Industrial Solvents Handbook, Revised And Expanded

Nicholas P. Cheremisinoff

• Publisher: CRC Press
• Year: 2003
• ISBN:
  9781135541880
• Edition: 2
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

Keeping pace with current trends in solvent production, this volume builds upon its previous edition with broader coverage of safe handling practices, health effects, physical properties, and chemical synthesis routes to some of the most important organic solvents used in the chemical and allied process industries. This handy reference features a glossary of solvent terminology and an easy-to-reference index of synonyms for chemicals and solvents. The Second Edition features new and updated chapters on the major classes of organic solvents, descriptions for general use, and the chemical formulation, thermodynamic properties, health and toxicity, and combustible characteristics of solvents.

PART 1
PROPERTIES AND SELECTION OF ORGANIC SOLVENTS

INTRODUCTION AND AN OVERVIEW OF PART 1

The term solvent refers to a substance in which another substance is dissolved forming a solution. Solvents are used to suspend or change the physical properties of a material.

Most organic liquids can act as a solvent. Solvents represent an important component in the chemical industry processes and in the application industries that employ solvents as ingredients in the manufacture of various products. Many organic solvents also serve as chemical intermediates in the synthesis of other organic chemicals.

This part of the handbook focuses on organic solvents. Specific information covered includes physical and chemical properties, typical uses, pertinent legislation, and selection criteria. The important solvent classes covered in this section include aldehydes, aliphatic and aromatic hydrocarbons, ethers, halogenated hydrocarbons, ketones, nitroparaffins, monohydric and polyhydric alcohols, glycol ethers, aliphatic and heterocyclic amines, esters, and some miscellaneous organic solvents.

The first section to Part 1 is devoted to general properties and descriptions of important classes of industrial organic solvents. The second section of Part 1 provides an overview of environmental and OSHA legislation. The third section describes the use of the Hansen solubility theory in the selection of solvents in industry applications or formulations. This section contains an extensive compilation of solubility parameters for solvents.

ABBREVIATIONS

The following abbreviations are used in both sections of the handbook.

See Table

SECTION 1
INDUSTRIAL ORGANIC SOLVENTS

ALCOHOLS

Alcohols contain a hydroxyl functional group (-CH₂OH). Monohydric alcohols are among the most common in this class of solvents. These are straight or branched chain aliphatic hydrocarbons that contain one hydroxyl group on:

• a primary carbon atom (RCH₂OH),
• a secondary carbon atom (RR₁CHOC), or
• a tertiary carbon atom (RR₁R₂COH).

An important cyclic alcoholic solvent is cyclohexanol. An important aromatic alcoholic solvent is benzyl alcohol.

The high hydrogen bonding character of alcoholic solvents makes these substances valuable solvents for dissolving many polymeric and resin-like materials. Alcoholic functional groups are also valuable reaction sites for a large number of synthetic reactions of commercial importance.

No gaseous alcohols are known. The lower members of the homologous series of aliphatic alcohols (containing C₁ to C₁₀) are clear colorless liquids at room temperature. They have varying solubility in water, the higher alcohols being less soluble. The alcohols higher than C12 are solids and are insoluble in water.

Methanol, ethanol and propanol are miscible with water. The alcohols are miscible in all proportions with most organic liquids. As we pass up the series, the specific gravity increases.

The boiling points of the straight chain alcohols increase as the number of carbon atoms in the molecule increases, For a given molecular weight, there is a decrease in the boiling point when branching of carbon atoms occurs. Thus, the primary alcohols boil at a higher temperature than the secondary alcohols of the same molecular weight, and similarly, secondary alcohols have higher boiling points than the tertiary alcohols. The boiling points are much higher than is to be expected from their molecular weights, For example, the boiling point of ethanol, 78°C, can be explained by the attraction of ethanol molecules by means of hydrogen bonds to form extended groups of molecules,

Hydrogen bonds can arise in ethanol because the area around the oxygen atom is relatively rich in electrons and can attract hydroxyl hydrogen from a neighboring ethanol molecule. These intermolecular bonds are considered to be intermediate in strength between weak van der Waals’ forces and the strong forces between ions. The a extra energy required to break the hydrogen bonds leads to an increase in boiling point. Alcohols react with sodium and potassium with the evolution of hydrogen.

