WO2018083149A1

WO2018083149A1 - Process to prepare normal paraffins

Info

Publication number: WO2018083149A1
Application number: PCT/EP2017/078009
Authority: WO
Inventors: Gerrit Leendert BEZEMER; Duurt Renkema
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Oil Company
Priority date: 2016-11-07
Filing date: 2017-11-02
Publication date: 2018-05-11
Also published as: US20190276754A1; EP3535353A1; ZA201902208B

Abstract

Process to prepare n-paraffins comprising the steps of: separating a Fischer-Tropsch product stream in a first gaseous hydrocarbon stream and a first liquid hydrocarbon stream; cooling and separating the first gaseous hydrocarbon stream to obtain second and third liquid hydrocarbon streams; separating second and third liquid hydrocarbon streams, thereby obtaining a n-paraffin fraction comprising 5-9 carbon atoms and a n-paraffin fraction comprising 10-35 carbon atoms; separating the n-paraffin fraction comprising 10-35 carbon atoms, thereby obtaining a n-paraffin fraction comprising 10-18 carbon atoms and a n-paraffin fraction comprising 19-35 carbon atoms; hydrogenation of the n-paraffin fraction comprising 10-18 carbon atoms and separation of the hydrogenated n-paraffin fraction comprising 10-18 carbon atoms, thereby obtaining a n-paraffin comprising 10-13 carbon atoms and a n-paraffin comprising 14-18 carbon atoms.

Description

PROCESS TO PREPARE NORMAL PARAFFINS

Field of the invention

The present invention relates to a process to prepare normal paraffins.

Background to the invention

Normal paraffins may be obtained by various

processes. EP2655565 disclose a method for deriving paraffins from crude oil. Also, paraffins may be obtained using the so called Fischer-Tropsch process. An example of such process is disclosed in WO2014095814 and

WO2016107864.

WO2016107864 discloses a process to prepare paraffins and waxes. In WO2016107864 the whole Fischer-Tropsch product stream comprising paraffins having from 10 to 300 carbon atoms is used to prepare a normal paraffin fraction comprising 10 to 17 carbon atoms. In this way a vacuum feed splitter is necessary to select the molecules to enter the hydrogenation unit. However, the relative costs of such a vacuum distillation becomes rather high when the plant size is reduced for smaller and simpler process line-ups to prepare normal paraffins.

It is an object of the invention to solve or minimize at least one of the above problems. It is a further object to provide a more efficient and simple method to prepare normal paraffins on a smaller scale.

Another object is to provide a cost-effective process, which requires less energy than the process as described in the prior art .

One of the above or other objects may be achieved according to the present invention by providing a process to prepare normal paraffins, the process comprises the steps of : (a) providing a Fischer-Tropsch product stream;

(b) separating the Fischer-Tropsch product stream of step (a) , thereby obtaining a first gaseous hydrocarbon stream and a first liquid hydrocarbon stream;

(c) cooling and separating of the gaseous hydrocarbon stream of step (b) in one or more steps to obtain a second liquid hydrocarbon stream and a third liquid hydrocarbon stream;

(d) separating the second and the third liquid

hydrocarbon streams of step (c) by atmospheric distillation, thereby obtaining a normal paraffin fraction comprising 5 to 9 carbon atoms and a normal paraffin fraction comprising 10 to 35 carbon atoms;

(e) separating the normal paraffin fraction

comprising 10 to 35 carbon atoms of step (d) by atmospheric distillation, thereby obtaining a normal paraffin fraction comprising 10 to 18 carbon atoms and a normal paraffin fraction comprising 19 to 35 carbon atoms;

(f) hydrogenation of the normal paraffin fraction comprising 10 to 18 carbon atoms of step (e) to obtain a hydrogenated normal paraffin fraction comprising 10 to 18 carbon atoms;

(g) separation of the hydrogenated normal paraffin fraction comprising 10 to 18 carbon atoms as obtained in step (f), thereby obtaining a normal paraffin comprising 10 to 13 carbon atoms and a normal paraffin comprising 14 to 18.

