CA2025501A1 - Addition of radical initiators to resid conversion processes - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The present invention is predicated on the discovery that the addition of certain free radical initiators to thermal conversion processes results in increased thermal conversion rate at a given tempera-ture without any substantial increase in the amounts of gaseous products formed. This permits operating the thermal conversion process at lower temperatures than otherwise practical. Indeed, the present inven-tion is especially useful in thermal cracking process-es like fluid coking. In this embodiment, a free radical initiator is added, without the addition of a hydrogen donor diluent, to a feedstock which is thermally cracked in a fluidized bed of particulate solids and at lower temperatures than otherwise employed, whereby increased amounts of liquid products are obtained.

Description

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ADDITION OF RADICAL INITIAI'ORS TO
RESID CONVERSION PROCESSES

FIELD OF THE INVENTION

This invention relates generally ts improve-ments in thermal processes f~r treatment of petroleum hydrocarbons. More particul,arly, the present inven-tion is concerned with free radical promotion o~ the thermal conversion of petroleum residua into more useful products.

BACKGROUND OF TE~E ~NVENTE~

There are a wide variety o~ thermal process-es used in the treatment o~ petroleum hydrocarbons, particularly heavy hydrocarbon ~eedstocks. As is well known, these thermal processe~ are predominantly used for breaking the covalent bonds of the hydrocarbons in the feedstock to convert the feedstock into products that have boiling points lower than the feedstock.
Illustrative ~h~rmal processes include visbreaking, catalytic hydroconversion, hydrogen donor diluent cracking, fluid coking and delayed coking.

For example, U.S. Patent ~,298,455 discloses a thermal visbreaking proces~ in which a heavy oil is ~ubjected to thermal treatment in the presence of a chain transfer agent and free radical initiator, the combined ef*ect o~ which is to inhibit the polymeri~a-~ion o~ lower molecular weight hydrocarbons produced during the visbreaking treatment.

In U.S. Patent 4,378,28~ there is disclosed a method of increasing coker distillate yield in a ~;

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thermal coking process hy adding a small amount of a free radical inhibitor.

U.S. Patent 4,642,175 discloses a method ~or reducing the coking tendency oP heavy hydrocarbon feedstocks in a non-hydrogenative catalytic cracking process by treating the feedstock with a free radical-removing catalyst so as to reduce the ~ree radical concentration of the feedstolck.

~ rench Patent 0269515 discloses the use of oxygenated sulfur or nitrogen compound in combination with hydrogen donating diluents in visbreaking heavy petroleum Practions.

Notwithstanding any advantages the Poregoing processes may have, there is need to be able to operate thermal residual conversion processes at ever lower temperatures in order to increasie the conversion of ~eed to desirable products. Unfortunately, as is known in the art, if the temperature o~ a thermal conversio~ process is decreased so as to increase the conversion of feed to more desirable products, gener-ally it is necessary to increase the residence time of ~he ~eed in the reactor. Increased residence time, of course, results in lowering of production rate, which i5 undesirable. Decreasing the temperature of a thermal conversion process can have other undesirable effects. For example, in fluid coking, lower tempera-ture conversion typically results in gross agglomer-ation of the fluid bed o~ coke and the bed o~ coke becomes unstable because of the lower cracking rate of the resid ~eed. On the other hand, if the t~mperature oP the conversion process is raised, production rate will incre~e but at the expense of forming less valuable gaseous products, such as products boiling ' ` , ' , ~ ' ' ' '. ' ' ' . :
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below 100F. Moreover, higher conve:rsion temperature~
generally make coke formation at the heaked walls of the reactor likely, which i5 clearly undesirable.
Thus t there r~mains a need for increasing the rate of thermal conversion processes without forming less desirable products and preferably increasing both the rate of conversion and yield of desired products.

