NO141829B - GENERATOR FOR STERILY, WASHABLE RADIOACTIVE MATERIAL - Google Patents

Abstract

Generator for sterile, washable radioactive material.

Description

Process for the catalytic, selective hydrogenation of light,

diene-containing hydrocarbon oils.

The invention relates to a method

for the catalytic, selective hydrogenation of light, diene-containing, cracked hydrocarbon oils.

By light, cracked hydrocarbon oils is meant hydrocarbon oils with a final boiling point (A.S.T.M.) of no more than 375° C.

It is already known that diene-containing,

Cracked gasolines and other light, cracked hydrocarbon oils can be selectively hydrogenated by passing these starting materials over a suitable hydrogenation catalyst in the presence of a gas containing at least 25 vol. hydrogen, for example an excess gas from catalytic reforming or essentially pure hydrogen.

Particularly suitable catalysts are those which contain nickel on a support (for example Al2Oa or a material containing Al20;1, BaSO,, BaCO.j etc.) These catalysts are preferably first sulfurized before use.

In these selective hydrogenation processes, the dienes (which can also be of the cyclopentadiene type) are hydrogenated to the corresponding alkenes (cycloalkenes). It is in many cases necessary to remove alka-dienes and similar compounds, as the presence of these highly reactive, unsaturated compounds makes the light, cracked hydrocarbon oils very unstable and therefore usually unsuitable for use as, for example, components in motor fuel. Such highly reactive compounds are found in relatively large quantities in gasolines and kerosenes obtained by very drastic, thermal cracking.

With regard to the operating conditions

it can be said that these selective hydrogenation processes use temperatures which are usually significantly lower than those used in complete hydrogenation and hydrodesulfonation and similar processes. In the selective hydrogenation, the temperature is not higher than 280° C and usually not higher than 200° C. Preferably the temperature is between 70 and 150° C.

In most cases the absolute pressure is no higher than 100 kg/cm2 and more usually within the range 10-80 kg/cm2. The space velocity of new starting material is usually within the range of 0.5-5 kg of liquid starting material per hour per liter of catalyst, preferably within the range of 1-3 kg/hour.liter, while the ratio between the amount of hydrogen-containing gas and the total amount of hydrocarbon oil is usually between 50 and 300 N l/kg.

If desired, part of the treated oil can be recycled and/or a suitable dilution oil (cooling oil) added. Mixing with the oil to be hydrogenated can be carried out before the first (or only) catalyst layer and/or at one or more

points between the catalyst layers (when

more than one such is used). The reaction conditions are preferably such that

oil to be refined remains at least partially liquid during the reaction, namely at least 50 wt. hence.

In practice, the gas used is a gas mixture containing hydrogen. It preferably contains more than 60% by volume. hydrogen. In general, hydrogen-containing gases are obtained, e.g. very well suited for catalytic conversion of petrol fractions.

However, it has now been found that in the case of selective hydrogenation of certain hydrogen-containing gases which may well be used in conventional, complete hydrogenation and hydrodesulphurisation, causes very undesirable phenomena which do not occur with other hydrogen-containing gases, namely an increase in the sulfur content of the oil and a very sudden reduction in the activity of the catalyst.

Closer examination has shown that these undesirable phenomena are caused by an excessively high concentration of hydrogen sulphide in the reaction mixture, and that they do not take place if precautions are taken to ensure that the amount of hydrogen sulphide in the reaction mixture is sufficiently small.

The invention thus relates to a method for catalytic, selective hydrogenation of light, diene-containing, cracked hydrocarbon oils at temperatures below 280° C and in the presence of a gas containing at least 25% by volume. hydrogen, e.g. an excess gas from catalytic conversion or mainly pure hydrogen, as the gas also contains hydrogen sulphide, and the main characteristic is that the total amount of hydrogen sulphide in the streams supplied to the reaction zones is no more than 0.1 kg per 1000 kg, preferably no more than 0.01 kg per 1000 kg of the total amount of hydrocarbons present in these streams.

If the components of the reaction mixture in the method according to the invention (new gas, recycled gas, new oil, any recycled oil, any dilution oil, etc.) cannot be selected so that the H2S content of the mixture remains sufficiently low, the H2S must be removed from the reaction mixture or from one or more of the streams of which it is composed.

