WO2018045396A1

WO2018045396A1 - Olefinic naphtha oligomerisation

Info

Publication number: WO2018045396A1
Application number: PCT/ZA2017/050047
Authority: WO
Inventors: Masikana Millan Mdleleni; Nonyameko Prudence SINCADU; David Key; Natasha Denise THOMAS; Letlhogonolo Blanche SIMA
Original assignee: The Petroleum Oil & Gas Corporation Of South Africa (Pty) Ltd
Priority date: 2016-09-01
Filing date: 2017-08-28
Publication date: 2018-03-08

Abstract

The invention provides a COD process. The COD process includes contacting a blend of Fisher-Tropsch derived olefins and crude derived olefins containing crude Fluid Catalytic Cracking (FCC) derived naphtha with a ZSM-5 (Zeolyst Int., SiO₂/Al₂O₃ ≈ 30)(COD-9) catalyst at pressures of about 50barg or below to produce olefinic distillates including gasoline and diesel fractions.

Description

Title: Olefinic Naphtha Oligomerisation

Technical field of the invention

This invention relates to the use of crude derived olefins as feed and co- feed for the conversion of olefins to distillates (COD).

Background to the invention

The Applicant's COD process comprises a process for catalytical conversion of Fisher-Tropsch derived olefins to distillates (COD), which process includes the step of contacting Fisher-Tropsch derived olefins with a ZSM-5 (Zeolyst Int., SiO₂/AI₂O₃ ~ 30)(COD-9) (MFI type catalyst as defined by the International Zeolite Association (IZA) catalyst supplied by Sud Chemie at pressures of more than 50barg to produce a low aromatic olefinic distillates including gasoline and diesel fractions.

It is an object of the invention to use a low value crude derived naphtha product as a feed or co-feed for the COD process to produce higher value distillates.

General description of the invention According to the invention there is provided a COD process, which includes the contacting of a blend of Fisher-Tropsch derived olefins and crude derived olefins containing crude Fluid Catalytic Cracking (FCC) derived naphtha with a ZSM-5 (Zeolyst Int., SiO₂/AI₂O₃ ~ 30)(COD-9) catalyst at pressures of about 50barg or below to produce a olefinic distillates including gasoline and diesel fractions.

The FCC feed may be fractionated before being used as a feed or co-feed to remove sulphur containing compounds. The invention may include varying the feed over time to manipulate the product distribution over time.

The feed may be selected from 50/50% Fisher Tropsh derived olefins and FCC crude derived naphtha for about 5 days followed by 100% Fisher Tropsch derived olefins for about two days followed by 100% FCC crude derived naphtha for about 8 days followed by 100% Fisher Tropsch derived olefins for about two days.

Detailed description of the invention

The invention is now described by way of example with reference to the accompanying drawings.

In the drawings:

Figure 1.1 shows the carbon number distribution of C5/C6 product with time; Figure 1.2 shows conversion of the C5/C6 feed over HZSM5 catalyst (based on C5 olefin); Figure 1.3 shows product distribution over time for the C5 minus (<C5), gasoline (C5-C9), distillate (>C9) and the aromatics;

Figure 1.4 shows the carbon number distribution of the different feeds;

Figure 1.5 shows the amount of distillate produced after 16 hours for the 5 feeds screened; Figure 1.7 shows the sulphur content in the reaction product with time for the 100% Full FCC Feed;

Figure 1.8 shows the sulphur content in the reaction product with time for the 40% Full FCC Feed;

Figure 1.9 shows the sulphur content in the reaction product with time for the 100% Light FCC Feed;

Figure 1.10 shows the sulphur content in the reaction product with time for the 40 % Light FCC Feed; Figure 1.11 shows the catalyst weight bed loading;

Figure 1.12 shows product yields at various stages per time on stream;

Figure 1.13 shows Carbon No: Feeds;

Figure 1.14 shows Carbon No: Distillate; Figure 1.15 shows Carbon No: Gasoline;

Figure 1.16 shows boiling properties of feed;

Figure 1.17 shows boiling properties of distillate;

Figure 1.18 shows boiling properties of gasoline;

Figure 1.19 shows boiling properties from the high pressure separator;

Figure 1.20 shows sulphur content of a low pressure separator;

