IL26181A - Simultaneous preparation of saturated aliphatic hydrocarbons containing 1-4c atoms,and benzene with its homologues,from light virgin naphtha - Google Patents

Description

ninii ΙΠ3 TJinrn n PATENT ATTORNEYS · □ ' 0 ] Q 3 ' Ώ 11 ϋ DR. REINHOLD COHN |Π Τ)1Π1" Ί ' Π DR. MICHAEL COHN I Π 3 *J N 3 · D ' 1 Ί ISRAEL SHACHTER B.Sc. .0.-1 103 III 1 K Ί 01 ' ■lis l 24959 PATENTS AND DESIGNS ORDINANCE SPECIFICATION SIMULTANEOUS PREPARATION OP SATURATED ALIPHATIC HYDROCARBONS CONTAINING 1-40 ATOMS, AND BENZENE I (we) 3TAMIC ARBON N.V. , A DUTCH COMPANY OF VAN OER MAESj-?EN8T AAT 2, HEERLEN, THE NETHERLANDS. do hereby declare the nature of this invention and in what manner the same is to be performed, to particularly described- and ascertained in and' by th following statement : - This invention relates to hydrocarbon conversion processes, and particularly relates to the conversion of light naphthas' to - saturated aliphatic hydrocarbons and to aromatic hydrocarbons.

Hydrocarbons present in light naphtha(e.g. having a boiling range within the range from 40 to an upper boiling point of from 110 to 180 °C) , in particular C,. - C hydrocarbons, can, by thermal 9 cracking at temperatures of 700 - 900 °C, be largely converted into gaseous unsaturated ~ hydrocarbons and minor proportions of methane and hydrogen. Depending on the composition of the light naphtha feedstock and on the process conditions, 20 to 25 % by weight of the naphtha may be converted into ethylene, 35 to 55 % into methane, propylene, and unsaturated hydrocarbons, and 20 to 30 % into liquid hydrocarbons, the so-called "cracked naphtha" which in most instances has a higher aromatic content than the original naphtha .Cracked naphthas thereby obtained are useful as fuel for petrol engines, owing to their somewhat higher aromatic content. However, they are not very suitable as a starting material for the recovery of pure aromatics, because, although the aromatic content has been increased, it is still not sufficiently high for the economic production of aromatics . The presence of unsaturated hydrocarbons also causes difficulty in extraction. Of the gaseous products obtained in the cracking process, .ethylene, and butadiene are particularly valuable as starting materials for chemical synthesis . rocesses , The value of other gaseous products is generally limited to their use as fuels.

The cracked naphtha, after separation of gases therefrom, may be subjected to catalytic hydrogenation under pressure and mild conditions of temperature, so as to saturate the olefines present in the cracked naphtha and thus to enhance its value as a starting material for the extraction therefrom of aromatics. After such an extraction, the remaining liquid may be recycled to the thermal cracking stage. However, the aromatic content of the thus-treated liquid fraction is still not sufficiently high to provide a practical source of aromatics.

In another known process for the recovery of aromatics and olefines of low boiling point, the starting material is an oil distillate containing naphthenes, which, in the vapour phase, is subjected to a catalytic reforming treatment whereby naphthenes are converted to aromatics, the reaction mixture being subsequently subjected to a non-catalytic cracking process in order that the paraffins having a higher boiling point than the aromatics, and also any remaining naphthenes, may be converted to olefines and paraffines of relatively lower boiling point, the reaction mixture being thereafter separated by rectification into a tar fraction, an aromatic fraction, fractions consisting of paraffins and olefines, and gaseous hydrocarbons .

To recover pure aromatics, the aromatic fraction thus obtained is further subjected to an extraction treatment to effect a separation between the non-aromatics still present in the aromatic fraction and the aromatics which form a solution with the extraction agent.

The invention provides a process for obtaining from light naphtha a liquid fraction containing an enhanced proportion of aromatic compounds which can be recovered from the fraction by a simple separatory process which is cheaper than solvent extraction, for instance by rectification, and also for obtaining from the said light naphtha gaseous saturated hydrocarbons consisting substantially of C - C. hydrocarbons. Such saturated hydrocarbons are particularly 2 4 useful for the preparation of ethylene by thermal cracking (steam-cracking) yielding a product which contains only a small proportion^ of less valuable by-products, such as propylene. The process according to the invention has the added advantage of flexibility in that by controlling the reaction conditions, the proportions of aromatics and gaseous hydrocarbons in the product may be controlled.

