PRODUCTION OF SORBITOL B Y T H E USE OF AMMONIA SYNTHESIS GAS E R N 0 H A I D E G G E R , ' I S T V A N P E T E R , I S T V A N G E M E S , A N D JOZSEF K A R O L Y I
High Pressure Research Institute, Budapest 5, P.O.B. 208, Hungary A new process for the production of sorbitol b y high pressure hydrogenation and the kinetics involved are discussed. Tests were carried out on laboratory and pilot plant scales. Production is b y ammonia synthesis gas in two in-line reactors. The ammonia synthesis gas returns to the ammonia plant under pressure; therefore there is no independent gas circulation in the sorbitol plant. In a plant with a capacity of 1000 tons per year, the production cost of sorbitol b y this process is $ 1 6 per ton less and the investment cost $24 per ton less than conventional processes. The determination of glycerol and deoxysorbitol impurities is also described.
HE world-wide production of sorbitol has increased rapidly T i n the last 10 to 15 years. New consumers have appeared and the increased demands have resulted in the development of new technologies (Haidegger, 1961). Sorbitol production in the United States, where sorbitol production is now highest, has increased as shown in Figure 1. T h e consumption expected until 1970 is also indicated. Approximately one third of the sorbitol produced is required for the production of vitamin C. As a n aqueous solution of sorbitol is a n excellent moisture-stabilizing material, many industries use it as a substitute for glycerol and glycol: cosmetic, tobacco, textile, pharmaceutical, confectionery, leather, paper, glue, and telecommunication industries. Its properties are utilized in the production of emulsifying agents, alkyd resins, and polyurethane foams. Its organoleptic properties make it suitable as a diabetic food sweetener.
Theory, Kinetics, and Technology of Sorbitol Production
Sorbitol is now produced by the catalytic reduction of D-glucose. I n the hydrogenation of D-fructose, 5070 D mannitol is produced in addition to sorbitol. T h e reaction kinetics of high-pressure hydrogenation was investigated by Hoffman and Bill (1959) and Brahme et al. (1964). They stated that the slowest processes are the transport phenomena taking place between gas-liquid-solid phases and their interfaces. Therefore the rate-determining step of the reaction is the diffusion of the dissolved glucose and sorbitol molecules through the film covering the surface of the catalyst. A valuable result is obtained by measuring the initial rate of reaction as expressed in the following equation.
-Ro
pn, I , m, n
= =
actual pressure of hydrogen, atm. order of reaction
Experimental results show that the order of reaction relative to hydrogen was 0.5, while that with respect to catalyst concentration was 1. I n process technology, both batch and continuous processes and, in the latter case, fixed and suspended catalysts, are known. Batch processes worth mention are those of Merck put in operation in 1956 (Fedor, 1960) and of Howards of Ilford Ltd. put in operation in 1961 (Robertson, 1966). Similar processes of the Incorporated Pharmaceutical and Food Works (Egyesiil t Gy6gyszer is TBpszergyBr, Budapest) and the Vitamin Works (Leningrad) are of minor interest. I n the Merck process, a 50y0 aqueous solution of dextrose is hydrogenated in the presence of Raney nickel a t 70 atm. and 150' C. The reaction time is 3 hours, and hydrogen is supplied by electrolytic cells. T h e specific consumption is 110 std. cu. meters per 100 kg. of dextrose. T h e product is concentrated to 7oyOa t 45 to 50' C . and 50 to 80 torr. T h e raw material and product are purified by ion exchange. VEB Deutsches Hydrierwerk (Rodleben, Eastern Germany) uses a fixed-bed process. T h e fixed catalytic bed contains a copper-nickel catalyst (1 to 2, w./w.) and hydrogenation is carried out a t 135' C. and 200 atm. Pliva Pharmaceutical Works (Zagreb) produces sorbitol by an up-to-date suspended-catalyst process. Crystalline dextrose is dissolved in water, and 2.57, Raney nickel catalyst is mixed. T h e suspension is then passed through a preheater and fed to the reactor. T h e product is separated from the I
= K CoGICrmpa:
where
Ro K COG C,
initial rate of reaction, gram-molecules of transformed glucose liter X hour = reaction rate constant, hr.-l = initial concentration of glucose gram = concentration of catalyst, gram-molecule of glucose =
1980
fP50
I070
Yeor 1 Present address, Minister of Heavy Industries, Budapest V., Markb-u 16, Hungary.
