Abstract:
A safety apparatus has been found for recovering an airborne hydrogen fluoride release in a hydrocarbon alkylation process. The safety apparatus comprising containment baffles and hydrogen fluoride detectors. Hydrogen fluoride detectors activate water flood means which discharge into the containment baffles. The water flood containing essentially all of the hydrogen fluoride release is recovered for disposal. Recoveries of 90 wt % have been demonstrated.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is related to Ser. No. 07/944,619 filed Sep. 14, 1992, for Hydrogen Fluoride Alkylation Apparatus and Vapor Recovery Method to G. P. Partridge, Jr.; K. R. Comey, III; J. Mudra IV and L. K. Gilmer now U.S. Pat. No. 5,277,881. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention is an environmental safety apparatus in combination with means for using hydrogen fluoride. The invention is also a safety method of collecting an airborne release of hydrogen fluoride. 
     2. Description of the Related Art 
     The catalytic alkylation of an isoparaffin with an olefin to produce a branched paraffin is a commercially important process for producing high octane gasoline. In general, the process comprises the reaction of an isoparaffin such as isobutane with an olefin such as propylene, 1-butene, 2-butene or mixtures thereof in the presence of a liquid acid alkylation catalyst in a reaction zone. Reaction is followed by separation of the product and unreacted hydrocarbons from the liquid alkylation catalyst in a settling zone and purification of the alkylate product. If the isoparaffin is isobutane and the olefin is a butene, the alkylate product is isooctane. Alkylate product is used to enhance the octane number of automotive gasoline and aviation gasoline. 
     Anhydrous hydrogen fluoride is a particularly effective catalyst for the alkylation process. Though effective, the volatility and destructive effect of hydrogen fluoride on animal tissue has curtailed expanded use of this catalyst in the petroleum refining industry due to a concern over accidental releases. 
     There is a need in the petroleum refining industry for an apparatus and method which will contain an accidental release of hydrogen fluoride from a major process vessel. 
     SUMMARY OF THE INVENTION 
     The invention is an environmental safety apparatus for collecting an airborne release of hydrogen fluoride from a hydrogen fluoride utilizing means. 
     The environmental safety apparatus comprises a containment baffle defining a volume sufficient to substantially enclose the utilizing means. At least one hydrogen fluoride detecting means is mounted within the containment baffle. Flood means has a capacity to substantially flood the containment vessel with an aqueous liquid. Means is provided responsive to detecting means to activate the flood means. Means is provided to receive the aqueous liquid from the containment baffle. 
     The invention is used in combination with hydrogen fluoride utilizing means such as an alkylation process vessel, containment vessel or transportation vessel to capture an accidental airborne release of hydrogen fluoride. As a result, escape of the release is prevented and damage to the environment is prevented. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The Drawing is a schematic flow diagram illustrating a preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The alkylation reaction is carried out between an isoparaffin and a monoolefin in the presence of alkylation catalyst. The preferred isoparaffin is isobutane. Isopentane is also used. Common monoolefins include propylene, isobutylene, 1-butene, 2-butene, pentylenes and mixtures thereof. The preferred monoolefin is a C 4  olefin, typically a mixture of 1-butene, 2-butene and isobutene. A typical C 4  olefin mixture is one fraction from a fluid catalytic cracking process comprising about 25 vol % 1-butene, 45 vol % 2-butene and 30 vol % isobutylene. Diolefins or higher functionality olefins are to be avoided in the reaction. Higher functionality olefins alkylate at each double bond, forming polymers which are not useful for gasoline blending. 
     The alkylation catalyst is hydrogen fluoride, referred to in the art as hydrofluoric acid or simply by its molecular symbol HF. Generally, anhydrous hydrogen fluoride is supplied to the process. In use, a typical analysis shows 1 wt % to 2 wt % water and 5 wt % to 15 wt % acid soluble oil. 
