US20180258354A1

US20180258354A1 - Process to prepare paraffins and waxes

Info

Publication number: US20180258354A1
Application number: US15/756,247
Authority: US
Inventors: Gerrit Leendert Bezemer; Harold Boerrigter; Hai Ming TAN
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 2015-09-04
Filing date: 2016-09-01
Publication date: 2018-09-13
Also published as: ZA201801287B; CN107922852A; EP3344730A1; MY191351A; WO2017037177A1; CN107922852B

Abstract

A process for preparing paraffins and waxes includes providing a gas mixture comprising hydrogen and carbon monoxide to at least two conversion reactors for catalytically converting the gas mixture to obtain an initial Fischer-Tropsch product comprising paraffins having from 5 to 300 carbon atoms. The initial Fischer-Tropsch product streams from each of the reactors are combined before being subjected to a hydrogenation step. The hydrogenated product stream is separated into C5-C9, C10-C17 and C18-300 fractions. The C18-C300 fraction is separated to obtain one or more light waxes having a congealing point in the range of 30 to 75° C. and a heavy wax having a congealing point in the range of 75 to 120° C. The relative concentrations of the C5-C9 and the C10-C17 fractions, and the concentrations of the light and heavy waxes is changed by raising, lowering or maintaining the reaction temperature of at least one of the reactors.

Description

FIELD OF THE INVENTION

The present invention relates to a process to prepare paraffins and waxes from a gaseous feed stream comprising hydrogen and carbon monoxide, in at least two conversion reactors, being the first and second reactor, said reactors comprising catalysts.