Figure 1 . VOL. 7
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JANUARY 1968
107
gas, filtered, and passed through an ion-exchange column. T h e electrolytic decomposition of water is the source of hydrogen. The plant capacity is 500 tons per year. The Atlas Powder Co. (Wilmington, Del.) has produced sorbitol since 1947 by high-pressure hydrogenation (Chem. Eng., 1959). Activated carbon is used for purification, and the product is concentrated by vacuum evaporation. This process is similar to that of Pliva Pharmaceutical. Production of Sorbitol by Ammonia Synthesis Gas
Experiments performed in autoclaves (Institute of Chemical Technology, Technical University, Budapest) have justified the assumption that ammonia synthesis gas above a given pressure is a hydrogen source equivalent to pure hydrogen a t that pressure. Research a t the High Pressure Research Institute has experimentally determined the optimal values of parameters of the continuous process in a 200-ml. reactor. These parameters are reaction temperature, total pressure, partial pressure of hydrogen, space velocity, gas-liquid ratio, catalyst concentration, and the rate of decrease of catalyst activity. The best experimental results obtained were reproduced in highpressure equipment provided with a 30-liter reactor. Following the determination of the optimal conditions in this equipment, 300 tons of sorbitol were test-produced for use in vitamin C synthesis. As no modification of the standard process for the conversion of sorbitol to vitamin C was required, the product could be regarded as equivalent to the imported sorbitol previously used. O n the basis of experimental results, a 1000-ton-per-year sorbitol plant was designed (Peti Nitrogenmuvek) and has been producing continuously since January 1963. A schematic flow sheet of the process is shown in Figure 2. Crystalline dextrose is dissolved by recycle water in a 1.2-cu. meter heated autoclave, 1, 2 to 4% Raney nickel catalyst is added to the 50% solution, and the autoclave is provided with a stirrer, 2. The solution is fed by a high-pressure pump, 3, to a mixing point, where it is blended with the high-pressure synthesis gas coming from the ammonia plant. T h e gas is a
mixture of hydrogen and nitrogen (75 to 25, by volume). Accordingly, the plant has no independent hydrogen source, but a part of the synthesis gas is compressed in the ammonia plant, expanded to 200 atm., and flows through to the sorbitol plant. At the same time, the hydrogen content of the gas decreases slightly and then is separated from the liquid product, expanded to 20 atm., and recirculated back to the ammonia synthesis plant. The product-catalyst mixture accumulated in the bottom of the separator is discharged to an atmospheric tank, 11. The catalyst is filtered out on a filter press, 12. A service tank, 13, is used to store the catalyst-free solution, which can then be concentrated to 70% by a film-evaporator, 14. Finally, the concentration of the solution is adjusted accurately by dilution in another service tank, 15. T h e filtered catalyst, after washing on the filter press with water, can be re-used for hydrogenation. Analytical Methods
The quality of the laboratory-produced sorbitol and that produced in the plant was characterized by the efficiency of the oxidation of sorbitol to sorbose. I n some samples, a higher quality of contaminating components could be stated from the values of the efficiency of sorbitol to sorbose fermentation and the efficiency of sorbose crystal production as well. An analytical method to characterize the contaminants was devised on the basis of oxidation by periodic acid. Each of the following reactions occurs in the mixture. SORBITOL
+51 0 4 -
CHZOH-(CHOH)~-CH~~H 2CH20
=
+ 4HCOOH + 5
+ H2O
103-
+2 = 2 C H z 0 + H C O O H + 2 1 0 4 - + H2O
CH20H-CHOH-CH20H
104-
DEoXYSoRBIToL
+4 104- = + CHzO + 3 H C O O H + 4
CH~-CHOH(CHOH)~CHZOH CHICHO
103-
+ H2O
Synthesis Gas
Synthesis
Gas
!
Figure 2. 1. 2. 3.
Autoclave Stirrer High-pressure pump
108
4. 5. 6.
Schematic diagram of Peti Nitrogenuvek sorbitol plant
Steam-heated spiral tube apparatus Reoctor I Steam-heated spiral apparatus
I&EC PROCESS DESIGN A N D DEVELOPMENT
7. 8.
9.
Reactor II Cooler Gas-liquor separator
10. 1 1. 12.
Receiver Atmospherical tank Press filter
13.
Storage tank Film evaporating equipment 15. Container for the flnal product
14.
