n increased demand for spandex fibers and polyvinylchloride. At present, commercial production of T H F involves either one of two methods: the furfural process or the Reppe process. I n the former, furfural extracted from corn husks is used as the raw material. And in the latter process, acetylene and formaldehyde are used as the raw materials. The major disadvantage of the furfural process is the difficulty of ensuring a constant supply of furfural, because the supply is always dependent on agricultural conditions. Therefore, the trend has been to switch from the furfural process to the Reppe process which is a fully synthetic method (7). 24
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
Another possible T H F process, using butadiene as a raw material, was reported (2). The reaction scheme is represented as follows
However, this process is not practical for obtaining high yields of the product. The new process of obtaining T H F from maleic anhydride in one stage with high selectivity has been developed. T h e reaction is expressed as follows
+ 0
5H2
-+
-t 2H20
duced simultaneously in the wide range of T-BL to T H F ratio. New THF Process
This new T H F process was developed on the basis of the research carried out in Mitsubishi Petrochemical Company Ltd. since 1963. The pilot plant designed to take the engineering data has been operating successfully since January, 1968. The engineering facilities vital to the process were developed jointly by the Mitsubishi Petrochemical Company Ltd. and Chiyoda Chemical Engineering and Construction Go. Ltd. T h e main advantages of this process are : Maleic anhydride is easily and inexpensively supplied by oxidation of benzene or (&fraction. Due to the simple process and single-stage reactor, only a low capital investment is required. High conversion and high selectivity : T h e selectivity to THF is more than 90% and per-pass conversion of maleic anhydride is 100%. High product purity of 99.95% or higher is easily assured. y-Butyrolactone (7-BL), which is the raw material of 2-pyrrolidone and n-methyl-2-pyrrolidone, can be pro-
I n this process, T H F can be produced continuously by the direct hydrogenation of maleic anhydride. Before the direct use of maleic anhydride, a number of catalysts were investigated for this reaction ( 3 ) . They were nickel molybdenum oxide, cobalt molybdenum oxide, Raney nickel, etc. However, none of these catalysts was adequate for industrial use. For example the hydrogenation of maleic anhydride at 180 to 300 "C and a t a pressure of 150 kg/cm2 for 2 to 10 hr using a nickel catalyst leads to the formation of a considerable amount of solid succinic acid, which gives the reaction mixture a viscous, slurry-'like appearance. This means that the yield of desired 7-BL and T H F is low, while operational efficiency involved in the transportation of the reaction products, separation of catalyst from reaction products and reuse of catalyst suffers. Moreover, in the direct hydrogenation of carboxylic acid such as maleic anhydride, the reaction produces dicarboxylic acids such as maleic acid or succinic acid and lower organic acids which are by-produced continuously through the reaction along with water. Maleic acid, especially, has a strong acidity. The pK, values of these acids are shown in Table I. So, the conventional hydrogenation catalyst is adulterated and sometimes converts to the salt which dissolves into the reactant solution. Thus, the catalytic activity is greatly decreased in the course of reaction. We have attempted to obtain a catalyst which yields the reaction product in nonviscous liquid form, and shows less deactivating tendency through the reaction (4). Our newly developed catalyst proved to resist the catalyst poisoning, and to keep continuously active in the pilot plant operation. Kinetic study in batch-type reaction. Because the batch-type system is generally more convenient to investigate than the flow-type, the batch-type reaction was applied for maleic anhydride, succinic anhydride, 7-BL, succinic acid and polyester. Except for maleic anhydride, all are the intermediate products, and the polyester is produced from succinic acid and 1,4-butandiol through the condensation polymerization. Procedure. A conventional 300 ml autoclave provided with an electromagnetic stirrer was used. 100 g
TABLE I .
pK, VALUES
Organic acid Maleic acid Succinic acid Propionic acid Butyric acid
VOL. 6 2
Value of ljKa 1.8 4.1 4.9 4.8
NO.
