1,3-Butadiene and I-Butene Development of new technical processes based on unsaturated hydrocarbons hemische Werke Huels A.G. has developed, in the past few years, several new technical processes, based on unsaturated hydrocarbons obtained from Cd cuts, to the point where they can be used in production. Inasmuch as large supplies of Cd cuts are expected to be readily available in the near future, we shall have access to relatively inexpensive raw materials for our processes (Figure 1).
C
Polyamide 12
From butadiene, the starting material, we proceed by means of trimerization, using a Ziegler-Natta catalyst, to cyclododecatriene, which is subsequently hydrogenated into cyclododecane. Cyclodecanone is then forrned through air oxidation in the presence of boric acid, and its oxime is rearranged into lauryl lactam. The polyamide 12 obtained from lauryl lactam possesses a carbon chain which is six carbon atoms longer than nylon 6. This is the reason why polyamide 12 has a much lower water absorption capacity and, besides other areas of application, is consequently used with preference for precision parts in valves. Its use for powder coating by the fluidization dip and electrostatic technique should also be mentioned. The present capacity of our polyamide 12 plant is 3,000 tons per year. This output will be expanded to 12,000 tons annually within the next few years. l o w Molecular Weight 1,4-cis-Polybutadiene
Butadiene can also be polymerized with ZieglerNatta catalysts in the presence of a modifier into linear products whose molecular weight is below 4,000. These products are liquid, incorporating butadiene in a 1,4 configuration. Over 75y0of the C-C double bond in each basic unit is in cis form. From this structure of the polymer chain results the good oxidative drying property of the polymers and the possibility of addition reactions on the C-C double bonds. Low molecular weight 1,4-cis-polybutadiene can therefore be put to versatile use as a raw material in the lacquer industry. Our productive capacity at present amounts to 800 tons annually and this will be raised to at least 4,000 tons per year by 1970. 2-Butene and 1-butene, respectively, serve as source material for the following two processes: 48
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
Acetic Acid
T o make acetic acid, 2-butene and 1-butene are oxidized in the gas phase at 240°C and an air pressure of about 3.5 atm gauge in the presence of vanadates. When using 1-butene, acetic acid, not propionic or acrylic acid, is obtained. Isobutene also gives off acetic acid, but in a much smaller yield. Alkanes are not oxidized under these reaction conditions. The process is being operated at present on a pilot plant scale.
I Once the butadiene is removed, 1-butene can, after special preparation, be selectively polymerized out of the residual Cd cut by means of Ziegler-Natta catalysts. 2-Butene does not interfere with the polymerization process; it acts, in conjunction with butane and isobutane, as a diluent, thus making it unnecessary to employ additional diluting agents. Against the other polyolefins, the polybutene-1 obtained in this manner has a number of remarkable characteristics for applications development. The capacity of our pilot plant is about 1,000 tons per year. A plant facility based on an annual output of 12,000 tons is due to come on stream at the end of 1970. Of the four techniques mentioned, the following discussion deals in somewhat more detail with the production of low molecular weight polybutadiene and the polybutene process. Low Molecular Weight 1,4-cis-Polybutadiene. Polybutadienes of molecular weights below 4,000 have a liquid consistency and shall therefore be briefly referred to in what follows as liquid polybutadienes. Liquid polybutadienes can be produced by polymerization or by degradation of high molecular weight polybutadiene (Figure 2). The polymerization process to be described here is broken down into 3 stages: polymerization, washing, and concentration. Polymerization can be accomplished batchwise or continuously. The solvent used is benzene which is dried by means of azeotropic distillation. I n aliphatic hydrocarbons, on the other hand, lower conversions and higher average molecular weights are obtained. T h e aluminum and nickel organic compounds making up the mixed catalyst are added as benzene solutions (7). T h e Polybutene-
II
AND APANESE HEMICAL INDUSTRIES SYMPOSIUM
-
Butadiene
k
1. Polyamide 12 Ziegler-Catalyst
Oxime Polyamide 12 Capacity: 3000 MT/yr
2. Low Molecular 1.4-~is-Polybutadiene Z iegler-Natta-Cat.
Butadiene -1.4-cis-Polybutadiene Modifier
(MW 3500)
Capacity: 500 MT/yr (1970) 4000 MT/yr Butenes
Acetic Acid Air
2-Butene 1-Butene
+ Vanadate Cat. 24OoC
*Acetic Acid
Pilot Plant
-
Polybutene-1
Ziegler-Natta-Cat.
1-Butene
Polybutene-1
Capacity: 1000 MT/yr (1970) 12,000 MT/yr
Figure I. Modern commercial processes on basis of unsaturated hvdrocarbons from C4 cuts
amount of mixed catalyst is roughly 1%, based on butadiene. The butadiene used must satisfy the requirements of a Ziegler polymerization-that is, acetylenes have to be screened out as catalyst poisons. aOlefins and olefins with double bonds occupying a middle position are, by comparison, only mildly disturbing. Cumulenes, such as 1,2-butadiene and allene, which are used as modifiers in the manufacture of polybutadiene rubber, are unsuited for the production of liquid polybutadienes. I n order to secure a measurable reduction in molecular weight, they would have to be applied in a concentration of more than 0.2Oj, by weight, based on 1,3-butadiene. I n such high concentrations, however, they have a definitely inhibiting effect. By contrast, electronic donors (2)-such as ethers, amines and ammonia-have proved to be excellent modifiers which, in a concentration of no more than several hundred parts per million, are capable of influencing the catalyst and thus diminishing the molecular weight. When, in less than 10 hours, the polymerization has attained a conversion of goyo,water is added in a mixer
WOLFRAM PASSMANN to stop the reaction and wash out the catalyst residues ( 3 ) . After the water has been separated in a settler, the solvent is drawn off, subjected to intermediate treatment and then recycled. The liquid polybutadiene coming out from the evaporator is a water-clear, highly fluid polymer, in which the volatile components amount to less than 0.1%. The warm product is left for further cooling in the storage tank and from there is filled in drums. The main types BL 801 and BL 803 have the following specifications (Figure 3). Compared to other known liquid polybutadienes these feature
1) a lower viscosity 2) a higher iodine number 3) a far higher cis-double bond content 4) practically only double bonds which occupy a middle position, and 5) a smaller catalyst consumption in polymerization As a consequence of the high cis-double bond content, these ' products are possessed of good oxidative drying properties and are capable of a variety of addition reactions. Possible areas of application are the following :
Figure 2. L o w molecular weight polybutadiene (process) VOL. 6 2 NO. 5
MAY 1970
49
BL 801
Viscosity (cP/20° C) Residue (% by weight) (not volatile without decomposition) Ashes (% by weight) Clarity Iodine color number Powder drying (hours) as per DIN Standard 53 150 Complete drying (hours) as per DIN Standard 53 150 Iodine number Molecular weight (Vapor pressure osmometer) Refractive index (nDzoo) Density (d4200) Double bond content in %
BL 803
750 f 10%
3000 f 10%
2 99.9 50.1
52
-