GLUCOSE CH*OH(CHOH)4CHO
f 5104-
therefore requiring larger storage tanks. Also, consumption of steam and electrical energy and labor requirements are higher because of the higher reaction time. Considerably high rates of reaction can be reached in continuous processes. I n the autoclave experiments of Hoffman and Bill the calculated rate constant is 6 hr.-I I n the authors’ continuous plant experiments, the rates calculated a t different space velocities are as follows:
=
CHzO
f 5HCOOH f 5 1 0 3 -
Periodic acid oxidizes the -CHOHgroups to formic acid and the -CH20H groups to formaldehyde. Products of the periodate oxidation were measured to determine the quantity of each impurity. I n addition to measuring excess periodic acid, determination of the formic acid and formaldehyde was necessary. Deoxysorbitol was determined by the acetaldehyde fornied in the oxidation. For quick qualitative assessment, two quantities that characterize the quality of the sorbitol can be obtained from the results of the periodate oxidation-formic acid-to-formaldehyde and formaldehyde-to-periodate ratios. T h e formic acid-formaldehyde ratio is 2 in the case of sorbitol and 0.5 in the case of glycerol. Thus, diminution of the molar ratio definitely indicates breaking of the chain. T h e above method can be used only when no other impurities are indicated by preliminary paper chromatographic investigation. Mannitol was determined on the basis of optical rotation of the sorbitol solution with the addition of borax. For comparison of the products of other plants, samples of different origin were purchased and analyzed (Table I).
Space velocity, kg./liter hr. Rate constant, hr.-l
Parameters of the different processes are summarized in Table 11. T h e drawback of batch processes is that their capacity relative to the volume of the high-pressure reactor is very small,
,Vame and Origin of Sample Karion fluss, Merck Neosorb 707, D-sorbitol Qualitt spec. pour fabr. de Vit. C Atlas Sorbo R 707, U.S.P. Atlas Powder Esasorb-N 707, SMIC SOC.Milanese Ind. Chem. Sorbitol Syr. 707, Howards of Ilford VEB Deutsches Hydrieswerk Rodleben Sorbitol I. Pet Sorbitol 11. Pet
2.0
2.5
3.8
6.0
196
114
164
185
190
Sorbitol is produced in a continuous process a t Rodleben; a fixed-bed catalyst is used for the hydrogenation. This has the disadvantage, however, that the heat of reaction may cause a local overheating on the surface of the catalyst grains which leads to isomerization, cracking, and carmel formation. This may be the origin of the mannitol content of the product. This leads to the general statement that flow conditions in the case of a fixed-bed catalyst are not so ideal as in a continuous reactor with suspended catalyst. T h e productivity of the continuous process plant (Pliva Pharmaceutical), as indicated by the space velocity, is rather low. This may be due to a discontinuous withdrawal of the product, although the feed of the raw material is continuousLe., the product accumulated i n the separator is subject to expansion in the 20-minute period before the gas appears. Then a relative vacuum is formed in the separator, causing a greater quantity of product to be sucked over from the reactor, so there is a n equilibrium disturbance in the high-pressure system. T h e retention time i n the reaction volume is not
Comparison of Processes
Table 1.
1.0
Composition of Different Sorbitol Samples Components, yo Deoxysor bitol Glycerol 0 0
Sorbitol 70.68
Glucose 0.07
Aldehyde-Periodate Ratio 70.58170.78
71.46
0
0.99
0.07
73.43/72.91
71.45
0
0
0.04
70.75/72.06
70.46
0
0
0.02
69.83/71.10
67.78
0.44
0.68
0.06
69.40/69.08
61.03 69.70 69.70
0 0 0
0 0 0
0.38 0.02 0.05
60.86/61.21 69.79/69.65 69.62/69.26
Table II.
Characteristic Data of Different Sorbitol Plants
Catalyst Plant
Press., Atm.
Temp., C.
50
110
100 70
Egyesult Gyogyszeres Tapszergyar (Budapest) Vitamin plant (Leningrad) Merck (U.S.A.) Howards (G. B.)
110
135 140 135
VEB D. Hydrierwerk (GDR)
200
135
Pliva (Yugoslavia) Atlas (U.S.A.) Peti Nitrogenmuvek (Hungary )
200
120
125 200
140 170
Concn. of Retention Space Dextrose Time, Hr. Velocity Soln., yo BATCHPROCESSES 8 ... 50
3.5 3
...
50 50 ... ... 60 CONTINUOUS PROCESSES ... 1 .o 25
... ... ...
...
Qual.
Quant., Productivity wt. of Reactor, of soh. Kg. Sorbitol/Hr.
Raney Ni Raney Ni Raney Ni
... ... ... ...
Cu-Ni
Raney Ni
capacity, lo00 Tons/ Year
0.075 0.171 0.200
... ...
...
7.5 2.1
...
0.250
0.8
ifixrd) ,------I
0.3
50
Raney Ni
2.5
0.150
0.5
1-3
5b-60
Raney Ni
2
0.500-
1.5
...
...
...
