Photochemical reactor and irradiation process

A photochemical reactor and processes for irradiation of fluid reactants for production of products by radiation catalysis are provided. The reactor is particularly adapted for radiation catalysis of fluids which are substantially opaque to radiation and hence must be mixed thoroughly during irradiation for satisfactory radiation catalysis to occur. The processes are similarly particularly adapted for irradiation of substantially opaque fluids and provide thorough mixing of the fluid reactants.

DESCRIPTION OF THE PRIOR ART 
Photochemical technology heretofore has depended upon the transparency of 
the fluid reactants to the radiation employed. Prior art systems have 
sought to expose extreme depths or thicknesses of fluid to radiation. Such 
prior art systems have utilized processes and apparatus to reflect 
radiation back and forth through the fluid reactants to promote complete 
irradiation thereof. Agitation or mixing of the reactants in prior art 
reactors tends to minimize differences in the length of the flow path of 
various portions of fluid reactant stream as the reactants pass through 
the reactor. This mixing tends to improve the uniformity of exposure of 
the fluid reactants to radiation. Unfortunately, in prior art apparatus 
agitation effects upon reaction rate are minor. 
The present invention provides a photochemical reactor which promotes a 
high degree of mixing of fluid reactants in the immediate neighborhood of 
a radiation source thereby increasing the reaction rate substantially over 
reactors known heretofore. Additionally, the present invention provides 
processes for radiation catalysis of fluid reactants which provide more 
complete radiation catalysis of the reactants than has been known 
heretofore due to a high degree of mixing of the fluid reactants. The 
present invention also provides a photochemical reactor which is safer and 
more reliable than those available heretofore due to isolation of 
radiation sources from the fluid reactants by an at least translucent 
barrier and, in one embodiment, the presence of a moderating fluid 
interposed between radiation sources and the reactant fluid. 
FIELD OF THE INVENTION 
The present invention is in the field of photochemical technology and more 
particularly is in the field of reactors and processes for practice of 
photochemical reactions. The present invention specifically provides a 
reactor for radiation catalysis of fluids which are substantially opaque 
to radiation. The present invention also provides processes for radiation 
catalysis of reactants which are substantially opaque to radiation. 
It is a principal to object of the present invention to provide a 
photochemical reactor and processes for radiation catalysis of fluid 
reactants which are particularly adapted for efficient performance of the 
photochemical reaction. 
It is a further object of the present invention to provide a photochemical 
reactor and processes for practice of a photochemical reaction which are 
particularly adapted for irradiation of a fluid substantially opaque to 
radiation, thereby promoting radiation catalysis of the reactant fluid. 
It is a further object of the present invention to provide a photochemical 
reactor in which a high degree of mixing of the reactant fluid takes place 
in the immediate neighborhood of a radiation source. 
It is a further object of the present invention to provide a photochemical 
reactor which is safer than those known heretofore, in which effects of 
breakage of a radiation source are minimized and substantially confined to 
the inside of the reactor. 
It is a further object of the present invention to provide a photochemical 
reactor which uses more efficient radiation sources than used heretofore 
in photochemical reactors. 
It is a further object of the present invention to provide a photochemical 
reactor in which the radiation source operating temperature is in the 
neighborhood of the fluid reactant temperature thereby minimizing heat 
transfer through any barrier between the radiation source and the fluid 
reactants thereby minimizing thermal stress within the barrier. 
These and other objects of the present invention will become apparent to 
those of skill in the art from a reading of the following specification 
and the attached claims and an inspection of the accompanying drawing 
figures. 
The present invention accomplishes these objects by providing a 
photochemical reactor and processes for radiation catalysis of a fluid 
with greater mixing of the reactant fluid in the neighborhood of the 
radiation source and therefore greater exposure of a substantially opaque 
reactant fluid to radiation than has been known heretofore.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Reference is made to FIG. 1 where the preferred embodiment of the 
photochemical reactor of the present invention is designated 10. The 
periphery of the reactor is formed by shell 12 which has moderating fluid 
inlet and outlet ports 14 and 16 and inboard thereof has reactant fluid 
inlet and outlet ports 18 and 20. End plates 22 seal the ends of shell 12 
with suitable nut and bolt assemblies in combination with suitable 
gaskets. Locations of moderating fluid inlet and outlet ports 14 and 16 
and reactant fluid inlet and outlet ports 18 and 20 are not limited to 
those shown in FIG. 1. 
