Patent Application
20100084315
The invention provides a process for treating a stream of elemental sulphur comprising an organic polysulphide and/or a thiol for smell improvement.
Elemental sulphur is a by-product of oil and gas refining processes. It is known that elemental sulphur obtained as a by-product of oil and gas refining may be used as raw material for sulphuric acid or as a binder in sulphur cement or in other sulphur cement products, for example sulphur cement-aggregate composites like sulphur mortar, sulphur concrete or sulphur-extended asphalt.
In refineries, sulphur compounds in liquid hydrocarbonaceous streams are typically converted by reaction with hydrogen into hydrogen sulphide. Thus, a gaseous stream comprising hydrogen sulphide and hydrogen is obtained. The hydrogen sulphide separated from this gaseous stream or hydrogen sulphide separated from natural gas is typically converted into elemental sulphur. A well-known example of such process is the so-called Claus process.
Conversion of hydrogen sulphide into elemental sulphur using the Claus process has certain disadvantages. The oxidation step in the Claus process is not selective for hydrogen sulphide, therefore separation of the hydrogen sulphide from the remainder of the gas stream is necessary. In view of thermodynamic limitations, no complete conversion of hydrogen sulphide in a single process stage can be obtained.
An alternative for the Claus process is selective oxidation of hydrogen sulphide comprised in a hydrocarbonaceous gas stream. Selective oxidation processes are disclosed in for example U.S. Pat. No. 4,886,649, U.S. Pat. No. 4,311,683, U.S. Pat. No. 6,207,127 and WO2005/030638. Compared to the Claus process, selective oxidation has several advantages. An advantage is that a high conversion of hydrogen sulphide can be obtained in a single process stage. Another advantage is that the oxidation is selective for hydrogen sulphide, thus avoiding the need for separation of hydrogen sulphide from the other gas components.
In WO2005/030638 is disclosed a process for the selective oxidation of hydrogen sulphide by contacting a hydrogen sulphide containing feed gas and molecular-oxygen containing gas with a particulate oxidation catalyst in the presence of liquid elemental sulphur. The liquid elemental sulphur acts as an inert liquid medium that absorbs the heat generated by the exothermic oxidation reaction and thus prevents sulphur polymerisation and clogging of the catalyst or reactor due to an increase in sulphur viscosity.
In the selective oxidation process as described in WO2005/030638, a stream of liquid elemental sulphur, optionally containing catalyst particles, might be discharged from the selective oxidation reactor. Such elemental sulphur could for example be used as a binder in sulphur cement or in other sulphur cement products. It has, however, been found that in case the hydrogen sulphide containing feed gas comprises thiols, the elemental sulphur that might be discharged from the selective oxidation reactor has an obnoxious smell. This smell is believed to be due to the presence of organic polysulphides that are formed from the thiols during the oxidation process. Also unconverted thiols remaining in the elemental sulphur might contribute to this smell. This smell disadvantageously limits the applicability of elemental sulphur obtainable from the selective oxidation process as described in WO2005/030638.
It has now been found that the obnoxious smell of elemental sulphur that contains organic polysulphides and/or thiols can be removed or diminished to an acceptable level by adding a small amount of an unsaturated compound to the elemental sulphur whilst the elemental sulphur is kept at a temperature in the range of from 120 to 160° C.
Accordingly, the invention provides a process for treating a stream of elemental sulphur comprising an organic polysulphide and/or a thiol for smell improvement, the process comprising the following steps:
(a) providing a molten stream of elemental sulphur comprising an organic polysulphide and/or a thiol at a temperature in the range of from 120 to 160° C.;
(b) admixing a liquid unsaturated compound with the molten elemental sulphur in an amount in the range of from 0.01 to 10.0 wt % based on the weight of sulphur to allow the organic polysulphide and/or thiol to react with the unsaturated compound.
In the process according to the invention, a liquid unsaturated compound is admixed with a molten stream of elemental sulphur that contains an organic polysulphide and/or a thiol at a temperature in the range of from 120 to 160° C. Thus, the organic polysulphide and/or thiol is allowed to react with the unsaturated compound in order to remove the sulphide smell caused by the presence of the organic polysulphide and/or thiol.