Figure 1.21 shows the acid number of gasoline;

Figure 1.22 shows the bromine number of gasoline;

Figure 1.23 shows the aromatic content of gasoline;

Figure 1.24 shows carbon number distribution of 100% FCC naphtha (42 °C - 104 °C) product;

Figure 1.25 shows carbon number distribution of 40% FCC naphtha (42 °C - 104 °C) product;

Figure 1.26 shows carbon number distribution of 100% FCC naphtha (35 °C - 168 °C) product; Figure 1.27 shows carbon number distribution of 40% FCC naphtha (35 °C - 168 °C) product;

Figure 1.28 shows Product Distribution of 100% Light FCC naphtha (42 °C - 104 °C) product over time;

Figure 1.29 shows Product Distribution of 40% Light FCC naphtha (42 °C - 104 °C) product over time;

Figure 1.30 shows Product Distribution of 100% FCC naphtha (35 °C - 168 °C) product over time;

Figure 1.31 shows Product Distribution of 40% FCC naphtha (35 °C - 168 °C) product over time; Figure 1.32 shoes Conversion of 100% FCC naphtha (42 °C - 104 °C) product (based on C5 ) over time;

Figure 1.33 shows Conversion of 40% FCC naphtha (42 °C - 104 °C) product (based on C5) over time; Figure 1.34 shows Conversion of 100% FCC naphtha (35 °C - 168 °C) product (based on C5) over time; and

Figure 1.35 shows Conversion of 40% FCC naphtha (35 °C - 168 °C) product (based on C5) over time.

EXPERIMENTAL

The naphtha feeds tested for oligomerisation over the ZSM-5 (Zeolyst Int., Si0₂/Al₂0₃ ~ 30)(COD-9) catalyst are tabulated in Table 1 .1 . Table 1.1 Naphtha Feed Screened

The reaction conditions are tabulated in Table 1 .2. Table 1.2 Reaction Conditions

The reactor was loaded according to the following schedule:

48 cm: length of the reactor

1 1 cm: length of bottom cotton wool plug 9 cm: length of bottom glass beads

7 cm: length of diluted COD-9 catalyst (5g COD-9 catalyst + 5g glass beads) 16 cm: length of top glass beads

5 cm: length of top cotton wool plug

After loading the reactor, as per the diagram above, the reactor is connected to the system. The back-pressure regulator and the reactor are slowly pressurized to 46 bar, which is currently the maximum pressure attainable on the micro-scale. The nitrogen make-up over the wet gas meter was set to ensure that there is flow through the entire system.

The system is purged with N₂-gas and off-gas analysis is done in order to establish the O₂ content. An O₂ content of <0.2% is required before the experiment proceeds.

The reactor is heated up, whilst pumping the liquid feed. Once the reactor temperature is reached, the liquid product is drained from the sample catch pot. The mass balance of the various experiments was not done and hence the component yields (absolute values) are not available. The liquid product was analysed by GC and hence the volume% of the components is used to demonstrate the product distributions.

RESULTS

PetroSA C5/C6 feed The PetroSA C5/C6 feed, a mixture of C5/C6 olefins from the Iron based High Temperature Fisher-Tropsch process, was used as a base case for the screening of various naphtha feeds. The C5/C6 feed was fed over a HZSM5 catalyst (COD9) for a period of 240 hours and samples were collected at different time intervals. The carbon number distribution of the product collected at various time intervals is shown in Figure 1 .1 .

The carbon number distribution, during the first 16 hours, shows the formation of higher carbon number range (distillate range) species with some formation of species below C5. After 16 hours, a decrease in the formation of species below C5 and above C8 (i.e. distillate range) is observed. This carbon number change with time could indicate catalyst deactivation which corresponds with the decrease in conversion (based on C5 olefin) observed with time, see Figure 1 .2.

In the first 16 hours, 97 % of the C5 molecules are converted and this corresponds with the maximum amount of distillate formed as shown in Figure 1 .3 below. Between 168 hours and 240 hours a constant conversion of about 55% is obtained. In Figure 1.3 however a decline in distillate formation continues within the 168 hour to 240 hour period, which indicates that despite the constant conversion observed in Figure 1.2, the product distribution is not constant.