BACKGROUND TO THE INVENTION

Paraffin wax and paraffins may be obtained by various processes. U.S. Pat. No. 2,692,835 and EP2655565 disclose a method for deriving paraffin wax and paraffins from crude oil. Also, paraffin wax and paraffins may be obtained using the so called Fischer-Tropsch process. An example of such process is disclosed in WO 2002/102941, EP 1 498 469, WO 2004/009739, WO 2013/064539 and in WO2014095814.
The Fischer-Tropsch process can be used for the conversion of synthesis gas into liquid and/or solid hydrocarbons. The synthesis gas may be obtained from hydrocarbonaceous feedstock in a process wherein the feedstock, e.g. natural gas, associated gas and/or coal-bed methane, heavy and/or residual oil fractions, coal, biomass, is converted in a first step into a mixture of hydrogen and carbon monoxide. This mixture is often referred to as synthesis gas or syngas. The synthesis gas is then fed into a reactor where it is converted in one or more steps over a suitable catalyst at elevated temperature and pressure into paraffinic compounds and water in the actual Fischer-Tropsch process. The obtained paraffinic compounds range from methane to high molecular weight modules. The obtained high molecular weight modules can comprise up to 200 carbon atoms, or, under particular circumstances, even more carbon atoms. Numerous types of reactor systems have been developed for carrying out the Fischer-Tropsch reaction. For example, Fischer-Tropsch reactor systems include fixed bed reactors, especially multi-tubular fixed bed reactors, fluidised bed reactors, such as entrained fluidised bed reactors and fixed fluidised bed reactors, and slurry bed reactors such as three-phase slurry bubble columns and ebulated bed reactors.
Catalysts used in the Fischer-Tropsch synthesis often comprise a carrier-based support material and one or more metals from Group 8-10 of the Periodic Table of Elements, especially from the cobalt or iron groups, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. Such catalysts are known in the art and have been described for example, in the specifications of WO 9700231A and U.S. Pat. No. 4,595,703.
One of the limitations of a Fischer-Tropsch process is that the activity of the catalyst will, due to a number of factors, decrease over time. The activity of the catalyst is decreased as compared to its initial catalytic activity. The initial activity of the catalyst can be its activity when fresh prepared. A catalyst that shows a decreased activity after use in a Fischer-Tropsch process is sometimes referred to as deactivated catalyst, even though it usually still shows activity. Sometimes such a catalyst is referred to as a deteriorated catalyst. Sometimes it is possible to regenerate the catalyst. This may be performed, for example, with one or more oxidation and/or reduction steps.
After regeneration, catalysts often show an activity that is lower than the activity of fresh prepared catalysts. Especially after multiple regenerations, it often proofs hard to regain an activity level comparable to the activity of fresh prepared catalysts. In order to be able to use a catalyst for a long time, it thus may be desirable to start a Fischer-Tropsch process with a fresh catalyst that has a relatively high activity.
The use of fresh or rejuvenated catalysts with a relatively high initial activity may have disadvantages. This may especially be the case when the amount of catalyst used in a reactor tube is fixed after loading of the catalyst in the reactor tube. One example of a reactor tube filled with a fixed amount of catalyst is a reactor tube filled with a packed bed of catalyst particles.
In a Fischer-Tropsch process with a catalyst with a relatively high initial activity, the activity of the catalyst is especially high at the start of the process. And, due to the high activity of the catalyst, a lot of water is produced in the Fischer-Tropsch hydrocarbon synthesis, resulting in a high relative humidity at the start of the Fischer-Tropsch process. During start-up of a Fischer-Tropsch reactor with a very active catalyst, the reaction temperature is typically kept at a relatively low value, e.g. below 200° C., in order to avoid a too high product yield and accompanying high temperature rise due to the exothermic reaction.
Due to the deactivation over time of a catalyst the temperature of the reactor has to be increased. The increase in temperature in the reactor results in an increase of the activity of the catalyst. By increasing the temperature the activity of an aged catalyst can be partially compensated.
Higher operating temperature for an “end of run” (EOR) catalyst results in a lower C5+ selectivity and a lighter wax. On the other side, the freshly started (Start of Run (SOR)) catalyst operation at high C5+ selectivity and a heavy wax. The relation between the operating temperatures of the catalyst and the selectivity is for example described on page 217 of “The Fischer-Tropsch and related synthesis”, H. H. Storch; N. Columbic; R. B. Anderson, John Wiley & Sons, Inc., New York, 1951. With the term “lighter wax” is meant that the heavy wax C40+ fraction has less tailing to very long chains. With the term “heavy wax” is meant a C40+ fraction with tailing to long chain number.
The hydrocarbon product stream obtained after the Fischer-Tropsch synthesis comprises mainly paraffinic compounds ranging from methane to high molecular weight molecules. Of this range of products the lighter part (i.e. methane (C1) to butane (C4)) are the least desired part of the product stream and the heavier part the more desired part of the product stream. For the production of paraffins and waxes, the most valued are the hydrocarbons ranging from C5 to C41+ (C indicating the carbon chain length). The lighter part of the product stream is normally recovered from the product stream as tail gas and can be reused upstream of the Fischer-Tropsch process (for example in the synthesis gas production).
There are several ways known to improve the yield of the paraffins and waxes comprising hydrocarbons ranging from C10 to C40 of the product stream obtained from a Fischer-Tropsch reaction. It is possible to change the catalyst formulation and select a catalyst with an improved yield to this desired part of the product stream. The relation between the catalyst formulation and the improved yield of this catalyst due to the formulation change is for examples described in Applied Catalysis A, 161 (1997), page 59-78. Once the catalyst has been selected the distribution is fixed for a large extent. Moreover, even with the same catalyst a relative small change is possible by varying the concentration of CO, H2 and inert in the gaseous stream towards the reactor. The impact of partial pressures and H₂/CO on activity and methane selectivity is for example described in Ind. Eng. Chem. Res. 2005, 44, page 5987-5994 and described on page 330, and on 370-372 of “The Fischer-Tropsch and related synthesis”, H. H. Storch; N. Columbic; R. B. Anderson, John Wiley & Sons, Inc., New York, 1951. Finally it is possible to change the operating temperature of the catalyst. The temperature impact on product distribution is for example described on page 217 of “The Fischer-Tropsch and related synthesis”, H. H. Storch; N. Columbic; R. B. Anderson, John Wiley & Sons, Inc., New York, 1951. There is a continuing desire in the art to improve the Fischer-Tropsch process, especially to tune the product distribution for a given catalyst during its use.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an improved Fischer-Tropsch process in which a cobalt catalyst is used that has a relatively high initial activity. Especially the way of improving the yield of the paraffins and the waxes is improved.
One of the above or other objects may be achieved according to the present invention by providing a process to prepare paraffins and waxes from a gas mixture comprising hydrogen and carbon monoxide in at least two conversion reactors, being a first and second reactor, said reactors comprising catalysts, which process at least comprises the following steps:
(a) providing the gas mixture to at least two conversion reactors;
(b) catalytically converting the gas mixture of step (a) at an initial reaction condition to obtain an initial Fischer-Tropsch product comprising paraffins having from 5 to 300 carbon atoms;
(c) combining the initial Fischer-Tropsch product streams from each of the at least two reactors of step (b) to obtain a combined Fischer-Tropsch product stream;
(d) subjecting the combined Fischer-Tropsch product stream of step (c) to a hydrogenation step to obtain a hydrogenated Fischer-Tropsch product stream;
(e) separating the hydrogenated Fischer-Tropsch product stream of step (d), thereby obtaining at least a fraction comprising 5 to 9 carbon atoms, a fraction comprising 10 to 17 carbon atoms and a fraction comprising 18 to 300 carbon atoms;
(f) separating the hydrogenated fraction comprising 18 to 300 carbon atoms of step (e), thereby obtaining one or more light waxes having a congealing point in the range of 30 to 75° C. and a heavy wax having a congealing point in the range of 75 to 120° C., wherein subsequently the relative concentration of the fraction comprising 5 to 9 carbon atoms, the fraction comprising 10 to 17 carbon atoms, the concentration of the light waxes and the concentration of the heavy waxes is changed by raising, lowering or maintaining the reaction temperature of at least one of the reactors.
It has now been found that in case hydrocarbon synthesis is performed in two or more reactors, a more flexible way of producing paraffins and waxes comprising hydrocarbon ranging from C5 to C41 can be managed.
This means that the method allows for tuning the reaction temperature in the different reactors such that the product stream obtained from a system comprising at least two reactors can be optimized towards the desired products.
Another advantage of the present invention is that in case hydrocarbon synthesis is performed in two or more reactors the deactivation over time of the Fischer-Tropsch catalyst can be managed by varying the reaction temperature of the at least two reactors.
A further advantage is that by controlling the process temperature in the different reactors the difference between the start of the run temperature of the catalyst and end of the run temperature of the catalyst is smaller compared to operating without the possibility of varying the reaction temperature of the different reactors. Over lifetime the difference in product distribution for each reactor is hence reduced.

