TECHNOLOGY
Methanol: pluses for low-pressure plants Engineers at AlChE meeting in New Orleans hear about advantages of making methanol at 50 atm. The swing to technology for making methanol at relatively low pressures accelerates as the economic advantages become clearer. The preference for operating at 50 atm. in contrast to 300 to 350 atm. was spelled out at the American Institute of Chemical Engineers meeting in New Orleans, La. The economic advantages of operating at lower pressures to make methanol are widely recognized in all three major areas of manufacturing c o s t production, capital, and maintenance. The advantages are greater in big plants where large centrifugal compressors can be used at high efficiency. The lower limit on capacity for low-pressure technology may be about 150 tons per day, but agreement is not general on this limit because of special conditions which could be encountered in the plant size, such as limited choice of raw materials and fuel, power, or transportation cost. Low-pressure technology, as ex-
Feed hydrocarbons
Low boiling impurities
emplified by Imperial Chemical Industries' process, developed from ICI's work on catalysts. Starting in the late 1950's, ICI added to basic knowledge of copper oxide catalysts for making methanol and developed a catalyst of copper oxide with other metal oxides as promoters. The catalyst is made by precipitating the metal oxides from nitrates in a sodium carbonate solution (U.S. patent No. 3,326,956). The key to successful use of the copper-based catalyst and low-pressure technology is the availability of virtually sulfur-free hydrocarbons as feedstock, says P. L. Rogerson of ICI. The zinc-chromium oxide catalysts used in high-pressure methanol production are much less sensitive to poisoning by sulfur, but are not economical to use in making methanol at temperatures below about 340° C , unless pressures are 300 to 350 atm. For low-pressure technology, conversion per pass is about half (2 to
Heat exchanger
3%) that of high-pressure technology (5%), points out R. J. Kenard, Jr., of Power-Gas Corp. of America, and requires larger synthesis loop circulation rates. Thus, the transportation of some equipment items for a plant with a capacity in the 1500 ton-perday range becomes a major factor in design and could lead designers to use two smaller synthesis converters and two crude methanol separators. The 50-atm. pressure was selected by ICI because gas at this pressure was available from a stage of existing plant compressors and a gas pipeline system was in place which had 50 atm. as the operating pressure. In addition, a pressure of 50 atm. caused no new problems in design of large centrifugal synthesis gas compressors. Lower operating pressures aid large plants mostly through the lower power requirements for compression. A second production cost advantage comes from much improved use efficiency of plant steam. In addition, the relatively mild conditions permit use of standard equipment and materials. In making methanol by either highor low-pressure processes, the same general steps are involved—reforming of hydrocarbons to synthesis gas, compression, conversion, separation, and purification. The details vary as widely as the conditions and critically affect the economics.
High pressure compressor
High purity methanol
Heat exchanger
Heat exchanger Turbine compressor
Purge to fuel gas High boiling impurities
Turbine compressor
TWO ROUTES. Differences in operating conditions and catalysts distinguish high-pressure (red) process for making methanol from low-pressure (white). In addition, low-pressure process need use only turbine compressors 42 C&EN MARCH 31, 1969
Space technology spin-off at TRW yields a new family of high-performance resins
Borden's Geismar facility All-centrifugal compressor plant
The reformer used to make synthesis gas is generally similar to that used in making ammonia. The major exception from ammonia production is that carbon dioxide is often, but not always, added along with steam and hydrocarbons to the reformer. Waste heat and effluent gases at about 750° C. from the reformer are used to make steam, typically superheated and at pressures higher than 600 p.s.i.g. To get the 300- to 350-atm. pressure required for the high-pressure process, both centrifugal and reciprooating compressors are used for small- to medium-sized plants, according to Samuel Strelzoff of Chemical Construction, whose paper was read by John Clarke of Chemico. If a methanol plant has a capacity of 700 or more tons per day, all-centrifugal compression methanol plants are practical. For high-pressure plants, cooling is needed in the converter. This cooling is effected by passing the inlet gas through tubes in the catalyst bed (medium and small plant size) or by injecting cool synthesis gas into and over the catalyst arranged in several separate baskets in series. No cooling is needed for the low-pressure process. Lower temperatures of the low-pressure process cause fewer impurityproducing side reactions than in the high-pressure process. However, in either process, gases from the converter are cooled to condense crude methanol, passed through a gas-liquid separator and a pressure-reducing valve, and sent to a surge tank. Pretreatment of the crude methanol before purification is needed in the high-pressure process to convert aldehydes present to organic acids. In the actual purification, extractive distillation (with water) removes acetone in the first of two columns. Ethamol and other higher alcohols are removed in a second column to give a commercial grade of 99.85% methanol.
