Polyethylene from Ethanol/Research Development
|Polyethylene from Ethanol|
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- 1 Literature and patent review
- 1.1 Ethanol production
- 1.2 Fluid Bed Reactor
- 1.3 Ethanol to ethylene catalysis
- 1.4 High purity ethylene product purification
- 1.5 Ethylene product measurements and quality control
- 1.6 Ethylene to polyethylene polymerization catalysis
- 1.7 Polyethylene product characterization
- 1.8 Value adding
- 1.9 Polyethylene recycling
- 2 Analysis of Industry Standards
- 3 Preliminary Economic Analysis
Literature and patent review
Ethanol is being developed as part of its own OSE product ecology and can be produced on-site or purchased.
Fluid Bed Reactor
Fluidized bed reactor allows for easy interface of solid catalyst and gas phase reagents and separation of gas phase products. It has many advantages for alkene polymerization processes. Designs can incorporate a number of features for continuous use such as catalyst recycling and constant input and output of substrate and product. Production of ethylene from ethanol and the polymerization of polyethylene from ethylene are carried out in fluidized bed reactors. Development of a multipurpose machine is proposed as part of the OSE product ecology. Information on the the design of FBRs and the first open source FBR purposed for plastic production should be collected on the Fluid Bed Reactor wiki page.
Ethanol to ethylene catalysis
Ethanol’s hydroxyl group can be removed and replaced with a double bond via a dehydration reaction. The endothermic reaction is best catalyzed between 500-700 C and a reactor device capable of controlling the mixing of reaction reagents and catalysts under ideal conditions will be necessary to produce high-quality ethylene capable of being polymerized. Steam has been used successfully to provide heat for the reaction and should be modular with the OSE steam generator and solar concentrator. http://www.cheresources.com/invision/topic/7179-ethylene-from-ethanol/
Acids or metals may be used for catalysts for this reaction, however aluminum silicate is a catalyst that offers high yields and is easy to obtain and work with. AlO3 is a favored catalyst which will be produced by the soil aluminum extractor. However, the addition of other compounds as either supporting material or doping of the catalyst has been found to increase yield and purity.
US patent 4,234,752 Dehydration of alcoholsissued to Wu et al. on November 18, 1980 details a method of using treated gamma-alumina as a catalyst for the dehydration of alcohols. The catalyst is base treated to remove excess surface acid sites which contribute to isomerization. An inert gas transports gaseous alcohol through the catalyst and minimizes side reactions. The described method has been found be effective with primary, secondary, and tertiary alcohols of 2 to 20 carbons with temperatures 200 to 500 C and pressures of 50 to 3500 kPa.
US patent 4,302,357, Catalyst for production of ethylene from ethanol, issued Nov 24, 1981 to Kojima et al. details a catalyst of high purity aluminum silcate of at least 99.6% purity with a phosphate of group IIa, IIb, IIIa, IVb in the wt% of .05 to 5 with a process for its preparation. Aluminum starting material that is capable of producing aluminum silcate under hydrolysis conditions should be utilized and higher purity organic aluminum salts or metallic aluminum is preferred. The primary factor influencing yield is purity of catalyst but pore volume and specific surface area also affect the reaction and ranges 0.15 to 0.50 cc/g and 100 to 350 m2/g respectively are recommended. Magnesium, calcium or zinc is recommended as a phosphate metal cation. The catalyst should be maintained at a temperature between 300 and 450 C.
Catalytic dehydration of bioethanol to ethylene over TiO2/g-Al2O3 catalysts in microchannel reactors by Chen et al. gives a general description of microreactors, catalyst configurations, and details a AlO3 catalyst with TiO2. Microreactors are small precision engineered devices to mix small reactions with a catalyst and heat. Microreactors may be a more suitable design for OSE specifications over traditional fluid bed reactors and were found to be more efficient than fixed bed reactors in this study. Chen et al found AlO3 doped with 10% wt TiO2 have high ethanol conversion efficiency, ethylene selectivity, and long-term stability of over 400 hrs. TiO2 increases that range of active lewis base configurations in the AlO3 matrix and enhances catalytic activity. Temperatures of 420+ C and ethanol concentration of 30-50% were found to be optimal.
Ethylene is a key plant hormone and is produced in "large" amounts by some ripening plants. Is there any feasibility in trying to capturing ripening fruits ethylene gas?
High purity ethylene product purification
Very high purity ethylene is required for polymerization, however processes for doing so are known in the art. Removing unreacted ethanol from the product stream by cooling below ethanol's point of 78 C and optimizing conditions for condensation removes low volatility molecules mainly water and ethanol. Breakdown and side products are mainly acetylaldehyde and more minorly ethane as reported by cheresource forums to be the side products of organic ethanol conversion to ethylene. Contamination such as higher complexity molecules, thiols, and other organic contaminants from the ethanol substrate can have unpredictable effects on the the reaction. Strategies to remove impurities from ethylene derived from hydrocarbon cracking have been the predominant focus of research and information on purification of organic ethanol derived ethylene is minimal. In industry fractionation columns used in tandem is a common strategy capable of producing very high purity ethylene suitable for polymerization. A process to dehydrate ethanol to ethylene can minimize the range and amount of contamination and should be a key design goal for the process. OSE may be benefited by pursuing strategies to produce high purity hydrous ethanol for use with a AlO3 and TiO2 under optimal conditions and a simple purification strategy that removes high volatility condensable gas products from what should be the majority product, ethylene.