DETAILED DESCRIPTION OF THE INVENTION

The process according to the invention is a process for preparing paraffins and waxes from a gas mixture comprising hydrogen and carbon monoxide in a Fischer-Tropsch reactor. The gas mixture comprising hydrogen and carbon monoxide is also referred to as syngas or synthesis gas. At least two conversion reactors are operated, being the first and second reactor, said reactor comprising a fixed bed of reduced Fischer-Tropsch catalyst. The catalyst comprises cobalt as catalytically active metal.
The catalyst may be a fresh catalyst or a rejuvenated catalyst. Reference herein to a fresh catalyst is to a freshly prepared catalyst that has not been subjected to a Fischer-Tropsch process. Reference herein to a rejuvenated catalyst is to a regenerated catalyst of which the initial activity has been at least partially restored, typically by means of several reduction and/or oxidation steps. The catalyst is preferably a fresh catalyst, since in particular fresh catalysts have a very high initial activity.
Fischer-Tropsch catalysts comprising cobalt as catalytically active metal are known in the art. Any suitable cobalt-comprising Fischer-Tropsch catalysts known in the art may be used. Typically such catalyst comprises cobalt on a carrier-based support material, optionally in combination with one or more metal oxides and/or metals as promoters selected from zirconium, titanium, chromium, vanadium and manganese, especially manganese. A most suitable catalyst comprises cobalt as the catalytically active metal and titania as carrier material.
The catalyst may further comprise one or more promoters. One or more metals or metal oxides may be present as promoters, more particularly one or more d-metals or d-metal oxides. Suitable metal oxide promoters may be selected from Groups 2-7 of the Periodic Table of Elements, or the actinides and lanthanides. In particular, oxides of magnesium, calcium, strontium, barium, scandium, yttrium, lanthanum, cerium, titanium, zirconium, hafnium, thorium, uranium, vanadium, chromium and manganese are suitable promoters. Suitable metal promoters may be selected from Groups 7-10 of the Periodic Table of Elements. Manganese, iron, rhenium and Group 8-10 noble metals are particularly suitable as promoters, and are preferably provided in the form of a salt or hydroxide.
The promoter, if present in the catalyst, is typically present in an amount of from 0.001 to 100 parts by weight per 100 parts by weight of carrier material, preferably 0.05 to 20, more preferably 0.1 to 15. It will however be appreciated that the optimum amount of promoter may vary for the respective elements which act as promoter.
A suitable catalyst comprises cobalt as the catalytically active metal and zirconium as a promoter. Another most suitable catalyst comprises cobalt as the catalytically active metal and manganese and/or vanadium as a promoter. If the catalyst comprises cobalt as the catalytically active metal and manganese and/or vanadium as promoter, the cobalt: (manganese+vanadium) atomic ratio is advantageously at least 12:1.
References to “Groups” and the Periodic Table as used herein relate to the new IUPAC version of the Periodic Table of Elements such as that described in the 87th Edition of the Handbook of Chemistry and Physics (CRC Press).
In operating at least two conversion reactors according to the present invention the catalyst is a reduced catalyst. In a reduced catalyst the cobalt is essentially in its metallic state. The at least two reactors may be provided with a fixed bed of reduced catalyst by reducing a fixed bed of catalyst precursor in-situ, i.e. in the same reactors wherein the Fischer-Tropsch hydrocarbon synthesis will take place, or by loading the reactors with a reduced catalyst that has for example be prepared by reducing a catalyst precursor in a separate vessel or reactor prior to loading the reduced catalyst in the reactors. Preferably the at least two reactors are provided with a fixed bed of reduced catalyst by reducing a fixed bed of catalyst precursor in-situ.
Reference herein to a catalyst precursor is to a precursor that can be converted into a catalytically active catalyst by subjecting the precursor to reduction, usually by subjecting the precursor to hydrogen or a hydrogen-containing gas using reducing conditions. Such reduction step is well-known in the art.
In step (a) of the process according to the present invention the gas mixture is provided to at least two conversion reactors.
In step (b) of the process according to the present invention the gas mixture of step (a) is catalytically converted at an initial reaction condition to obtain an initial Fischer-Tropsch product comprising paraffins having from 5 to 300 carbon atoms.
By the part “a Fischer-Tropsch product stream comprising paraffins having from 5 to 300 carbon atoms” is meant 5 to 300 carbon atoms per molecule.
The Fischer-Tropsch product stream as provided in step (b) is derived from a Fischer-Tropsch process. Fischer-Tropsch product stream is known in the art. By the term “Fischer-Tropsch product” is meant a synthesis product of a Fischer-Tropsch process. In a Fischer-Tropsch process the synthesis gas is converted to a synthesis product. The synthesis gas or syngas is obtained by conversion of a hydrocarbonaceous feedstock. Suitable feedstocks include natural gas, crude oil, heavy oil fractions, coal, biomass and lignite. A Fischer-Tropsch product derived from a hydrocarbonaceaous WO 2017/037177 PCT/EP2016/070617 feedstock which is normally in the gas phase may also be referred to a GTL (Gas-to-Liquids) product. The preparation of a Fischer-Tropsch product has been described in e.g. WO2003/070857.
Known to those skilled in the art is that the temperature and pressure at which the Fischer-Tropsch process is conducted influences the degree of conversion of synthesis gas into hydrocarbons and impacts the level of branching of the paraffins (thus amount of isoparaffins). Typically, the process for preparing a Fischer-Tropsch derived wax may be carried out at a pressure above 25 bara. Preferably, the Fischer-Tropsch process is carried out at a pressure above 35 bara, more preferably above 45 bara, and most preferably above 55 bara. A practical upper limit for the Fischer-Tropsch process is 200 bara, preferably the process is carried out at a pressure below 120 bara, more preferably below 100 bara.
The Fischer-Tropsch process is suitably a low temperature process carried out at a temperature between 170 and 290° C., preferably at a temperature between 180 and 270° C., more preferably between 200 and 250° C.