Reference herein to an organic polysulphide is to a compound comprising a chain of sulphur atoms with an organic radical covalently-bound with an carbon atom to each end of the chain. Such compounds have the general molecular formula X—Sn—X′, wherein n is an integer with a value of at least 2, and X and X′ are, independently, an organic radical that is bound with a carbon atom to the sulphur chain Sn. Typically, X and X′ each are an alkyl radical.
Reference herein to a thiol is to a compound of the general molecular formula R—SH, wherein R is an organic radial, typically an alkyl radical such as methyl, ethyl, propyl, isopropyl or butyl, that is bound with a carbon atom to the sulphur atom.
Reference herein to an unsaturated compound is to a compound having an aromatic or an olefinic group. The compound may have both an aromatic and an olefinic group, such as for example styrene. Cycloalkanes without a double bond, such as for examples cyclohexane, are not considered an unsaturated compounds in this respect.
Reference herein to a liquid unsaturated compound is to an unsaturated compound that is liquid at the conditions at which the compound is admixed with the molten elemental sulphur in step (b).
In step (a) of the process according to the invention, a molten stream of elemental sulphur comprising an organic polysulphide and/or a thiol is provided at a temperature in the range of from 120 to 160° C. In step (b) of the process according to the invention, a liquid unsaturated compound is admixed with the molten elemental sulphur in an amount in the range of from 0.01 to 10.0 wt % based on the weight of sulphur to allow the organic polysulphide and/or thiol to react with the unsaturated compound.
The stream of elemental sulphur is provided at a temperature in the range of from 120 to 160° C. in order to have a good miscibility with the liquid unsaturated compound. At temperatures below 120° C., elemental sulphur is in its solid state. At temperatures above 160° C. the sulphur viscosity increases due to polymerisation reactions, therewith importantly reducing the miscibility.
The admixing in step (b) may be carried out at any suitable pressure. The pressure applied will mainly depend on the boiling point of the compound that is admixed with the elemental sulphur. If that compound has a boiling point below the temperature of the molten elemental sulphur, an elevated pressure will be applied in step (b) in order to maintain the compound in the liquid phase.
The unsaturated compound may be any compound that reacts with polysulphides and thiols at a temperature in the range of from 120 to 160° C. Preferably, the unsaturated compound is a hydrocarbon, i.e. a compound consisting of carbon and hydrogen atoms without heteroatoms like sulphur, oxygen or nitrogen. Preferably, the unsaturated compound has at most 20 carbon atoms, more preferably in the range of from 4 to 14 carbon atoms.
Olefinic compounds that are known to be suitable as modifier or plasticizer for elemental sulphur appear to be particularly suitable compounds for the process according to the invention. Examples of such compounds are styrene, dicyclopentadiene, 5-ethylidene-2-norbordene, 5-vinyl-2-norbordene, 1-dodecene, 1-decene, dipentene, limonene. An advantage of using such compounds is that the resulting treated elemental sulphur may be used as binder in sulphur cement or a sulphur cement-aggregate composites. As a result less or no additional sulphur modifiers (also referred to a sulphur plasticizers) need to be added to the sulphur binder.
Also aromatic compounds without an olefinic functionality are suitable compounds for the process according to the invention. Examples of particularly suitable aromatic compounds are benzene, ethyl benzene, toluene and naphthalene.
The unsaturated compound may be admixed with the molten elemental sulphur in an amount in the range of from 0.01 to 10.0 wt %, preferably of from 0.05 to 5.0 wt %, more preferably in the range of from 0.1 to 4.0 wt % based on the weight of sulphur.
The time period during which the organic polsulphide(s) and/or the thiol(s) present in the molten elemental sulphur are allowed to react with the unsaturated compound in step (b) is preferably at least 5 minutes, more preferably 30 minutes. It will be appreciated that the admixing time in step (b) needs to be sufficient for the organic polsulphide(s) and/or the thiol(s) to be removed in order to achieve sufficient smell improvement. The optimum admixing time will depend on the concentration of the organic polysulphide and thiol in the elemental sulphur and the reactivity of the unsaturated compound used.