Ethylene product measurements and quality control
Ethylene to polyethylene polymerization catalysis
The earliest used industrial catalyst for polymerization of olefins was supported phosphoric acid but were replaced with Ziegler-Natta catalysts in the 1960s.
Polymerization from ethylene to polyethylene takes controlled high temperatures and pressures, and requires the precise control of the movements of reagents. A reactor chamber capable of processing ethylene to polyethylene without fouling will be required. Catalysts capable of polymerizing oleofins with high efficiency and selectivity for long-chain, with low branching, and high crystallinity have been in use for many decades and much information on their use is freely available.
http://www.google.com/patents?id=cupVAAAAEBAJ US patent 2,395,381 issued to Squires on Feb 19, 1943 details methods to polymerize ethylene with vinyl acetate using oxygen or more preferably peroxy catalysts under high pressure and elevated temperatures.
US Patent 4,003,712 issued to Miller on Jan. 18, 1977 details a catalyst of silyl chromate for olefin polymerization with high reactivity and fluid bed reactor for its use. The reactivity of the catalyst allows small enough quantities to be used to avoid product fouling. The catalyst can be supported with a number of materials to enhance its action and extend its use.
US patent 4,124,532 issued to Giannini et al on Nov 7, 1978 details preparation of organoalumina and titanium/magnesium catalysts for the polymerization of olefins. A formula for an effective catalyst is defined as 1. Mm M' X2m Y .nE paired with an organometallic compound of groups I and III M = Mg, Mn, or Ca (divalent cations) m = 0.5-2.0 M'= Ti, V, and/or Zr (monovalent cations) X = Cl, Br, I Y = a number to satisfy M' valences n = 0.5 to 20 E = electron donor molecule Electron donors of interest are alkyl radicals particularly from 2-8 carbon aliphatic or aromatic acids or alkyls from ROR' ethers of duplicate or differing side chains, including: ethyl acetate, ethyl benzoate, methanol, ethanol etc. To obtain a highly active catalyst MX/M'Y are prepared with a molar ratio of 2 or more. E should be a suitable solvent and the reaction is carried out at room temp to 150 C. Purification of the catalyst is via crystallization or precipitation from solvent E or a less soluble E'. A test for the formation of the catalyst (or change of starting substrate) is the measurement of X-ray spectrum of the baseline magnesium dihalide to a decreased intensity from incorporation in the catalyst. Examples 3 and 4 are of particular interest to current OSE efforts. Examples of the polymerization reactions conducted in liquid and gas phase are detailed.
US patent 4,302,565 issued to Goeke et al on Nov 28, 1981 details a titanium, magnesium, halogen catalyst with an activated organoalumina compound that produces a polyethylene product suitable for forming into films.They build on the catalyst detailed in US patent 4,132,532 containing titanium compound with a hydrocarbon free radical and halogen. The catalyst is supported on a bed of inert porous material such as silica.The formula of the catalyst is Mgm Ti1 (OR)n Xp (ED)q Mg = magnesium m = 0.5-56 OR = alumina alkyl of c1-c14 n = 0,1,2 X = Cl, Br, I p = 2 - 116 q = 1.5m + 2 ED = electron donor (suitable solvent) The patent describes a polymer with good good film properties that is produced by polymerizing with a minor comonomer (<10%) of C3-C8 without branching within 4C of the polymerization end. The comonomer is in the form of the terminal alkenes and controls the density of the resulting polymer.
US patent 4,383,095 issued to Goeke et al on May 10 1983 details a catalyst made of magnesium and titanium which is capable of polymerizing high density polyethylene polymers in a fluid bed reactor that display many favorable characteristics for casting and injection molding. They build on the catalyst detailed in US patent 4,132,532 and 4,302,565 containing titanium compound with a hydrocarbon free radical and halogen. The catalyst is supported on a bed of inert porous material such as silica. The formula of the catalyst is Mgm Ti1 (OR)n Xp (ED)q Mg = magnesium m = 0.5-56 OR = alumina alkyl of c1-c14 n = 0,1,2 X = Cl, Br, I p = 2 - 116 q = 1.5m + 2 ED = electron donor (suitable solvent) Magnesium halogen salts are preferred with anhydrous MgCl2 being favored. A process for the preparation of a precursor of the magnesium titanium catalyst involves dissolving the magnesium and titanium compounds in a suitable electron donor solvent at a temperature >20 C but not above the boiling point of the solvent. The catalyst precursor is purified with a C5-c8 hydrocarbon and crystallization or precipitation. The patent details procedure to impregnate the support material with the titanium and magnesium catalyst. The Mg/Ti precursor is dissolved in ED solvent again and the support material is added in a weight ratio or 0.0333 to 1.0, preferably with a molar ratio of 0.1 to 0.43. The solvent is removed by drying at a temperature of under 70 C. Preferably, the original purification of the Mg/Ti catalyst precursor may be skipped and the support matrix added directly to the precursor in the ED solvation. Drying must be carefully controlled to maintain the ED stoichiometry defined by q. Activator may be added to dried silica support in the range of 1-10% by weight before impregnation with catalyst precursor. Density of the resulting polymer is controlled by the addition of C3-C8 terminal alkene comonomers and for the current invention are kept under 2% of mixture. Activator (5-30%) in a hydrocarbon solution is added directly to the reactor through a separate port so as to maintain an activator:Ti ratio of 10-400:1, and preferably 15-60:1. A gas input of 1.5 to 10 and preferably 3 to 6 Gmf (velocity required to maintain fluidization) is suggested and gas recycle to make-up of 50:1 is usual. Charging of the reactor bed with prepolymer is conducted before the addition of catalyst and substrate. Discussion of the fluid bed reactor operation can be found in the fluid bed reactor for plastic synthesis literature review.