Space technology spin-off is giving TRW's Systems Group its first commercial chemical product—a family of resins based on high-vinyl 1,2-polybutadiene. The new resins, the company says, produce a variety of plastics with exceptional thermal, chemioal, and electrical properties. But one of the most interesting properties is a stable, intermediate rubber stage that is a boon to processing. To market die product, called HYSTL polybutadiene resins, TRW has entered into a 50-50 venture with Commonwealth Oil Refining Co. (CORCO) of Puerto Rico. The resulting HYSTL Development Co. is headquartered in TRW's complex at Redondo Beach, Calif., and is headed by Nicholas M. Stefano, former head of special projects for the power systems division. Nippon Soda Co. of Japan, although not a partner in the new company, is a third major factor in the arrangement. This company makes a series of 1,2-polybutadienes that are the heart of the new resin system. HYSTL Development is the exclusive sales agent for these in the U.S. Although the marketing arrangements were announced last November, little was said at that time about the resins themselves. HYSTL Develop-
ment (HDC) has now released more details, although exact formulations for the various applications will be disclosed only to licensees under a secrecy agreement. The resins were spawned by TRW's work for the National Aeronautics and Space Administration on heat-resistant coatings for rocket thrust chambers. The idea was to make condensed polyaromatic compounds from polybutadiene. This didn't work out, but the intermediate material, a condensed polycyclohexane, showed very promising properties. Chemist Hyman R. Lubowitz decided to explore the possibilities further by using 1,2-polybutadienes with a reactive "handle" on each end. The one on which he worked most is the dihydroxy resin, now called the G-series. Another is the dicarboxy resin, the C-series. With the dihydroxy resins, Mr. Lubowitz uses a diisocyanate as a chain extender. The chain extender for the carboxy resins is a diepoxide. In both cases, the resins themselves can have molecular weights ranging from 1000 to 3000. One of the most exciting aspects of the HYSTL polybutadiene resin system, Lubowitz believes, is the existence of the intermediate. This stable
Properties of cast HYSTL resin formulation 110 Electrical Dielectric strength 1800 volts/mil (ASTM D149) short time, 0.020-inch thickness 2.4-2.7 (ASTM D150) Dielectric constant 100 kc-10 Mc. 0.0048-0.0058 (ASTM D150) Dissipation factor 100 kc-10 Mc. Chemical Weight change (%) Time of test (days) Test chemical +1.2% 7 Acetone +0.5 7 Benzene +1.33 216 Hexane +0.43 216 Sulfuric acid (12N) +0.22 216 Sodium hydroxide (19M) +0.68 216 Sodium hydroxide (3M) +0.11 63 Nitrogen tetroxide +0.24 302 hours at 100° C. Sea water 44 hours at 71° to 90° C. No change Nitric acid (cone.) Thermal 0.47-0.52 Specific heat 855° F. Incipient decomposition temperature (in nitrogen) 500° to 518° F. Secondary transition temperature Weight loss in air 88 days at 338° F. 100 hours at 572° F. Heat distortion temperature 264 p.s.i.
2.17% 3.9% >490° F. MARCH 31, 1969 C&EN 43