2C₂H₅OH + 2Na = H₂ + 2C₂H₅ONa

Ethylene glycol, CH₂OHCH₂OH, is the most important dihydric alcohol and approximately 75% of that produced is used as an anti-freeze agent. An example of a trihydric alcohol is glycerol. Glycerol, CH₂OH●CHOH●CH₂OH, is the most important trihydric alcohol and it is an important industrial chemical having many uses in war and peace. Glycerol is used in the production of explosives, as a moistening agent for tobacco, as a softening agent for cellophane films, in cosmetics, in food products, as a commercial solvent, and in the manufacture of plastics known as alkyd resins, which are used in paints.

The chemical properties of any given aliphatic alcohol depends on the nature of the alkyl group in the molecule and on the properties of the hydroxyl group. Alcohols react with organic acids to form esters. The reaction proceeds slowly but the rate of esterification is increased by the presence of hydrogen ions, which act as a catalyst in the reaction. Sulfuric acid in addition to acting as a source of hydrogen ions also helps to increase the yield of ester by absorbing the water as it is formed in the reaction. Alcohols are very weak acids, intermediate in strength between acetylene and water. They undergo substitution with strongly electropositive metals such as sodium. Alcohols react with phosphorus pentachloride, when the hydroxyl group is replaced by a chlorine atom. Thus, when the hydroxyl group is replaced by a chlorine atom from phosphorus pentachloride fumes of hydrogen chloride are evolved and this is used in testing for the presence of the hydroxyl group in a compound.

Common names for alcohols are Methanol, Ethanol, Isopropanol, n-Butanol, Isooctanol, Methyl Isobutyl Carbinol, Isoamyl Alcohol, Isobutyl Alcohol, Cyclohexanol, Methyl Cyclohexanol. The alcohols are versatile solvents that are used in many products from antiseptics and cough syrups to coatings and adhesives. Alcohols are used extensively as base materials for further processing into other chemicals such as esters, plasticizers and synthetic lubricants. Methyl alcohol is a strongly toxic material used in glass cleaners, shellac, NGR stains, dyes, inks, lacquer solvents, fuel additives and as an extractant for oils. Isopropanol (also known as Rubbing Alcohol) is used in cosmetics, perfumes, some types of coatings, cleaners, liniments, antiseptic solutions, liquid soaps and medications.

Nomenclature

The common name for an alcohol involves naming the longest chain that includes the carbon atom attached to the hydroxyl group, and affixing the suffix “ol” to the hydrocarbon name. The proper nomenclature numbering assigns the lowest number to the position of the hydroxyl group and other numbers to indicate the alkyl or others groups associated with the main hydrocarbon chain. Table 1 provides a list of common chemical names along with Chemical Abstract Index names (CA -Chemical Abstract Index, American Chemical Society) and CAS numbers (Chemical Abstract Service, American Chemical Society). CAS numbers in this case refer to the major alcohol component.

Table 1. Nomenclature for Common Alcohols

General Properties

Physical properties for many alcohols can be found among the chemical-specific profiles provided in Part 2. Some data are reported in Tables 2 and 3. Table 2 shows alcohols with minimum boiling azeotropes with water. Table 3 reports evaporation rates for common alcohols.

Table 2. Alcohol and Water Azeotropes

Table 3. Alcohol Evaporation Rates (relative to n-Butyl Acetate; i.e., n-Butyl Acetate =1.0)

The low surface tension of alcohols is a property which favors their use in coating formulations. Alcoholic solvents afford a wide range of evaporation rates and excellent solvency for various resins and polymer compositions. The four lowest molecular weight alcohols are completely miscible with water and with most organic solvents. Tertiary butyl alcohol, diacetone alcohol, furfuryl alcohol, and tetrahydrofurfuryl alcohol are also completely soluble in water. A compilation of general physical properties data is reported in Table 4. Table 5 reports solubility data.