It has been found according to the present invention that by selecting only a light wax, notably the second and third liquid liquid hydrocarbon stream, as feed for the preparation of normal paraffins separation by distillation can be accomplished at atmospheric

conditions .

A further advantage is that by selecting the light wax stream the equipment size gets smaller and the separation easier. In this way the production of normal paraffins is also attractive on smaller scale. Yet a further advantage is that less energy is required for the heating and distillation.

Another advantage is that the composition of the normal paraffins can be influenced such that the normal paraffins composition will be lighter because the heavier molecules reside in the heavy wax.

Detailed description of the invention

The Fischer-Tropsch product stream as provided in step (a) 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 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.

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 product stream 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 iso-paraffins, cyclo-alkanes and alkyl benzene.

The Fischer-Tropsch process for preparing the Fischer-Tropsch derived product stream 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. Preferably, the Fischer-Tropsch process is a fixed bed Fischer-Tropsch process.

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 CI to C4, and a C5+ stream. The Fischer-Tropsch product stream comprises preferably a wax and a liquid stream.

The full Fischer-Tropsch hydrocarbonaceous product suitably comprises a CI to C300 fraction.

Lighter fractions of the Fischer-Tropsch product, which suitably comprises CI 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 (b) of the process according the present invention the Fischer-Tropsch product of step (a) is separated to obtain a first gaseous hydrocarbon stream and a first liquid hydrocarbon stream. The separation in step (b) is suitably carried out at a temperature in a range of from 160 to 350°C, preferably from 190 to 250°C and at a pressure in a range of from 5 to 150 bar. Also, the separation preferably takes place in the Fischer- Tropsch reactor.

The first gaseous hydrocarbon stream as obtained in step

(b) preferably comprises 1 to about 35 carbon atoms.

Suitably, the first liquid hydrocarbon stream as obtained in step (b) comprises about 16 to 90 carbon atoms. The first liquid hydrocarbon stream can be considered as heavy product that is solid and ambient pressure and temperature. It can be seen that the carbon distribution of the first liquid hydrocarbon stream and the gaseous hydrocarbon stream as obtained in step (b) overlap partially as the partitioning in the two phases is related to the vapour pressure at conditions of

separation. The starting point and the end point of the carbon distribution of liquid hydrocarbon stream were determined using the 0.5 wt% cut off point of the hydrocarbon pool . Both the end point of the carbon distribution of the first gaseous stream and the starting point of the first liquid hydrocarbon stream can differ from the mentioned 35 and 16 depending on the conditions of separation.

Hence, the end point of the carbon distribution of the first gaseous stream is in a range of from 25 to 50 carbon atoms, preferably from 35 to 40 and the starting point of the first liquid hydrocarbon stream is in a range of from 5 to 25 carbon atoms, preferably from 10 to 20 carbon atoms.

In step (c) of the process according to the present invention the first gaseous hydrocarbon stream of step

(b) is cooled and separated in one or more steps to obtain a second liquid hydrocarbon steam and a third liquid hydrocarbon stream.

Cooling and separation in step (c)of the first gaseous hydrocarbon stream of step (b) is suitably carried out at a temperature in a range of from 5 to 180°C and at a pressure in a range of from 5 to 145 bar.

Preferably, the first gaseous hydrocarbon stream of step (b) is cooled and separated in two steps in step

(c) . Suitably, first the first gaseous hydrocarbon stream of step (b) is cooled to obtain a second gaseous

hydrocarbon stream and a second liquid hydrocarbon stream followed by the cooling of the second gaseous hydrocarbon stream to obtain a third gaseous hydrocarbon stream and a third liquid hydrocarbon stream.

Cooling of the second gaseous hydrocarbon stream is also carried out at the conditions as described above for the cooling in step (c) .

Preferably, the second liquid hydrocarbon stream comprises 5 to 29 carbon atoms. The second gaseous hydrocarbon stream suitably comprises 1 to 25 carbon atoms. Also, the third gaseous hydrocarbon stream comprises 1 to 4 carbon atoms. The third liquid

hydrocarbon stream suitable comprises 3 to 20 carbon atoms .