In a larger commercial unit, the 168 hours (7 days) correspond with the production of an "off-specification product" and after 7 days the conversion stabilizes and the product distribution becomes consistent (i.e. gasoline to distillate ratio is constant). A similar trend seems to be observed on the micro- scale except that the gasoline to distillate ratio continues to change as seen in Figure 1 .3. It is worth noting that the reaction conditions remained the same throughout the 10 day experiment as compared to commercial operations where the temperature is increased in order to maintain stable conversion and distillate formation.

At 240 hours only 56 % of the C5 molecules are converted compared to 97 % conversion in the first 16 hours. The distillate yield drops from 57 % to 15% due to a decrease in catalyst activity, see Figure 1.3.

Figure 1 .3 shows the product distribution curve over time for the C5 minus (<C5), gasoline (C5-C9), distillate (>C9) and the aromatics. The product distribution curve in Figure 1 .3 indicates that in the first 16 hours the following reactions may be present; 1 ) Oligomerisation (see Scheme 2), resulting in the decrease of gasoline and the accompanying formation of distillate.

2) Cracking and disproportionation (see Scheme 2), resulting in the formation lighter hydrocarbons. 3) Aromatisation, resulting in the formation of aromatic components

After 16 hours, a steady decrease in the formation of distillate is observed. This trend may indicate that less oligomerisation is occurring as a result of the decrease in catalyst activity.

The following trends were observed for all the naphtha feed screened in this study;

• maximum distillate production during the first 16 hours

• decline in catalyst activity and distillate with time

FCC Naphtha feed

The Fluid Catalytic Cracking naphtha feed derived from crude contained approximately 1520ppm of sulphur and includes a wide range olefinic or olefinic- parafinic mix of hydrocarbons from C3 - C9. The majority of the sulphur components present in the feed have boiling points above 100 °C. The FCC naphtha feed was therefore fractionated in order to mitigate the effects and/or the presence of the sulphur components in the COD process. The resultant fractions were;

• Lighter FCC naphtha with a boiling range of between 42 °C - 104 °C and a sulphur content of 590 ppm

• FCC naphtha with a boiling range of 35 °C - 168 °C and a sulphur content of 2660ppm. The feeds studied were the following;

C5/C6

100 % Light FCC naphtha (42 °C 104 °C)

40 % Light FCC naphtha (42 °C 104 °C)(blended with 60% C5/C6)

100 % FCC naphtha (35 °C - 168 °C)

• 40% FCC naphtha (35 °C - 168 °C) (blended with 60% C5/C6)

Figure 1 .4 shows the carbon number distribution curves of the feed screened.

All the feeds screened have a carbon number range within the gasoline range i.e. between C5 and C9. The 100% FCC naphtha feed contains higher carbon number species compared to the other feeds. The effect of blending C5/C6 feed to the FCC naphtha feed results in the addition of lighter molecules to the feed. The addition of C5/C6 feed to the Light FCC naphtha feed results in an increase in heavier molecules.

The various feeds were all studied under the same conditions and yielded similar product distribution curves (based on volume % and not absolute yield values) with time. The product distribution curves for the various feeds study are shown in the Appendix section. The distillate yield produced from the various feeds screened after 16 hours is shown below in Figure 1 .5. Figure 1 .5 shows the amount of distillate produced after 16 hours for the 5 feeds screened

The 40% Light FCC naphtha feed and the 100% FCC naphtha feed performed the same with respect to distillate formation despite having different carbon number ranges. The mass balance of the various experiments was not done and hence the component yields (absolute values) are not available. The liquid product was analysed by GC and hence the volume% of the components is used to demonstrate the product distributions. Of the 5 feeds screened the 100% Light FCC naphtha produced the most distillate. This would indicate that the sulphur present in the feed does not adversely affect the formation of distillate (i.e. oligomerisation).

Figure 1 .7 Shows the sulphur content in the reaction product with time for the 100% Full FCC Feed

The sulphur content of the reaction products of the FCC feeds was analysed. Figure 1 .7, Figure 1 .8, Figurel .9 and Figure 1.10 show the sulphur content in the product with time. Figure 1 .8 shows the sulphur content in the reaction product with time for the 40% Full FCC Feed. Figure 1 .9 shows the sulphur content in the reaction product with time for the 100% Light FCC Feed. Figure 1 .10 shows the sulphur content in the reaction product with time for the 40 % Light FCC Feed.