Refer now to FIG. 2. Within shell 12 bulkheads 36 extend from the inner 
surface thereof. Wire carrying tubes 64 rigidly connect bulkheads 36 with 
thrust plates 34. Tie rods 24 extend from and connect together thrust 
plates 34 and support baffles 26. Radiation sources 58 extend 
longitudinally between thrust plates 34. The rigid assembly of bulkheads 
36, wire carrying tubes 64, thrust plates 34 and tie rods 24 provides 
means for connecting shell 12 with radiation sources 58 and baffles 26 and 
for maintaining radiation sources 58 in spaced disposition from each other 
and from interior surfaces of shell 12. 
Baffles 26 provide longitudinal support for radition sources 58. Each 
radiation source 58 extends longitudinally within shell 12 and preferably 
comprises at least one lamp for emitting radiation and a housing or tube 
preferably disposed concentrically about each set of one or more 
preferably coaxial lamps, with the housing at least translucent to the 
emitted radiation. A transparent housing is preferable but not required. A 
void, preferably of annular configuration, preferably separates the lamps 
from the housing; however a void is not required. The baffles are of 
sandwich construction and provide as a radiation source support a teflon 
sheet within the sandwich, between two preferably stainless steel plates. 
Ferrules 32 secure tie rods 24 and baffles 26 together. 
Each baffle 26 preferably intersects a straight line path between reactant 
fluid inlet and outlet ports 18 and 20. When reactant fluid is passed 
through the shell from reactant fluid inlet port 18 to reactant fluid 
outlet port 20, radiation sources 58 are preferably surrounded by reactant 
fluid, thereby resulting in irradiation of the fluid, and each baffle 26 
preferably diverts at least a portion of reactant fluid from the straight 
line path thus promoting mixing of reactant fluid proximate the radiation 
sources. 
Bulkheads 36 are secured within shell 12 in fluid-tight relationship and 
seal off portions of shell 12 thereby forming fluid-tight chambers 88 and 
90. Fluid-tight chamber 88 is a moderating fluid inlet chamber while 
fluid-tight chamber 90 is a moderating fluid outlet chamber. End plates 22 
form portions of fluid-tight chambers 88 and 90. Sight glass assembly 78 
allows visual inspection of conditions within the photochemical reactor. 
With reference to the photochemical reactor, arrow A denotes an arbitrarily 
designated first direction which is the major direction of reactant fluid 
flow through the reactor. Arrow B denotes an arbitrarily designated 
direction transverse to first direction A. Arrow B' denotes another 
arbitrarily designated direction, opposite in direction to direction B, 
where both B and B' are transverse to first direction A. Although first 
direction A is shown parallel to the axis of rotation of preferably 
cylindrical shell 12, the processes described herein are independent of 
the configuration of the photochemical reactor and may be practiced with 
any suitable reactor configuration. the configuration shown is the 
preferred embodiment of the apparatus of the present invention. 
In the process of the present invention, the reactants, which are generally 
liquid but may be in the gaseous phase, are fed in through reactant inlet 
port 18, preferably substantially transversely to the first direction, as 
shown by the arrow "Reactants In." Reactant fluid flows around tie rods 24 
and around radiation sources 58, as shown by the curved arrows within 
reactor 10, as it passes through the reactor generally in the first 
direction. Reactant fluid eventually reaches reactant fluid outlet port 20 
whereupon it is removed as shown by the arrow "Reactants and Products Out" 
preferably along a direction substantially parallel to the inlet 
direction. Mixing flow around radiation sources 58 is promoted by baffles 
26, each of which preferably blocks a major portion of the cross sectional 
area of reactor 10 whereby flow of reactant fluid along a straight line 
from reactant fluid inlet port 18 to reactant fluid outlet port 20 is 
precluded. While reactant fluid is passing through the reactor generally 
in the first direction, the baffles result in the illustrated oscillatory 
reactant fluid flow pattern at angles to the first direction. As the 
reactant fluid flows around the baffles, a high degree of mixing takes 
place thereby promoting exposure of the reactant fluid to radiation from 
the radiation sources. The high degree of mixing of the reactant fluid is 
necessary since experimental data have shown that for one substantially 
opaque reactant fluid, H.sub.2 S, 99% of the radiation incident on the 
fluid is absorbed within one fourth of a millimeter of the fluid interface 
at which the radiation is applied. 