4 APRIL 1970
25
of each reactant was used and the amount of catalyst was 0.05 wt% or 0.1 wtYG for maleic anhydride and 5 wt% for the other reactants. The reaction pressure was 60 kg/cm2 for the former and 120 kg/cm2 for the latter. The range of reaction temperature was from 160" to 200°C for maleic anhydride, 240" to 270°C for succinic anhydride, 240" to 280°C for 7-BL, and 260°C for succinic acid and polyester. To ascertain the relationship between molecular weight and the reaction rate, the polyesters with mean molecular weight 1000 and 2000 were examined. T o let the reaction proceed as slowly as possible before reaching the prescribed reaction temperature, the autoclave with reactant and catalyst was kept a t 5 to 30 kg/cm2 for hydrogen pressure and agitated a t 50 rpm. The reaction then proceeded at constant pressure and 1000 rprn through the prescribed reaction time, after which the autoclave was immediately cooled off in water to stop subsequent reaction. After separating out the catalyst, the several components of reaction product were analyzed, THF, y B L , n-propanol, n-butanol, propionic acid and butyric acid by gas chromatography, while maleic anhydride, succinic anhydride, succinic acid and polyester were done vza nuclear magnetic resonance spectra.
3,O h
I 4
I
2.0
Y U
I
u
v
1.0
c -
0 Reaction Time (hr) Figure 7. Test of Jut-order reaction mechanism for hydrogenation from maleic anhydride to succinic anhydride Reaction pressure, 60 kg/cm2; concentration of catalyst, 0.1 for 150°C, 0.05 wt7, for the others 0 15OoC, 0 160°C, 180°C, 2OOOC
Result and Discussion
~ t 7 ~
0.14
This reaction involved the following consecutive reaction mechanism
c
-In
h 0
+ U 0
0.12
0. IO _I
rn I
?. c 0
(4)
+
HZ
-
I!
.-e,
>
0.06
(5)
C4H90H
0
Hydrogenation of maleic anhydride to succinic anhydride. As the reaction rates of Step 1 were too fast to estimate, the data were gained using lower reaction temperatures and a lower concentration of catalyst than the other steps. Under these conditions, only the double bond was hydrogenated. If the reaction proceeds in the first order for the concentration of maleic anhydride under the constant hydrogen pressure, the rate equation may be written as
When we integrate the above equation, we note that, a t t = 0, CMAH= C,wAHO In ( C - w ~ H o I C , ~ A=d k~ t
(7)
where CAWAH is concentration of maleic anhydride, k l is rate constant, and t is reaction time. 26
0.08
INDUSTRIAL AND ENGINEERING CHEMISTRY
Figure 2. anhydride
I
2 3 Reaction Time (hr)
4
5
Yield of 7-BL us. reaction time in hydrogenation of succinic
Reaction pressure, 120 kg/cm2, concentration of catalyst, 5 w t r o 0 240°C, 0 250°C, 260°C, rn 270°C
0.10
0.08
4.0
0.06
3.0
0.04
2.0
0.02
1.0
0
I
2
3
0
4
I
2
Reaction pressure, 120 kg/cm2; concentration of catalyst, 5 wt% 0 240°C, 0 25OoC, 0 26O0C, 270'C
T h e plot applied the data to Equation 7 shows the linear dependence as shown in Figure 1. Hydrogenation of succinic anhydride. The relation between the yield obtained over unit catalyst and reaction time is shown for y-BL and T H F in Figures 2 and 3, respectively. The reaction rate of y-BL formed from succinic anhydride is extremely rapid in the early stage and then gradually slows after the reaction time elapses. T H F is obtained from the successive reaction of 7-BL (Figures 2, 3). Though by-products such as n-propanol and n-butanol are not shown, their production increases with increasing yields of THF. T h e kinetic expression for this reaction is
where
= concentration of succinic anhydride kz' = rate constant K = adsorption coefficient of succinic anhydride C, = concentration of inhibitor component Kp' = adsorption coefficient of inhibitor component
C,vAH
Succinic acid and water may be considered as the chief inhibitor components. Water is produced throughout the reaction from succinic anhydride, y-BL, and THF. Furthermore the concentration of water is proportional to the conversion of succinic anhydride. The concentration of succinic acid can be proportional to the
4
t (hr)
Reaction Time (hr) Figure 3. Yield of T H F us. reaction time in hydrogenation of succinic anhydride
3
Figure 4.
