DE19504595A1 - Process for the joint hydrogenation of hydrocarbon-containing gases and condensates - Google Patents

Description

The present invention relates to a new method for ge joint hydrogenation of hydrocarbon gases and Kon densaten.

In the thermal processing of plastic waste by De Polymerization produces gaseous and liquid product flows. These product streams essentially contain saturated coals Hydrogen, but also some significant proportions olefinically or acetylenically unsaturated compounds. The unsaturated hydrocarbons tend to polymerize where are formed by solids in subsequent processing tion processes interfere, for example, with catalysts deactivate or coke reactor, pipe and heat lead exchange surfaces.

DE-A 43 11 034 proposes that by Depoly Gasification of plastic waste, condensate and the bottom phase containing the viscous depolymerization products in deduct separate substreams and the condensate and sump phase separately. This also teaches Document a one-step hydrogenation of the condensate at a festival bed catalyst.

This way of processing is technically complex because it requires separate technical systems for the individual streams. Wei fluctuating compositions of the condensate and of gas due to different compositions of art waste of material to strong temperature fluctuations in the hydrogenation catalyst guide and shorten its service life.

The object of the present invention was to prepare a method deliver that in a technically simpler way than according to the state the technology to reduce polymer formation in the we contain substantial saturated and unsaturated hydrocarbons gases and condensates. Another aspect of the on The challenge was to find a procedure that, despite fluctuations a constant in the composition of the input flows Operation mode enabled.  

Accordingly, a process for the catalytic hydrogenation of a Gases and a condensate, each essentially sown saturated and unsaturated and in the case of condensate aromatic Contain hydrocarbons, found with hydrogen, that there is characterized in that a hydrogen partial pressure of 1 to 50 bar the condensate and part of the gas catalytically hydrogenated in a first stage at 160 to 250 ° C, the Hydrogen product adds the remaining part of the gas and so obtained mixture in a second stage at 250 to 420 ° C catalyzed table hydrogenated.

The gases and condensates to be hydrogenated according to the invention are gaseous or liquid under normal pressure.

The main components of the gases are saturated hydrocarbons substances such as methane, ethane, propane, n-butane, isobutane and n-pentane. As unsaturated hydrocarbons they contain e.g. B. Ethylene, propylene, 1-butene and 1-pentene.

In addition, the gases to be processed can include other components such as Hydrogen, carbon monoxide, carbon dioxide, ammonia, sulfur water hydrogen and nitrogen, but also chlorinated carbons such as methyl contain chloride.

As a rule, the content of unsaturated hydrocarbon is fen in the gas at 0.5 to 35 wt .-%, in special cases it can but also higher. The gas preferably contains at least 50% by weight saturated hydrocarbons, but can only about 30 wt .-% occur in such gases that are particularly high contain parts of unsaturated hydrocarbons. The whole The chlorine content is generally 0.01 to 1% by weight.

The condensates generally start to boil at approx. 60 ° C and a boiling end at approx. 180 ° C (ASTM D-86). It contains isomers as saturated hydrocarbons in general Pentanes, hexanes, heptanes, octanes and nonanes, but also longer chain alkanes. The main components are aromatic coals Hydrogen such as benzene, toluene and ethylbenzene occur, white thereafter xylenes. The polymerizable unsaturated compounds are generally essentially styrene, methylstyrene and In the. Condensates with a styrene content of 1 to are preferred 4% by weight. The diene number of the condensate is preferably 5 to 50 g / 100 g (UOP method 326-82), the bromine uptake at 20 to 60 g / 100 g (DIN 51 774), particularly preferably 40 to 50 g / 100 g.

The condensate can also contain chlorine-containing compounds (in usually less than 500 ppm chlorine content, based on the mass)  and sulfur compounds (usually less than 100 ppm Sulfur, by mass).