Preferably, the Fischer-Tropsch reactors are operated at an initial reaction condition of step (b) comprises an initial temperature in the range of from 200 to 250° C. and preferably from 205 to 230° C.
The conversion of carbon monoxide and hydrogen into hydrocarbons in the process according to the present invention may be carried out at any reaction pressure and gas hourly space velocity known to be suitable for Fischer-Tropsch hydrocarbon synthesis. Preferably, the reaction pressure is in the range of from 10 to 100 bar (absolute), more preferably of from 20 to 80 bar (absolute). The gas hourly space velocity is preferably in the range of from 500 to 25,000 h-1, more preferably of from 900 to 15,000 h-1, even more preferably of from 1,300 to 8,000 h-1. Preferably, the reaction pressure and the gas hourly space velocity are kept constant.
The amount of isoparaffins is suitably less than 20 wt % based on the total amount of paraffins having from 9 to 24 carbon atoms, preferably less than 10 wt %, more preferably less than 7 wt %, and most preferably less than 4 wt %.
Suitably, the Fischer-Tropsch derived paraffin wax according to the present invention comprises more than 75 wt % of n-paraffins, preferably more than 80 wt % of n-paraffins. Further, the paraffin wax may comprise isoparaffins, cyclo-alkanes and alkyl benzene.
The Fischer-Tropsch process for preparing the Fischer-Tropsch derived wax according the present invention may be a slurry Fischer-Tropsch process, an ebullated bed process or a fixed bed Fischer-Tropsch process, especially a multitubular fixed bed.
The product stream of the Fischer-Tropsch process is usually separated into a water stream, a gaseous stream comprising unconverted synthesis gas, carbon dioxide, inert gasses and C1 to C4, and a C5+ stream.
The full Fischer-Tropsch hydrocarbonaceous product suitably comprises a C1 to C300 fraction.
Lighter fractions of the Fischer-Tropsch product, which suitably comprises C1 to C4 fraction are separated from the Fischer-Tropsch product by distillation thereby obtaining a Fischer-Tropsch product stream, which suitably comprises C5 to C300 fraction.
The above weight ratio of compounds having at least 60 or more carbon atoms and compounds having at least 30 carbon atoms in the Fischer-Tropsch product is preferably at least 0.2, more preferably 0.3.
Suitably, in case of preparation of Fischer-Tropsch derived wax fraction having a congealing point of above 90° C. the above weight ratio is at least 0.5.
The weight ratio in the Fischer-Tropsch product may lead to Fischer-Tropsch derived paraffin waxes having a low oil content.
In step (c) of the present invention, the initial Fischer-Tropsch product streams from each of the at least two reactors of step b) are combined to obtain a combined Fischer-Tropsch product stream. Typically, the combined Fischer-Tropsch product stream comprises paraffins having from 5 to 300 carbon atoms.
In step (d) of the present invention, the combined Fischer-Tropsch product stream of step (c) is subjected to a hydrogenation step to obtain a hydrogenated Fischer-Tropsch product stream.
The hydrogenation is suitably carried out at a temperature between 200 and 275° C. and at a pressure between 20 and 70 bar. Typically, hydrogenation removes olefins and oxygenates from the fractions being hydrogenated. Oxygenates are preferably hydrocarbons containing one or more oxygen atoms per molecule. Typically, oxygenates are alcohols, aldehydes, ketones, esters, and carboxylic acids.
In step (e) of the present invention, the hydrogenated Fischer-Tropsch product stream of step (d) is separated to obtain at least a fraction comprising 5 to 9 carbon atoms, a fraction comprising 10 to 17 carbon atoms and a fraction comprising 18 to 300 carbon atoms.
Preferably, the amount of the fraction comprising 5 to 9 carbon atoms of step (e) is in the range of from 3-14 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction.
Also, the amount of the fraction comprising 10 to 17 carbon atoms of step (e) is in the range of from 7-21 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction.
The fraction preferably is separated into a fraction comprising 10 to 13 carbon atoms and a fraction comprising 14 to 17 carbon atoms. Further, the amount of the fraction comprising 10 to 13 carbon atoms is in the range of from 3-11 wt. % and the amount of the fraction comprising 14 to 17 carbon atoms is in the range of from 4-10 wt. % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.
In step (f) of the present invention, the hydrogenated fraction comprising 18 to 300 carbon atoms of step (e) is separated, thereby obtaining one or more light waxes having a congealing point in the range of 30 to 75° C. and a heavy wax having a congealing point in the range of 75 to 120° C., wherein subsequently the relative concentration of the fraction comprising 5 to 9 carbon atoms, the fraction comprising 10 to 17 carbon atoms, the concentration of the light waxes and the concentration of the heavy waxes is changed by raising, lowering or maintaining the reaction temperature of at least one of the reactors.
Preferably, the relative concentration of the fraction comprising 5 to 9 carbon atoms, the fraction comprising 10 to 17 carbon atoms, the concentration of the light waxes and the concentration of the heavy waxes is changed by the addition of a nitrogen containing compound to at least one of the reactors.
Preferably, the nitrogen-containing compound is added to the gas mixture in step (a) such that the nitrogen-containing compound is present in the gas mixture in a concentration in the range of 0.05 to 10 ppmV.
Examples of suitable nitrogen-containing compounds are ammonia, HCN, NO, amines, organic cyanides (nitriles), or heterocyclic compounds containing at least one nitrogen atom as ring member of a heterocyclic ring.
Suitably, the nitrogen-containing compound is a compound selected from the group consisting of ammonia, HCN, NO, an amine and combinations or two or more thereof.
Preferred amines include amines with one or more alkyl or alcohol groups having up to five carbon atoms. More preferably, the amine is a mono-amine. Examples of especially preferred amines include trimethylamine, dipropylamine, diethanolamine, and methyl-diethanolamine.
A particularly preferred nitrogen-containing compound is ammonia.
By light wax is meant wax having a congealing point in the range of from 30 to 75° C. By heavy wax is meant wax having a congealing point in the range of from 75 to 120° C.
The congealing points of the paraffin waxes according to the present invention are determined according to ASTM D938.