The reaction products indicate that the amount of sulphur is different for different samples collected. From the figures above, the general trend observed suggests an initial absorption/adsorption of the sulphur species. In order to establish whether any sulphur is deposit on the catalyst during the reaction the spent catalyst was analysed for sulphur as well as carbon deposition. The carbonaceous and sulphur (only from FCC feed) material present on the spent catalyst indicates the presence of coke formation (i.e. the carbonaceous material) and no significant sulphur deposition (for the FCC naphtha runs) on the catalyst, see Table 1 .3 below.

Table 1.3 Carbon and Sulphur on spent catalyst

40% Light FCC naphtha 1 1 .5 <0.005 (42 °C - 104 °C)

100 % Full FCC naphtha 1 1 .5 <0.005 (35 °C - 168 °C)

40 % Full FCC naphtha 1 1 .2 <0.005 (35 °C - 168 °C)

RESULTS AND ADVANTAGES SHOWN BY MICROSCALE STUDIES

• All the feeds screened showed a potential to produce distillate.

• The distillate formation decreases with time.

• Carbonaceous material was found on the spent catalyst.

• No significant deposition of sulphur on the spent catalyst occurs.

• The deactivation of the catalyst with time was observed for all feeds screened.

• After 168 hours a constant conversion seems to be observed however, the accompanying product distribution does not remain constant as seen on commercial scale.

Pilot Plant Studies

The main purpose of the pilot plant run was to test the impact of sulphur on the COD catalyst and the sulphur content of the end product. This test run was performed in three stages; namely;

1 . The blended feed which contained 50% FCC naphtha and 50% C5/6 was fed on first stage with propylene.

2. Secondly C5/C6 feed with propylene for a short period then,

3. Lastly; 100% FCC naphtha was fed with butylene. Various analyses were performed on end products and primary feed to check their status with regard to quality. The carbon numbers and boiling properties of all the feeds were determined in order to compare with product results. The sulphur content of the blended feed was 610ppm and that of 100% FCC naphtha feed was 1610ppm. The C5/6 feed produced distillates with longer carbon chains (C7 to C15) when compared to FCC blended feed (C8 to C14) and 100% FCC feed (C8 to C14). The distillates final boiling point of the C5/6 feed was 350°C whereas that of FCC naphtha feed was 270 °C.

Experimental Procedure On the first stage, the blend was fed for five days, consisting of 50% FCC naphtha and 50% C5/6, with propylene to track the conversion. On stage three 100% FCC Naphtha was fed for a period of nine days, with butylene as a standard to track conversion. Between these two stages, the standard COD feeds were fed for three days to check if the conversion was still acceptable or if the catalyst was still active.

Stage 1 : Propylene (C3) + Naphtha blend (50% FCC naphtha + 50% C5/6); 20 October to 25 October.

Stage 2: Propylene (C3) and C5/C6; 25 October to 27 October.

Stage 3: Butylene (C4) + 100% FCC Naphtha; 28 October to 5 November.

The table below shows the basic operating conditions for run four. The operating conditions were consistent throughout the three stages with the plant holding pressure of 55bar at all times. The WHSV of 1 was also achieved. Table 3.1 Operating conditions for Run 4

Catalyst loading diagram

The reactor is divided into 4 zones, namely bed 1 , bed 2, bed 3 and bed 4. The catalyst masses in each bed were as follows 38.25g, 85.5g, 162g and 214.25g. Figure 1.1 1 below shows a loading diagram with the catalyst masses indicated in each bed. A loading diagram is used when loading the catalyst, to ensure safe, correct handling and reloading of the catalyst in the reactor. Fig. 1 .1 1 shows the catalyst weight bed loading.

Results & Discussion Product Yields

The gasoline and distillate produced was determined per time on stream on daily basis and the results are shown below; Figure 1.12 Although gasoline is the major product as compared to distillate; the impact of the sulphur on the catalyst needs further analysis at longer run periods. It seems the distillate yields were below 15% when 100% FCC naphtha was introduced and this did not change when the naphtha was removed.