The , invention consists of a process for the conversion of light naphtha, which comprises contacting the light naphtha with hydrogen in the presence of a catalyst suitable for the dehydrogenation of organic materials under conditions of temperature and. pressure and hydrogen light naphtha ratio so that at least half of the light naphtha is converted to saturated - hydrocarbons; and the remaining part into a liquid having at least 70 % by weight of aromatics, the remaining part consisting mainly of saturated C hydrocarbons. o In the hydrocarbon conversion reaction according to the invention two reactions take place, one of the reactions being the so-called catalytic hydroforming reaction leading to the formation of aromatics by dehydrogenation of C„ - C0 naphthenes, by isomerization of b o naphthenes with 5 carbon atoms in the ring to naphthenes with 6 carbon atoms in the ring followed by dehydrogenation, and also by cyclization with concomitant, dehydrogenation. of paraffins. The other reaction is a hydrocracking reaction of paraffins to lower boiling saturated -hydrocarbons .

The conditions under which the hydrogen treatment of the light naphtha takes place according to the invention are different from those under which hydroforming of naphtha is generally performed, leading to a different product .

The object of hydroforming naphtha is the formation of aromatics, in particular toluene and xylene, and the isomerization of liquid hydrocarbons in this naphtha; this well-known process gives rise to release of hydrogen and is so controlled that the amount of gaseous hydrocarbons formed will be as small as possible.

In the hydrogen treatment according to the invention likewise aromatics are formed, but, in contradistinction to hydroforming proper, the present process futher effects, by an increase of temperature, the conversion into gaseous saturated - hydrocarbons of a large proportion of the liquid non-aromatic hydrocarbons present in the starting material, attended with absorption of hydrogen.

The hydrogen treatment in general involves the overall consumption of a little hydrogen, e.g., 0 to 3 % by weight; calculated on the amount of naphtha treated, depending on the composition of the original naphtha and the ratio between the aromatics and the gaseous products formed. The greater the hydrogen consumption increases with the amount of gas formed. Further, if in the hydrogen treatment a higher temperature is used, the ratio of benzene to its homologues in the resulting liquid containing aromatics can be controlled to increase the proportion of benzene.

The desired conversions are effected with the use of normal dehydrogenation catalysts, for organic materials, e.g. metal catalysts such as Cr, Mo, Pt , Pd, or other noble metals, supported on a carrier.

Preference is given to the use of active platinum catalysts, with the platinum applied, in an amount of between 0.1 and 2 % by weight, to a carrier material consisting mainly of alumina or silica or a mixture o alumina and silica.

The conditions of temperature and pressure, and the hydrogen-to-naphtha ratio in the hydrogen treatment are so chosen that the aromatic content in the resulting liquid fraction will be at least 70 % by weight - this--fraction otherwise consisting mainly of saturated C, hydrocarbons · - and that, at the same time, at least half or more 5 of the original starting material is converted into gaseous saturated - hydrocarbons. The pressures needed to achieve this result may be, for instance, from 15 to 90 atm., preferably from 25 to 60 atm., the molar hydrogen-to-naphtha ratio being from 4 to 20, while the o final temperatures may be, for instance, within the range 550 to 600 i the light naphtha may be passed over the catalyst at a space velocity of 0.5-10 V/V/hr.

At the start of the hydrogen treatment the temperature may be lower than those indicated above as the formation of aromatics will o proceed at temperatures of, 450 to 525 C, but in order to effect the conversion of the greater part of the paraffins that cannot be converted to aromatics to gaseous saturated - hydrocarbons, it is then necessary to raise the temperature by 100 to 50 °C towards the end of the hydrogen treatment .

It will be advantageous, therefore, to carry out the hydrogen treatment in successive stages, each stage working with a different type of catalyst, if so desired, with a relatively low temperature and/or pressure being maintained in the first or first few stages, and a higher temperature and/or pressure in the final stages . The hydrogen treatment may be carried out with the catalyst mass present either as a fluid bed or as a fixed bed.

The; process according to the invention has the advantage of yielding a liquid with a high content of valuable aromatics and doing away with the necessity of recovering these aromatics by extraction, since a simpler, less costly separation, viz. by rectification, will suffice.

A separation process of this kind, in which use is made of distillation, may be carried out for example, in a first stage, yielding an overhead product consisting of benzene and non-aromatic hydrocarbons and a bottoms product capable of further separation into toluene as the overhead product and xylene contaminated with ethyl benzene as the bottoms product thereof.

The mixture obtained as the overhead in the first - ree"tifi-cation can be used for the recovery of pure benzene in a known way by subjecting it to azeotropic distillation with an auxiliary liquid for instance, acetone.

In order to produce ethylene, the saturated gaseous hydro-carbons obtained in the hydrogen treatment are subjected to thermal cracking. Prior to the cracking proper, methane and hydrogen, which do not contribute to the formation of ethylene, can be separated from these gases .