1.800
VOL. 7
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109
uniform, which must affect the quality of the product; as a consequence, mild reaction parameters must be chosen to ensure the quality of the product. I n this latter case, the capacity of the plant is small, as proved by the productivity of the reactor. Only a schematic outline of the Atlas Powder process is known; however, on the basis of this outline, the authors assume that the parameters of the process are similar to those described in the present work. T h e difference in the two processes is in the gas circulation system-Le., in the Atlas Powder process, the gas is recirculated, while the Hungarian process uses a single-pass gas flow. T h e advantage of the authors' process is that with the aid of stepwise heating and gradual conversion, a product of high and uniform quality may be produced with a high capacity. The lack of hydrogen recirculation is a novel solution. This was possible because the plant was located near a n ammonia plant, which is a high capacity hydrogen source. T h a t a synthesis gas of 25% Nz by volume was used for hydrogenation rather than pure hydrogen is novel. I n using the 420 ton-per-day ammonia synthesis plant as a hydrogen source for 1000 tons of sorbitol per year, the flow of the gas is modified as follows (volumes are expressed under standard conditions). T h e fresh synthesis gas (0.32%) is diverted through the sorbitol plant, reduced in volume by the amount of hydrogen necessary for the reduction, and expanded to a lower pressure (20 atm.). Following the absorption of carbon dioxide, it is led back to the main flow of the synthesis gas. T h e 7570 Hz content of the synthesis gas is reduced by the hydrogen consumption of the sorbitol plant by only 0.05%. The above data show that the operation of the ammonia synthesis plant is not disturbed. Factors which influence the operation more significantly include compression capacity change caused by the winter-summer temperature differences, fluctuations of the efficiency of the gas purification, and fluctuation of the efficiency of hydrocarbon reforming. If the sorbitol production were increased tenfold-Le., to 10,000 tons per year-the gas diverted to the sorbitol plant could be compensated for by production in the ammonia synthesis plant of a gas of greater than 75% hydrogen content.
Hydrogenation by the aid of ammonia synthesis gas provides significant economical advantages. The investment and production costsfor a plant producing 1000 tons of sorbitol per year by electrolytically produced hydrogen and an independent gas circulation, and sorbitol production by hydrogen diverted from the 420 ton-per-day ammonia synthesis plant are compared below. Investment Costs
Investment costs for 1 std. cu. meter per year synthesis gas compressed to 300 atm. Investment costs for 1 std. cu. meter pure HZ in synthesis gas a t 300 atm. B. Investment costs for 1 std. cu. meter per year electrolytic hydrogen compresses to 300 atm.
A.
$0.013 0.017 0.15
Production Costs
A.
B.
Hydrogenation with synthesis gas Production costs of synthesis gas necessary to produce 1 ton of sorbitol Hydrogenation with electrolytic hydrogen Production costs of hydrogen necessary to produce 1 ton of sorbitol
$ 4.40
$20.80
Thus, combination of the sorbitol with the ammonia plant lowers the investment cost of the production of 1 ton of sorbitol by $24 and the production costs by $16.40, as compared with the same costs using an independent hydrogen source. For a plant with a capacity of 1000 tons per year, the savings are $16,400 and $24,000 per year for production and investment costs, respectively. literature Cited
Ashcroft, W. K., Chem. Age (London) 89, 907 (1963). Brahme, P. H., Pai, M. V., Narsimhan, G., Brit. Chem. Eng. 9, 684 (1964). Chem. Eng. 59, 208 (1959). Fedor, W. S., Ind. Eng.Chem. 52, 282 (1960). Haidegger, E., Magyar Ke'm. Lapis 10, 351 (1961). Hoffman, H., Bill, W. I., Chem. Zng. Tech. 31, 81 (1959). Robertson, J. H., Ind. Chemist 39, 233 (1966). RECEIVED for review March 8, 1966 ACCEPTEDAugust 29, 1967
HYDROGEN PEROXIDE CATALYTIC OXIDATION OF REFRACTORY ORGANICS IN MUNICIPAL WASTE WATERS D. F . B I S H O P , G . S T E R N , M . F L E I S C H M A N , A N D L . S . M A R S H A L L Advanced Waste Treatment Research Activities, Cincinnati Water Research Laboratory, Federal Water Pollution Control Administration, Cincinnati, Ohio 45226
organic pollutants entering the nation's water reoxidation in municipal waste treatment facilities or in natural water courses. These refractory organics, after chlorination, may form noxious chlorinated organics and cause general deterioration in water quality. T h e increasing re-use of water demands better removal of organic contaminants. ANY
M sources are not effectively removed by biological
110
I&EC PROCESS DESIGN A N D DEVELOPMENT
Therefore, an experimental study was undertaken to determine the technical feasibility of combining active oxygen (hydroxyl radicals) chemical oxidation and molecular oxygen oxidation (autoxidation) to destroy the broad spectrum of refractory organics in municipal waste waters. An important aim of the study was to determine in various waste waters the capabilities of autoxidation initiated with small amounts of
