Butene-isobutane feed mixture

The next step in the cracker C4 treatment is the isolation of isobutene from Raffinate 1. To realize this step. Raffinate 1 is reacted with water or methanol to form tert-butanol or methyl-iert-butyl ether, respectively. Ahematively, Raffinate 1 can be treated with an acid catalyst to convert isobutene selectively into isooctene, an important fuel additive. All Raffinate 1 treatment processes have in common that isobutene reacts selectively from the mixture to form a compound of significantly lower vapor pressure. Thus, in the subsequent distillation process, the isobutene adduct is the low boiling component and remains at the bottom of the distillation column while the remaining C4-compounds can be isolated at the top. The obtained distillate is called Raffinate 2 and consists typically of 45% 1-butene, 30% 2-butenes, 19% butanes, 6% isobutane, and traces of 1,3-butadiene. Raffinate 2 can be applied as feedstock for a distillation unit that isolates 1-butene from the mixture for copolymerization apphcations. Alternatively, Raffinate 2 can be fed into a dimerization unit where either a homogeneous (Dimersol-process) or a heterogeneous Ni-catalyst (Octol process) converts the butenes into Cg dimers. Unconverted feedstock of this unit is called Raffinate 3. It typically contains around 70% butane and isobutane and 30% of remaining linear butenes. Raffinate 3 is recycled to the cracker to serve their as an addition to the cracker feed. 

A typical feed to a commercial process is a refinery stream or a steam cracker B—B stream (a stream from which butadiene has been removed by extraction and isobutylene by chemical reaction). The B—B stream is a mixture of 1-butene, 2-butene, butane, and isobutane. This feed is extracted with 75—85% sulfuric acid at 35—50°C to yield butyl hydrogen sulfate. This ester is diluted with water and stripped with steam to yield the alcohol. Both 1-butene and 2-butene give j -butyl alcohol. The sulfuric acid is generally concentrated and recycled (109) (see Butyl alcohols). 

The use of acidic chloroaluminates as alternative liquid acid catalysts for the allcy-lation of light olefins with isobutane, for the production of high octane number gasoline blending components, is also a challenge. This reaction has been performed in a continuous flow pilot plant operation at IFP [44] in a reactor vessel similar to that used for dimerization. The feed, a mixture of olefin and isobutane, is pumped continuously into the well stirred reactor containing the ionic liquid catalyst. In the case of ethene, which is less reactive than butene, [pyridinium]Cl/AlCl3 (1 2 molar ratio) ionic liquid proved to be the best candidate (Table 5.3-4). 

In alternated feeding mode, the reagents, pure isobutane rind a mixture of isobutane /1-butene (10/1 ratio), were fed alternatively by two HPLC pumps pure isobutane was fed for twenty seconds and then stopped while the feeding of the mixture of isobutane/1-butene has begun after ten seconds the feeding of the mixture stopped and the feeding of pure isobutane started again (mode 2). 

The surface active cations also improve product quality when alkylating with a typical refinery feed. Table V contains a list of additives studied with a feed containing 94 percent Isobutane and 6 percent butenes. The butenes contained 42 percent isobutylene and an equilibrium mixture of 1- and 2-butene. 

Weitkemp studied the time course of alkylation of isobutane with n-butenes over CaX and CaY zeolites. At low times on stream, alkylation is extremely selective no olefins, naphthenes or aromatics are formed. During this initial alkylation stage, the conversion of the feed olefins is 100%. Carbon number distribution of the products at this stage is given in Fig. 4.6. A complex mixture ofCs to C12 isoparaffins is formed. In all cases, isooctanes predominate, though the distribution changes with time on... 

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