The gases and condensates mentioned occur in thermal and kata lytic splitting plants of hydrocarbon mixtures. in the Some are coker, coking plants, catalytic crackers or To name Visbreaker, whose product range includes the gases mentioned and includes condensates which, when appropriately processed can be made available by distillation, for example.

However, gases and condensates which are preferred after a thermi depolymerization of plastic waste, as they occur e.g. B. in DE-A 43 11 034 or the German patent application P 43 24 112.3 are described. Serve as the starting product in this process plastic waste, usually as a mixture of polymers such as polyolefins, e.g. B. polyethylene and poly propylene, polystyrene, polyvinyl chloride, blends like ABS, but also used by polyurethanes, polyesters and polyamides will. This waste is crushed and broken up if necessary melted. In a reactor, the melt, e.g. B. at 400 to 550 ° C, converted into products, which are then usually distilled be separated. The resulting distillation residues can be returned to the reactor, previously solid substances and optionally acids are separated.

Particularly preferred for the preparation of the invention Hydrogenating starting materials becomes one procedure, accordingly from the depolymerization product in one directly to the reactor downstream first column at 200 to 280 ° C Top product is separated after partial condensation is fed to a second column at 70 to 150 ° C and therein in a gas mixture emerging at the top of the column and one at the bottom of the Column resulting condensate is separated. The gas thus obtained and condensate can then be hydrogenated according to the invention.

The hydrogenation is carried out in two stages. The temperature in the first stage is 160 to 250 ° C, that in the second stage 250 to 420 ° C, the temperatures of the individual stages before trains are different. The partial pressure of the ver Hydrogen used is 1 to 50 bar, the pressure range of 5 to 20 bar is preferred.

The hydrogenation is carried out on catalysts as are known to the person skilled in the art the hydrogenation of coals containing unsaturated compounds hydrogen flows are known per se (e.g. pyrolysis gasoline hydrogenation, Ullmann’s Encyclopedia of Industrial Chemistry, 5th edition, VCH, vol. A3, p. 489, and benzene printing refining,  Ullmann’s Encyclopedia of Technical Chemistry, 4th edition, VCH, Vol. 8, p. 389). There are in particular catalysts with the ka analytically active metals nickel, cobalt, chromium, molybdenum, wolf ram, palladium and platinum and mixtures thereof, which on supports such as aluminum oxide, silicon dioxide, titanium oxide and Zirconium oxide are applied. Those are particularly preferred commercial catalysts, the cobalt and molybdenum or Contain nickel and molybdenum as active catalysts, so-called called Co-Mo and Ni-Mo catalysts, such as those in DE-A 23 00 038, DE-A 29 03 193 and EP-A 8 424 are.

The catalysts in both hydrogenation stages are on as a fixed bed orderly. A vertical first hydrogenation is preferred flowed through the reactor from bottom to top, possibly in the reactor liquid or liquid appearing on the catalyst to drain at the bottom and remove in the bottom of the reactor can.

According to the gas to be hydrogenated on both hydrogenation split. A part is with the condensate to be hydrogenated hydrogenated in the first stage. The hydrogenation product thus obtained the remaining part of the gas is then added before this The mixture obtained is fed to the hydrogenation in the second stage becomes. This ensures that the heat of reaction released both levels are distributed. A regulation of the distribution of gas Quantities on the first and second stages are advantageously carried out in such a way that the temperature of the hydrogenation leaving the first stage product is measured. If this temperature rises, less will occur Gas metered into the first stage and vice versa. Through this procedure In addition, it can also be used with fluctuating concentrations Individual components in the mixture to be hydrogenated are relative Ensure constant reaction temperature on the catalyst.

The amount of gas added to the first stage is determined according to the amount of heat released during the hydrogenation of the gas, which depends on its composition, as well as on the reaction temperature in the first reactor. It can easily be carried out by a specialist appropriate preliminary tests can be determined.

