US3103485A - Temperature - Google Patents

Description

Sept. 10, 1963 3,103,485

R. P. CAHN PROCESS FOR CRACKING PETROLEUM WAXES Filed Feb. 12, 1960 5 Sheets-Sheet 1 STEAM CRACKING FURNACE 3 TO FURTHER 2 QUENCH AND 5 FRACTIONATOR I [A I I [A '2 L:\\ II \\\y/ \\\y// \CVI I LIGHT V 4 Q Q NAPHTHA 7 8 9 40 ll 42 I3 I4 FEED WAXY DISTILL ATE QUENCH OIL ESL-l Robert P Cohn Inventor By 77M Patent Attorney Sept. 10, 1963 R. P. CAHN PROCESS FOR CRACKING PETROLEUM WAXES 3 Sheets-Sheet 2 Filed Feb. 12, 1960 2 .3 OOO 0% 2 52528 NEE R O F h K m T S N O C E A R WAX CRACKING vs. TEMPERATUREJ I200 I300 f, TEMPERATURE, F.

Robert P. Cohn FIG-IE Patent Attorney United States Patent 3,103,485 PROCESS FUR fiRACKENG PETROLEUM WAXES Robert P. :Cahn, Millburn, N .11., assignor to Essa Research and Engineering Company, a corporation of Delaware Filed Feb. 12, 1960, Ser. No. 8,416

7 Claims. (Cl. 208-130;)

The present invention relates to an improved process for the steam cracking of a petrolatum at low conversions to produce straight chain olefins in the C C range. More particularly this invention relates to producing said olefins as an additional product from a conventional (high conversion) steam cracking of .light naphtha to produce predominantly C -C unsaturates such as butadiene, isoprene, propylene, etc. Most particularly this invention relates to feeding the stream of liquid petrolaturn to be cracked at. low conversions to the unquenched l4001500 F. eflluentstream from the naphtha cracker. Thereby, both the necessary rapid quench of the high temperature steam cracker effiuent and the desired low conversion cracking of the petrolatu-m are obtained.

The cracking of petrola-tum or waxes at low conversion to produce straight chain olefins in the C5-C13 range is known at this time. Thus, according to this prior art process, cracking is conducted at temperatures of about 1100 F., utilizing residence times to obtain conversions to Cf' of about 8 wt. percent. Likewise convention-a1 (high conversion) steam crackingof naphthas at temperatures of 1400-1500 F. to obtain conversions to C o-f about 45-80 wt. percent and thus produce mainly linear olefins it is apparent that the present process will be.

C -C diolefins and olefins is also known and widely commercially utilized throughout the world. According to this latter process residence times at these very high temperatures must be closely controlled and a rapid quench utilized to. prevent addition-a1 cracking as well as polymerization of the desired olefinand diolefinprodnot to undesirable materials such as methane, tarsLand carbon. Thus, rapid quenching to temperatures below about 1000 F. with water or a refractory oil has been employed. i I

It has now been discovered that an efiicient rapid quench of this l400 l500 -F. efiluent from conventional highconversi'on steam cracking can be obtained utilizing a petrolatum. oil which is itself at the same time steam cracked to yield desired C -43 straight chain olefins.

It should be noted that the straight chain olefins of particular interest for detergents are in the C Ci range.

Further, it has been discovered that the mixed product obtained is highly compatible and can be easily separated by simple distillation. Thus, until the .present it might have been supposed that the polymer produced in the conventional high conversioncracking process would contaminate the C 5C g straight chain olefins produced in thewax cracking operation. It has now been found that the boiling range andex-tent of the formation of this polymer is such that these C C olefins may be separated by simpleidistillation with little contamination by polymeric-materials formed in the light naphtha cracking operation.

' Thus ithas now been found. that the amount of the polymeric materials formed from the light naphtha cracking operation which boil in the same range as the C -C straight chain olefins produced from wax crack- "ice Patented Sept. 10, 1 963 of the necessary clean-up, and does not substantially increase its cost.