Fig.1 .12 shows product yields at various stages per time on stream.

Table 3.1 Table of Mass Yields Average

Carbon Number Distribution

Carbon Number - Feeds

The carbon number of all the feeds was determined in order to compare with product results, if longer carbon chains were formed. The main components of C5/6 feed are C5 to C8 from fig.1 .13 above. The blended feed (50% FCC naphtha and 50% C5/6) also shows components from C4 to C12. The main components of the blend feed were C5, C6 and C8. The FCC naphtha feed (fig.1 .13) carbon numbers are from C3 to C12 with the main components from C5 to C9. Carbon Number - Distillate

The main components on the distillate product (fig.1 .14) are from C8 to C14 for the C5/6 feed. The distillate product carbon numbers were from C8 to C16, with C9, C10, C1 1 and C12 being more dominant for the blended feed.

The distillate product (fig.1 .14) carbon numbers are from C7 to C15, with main components from C9 to C12. The sharp curve on fig.1 .13, distillate carbon numbers shows FCC naphtha feed to be producing mainly C10s.

Carbon Number - Gasoline

The gasoline product (fig.1 .15) was concentrated mainly of C7 and C8 components for the C5/6 feed. The gasoline product carbon numbers (fig.1 .15 were mainly C7 and C8 for the blended feed.

Boiling Properties

The C5/6 feed had a FBP of 130°C (fig.1.16) when compared to the FCC naphtha feed which had a FBP of 180°C. The C5/6 product, distillate had a higher final boiling point (FBP) of 350°C (fig.1 .17) compared to FCC naphtha product with FBP of 270°C. FCC naphtha formed less long chains (distillate) when compared to C5/6. C5/6 formed longer chains (distillate) compared to FCC naphtha and blended feed, therefore it had higher FBP. The final boiling point for gasoline product (fig.1 .18) was between 120 to 140°C for the two stages of the test run. The same can be observed on the carbon number distribution of gasoline product for the two stages of the run. Fig.1 .16 shows D86 Feed

Fig.1 .17 shows D86 Distillate

Fig.1 .18 shows D86 Gasoline

Fig.1 .19 shows D86 VD 305 D86 refers to the method used to determine the boiling range of the hydrocarbon mixture. Figure 1 .17 shows the boiling properties of the product from a High Pressure Separator, which contains the mixed product after the reactor and prior to fractionation. Sulphur

Fig.1 .20: Shows sulphur content of low pressure separator. The graph (fig.1 .20) shows the sulphur content of low pressure separator (VD305) throughout the run. VD305 gives the product mixture after the reactor before fractionation. The initial sulphur content of 50%FCC naphtha and 50% C5/6 mixture feed was 610ppm. Fig.1 .20 above shows a decreasing trend on the sulphur concentration between the 20^th and 25^th. On the 20^th sulphur concentration is high at 570ppm; the fluctuation of the pump stroke could have contributed to these results. As the feeding normalised to the set point the concentration decreased to 300ppm.The graph also clearly shows that the sulphur content was low when normal COD feeds were fed between the 25 and 28^th. Pure FCC naphtha was fed on the 29^th October with feed sulphur content of 1610ppm. It can be observed in fig.1.20 that from the 29^th October to 5^th November the sulphur concentration was 600ppm on average. Therefore it can be concluded that sulphur concentration decreased after dilution with recycle.

Acid Number - Gasoline

Fig.1 .21 shows acid Numbers. The acidity of gasoline was much lower than that of the base case run which was 1 .5mgKOH/g. The feeds acid number of C5/6 was 0.55mgKOH/g higher than that of recycle which was 0.27mgKOH/g. Fig1 .21 above shows that when feeding 50% FCC naphtha and 50% C5/6 together with recycle the acid number was higher compared to other feeds. It can be observed that when feeding pure FCC naphtha that the acid number was lowest. Therefore it can be concluded that FCC naphtha does not contribute to acidity. Bromine Number - Gasoline

Fig.1 .22 shows the bromine number. The Bromine Number is useful as a measure of aliphatic unsaturation i.e. measure the amount of olefins in the gasoline. The higher the Bromine numbers the greater the amount of unsaturated hydrocarbons (olefins) present in the fuel. On the graph above it is evidence that FCC naphtha has low bromine number compared to the days when feeding C5/6. Bromine number is in the 60 to 80 range during the period when feeding FCC naphtha. Whereas when feeding C5/6 and the blend feed it is in the 80 to 1 10 range. Thus it can be concluded that more unsaturated hydrocarbons are produced when feeding C5/6.