I~R OF THE INVENTIO~

Simply stated, the present invention is predicated on the discovery that the addition of certain free radical initiators to thermal conversion processes, without added hydrogen~-donor diluents, results in increased thermal conversion rate at a given temperature without any substantial increase in the amount of gaseous products formed. This permits operating the thermal conversion process at a tempera-ture lower than the given temperature with the produc-tion o~ decreased amounts o~ gaseous products and increased amounts of low boiling liquid products.
Basically, the ~ree radical initiators are s~lected from compounds that are substantially thermally stable at temperatures below the temperatures used in carry-ing out the th2rmal conversion process, but that will spontaneously thermally crack at the thermal conver-sion process conditions to form free radicals at a rate higher than that formed by the feed~

Indeed, the present inven~ion is esp~cially useful in thermal cracking processes, especially fluid bed processes~ In thi~ embodiment, a free radical initia~or is added tc a feedstocX which is thermally cracked in a ~luidized bed of paxticulate solids at a given temperature in the absence of added hydrogen-donor diluents, the amount of free radical initiator 7 ~

~dded being suf~icient to increase the rate of crack-ing at the given temperature without any substantial increase in the formation of gaseous products, and thermally cracking the ~eedstock at a temperature lower than the given temperature whereby increased amounts o low boiling liquid products are produced.

DETAILED DESCRIPTION OF THE INVENTION

The principal charging stock for carrying out thermal conversion processes in which the prin-ciples of the present invention are particularly applicable include high boiling virgin or cracked petroleum residues which are kypically unsuitable as heavy fuel oils. A typical crude oil feedstock useful in thermal conversion process~s has the composition and properties set ~orth in Table 1 below.

TABL~ 1 TYPIÇAL FEEDSTOCK

Conradson Carbon 23.2 wt.%
Sulfur 6.0 wt.%
Hydrogen 9.8 wt.%
Nitrogan 0.48 wt.%
Carbon 83.1 wt.%
Metals 269 ~ppm ~oiling Point 565C~
5ravity 3.0 n API

~ost o~ the suitable feedstocks used in the practice of the present invention will hav~ compositions and properties within the ~ollowing ranges, set forth in Table 2:

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RANGES OF FEEDSTOCIC

Conradson Carbon 5 to 50 wt.%
Sulfur 1.5 to 8,0 wt.%
~ydrogen 9 to 11 wt.%
Nitrogen 0.2 to 2 wt.~
Carbon 80 to 86 wt.%
Metals 1 to 500 wppm Boiling Point 340C~ to 650+
Gravity 10 ts 35 API

The thermal processes suitable in the practice o~ the present lnvention include those thermal treatment methods known in th~ art such as delayed, fluid and moving bed coking processes, visbreaking, catalytic hydroconversion, the~mal cracking, and the like.
Indeed, this invention is particularly sui~ed to ~luid coking processes. The precise technigues for carrying out these processes are well known.

It is an essential feature of the present invention to add free radical initiators to the feedstock used in thermal conversion processes in an amount sufficient to increase the thermal conver~ion rate of the feedstock at a given temperature and to conduct that thermal conver~ion process at a tempera~
ture lower than the given temperature to thereby produce more desirable lower bviling products in lieu of less desirable gaseous products. Importantly, the fe~d tock i~ sub~ec~ed ~o a ~hermal conver~ion process wi hout having added a hydrogen-donor diluent. Stated differently, the free-radical initiator is a~ded in amounts su~icient ~o permit conducting the thermal conversion process at lower temperatures than would otherwise be practical. For example, adding : `

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~ 6 -suf~icient free radical initiator to a thermal conver sion process in an amount suf~icient to increase the rate of conversion by about 25% permits operating the thermal conversion process at about 10F lower, thereby producing more liquid products.

Basically, the free radical initiator used in the present invention i5 an organic compound that is substantially thermally stable at temperatures below those used in carryincl out the thermal conver-sion proce~s but which have one or more bonds that.
will spontaneously thermally crack at the conditions at which the the~mal conversion process is to be conducted to form free radicals at a rate higher than free radicals formed by the feed. Desirably, the ~ree radical initiator will also have a sufficiently high boiling point or sufficiently low vapor pressure to assure thak an efPective amount o~ initiator is present in the ~eedstock being treated ~or ~orming free radicals at proce~s conditions. Typical and useful free radical initiators include polymeric ethers like poly(methylene oxonaphthalene), poly(di-methylene oxonaphthalene), poly(methylene oxobenzene) and the like. In addition to uslng discrete chemical compounds as free radical initiators, mixtures o~
compounds may be employed. Indeed, the free radical initiator may be another petroleum residua or liquid petroleum stream that thermally cracks at substantial-ly a higher rate than the feed because it contains more chemical bonds that spontaneou~ly thermally crack at the thermal conversion temperaturesO Hondo and Cold Lake vacuum resid~1a are examples of petroleum feeds that are very thermally reactivs bPcau~e of high concentration o~ free radical initiators.