Radiation catalysis of the reactant fluid takes place substantially in an 
irradiated zone of the reactor inboard thrust plates 34. Thrust plates 34 
are not fluid-tight and reactant fluid occupies the spaces between thrust 
plates 34 and bulkheads 36; however substantially no radiation catalysis 
takes place in these areas because substantially no radiation enters these 
areas due to the blocking effect of thrust plates 34. As the reaction 
occurs, an at least translucent and preferably transparent moderating 
fluid, preferably gaseous nitrogen, may be fed in through moderating fluid 
inlet 14 to fluid-tight chamber 88 from where it would flow to fluid-tight 
chamber 90 and out moderating fluid outlet 16. It will be assumed for 
purposes of further discussion of the process that the moderating fluid is 
used; however it is to be understood that an embodiment of the process of 
the present invention may be practices without use of a moderating fluid. 
It is also to be understood that the moderating fluid may be statically 
maintained at the locations described or may be dynamically flowed through 
the locations described either by recirculation or by introduction of 
fresh fluid. Dynamic flow of the moderating fluid will be assumed for 
purposes of further discussion. As moderating fluid flows from chamber 88 
to chamber 90, it is maintained around lamps 38 within radiation sources 
58 by at least translucent tubes 59 and thereby provides a fluid medium 
through which radiation passes prior to irradiating the reactant fluid. 
Flow of moderating fluid from chamber 88 to chamber 90 preferably results 
in continuous replacement of moderating fluid in the preferably annular 
voids 86 between lamps 38 and tubes 59. 
Reference is made to FIG. 3 where shell 12 is shown in section with baffle 
26 installed therein. Four of six tie rods 24 pass through baffle 26. 
Baffle 26 is secured to the four tie rods passing therethrough by ferrules 
32. Radiation emitting lamps 38 are surrounded by peferably concentrically 
disposed tubes 59 which peferably are quartz and which are at least 
translucent to radiation of the wave length emitted by lamp 38 
therewithin. Lamps 38 preferably emit radiation in the ultraviolet range, 
with substantially all the radiation being in the wavelength band between 
about 2000 Angstroms and about 2900 Angstroms. Each radiation source or 
lamp and tube assembly is supported by radiation source support 28, 
preferably teflon or equivalent, the center portion of the sandwich 
construction of baffle 26. The sandwich is fastened together by rivets 98. 
In FIG. 3, edge portion 94 of baffle 26 proximate the inner surface of 
shell 12 is a major or greater edge portion of the baffle while edge 
portion 96 of baffle 26 remote the inner surface of shell 12 is a minor or 
lesser edge portion of the baffle. Baffle 26 is preferably configured with 
the major edge portion comprising more than 50% of the total edge portion 
such that baffle 26 blocks more than 50% of the total reactant fluid flow 
area, the circular cross-sectional area within shell 12. Baffles 26 are 
peferably disposed at least partially transverse the radiation sources. 
The reactor is constructed with radiation sources 58 closely packed 
together. Bunching of tubes 59 with lamps 38 therewithin is limited only 
by structure at either end of the lamp-tube assembly used to secure the 
lamp-tube assembly to thrust plates 34. In one construction of the present 
reactor, tubes 59 all have an outside diameter of about 1 and 3/16 inches. 
The distance between centers of closest adjacent tubes is about 1.48 
inches, which yields a minimum distance between outer surfaces of closest 
adjacent tubes of bout 0.293 inches. This results in a dimensionless ratio 
of minimum distance between outer surfaces of most adjacent tubes to tube 
diameter of 0.246. 
Reference is made to FIG. 4 where another baffle 26 is shown within shell 
12. The baffle in FIG. 4 is adjacent the baffle shown in FIG. 3 but has 
been rotated 180.degree. with respect thereto. When reactant fluid flows 
through shell 12 and successively passes the baffles shown in FIGS. 3 and 
4, an oscillatory pattern of reactant fluid flow across radiation sources 
58 results. The cross flow results from the positioning of the reactant 
fluid flow areas, where no portion of a baffle is present, on opposite 
sides of th bundle of radiation sources for adjacent baffles. Thus for 
reactant fluids to flow through the reactor, it clearly must pass across 
radiation sources 58 at angles thereto as it proceeds from the reactant 
fluid flow area in FIG. 3 to the reactant fluid flow area in FIG. 4. 