Test of Equation 70
Reaction pressure, 120 kg/cm2; concentration of catalyst, 5 wt% 0 240 O C , 0 250 " C , 260 'C, 270 "C
concentration of water.
where
CLAH
Therefor.;, Equation 8 becomes
= initial concentration of succinic an-
hydride a = nKp,H20 mKp,SA n = coefficient to link the concentration of water with the conversion of succinic anhydride: n = 1 for r - g L , n = 2 for T H F m = coefficient concerning the concentration of succinic acid If Kp' >> K, then the term [1 f K C s A H ] can be neglected in comparison with a ( C E A H - C S A H ) : the integrated form of the resulting equation is given as follows
T h e plot of the data according to Equation 10 is shown in Figure 4 and satisfies the above assumption. From this result, it is difficult to distinguish which is the stronger inhibitor between succinic acid and water. However it was confirmed that succinic acid is the strong inhibitor through the experiments in which succinic anhydride including succinic acid was used as the initial reactant. VOL. 6 2
NO. 4 A P R I L 1 9 7 0
27
Hydrogenation of y B L . T o eliminate the inhibition term by succinic acid, Reactions 3, 4, and 5, were analyzed in the hydrogenation of r-RL, as a starting material. I n Figure 5 the conversion of 7-BL us. reaction time is plotted. I t is clear that the rate of this step obeys zeroorder kinetics as follows
Integrating Equation 11 results in Equation 12
100
80
where C Y - ~ ~=Oinitial concentration of y B L C Y - B L = concentration of y B L a t reaction time t ka = k z ' / C y - B L o
60
The rate of side reactions 4 and 5 are considered as first-order kinetics with respect to the concentration of
THF. 40
20 where CprOH= concentration of n-propanol C B ~ O I=~ concentration of n-butanol
0
I
2
3
4
5
From the material balance, we get Equation 15
6
0
CTHF= k3CY-BLt Reaction time (hr)
CPrOIl
t
+ CBUOH)
Reactions 4 and 5 are parallel reactions. tions 13 and 14, we get Equation 16.
Figure 5. Conversion of 7-BL us. reaction time i n hydrogenation of y-BL Reaction pressure, 120 kg/cm2; concentration of catalyst, 5 ~ 0 24OoC, 0 250°C, E 260°C, W 270°C, A 28OoC
(CPrOH
7
~
(15)
From Equa-
- kd
C B ~ H k:
Substituting Equations 15 and 16 into Equation 13
fl
When we integrate, we note that, at t = 0, C p r ~ l ~0
15
=i
-
CPrOH
Q)
=
E
0
c
C
0
IO
?a
Similarly, for n-butanol
I
C B ~ O= H
K
2
5
c
.-0 v)
L
a
!= 9
0
0
0
I
2
3
4
5
6
Reaction time (hr) Figure 6. Comparison between calculation curve and experimental pointsfor conversion to n-popanol in hydrogenation of 7-BL Reaction pressure, 120 kg/cm2; Concentration of catalyst, 5 ~ 0 240°C, 0 250°C, 0 260°C, 27OoC, A 28OOC 28
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
t
I n Figures G and 7, the calculated curves and the experimental points of conversion for n-propanol and n-butanol us. reaction time are shown. T h e calculated curves were interpolated by the trial and error method giving several values to kd and k5 in Equations 18 and The values of k 4 and ka used in calculation are 7 19. ~ shown in Table 11, and were estimated for per unit