Finally, in view of the fact that existing steam cracking facilities can be utilized according to this invention essentially without modification todo double duty and thus additionally produce large amounts of C C extremely economic. Thus, essentiallyi theonly major new process investment items required are'thewfractiona tion facilities torecover the C C cut gf'rom a side stream ofiithesteam cracker quench tower, and the necessary treating facilities on the product stream to remove diolefins and aromatics'. a Advantages of the present newf process are:

(1) If the wax cracking were'carried out separately,

(3) Whilewax and petrolatum are preferred teedstocks to the wax cracker, theykare also ofprernium I value. A paraflinic crude refinery stream "(virgingasl on, cat cycle stock raffinate) is cheaper, butrthe tolerable percent conversions to produce high'quality linear olefins is'lower than with waxfi'lhtis, the cracker ismore ex pensive since more feedstock has to be handled than with pure wax or petrolatum. 'In the present invention process the quench oil is only (in the most economical operation) cracked to the extent ofa few percent -(3-5) anyway andthus thelow conversions and large amounts of oil required to be cracked in this mild gas oil cracking may be extremely economically tolerated.

(4) Pour and cloud point of the quenchtnaterial'is lowered 540 -F. by this technique. Hence, by using a gas oil or cycle stock rafiinate for this quench we:

(a) Quench the light naphtha stearncracker efiluent (b) Make straight chain olefin out of the cheapest vfeed stock.

(c) Lower the distillate products obtained from the quench oil.

The present invention will be more clearly understood from a consideration of the accompanying diagra'rm matic illustration of a stea-mcracking'furnace and quench system for carrying out the present invention.

Turning now to FIGURE 1, a naphtha," specifically a light naphtha boilingin the range of to 300 F.,

preferably 100 to 220 F., e.g. to 220 5., is supplied through line 1 with steam supplied through line 2 to a cracking furnace 3. This furnace is operated at estates parafiinic stock which is pourand cloud point of the middle temperatures of 1300 to 1500 F., preferably 1380 to 1450 F., e.g. 1400 F., pressures of to 50 p.s.i.g., preferably to 25 p.s.i.g., e.g. p.s.i.g., with residence times of 0.1 to 5, preferably 0.5 to 2, e.g. 1 second and with amounts of steam supplied being in the range of 0.1 to 1, preferably 0.2 to 0.5, e.g. 0.25 lb. of steam per lb. of oil. These conditions are preferably adjusted to obtain C conversions of above 40' Wt. percent, preferably 45-80 Wt. percent. A waxy distillate quench oil is supplied through line 6 to quench the efiiuent from the cracking zone which is passed through line 4 to quench zone 5. This quench zone maybe an elongated tube with provision for multiple or alternate injection of the waxy distillate oil through lines 7, S, 9, 10, 11, 1 2, 13, and 14 in addition to line 6, if. desired, as the vapors pass through the tube. The quenched products from the cracking of the light naphtha feed and from the low conversion cracking of the waxy distillate are passed from the quench zone 5 through line 15 to further quench facilities and of course, fractionation facilities for separation of theproducts.

Suitable waxy distillate quench oils may be certain highly paraflinic crude oils containing less than 50 Wt. percent aromatics and naphthenes, boiling in the range of 500 to 1200? F., preferably 600 to 1100 F., e.g. 650 to 800 F. These paraliinic oils may be obtained for example from Lirik, Bahia and San Joaquin crudes. I Likewise, an excellent quench oil is a petrolatum boiling in the range of 650 to 1100 F., containing about 10 to 60% wax. Other suitable feedstocks are heavy gas oil fractions from less paraffinic crudes, such as a Middle East crude 'but the quality of the straight chain olefins produced is poorer. Other feedstocks are extracted gas oils (to remove some of the aromatics and naphthenes) and the raflinate from the extraction of catalytic cracking unit cycle stocks boiling in the range of 650 to 900 t P. All of the materials above described will produce high yields of the desired. C to C linear olefins.

