Seeded mesophase pitch process

Abstract

Producing mesophase pitch from liquid hydrocarbon feed comprising multi-ring aromatic compounds. In a first stage reactor feed is converted to isotropic pitch product contaminated with mesophase pitch. Contaminated isotropic pitch is charged to a second stage reactor where mesophase formation by self-assembly into spherical crystal clusters produces a mesophase pitch product. Water or steam added to the first stage reactor increases conversion of aromatic liquid feed, increases mesophase contamination of isotropic pitch product and reduces coke formation in the isotropic pitch reactor.

Claims

1. A process for producing mesophase pitch from isotropic pitch comprising a. Charging an isotropic pitch feed containing at least 10 wt % mesophase feed to a mesophase forming tubular reactor operating in turbulent flow and b. converting in said tubular reactor, isotropic pitch to mesophase pitch by self-assembly into spherical crystal clusters to produce a mesophase pitch product.

2. The process of claim 1 wherein said mesophase forming tubular reactor is a straight tube.

3. The process of claim 1 wherein said isotropic pitch is formed in a tubular reactor operating at thermal polymerization conditions including a temperature above 600° F. and pressure above 500 psia.

4. The process of claim 3 wherein 0.1 to 50 wt % water is in the feed to said isotropic pitch reactor.

5. The process of claim 3 wherein 1 to 10 wt % water is in the feed to said isotropic pitch reactor.

6. The process of claim 1 wherein at least 90% by volume of flow within said mesophase forming tubular reactor is vapor.

7. The process of claim 1 wherein at least 99% by volume of flow within said mesophase forming tubular reactor is vapor.

8. The process of claim 1 wherein at least 99.9% by volume of flow within said mesophase forming tubular reactor is vapor.

9. The process of claim 3 wherein said isotropic pitch reactor effluent discharges into a vapor liquid flash separator to produce a separator isotropic pitch liquid product containing more 10 wt % mesophase pitch.

10. The process of claim 3 wherein an aromatic liquid selected from the group of catalytic cracking slurry decant oil, ethylene cracker bottoms, coal tar pitch and other highly aromatic hydrocarbons is fed to said isotropic pitch reactor.

11. The process of claim 3 wherein said thermal polymerization conditions include a superficial vapor velocity in said isotropic pitch forming tubular reactor of 0.5 to 100 ft/sec.

12. The process of claim 11 wherein said superficial vapor velocity is 2 to 25 ft/sec.

13. A process for producing mesophase pitch from an aromatic rich liquid hydrocarbon feed selected from the group of catalytic cracking slurry decant oil, ethylene cracker bottoms and coal tar comprising a. Charging said feed and 0.1 to 50 wt % water to a tubular isotropic pitch reactor operating at thermal polymerization conditions including a temperature of 800 to 1000° F., a tubular reactor inlet pressure of 750 to 2500 psia, and thermally polymerizing therein at least a portion of said feed to produce an isotropic pitch intermediate product containing more than 10 wt % mesophase pitch; b. Charging said isotropic pitch intermediate product to a tubular mesophase pitch forming reactor at mesophase forming conditions including fully developed turbulent flow, a tubular reactor inlet pressure less than one half that of said isotropic pitch reactor and operating said tubular mesophase pitch forming reactor with at least 90 volume % vapor phase and with a velocity exceeding 200 feet per second and forming mesophase pitch in said tubular mesophase pitch forming reactor by self-assembly into spherical crystal clusters to produce a mesophase pitch product with less than 50% isotropic pitch.

14. The process of claim 13 wherein said mesophase tubular reactor is a straight tube.

15. The process of claim 13 wherein said tubular isotropic pitch reactor operates at 800 to 1000° F., a tubular reactor inlet pressure of 800 to 2000 psia, a residence time of 1 to 20 minutes, an average velocity of 1 to 20 ft/sec, and operates with 30 to 80 vol % vapor phase within said tubular reactor.

16. The process of claim 13 wherein said mesophase reactor operating conditions are 750 to 900° F., a 30 to 100 psia inlet pressure, 200 to 1000 ft/sec average velocity and 99.9+ vol % vapor phase within said tubular reactor.

Description

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(1) Our process does not require a new feedstock, plant or process flow. We operate the isotropic pitch process to ensure sufficient mesophase contamination of the isotropic pitch product. Contamination can be ensured thermally or preferably with water, steam, or inert gases, e.g. He, N.sub.2, and CO.sub.2. It can be done thermally by running the plant harder, e.g., a higher reaction temperature and/or longer reaction time to ensure mesophase is formed which ends up in the isotropic pitch product. Preferably the additive approach is used, steam or water to the feed to the isotropic pitch reactor to contaminate the product and keep the reactor clean. Water or steam is believed to favor the production of mesophase pitch in the isotropic pitch reactor and also reduce coking, based on visual observations.