The elemental sulphur comprising an organic polysulphide and/or a thiol may be obtained from any source. A particularly suitable example of elemental sulphur that comprises organic polysulphides is the stream of elemental sulphur that may be withdrawn from a process of selective oxidation of hydrogen sulphide as is described in WO2005/030638. If the feed gas for the selective oxidation process comprises one or more thiols and the selective oxidation process is carried out in a liquid elemental sulphur phase, then the elemental sulphur that is discharged from the process comprises organic polysulphides, typically alkylpolysulphides, formed from the reaction of alkanethiols with elemental sulphur.
Therefore, the process according to the invention preferably further comprises the following steps:
(c) supplying a gaseous feed stream comprising hydrogen sulphide and a thiol and a molecular-oxygen containing gas to a reaction zone comprising liquid elemental sulphur and particulate oxidation catalyst at a temperature in the range of from 120 to 160° C. to selectively oxidise hydrogen sulphide to elemental sulphur; and
(d) discharging a stream of elemental sulphur comprising polysulphides from the reaction zone,
wherein the stream of elemental sulphur discharged from the reaction zone in step (c) is treated according to steps (a) and (b).
Process conditions and oxidation catalysts suitable for selective oxidation step (c) are described in more detail in WO2005/030638.
An alternative way to obtain a stream of elemental sulphur comprising an organic polysulphide and/or a thiol is by contacting a thiol-loaded purge gas from a thiol absorber with liquid elemental sulphur at a temperature in the range of from 120 to 160° C. Under these conditions, at least part of the thiols is converted into organic polysulphides. The conversion is preferably carried out in the presence of molecular oxygen and a particulate oxidation catalyst. The stream of elemental sulphur thus obtained comprises organic polysulphide and typically also unconverted thiol and may suitably be used in the process according to the invention.
The treated elemental sulphur obtained with steps (a) and (b) may be used for any known application of elemental sulphur. A particularly suitable application for the treated elemental sulphur is its use as binder in sulphur cement or a sulphur cement-aggregate composite. It is an advantage that the presence of carbon-containing compounds, such as the reaction product of the organic polysulphides or thiols with the unsaturated compound, is allowed in this application.
Sulphur used as binder may be modified or plasticised in order to prevent allotropic transformation of the solid sulphur. Modified sulphur is typically prepared by reacting a portion of the sulphur with a sulphur modifier, also referred to as sulphur plasticiser. Modifiers are typically added in an amount in the range of from 0.05 to 25 wt % based on the weight of sulphur, usually in the range of from 0.1 to 10 wt %. A well-known category of sulphur modifiers, are olefinic compounds that co-polymerise with sulphur. Known examples of such olefinic sulphur modifiers are dicyclopentadiene, limonene, styrene.
Sulphur cement is known in the art and at least comprises sulphur, usually in an amount of at least 50 wt %, and a filler. Usual sulphur cement fillers are particulate inorganic materials with an average particle size in the range of from 0.1 μm to 0.1 mm. Examples of such sulphur cement fillers are fly ash, limestone, quartz, iron oxide, alumina, titania, graphite, gypsum, talc, mica or combinations thereof. The filler content of sulphur cement may vary widely, but is typically in the range of from 5 to 50 wt %, based on the total weight of the cement.
A sulphur cement-aggregate composite is a composite comprising both sulphur cement and aggregate. Examples of sulphur cement-aggregate composites are sulphur mortar, sulphur concrete and sulphur-extended asphalt. Mortar comprises fine aggregate, typically with particles having an average diameter between 0.1 and 5 mm, for example sand. Concrete comprises coarse aggregate, typically with particles having an average diameter between 5 and 40 mm, for example gravel or rock. Sulphur-extended asphalt is asphalt, i.e. aggregate with a binder containing filler and a residual hydrocarbon fraction, wherein part of the binder has been replaced by sulphur.
Accordingly, the process according to the invention preferably further comprises the following steps:
(e) admixing the elemental sulphur treated according to steps (a) and (b) with at least any one of a sulphur cement filler, a sulphur modifier, or aggregate at a temperature at which sulphur is molten; and
(f) solidifying the mixture obtained by cooling the mixture to a temperature below the melting temperature of sulphur to obtain modified sulphur, sulphur cement or a sulphur cement-aggregate composite.