This can be done in a manner known per se, for example by absorption of H2S in an aqueous solution of one or more phosphates, NaOH, KOH or an organic amine. This treatment is preferably applied to new, hydrogen-containing gas which is usually excess gas from catalytic conversion, as this stream is in most cases richest in hydrogen sulphide.

After the treatment with such absorption liquid, the stream from which the HoS has been completely or largely removed is preferably washed with water to thereby remove any small droplets of absorption liquid caught therein, during which treatment the said stream is saturated with

water. This is not a disadvantage, as one

have found that while H2S affects the process

even in relatively low concentration, water vapor has no such effect, and drying is therefore not necessary.

It is remarkable and surprising that the above-mentioned undesirable effects caused by H2S (and this is particularly the case when it comes to the reduction of activity) also take place in catalysts that are sulphided before use, for example in nickel catalysts on a support, which before its use as a catalyst for selective hydrogenation has been sulphided with H2S or sulfur-containing hydrocarbon oils.

The present method is particularly important in the selective hydrogenation of

petrols (and kerosenes) obtained as a by-product in the production of normally gaseous alkenes (especially ethylene and propene),

by drastic, thermal cracking of hydrocarbon oil. These cracking reactions are usually carried out in such a way that more than 50 wt. of the starting hydrocarbon oil

are converted into compounds with 4 or fewer carbon atoms in the molecule. The by-product formed by this cracking is a petrol which usually contains more than 30% by weight. and often more than 60 wt.

aromatic compounds and an essential

content of alkenes with a relatively high octane number. Such petrols consequently have a high octane rating. It is also an advantage that these petrols are in most cases practical

free of sulphur, i.e. they have a content of

sulfur compounds (calculated as elemental sulphur), which is significantly lower than 0.1% by weight.

However, these gasolines contain significant amounts of highly reactive compounds, such as dienes (including cyclopentadiene-type compounds), alkynes and styrene-type compounds, and it is often highly desirable to remove these highly reactive compounds by selective hydrogenation, considering that these petrols, due to the presence of said compounds, are extremely unstable and therefore usually unsuitable for use e.g. as a component in motor fuel.

It may be mentioned that the drastic thermal cracking for the production of lower alkenes is preferably carried out in pipe stills and in the presence of steam. This steam cracking is generally carried out at temperatures in the range of approx. 550° C to approx. 900° C, preferably between 750 and 800° C, and preferably at pressure below approx. 5 atm.abs. Usually 0.1-10 parts by weight of water vapor are used, preferably approx. 1 part by weight per weight fraction starting material. However, the above-mentioned very drastic cracking can also be carried out in other ways, for example by bringing the starting material for the cracking into contact with a very strongly heated, finely divided solid material, such as sand, or with a strongly heated, molten salt.

Low-boiling hydrocarbon oils which are relatively rich in aliphatic hydrocarbons are preferably used as starting material for said drastic thermal cracking. Consequently, untreated (straight-run) petrol fractions are very well suited.

Other hydrocarbon mixtures than the aforementioned gasolines and kerosenes can also be selectively hydrogenated according to the present method, for example diolefins containing higher-boiling olefin fractions (e.g. the higher-boiling olefin fractions (rich in <C>14-<C>18-olefins) obtained by cracking high-boiling hydrocarbon fractions).

Example.

The starting material was a gasoline obtained as a by-product in the production of ethene and propene by steam cracking of an untreated hydrocarbon oil with a final boiling point of 230° C. Said gasoline was free of naphthene hydrocarbons and contained 11 wt. dienes, 10 wt. alkenes, 36 wt. aromatic hydrocarbons and 43 wt. saturated hydrocarbons.

The petrol's other properties were: boiling range 41-180° C (A.S.T.M.), bromine number 55 g/100 g (Mcllhiney's method), maleic anhydride number 110 mg/g (Ellis and Jones' method), sulfur content 15 parts by weight. million. Due to the high diene content, the petrol was very unstable.