The starting material used in the hydrogen treatment according to- the invention need not be entirely freed of sulphur compounds. Thus, light naphtha having a sulphur content of, say, 1000 ppm may be processed as such.. Although slightly less aromatics will then be formed, the amount of gaseous hydrocarbons that can be cracked to produce ethylene will be higher.

The accompanying drawings and description illustrate the invention .

In the process schematically illustrated in Fig. I of the accompanying drawings naphtha is supplied through conduit I to reactor: R, in which the hydrogen treatment under pressure is effected .

The reaction mixture thus formed is passed through conduit 2, to a. separator S^, in which the gases are separated from the liquid fraction subsequent to cooling. The resulting liquid fraction is passed through conduit 3 into a stripper column D, the overhead fraction from which consists of still dissolved gases, and the liquid bottoms product is passed to a following rectifying column D2 through a conduit 4. In this column a separation is made of benzene and non-aromatic, mainly C_ , hydrocarbons - discharged through conduit 6 - 5 from the higher-boiling toluene and xylene, the toluene-xylene mixture being sent, through conduit 5 to a rectifying column D,_, the overheads from which, flowing through conduit 7, is toluene, and the bottom product, removed through conduit 8, is xylene associated with some ethyl-benzene.

The mixture of benzene and paraffins removed as the overheads from column D can be separated in known manner by distillation, with e.g. acetone as an auxiliary liquid, to recover pure benzene.

The gaseous mixture of hydrogen and saturated -hydrocarbons to.be discharged from separator is sent, through conduit 9 , to a separator S_, in which hydrogen is separated from the hydrocarbons by cooling. This hydrogen, rec0mpress~ed~~iTf necessary by compressor P, is recycled to reactor R.

The hydrocarbons to be discharged from separator S , and also the hydrocarbons recovered as the overheads in distillation column , are passed, through conduits 10 and 11, respectively, to cracker unit , where the ethane, propane, and butane are subjected to a non-catalytic thermal cracking process in which ethylene is': formed; the resulting reaction mixture' being sent to a gas separator SQ through conduit 12.

The ethylene produced is discharged through conduit 13, and unconverted ethane is sent to ethane cracker unit through conduit 14. The cracked gas mixture is sent to gas separator S through conduit 16. Through discharge conduits 15, of which only one is shown, residual gases consisting substantially of a mixture of methane, propylene, and propane are removed from the system. If desired, these residual gases can be returned to a thermal cracker, whether or not after they have been separated into their constituents.

The process illustrated in Fig. II of the accompanying drawings differs from that according to Fig. I in that the hydrogen treatment is carried out in several reactors arranged in series, (designated as R.. and R ) and in that the gaseous mixture of saturated • l - hydrocarbons discharged from separator S2 and stripper through conduit 11 is first sent to a gas separator S4 for the removal of methane, so that the load on the crackers will be lighter. The methane fraction, which always still contains components that can be cracked to produce ethylene, is then sent to gas separator S„ through conduit 18. The - fraction to be discharged from separator S4 is fed to cracker K.. through conduit 17.

Reactor R^ may contain a catalyst more specifically suited for the formation of aromatics, for instance Pt on ΑΙ^Ο^, whether or not promoted by a small amount of a halogen (CI, F) , whereas reactor R^ may contain a catalyst more specifically adapted to the destructive hydrogenation of the paraffins, for instance Pt on Al 0 , promoted by a small amount of alkali or earth alkali metals, or Pt on SiOQ. It is also possible to raise the temperature in reactor R^ slightly above the level maintained in the reactor R^ , for instance 50 °C above this level.

As the dehydrogenation reactions are endothermic, the reaction temperature or the temperature variation in reactor R^ can be controlled as desired by the supply of heat, whereas in reactor R^ cooling if necessary, may be applied, to remove heat generated in the hydrocracking of the paraffins and olefines.

The procedures represented in Figures I and II show only the principles of operation. In practice use is made in the hydrogen treatment of several reactors, these being taken out of operation periodically in order to regenerate the catalyst which will have become inactive in the reactor, e.g. owing to the deposition of carbon.

Furthermore, in general it will be found necessary to apply hydrogen make-up, as in the hydrogen treatment hydrogen is consumed in an amount of 0 to 3 % by weight of the feed.

The following examples of the invention are provided: Example I In apparatus as represented in Fig. I a naphtha with a boiling range of 40 - 160 °C was first led over a platinum-on-alumina catalyst (0.6 % by weight of Pt, 0.66 % by weight of Cl) at a space velocity of I V/V/hr, together with a fivefold amount of hydrogen (calculated as gram molecules) , at a temperature of 565 °C and at 30 atm.