In step (d) of the process according to the present invention the second and the third liquid hydrocarbon streams of step (c) are separated by atmospheric

distillation, thereby obtaining a normal paraffin fraction comprising 5 to 9 carbon atoms and a normal paraffin fraction comprising 10 to 35 carbon atoms.

Preferably, prior the separation in step (d) gases such as carbon monoxide, carbon dioxide, water, hydrogen and lighter hydrocarbons are stripped from the second and third liquid hydrocarbon streams.

In step (e) of the process according to the present invention the normal paraffin fraction comprising 10 to 35 carbon atoms of step (d) is separated by atmospheric distillation thereby obtaining a normal paraffin fraction comprising 10 to 18 carbon atoms and a normal paraffin fraction comprising 19 to 35 carbons atoms.

Typically, the atmospheric distillation in steps (d) and (e) is at a temperature in the range of 200 to 400 °C, preferably 300 to 350°C.

Suitably, the separation of the second and the third liquid hydrocarbon streams of step (c)in steps (d) and (e) is done in one separation step by atmospheric distillation. To be more specific, second and the third liquid hydrocarbon streams of step (c) is separated by atmospheric distillation, thereby obtaining a normal paraffin fraction comprising 5 to 9 carbon atoms, a normal paraffin fraction comprising 10 to 18 carbon atoms and a normal paraffin fraction comprising 19 to 35 carbon atoms .

Typically, prior to the separation step (d) the second and the third liquid hydrocarbon liquid stream are combined .

In step (f) of the process according to the present invention the normal paraffin fraction comprising 10 to

18 carbon atoms of step (e) is subjected to a

hydrogenation step, thereby obtaining hydrogenated normal paraffin fraction comprising 10 to 18 carbon atoms. 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. The amount of oxygenates in the streams prior to hydrogenation is less than 5 ppm (mg/kg) .

Oxygenates are preferably hydrocarbons containing one or more oxygen atoms per molecule. Typically, oxygenates are alcohols, aldehydes, ketones, esters, and carboxylic acids.

In step (g) of the process according to the present invention the hydrogenated normal paraffin fraction comprising 10 to 18 carbon atoms of step (f) are

separated, thereby obtaining a normal paraffin comprising 10 to 13 carbon atoms and a normal paraffin comprising 14 to 18 carbon atoms.

The normal paraffin comprising from 10 to 13 carbon atoms is also known as light detergent fraction (LDF) and the normal paraffin comprising from 14 to 18 carbon atoms is also known as heavy detergent fraction (HDF) .

Preferably, the weight fraction of the normal paraffin comprising 10 to 13 carbon atoms is between 45 and 60 w.t%, preferably 49 wt . % and the weight fraction of the normal paraffin comprising 14 to 17 is between 40 and 55wt.%, preferably 51 wt . % based on the amount of the hydrogenated liquid carbon stream of step (f) .

Also, the normal paraffin comprising 10 to 13 carbon atoms of step (g) comprises a fraction comprising 10 carbon atoms in a range of from 10 to 11 wt.%, a fraction comprising 11 carbon atoms in a range of from 30 to 32 wt.%, a fraction comprising 12 carbon atoms in a range of from 30 to 32 wt.% and a fraction comprising 13 carbon atoms in a range of from 23 to 26 wt.%. Suitably, the normal paraffin comprising 14 to 18 carbon atoms of step (g) comprises a fraction comprising 14 carbon atoms in a range of from 25 to 27 wt.%, a fraction comprising 15 carbon atoms in a range of from 24 to 26 wt.%, a fraction comprising 16 carbon atoms in a range of from 22 to 23 wt.%, a fraction comprising 17 carbon atoms in a range of from 18 to 20 wt.% and a fraction comprising 18 carbon atoms in a range of from 4 to 6 wt . % .

Figure 1 schematically shows a process scheme of the process scheme of a preferred embodiment of the process according to the present invention.

For the purpose of this description, a single reference number will be assigned to a line as well as a stream carried in that line.

The process scheme is generally referred to with reference numeral 1.

