NO133493B - - Google Patents

Description

The object of the invention is the practically quantitative production of cyclopentadiene from a dicyclopentadiene-rich fraction formed by thermal treatment and fractionation of a C, pyrolysis gasoline by thermal cleavage of the contained dicyclopentadiene in the liquid phase.

By the pyrolysis of petroleum fractions to produce

of ethylene' appears next to a C^- and C^-fraction a C,--fraction, the so-called pyrolysis gasoline. 1 pyrolysis gasoline's C^-' fraction, it is, among other things, contained <:>isoprene, cyclopentadiene and piperylene^ In order to split this C^-fraction further, the procedure is usually such that the cyclopentadiene dimerizes before the further division of

The C^ fraction. to dicyclopentadiene. Thereby, it is possible to divide the C₂ fraction by distillation into an isoprene and piperylene containing part and. the substantially higher-boiling dicyclopentadiene. Both fractions can then be worked up further separately, for example the C₁ fraction containing isoprene and piperylene for the production of isoprene and the dicyclopentadiene part for monomeric cyclopentadiene.

As far as the further processing of dicyclopentadiene is concerned, it is known to split dicyclopentadiene into cyclopentadiene in the ga s-s phase (cf. US patents no. 2,409-259, 2,733,280, 2,733,283, 2,913,504, 2,99^ .724, 3,007,978, 2,511,936, 2,582.$20 and British, Patents Nos. 573-592, 1,018,046, 807,800).

Disadvantages of the gas-phase fission are the large energy required, which is conditioned by the high temperature necessary for the fission and furthermore the risk of coking of the reactor associated with the high reaction temperatures. To avoid coking, work is carried out in normal technical methods using inert diluents, e.g. inert gases or water vapour, whereby, however, the energy costs again increase considerably and the processing of the reaction products becomes difficult (-cf. US patents no. 2,453-044, 2,801,270, 2,508-9-22. and Hungarian patent no. 151,720

Monomerizing dicyclopentadiene in the liquid phase with long residence times has also been known from the literature for a long time. This, however, forms polymers of cyclopentadiene, which after some time leads to blockages in the apparatus (cf. N.F. Kononov , Is-vest. Akad. Nauk SSSR, Ser. "Khim 1953, pages 112-113;- Chem. Abstract-;48, 10377"e and 13.273d)~.

A way out from. these difficulties in the monomerization of dicyclopentadiene in the liquid phase consist in the fact that the dicyclopentadiene is only partially converted, as a considerable part of the unreacted dicyclopentadiene must be removed together with the polymers of the cyclopentadiene. from the process-.

It has also previously been mentioned, during the further distillative processing of the cyclopentadiene, to return it to the reaction during the dimerization. formed dicyclopentadiene \Sml. US Patents Nos. 2,636,056, 2..733-279, 2.-735-875, 2-751-422:, 2,753,326, 2,813,134, British Patents- Nos. 635-910, 759-327 , 775• H3, Dutch Patent No. 91-149 as well as Oil and Gas Journal of 15-. j anuar-1962", page 10-9). The formation of resin in the slit apparatus

is not prevented over longer periods of time by this precaution.

It was therefore proposed for the cleavage in the liquid phase to use an auxiliary liquid, to avoid resin formation or the high losses of application material. This method of working is mentioned in numerous patents. According to British patent no. 771,650, the addition of organic solvents, which boil above 250°C, is mentioned

and has no solubility for dicyclopentadiene. According to British patent no. 769,813, the addition of various organic solvents is mentioned, in which the dicyclopentadiene has been vaporized. According to US patent no. 2,887,517, the splitting of dicyclopentadiene is mentioned during the addition of three times the volume of higher paraffin hydrocarbons. According to British patent 612,893, the addition of gas oil is mentioned as an auxiliary liquid. According to US patents no. 2,387,993, 2,63-6,054 and 3-016,410, the cleavage with very small concentrations of dicyclopentadiene-

In order to avoid the difficulties, when splitting the dicyclopentadiene, it is further suggested to add inert gases such as e.g. water vapour, in addition to an applied foreign solvent (US patent no. 2 453 0441).

The invention therefore relates to a process for the production of cyclopentadiene by more than 90% cleavage of di-cyclopentadiene, which appears as a concentrate after the thermal treatment of a C.^ fraction of a -pyrolysisbenz.in and subsequent enrichment by fractionation distillation and containing thermally stable dimers of isoprene and codimers of cyclopentadiene, isoprene and piperylene, 1 liquid phase at normal or, slightly overpressure and at temperatures between approx. 170 and approx. 25-0°c, the method being characterized by maintaining a concentration of 10 to 10% for the thermally stable dimers of isoprene and codimers of cyclopentadiene, isoprene and piperylene formed in the bottom product from the cleavage and carrying out the cleavage of the dicyclopentadiene for residence times of less than 5 hours.