Novel High Performance Ziegler-Natta Catalyst for Ethylene Slurry Polymerization by Zifang et al describes an improved method for homogenizing catalyst particle size catalyst of MgCl/TiCl2 using tetrabutyloxsilicane as an electron donor. Heterogeneous catalyst particle size contributes to dispersion of the polymers molecular weight. This is undesirable because the characteristics of the product can vary unpredictably, as well as fouling machinery. The catalyst is prepared by combining 100 ml of toluene, 6 ml epoxy chloropropane, and 12.0 ml of tributyl phosphate in a reactor. The mixture was heated to 80°C with agitation, and after dissolving to form a homogeneous solution the reaction was cooled to -25°C. Then 3 ml tetrabutyloxsilicane and 60 ml of TiCl4 were added dropwise and the temperature was slowly raised to 80°C. The reaction was held for 2 hours before the supernatant was removed and residue was washed with toluene and with hexane. The catalyst was dried under pure N2 to give a solid catalyst component with narrow particle size distribution. The polyethene polymerization reaction was conducted in an autoclave reactor under N2. The solvent was 1 l of hexane, 1 mmol of TEA, and 0.25 mg were added and the heated to 75 C. Hydrogen was added until the pressure reached 0.28 MPa and ethylene was added until the pressure reached 0.73 Mpa. The reaction was heated to 80 C and held for 2 hr. A control was prepared with a commercial catalyst and the products compared with 13C NMR, gel filtration, strength tests, and comonomerization with 1-butylene. A number of improved characteristics are attributed high branching in larger molecules and lower branch in the smaller molecules including a higher strength and denser product.
A simple version of the Ziegler-Natta catalyst seems feasible for OSE and can utilize the same elements (Al and Ti) as the dehydration step. Triethylaluminium (TEA) is an organoaluminium activator cocatalyst that is available in commodity form and has a relatively straight forward synthesis. Purchased cocatalyst combined with titanium and/or magnesium, possibly on a silicate matrix could be prepared on a small scale and used in an polyethylene polymerization.
Polyethylene product characterization
Polyethylene can be characterized according to physical material characteristics and molecular structure measurements. Plastics are generally categorized by melt flow, density, and weight distribution. Shearing, clarity, and flexibility are examples of easily attributes that may be important to certain applications. Specialized tests are also employed and need to be reviewed. UV-visible light absorbance spectroscopy would give precise measurements of products suitability for greenhouse glazing (block UV, doesn't block blue and red). Measuring molecular structure is possible with various kinds of spectroscopy, especially advanced techniques such as NMR. While advanced equipment like this will probably not be available to OSE, the lessons of advanced study should be applied and correlated to available means.
http://www.google.com/patents/US5156789 Demonstrating particular uses such as 3D printer resin with raw material can be considered a value added process.
Increasing types of final product through comonomers and plasticizers.
Increasing quality of final product.
Production of advanced materials, such as greenhouse glazing, from local feedstocks and catalysts could yield dramatic cost reductions. Fulfilling a necessary product ecology and lowering costs is a multiplicative gain.
Nanocomposites of organic polymers and certain minerals have better mechanical, thermal, barrier characteristics are currently under development to utilize the right catalysts and substrates under the optimal conditions.
Polyethylene/clay nanocomposites in-situ exfoliation of montmorillonite during Ziegler-Natta polymerization of ethylene by Jin et details a method to prepare a pretreated clay composite for improved polymerization using AlR3/TiCl2. The pretreatment of the montmorillonite involves attachment of the catalyst TiCl4 to hydroxyl groups and activation with triethylaluminium, this was immediately followed by polymerization. MMT was dried under vacuum for 24 hr and ethylene was sieved through 3 A and deoxygenated. A 1 l glass high pressure reactor was charged with 200 ml toluene and 5 g MMT at 30 C, and 0.9 mm TiCl4 catalyst for fixation. TEA 36 mm was used to activate the catalyst. Polymerization was initiated with the addition of ethylene at 30-50 C at 4 bars.