The geometric pattern of the radiation sources and their spacing one from 
another is illustrated in FIGS. 3 and 4. The radiation sources are 
illustrated in a triangular pattern or "pitch;" square or diamond patterns 
are also within the ambit of the present invention. A triangular pattern 
or pitch, as illustrated, results when the radiation sources are 
positioned with their centers at the vertices of equilateral triangles. 
Similarly, a square pattern or pitch, not illustrated, results when the 
radiation sources are positioned with their centers at the vertices of 
squares while a diamond pattern or pitch, also not illustrated, results 
when radiation sources are positioned with their centers at the vertices 
of imaginary diamonds. 
Reference is now made to FIG. 5 wherein the preferred embodiment of the 
assembly of tube 59 about lamp 38, support of tube 59 by baffle 26 and 
structure permitting flow of moderating fluid between tube 59 and lamp 38 
while lamp 38 is emitting radiation is shown. Lamp 38 is supported within 
tube 59 primarily by connector sleeve 54 which maintains lamp 38 remote 
the inner wall of tube 59 such that preferably annular void 86 is created 
therebetween. Connector sleeve 54 is maintained in the proper orientation, 
retaining lamp 38 remote the inner wall of tube 59, by bushing 56, 
receiver 66, fitting 70, nut 71 and safety nut 72. Wire carrying tube 64 
connects void 86 with chambers 88 and 90 whereby moderating fluid may flow 
from chamber 88 through void 86 to chamber 90. Fittings 70 with associated 
hardware are used at both thrust plates 34 to maintain the lamp 38 and 
tube 59 assembly in supported disposition. Wire carrying tube 64 is 
secured to bulkhead 36 preferably in a fluid-tight manner by fastener 73, 
nut 74 and safety nut 76 with fastener 73 threaded into complemental 
threads in bulkhead 36. Wire carrying tube 64 preferably extends a short 
distance into chamber 88 and 90 to provide for entry and exit of purge 
fluid to and from the chambers from void 86. The constructions at both 
bulkheads 36 whereby wire carrying tube 64 is retained thereat are 
preferably identical. Similarly, the constructions at thrust plates 34, 
whereby the tube-lamp assembly is maintained thereat by suitable hardware 
comprising receiver 66 and associated parts, are preferably identical for 
each tube at each thrust plate. 
Reference is now made to FIG. 6 wherein a single thrust plate 34 and 
bulkhead 36 are shown with the preferred assembly of apparatus for 
connecting and retaining wire carrying tube 64, lamp 38 and tube 59 shown 
in section. Lamp 38 has lamp end fitting 40 extending therefrom, 
contacting connector 42 for flow of electrical energy therebetween. 
Connector 42 is maintained within insulating connector sleeve 54, which is 
preferably nylon, by neck 54A of connector 54 in interfering disposition 
with shoulder 42A of connector 42. Spring 44 electrically connects 
connector 42 to wire 48, the bare portion of which is denoted 48B while 
the insulated portion is denoted 48I. The end of spring 44 remote 
connector 42 is maintained within plug contact 46 by compression forces 
exerted on springs 44 by plug contacts 46 at either end of lamp 38. Lamp 
end fitting 40, connector 42, spring 44, and plug contact 46 together 
comprise means for sealing lamp 38 within tube 59 in fluid-tight relation 
and for structurally connecting the lamp and tube assembly to thrust plate 
34. Insulator 52 is provided between plug contact 46 and receiver 66 with 
receiver 66 threadedly connected to connector sleeve 54. 
A passageway through receiver 66 has wire 48 resident therein for passage 
of moderating fluid therearound to void 86 between tube 59 and lamp 38. 
Tube 59 is secured to receiver 66 by suitable O-rings 62. Tube sleeve 60 
is shrink fitted around tube 59 to maintain tube 59 in compression; this 
is required since the materials generally used for the at least 
translucent tube are generally much stronger in compression than in 
tension. Washer 68 separates peferably stainless steel bushing 56 from the 
end of tube 59. Bushing 56 has a convex spherical portion which touches a 
complemental convex spherical portion of receiver 66 for substantially 
frictionless contact therebetween. Fitting 70 threaded into receiver 66 
has wire 48 and wire carrying tube 64 passing therethrough; nut 71 secures 
wire carrying tube 64 and fitting 70. At bulkhead 36, fastener 73 is 
substantially the same as fitting 70 with nut 74 corresponding to safety 
nut 72. This combination secures wire carrying tube 64 to bulkhead 36 in 
fluid-tight disposition whereby no reactant fluid can pass between wire 
carrying tube 64 and the nuts and fittings used to secure it to bulkhead 
36. 