In a Fischer-Tropsch process reactor 2 a Fischer- Tropsch product stream is obtained. Separation into a first gaseous hydrocarbon stream 10 and a first liquid fraction 20 is accomplished in the reactor itself. The gaseous hydrocarbon stream 10 is fed to a cooling unit 3 wherein the gaseous hydrocarbon stream is cooled and separated to obtain a second gaseous hydrocarbon stream 30 and a second liquid fraction 40. The gaseous

hydrocarbon stream 30 is fed to another cooling unit 4 wherein the gaseous hydrocarbon stream 30 is cooled and separated to obtain a third gaseous hydrocarbon stream 50 and a third liquid fraction 60 . The second liquid fraction 40 and the third liquid fraction 60 are

distilled in an atmospheric distillation column 5 to recover a normal paraffin fraction 70 comprising 5 to 9 carbon atoms and a fraction 80 comprising 10 to 35 carbon atoms. The normal paraffin fraction 80 is distilled in an atmospheric distillation column 6 to recover a normal paraffin fraction 90 comprising 10 to 18 carbon atoms and a fraction 100 comprising 19 to 35 carbon atoms. Fraction 90 is fed to a hydrogenation reactor 7 to obtain a hydrogenated normal paraffin fraction 110 comprising 10 to 18 carbon atoms. Fraction 110 is distilled in a distillation column 8 to recover a normal paraffin 120 comprising 10 to 13 carbon atoms and a normal paraffin 130 comprising 14 to 18 carbon atoms.

Experimental

The following examples were obtained by a simulation of a facility with a multitude of Fischer-Tropsch reactors .

Example 1

Product distribution of the first, second and third liquid hydrocarbon streams

In Table 1 the flows of molecules with indicated chain length in three liquid hydrocarbon streams is given, with full distribution of the streams depicted in figure 2. The first liquid stream is obtained at a pressure of 55 bar and a temperature of 215°C, the second liquid stream at a pressure of 55 bar and a temperature of 159° and the third liquid stream at a pressure of 53 bar and a temperature of 15°C. It can be seen that the majority of the normal paraffins is present in the combined stream of 2^nd and 3^rd liquid.

The respective starting and end point of the carbon distributions (defined as the chain length equivalent to at least 0.5 wt% of the total amount of hydrocarbon) were 16-88, 5-29 and 3-20 respectively. It can be seen from Figure 1 that the distributions for the 2^nd and 3^rd liquid are reasonably sharp, whereas the 1^st liquid has significant tailing to higher carbon numbers,

concentrations below 0.5 wt%.

Table 1: Paraffin content in 1 , 2 and 3 liquid hydrocarbon streams.

Examples 2 to 6

Process to prepare normal paraffins

In the comparative examples 2-4 all the liquid hydrocarbon streams are combined and used for the production of normal paraffins. Separation of the normal paraffins from the full product mixture is done using both atmospheric and vacuum distillations at conditions indicated. In example 5 and 6 as per the invention, only the light wax streams, so the 2^nd and 3^rd liquid

hydrocarbon stream were selected. From the results in Table 2 it becomes apparent that in the comparative example atmospheric distillation results in very low recovery of the heavier part of the normal paraffin. For instance the C17 paraffin stream was only 3 tons per day at distillation temperatures of 345 and 370 °C

respectively. For these heavier paraffins vacuum

distillation is required as can be seen in example 4. Vacuum distillation however requires, which is undesired related to the high cost .

The cases according to the invention represented by example 5 and 6 result in excellent yields of paraffins without need to invest in vacuum distillation. By comparing comparative example 2 and example 5 with same distillation conditions, it can be seen that for all carbon chain lengths the recovery was higher when according to the invention only the 2^nd and 3^rd liquid hydrocarbon stream were selected. The total recovery was almost doubled.

*Before the vacuum distillation an atmospheric distillation remove lighter hydrocarbons was carried out .

Table 2: Paraffin recovery at different distillation conditions .

Comparison of example 6 (according to the invention) with comparative example 4 it can be seen that the paraffin total yields were only 15% lower. However, for the comparative example an expensive vacuum distillation operation was required and an atmospheric distillation (to remove the lighter components) . Hence the situation as per invention in example is much more attractive as the expensive vacuum distillation that requires high energy loads, could be eliminated.

