This is one very interesting patent, IMHO. I haven't read it completely as I'm really tired but have typed up the essential part... what makes this work so well is the exclusion of water and the low temperatures, giving a very clean alkyl hydrogen sulphate, which is needed for optimal yield in the conversion to DMS.
Patent DE133542 (http://l2.espacenet.com/dips/viewer?PN=DE133542&CY=gb&LG=en&DB=EPD)
Example 1
25 kg SO3 are slowly distilled into 10 kg anhydrous MeOH with good cooling and stirring - temp. is best between -10 to -5°C, should always stay below 0°C. The reaction mixture is then directly distilled in vacuo. Yield of dimethylsulphate is 19 kg, nearly quantitative.
Diethylsulphate can also be produced, but yield drops to ~50%.
--psyloxy--