As previously mentioned, quenching may be conducted by supplying quench oil at multiple points in stages through the quench zone or may be conducted by supplying the entire amount of the quench oil. initially. It should be noted that it may be preferred to introduce the major portion of the quench oil initially so as to quickly reduce the temperature to say 1200 to 1 300 F.,

e.g. 1250 F., to prevent deleterious cracking and polymerization of the high temperature light naphtha cracking 'efiiuent and also to obtain the major portion of the waxy distillate cracking at preferred temperatures of around 1100 F. Likewise, it is contemplated that .water may be supplied through lines 6- to 14 for additional control of temperature and that steam may be supplied at the beginning of the zone through line 6 to control the proportion of steam to hydrocarbon in the quench zone if desired. The waxy distillate oil may be introduced at temperatures of 400 to-800 F., preferably 500 to 700 F., e.g. 600 F. and supplied in amounts based on the gaseous efliuent (including H O) of 30' to 70 wt. percent, preferably 40 to 60 wt. percent, e.g. 55 Wt. percent. Quenching times may be in the range of 0.2 to 2 seconds preferably 0.2 to 1, e.g. 0.5 second (i.e. time to reduce the temperature to below about 1000 F.)

Following quenching, separation of the total cracked product may be obtained as follows:

The 1000 F. eflluent is passed to a conventional steam cracker quench tower wherein the original steam cracker product and the additional product from the wax cracking are separated by conventional fractionation means. The light products (C and lighter) are removed overhead as a gas to be processed further in a conventional light ends system. Steam cracked naphtha (300 F. End Point or so) is also removed overhead, as a liquid, and is sent to the same light ends system, and/or conventional naphtha fractionation and finally char treating.

The desired straight chain olefins are removed as one or several sidestreams from the quench tower and may be further processed by steam stripping to remove lighter materials and distillation to separate finer cuts. These steps may also be preceded or followed by extraction and/or selective hydrogenation, or similar treatments to remove or celan up undesirable diolefins and aromatics.

The heavier steam cracked products, as well as recycle quench oil are removed as sidestneams and bottoms streams from said quench tower.

The present invention will be more completely understood from a consideration of the following data and an example which further illustrate and define the present invention. Thus, it is shown below:

(1) that enough heat is available to carry out the desired cracking,

(2) that the kinetics are favorable for the reaction,

(3) that only small amounts (10 to 2.5 wt. percent) of contamination of the waxy cracked product with polymer in the same boiling range from the naphtha steam cracker are obtained,

(4) that conversions of the Waxy distillate of up to 10 to 20 wt. percent per pass can be obtained (unconverted materials can of course be separated by distillation and recycled),

(5) that large amounts of straight chain C to C olefins can be extremely economically produced in this manner (e.g. 16,000 st/yr. C to C olefins in a 6000 barrel/day naphtha steam cracker, and

(6) that the pour and cloud point of a middle distillate cut quench oil is reduced by this process.

A commercial high conversion steam cracker is operated under conventional furnace efiiuent conditions. Instead of the conventional cat cycle stock, a waxy distillate, preheated to 600 F., is used as the quench material in a system as described in the drawing, (FIG. 1). Sufficient waxy distillate is injected into the cracker efli uent to cool it from 1400 to 1000 F. A residence time of e.g. 0.5 second isutilized in the quench line, with uniform addition of quench material to the flowing gas 1 stream along the length of the line. Y The result obtained is similar to that obtained in a conventional quench utilizing a single injection point at the inlet.

To determine the extent of conversion of the quench oil obtained in the quench. line both reaction rate constants and the temperature gradient through the quench line were determined. With respect to the former, data obtained in a laboratory. steam cracker were used to determine the reaction rate constant for the cracking operation at a particular temperature and pressure as follows:

Wax feed temperature 800 F.. Coil-outlet temperature 1,100 Residence time 1 sec;

C Conversion -u 8 wt. percent.

From this single run, the cracking rate constan-t, K was calculated as follows:

x=wt.' percent 03- Conversion B=time, sec.