The amount o~ free radical initiator added should be an amount suf~icient to increase the rate of thermal conversion over that rate o~ conversion existing in the absence of the added Pree radical initiator. ~he pracise amount, of course, must be determined based upon the specific free radical initiator employed and the temperature at which ~he thermal conversion process i~3 going to be conducted.
As a general guideline, however, the amount of free radical initiator added to the feed will generally ba in the range o~ about 0.1 to 25 wt.% based on the total weight of feed and Pree radical initiator.

The thermal conversion process then is preferably conducted at a lower temperature than otherwise, thereby resulting in formation o~ more desirable producks.

The utility of the invention is further illustrated by the following examples.

Co~para~ive-E~m~

Thi~ example, an Arabian heavy vacuum resid, having the properties set forth in Table 3 below, was thermally cracked under nitrogen at 400~C for 90 minut~s in a tubing bomb. Vacuum distillation o~ the product out of the tubing bomh yielded 37.2 wt.% of a 950F- product.

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ARAB HEAVY A UUM RESIDW M

Conradson Carbon 22.3 wt.%
Sulfur 5.13 wk %
Hydrog~n 10 .18 wt. %
Nitrogen O . 42 wt . %
Carbon 83 . 67 wt. %
Metals (V ~ Ni)245 ppm Boiling Point 510~+
Gravity 7.8 API

~Qm~arative Example 2 A Hondo vacuum residuum with th~ propertles shown in Table 4 below was heated ~or 68 minutes in a tubing bol~ under nitrogen vacuum distillation and yielded 45.3 wt.% of 950F~ product.

Comparative E~ample 3 In this example, a ~eedstock was derived from a Hondo vacuum re~iduum having the properties set forth in Table 3 above by deasphalting the residuum in n-heptane to remove the asphaltenes, absorbing polar aromatics out of the heptane solution with attapulgus clay, evaporating off the n-heptane and ~iltering the methyl ethyl ketone solution of the remaining oil at -78C to remove the ~EK saturates, and evaporating o~f the methyl ethyl ketone to leave the MEK hydroaromat-ics (called Hondo ~X aromatic~). A yield oP 13 wt.%
was ob~ained. This Hondo MEK aromatic ~raction was thermally cracked in a tubing bomb under nitrogen at 400OC for 90 minutes. Vacuum distillation out oP the tubing bomb of the product yielded 73.6 wt.% o~ 950F-product. This show~ that the Hondo ~EK aromatics are `
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_ 9 _ more thermally reactive than the Arabian Heavy oil o~
Comparative Example 1.

TABL~E 4 l~u~s I pUUM

Conradson Carbon 24 . 6 wt. 9~
Sulfur 7 . 0~ wt. %
Hydrogen 9.85 wt.%
Nitrogen 1.23 wt.%
Carbon 82 . 02 wt. ~6 Metals ~V ~ Ni) 691 ppm Boiling Point 5240C~
&ravity -0.5 API

Example 4 This example illustrates the use of a ~ree radical initiator to improve the thermal conversion process. In this example, a mixture o~ 76~6 weight percent of Arabian Heavy 950F+ oil having the proper-ties set ~o~th in Table 3 of Example 1 and 23.4 wt.~
percent o~ the ~ondo MEK aromatics from Example 2 above were reacted for 90 minutes at 400~C under nitrogen in a tubing bomb. Vacuum distillation of the product out o~ the tubing bomb yielded 51.6 weîqht percent o~ 950F- product. The expected yield of 950F- product was 45.7 weight p~rcent. Since a significantly higher yield of 950~F~ product was actually obtained, this indicates tha~ the ~Iondo MEK
aromatics i.ncreased ~he thermal cracking rate of the Arabian Heavy Vacuum resid. The conversion of Arabian Heavy 950F~ increas~ from 37.2 wt.% to 4~.9 wt.%
under the same time and temperature. Thus, this example demon trates that the thermal cracking reac:-tivity of a residuum can be increased at a Constant :

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temperature hy co-reacting the residuum with a more thermally reactivs petroleum str~am.