Suitably, the hydrogenated fraction comprising 18 to 300 carbon atoms of step (d) is separated by vacuum distillation at a pressure between 5 and 20 mbar, preferably between 5 and 15 mbar, and more preferably between 10 and 15 mbar. Also the distillation is preferably carried out at a temperature of from 300 to 350° C.
Preferably, the first light one or more waxes are obtained as distillate and/or side cuts in vacuum distillation, e.g. a first light wax fraction having a congealing point in the range of from 30 to 35° C., a second light wax fraction having a congealing point in the range of from 50 to 60° C., and a third light wax fraction having a congealing point in the range of from 65 to 75° C.
Suitably, the first light wax fraction is obtained as top cut of the vacuum distillation, the second light wax fraction is obtained as a side cut of the vacuum distillation and the third light wax fraction is obtained as heavier side cut of the vacuum distillation.
Preferably, one or more wax fractions having a congealing point in the range of 30 to 75° C. of step (f) are hydrofinished to obtain one or more hydrofinished wax fractions having a congealing point in the range of 30 to 75° C. Suitably, a wax fraction having a congealing point in the range 30 to 75° C. is hydrofinished thereby obtaining a hydrofinished wax fraction having a congealing point in the range of from 30 to 75° C.
Optionally, the first and second light wax fractions are hydrofinished thereby obtaining a first light hydrofinished wax fraction having a congealing point in the range of from 30 to 35° C., and a second light hydrofinished wax fraction having a congealing point in the range of from 50 to 60° C.
Preferably, the amount of the hydrofinished wax fraction having a congealing point 30° C. is in the range of from 3-7 wt. % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction. Also, the amount of hydrofinished wax fraction having a congealing point of 50° C. is preferably in the range of from 5-13 wt. % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.
Further, the amount of hydrofinished wax fraction having a congealing point of 70° C. is in the range of 7-16 wt. % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.
Preferably at least the third light wax i.e. the heaviest side cut of the vacuum distillation step (f) is hydrofinished thereby obtaining a hydrofinished wax fraction having a congealing point in the range of 65-75° C.
Typical hydrofinishing conditions for hydrofinishing of the above fractions are described in e.g. WO2007/082589.
Suitably, the second heavy wax of step (f) is separated, thereby obtaining at least one distillate wax fraction having a congealing point in the range of from 75 to 85° C. and at least one residual wax fraction having a congealing point in the range of from 95 to 120° C.
Preferably, the heavy second wax of step (f) is separated, thereby obtaining at least one distillate wax fraction having a congealing point in the range of from 70 to 90° C., preferably 70 to 85° C. and more preferably 75 to 85° C.
Suitably, the heavy distillate wax fraction having a congealing point in the range of from 75 to 85° C. is hydrofinished thereby obtaining a hydrofinished heavy distillate wax fraction having a congealing point in the range of from 75 to 85° C.
Further, the heavy distillate wax fraction having a congealing point in the range of from 70 to 90° C., preferably in the range of from 70 to 85° C. and more preferably in the range of from 75 to 85° C. are hydrofinished thereby obtaining hydrofinished heavy distillate wax fraction having a congealing point in the range of from 70 to 90° C., preferably in the range of from 70 to 85° C. and more preferably in the range of from 75 to 85° C.
Preferably, the heavy residual wax fraction having a congealing point in the range of from 95 to 120° C. is hydrofinished thereby obtaining a hydrofinished heavy residual wax fraction having a congealing point in the range of from 95 to 120° C.
Typical hydrofinishing conditions for hydrofinishing of the above fractions are described in e.g. WO2007/082589.
The heavy second wax of step (f) is preferably separated by short path distillation at a pressure between preferably between 0.05 and 0.5 mbar, and more preferably between 0.1 and 0.3 mbar. The distillation is preferably carried out at a temperature of from 200 to 350° C. and more preferably from 250 to 300° C.
Typically, the residual heavy wax having a congealing point in the range of from 95 to 120° C. is obtained as the residual fraction of the short path distillation. By the term residual is meant a fraction obtained with distillation which is a residual bottom fraction and is neither a top cut nor a side cut.
Short path distillation, also known as molecular distillation is known in the art and therefore not described here in detail. An example of a form of short path distillation is a Wiped Film Evaporator. Typical short path distillations are for example described in Chapter 9.1 in “Distillation, operations and applications”, Andrzej Górak and Hartmut Schoenmakers, Elsevier Inc, Oxford, 2014.
Thus, preferably the heavy residual wax fraction having a congealing point in the range of from 95 to 120° C. is hydrofinished thereby obtaining a hydrofinished heavy residual wax fraction having a congealing point in the range of from 95 to 120° C.
Preferably, one or more Fischer-Tropsch derived waxes having a congealing point in a range of from 30 to 120° C. are obtained. More preferably, a Fischer-Tropsch derived wax having a congealing point in the range of from 30 to 35° C. or in the range of from 50 to 60° C. or in the range of from 60 to 70° C., or in the range of from 75 to 85° C. or in the range of from 95 to 100° C., or in the range of from 100 to 106° C. or in the range of from 106 to 120° C. is obtained by the process according to the present invention.
Suitably, the amount of a hydrofinished wax fraction having a congealing point of 100 to 105° C. is in the range of from 15-70 wt. % based on the full Fischer-Tropsch hydrocarbonaceous product comprising a C1 to C300 fraction.
Determining the content of each final product fraction in the full Fischer-Tropsch hydrocarbonadeous product can be achieved by analyzing a sample of this stream with chromatographic methods such as high temperature gas chromatography or distillation. Conveniently the gas phase, liquid phase and solid phase are quantified, analyzed with the respective chromatographic methods and combined to result in the Fischer-Tropsch product distribution, taking into account that olefins and oxygenates are hydrogenated to the respective paraffin's.
Suitably, the reaction temperature is raised by:

- increasing the amount of synthesis gas provided to the reactor;
- raising the temperature of the cooling water provided to the reactor; and/or
- providing a nitrogen containing compound, to the reactor, preferably by adding the nitrogen containing compound to the gas mixture prior to step a) and b), preferably the nitrogen containing compound is selected from the group of ammonia, HCN, NO, an amine and combinations or two or more thereof.

Suitably, the reactor operating point is raised by:

By reactor operating point is meant the operation temperature at which the target conversion of CO and H2 is achieved.
In an embodiment of the invention the reaction temperature and/or the reactor operating point is raised by increasing the amount of synthesis gas provided to the reactor. Since the Fischer-Tropsch reaction is an exothermic one providing more hydrogen and carbon monoxide will result in more heat being generated. The increase in heat will result in a decrease of the selectivity towards the heavier hydrocarbon products.
In an embodiment of the invention the reaction temperature and/or reactor operating point is raised by raising the temperature of the cooling water provided to said reactor. The reaction temperature and/or reactor operating point may be raised by providing a nitrogen containing compound to the reactor. By supplying a nitrogen-containing compound to the freshly prepared or rejuvenated reduced catalyst, the catalyst activity is decreased and the temperature can be increased. Such conditions of higher temperature and decreased activity result in a lower relative humidity and less catalyst deactivation. Moreover, since the effect of such nitrogen-containing compound on catalyst activity seems to be reversible, the catalyst activity can be tuned by adjusting the concentration of the nitrogen-containing compound. In particular, the gradual decrease in catalyst activity can be compensated by gradually decreasing the concentration of the nitrogen-containing compound in the feed gas stream supplied to the catalyst. Thus, reaction temperature and reactor productivity (yield) can be controlled and kept constant during a relatively long period after start-up of the reactor, resulting in improved catalyst stability.
In an embodiment a nitrogen containing compound is provided to one or more of the reactors while the reaction temperature and/or reactor operating point is raised.
Also, the reaction temperature is lowered by:

- decreasing the amount of synthesis gas provided to the reactor;
- lowering the temperature of the cooling water provided to the reactor; and/or
- providing a nitrogen containing compound, to the reactor, preferably by adding the nitrogen containing compound to the gas mixture prior to step a) and b), preferably the nitrogen containing compound is selected from the group of ammonia, HCN, NO, an amine and combinations or two or more thereof.

Also, the reactor operating point is lowered by:

In an embodiment the reaction temperature and/or reactor operating point in one or more reactors is lowered by decreasing the amount of synthesis gas provided to the reactor. By decreasing the amount of syngas provided to the reactor fewer hydrocarbons are synthesized. Since the FT reaction is exothermic less energy will be released if fewer hydrocarbons are synthesized.
In an embodiment the reaction temperature and/or reactor operating point in one or more reactors is lowered by lowering the temperature of the cooling water provided to the reactor. Also, lowering the temperature by decreasing the temperature of the cooling medium results in an increase in selectivity towards the heavy fractions.
In an embodiment the reaction temperature and/or reactor operating point in one or more reactors is lowered by providing a nitrogen containing compound, to the reactor.
In an embodiment of the invention, the method comprises one of the following steps:

- providing a nitrogen containing compound, to the first reactor in case the first reactor comprises the least active catalyst;
- providing a nitrogen containing compound, to the second reactor in case the second reactor comprises the least active catalyst. This may be done in case the temperature in the reactor is raised, resulting in an increase in activity of the catalyst but a decrease in selectivity towards the heavier hydrocarbons.