Using the same variation of K with-temperature (t F.) as .for other gas oil cracking rate constants, a relationship Well known in the art (K,=K, 3.1s 10 -Z%8 of the quench line was plotted and'is shown in attached FIG. III. In this figure the coordinates for each curve are indicated by the arrows shown, the x coordinate having a double scale which applies to both curves. Likewise from this temperature gradient and from the FIG. II plot of reaction constants vs. temperature, the extent of conversion of quench oil obtained at intervals through the quench line was calculated and is also presented in FIG. III. Thus from the figure it can be seen that after only of a second, the temperature has already been reduced to 1200 F. and nearly /a of the conversion has taken place, while only 20% of the quench oil has been introduced. At the A second point the temperature is below 1100 and 90% of the final conversion 'has occurred. It should be mentioned that since 90% of the final conversion is obtained at a point only half way through the quench line that if desired, a conventional (perhaps cheaper) quench oil can be substituted for the remaining one-half of the quench oil to be supplied to the quench line, if desired.

The yields of the C C linear olefins obtained from various gas oil feed stocks were determined in a laboratory reactor and are listed together with C conversion. This table shows that for a highly paraffinic feed, the yield of C C is of the order of 40-50% of the C conver- STEAM CRACKING YIELDS To determine C -C from the C -C figures, the latter were multiplied by 5/3 reflecting the molecular weight range. This factor, incidentally, agrees very well with the corresponding yields of these fractions from petrolatum cracking.

With respect to the yield of steam cracker polymer in the C C range, data were obtained from a commercially operating steam cracker. The unit was operating at high conversions to C; on a mixed naphtha feed stock.

Feed:

60 vol. percent 60/ 160 F. 40 vol. percent 280/ 360 F.

Conversion:

55 wt. percent Yields of Naphtha:

Initial/60 F 19.1 wt. percent on feed. 60/ 430 F 23.3 wt. percent on feed. 430/ 490 F 0.6 wt. percent on feed. 490 F.+ 1.9 wt. percent on feed.

The above data show that the polymer yield is of the order of 0.1 wt. percent on feed/ 10 F. boiling range, in the neighborhood of 400-5 00 F. However, when taking into account that other operating plants utilize a feed having a 220 F. end point, and that the conversion is 45 wt. percent, the polymer yield in C -C range for these units is probably only 0.05 wt. percent/ 10 F. boiling range. Based on these numbers it was assumed that the yield of polymer in the C -C boiling range is at the most 1 wt. percent on steam cracker feed.

Regarding pour point reduction by this quench tech- 6 nique, a 600 to 800 F. Aramco gas oil was cracked under conditions to obtain a C conversion of 8.3 to 9.2%. The following data were obtained.

Pour point of feed (600 to 800 F.), 65 F.

Pour point of 610+ F. product, 55 F.

The pour of the 600 to 800 F. product must be 55 F. The 610+ F. product was 63-66% of feed.

This shows that this method of cracking is a pour point reduction method for the quench oil. Actual reduction was therefore 10 F.

A design case based on the above discussion is presented below.

Example 'In a system as described in FIGURE I a light naphtha boiling in the range of 160220 F. is cracked under the following conditions:

(a) Furnace Outlet Conditions:

C Conversion of quench oil/ pass 12.5 wt. percent. 8.7 wt. percent on wax.

Yield of C -C 3,810 lb./ hr.

15,900 s.t./yr.

1.0 wt. percent on Naphtha Steam Cracker Steam cracker feed.

ploymer in ur- 1 range 628 1-b./-hr.

' 2,600 s.t./yr. Total C -C yield 18,500 s.t./ yr.

It should be noted that in the above discussion percent C3 conversion refers to the percent by weight of C gases obtained per weight of naphtha cracked.

The foregoing description contains a limited number of embodhnents of the present invention. It will be understood that this invention is not limited thereto since numerous variations are possible without departing from the scope of the following claims.

