SRI's novel chemical reactor technology has been demonstrated to improve the ratio of desired product to waste product by a factor of 20 over comparable current technology. In addition to reducing or eliminating waste disposal and increasing product quality, the technology also increases yields and thus decreases the cost of raw materials. The technology was demonstrated under the collaborative support of five chemical companies brought together with SRI by the Center for Waste Reduction Technologies (CWRT) along with matching funds from the Department of Energy.

Invention: Source and Basic Characteristics
As a proactive service to the process industries, SRI asked several corporations to identify a broad unresolved challenge in the industry. The Novel Reactor was invented in response to their challenge for better control inside reactors. This improved control inside the reactors could be used to improve the yield and purity of desired products by minimized waste product formation with both noncatalyzed and catalyzed reactions.

An exceptionally broad patent covering this process, U.S. Patent No. 5,583,240 Exothermic Process with Porous Means to Control Reaction Rate and Exothermic Heat," issued December 10, 1996. The process is called PERMIX^TM because it is based on permeating and mixing.

The basic concept of the invention is illustrated in Figure 1. This new reactor uses the progressive addition of one reactant permeating all along the reactor and mixing in the entire volume of the reactor to minimize or eliminate local high concentration gradients and hot spots as well as to control the ratio of the reactants as the reaction proceeds.

Figure 1. Basic New Concept

The combination of order-of-magnitude improvements in transport in the entire reactor volume with the addition of the permeating reactant from millions of pores in the walls all along the reactor provides a uniquely uniform reaction environment. It is clearly more uniform than could be achieved with several point injections of a reactant using a nonporous wall reactor, packed with catalyst particles, because of the high concentration gradients at the points of injection. The novel reactor environment is also more uniform than a series of mixed tanks containing slurries of catalyst particles with introduction into each tank. Stirred tanks have intense mixing at the turbine tips and minimal mixing in the bulk of the volume. In contrast, the Novel Reactor has uniform mixing in the entire reactor volume.

Before the invention of the Novel Reactor described here, increases in selectivities or yields in catalytic processes depended nearly totally on developing improved catalysts. The proposed Novel Reactor offers an additional, orthogonal method for increasing selectivities and yields using existing catalysts. Furthermore, with future improved catalysts, the Novel Reactor will produce higher selectivities and yields than could be achieved in currently used reactors.

The above description of the SRI reactor process focused on a single porous reactor tube. Commercial-scale, practical operation will require the use of many tubes in shell and tube configurations very similar to a heat exchanger. One of these is illustrated in Figure 2. These reactors will probably be fabricated on a heat exchanger assembly line by substituting the appropriate porous metal tubes for the conventional heat exchanger tubes. The permeability of the porous tubes would be adjusted to the value appropriate for the specific application in situ in the fabricated reactor by the appropriate filtering of fine particle slurries.

Figure 2. Diagram of Porous Wall Reactor Module

The SRI reactor process can be used with any combination of fluid phases. The sulfonations used for the economic projections in this feasibility study consisted of a liquid phase permeating through the barrier in the reactor and a liquid phase passing through the mixing elements in the interior of the reactor. However, combinations of gas/liquid, liquid/gas, gas/gas, and even mixtures of gas and liquid flowing through the barrier or through the mixing elements are equally operable.

The porous barrier can be made from any material provided it has the correct viscosity-normalized permeability for the specific reaction. Sintered porous metal is very rugged and is cost effective. The permeability of tubes in fabricated finished reactors can be adjusted in situ by filtering slurries of fine particles.

The developers of this novel reactor worked with SRI Consulting's Process Economics Program (PEP) to identify potential applications for this new PERMIX^TM process. The following general classes of reactions were identified:

• Alkylations
• Carbonylations
• Carbamylations
• Chlorinations
• Direct oxidations
• Ethoxylations
• Halogenations
• Hydroformylations
• Hydrogenations
• Nitrations
• Solution polymerizations
• Sulfations
• Sulfonations

More specific studies were then performed on the following 17 major commodity chemical intermediates considered to be prime initial candidates for PERMIX^TM based on analysis of current process technology in use in the chemical industry today (the list contains 18 entries because ethylene amines are produced by two distinct processes).

• Caprolactam from cyclohexane
• Adipic acid from phenol
• Cyclohexanol from benzene
• Ethylene glycol ethyl ethers from ethylene oxide and ethanol
• Ethylene oxide from ethylene by oxygen oxidation
• Ethanol from ethylene
• Hydrogen peroxide by the anthraquinone process
• Ethylene glycol from ethylene and oxygen
• Ethanol amines from ethylene dichloride
• Maleic anhydride from n-butane
• Ethylene amines from ethylene oxide
• Phenol from benzene and propylene
• Chloroacetic acid from acetic acid
• Propylene oxide by the Arco process
• n-Butanol from propylene
• Acrylic acid from propylene
• Tetrahydrofuran from maleic acid
• n-Butyl acrylate from acrylic acid by esterification

Developing and Scaling up for Commercialization
The characteristics of the process facilitate a rapid development time followed by a highly reliable scale-up to commercial operation. The computer model of the process being refined in the current CWRT project will be used to guide the development in a single-tube, bench-scale unit, in which parameters and equipment can be changed rapidly at low cost.

Detailed Economic Projections for One Reaction
SRI Consulting's Process Economics Program (PEP) economically evaluated the new SRI reactor process for the sulfonation of methyl laurate. A process incorporating a conventional falling-film reactor was used as the base case for comparison with a process using the new SRI reactor. The size, configuration, and operating parameters for the SRI reactor process were determined by using an expanded version of the same computer program that was used to determine operable parameters for a single tube.

The plant size selected for this study was 50 million lb/year of sulfonated product. The SRI reactor for this production rate required only 189 7/8-inch-diameter tubes, 39 inches long, contained in a 19-inch-diameter shell. This requirement contrasted to a conventional falling film reactor more than two stories in height containing 100 wetted wall tubes. The conventional process also requires a 400-HP compressor to move the air that is blown through the inside of the falling film reactor tubes. Dryers are required for this air before SO₃ introduction, and treaters are required to remove organic contaminants before air discharge to the atmosphere.

The typical multiple treatments for waste products from falling film sulfonation were assumed for the conventional process. For the SRI reactor process, we assumed reduced treating for reduced waste products. A typical yield of desired sulfonated product of 91.7% was assumed for the conventional process, and a modest increase to 96% was assumed for the SRI reactor process.

The results of these studies for a grass roots plant show a reduction of 30% or $4.4 million in capital costs using the SRI reactor process versus conventional processing. The product cost is reduced from $0.8716/lb to $0.7963/lb.

A retrofit of a reactor system (reactor, heat exchanger, and recirculating pump) for this size plant would have an F.O.B cost of only $250,000. Substantially more than half this cost is the combination of the heat exchanger and recirculating pump, which can be accurately costed.

To make a conservative estimate for the porous tube SRI reactor, the cost per unit area of specialty filters using about the same number of the same porous metal tubes was multiplied by three for the cost of the SRI reactor. Even with this conservative costing, the reactor itself was a factor of five less costly than the falling film reactor. These $250,000 F.O.B. retrofits would include all reduced waste product contaminants and increased yield benefits. These retrofits might be considered "heart transplants" for increased yields and profit margins.

Licensing
This technology is available for specific application development contracts or through licensing and sublicensing.

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