In an embodiment of the invention, the method comprises one of the following steps:

- providing a nitrogen containing compound, to the first reactor in case the first reactor comprises the most active catalyst;
- providing a nitrogen containing compound, to the second reactor in case the second reactor comprises the most active catalyst.

- providing a nitrogen containing compound, to the first reactor in case the first reactor comprises the most active catalyst;
- providing a nitrogen containing compound, to the second reactor in case the second reactor comprises the least active catalyst. This may be done in case the temperature in the reactor is raised, resulting in an increase in activity of the catalyst but a decrease in selectivity towards the heavier hydrocarbons.

The nitrogen containing compound added to increase or to lower the reaction temperature and/or reaction operating point in one or more reactors is similar to the nitrogen containing compound as described above.
In a further aspect the present invention provides a Fischer-Tropsch derived paraffins and waxes obtainable by the process according to the present invention.
The invention is illustrated by the following non-limiting examples.

Examples

In the present examples two Fischer-Tropsch reactors are connected in series. A cobalt-based Fischer-Tropsch catalyst was loaded in two reactors and reduced. The upstream reactor (named R1) is fed syngas and the downstream reactor (named R2) receives the off gas of the upstream reactor.
The off gas comprises the unreacted hydrogen and carbon monoxide. In each example, one reactor is freshly started and the other with deteriorated activity. In the base case both reactors are operated at the same productivity, but at different operating temperature. The amount of gaseous, solvents, LDF, HDF, SX-30, SX-50, SX-70, SX-100/105 is indicated in table 1.
In table one the reaction conditions are provided in the first three rows. The addition of ammonia is indicated with Y (Yes) or N(No). The products gas, solvents, LDF, HDF, SX-30, SX-50, SX-70, SX-100/105 are indicated in weight % based on the Fischer-Tropsch product stream.
In the first example according to the invention the productivity of the first reactor is decreased by addition of ammonia, meanwhile increasing the temperature. Meanwhile the productivity of the second reactor is increased. The distribution of the products is indicated in the table. It can be seen that the total amount of solvents, LDF, HDF, SX-30. SX-50 and SX-70 is increased from 36 to 41%.
In the second example according to the invention the load through the first reactor is increased and the load through the second reactor is decreased, keeping the overall production constant. It can be seen that the amount of SX-30, SX-50, SX-70, SX-100/105 is increased from 54 to 60%.
In the third example the production through the first reactor is increased and a N compound is added. The production through the second reactor is decreased by adding a N compound in the feed. It can be seen that the amount of solvents, LDF and HDF is increased from 36 to 41%.

TABLE 1

Comp.
Example	Example 1	Example 2	Example 3

R1

R2

Total

R1

R2

Total

R1

R2

Total

R1

R2

Total

STY	115	115		110	120		135	95		135	95
Temperature(° C.)	187	233		206	235		193	225		213	233
Ammonia	N	N		Y	N		N	N		Y	Y
Gas (C1-C4)	4	18	11	7	19	13	4	14	8	9	18	13
Solvents (C5-C9)	4	12	8	6	12	9	4	9	6	7	11	9
LDF (C10-C13)	4	10	7	5	10	8	4	8	6	6	10	8
HDF (C14-C17)	4	9	6	5	9	7	4	8	6	6	9	7
SX-30 (C18-C20)	3	6	4	4	6	5	3	5	4	4	6	5
SX-50 (C21-C27)	6	11	8	8	11	9	6	10	8	9	11	9
SX-70 (C28-C40)	9	13	11	11	12	12	9	13	11	12	13	12
SX-100/105	68	23	45	55	21	37	65	33	52	48	23	38
(C41+)

Discussion

Table 1, Example 1 clearly shows an increase in gas, solvents, LDF, HDF, SX-30, SX-50, SX-70 but a decrease in SX-100/105. These observations indicate that upon addition of ammonia to the syngas stream results in a decrease in C41+ selectivity of the Fischer-Tropsch catalyst.
Example 2 clearly shows a decrease in gas, solvents, LDF, but an increase in SX-100/105. The amount of HDF, SX-30, SX-50, Sx-70 was unchanged. These observations indicate that increasing the temperature of both reactors results in an increase in C41+ selectivity of the Fischer-Tropsch catalyst.
Example 3 clearly shows in increase in gas, solvents, LDF, HDF, SX-30, SX-50, SX-70 but a decrease in SX-100/105.
These observations indicate that upon addition of ammonia to the syngas stream and increasing the temperature in one reactor while decreasing the temperature in the other reactor result in a decrease in C41+ selectivity of the Fischer-Tropsch catalyst.
Hence the examples clearly show that by taking into account the state of the catalysts present in each of the reactors in a system of Fischer-Tropsch reactors allows for good control of the content of the product stream. References to “Groups” and the Periodic Table as used herein relate to the new IUPAC version of the Periodic Table of Elements such as that described in the 87th Edition of the Handbook of Chemistry and Physics (CRC Press).
While the invention has been described in terms of what are presently considered to be the most practical and preferred embodiments, it is to be understood that the disclosure need not be limited to the disclosed embodiments. It is intended to cover various modifications, combinations and similar arrangements included within the spirit and scope of the claims, the scope of which should be accorded the broadest interpretation so as to encompass all such modifications and similar structures. The present disclosure includes any and all embodiments of the following claims.
It should also be understood that a variety of changes may be made without departing from the essence of the invention. Such changes are also implicitly included in the description. They still fall within the scope of this invention. It should be understood that this disclosure is intended to yield a patent covering numerous aspects of the invention both independently and as an overall system and in both method and apparatus modes.
Any patents, publications, or other references mentioned in this application for patent are hereby incorporated by reference. In addition, as to each term used, it should be understood that unless its utilization in this application is inconsistent with such interpretation, common dictionary definitions should be understood as incorporated for each term and all definitions, alternative terms, and synonyms such as contained in at least one of a standard technical dictionary recognized by artisans.