If only a sulphur modifier is admixed with the treated sulphur in step (e), modified sulphur is obtained. If a sulphur cement filler and, optionally, a sulphur modifier is admixed, sulphur cement is obtained. If both a sulphur cement filler and aggregate are admixed, optionally together with a sulphur modifier, sulphur mortar or sulphur concrete are obtained. Preferably, the heat-treated elemental sulphur is admixed in step (e) with at least a sulphur cement filler and sulphur cement or a sulphur cement-aggregate composite is obtained in step (f).
In a preferred embodiment of the process according to the invention, the stream of elemental sulphur that is treated in steps (a) and (b) is a stream of elemental sulphur that is discharged from a reaction zone for selective oxidation step (c) and the treated elemental sulphur obtained after steps (a) and (b) is converted into modified sulphur, sulphur cement or a sulphur cement-aggregate composite according to steps (e) and (f). In a particularly preferred embodiment, the stream of elemental sulphur that is discharged from the reaction zone for selective oxidation step (c) comprises at least part of the particulate oxidation catalyst. The catalyst-comprising elemental sulphur is then treated in steps (a) and (b). Thus, a treated catalyst-comprising elemental sulphur is obtained that is converted into sulphur cement or a sulphur cement-aggregate composite according to steps (e) and (f). An advantage of this embodiment is that there is no need to separate elemental sulphur from the catalyst particles after selective oxidation step (c). As a consequence, very small catalyst particles may be used in selective oxidation step (c).
The invention is further illustrated by means of the following non-limiting examples. Throughout the examples, flow rates of gaseous streams are expressed in Nl/hr, which stands for normal litres per hour. Normal litres are litres at conditions of standard temperature and pressure, i.e. 0° C. and 1 bar (absolute).
Elemental sulphur comprising organic polysulphides was obtained as follows:
A 500 mL autoclave was loaded with 300 grams of elemental sulphur and 20 grams of small particles (average particle diameter is 10 μm) of iron oxide catalyst.
The iron oxide catalyst was prepared as follows. Silica extrudates having a surface area of 358 m2/g as measured by nitrogen adsorption (according to the BET method) and a pore volume of 1.34 ml/g as measured by mercury intrusion were provided with hydrated iron oxide. 100 grams of the silica extrudates were impregnated with 134 ml of a solution prepared from 28.6 grams of ammonium iron citrate (containing 17.5 wt % iron) and de-ionized water. The impregnated material was rotated for 90 minutes to allow equilibration. The material was subsequently dried at 60° C. for 2 hours, followed by drying at 120° C. for 2 hours and calcinations in air at 500° C. for 1 hour. The initial colour of the catalyst was black, but turned into rusty brown due to hydration of iron oxide. The resulting catalyst had a surface area of 328 m2/g, a pore volume of 1.1 ml/g and an iron content of 4.7 wt % based on the total catalyst weight.
The autoclave was then pressurised with nitrogen to a pressure of 40 bar (absolute) and the temperature was raised to 140° C. A stream of nitrogen containing 650 ppmV of methanethiol was bubbled through the autoclave at a flow rate of 33 Nl/kg sulphur/hr during 150 hours. Then, a stream of pentane comprising 1.0 wt % butanethiol was supplied at a feed rate of 1.5 ml/hr whilst nitrogen bubbled through the autoclave at a flow rate of 39 Nl/kg sulphur/hr during 100 hours. The autoclave was then depressurised and the catalyst particles separated from the elemental sulphur by filtration.
Gas chromatography analysis of the gaseous effluent and Pyrolysis Combustion Mass spectrometric Elemental analysis (PCME analysis) of the elemental sulphur showed that 98 wt % of the butanethiol and 70 wt % of the methanethiol were converted into organic polysulphides. The organic alkylpolysulphide content of the elemental sulphur was calculated to be 0.1 wt %. The elemental sulphur had a very strong sulphide smell.