time (hr), unit pressure (atm) and unit amount of catalyst (g). T h e activation energy and frequency factor of each reaction step are shown in Table 111. The frequency factor is estimated for unit time, unit pressure, and unit amount of catalyst as well as in Table 11. Hydrogenation of succinic acid and polyester. I n Equation 9, succinic acid is considered as the chief inhibitor component. Therefore, it was examined to see whether this catalyst is capable of hydrogenating even succinic acid to y-BL and T H F . Moreover, polyester was detected in the flow-type reaction; its content tended to increase according to the decrease of water content in the reactor, though it was not detected in the batch-type reaction. Accordingly, the examination for polyester was also carried out. In Figure 8, the yields of T H F and 7-BL us. reaction time are plotted for succinic acid and polyester. It may be concluded from Figure 8 that succinic acid is adsorbed more readily than y B L , thus the rate of reaction should adhere to zero-order kinetics for the concentration of succinic acid. In Figure 9 the conversion of succinic acid us. reaction time is plotted, and it appears that zero-order kinetics fits the data for the conversion under 70 mol %. Moreover it may be concluded that the hydrogenation rate of polyester is faster than the hydrolysis rate of polyester. Because, if hydrogenolysis and hydrolysis occur as the same grade, the amounts of y B L and T H F should be almost the same, but the amounts of both products are very different in Figure 8. With respect to the effect of molecular weight of polyester, it may be said that the reaction rate is diminished a little. Reaction rate of Step 1 is more rapid than in Step 2
TABLE 11. VALUES O F k4 AND ks ESTIMATED FOR SEVERAL REACTION TEMPERATURES
Reaction temp., O C
ka, I / h r atm g 1.43 x 10-4 2.14 x 10-4 3.16 x 10-4 3.77 x 10-4 6 . 6 6 X 10-4
240 250 260 270 280
TABLE 1 1 1 .
k 5, l / h r atm g 0.67 x 10-4 1 . 2 0 x 10-4 1.85 x 10-4 2.94 x 10-4 4.16 x 10-4
K I N E T I C DATA FOR EACH REACTION STEP
Activation energy E, kcal/mol
Species of rate constant ki kz ka
Frequency factor, 7/hr atm g
12.5 18.2 17.9 22.0 26.5
k4
ks
3.04 2.25 6.64 7.98 1.45
X X X X X
106 106
106 106 108
0.12
0.IO
0.08 -I
m I
h
a\o
h
0
L
Q)
-
0.06
0 LL
E
I I-
rc
0.04
0
I c
0.02
0 c E
.-0 v)
L 0)
0
> c
0 0
2
4
8
6
10
Reaction time (hr)
0
I
2
3
4
5
6
Reaction time (hr) Figure 7. Cvmparison between calculation curve and experimental points for conversion to 7-butanol in hydrogenation of y-BL Reaction pressure, 120 kg/cm2; concentration of catalyst, 5 wt% 0 24OoC, 0 25OoC, 0 260°C, 270°C, A 280°C
Figure 8. Yield of THF or I/-BL us. reaction time in hydrogenation of succinic acid and polyester Reaction temperature, 260 OC; reaction pressure, 120 kg/cm2; concentration of catalyst, 5 wt% 0 THF (succinic acid), 0 THF [polyester, mean molecular weight ofpolyester (MW) = 20001, 0 THF (polyester, M W = lOOO), 7BL (succinic acid), A y-BL (polyester M W = 2000), A y B L (polyester, M W = 1000) VOL. 6 2
NO. 4
APRIL 1970
29'
-
or 3, and proceeds almost instantaneously. The rate of Reaction 2 is next to Step 1. Reaction 3 is a ratedetermining one. Therefore, an appropriate choice of reaction conditions makes it possible to control the product distribution and the ratio of THF to y-BI,. It is also possible to produce only THF by means of recycling y-BLto the reactor. Reaction scheme. Figure 10 represents the overall reaction scheme, “via y B L ” means that its reaction proceeds mainly through the following steps.