.What is claimed is:

1. An improved process for preparing predominantly straight chain olefins in the C to C range along with olefins and diolefins boiling in the C to G range, which comprises cracking a light naphtha in a cracking zone in the presence of steam at temperatures in the range of 1300 to 1500 F. and under conditions to obtain conversions (to C of above 40 wt. percent, withdrawing the product vapors from said cracking zone, immediately contacting the withdrawn product vapors, with 30 to 70 wt. percent of a waxy distillate based on the product vapors thereby quenching said product vapors to below about 0 F. in from 0.2 to 2 seconds and also obtaining the major proportion of the waxy distillate cracking at about 1100 F. and separating a out high in C to C olefins and a cut high in C to C olefins and diolefins from the resultant mixture.

2. The process of claim 1 wherein the waxy distillate is a virgin gas oil boiling in the range of 500 to 1200 F.

3. The process of claim 1 wherein the waxy distillate is a petrolatum boiling in the range of 650 to 1100 F.

4. The process of claim 1 wherein the light naphtha is a naphtha boiling in the range of 100 to 300 F.

5. The process of claim 1 wherein quenching is conducted by supplying the quench oil at multiple points through a staged quench zone.

6. The process of claim 1 wherein the entire amount of the waxy distillate used as a quench oil is supplied at a single point in a quench Zone.

7. An improved process for preparing a fraction con taining a high proportion of straight chain and minimum branched chain olefins in the C to C range along With olefins and diolefins boiling in the C to C range, which comprises cracking a light naphtha in a cracking zone in the presence of steam at temperatures in the range of 1300 to 1500" F. under conditions to obtain C conversions of above 40 wt. percent and utilizing amounts of steam supplied in' the range of 0.2 to 0.5 lb. of steam per lb. of oil and residence times of 0.5 to 2 seconds, immediately quenching in a quench zone the product vapors from said cracking'zon'e with 40 to 60 Wt. percent based on the product vapors of a petrolatum boiling in the range of 650 to 1100 F. maintaining temperatures in the quench Zone in the range of 1400 to 1000 F. and residence times in said quench zone in the range of 0.2 to 2 seconds and separating a C to C fraction containing a high proportion of straight chain olefins, and a C to 0; fraction containing olefins and diolefins from the quenched product vapors.

References Cited in the file of this patent UNITED STATES PATENTS 2,731,508 Jahnig et a1 Ian. 17, 1956 2,736,685 Wilson et al Feb. 28, 1956 2,786,802 Harrision et al Mar. 26, 1957 2,951,029 Johnson et a1 Aug. 30, 1960

Claims (1)

1. AN IMPROVED PROCESS FOR PREPARING PREDOMINANTLY STRAIGHT CHAIN OLEFINS IN THE C8 TO C18 RANGE ALONG WITH OLEFINS AND DIOLEFINS BOILING IN THE C2 TO C7 RANGE, WHICH COMPRISES CRACKINNG A LIGHT NAPHTHA IN A CRACKING ZONE IN THE PRESENCE OF STEAM AT TEMPERATURES IN THE RANGE OF 1300 TO 1500*F. AND UNDER CONDITIONS TO OBTAIN CONVERSIONS TO C3 OF ABOVE 40 WT. PERCENT, WITHDRAWING THE PRODUCT VAPORS FROM SAID CRACKING ZONE, IMMEDIATELY CONTACTING THE WITHDRAWN PRODUCT VAPORS, WITH 30 TO 70 WT. PERCENT OF A WAXY DISTILLATE BASED ON THE PRODUCT VAPORS THEREBY QUENCHING SAID PRODUCT VAPORS TO BELOW ABOUT 1000*F. IN FROM 0.2 TO 2 SECONDS AND ALSO OBTAINING THE MAJOR PROPORTION OF THE WAXY DISTILLATE CRACKING AT ABOUT 1100*F. AND SEPARATING A CUT HIGH IN C8 TO C18 OLEFINS AND A CUT HIGH IN C2 TO C5 OLEFINS AND DIOLEFINS FROM THE RESULTANT MIXTURE.

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