Thirty grams of the polysulphide-comprising elemental sulphur prepared as described above was loaded in an autoclave. The autoclave was pressurised to 5 bar (absolute) and heated to 135° C. A quantity of 100 μL styrene was added to the sulphur under continuous stirring. The autoclave was kept at this temperature and pressure for 1.5 hours under continuous stirring. The autoclave was then cooled and de-pressurised and the smell of a sample of the elemental sulphur was assessed. Then, the autoclave was closed again, pressurised to 5 bar (absolute) and heated to 135° C. and a further 100 μL of styrene was added and the conditions maintained for another 1.5 hours. The autoclave was then cooled and de-pressurised and the smell of a sample of the elemental sulphur was assessed. This was repeated until a total amount of 1000 μL of styrene was added.
Ten grams of polysulphide-comprising elemental sulphur prepared as described in EXAMPLE 1 was loaded in an autoclave. The autoclave was pressurised to 5 bar (absolute) and heated to 135° C. A quantity of 300 μL of a 50/50 mixture of 1-decene and 1-dodecene was added to the sulphur under continuous stirring. The autoclave was kept at this temperature and pressure for 1.5 hours under continuous stirring. The autoclave was then cooled and de-pressurised and the smell of a sample of the elemental sulphur was assessed.
Elemental sulphur comprising organic polysulphides was obtained as follows:
In a slurry bubble column were loaded 25 grams of elemental sulphur and 2.20 grams of small particles (average particle diameter is 10 μm) of iron oxide catalyst. The catalyst particles were prepared as described in EXAMPLE 1. The column was heated to 130° C. and pressurised to 20 bar (absolute). Nitrogen was bubbled through the column at a flow rate of 15.6 Nl/hr and 1 wt % butanethiol in pentane was added at a flow rate of 0.025 ml/min for 100 hours. After 100 hours, a small quantity of oxygen (4 vol % oxygen in helium) was supplied to the column in order to remove the hydrogen sulphide that was formed in the conversion of butanethiol (by selectively oxidising the hydrogen sulphide into elemental sulphur). Then, the column was cooled to room temperature, depressurised to 1 bar (absolute) and the catalyst and the treated sulphur were unloaded. The catalyst particles were separated from the elemental sulphur by filtration. The butanethiol content of the elemental sulphur was determined by Pyrolysis Combustion Mass spectrometric Elemental analysis (PCME analysis). This analysis showed that 99 wt % of the butanethiol supplied to the reactor was converted into organic polysulphides. The alkylpolysulphide content of the elemental sulphur was calculated to be 0.4 wt %. The elemental sulphur had a pronounced sulphide smell.
Fifteen grams of polysulphide-comprising elemental sulphur prepared as described above was loaded in an autoclave. The autoclave was pressurised to 5 bar (absolute) and heated to 135° C. A quantity of 120 μL ethyl benzene was added to the sulphur under continuous stirring. The autoclave was kept at this temperature and pressure for 1.5 hours under continuous stirring. The autoclave was then cooled and de-pressurised and the smell of a sample of the elemental sulphur was assessed.
Fifteen grams of polysulphide-comprising elemental sulphur prepared as described above was loaded in an autoclave. The autoclave was pressurised to 5 bar (absolute) and heated to 135° C. A quantity of 145 μL benzene was added to the sulphur under continuous stirring. The autoclave was kept at this temperature and pressure for 1.5 hours under continuous stirring. The autoclave was then cooled and de-pressurised and the smell of a sample of the elemental sulphur was assessed.
Fifteen grams of polysulphide-comprising elemental sulphur prepared as described above was loaded in an autoclave. The autoclave was pressurised to 5 bar (absolute) and heated to 135° C. A quantity of 160 μL dodecane was added to the sulphur under continuous stirring. The autoclave was kept at this temperature and pressure for 1.5 hours under continuous stirring. The autoclave was then cooled and de-pressurised and the smell of a sample of the elemental sulphur was assessed.
The smell of the treated elemental sulphur of EXAMPLES 1 to 5 is given in the Table.
ato 30 grams of polysulphide containing elemental sulphur
bto 10 grams of polysulphide containing elemental sulphur
cto 15 grams of polysulphide containing elemental sulphur
| Number | Date | Country | Kind |
|---|---|---|---|
| 06121785.7 | Oct 2006 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP07/60490 | 10/3/2007 | WO | 00 | 7/20/2009 |