100
d
80 0 0)
E
Y
E 0 U
60
I c 0
40
I
0 .-
>
I1 4 I11
or
c
E
4
20
+ 11 + VI 4 VI1
“uza succinic acid” is
c
0
0
IV 0
2
4
6
8
IO
Figure 9.
I
Figure 10. Reaction scheme INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
4
4
v + IX
4
VI1
VI1
“oia polyester” is
Reaction temperature, 260OC; reaction pressure, 120 kg/cm2; concentration of catalyst, 5 wt%
30
VI11 4 IX
or
R e a c t i o n time (hr) Conversion of succinic acid us. reaction time
--f
x +XI
4
VI1
Figure 7 1. Processflow scheme
I t can be seen in Figure 10 that the following several reactions occur simultaneously :
1. hydrogenation for double bond: (I), (VIII) 2 . hydrogenative dehydration: (11), (III), (IX) 3. equilibrium reaction between hydration and dehydration: (IV), (V) 4. hydrogenative cyclization : (VI) 5. dehydrative cyclization : (VII) 6. equilibrium reaction between dehydrative condensation polymerization and hydrolysis : (X) 7. hydrocracking of polyester: (XI) The order of the reaction rates to T H F of the above three paths is
“via y-BL”
>
“via polyester”
>> “via
succinic acid”
The plan of this process should be scheduled as the above reactions are balanced mutually. T h e side reactions produce a small quantity of lower organic acids, such as propionic and butylic acid, and lower alcohols, such as n-propanol and n-butanol. The lower organic acids may be produced from the thermal cracking of dicarboxylic acids and y-BL. The lower alcohols are produced from the successive hydrogenation of T H F as previously mentioned. Thermodynamic consideration. The heat of formation included in this process is shown in Table IV.
AUTHORS Junichi Kanetaka, Taisuke Asano, and Shznobu Masamune are employed by the Mitsubishi Petrochemical Co., Ltd., in Tokyo, Japan. This paper was presented as part of the Symposium on Novel Processes and Technology of the European and Japanese Chemical Industry at the 158th National Meeting of the American Chemical Society in Nem York, N . Y., September 7-12, 1969.
The heat of formation of T H F and water by hydrogenating maleic anhydride in the liquid phase is so high that heat removal may be an important problem. In addition to the usual method-i.e., the internal heat exchange, the external circulating heat exchange, and so on, a special method of heat removal is applied in this process by which either heat removal or selectivity rise-up of T H F can be achieved effectively. Process flow sheet. A schematic flow diagram is illustrated in Figure 11. Maleic anhydride, recycled y B L from the distillation section, and hydrogen gas are all fed to the reactor after being preheated (the temperature of the feed is always kept lower than that of the reaction system). The reactor effluent is cooled down to about 40 to 60OC and comes to the flash drum, where gas can be partially separated from the liquid product. The
TABLE IV. HEAT OF FORMATION FROM MALEIC ANHYDRIDE TO EACH PRODUCT A T 260°C, I 2 0 KG/CM2
By-Froduct
Heat of formation, kcallmol
7Hz 6Hz 5Hz
H2 0 2H20 2H20, CHI 2Hz0 HzO, CH4
-30.57 -50.42 -75.46 -112.90 -100 87 -93.20
HP, HzO
con
Product
Reactant
Succinic anhydride y-Butyrolactone Tetrahydrofuran n-Propanol n-Butanol Propionic acid (via y B L ) Propionic acid (via succinic acid)
Hz 3Hz 5Hz
VOL. 6 2
-29.22
NO. 4 A P R I L 1 9 7 0
31
,
TABLE V.
QUALITY O F T H F PRODUCT
Analytical data ofpilot plant product Boiling point ("C) Color (APHA) Specific gravity (20/4'C) Refractive index ( n ~ " ) Purity (wt70) Water content (wt%) Peroxide (wt%) Carbonyl compound (wt%) Hydroxyl compound (wt%)
64.6-66,2 2 0.887 1.407 99.99 0.0002 0
Design oj commercial plant product . I .