The petrol was passed over a catalyst together with pure hydrogen at a temperature of 100-110° C, a pressure of 40 atm.abs. and a space velocity of 1 kg/ hour.liter. The amount of hydrogen was 170 Nl/kg petrol. The catalyst was a nickel catalyst on aluminum oxide (10 per cent nickel) sulphided with a "straight-run" naphtha (0.05 per cent sulphur).

The product had a bromine number of 38 g/100 g and a maleic anhydride number of 1.0 mg/g, which shows that the hydrogenation was quite selective. The sulfur content was 15 parts per million. When the experiment was continued for 825 hours, the maleic acid an-1 hydride number and bromine number remained constant within the observational errors.

The hydrogen was then replaced with a mixture of hydrogen and hydrogen sulphide containing 0.7% by volume. HL, S. Other conditions were kept unchanged. The total content of H2S in the streams fed to the reactor was now 1.82 kg per 1000 kg of petrol. The bromine number and maleic anhydride number of the reaction product rose almost immediately to 51 g/100 g and 108 mg/g, showing that there was virtually no further hydrogenation. The reaction product liberated from H2S contained sulfur in an amount of 515 parts per million.

After returning to the original H.,S-free gas, the catalyst slowly became usable again. After 100 hours the bromine value of the product was 45 g/100 g and the maleic anhydride value 4.7 mg/g. This shows that the activity and selectivity again practically reached the original, satisfactory level. The sulfur content was again 15 parts per million.

In a subsequent experiment (with other conditions unchanged) hydrogen containing 0.002% by volume was used. H2S. The total content of H.2S in the reaction mixture was therefore 0.0052 kg/1000 kg of petrol. The maleic anhydride number was originally 1.0 mg/g and the bromine number 35 g/100 g; after 60 hours these had respectively risen to 1.6 mg/g and 40 g/100 g, which shows that there was a reduction in activity which was insignificant and usually still acceptable. The sulfur content in the product was originally 15 parts per million and after 60 hours 17 parts per million.

In another experiment (conditions otherwise unchanged) a gas containing 0.008% by volume was used. H2S, where the rest consisted of hydrogen. The total content of H2S in the reaction mixture was now 0.02 kg/1000 kg of petrol.

The maleic anhydride number was originally 1.0 mg/g and the bromine number 35 g/100 g;

after 60 hours, the maleic anhydride number had eventually risen to 3.0 mg/g, while the bromine number was 41 g/100 g, which shows that an H2S content of 0.02 kg/1000 kg of gasoline in practice usually results in an undesirable rapid reduction in catalyst activity. The sulfur content in the product was originally 15 parts per million and after 60 hours 21 parts per million.

Claims (7)

1. Process for the catalytic, selective hydrogenation of light, diene-containing, cracked hydrocarbon oils at temperature trips below 280° C and in the presence of a gas containing at least 25% by volume. hydrogen, e.g. an excess gas from catalytic conversion or mainly pure hydrogen, the gas also containing hydrogen sulphide, characterized in that the total amount of hydrogen sulphide in the streams supplied to the reaction zones is not more than 0.1 kg per 1000 kg, preferably no more than 0.01 kg per 1000 kg, of the total amount of hydrocarbons present in these streams. 2. Process according to claim 1, characterized in that the selective hydrogenation is carried out at temperatures of no more than 200° C, preferably within the range 70-150° C. 3. Process according to claim 1 or 2, characterized in that the selective hydrogenation is carried out at a pressure of not more than 100 kg/cm2 abs., preferably within the range 10-80 kg/cm2 abs. 4. Method according to any one of the preceding claims, characterized in that the ratio between the amount of hydrogen-containing gas and the total amount of hydrocarbon oil is in the range 50-300 N l/kg. 5. Method according to any one of the preceding claims, characterized in that the oil to be refined remains at least partially liquid during the reaction. 6. Method according to any one of the preceding claims, characterized in that the oil to be refined is a gasoline obtained as a by-product from the cracking of hydrocarbon oils under strict conditions for the production of normally gaseous alkenes. 7. Method according to claim 6, characterized in that the gasoline to be refined is obtained by cracking hydrocarbon oils in the presence of water vapor under strict conditions.