(2) The basic process, and process flow diagram, for making both isotropic and mesophase pitch remains the same as disclosed in our issued patents, which have been incorporated by reference.

(3) Any conventional aromatic rich hydrocarbons traditionally used to prepare isotropic pitch may be used. We used slurry oil, the bottoms product recovered from the FCC column main fractionator, as feed for the isotropic pitch reactor. Similar results will be achieved with similar streams, e.g., ethylene cracker bottoms.

(4) Our new approach should also work with coal tar as a feedstock, but we have not tested this feedstock yet.

(5) The feed to the mesophase forming reactor is isotropic pitch containing, sufficient mesophase to seed mesophase formation in the tubular mesophase forming reactor.

(6) Experiments—Isotropic Pitch Reactor

(7) The experiments which follow show operation of the isotropic pitch reactor to form an isotropic pitch product with mesophase contamination.

(8) We used a 9.52 mm (⅜″) outside diameter (OD) tube 15.24 m (50 ft.) long with a 0.711 mm (0.028″) wall thickness made of type 316 L stainless steel (ss) heated by a Miller 300 CP welding machine that passed current through the reactor tube for our experimental studies. The residue and overhead were drained every 2 hours. Samples from these drains were analyzed for softening point and once for coking value. The lab notebooks are abstracted below.

(9) Experiment 1

(10) This run noted that 10% water by weight was added to the feed barrel.

(11) This produced pitch with a softening point of 103-124° C. and coking values between 52-59%

(12) Feed was at 6.2 lb/hr with the coils at between 985-990° F.

(13) Shutdown was due to blockage in the coil tube, most likely due to coking.

(14) A sample of the product was polished and a mesophase content was determined to be approximately 1%.

(15) Experiment 2

(16) Another run was conducted with 10% by weight of water in the feed.

(17) This produced a pitch with a softening point of approximately 100° F. and a mesophase content of 10-15%.

(18) Discussion

(19) Our new process, using mesophase “contaminated” feed to seed and make mesophase pitch will improve the operation of a mesophase pitch plant. We prefer to make isotropic pitch contaminated with 1, 2, 5, 10 or 20 wt % mesophase. Even more mesophase “contamination” can be tolerated, 25, 30, 40 wt % or more, but we prefer to use conditions in the isotropic pitch plant which favor isotropic pitch and leave most mesophase formation to the mesophase reactor. The mesophase reactor preferably operates at less than half, preferably one fourth or less, of the pressure in the isotropic pitch plant.

(20) Preferably the isotropic pitch plant is closely coupled with a mesophase pitch plant, preferably close enough that molten “contaminated” isotropic pitch can be directly charged to the mesophase pitch plant. For this use, the presence of some mesophase is beneficial and shifts some of the work normally done in the mesophase plant to the isotropic pitch plant. For this use, where the isotropic pitch plant functions as feed prep for the mesophase pitch plant, higher amounts of mesophase pitch are preferred, from 5 wt % mesophase to 10, 15, 20, 25, 30 wt % mesophase or more.

(21) Any conventional isotropic pitch plant or process may be used to create a contaminated or mesophase containing isotropic pitch. When a tubular reactor process is used, preferred operating conditions are 800-1000° F., 800-2000 psi inlet pressure, one to 20 minutes residence time, 1-20 ft/sec average velocity and 30-80 vol % vapor (avg).

(22) Ideally, the “contaminated” isotropic pitch is kept as a liquid and charged as a liquid to the mesophase reactor within 24 hours, preferably within 1 hour and ideally within 5 minutes or less. There is some heat savings and, more importantly, the contaminated product from the isotropic pitch reactor will not separate. If we have hot feed from the isotropic pitch plant to the mesophase pitch plant, the feed is homogeneous.

(23) Our preferred mesophase forming reactor when making a mesophase product can operate at conventional conditions such as those disclosed in U.S. Pat. No. 9,376,626, discussed previously. In general, preferred tubular reactor operating conditions are 750-900° F., 30-100 psi inlet pressure, 200-1000 ft/sec velocity (avg) and 99.9+ vol % vapor.

(24) While thermal conditions alone can generate isotropic pitch with a sufficient amount of mesophase to promote seeding, we prefer to add 0.1 to 50 wt %, preferably 1 to 10 wt %, water or steam to the isotropic pitch reactor feed because adding water or steam to the isotropic pitch reactor will reduce coke formation. When liquid water is added to or present in the feed, it will turn into steam at reactor operating temperatures.