A particularly advantageous way of working with the method according to the invention consists in maintaining a concentration of up to 50% in the sump of the splitting apparatus for the polymer part. In addition, codimers or dimers as well as the concentration of the polymer part - depending on the product used, quality, the required amount of sump product, which is added to a distillative work-up, where - as top product, the above-mentioned codimers and dimers appear, which are fully or partially returned to the process.

For the enrichment of codimers and dimers, use is appropriate

a thin film evaporator. The cleavage of the dicyclopentadiene can be carried out in this way to a proportion of more than 90%. For the splitting reaction itself, it is appropriate to have a residence time of less than 5 hours at the highest possible heating surface loads.

The advantage of the method according to the invention in relation to a working method, as it is carried out in the previously known methods, consists in the fact that it is now possible by using a. of a pyrolysis gasoline to carry out the cleavage into monomeric cyclopentadiene without the addition of a foreign auxiliary liquid and practically tolerated without the return of the dicyclopentadiene approximately quantitatively, without the danger of resin formation in the cleavage apparatus. It must be described as distinctly surprising that resin formation does not occur when in the sump of the splitting apparatus for the codimers or dimers. of cyclopentadiene, isoprene and piperylene'maintains a concentration of approx. 10 more. 70%. The resin formation is not prevented when mart does not use reacted dicyclopentadiene as a diluent for the resin formed, as has been proposed in a number of patents, to which reference has already been made previously.

It. general implementation of the method according to the invention shall be explained as follows.

The monomerization can be carried out without pressure or under slight overpressure in a distillation apparatus, consisting of an evaporator, advantageously a circulation evaporator, a separator, a fractionation column with some bottoms, preferably 2-10 bottoms, and a dephlegmator or condenser with a reflux pump. The thus-decomposing product with a dicyclopentadiene content above 70 percent by weight, which originates from the fractional distillation of dicyclopentadiene-containing C^- ■ section of a pyrolysis gasoline and- the return codimers mentioned below- is continuously pumped into the sump or, in fractionation- the pillar. The product used contains wood. side of the dicyclopentadiene as codimers and dimers denoted other C-2-hydrocarbons as well as any residues of C-2-hydrocarbons. The cleavage product i

The splitting apparatus therefore consists of dicyclopentadiene, thermally stable codimers of cyclopentadiene with isoprene and cyclopentadiene with piperylene, dimers of isoprene and of the polymers of cyclopentadiene formed during the splitting process. The sump product is heated to

boiling temperature (170-200°C7, appropriate in the circulation evaporator with natural or forced circulation. To increase the yield, the residence time is as short as possible, preferably under 5 hours, the heating surface load is selected as high as possible. With discontinuous or continuous sump extraction, the sump level is kept constant in the splitting apparatus. The production of dicyclopentadiene which is to be split, is chosen so high that the main part of the dicyclopentadiene is split at once. In the sump boiling under reflux, a temperature and concentration erosion profile is formed in the fractionation column, which can be influenced by the dicyclopentadiene dosage, the further return of codimers and by the heating surface load and the reflux The conditions are to choose the corresponding desired purity of the cyclopentadiene. The cyclopentadiene formed preferably contains less than 2% by weight of dicyclopentadiene and codimers. When using a dephlegmator, the thus formed cyclopentadiene can be used without condensation directly in the following ..processes., e.g., in a hydrogenation. If you want to extract cyclopentadiene in a liquid state, you must cool it down after condensation to temperatures below -20°C (since it dimerizes again very quickly at cooler temperatures, as is well known),

and it can then be further processed-

With the method described here, the overall turnover amounts to 90 to 95% referred to. used .dicyclopentadiene,. the resin formation 5 to 10 percent by weight. Véd'side of a maximum of 2% by weight of C-^-hydrocarbons, especially dicyclopentadiene,. the cyclopentadiene contains only the volatile C₁ compounds, which were already present in the product used.

With regard to the concentration indications, according to the invention, it is appropriate to preferably remove 5-20%, referred to the amount used, of the dicyclopentadiene from the sump of the splitting apparatus and then preferably to work it up in a thin-layer evaporator.

In the thin-layer evaporator, a distillate is removed at 180-250°C which

for the most part consists of codimers and which are "completely or partially returned to the splitting apparatus.