Aromatic Content - Gasoline

Fig.1 .23 shows aromatic content. The commercial plant (Unit 24) specification for gasoline aromatic content is between 0 and 10%. The aromatic content for the C5/6 feed is between 2 to 3%. The FCC naphtha and blended feeds has a higher aromatic content compared to C5/6.

Conclusion

The results showed a low bromine number and low acid number for the FCC naphtha feed while compared to C5/6 feed. It can be concluded from the carbon number distribution that more gasoline was formed as compared to distillate product. The C5/6 feed formed longer chains when compared to FCC naphtha feed.

· The catalyst may preferably be diluted as 500g was used, to use less catalyst

• The catalyst loading may preferably be packed opposite to the current loading.

• The feeds flowrates may be increased to spend less contact time with the catalyst in order to form longer carbon chains.

Carbon Number Distribution Curves with time

Figure 1.24 shows carbon number distribution of 100% FCC naphtha (42 °C - 104 °C) product.

Figure 1.25 shows carbon number distribution of 40% FCC naphtha (42 °C - 104 °C) product.

Figure 1.26 shows carbon number distribution of 100% FCC naphtha (35 °C - 168 °C) product. Figure 1.27 shows carbon number distribution of 40% FCC naphtha (35 °C - 168 °C) product.

Product Distribution Curves with time Figure 1.28 shows Product Distribution of 100% Light FCC naphtha (42 °C - 104 °C) product over time.

Figure 1.29 shows Product Distribution of 40% Light FCC naphtha (42 °C - 104 °C) product over time.

Figure 1.30 shows Product Distribution of 100% FCC naphtha (35 °C - 168 °C) product over time.

Figure 1.31 shows Product Distribution of 40% FCC naphtha (35 °C - 168 °C) product over time.

Conversion over time Curves Figure 1.32 shoes Conversion of 100% FCC naphtha (42 °C - 104 °C) product (based on C5 )over time.

Figure 1.33 shows Conversion of 40% FCC naphtha (42 °C - 104 °C) product (based on C5) over time.

Figure 1.34 shows Conversion of 100% FCC naphtha (35 °C - 168 °C) product (based on C5) over time.

It shall be understood that the examples are provided for illustrating the invention further and to assist a person skilled in the art with understanding the invention and are not meant to be construed as unduly limiting the reasonable scope of the invention. REFERENCES

1 ) S Tabak, F Krambeck and W Garwood Conversion of Proylene and Butylene over ZSM-5 Catalyst, AlChE Journal, vol 32, 9 September 1986, 1526-1531 2) M.Sanati, C Hornell and S.G. Jaras, The oligomerisation of alkenes by heterogeneous catalysts, Catalysis, Vol 14, The Royal Society of Chemistry, 1999

Claims

1 . A COD process, which includes:

contacting a blend of Fisher-Tropsch derived olefins and crude derived olefins containing crude Fluid Catalytic Cracking (FCC) derived naphtha with a ZSM-5 (Zeolyst Int., SiO₂/AI₂O₃ ~ 30)(COD-9) catalyst at pressures of about 50barg or below to produce olefinic distillates including gasoline and diesel fractions.

2. A COD process as claimed in Claim 1 , wherein the FCC feed is fractionated before being used as a feed or co-feed to remove sulphur containing compounds.

3. A COD process as claimed in Claim 1 or Claim 2, which includes the step of varying the feed over time to manipulate the product distribution over time.

4. A COD process as claimed in Claim 3, wherein the feed is selected from 50/50% Fisher Tropsh derived olefins and FCC crude derived naphtha for about 5 days followed by 100% Fisher Tropsch derived olefins for about two days followed by 100% FCC crude derived naphtha for about 8 days followed by 100% Fisher Tropsch derived olefins for about two days.

5. A COD process substantially as described herein with reference to the accompanying images.