Chemistry of hydrocarbon compounds – Purification – separation – or recovery – By contact with solid sorbent
Patent
1998-10-21
2000-08-22
Griffin, Walter D.
Chemistry of hydrocarbon compounds
Purification, separation, or recovery
By contact with solid sorbent
585820, 585826, 208208R, 208254R, 208307, 208245, 208299, 208305, C07C 712, C10G 2500, C10G 2512
Patent
active
061075353
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a process for selectively removing nitrogenated and/or sulfurated contaminants from streams prevalently containing hydrocarbons with from 3 to 8 carbon atoms.
Many refinery and petroichemical processes are sensitive to the presence of nitrogenated and sulfurated compounds, as they more or less seriously deactivate the catalytic systems. The nitrogenated compounds are generally of a basic nature and consequently preferably, but not exclusively, interfere with acid-catalyst processes.
The removal of heteroatoms such as nitrogen and sulfur is generally an extremely significant aspect in the treatment of the raw material, with respect to both the quality of the cuts obtained and the formation of oxides, especially nitrogen, in combustion when this species enters the carburating pools.
The removal of nitrogen is generally carried out hydrogenating treatment under strict conditions of temperature and pressure, especially for cuts to be sent to hydrocracking and/or reforming. Sulfur is also preferably removed by hydrogenation.
It is not generally considered useful or conveient to remove contaminated products, especially nitrogenated, from light cuts. It has been observed however that C.sub.4 and C.sub.5 fractions coming from an FCC unit can contain nitriles, typically acetonitrile and propionitrile, extremely harmful for catalytic systems of both etherification reactions of iso-olefins with alcohols to give the respective ethers (MTBE, ETBE, TAME, TAEE) and skeleton isomerization reactions of olefins, from linear to branched. The role of the ethers is to bring oxygen and possibly improve the octanic properties as well as to reduce the olefin degree of the gasolines mainly with the aim of their reformulation (U.S. Clean Air Act Amendments, Publication 101-549-Nov. 15, 1990).
It is therefore of primary importance to be able to eliminate the nitriles, generally present at very low levels measurable in ppm, in the cuts which are used in the above technologies.
This removal can essentially take place in two ways: reactive group of the molecul;
The present art provides disclosures for both procedures.
For procedure (a) U.S. Pat. No. 5,414,183 claims the removal of nitriles, by hydrolysis, by putting the hydrocarbon stream in contact with an alkaline solution of NaOH at temperatures of about 100.degree. C. and a pressure of 14 atm in a static mixer. The total removal of the nitrogen is obtained only with relatively long contact times.
Method (a) is limited to those compounds having a functional CN group and it is therefore necessary to resort to other separation techniques when other contaminants are present, whether they be nitrogenated or not.
For procedure (b) the material must selectively remove the contaminants with respect to the stream in which they are inserted.
A first disclosure is provided in U.S. Pat. No. 4,831,206 where the impurities containing sulfur and nitrogen of a hydrocarbon stream are removed in two steps: in the first, there is the hydrogenation of these substances to hydrogen sulfide and ammonia, which are then adsorbed in the second step by putting the outgoing stream in contact with a material selected from zeolite 4A, 5A and clinoptilolite.
This adsorption can take place in both liquid phase and gas phase, with temperatures of between 150 and 290.degree. C. and adsorption periods of between 0.2 and 2 hours, the pressure being determined by the process downstream (isomerization, reforming, etc.) and in any case between 100 and 400 psig. The adsorption beds are regenerated before there is, by saturation of the bed itself, the release of hydrogen sulfide and ammonia. The same disclosure is provided in U.S. Pat. No. 4,831,207 which also claims zeolite 13X as adsorbing agent, whereas the configuration of the plant comprises two adsorption beds, for ammonia and hydrogen sulfide, one being for adsorption, the other for desorption. It has been observed that in both cases a hydrogenation step is necessary to reduce the nitrogenated and sulfurated compounds present to hyd
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Piccoli Valerio
Rossini Stefano
Griffin Walter D.
Nguyen Tam M.
Snamprogette S.p.A.
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