Example 7 Process to prepare ClO-13 and C14 to 18 normal paraffins

The recovered paraffins will need further

distillation after hydrogenation to meet the product specification of the lighter C10-C13 normal paraffins and C14-C18 normal paraffins final products. The resulting compositions are given in Table 3 and Table 4. It can be seen that the compositions according to the invention are lighter compared to the comparative example .

Table 3: Composition of LDF for comparative example 4 and example 6 as per invention

Table 4: Composition of HDF for comparative example 4 and example 6 as per invention

In Table 5 the normal paraffin final product weight fractions are given. It can be seen that in example 6 according to the invention almost the same amount of LDF is obtained, with a lower amount of HDF. The LDF content out of the NP products increases hence from 44 to 49%.

Related to the bigger market and higher premiums for LDF, it is advantaged to have a bigger fraction of the normal paraffin product as LDF.

Table 5: Weight fraction of NP in LDF and HDF for comparative example 4 and example 6 as per invention

Claims

C L A I M S

Process to prepare normal paraffins, the process comprises the steps of:

(a) providing a Fischer-Tropsch product stream;

(c) cooling and separating of the first gaseous

hydrocarbon stream of step (b) in one or more steps to obtain a second liquid hydrocarbon stream and a third liquid hydrocarbon stream;

(d) separating the second and the third liquid

(e) separating the normal paraffin fraction

(g) separation of the hydrogenated normal paraffin fraction comprising 10 to 18 carbon atoms as obtained in step (f), thereby obtaining a normal

16 paraffin comprising 10 to 13 carbon atoms and a normal paraffin comprising 14 to 18 carbon atoms.

2. Process according to claim 1, wherein the Fischer- Tropsch product stream of step (a) is separated in step (b) at a temperature in a range of from 160 to

350°C, preferably from 190 to 250°C and at a pressure in a range of from 5 to 150 bar.

3. Process according to claim 1 or 2, wherein the first gaseous hydrocarbon stream of step (b) is cooled and separated in step (c) at a temperature in a range of from 5 to 180 °C and at pressure in a range of from 5 to 145 bar.

4. Process according to any one of claims 1 to 3, wherein the first gaseous hydrocarbon stream of step (b) is cooled and separated in two steps in step (c) .

5. Process according to any one of claims 1 to 4, wherein the atmospheric distillation in steps (d) and (e) is at a temperature in the range of 200 to 400°C, preferably 300 to 350°C.

6. Process according to any one of claims 1 to 5, wherein the separation of the second and the third liquid hydrocarbon liquid streams of step (c) in steps (d) and (e) is done in one separation step by atmospheric distillation .

7. Process according to any one of claims 1 to 6, wherein prior to the separation in step (d) the second and the third liquid hydrocarbon liquid stream are combined.

8. Process according to any one of claims 1 to 7, wherein the weight fraction of the normal paraffin comprising 10 to 13 carbon atoms is between 45 and 60 wt.%, preferably 49 wt.% and the weight fraction of the normal paraffin comprising 14 to 17 is between 40 and

17 55, preferably 51 wt . % based on the amount of the hydrogenated liquid hydrocarbon stream of step (f) .

9. A process according to any one of claims 1 to 8,

wherein the normal paraffin comprising 10 to 13 carbon atoms of step (g) comprises a fraction comprising 10 carbon atoms in a range of from 10 to 11 wt.%, a fraction comprising 11 carbon atoms in a range of from 30 to 32 wt.%, a fraction comprising 12 carbon atoms in a range of from 30 to 32 wt.% and a fraction comprising 13 carbon atoms in a range of from 23 to 26 wt . % .

10. A process according to any one of claims 1 to 9,

wherein the normal paraffin comprising 14 to 18 carbon atoms of step (g) comprises a fraction comprising 14 carbon atoms in a range of from 25 to 27 wt.%, a fraction comprising 15 carbon atoms in a range of from 24 to 26 wt.%, a fraction comprising 16 carbon atoms in a range of from 22 to 23 wt.%, a fraction

comprising 17 carbon atoms in a range of from 18 to 20 wt.% and a fraction comprising 18 carbon atoms in a range of from 4 to 6 wt.%.

18