Example 5 This example illustrates the use of a polymer free radical initiator to improve the resid thermal conversion process. Here, a polyether o~ the following structure --~CH2-- ~

was used in which n was abouk 100. Two mixtures of this polymer (5 and 10 wt.%) and Arabian Heavy 1289F-~were prepared by dissolving thP components in tolu~ne and evaporating of~ the toluene. The rate of forma-tion o~ volatile products from thermally cracking these mixtures was measured by rapidly heating in a Thermogravimetric Analyzer (TGA) to 510C and measur-ing accurately the rate of weight loss with time. As compared with the Arabian Heavy 1289F+, the mixture containing 5% polymer increased the rate of conversion by 27% and the mixture containing 10~ polymer in-creased the rate of conversion by 4~. This means that with 5 wt.~ pol~mer, the conversion temperature could have been lowered from 510C to 504C without decreasing the cracking rate. With 10 wt.~ polymer, the conv~rsion temperature could have been lowered from 510C to 501C.

Exam~le ~

In this example, a mixture o~ 75 wt.% of an Arabian heavy vacuum resid having the properties set forth in Table 3 and 15 wt% of a Hondo vacuum resid - , having the properties set forth in Table 4 was heated for 68 minutes at 400C in a tubing bomb under nitro-yen. A yield o~ 40.4 wt~ oE 950F- product was obtained, which wa~ greater than 35.2 wt% of 950F-that is calculated from the daka in Comparative Examples 1 and 2.

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Claims (11)

1. In a thermal conversion process wherein a petroleum feedstock is heated at elevated tempera-tures to form low boiling liquid products and wherein gaseous products are formed, the improvement consist-ing essentially of: carrying out the thermal conver-sion in the presence of a free radical initiator and in the absence of added hydrogen-donor diluent, the free radical initiator being present in an amount sufficient to increase the rate of thermal conversion without substantially increasing the formation of gaseous products.

2. The improvement of claim 1 wherein the free radical initiator is selected from organic compounds and mixtures thereof that have a sufficient-ly high boiling point to remain present in the feed-stock under process conditions and that will spontane-ously thermally crack under process conditions at a rate higher than free radicals formed by the feed.

3. The improvement of claim 2 wherein free radical initiator is present in an amount ranging between about 0.1 wt.% to about 25 wt.% based on total weight of feedstock and initiator.

4. The improvement of claim 3 wherein the initiator is a petroleum residuum or fraction thereof that cracks at a higher rate than the feedstock.

5. The improvement of claim 3 wherein the initiator is a polymeric ether.

6. The improvement of claim 5 wherein the polymeric ether is selected from poly(methylene oxonaphthalene), poly(dimethylene oxonaphthalene) and poly(methylene oxobenzene).

7. A process for converting a petroleum feedstock to liquid products consisting essentially of:

subjecting the feedstock to a thermal conversion process selected from the group consisting of delayed coking, fluid coking, visbreaking, thermal cracking, and hydroconversion in the presence of a free radical initiator and in the absence of added hydrogen-donor diluent, the amount of free radical initiator being sufficient to increase the rate of thermal conversion without substantially increasing the formation of gaseous products.

8. The process of claim 7 wherein the free radical initiator is selected from organic compounds and mixtures thereof that will spontaneously thermally crack under conditions of use at a rate higher than free radicals formed by the feed.

9. The process of claim 8 wherein the free radical initiator is present in an amount ranging between about 0.1 wt.% to about 25 wt.% based on total weight of feedstock and initiator.

10. The process of claim 9 wherein the thermal conversion process is fluid coking and the temperature at which the fluid coking is conducted is a lower temperature than that in the absence of the free radical initiator.

11. In a fluid coking process wherein a petroleum feedstock is heated in a fluidized bed of particulate solids at temperatures and pressures sufficient to convert at least some of the feedstock to liquid products, the improvement consisting essen-tially of:

conducting the fluid coking process in the presence of a free radical initiator and in the absence of any added hydrogen donor diluent, the free radical initiator being selected from compounds and mixtures thereof that have a sufficiently high boiling point to remain present in the feedstock under the process conditions and that will spontaneously ther-mally crack at the fluid coking process conditions to form free radicals at a rate higher than that formed by the feedstock, the free radical initiator being used in an amount sufficient to increase the rate of thermal conversion over that in the absence of the free radical initiator, and conducting the fluid coking process at lower temperatures than otherwise practical, whereby increased amounts of liquid prod-ucts are obtained.