     The reaction may be carried out at pressures varying from atmospheric to as high as 1000 psia (68 atm) or higher, preferably about 125 to 220 psia (8.5 to 15 atm) and at residence times of 20 seconds to 5 minutes. The pressure is selected in cooperation with the temperature to maintain the hydrocarbon reactants in liquid phase and generally ranges from −40° F. (−40° C.) to about 150° F. (66° C.). In the preferred reaction of isobutane with a C 4  monoolefin the reaction temperature is between about 60° F. (15° C.) and about 100° F. (38° C.) and most preferably about 90° F. (32° C.). 
     In the alkylation reaction a substantial molar excess of isoparaffin to olefin is employed to provide an isoparaffin/olefin feed ratio in excess of about 1/1, generally 4/1 to 70/1 and preferably 5/1 to about 20/1. 
     Reference is made to the Drawing. The isoparaffin feed in line  24  and the olefin feed in line  25  are combined and introduced into reactor vessel  30  via lines  26 ,  27  and  28 . Fresh, anhydrous hydrogen fluoride in tank  10  is passed via line 17 into reactor vessel  30  which is either horizontally or vertically elongated and cylindrical in shape. The volume of anhydrous, liquid hydrogen fluoride exceeds the volume of the isoparaffin and monoolefin mixture. The liquid hydrogen fluoride constitutes a continuous phase in reactor vessel  30  and the hydrocarbon feedstocks constitute a discontinuous phase. Coolant, such as cooling water is passed via line  21  through heat exchanger tubes (not shown) exposed to the reaction mixture in reactor vessel  30 , thereby moderating reaction temperature to the selected range. Coolant is discharged via line  22 . 
     Reaction effluent, comprising alkylate product, unreacted isoparaffin and liquid catalyst are withdrawn from reactor vessel  30  via line  34  and discharged into catalyst settler vessel  50  which is vertically elongated and cylindrical in shape. The catalyst settler vessel  50  allows for separation of the reaction effluent from the alkylation reactor into an upper liquid hydrocarbon phase and a lower liquid catalyst phase containing hydrogen fluoride catalyst, acid soluble oil, and water. The catalyst settler vessel  50  may contain separation trays and vertical downcomers (not shown) positioned within the vessel to enhance separation. 
     The alkylate product phase is withdrawn via line 57 and processed by fractional distillation (not shown) to recover unreacted isoparaffin and alkylate product. 
     The liquid catalyst phase is withdrawn via line 60 and passed to spent acid tank  70 . A portion of this acid may be recycled (not shown) from spent acid tank  70  to reactor vessel  30 . 
     Surrounding and enclosing each of the major process vessels is a containment baffle. The containment baffle allows for a vapor space between the vessel and the baffle. Fresh acid tank  10  is enclosed by containment baffle  12 , providing vapor space  11  and fluid communication with the air via slots  12 s. Reactor vessel  30  is enclosed by containment baffle  32 , providing vapor space  31  and fluid communication with the air via slots  32   s.  Acid catalyst settler  50  is enclosed by containment baffle  52 , providing vapor space  51  and fluid communication with the air via slots  52   s.  Spent acid tank  70  is enclosed by containment baffle  72 , providing vapor space  71  and fluid communication with the air via slots  72   s.    
     Each of the vessels is cylindrical in shape as is each containment baffle. Preferably each containment baffle has a cylindrical radius 0.25 inches (0.635 cm) to 36 inches (91.44 cm) greater than the cylindrical radius of the vessel. Should a major process vessel leak, the vapor space provides volume for hydrogen fluoride to collect while limiting escape to the atmosphere via the slots. Hydrogen fluoride vapor at an initial escape velocity of 50 ft./sec. to 1500 ft./sec. has been found to condense on the baffle at atmospheric temperature and pressure, forming a vapor-condensate mixture. 
     The containment baffles dissipate the momentum of the escaping hydrogen fluoride vapor and reduce the velocity of the vapor-condensate mixture to that of the ambient air or less, generally 0 to 15 miles/hr. (22 ft./sec.), typically 0 miles/hr (0 ft./sec.) to 5 miles/hr. (7.3 ft./sec.). 