... * . e
99.95 0.0002 0 0
0 trace
0.01
TABLE VI. ECONOMIC DATA BASED ON 5000 M E T R I C TONS/YEAR (105.7 BPSD) O F TETRAHYDROFURAN W I T H PRODUCTION 333 STREAM DAYS/YEAR
Item Raw materials Feed stock (MAH) Net hydrogen (as 10070 purity) (as including 5y0 mechanical loss) Products Tetrahydrofuran
Unit
Consumption
IO3 ton/year (1 03 lb/day)
8 .O (52.8)
108 NM3/year (million cu. ft.jday)
9.7
103 tonsjyear (barrel/stream day 1
(1.03) 5 .0 (105.7)
Utilities Steam (180h)
Cooling water (At = 9 . 5 ' c ) Boiler feed water Fuel Gas Electric power Catalyst and chemicals Plant costs
tons/year ( l o 3 lb/hr) tons/year !gpm) T / H tonsjyear (gpm) 103 kcal/hr (MM Btu/I-I) kWh/hr lo3 USA $/Year 106 USA $
2.12 (4.7) 249 (1100) 2.28 (10.1) 1.25 (4.96) 366 84.6 P .38
separated gas is fed to the water-scrubber to recover T H F accompanied with the unconverted gas. The liquid product is diverted to the distillation section, composed of four columns. I n the first coIumn, y B L is recovered from the bottom and recycled to the reactor to undergo the further reaction to T H F . However, if desired, it can be withdrawn as a final product. The overhead product of the first column is purified to THF through successive columns by removing byproducts such as water, n-propanol, and n-butanol. Finally, purified THF is withdrawn from the top of the last column. Purity of final T H F is 99.95 wt% or higher. Raw materials for THF production. Maleic anhydride, produced by the oxidation of benzene or (&fraction, is usually used as a raw material. Succinic anhydride and y-IBL could also be used, if desired. THF can be produced directly from benzene or Cqfraction by a two-stage oxidation-reduction process which involvcs effectively combining this T H F process with the existing maleic anh>-drideprocess. Impurities contained in hydrogen come into question for this process. T h e catalyst is permanently adulterated by sulfur compounds and teniporarily by carbon monoxide. Thus, hydrogen sulfide and carbon monoxide must be removed by conventional methods. Methane, ethane, and nitrogen have little effect on the catalyst activity . Quality of THF product. Pilot plant data indicate that the purity of T H F product is 99.95 to 99.99 wt7$. I t easily passes the strict performance te.st for the raw material used for spandex fiber and urethan elastomer and easily qualifies as a solvent for polyvinylchloride (PVC). Analytical data of this pilot plant product are listed in Table V together with the design of the first commercial plant. Economics. Economic data for the process are illustrated in Table VI. 5000 metric tons per year (106 barrelsjstream day) of tetrahydrofuran is manufactured in 333 annual stream days. Plant costs listed in Table V I include engineering fee and all the investmrnt inclusive of facilities without battery limit. (Investment without battery limit is taken as 15yc of investment within battery limit.) Although the cost of maleic anhydride is approximately 12p!/lb and the plant is operated a t full capacity of 5000 tons per year, the production cost of tetrah>-drofuran is about 29.1#/lb with this proccss. Thcreforc, payout time will be 2.2 years for 38.0d/lb of the THF selling price. REFERENCES (1) European Chemical News, 34 (Dec. 16, 1966).
(2) U S Patent 3,238,225. (3) US Patent 2,772,291, 2,772,292, and 2,772:293. (4) Chemical Week, 63 (Mar. 5 , 1969). Patents
Japanese Patent Publication No. 43-6946, 43-6947, 44-7934. Netherland Patent 6,611,852. France Patent 1,519,062. Italy Patent 791,831. (12 additional patents have been applied i n J a p a n a n d other foreign countries)
32
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