Moderating fluid in void 86 travels between connector 42 and connector 
sleeve 54 into proximity with spring 44, around wire 48 and into the space 
between wire 48 and wire carrying tube 64. Once in that space, moderating 
fluid travels between wire 48 and wire carrying tube 64 until reaching the 
end of wire carrying tube 64 whereupon the moderating fluid is released 
into fluid-tight chamber 90. 
The reactor may also be constructed in such a way that no moderating fluid 
is supplied intermediate lamps 38 and tubes 59. In such an embodiment, 
tubes 59 preferably are still provided preferably concentrically around 
lamps 38 to protect the lamps from the reactant fluid. In such embodiment, 
moderating fluid inlet and outlet ports 14 and 16 are eliminated and 
moderating fluid inlet and outlet chambers 88 and 90 are eliminated with 
suitable means provided for carrying the electrically conducting wires 48 
to the lamps 38 through bulkheads 36. Wire carrying tubes 64 do not extend 
through bulkheads 36. Fluid tight seals are provided to prevent passage of 
reactant fluid through the annulus between wire carrying tube 64 and wire 
48 thereby preventing flow of reactant fluid inside transparent tube 59 
into contact with lamp 38. Alternatively, a seal can be provided at 
receiver 66 or in the neighborhood thereof. 
Reference is now made to FIG. 7 wherein the sight glass safety assembly 78 
is shown secured to shell 12. Sight glass 82 allows inspection of 
conditions inside the reactor while radiation catalysis is proceeding. 
Shield 84 is preferably welded to shell 12 about sight glass 82. Safety 
ball valve 80 when closed prevents escape of reactant from shell 12 upon a 
failure of sight glass 82. When ball valve 80 is open, a viewer may look 
through ball valve 80, when it is in the position shown in FIG. 7, and 
through sight glass 82 into the reactor. Means 92 for opening and closing 
safety valve 80 may be actuated by any suitable pneumatic, hydraulic or 
manual means. Normally ball valve 80 is in the closed position, shown in 
phantom lines in FIG. 7, and is opened only when an operator desires to 
look into reactor 10. This insures that upon any failure of sight glass 
82, reactants and products do not escape from the reactor. Positive means, 
such as a spring, are preferably provided, to maintain ball valve 80 
closed whereby the ball valve only opens upon an operator pressing a 
suitable actuation button. Upon release of the actuation button, the 
positive means closes ball valve 80 automatically. 
We present the following working example of practice of the process of the 
present invention. Irradiation of fluid reactants for production of 
products by radiation catalysis was practiced using the reactor disclosed 
herein by providing a closed loop liquid flow system for connecting 
reactant fluid inlet and outlet ports 18 and 20. Provided in the closed 
loop were a conventional heat exchanger, a holding tank and a pump. 
Conventional means were provided outside the reactor for removal of a 
stream of reactants and products, whereupon the products were separated 
from the reactants. 
The following table summarizes the contents of the reactant inlet fluid and 
the reactant and product outlet fluid for typical production practice of 
the process described herein. 
______________________________________ 
Component Mol Fraction at Inlet 
Mol Fraction at Outlet 
______________________________________ 
H.sub.2 S 0.8108 0.8107 
nC.sub.12 Olefin 
0.0919 0.0904 
NC.sub.12 Mercaptan 
0.0550 0.0564 
nC.sub.12 Sulfide 
0.0051 0.0052 
Other 0.0372 0.0373 
______________________________________ 
The mixture feed ratio of raw H.sub.2 S and olefin input was substantially 
stoichiometric with sufficient excess H.sub.2 S to account for reactant 
loss. The temperatures of the reactant inlet fluid was 106.degree. F while 
the temperature of the reactant and product outlet fluid was 114.degree. 
F. Pressure in the reactor was 365 psia. Reactant fluid was circulated 
through the reactor at a rate of 500 gallons per minute; normal C.sub.12 
mercaptan was produced at a rate of 833 pounds per hour. 
Removal of the product from the side stream was affected by initially 
vaporizing the H.sub.2 S. The organic portion of the reactant and product 
fluid was then subjected to vacuum fractionation, whereupon the mercaptan 
product was recovered, unreacted raw material was separately recovered and 
reintroduced into the system and waste was discarded.