For every 100 grammes of feed, this hydrogen treatment yielded 68 grammes of gaseous - hydrocarbons , viz . : 11 grammes of CH4 grammes of C2Hg 26 grammes of C HQ o II grammes of C4H10f which, together with steam, were fed to thermal cracker and were o there cracked at a temperature of 800 C. The cracked reaction mixture was passed to the gas separator S , from which 21.6 grammes of ethane were sent, through conduit 14, to ethane cracker K^, to be again sub- o jected to a cracking treatment, carried out at a temperature of 820 C.

Eventually, the gas separation yielded, per 100 grammes of the original naphtha, 29.2 grammes of ethylene, plus residual gases consisting of a hydrogen-methane fraction (23.8 grammes), a propylene-propane fraction (11.5 grammes), and a butylene-butane fraction (2.9 grammes) . The liquid fraction (34 grammes) obtained in the hydrogen treatment, which had an. aromatic content of 87.6 %, can be separated into: .3 grammes of benzene 13.1 grammes of toluene 11.4 grammes of xylene and ethyl-benzene 4.2 grammes of non-aromatics , mainly consisting of saturated Cc and + a small amount of CL hydrocarbons . o If the original naphtha* was. cracked direct , "i;e" without having undergone the hydrogen treatment, this would have resulted in the pro- duct ion of: 23.5 grammes of ethylene .5 grammes of methane + hydrogen 18.5 grammes of propylene + propane 11.5 grammes of hydrocarbons 26 grammes of cracked naphtha with an aromatic content of 43 %.

Example II In the same way as described in example I a naphtha with a o boiling range of 40 - 116 C was processed.

After the hydrogen treatment, every 100 grammes of the original naphtha yielded 64 grammes of gaseous - hydrocarbons, viz . : grammes of CH^ 19 grammes of CgHg 24 grammes of C HQ «3 O 11 grammes of c4H1(-), After the thermal cracking these yielded 27.9 grammes of ethylene, and residual gases consisting of a hydrogen-methane fraction (21.7 grammes), a propylene-propane fraction (10.9 grammes), and a butylene-butane fraction (2.9 grammes) .

The liquid fraction (37 grammes) obtained after the hydrogen treatment, which had an aromatic content of 89 %, could be separated int 9.3 grammes of benzene 16.9 grammes of toluene 6.7 grammes of xylene + ethyl-benzene 4.1 grammes of non-aromatics , mainly consisting of C_ , and for the remaining part of hydrocarbons .

If this naphtha had been subjected direct to thermal cracking, without having undergone the hydrogen treatment, the resulting products would have been: 24.5 grammes of ethylene 14 grammes of methane + hydrogen .5 grammes of propylene + propane 12 gi.ainmes of hydrocarbons 23 grammes of cracked naphtha with an aromatic content of 20 %.

Claims (1)

1. HAVINO NOW PA ICULARLY DESCRIBED ANO ASOERTAINEO THE NATURE ©r OUR 3AI0 INVENTION ANO IN WHAT MANNER THE SAME IS TO SS PERFORMEDf WE OBCLARE THA WHAT WE OUAIM IS| A process for the conversion of light naphtha, which comprises contacting the light naphtha with hydrogen in the presence of a catalyst suitable for the dehydrogenation of organic materials under conditions of temperature and pressure and hydrogen/light naphtha ratio so that at least half of the light naphtha is converted to saturated - hydrocarbons and the remaining part into a liquid having at least 70 % by weight of aromatics, the remaining part consisting mainly of saturated hydrocarbons. A process as claimed in claim 1, in which the said dehydrogenation catalyst comprises 0.1 to 2 % by weight of platinum, supported on an alumina, silica, or alumina-silica carrier. A process as claimed in claim 1, which is carried out in two stages, the first stage in the presence of a catalyst comprising platinum on alumina promoted by halogen: and in the second stage in the presence of a catalyst comprising platinum on alumina promoted by an alkali s or alkaline earth - metal, or in the presence of a catalyst comprising platinum on silica. A process as claimed in any of claims 1 to 3 in which the reaction pressure is from 15 to 90 atmospheres, the reaction temperature at least at the end of the process is between 550 and 600 °C, and the molar hydrogen/light naphtha ratio is maintained in the range 4:20, and the space velocity is from 0.5 to 10 V/V/hr . A process as claimed in any of claims 1 to 4 in which the liquid product containing aromatics is fractionated to recover the said aromatics therefrom. A process as claimed in any of claims 1 to 5, in which the saturated - hydrocarbon product is thermally cracked to ethylene . A process as claimed in claim 6 in which the saturated C, - C„ 1 4 hydrocarbon produced is treated to remove methane before the said thermal cracking. A process for the conversion of light naphtha as claimed in claim 1, substantially as hereinbefore described. Saturated - hydrocarbons and aromatic hydrocarbons obtained by a process claimed in any of the preceeding claims.