Claims

1. Process to prepare paraffins and waxes from a gas mixture comprising hydrogen and carbon monoxide in at least two conversion reactors, being a first and second reactor, said reactors comprising catalysts, which process at least comprises the following steps:

(a) providing the gas mixture to the at least two conversion reactors;

(b) catalytically converting the gas mixture of step (a) at an initial reaction condition to obtain an initial Fischer-Tropsch product comprising paraffins having from 5 to 300 carbon atoms;

(c) combining the initial Fischer-Tropsch product streams from each of the at least two reactors of step (b) to obtain a combined Fischer-Tropsch product stream;

(d) subjecting the combined Fischer-Tropsch product stream of step (c) to a hydrogenation step to obtain a hydrogenated Fischer-Tropsch product stream;

(e) separating the hydrogenated Fischer-Tropsch product stream of step (d), thereby obtaining at least a fraction comprising 5 to 9 carbon atoms, a fraction comprising 10 to 17 carbon atoms and a fraction comprising 18 to 300 carbon atoms;

(f) separating the hydrogenated fraction comprising 18 to 300 carbon atoms of step (e), thereby obtaining one or more light waxes having a congealing point in the range of 30 to 75° C. and a heavy wax having a congealing point in the range of 75 to 120° C., wherein subsequently the relative concentration of the fraction comprising 5 to 9 carbon atoms, the fraction comprising 10 to 17 carbon atoms, the concentration of the light waxes and the concentration of the heavy waxes is changed by raising, lowering or maintaining the reaction temperature of at least one of the reactors.

2. A process according to claim 1, wherein the Fischer-Tropsch reactors are operated at an initial reaction condition of step (b) comprising a temperature in the range of 200 to 250° C. and preferably from 205 to 230° C.

3. Process according to claim 1, wherein the amount of the fraction comprising 5 to 9 carbon atoms of step (e) is in the range of from 3-14 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction.

4. Process according to claim 1, wherein the amount of the fraction comprising 10 to 17 carbon atoms of step (e) is in the range of from 7-21 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction.

5. Process according to claim 1, wherein one or more wax fractions having a congealing point in the range of 30 to 75° C. of step (f) are hydrofinished to obtain one or more hydrofinished wax fractions having a congealing point in the range of 30 to 75° C.

6. Process according to claim 1, wherein the amount of hydrofinished wax fraction having a congealing point of 30° C. is in the range of from 3-7 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction.

7. Process according to claim 1, wherein the amount of hydrofinished wax fraction having a congealing point of 50° C. is in the range of from 5-13 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction.

8. Process according to claim 1, wherein the amount of hydrofinished wax fraction having a congealing point of 70° C. is in the range of from 7-16 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction-.

9. Process according to claim 1, the heavy wax of step (f) is separated, thereby obtaining at least one distillate wax fraction having a congealing point in the range of between 75 to 85° C. and at least one residual wax fraction having a congealing point in the range of from 95 to 120° C.

10. Process according to claim 9, the heavy distillate wax fraction having a congealing point in the range of between 75 to 85° C. is hydrofinished to obtain a hydrofinished heavy distillate wax fraction having a congealing point in the range of between 75 and 85° C.

11. Process according to claim 9, wherein the heavy residual wax fraction having a congealing point in the range of 95 to 120° C. is hydrofinished to obtain a hydrofinished heavy residual wax fraction having a congealing point in the range of 95 to 120° C.

12. Process according to claim 1, wherein the amount of hydrofinished wax fraction having a congealing point of 100 to 105° C. is in the range of from 15-70 wt. % based on the full Fischer-Tropsch hydrocarbonaceous comprising a C1 to C300 fraction.

13. A process according to claim 1, wherein the reactor operating point is raised by:

increasing the amount of synthesis gas provided to the reactor;

raising the temperature of the cooling water provided to the reactor; and/or

providing a nitrogen containing compound, to the reactor, preferably by adding the nitrogen containing compound to the gas mixture prior to step a) and b), preferably the nitrogen containing compound is selected from the group of ammonia, HCN, NO, an amine and combinations or two or more thereof.

14. A process according to claim 1, wherein the reactor operating point is lowered by:

decreasing the amount of synthesis gas provided to the reactor;

lowering the temperature of the cooling water provided to the reactor; and/or