The process according to the invention is preferred in cycle gas driving operated wisely, d. H. there will be gas in the hydrogenation stages in the circuit driven, which only the freshly supplied gas and Kon corresponding amount of hydrogenation product is removed. The Product obtained after the second stage can become known in itself ter way, for example, worked up by distillation. Be  an expansion of the mixture in a column and subsequent fractionation.

The process products can be used in many ways, for example as raw gas for a steam cracker or as gasoline. It is further possible, the hydrogenation product in an aromatic plant for Ge processing of pure aromatics.

The following are two particularly preferred embodiments described the invention.

Referring to FIG. 1 Condensate 1 is fed with a part of the gas to be hydrogenated 2 and 3 of the cycle gas as well as hydrogen 4 an evaporator 5. If necessary, high-boiling fractions in the form of sludge are withdrawn from the bottom of the evaporator. The overhead vapors are heated against the outlet stream 6 from the second hydrogenation reactor and fed to the first hydrogenation reactor 7 , which is flowed through from bottom to top. If necessary, any liquid can be removed from the sump. The remaining part of the gas 2 to be hydrogenated is added to the hydrogenation product and fed to the second hydrogenation reactor 8 . Previously, the feed stream 9 is heated against the effluent from the second hydrogenation reactor 6, optionally, a further heater is interposed. The hydrogenated product is cooled and optionally washed, e.g. B. with water or caustic soda 10 for the separation of hydrogen chloride. In a Abschei the 11 , the hydrogenated condensate and optionally washing water is withdrawn via a line 12 . The gas phase is partly discharged via a line 13 in order to avoid the build-up of undesired components in the cycle gas. The remaining part is mixed with hydrogen 4 and returned to the process via a compressor 14 .

Fig. 2 shows the method described with an optimized heat system. Here, a pre-evaporator 15 is attached in front of the evaporator 5 . The pre-evaporation occurs in countercurrent to the reactor outlet stream 6 after preheating the pre-evaporator inlet stream. The stream fed directly to the evaporator 5 is also preheated against the outlet stream of the pre-evaporator 16 . These measures can achieve significant savings in the heating capacity of the evaporator.

According to the method according to the invention, gases and condensates, which essentially contain hydrocarbons from unsaturated exempted connections, so that in further processing the process products no undesirable polymerization products occur. The special distribution of the gas flow over both Hy  The three stages ensure an even temperature at the catalytic converter gate, which leads to longer catalyst life. By ver Avoid excessive temperature increases on the catalyst the process is operated adiabatically, d. H. there are no more Cost of corresponding components for heat dissipation from the reak gate. It was also found that the process contains chlorine Hydrocarbons dehalogenated, as they are mainly used substances from the depolymerization of plastic waste are. The hydrogen chloride formed can easily be in one Laundry are separated from the process product.

Claims (7)

1. A process for the catalytic hydrogenation of a gas and a condensate, each of which is essentially saturated and unsaturated and, in the case of the condensate, furthermore contains aromatic hydrocarbons, with hydrogen, characterized in that the condensate and part of the gas is catalytically hydrogenated in a first stage at 160 to 250 ° C., the remaining part of the gas is added to the hydrogenation product and the mixture thus obtained is catalytically hydrogenated in a second stage at 250 to 420 ° C. 2. The method according to claim 1, characterized in that one the first stage in a vertical reactor leads from the gas and condensate to be hydrogenated from below is flowed upwards. 3. The method according to claim 1 or 2, characterized in that you work in a cycle gas mode. 4. The method according to claims 1 to 3, characterized in net that one in the first stage, the second stage or in two stage catalysts used, the cobalt and molyb dan or nickel and molybdenum as catalytically active stocks parts included. 5. The method according to claims 1 to 4, characterized in net that one uses a gas and a condensate, which in the thermal depolymerization of plastic waste. 6. The method according to claims 1 to 5, characterized in net that you have a condensate with a bromine uptake of 20 to 60 g / 100 g according to DIN 51 774 used. 7. The method according to claims 1 to 6, characterized in net that you have a condensate with a styrene content of 1 to 4 wt .-% used.