Table 4. General Physical Properties of Alcohol Solvents

Table 5. Solubility Data

The following are descriptions of some of the uses of and synthesis routes for several important alcoholic solvents.

Methanol

One of the major end uses of methanol is for the production of methyl tertiary-butyl ether (MTBE), a motor gasoline oxygenate for octane enhancement. Continued use of MTBE in the U.S. is, however, questionable. Environmental concerns related to high groundwater contamination has caused the US EPA (Environmental Protection Agency) to reverse its position on the toxic risks associated with MTBE and has more recently recommended replacement with ethanol. Despite this, the prospects for MTBE demand growth in Europe and Asia continue to be promising. New gasoline specifications were introduced by the European Union on January 1, 2000 and more stringent specifications will become effective in 2005. These new regulations phase out lead content and reduce the amount of sulfur and aromatics such as benzene, a known carcinogen. The octane provided by the lead and aromatics will have to be replaced. MTBE would be the easiest and most economical source of octane. This would result in additional methanol demand growth for MTBE in Europe. Industry consultants expect methanol demand for MTBE in Asia to grow at about 7% per year for the next few years. MTBE demand will be driven by strong economic growth in the region and a focus on better air quality in the major industrial centers. For example, China has started to phase out lead in gasoline and Thailand, Korea and Taiwan require the use of oxygenates in gasoline.

Miscellaneous uses of methanol form the basis for many products including silicones, refrigerants, adhesives, specialty plastics and coatings, textiles, and water-treatment chemicals. Winter driving is made safer by methanol-based windshield antifreeze. Acrylic plastic light-coverings in homes and cars are based on another methanol derivative, methyl methacrylate. Other acrylic polymers are used in water-based interior and exterior coatings where superior durability is required. Paper products are usually bleached using chlorine dioxide, a process which produces significantly fewer pollutants than traditional bleaching methods. Similar to formaldehyde and acetic acid, overall growth of other derivatives is largely driven by general economic growth with some indicators including housing starts, new car production and industrial production. The largest solvent use for methanol is as a component of windshield wash antifreeze, where it can account for up to 50% of the solution depending on local climatic conditions. While not showing substantial growth, the expanded use of summer windshield cleaning solutions has changed the seasonal nature of this market. Methanol’s purity and physical properties enable it to be used to extract, wash, dry and crystallize pharmaceuticals and agricultural chemicals. It also acts well as a solvent in the production of ethyl cellulose, polyvinyl acetate, nitrocellulose, dyes, shellacs and numerous other chemicals.

Formaldehyde—Methanol is also used as a raw material for producing formaldehyde, which is used extensively in the construction industry to manufacture strand board and fiberboard. Formaldehyde continues to be the largest single end use for methanol, representing 36% of 1999 demand. Changes in the market mix of wood panel products, coupled with high growth in plastics and fibers derivatives, are providing new growth potential for formaldehyde beyond the traditional demand stemming from the construction industry. Phenol formaldehyde resins (PF) for plywood and oriented strandboard (OSB), and urea formaldehyde resins (UF) for particleboard and medium density fiberboard (MDF) are the largest markets for formaldehyde. The declining availability of old-growth timber has accelerated the switch to engineered wood products such as particleboard, OSB and MDF. Engineered wood products can use lower quality woods and wood wastes as feedstocks, providing unique advantages over solid timber products. The non-structural panels industry has addressed the health concerns related to formaldehyde emissions by using re-engineered UF resins that have reduced emissions to one-tenth the level typical of older resins. Non-structural panels continue to grow and have had particular strength due to the popularity of “ready to assemble” (RTA) furniture and cabinetry markets. Particleboard overlaid with wood veneer or plastic laminates has been a mainstay for these applications. MDF is the fastest growing segment of the wood panel adhesives market. MDF is beginning to replace traditional particleboard in many applications. The unique properties of MDF—its small particle size and uniform density—allow it to be machined or pressed into complex shapes. MDF applications include construction molding trim (baseboards, copings), architectural shapes (pillars, columns), and interior automotive trim parts (interior door panels and head liners), The urea formaldehyde adhesives used to bind the wood fibers in particleboard and MDF use a high proportion of formaldehyde in comparison to other resins. Industry forecasts suggest that MDF output will continue to grow. Plywood has been the traditional structural panel, but the declining availability of high-quality veneer timber is accelerating its replacement with cost advantageous products such as OSB. OSB uses lower quality and faster growing woods which are “waferized” into small chips, combined with a phenol-formaldehyde adhesive and pressed into finished panels. OSB uses approximately twice the amount of phenol-formaldehyde adhesive per board relative to plywood. OSB is forecast to continue gaining increasing share of the structural panel market.