With the method according to the invention, it is therefore possible without added auxiliary liquid in the liquid phase to monomerize as much dicyclopentadiene as possible. Thus, the costs for these auxiliary fluids and the difficulty in quantitatively removing foreign substances from the final product, which is mostly necessary for further processing, are eliminated.

Example.

In the sump (8 litres) of a distillation column, per hour continuously pumped in 1,500 g of an 82% dicyclopentadiene, which had been formed by dimerization of the cyclopentadiene contained in a C 2 pyrolysis benzene fraction and subsequent fractionation. The crude dicyclopentadiene contained the codimers of cyclopentadiene formed by the dimerization with isoprene re.sp. piperylene, as well as dimers of isoprene.

The sump was heated under atmospheric pressure by natural circulation in a steam-heated circulation steamer to boiling temperature (170-180°C). The boiling components and the cyclopentadiene formed by cleavage of the dicyclopentadiene were rectified in a 3.50 m long, 50 mm wide, 10 mm filler filled fractionation funnel located on the evaporator. In the fractionation column, a temperature profile between 180 and 50°C was formed. .The dicyclopentadiene concentration fell from 20% by weight at the lower end to approx. 2 percent by weight at the upper end of the fractionation column. On the gration column there was a deflegmator which was operated with 50°C hot water. Behind the deflegmator, it was per hour -formed .1-205 g -top product with 92.3% cyclopentadiene.

The yield was 91$, referred to the dicyclopentadiene used.

Por to maintain the sump level in the distillation flask was

it primarily removed a certain amount of swamp. This sump was pumped into a thin layer evaporator operated at 225°C. At the lower end of the thin-layer evaporator, thixotropic sump with a pasty consistency was removed.

The distillate was added to the dicyclopentadiene used and thus returned to the sump of the cleavage apparatus. After some time an equilibrium had formed. Of the 1500 g per hour used 82$-ig dicyclopentadiene was 1205.g per hour removed behind deflegma-

the tower; 1120 g of this was cyclopentadiene (92.9% by weight),

75 g of C₁ hydrocarbons (6.2% by weight) and 10 g of C₁₂ hydrocarbons (0.8% by weight). The cyclopentadiene conversion in this case was 91%, it was during long-term trials at 90-9-5$.

After setting the equilibrium, 395 g/hour were removed from the sump of the splitting apparatus and fed into the thin-layer evaporator operated at 2'25°C. As the bottom of the thin-layer evaporator, 80 g/hour of resin and 215 g/hour of distillate were formed, which. consisted of 20 g of dicyclopentadiene (9.3% by weight) and 195 g of thermally stable codimers and dimers (90.7% by weight). Of this distillate, 110 g/hour was pumped with the dicyclopentadiene used into the splitting apparatus, so that the portion of the thermally stable compound in the monomerization reactor was kept at approx. 70%. The polymer portion was 22%. The splitting of the dicyclopentadiene could under these conditions be operated over 1500 operating hours with a cyclopentadiene yield of 90-95$, referred to the dicyclopentadiene used, without the splitting equipment sump becoming too viscous for a circulation due to resin phenomena.

Claims (3)

1. Process for the production of cyclopentadiene by more than 90% cleavage of dicyclopentadiene, which appears as a concentrate after the thermal treatment of a C^ fraction of a pyrolysis gasoline and subsequent enrichment by fractional distillation and which contains thermally stable dimers of isoprene and codimers of cyclopentadiene, isoprene and piperylene, in the liquid phase at normal or slightly overpressure and at temperatures between approx. 170 and approx. 25-0°C, characterized by. that for the thermally stable dimers of isoprene ..and codimers of cyclopentadiene, isoprene and piperylene formed in the bottom product during the cleavage, a concentration of 10 to 70% is maintained and the cleavage of dicyclopentadiene is carried out with residence times of less than 5 hours. 2. Method according to claim 1, ka. rakteri — certed by removing from the fission reactor at least such an amount of sump product that a concentration of a maximum of 50% is maintained for the part of polymers of cyclopentadiene in the sump. 3. Method according to claims 1 and 2, characterized in that the sump product removed from the fission reactor is split by distillation into an overhead product which contains keep the thermally stable codimers and dimers of isoprene resp. cyclopentadiene and piperylene and a sump product which essentially contains the polymers of cyclopentadiene. ~ H. Method according to claims 1-3, characterized in that the thermally stable codimers of cyclopentadiene, isoprene and piperylene and dimers of isoprene formed by the distillative processing of the removed sump product as top product are completely or partially returned to the split reactor. 5- Method according to claims 1-4, characterized in that a thin-layer evaporator is used for the distillative cleavage of the sump product removed from the reaction.