     This slow moving mixture under the containment baffle is sufficiently concentrated that it is detectable by detecting means. Commercially available hydrogen fluoride composition detectors are sufficiently sensitive to react to concentrations of 1 part per billion parts by weight to 1 part per million by weight in 15 seconds to 1 minute. This threshold is below the concentration of 20 parts per million by weight considered an immediate danger to life and health by the National Institute of Occupational Safety and Health. As little as 50 parts per million parts by weight is considered lethal. Secondary hydrogen fluoride detecting means includes hydrocarbon detectors and temperature and pressure sensors. A massive release would be indicated by the presence of hydrocarbon or a sudden or large temperature or pressure change under an impingement baffle. For example, a temperature change of 10° F. (5.5° C.) or more or a pressure change of 1 psi or more would indicate a vapor release. 
     Primary, composition detectors and secondary detectors are shown as detector  110  associated with tank  10 , detector  130  associated with reactor vessel  30 , detector  150  associated with catalyst settler vessel  50  and detector  170  associated with spent acid tank  70 . It is understood that the drawing is schematic and an array of detectors may be distributed within each containment baffle. Such an array would incorporate both primary, composition detectors and secondary detectors including hydrocarbon detectors, thermocouples and pressure sensors. 
     Each detector produces a signal when activated by the presence of hydrogen fluoride. Detector  110  produces signal  111  which is transmitted to valve actuator  113 . Valve actuator  113  actuates quick open valve  115  providing a flood of aqueous liquid from water supply  114  into containment baffle  12  via flood line  116 . The aqueous liquid is water. Incorporated in the liquid water may be alkali agents, buffers and surfactants to improve effectiveness in dissolving and neutralizing hydrogen fluoride. The water is passed via fog nozzle  117  which is representative of a plurality of fog nozzles positioned around containment baffle  12 . Fog nozzles are available which produce water mists having an average droplet size of 300 micron to 2000 micron and greater. This droplet size provides a large amount of surface area for the capture of hydrogen fluoride vapor. 
     The hydrogen fluoride dilute aqueous liquid is passed via drain line  15  to vented sump  90  where it is collected. Vapor recoveries up to 90% have been demonstrated experimentally with water/hydrogen fluoride vapor ratios of 6/1 to 40/1 by weight. 
     Likewise detector  130 , signal  131 , actuator  133 , water supply  134 , quick open valve  135 , flood line  136  and external spray head  138  are shown. Likewise detector  150 , signal  151 , actuator  153 , water supply  154 , quick open valve  155 , flood line  156   a,  flood line  156   b,  fog nozzle  157  and external spray head  158  are shown. Likewise detector  170 , signal  171 , actuator  173 , water supply  174 , quick open valve  175 , flood line  176   a,  a flood line  176   b,  fog nozzle  177  and external spray head  178  are shown. The drawing is schematic and each vessel may contain a plurality of fog nozzles and external spray heads. 
     Hydrogen fluoride dilute aqueous liquid is passed via drain lines  35 ,  55  and  75  to vented sump  90  where it is collected. Sump  90  may be used in combination with ground containment means such as earthen, concrete and asphaltic dikes. 
     U.S. Pat. No. 5,073,674 to Olah incorporated herein by reference discloses catalytic alkylation using liquid onium polyhydrogen fluoride complexes. These compositions show less volatility at alkylation conditions than anhydrous hydrogen fluoride. These complexes in combination are therefore more susceptible to recovery by water flood and are the Best Mode for carrying out the invention contemplated by inventors. 
     While particular embodiments of the invention have been described, it will be understood, of course, that the invention is not limited thereto since many modifications may be made, and it is, therefore, contemplated to cover by the appended claims any such modification as fall within the true spirit and scope of the invention. For example, hydrogen fluoride utilizing means is understood to include vessels for carrying out hydrogen fluoride manufacture, fluorocarbon manufacture, fluorination, and the aromatic alkylation process.