There are a wide range of other formaldehyde specialty products and applications such as:

• 1,4 Butanediol is used in the production of tetrahydrofuran, a solvent used in the manufacture of “Spandex” fibers. This market has expanded rapidly with the increased sale of specialty sport and leisure clothing.
• Acetyl thermoplastics are made using formaldehyde resins and offer high impact and durability. They continue to find increased use in automotive and plumbing applications including molded parts, gears and pump housings.

Formaldehyde is also used in the manufacture of methylene di-para-phenylene diisococyanate (MDI) which is used to produce rigid urethane foams and elastomers. High impact resistance and the ability to recover its original shape make this the ideal material for construction of bumpers and body panels.

Markets and Miscellaneous Information—Methanol is methyl alcohol and at the present 99% of the production of methanol in the world is produced either from natural gas or gases out of oil. The reformed gas is compressed and passed to a methanol reactor. Carbon monoxide and carbon dioxide react with hydrogen over a catalyst to produce methanol. Also it is possible to produce methanol and ammonia in one complex by using CO₂, which is produced from an ammonia plant to produce methanol and urea. Methanol can be made from renewable resources such as municipal solid waste and biomass crops.

Methanol production is a major market for U.S. natural gas, using over 194 trillion Btu of domestic natural gas in 1995. The United States produces almost one-quarter of the world’s supply of methanol. In 1998, U.S. methanol production capacity totaled more than 2.2 billion gallons. Methanol plants meet three-quarters of U.S. methanol demand. The remaining supply comes from imports, of which Canada supplies well over one-half. In 1998, 90% of methanol supplied to the U.S. was produced in North America, 8% from Trinidad, Venezuela and Chile, with the remaining 2% produced in Europe, Asia and the Middle East. The largest market for methanol in the U.S. is for the production of MTBE, Produced in nearly 50 U.S. plants in 14 states, it is estimated that 3.3 billion gallons of MTBE was made in 1996 for blending in clean, reformulated gasoline serving 30% of the U.S. gasoline market. MTBE displaces 10 times more gasoline than all other alternative vehicle fuels combined.

The single largest use of methanol is in formaldehyde and dimethyl terephthalate production. Methanol is also used in the manufacture of methyl acrylate, methyl methacrylate, methyl chloride, dimethyl ether, dimethyl sulfate, and various other intermediates and dyes. Methanol is useful in dissolving phenolic laminating resins, ethyl cellulose, cellulose nitrate, and a variety of other resins. Low-viscosity resin solutions are possible using methanol.

Methanol burns with lower emissions than hydrocarbon fuels and is used as a fuel for many gasoline and diesel-type engines, stationary and aircraft turbines, industrial boilers, and in fuel cells. Methanol burns with a pale-blue, non-luminous flame to form carbon dioxide and steam.

2CH₃OH + 3O₂ = 2CO₂ + 4H₂O

Manufacture—Most of world methanol is manufactured from natural gas by a steam reforming process. Methane of natural gas is first mixed with steam at a 3/1 ratio. It is then reformed to carbon oxides and hydrogen under nickel catalyst at 1000°C and 20 atm. Carbon oxides and hydrogen react exothermically at about 70 atm pressure in...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Preface
• Part 1 Properties and Selection Of Organic Solvents
• Part 2 Hazardous and Toxic Chemical Profiles
• Glossary of Relevant Solvent Terminology